A Sűrűzagy Alkalmazása a Környezetvédelemben

A Sűrűzagy Alkalmazása a Környezetvédelemben Kránitz Lili1, Walter Géza2 (1 Regionális és Környezetgazdaságtan MSc., 2 Gépészmérnök MSc./Tüzelési Technológiák PhD.) GEA-EGI Energiagazdálkodási Zrt, Budapest 1117, Irinyi J. u. 4-20. KULCSSZAVAK: salak-pernyekezelés, füstgáz kéntelenítési maradékok, ettringit

képződés, szivárgási tényező BEVEZETÉS A villamosenergia-termelés szükségszerű velejárója egy bizonyos szintű környezeti terhelés – ez az ára modern társadalmunk kényelmének és „jólétének”. Elengedhetetlen ugyanakkor az állandó törekvés e környezeti hatások csökkentésére, s a kockázatok ésszerű legalacsonyabb szinten való tartására. Energiaforradalom ide vagy oda, a világ ma is a széntüzelésből nyert villamosenergiára támaszkodik. Az egyre nagyobb energiaéhségű fejlődő országok energiaintenzív ipari tevékenységei és nagy mennyiségben rendelkezésre álló szén készletei világszinten növekvő szén felhasználást vetítenek előre1. Ez jelentős környezeti stresszt jelent globálisan a klímára nézve – gondoljunk csak a mérhetetlen szén-dioxid kibocsátásra – de káros hatást gyakorol a helyi környezetre is. A szén-dioxid és a nitrogén-oxidok például hatással vannak az ózon-rétegre, a szénmonoxid belélegezve veszélyes komponens, a kén-dioxid a savas esőkért felelős, a szilárd szennyezők pedig olyan nehézfémeket tartalmazhatnak, amelyek a talajba és vizekbe jutva mérgezhetik az élővilágot. E környezeti hatások minimalizálására illetve elkerülésére számos különböző technológiát fejlesztettek. A szén-dioxid kibocsátás az erőmű hatásfokával csökkenthető, a nitrogén- és kén-dioxidok leválasztására komplett berendezések állnak rendelkezésre, a szilárd fázisú szennyezők ellen porleválasztóval védekeznek, s végül hatékony megoldást keresnek a képződő salak és pernye környezetbarát deponálására is. A tüzelési maradékok a tüzelő berendezés számos pontján felhalmozódhatnak. Ezek mennyisége és minősége nagyban függ az eltüzelt szén minőségétől illetve a tüzelési technológiától. A porleválasztóban képződő pernye teszi ki az összes 1

International Energy Agency: CO2 Emissions From Fuel Combustion, Highlights, 2012 http://www.iea.org/co2highlights/co2highlights.pdf

18th International T H E R M O Conference

tüzelési maradék 80 százalékát, a maradék 20 százalék a képződő salak. Jelentős ezen kívül a kéntelenítő berendezésben keletkező hulladék, elsősorban gipsz, ami értékesítési lehetőségek hiányában sok esetben egyszerűen lerakásra kerül. E hulladékok mennyisége általában nem több a pernye 20 százalékánál. A tüzelési maradékok ártalmatlanítására több különböző technológia létezik. Az úgynevezett száraz technológia jelentős porterhelést jelent a helyi környezetre nézve, míg a hígzagyos rendszerek jelentős vízigénnyel működnek, illetve elfolyó vizeikkel sokszor elszennyezik a talajt és a talajvizet. A sűrűzagy rendszer egy ezektől eltérő salak-pernyekezelési technológia, aminek alapja a tüzelési maradékok és víz intenzív keverése. A rendszer képes egyszerre kezelni a salakot és pernyét, sőt, füstgáz-kéntelenítési maradékok bekeverésére is alkalmas. A folyamat végén a depónián egy szilárd, homogén, környezetet kímélő anyag keletkezik, ami minden minőségi követelményt képes teljesíteni. PERNYEKŐ KÉPZŐDÉS A hamu egyes komponensei víz jelenlétében hajlamosak szilárd fázisba kerülni. E kémiai folyamat lényege az, hogy a „puzzolános” (szilícium, alumínium) tulajdonságú szilárd anyagszemcsék felületének nedvesítésével a kalcium-hidroxiddal (mely a szabad kalcium oxidból keletkezik a vízzel való keveredéssel) reakcióba lépnek. A kalcium-hidroxid a reakcióban leépül, de a reakciót követően vízben nem oldható, szintetikus kalcium-szilikát tartalmú, másrészt vízben rosszul oldódó kalciumaluminium-szulfát vagy kalcit (CaCO3) keletkezik (ez az úgynevezett ettringit képződés). Maga a kémiai reakció hosszabb folyamat, így a teljes reakció lejátszódása során fokozatosan vesz fel még vizet2.

Balra: Elektron mikroszkópos felvétel kalcium-hidroxid lemezekről és ettringit tüskékről; jobbra: beágyazódott pernyeszemcse 2

Veszprémi Egyetem, Mérnöki Kar, Folyamatirányítás Tanszék: Preparation of High Concentration Ash Slurry Disposal at Eesti Power Plant


E reakciók a víz és a hamu alkotói között spontán mennek végbe, adalékanyag hozzáadása nélkül. A kémiai folyamat kimenetelét ugyanakkor több körülmény is erősen befolyásolja; ilyen például több reakcióban résztvevő komponens jelenléte, a felhasznált víz pH-ja, a szemcseeloszlás, vagy a keverés módszertana. A sűrűzagy technológia lényege éppen abban rejlik, hogy biztosítja a kémiai reakció létrejöttéhez szükséges lehető legjobb körülményeket. Ehhez elsősorban két fontos részletet kell pontosan beállítani: az optimális vízmennyiséget és a keverés intenzitását. A vízmennyiség pontos beállítása a reakcióhoz illetve a szivattyús kiszállításhoz szükséges; az intenzív keverés a homogén keverék előállításához fontos. A megoldás: keverőlapátok nélküli hidrodinamikus keverés alkalmazása. A megkevert sűrűzagy ezután szivattyúk segítségével csővezetéken keresztül kerül kiszállításra turbulens áramlást fenntartva3. A KEVERÉSI FOLYAMAT A sűrűzagy technológia legfontosabb eleme a mixer. A sűrűzagy mixer fogadja a pernyét, és 0,8:1-1,2:1 víz:szilárd tömegarányban elvégzi a keverést. A pernyén kívül 15-25 mm szemcsenagyságú salak és gipsz bekeverése is lehetséges. A keverék előállításához szükséges víz, bizonyos pH határok között – bármilyen erőművi hulladékvíz lehet.

Két beépítésre váró sűrűzagy mixer 3

BME Hidrodinamikai Rendszerek Tanszék: Sűrűzagy Keverő Áramlástechnikai Vizsgálata, 2010, Budapest.


A sűrűzagy mixer a következő elemekből épül fel: -

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Előkeverő fej a száraz pernye és egyéb opcionális száraz input fogadására. Az előkeverés a megkevert sűrűzagy, a szárazanyagok és a szükséges mennyiségű víz keverését végzi; Keverő tank a nedves input anyagok fogadására (salak, gipsz zagy). A keverő tankban történik az előkevert pernye és a nedves inputok keverése. A keverő tankban a megfelelő tartózkodási idő biztosítja a homogén keverék létrejöttét. Két, szivattyúval ellátott recirkulációs kör (tartály-visszakeverés és fejvisszakeverés) a hidrodinamikus keverés és a homogén állag elérésének biztosítására. E két recirkulációs körnek nagy szerepe van a végső anyag minőségének kialakításában. A pernyeadagolás és a kiszállítás beállításához szükséges, a sűrűzagy keverék minőségét szabályozó segéd berendezések.

A sűrűzagy mennyiségét és minőségét egy beépített sűrűségmérő rendszer figyeli. A mért zagysűrűségtől függően lép működésbe a pernyeadagolásért felelős forgócellás adagoló. Ezzel érhető el és tartható fenn a zagy állandó sűrűsége A sűrűzagy keverőn belüli magassága is állandó megfigyelés tárgya, ennek beállítását a hozzáadott víz mennyiségével lehet szabályozni. A sűrűzagy keverő megfelelő öblítő rendszerrel és ürítő pontokkal felszerelt; ez megakadályozza a bármilyen leállás következtében fellépő dugulás lehetőségét. A SŰRŰZAGYOT ALKOTÓ ANYAGOK Pernye: a sűrűzagy rendszer használatához a pernyét száraz formában szükséges összegyűjteni. A pernye silókba való szállításához száraz pneumatikus szállítórendszer használata ajánlott. A silók vésztárolási lehetőséget jelentenek a rendszer bármilyen vészleállása esetén. Egyes esetekben a pernyét eltérő keletkezési helye miatt két külön rendszerben gyűjtik (filter-pernye és eco-pernye). A sűrűzagy keverő probléma nélkül képes kezelni a két helyről érkező pernyét is. Technológiai víz: a sűrűzagy rendszer számára szükséges a technológiai víz állandó elérhetősége a kívánt nyomástartományban, hiszen víz hozzáadásával szabályozható a keverék szilárd-folyékony aránya. A technológiai víz lehet ipari víz, illetve gyakorlatilag bármilyen, az erőműben használt technológiák által termelt hulladékvíz is, mint például a füstgáz kéntelenítő hulladékvize, vagy a nedves hűtőtornyok lelúgozásából származó hulladékvíz. Korlátot egyedül a víz pH értéke jelenthet. Salak: a salak gyűjtése többféle módon történhet, ezek két csoportra oszthatóak: nedves és száraz salakeltávolításra. Nedves módszer többek között a kaparós salakeltávolítás, s száraz technológia például léghűtéses szállítószalag használata. 18th International T H E R M O Conference

A kazánból összegyűjtött salak formátlan, üvegszerű anyag, amit a keverőbe való adagoláshoz 20-25 mm-es szemcseméretre szükséges törni. A részecskék nem tartalmaznak oldható anyagot, szállításuk nedves salakeltávolítás esetén vízzel történik. Ebben az esetben besűrítő alkalmazása ajánlott a megfelelő, 1:3-1:5-ös arányú víztartalom eléréséhez. A besűrített salak ezután a keverőbe vezethető. A salak siló és a keverő közti távolságtól függően a salak mixerbe való elszállítása száraz és nedves formában is történhet; az utóbbi esetben használt salak-víz arány a föntieknek megfelelően 1:3-1:5. Füstgáz kéntelenítői gipsz: a kén-dioxid füstgázból való eltávolítására számos technológia létezik. Ezek közül a legelterjedtebb a nedves mosatás, amikor a füstgázban található légszennyező anyagokat mésztej befecskendezésével közömbösítik. A folyamat mellékterméke egyrészt a 10-15%-os víztartalmú gipsz, másrészt az igen szennyezett, gáztisztítóból származó hulladékvíz. E keletkező hulladékok mennyisége és minősége elsősorban a tüzelőanyagként használt szén minőségétől függ. Hangsúlyozandó, hogy a sűrűzagy előállításához nem szükséges kéntelenítői maradékok bekeverése, de igény esetén lehetséges.

A SŰRŰZAGY SZÁLLÍTÁSA A sűrűzagy valójában pernye és víz által képzett sűrű szuszpenzió, aminek sűrűsége és viszkozitása jóval a víz értéke fölötti. Ez azt jelenti, hogy a kiszállításhoz nagyobb nyomás szükséges a csövekben, mint a víz esetében. A nagyobb salak szemcsék az áramló sűrűzagyban lebegésben maradnak és nem ülepednek le a csőben, ehhez azonban nagyobb áramlási sebesség szükséges (legalább 1,2-1,5 m/s). A sűrűzagy rendszer leállása esetén a keverőt és a csöveket vízzel át kell mostani, ezzel megelőzhetők az esetleges dugulások. A szállításhoz használt szivattyúk centrifugál vagy dugattyús szivattyúk, 4 km feletti kiszállítási távolság esetében a dugattyús szivattyú ajánlott. A kiszállító és elosztó csővezetékek kopásálló szénacélból készülnek, méretezésük a megfelelő szállítási sebességet figyelembe véve történik. Ez azért fontos, mert a turbulens áramlás megszakadásakor a zagyban lévő részek elkezdenek kiülepedni, ami akár duguláshoz is vezethet. A csővezeték rendszer a keverő berendezés után elhelyezett szivattyúnál indul, adott távolságonként ürítő pontokkal felszerelt. A csővezeték karimás kötésekkel kapcsolódik össze, ezek azonban szükség esetén könnyen megbonthatóak és leüríthetőek (például az elfagyás elkerülése végett).


A sűrűzagy optimális sűrűsége által megkövetelt nyomás viszonylag alacsony, körülbelül 40 bar 6-8 km-es kiszállítási távolság és nem túl nagy magasságbeli különbség esetén. A MEGSZILÁRDULT ANYAG KÖRNYEZETVÉDELMI ELŐNYEI A sűrűzagy rendszer legfőbb előnyeit leginkább a deponált sűrűzagy kedvező tulajdonságain lehet megfigyelni. Az intenzív keverés által beindított kémiai reakciók olyan végterméket eredményeznek, amely a depóniára kiöntve szilárd fázisú, tömör anyag lesz4. A technológia eredményeként létrejött anyagban a keveréskor hozzáadott víz egy része kémiai kötésbe kerül, egy másik része pedig az anyag pórusaiban raktározódik. Ehhez képest elenyésző mennyiség képes csak átfolyni a megszilárdult zagyon, így a kifolyó csurgalékvizek mennyisége igen kevés. A szivattyúzás költsége ezért alacsony. A csurgalékvizek kis mennyiségén túl azok minőségében is előnyös változás tapasztalható. Ez egyrészt az alacsony szivárgási tényezőnek köszönhető, másrészt pedig annak, hogy a megszilárdult anyag a kémiai reakció során úgy zárja magába a szennyező elemeket, hogy azok nem oldódnak ki az átszivárgó vizek hatására. A csurgalékvizek így általában megfelelnek minden környezetvédelmi határértéknek. A megszilárdult depónia nyomószilárdsága igen magas, az egymásra hordott rétegek összmagassága elérheti akár a 40-60 métert is. Az egyes szintek 3-4 méterenként töltik fel; a műtárgy így egy piramist alkot, ami akár 15 emeletből is állhat. Az egyes szinteken kialakított gátak anyagának legalább 70%-a a megszilárdult sűrűzagyból készíthető. A depónia művelése egyszerű, nem igényel állandó személyzetet; az egyetlen gyakoribb művelet a kifolyási pontok heti rendszerességű váltása. A szilárd felületet nem erodálja a szél, a felszín nedvesítésére nincs szükség, nem jelentkezik olyan kiporzás, ami a hasonló technológiák velejárója5. A lezárt, rekultivált lerakót az egyes gátak felszínéhez hasonlóan növénytakaróval borítják (lásd a képet alább), így az jól illeszkedik a tájba.

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Energiagazdálkodási Intézet; Wenzel G. Béla, Dr. Csáki Ferencné: Erőművi Zagyterek Környezeti Hatásainak Vizsgálata, 1992, Budapest. 5 Energiagazdálkodási Intézet; Dr. Vámos György, Dr. Sz. Tóth György, Dr. Csáki Ferencné: A Pécsi Hőerőmű Vállalatnál tervezett sűrűzagy depónia környezeti hatásainak vizsgálata; 1990, Budapest.


Használatban lévő sűrűzagy depónia a Mátrai Erőműben

A lerakó környezetvédelmi engedélyezése nemzeti illetve nemzetközi szabályozásokhoz kötött. A sűrűzagy rendszer által előállított szilárd zagy eddig minden esetben teljesítette azokat a kívánalmakat, amiket az illetékes hatóságok a rendszer üzemeltetésének feltételeként megszabtak, legyen szó Európáról vagy az Egyesült Államokról. IRÁNYÍTÁSTECHNIKA A sűrűzagy rendszer az erőművi technológia egy eleme. Amennyiben az információk gyűjtése, illetve a rendszermonitoring egy közös vezénylőben történik, úgy a sűrűzagy rendszerről érkező szükséges információ adatbusz rendszeren keresztül érkezik a vezénylőbe. Amennyiben minden információt elosztva jegyeznek és kontrollálnak, úgy a sűrűzagy rendszer külön vezénylő egységgel is ellátható, amiben operátor konzol és adatgyűjtő van. A sűrűzagy rendszer esetében folyamatosan figyelt paraméterek a sűrűség, a hőmérséklet és az áramlási sebesség. A sűrűzagy rendszer egy erőművi segédberendezés, ami ennek megfelelően önállóan, állandó felügyelet nélküli üzemelésre is képes.

KÍSÉRLETI MINI-MIXER Minden egyes sűrűzagy rendszer különböző. A kialakított rendszer minden esetben a felhasználó igényeihez, a tüzelési maradékok mennyiségéhez, és a bekeverni szándékozott anyagok minőségéhez igazított. A sűrűzagy rendszer széleskörű alkalmazhatóságának demonstrálására GEA-EGI Zrt. kifejlesztett egy kísérleti minimixert; egy olyan kisméretű keverő rendszert, amely a világ minden tájára


elszállítható demonstrációs kísérleti keverések elvégzésére és az üzemszerű működés szimulálására.

A kísérleti mini-mixer elfér egy konténerben

A kísérleti mini-mixer az igazi rendszerhez hasonlóan a pernye mellett salak és gipsz bekeverésének, illetve hulladékvizek használatának demonstrálására is képes. Az általa előállított sűrűzagy keverék minták alkalmasak különböző környezetvédelmi vizsgálatok elvégzésére, a rendszer által előállított szilárd végtermék tulajdonságainak elemzésére. A mini-mixer alkalmas tehát a Vevő igényeinek megfelelő rendszer teljes körű szimulálására. GEA-EGI ENERGIAGAZDÁLKODÁSI ZRT. A sűrűzagy technológia alapját képző keverő berendezés egy szabadalom alatt álló magyar találmány, amit a ’90-es évektől folyamatosan fejlesztenek és tökéletesítenek. A technológia 15 éves üzemeltetési tapasztalattal rendelkezik; az első rendszert 1998-ban helyezték üzembe a Mátrai Erőműben, s ez azóta is problémamentesen üzemel. A szabadalom tulajdonosa és forgalmazója a GEA-EGI Energiagazdálkodási Zrt. EGI a német tulajdonú GEA Csoport, egy nagy élelmiszer és energiaipari rendszereket forgalmazó, 24 500 főt foglalkoztató, 2012-ben 5,7 milliárd eurós bevételű vállalatcsoport tagja. A sűrűzagy technológia mellett az EGI által szállított másik legfontosabb technológia a Heller-féle száraz hűtőtorony, így lehetséges az, hogy GEÁ-n belül a vállalat a Hőcserélő szegmensben foglal helyet. A Heller-féle hűtőtornyon és a sűrűzagy technológián kívül EGI egyéb BoP típusú feladatok elvégzését is vállalja; ilyen többek között távfűtési rendszerek tervezését és kivitelezését, illetve folyamatautomatizálást.


1948-as alapítása óta EGI számtalan nemzetközi és hazai energetikai piacon szerzett tapasztalatot. Az általa szállított fejlett technológia és magas mérnöki kultúra a világ minden táján büszkén megállja helyét. HIVATKOZÁSOK [1] International Energy Agency: CO2 Emissions From Fuel Combustion, Highlights, 2012, 7. old.; http://www.iea.org/co2highlights/co2highlights.pdf [2] Veszprémi Egyetem, Mérnöki Kar, Folyamatirányítás Tanszék: Preparation of High Concentration Ash Slurry Disposal at Eesti Power Plant; 2005, Veszprém. [3] BME Hidrodinamikai Rendszerek Tanszék: Sűrűzagy Keverő Áramlástechnikai Vizsgálata; 2010, Budapest. [4] Energiagazdálkodási Intézet; Wenzel G. Béla, Dr. Csáki Ferencné: Erőművi Zagyterek Környezeti Hatásainak Vizsgálata; 1992, Budapest. [5] Energiagazdálkodási Intézet; Dr. Vámos György, Dr. Sz. Tóth György, Dr. Csáki Ferencné: A Pécsi Hőerőmű Vállalatnál Tervezett Sűrűzagy Depónia Környezeti Hatásainak Vizsgálata; 1990, Budapest.


Environmental protection with Dense Slurry System Lili Kránitz1, Géza Walter2 (1MSc. in Regional and Environmental Management, 2PhD. in Mech Eng. / Combustion Technologies) GEA-EGI Contracting/Engineering Co. Ltd, Budapest, Irinyi J. str. 4-20, Hungary, 1117

KEYWORDS: ash handling, FGD products, ettringite formation, hydraulic conductivity, leach performance INTRODUCTION Operation of thermal power stations always involves some kind of environmental pollution. it’s the money we pay for the commodity and ”welfare” of our modern society. It is, however, of high importance to reduce this negative impact to the smallest necessary level and to eliminate as many risk factors as possible. No matter what we do the world still mostly runs on power gained from coal combustion. Currently, coal is the resource that is used to satisfy the ever-growing energy demand of developing countries (think of China and India) with energyintensive industrial activity and large available coal reserves1. This poses significant stress on the global environment primarily in the form of CO2 emissions but several harmful impacts on the local environment, too. Carbon dioxide and nitric oxides are, for instance, harmful to the ozone layer, carbon monoxide is a hazardous gas, sulfuric oxides cause acid rains and solid particles often carry heavy metals that pollute the vegetation and the natural water resources. Various technologies were developed and introduced in order to minimize these unfavorable effects. Carbon dioxide can be reduced by increasing the plant efficiency, DENOX and DESOX technologies are applied in order to remove harmful pollutants from the flue gases, more efficient fly ash or dust precipitators are introduced and, finally, more effective ash processing is adopted for environmentally friendly disposal of firing residues. Firing residues accumulate at various points of the firing system. The quantity and composition of these residues are basically determined by the coal and ash quality and by the applied firing technology. Bottom ash or bed ash may exceed 20 percent of residues. About 80 percent of firing residues is collected as fly ash, mostly in the precipitator. Desulfurization is another operational issue of high importance. The removal of sulfur oxides from the flue gas generates additional by-products such as 1

International Energy Agency: CO2 Emissions From Fuel Combustion, Highlights, 2012 http://www.iea.org/co2highlights/co2highlights.pdf


gypsum that in many cases is simply landfilled. The amount of the by-products from the desulfurization process generally does not exceed 20 percent of the fly ash. Several ash-handling technologies exist for the final disposal of the firing residues. Dry disposal systems involve fugitive dusting on surface while wet or lean systems suffer from dissolution into local surface or ground waters not to mention the risk of spill out in case of dam failures. The Dense Slurry System is a distinct ash-handling technology that is based on the intensive mixing of coal combustion residues and water. It is capable of handling all these solid and liquid residues in one mixing system. It provides an environmentally sound collecting, processing and disposal method with a final product that meets all quality standards. ASH STONE FORMATION Several components of ash tend to form solid mineral phases in presence of water. This transformation consists of a reaction between the so called pozzolanic materials (siliceous or aluminous) and the calcium hydroxide. Calcium hydroxide deteriorates while indissoluble synthetic calcium silicate and poorly soluble calcium aluminum sulfate (calcite, CaCO3) is formed (this is the so called ettringite formation). The chemical reaction itself is a longer process therefore the water intake is performed gradually over a longer period of time2.

On the left: Scanning electron microscopy image of fracture surfaces of hardened cement paste, showing plates of calcium hydroxide and needles of ettringite; on the right: Scanning electron microscopy image of ash showing an aluminosilicate sphere with precipitated Ca-rich phase

These reactions can happen spontaneously, no additives are needed to start the reaction. The process, however, is influenced by several conditions like the presence 2

Veszprem University, Engineering Faculty, Dept. Of Silicate and Process Engineering: Preparation of High Concentration Ash Slurry Disposal at Eesti Power Plant


of several components, water alkalinity, size distribution and the quality of mixing. The final material is a solid, cement-like product that is physically stable and has high compressive strength. The objective of the Dense Slurry technology is to ensure the possible best conditions for the ash transformations. This means first of all to focus on the optimum quantity of water. Sufficient amount of water is important for the reactions but also ensures that the mixture shall be easily pumpable. Second of all intensive mixing is needed to generate homogenous slurry. As a solution hydrodynamic mixing is applied without the use of any paddles or mechanical agitators, and then the slurry is transported by pumps through pipelines with turbulent flow3. THE MIXING PROCESS The core component of the Dense Slurry technology is the Mixer. The role of the Dense Slurry mixer is to receive the fly ash, mix it with the necessary make-up water to produce homogenous dense slurry with 0.8:1 to 1.2:1 water-to-solid ratio on weight basis to be discharged to the ash disposal area by the dense slurry transport pumps. In addition to fly ash other solid residuals may be mixed in the slurry such as coarse ash from the economizer and air heaters, bottom or bed ash from the furnace with particle size of 15-25 mm (3/4”-1”), or gypsum from the FGD scrubber. Waste waters can also be utilized as make-up water in the system.

Two mixers ready to be installed 3

BME Hidrodinamikai Rendszerek Tanszék: Sűrűzagy Keverő Áramlástechnikai Vizsgálata, 2010, Budapest.


Each Dense Slurry mixer consists of: -

-

-

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a pre-mixer head which receives dry fly-ash and other optional dry input material streams to produce premix slurry by mixing these with the recirculated slurry from the retention tank and with the necessary make-up water; a retention tank or mixing tank, which receives the wet input material (bottomash, coarse ash and gypsum slurry) streams and mixes them with the premix slurry from the pre-mixer head; it also provides ample residence time for homogenization; two recirculation lines with pumps (head and mixer tank slurry recirculation) which ensure the hydrodynamic agitation and thus the proper mixing and homogenization of the slurry to produce dense slurry of the required quality; auxiliary equipment that are necessary for the proper dosing, feeding and discharge of the input and output material streams in order to achieve proper control of dense slurry quality.

The quantity and quality of the dense slurry is checked and controlled by an installed slurry density metering system. Based on the metered slurry density, the input stream of fly-ash is controlled via rotary dosing feeders on the input lines, in order to maintain an adequate and constant density of the discharged dense slurry stream. The level of slurry within the mixer retention tank is also monitored and maintained by adjusting the make-up water flow. The entire DS mixer system is equipped with adequate flushing devices and drains that prevent the formation of blockages in the system in case of any outages. MATERIALS FORMING THE DENSE SLURRY Fly ash: The fly ash must be collected in dry form. Dry pneumatic fly ash conveying system to transport fly ash into storage silo(s) is recommended. The purpose of the silo(s) is to provide buffer capacity in emergency situations. Fly ash is generally classified as fine and coarse ash. It may happen that separate collection of the two types for quality classification is required. The mixer can be easily integrated even when two separate collection systems are in place. Make-up water: Make-up water shall be continuously available within the specified pressure range to be used by the Dense Slurry process in order to ensure the appropriate solid water ratio in the mixture. The make-up water can be fed from the process water system or from practically any plant waste water sources such as FGD waste water, wet cooling tower blow-down or thickener overflow streams. Bottom ash: The bottom / bed ash can be collected by any of the usual methods: Wet: Bottom / bed ash, as wet granulate may be removed from under the boiler with water filled ash scraper / drag chain conveyor / jet ejectors / etc. 18th International T H E R M O Conference

Dry: Bottom / bed ash may be removed from under the furnace by an air cooled belt conveyor system that allows proper after burning and cooling of the BA particles, with less radiative heat losses of the furnace. Bottom ash is reclaimed from the furnace as a mostly amorphous and glassy material that is then crushed to less than 20-25 mm particle size. The particles do not contain soluble compounds and are, usually, transported as lean ash – water slurry, in case of wet BA handling. Due to the use of too much water in such systems DSS requires that an additional facility needs to be applied in order to reduce water content up to 1:3 - 1:5. For this purpose GEA recommends that a thickener is used. The thickened bottom ash slurry can be fed into the mixer. Bottom-ash thickener is in the product portfolio of GEA. Depending on the distance between these bottom-ash silos and the mixers the bottom ash can either be transported in dry form or as bottom-ash slurry with 1:3-1:5 ash to water ratio. FGD gypsum: Various techniques are used for removing sulfuric oxides from flue gases. One solution is the recirculating fluidized bed firing where pulverized limestone is introduced already in the furnace in order to capture sulfuric oxides. Excess limestone and calcium sulfite are removed with the bed ash. The most widely applied technology is, however, the wet scrubbing where hazardous gaseous pollutants are removed by injected limestone and water slurry. The product is gypsum with 10 to 15 per cent water content. Another by-product is the heavily polluted waste water that is blown down from the scrubber. The quantity and quality of gypsum and waste water primarily depends on the sulfur content of coal. Waste water for make-up purposes: Other waste waters such as FGD waste water, wet cooling tower blow-down can be used as make-up water although certain limitations may apply. TRANSPORTATION OF DENSE SLURRY Dense slurry is a thick suspension of fly ash and water that has higher density and viscosity than water has. This means that much higher pump heads are required for transportation in pipelines than with clean water. The bigger bottom ash or bed ash particles may be suspended in the fly ash slurry. In order to prevent settling of solid particles and blockage of pipelines, flow velocity may not decrease below a limit value of about 1.2 to 1.5 m/s. In case the dense slurry plant is shut down its vessels and pipelines shall be flushed with clean water. Variable speed centrifugal pumps or piston, piston diaphragm pumps are used for transportation. For power plant to landfill distances over 4 km piston pumps or hydrohoist can be used.


The DS transport and distribution pipelines are of simple carbon steel pipes sized to allow sufficient transport velocity to avoid settling of the slurry and maintain turbulent flow. The pipeline starts downstream of the DS distance transport pump. Discharge flange can be isolated by remote actuated shut-off valves. The pipeline is equipped with the necessary drains. The pipeline is constructed of sections according to the terrain topology. Each section can be separately drained to empty the line after flushing to avoid freezing, for example. The optimum density of the DSS allows using pipes and valves of low pressure ratings. The pressure rating of the pipeline components is in accordance with the maximum allowable head of the pump train. As an example, the pressure rating is 40 bar if the discharge distance is around 6–8 kms (ca. 4 – 5 miles) and the geodetic elevation is not too much. ENVIRONMENTAL ADVANTAGES OF THE FINAL PRODUCT The consistency and quality of the discharged dense slurry as end-product represents best the principal advantage of the Dense Slurry System. The effective homogenous mixing favors chemical reactions in the dense slurry which has important positive impact on the final quality of the settled deposited slurry4. The technology involves insignificant amount of return water. Consequently, the water usage and water pumping demand is as low as possible resulting in compatible operation costs. Leach performance is significantly lower than in other technologies. The solidified material shows no significant dissolution while all hazardous elements are firmly bound in the final product that generally meets quality standards. Homogenous dense slurry deposits have the achievable highest compressive strength and lowest hydraulic conductivity among the competing technologies, if the same feedstock materials are considered. As a consequence, the disposal site is characterized by dry, solid surfaces with no fugitive dust, low leachate rates with authority accepted leachate quality, easy maintenance and operation.

4

Energiagazdálkodási Intézet; Wenzel G. Béla, Dr. Csáki Ferencné: Erőművi Zagyterek Környezeti Hatásainak Vizsgálata, 1992, Budapest.


Dense Slurry System in operation at Mátra Power Plant

High compressive strength results in more economical filling-up; over the years, the ashfield can be filled up cell by cell of approximately 3-4 meters each level, forming a pyramid5. At least 70% of material of the additional dykes can be the settled coal combustion residue (CCR) deposit itself. Since no fugitive dusting occurs on surface, no specific sprinkler wetting system is needed. The closed down and rehabilitated ash field can nicely fit in the environment. The licensing of disposal area is subject to local and international regulations and requirements. The solidified slurry produced by GEA EGI's DS system has always met the requirements and the authorities approved the operation of the dense slurry system in the EU as well as in the USA. CONTROL SYSTEM The Dense Slurry System is a part of the power station technology. In the case all information is collected in a central control room for processing, the required data are transmitted via the data bus system. If the distributed control philosophy is adopted, the dense slurry plant is equipped with its own control room where operator consoles and data loggers are placed. There are up to 100 pumps, valves, motors, etc. in a typical plant supervised by a programmable computer. Fluid density, temperature and flow velocity are the main controlled parameters. The dense slurry mixer is an auxiliary facility in the power station that is capable to operate without continuous supervision. 5

Energiagazdálkodási Intézet; Dr. Vámos György, Dr. Sz. Tóth György, Dr. Csáki Ferencné: A Pécsi Hőerőmű Vállalatnál tervezett sűrűzagy depónia környezeti hatásainak vizsgálata; 1990, Budapest.


PILOT MOBILE PLANT All Dense Slurry Systems are tailor-made and adapted for each Customer on the basis of the actual coal properties, ash quantity and composition. In order to be able to demonstrate the efficiency of the technology under various conditions GEA EGI has developed a Pilot Mobile Plant, a pilot scale copy of the core system that can be shipped and operated all around the world. This enables us to demonstrate the technology process and simulate real-operation conditions.

The pilot mobile mixer fits in a container

In addition, other coal combustion residues, as bottom ash, coarse ash and gypsum slurry can be added while waste waters as FGD water or boiler blow-down water can be used for make-up purposes. It is also suitable for the production of samples for further environmental investigations and different slurry property measurements. This ensures the demonstration of the workability of the Dense Slurry System under any conditions given by the Client.

GEA EGI CO. LTD. The essence of the technology, the mixer is a Hungarian patent that is continuously developed from the 90’s. It has over a decade of operational experience since 1998 when it was installed in Mátra Power Plant. The owner and distributor of the Dense Slurry Technology is GEA EGI Co. Ltd. EGI is a member of GEA Group, a large system provider for food and energy processes with over 24 500 employees and EUR 5.7 billion revenues in 2012. Since one of the product lines of EGI is the Heller type dry cooling tower, the company is situated in the Heat Exchangers segment within the GEA Group. Besides DSS and Heller type cooling towers EGI provides BoP systems of other kind such as district heating and process automation. 18th International T H E R M O Conference

Since 1948 when EGI was founded the company has gained great experience in the national and international power industry. The technologies in use are mature, welldeveloped systems ready to serve their Clients over the world. REFERENCES [1] International Energy Agency: CO2 Emissions From Fuel Combustion, Highlights, 2012, p. 7.; http://www.iea.org/co2highlights/co2highlights.pdf [2] Veszprem University, Engineering Faculty, Dept. Of Silicate and Process Engineering: Preparation of High Concentration Ash Slurry Disposal at Eesti Power Plant; 2005, Veszprém. [3] BME Hidrodinamikai Rendszerek Tanszék: Sűrűzagy Keverő Áramlástechnikai Vizsgálata; 2010, Budapest. [4] Energiagazdálkodási Intézet; Wenzel G. Béla, Dr. Csáki Ferencné: Erőművi Zagyterek Környezeti Hatásainak Vizsgálata; 1992, Budapest. [5] Energiagazdálkodási Intézet; Dr. Vámos György, Dr. Sz. Tóth György, Dr. Csáki Ferencné: A Pécsi Hőerőmű Vállalatnál Tervezett Sűrűzagy Depónia Környezeti Hatásainak Vizsgálata; 1990, Budapest.


eRTM – A Vezetéknélküli Sínhőmérséklet Monitorozó Rendszer PECHAN IMRE, SZEPESSY ZSOLT evopro Innovation Kft. Budapest, Hauszmann Alajos u. 2, Magyarország, H-1116

ÖSSZEFOGLALÁS A sínhőmérséklet folyamatos monitorozása jelentősen javíthatja a vasúti közlekedésbiztonságot. A sín mentén több pontban történő hőmérsékletmérés megvalósítható vezetéknélküli szenzorhálózat alkalmazásával. Az eRTM az evopro Innovation Kft. által fejlesztett vezetéknélküli sínhőmérséklet monitorozó rendszer, mely a sínre szerelt szenzormodulokból, egy központi adatgyűjtő gateway egységből, egy adatbázisszerverből és kliens alkalmazásokból áll. A pilot rendszer nagyjából egy évig üzemelt a Magyar Államvasutak egy pályaszakaszán Tatabánya közelében.

1. Motiváció Manapság egyre nagyobb igény mutatkozik a vasúti közlekedés biztonságának és minőségének növelésére az ipari méréstechnika, a beágyazott informatika és a telekommunikációs technológiák legújabb vívmányainak alkalmazásával. A hőmérséklet a vasúti sín egy fontos paramétere, melynek folyamatos mérésére vagy becslésére közlekedésbiztonsági célból van szükség. A mai modern vasúti pályák javarészt hézagnélküli vágányok, melyek karbantartása lényegesen olcsóbb, mint a régebbi, hagyományos felépítményű, a sínvégek közt hézagokkal rendelkező pályáké. A hézagnélküli vágányoknál a sínszálak akár több kilométeres hosszúságban össze vannak heggesztve. A sínszál hosszirányú és laterális stabilitását az aljak, a sínleerősítés és az ágyazat biztosítják. Azt a hőmérsékletet, amely mellett a hézagnélküli vágány egy szakaszában ébredő feszültség éppen nulla, semleges hőmérsékletnek nevezik. Ennek értéke általában nagyjából 25°C. Amennyiben a sínszál tényleges hőmérséklete ezen értéknél magasabb vagy alacsonyabb, abban nyomóilletve húzófeszültség keletkezik, ami szélsőséges esetben akár a sín deformálódásához, kivetődéséhez vezethet [1]. Az esetleges sínkivetődés elkerülése érdekében sebességkorlátozás bevezetése válhat szükségessé a pályán az aktuális sínhőmérséklet függvényében. A gyakorlatban ugyanakkor a sínhőmérséklet követése gyakran csak ad hoc mérésekkel, vagy a várható időjárási körülményeken alapuló becslésekkel történik meg. A sínhőmérséklet folyamatos monitorozása megalapozottabb döntések meghozására adna lehetőséget a sebességkorlátozások esetleges bevezetésekor. Egy valósidejű sínhőmérséklet monitorozó rendszer összességében számos előnnyel és alkalmazási lehetőséggel járhat, mint például: - a közlekedésbiztonság növelése, illetve a vasúti infrastruktúra védelme a sínkivetődések és esetleges járműkisiklások megelőzésével


-

az alkalmazandó sebességkorlátozások időtartama és geográfiai kiterjedése pontosabban megválasztható, így elkerülhetők a felesleges korlátozások, ami javítja a vasúti szolgáltatás minőségét - téli időszakban a váltófűtés vezérlésének támogatása vagy teljes automatizálása energiamegtakarítási célokból - a hőmérséklet-ingadozással összefüggő pályaproblémák detektálása, előrejelzése, a karbantartások ütemezésének támogatása - a meglévő pályaszakaszok egyedi mikroklímájának feltérképezése, ami különösen hasznos lehet hidak, alagutak és egyéb műtárgyak közelében Jelen cikk elsődleges célja az eRTM rendszer bemutatása. Az eRTM egy vezetéknélküli, valósidejű sínhőmérséklet monitorozó rendszer, melyet az evopro Innovation Kft. fejlesztett ki, a fent említett célokból. 2. Elméleti háttér 2.1 A sín termikus modellje Amint arról már szó volt, a hőmérséklet mérés jelen fő célja a veszélyes mértékű, síndeformációt okozó hőmérsékleti értékek észlelése. A valóságban a sínen belül a hőmérséklet nem állandó, függ mindhárom térbeli koordinátától és persze az időtől is. Ésszerű egyszerűsítés ugyanakkor a sínhőmérsékletet állandónak tekinteni a sín egy adott keresztmetszetében. Ezen modell esetén a független változók a sín menti lineáris pozíció (x) és az idő (t), a függő változó pedig a hőmérséklet (T): (1)

T = f(x, t).

A vasúti sín egy dinamikus termikus rendszernek tekinthető (1. ábra), amely hősugárzással, hővezetéssel és konvekcióval hőmennyiséget vesz fel, illetve ad le környezetének az aktuális időjárási körülményeknek megfelelően. A hősugárzással megvalósuló hőcserét elsősorban a napsugárzás és a felhőzöttség mértéke határozza meg. A konvekció a levegő hőmérsékletétől, a páratartalomtól és a szélerősségtől függ. A hővezetés a sínszakasz mentén a különböző környezeti adottságok miatt kialakuló hőmérsékletkülönbségtől függően változik. Eközben a síndarab energiatároló képességét az öntvény hőkapacitása jellemzi. Amennyiben valamennyi tér- és időfüggő környezeti paraméter (peremfeltételek), továbbá a sín hőmérsékletének kezdeti hősugárzás

hővezetés

visszaverődés konvekció hősugárzás

hőkapacitás

hővezetés 1. ábra: Termikus modell


x [m]

eloszlása ismert, a sínszakasz hőmérséklet függvénye (f az 1. egyenletben) elméletileg meghatározható. Természetesen a gyakorlatban ez nem valósítható meg, hisz minden egyes környezeti paraméter mérésére nincs lehetőség. A műszakilag kivitelezhető megoldás a sín hőmérsékletének diszkrét pontokban történő mérése, és így egy koncentrált paraméterű, egyszerűsített termikus modell a-posteriori feltérképezése. 2.2 Hőmérsékletmérés A sín hőmérsékletének mérésére szolgáló alkalmas módszer és eszközök kiválasztása rendkívül fontos a megbízható eredmények elérése érdekében. A megfelelő mérési pont sínen való kijelölésekor, illetve az alkalmazott szenzor típusának megválasztásakor mind a mérési pontosságra, mind a terepi körülményekre tekintettel kell lenni. Azt is fontos szem előtt tartani, hogy a mérés legfontosabb célja továbbra is annak észlelése, hogy mikor válik a hőmérséklet miatt a sínszálban keletkező feszültség veszélyes mértékűvé. A szakirodalomban elérhető egy RSSB tanulmány, mely a vasúti sín termikus viselkedésével foglalkozik [2]. A tanulmányban leírt kísérletek során egy 90cm-es síndarab melegítésére és hőmérsékletének különböző eszközökkel, különböző pontokon történő mérésére került sor. LVDT szenzorok segítségével a sín hosszirányú hőtágulása is detektálva lett. A kísérlet során a sín mért hőtágulása és a hőtágulási együttható ismeretében meghatározták a sín elméleti, úgynevezett „bulk” hőmérsékletét, és összevetették azt a sín különböző pontjain tapasztalt hőmérsékleti értékekkel. A „bulk” hőmérséklet a síndarab integrális, átlagos hőmérséklete. Mivel egy adott síndarab hőmérséklete a valóságban nem állandó a sín mentén, a tényleges hőtágulás mértéke a „bulk” hőmérséklettől függ. Habár ennek mérésére nincs lehetőség, a tanulmány szerint meglehetősen pontosan becsülhető diszkrét pontokban történő mérésekkel. A kísérlet során a hőmérsékletet mind a sínfej, síngerinc és síntalp felületén és belsejében mérték. Ezek közül a síngerinc bizonyult a legmegfelelőbbnek a hőmérsékletmérés szempontjából annak gyorsabb és konzisztensebb viselkedése miatt. A kíséleti ereményekből lineáris regresszióval meg lett határozva, hogy a síngerinc felületének hőmérséklete segítségével a „bulk” hőmérséklet a következőképp számítható: TBULK = 0.999*TGERINC + 2.09.

(2)

Amint arról már szó volt, az alkalmazott szenzor típusa szintén befolyásolja a mérés minőségét. Széles körben alkalmazott, lehetséges szenzorfajták például: - digitális hőmérő (félvezető bandgap hőmérő szenzor) - termisztor - hőelem - optikai (IR) hőmérő A hőelem érzékelők pontossága meglehetősen korlátozott. Optikai alapú hőmérőket elsősorban olyan esetben alkalmaznak, ahol érintkezés nélküli hőmérésre van szükség. Figyelembe véve a szükséges mérési pontosságot (1°C-nál jobb), a széles mérési tartományt (-40...+70°C) és a környezeti adottságokat, a termisztorok és a digitális hőmérők merülen fel lehetőségként. Ha a szenzor egy furatban helyezkedik majd el a sínen, a termisztor a jobb választás a könnyebb szerelhetőség miatt. 2.3 Vezetéknélküli szenzorhálózatok A vezetéknélküli szenzorhálózatok [3, 4] egyre szélesebb körben terjedtek el az elmúlt években az olcsó, kis fogyasztású érzékelők, mikrokontrollerek és a vezetéknélküli


technológiák gyors fejlődése miatt. Manapság a vezetéknélküli szenzorhálózatoknak számos alkalmazási területük van, mint például a környezet monitorozása, épületautomatizálás, intelligens otthon, folyamatirányítás, egészségügyi alkalmazások, vagyonvédelem, katonai alkalmazások, tudományos kísérletek stb. Az ilyen rendszerek számos olyan tulajdonsággal rendelkeznek, melyek alkalmassá teszik őket a jelen célra is, vagyis a hőmérséklet folyamatos monitorozására egy sínszakasz mentén. A vezetéknélküli szenzorhálózatok térben elosztott autonóm szenzoregységekből állnak, melyek vezetéknélküli médiumon keresztül kommunikálva, kooperálva látnak el egy adott feladatot. Amint arról szó volt, egy tipikus ilyen feladat a környezet valamely paraméterének (pl. hőmérséklet) elosztott monitorozása. Egy ilyen rendszer működésének egyik alapelve az „adatfúzió”: az egyes szenzorok által előállított adatok együttesen kerülnek feldolgozásra és értékelésre, mely által előáll valamilyen értelmes, jelentőségteljes információ (ilyen lehet például a sín térbeli hőmérséklet-eloszlásának meghatározása a diszkrét mérésekből, vagy annak eldöntése, hogy szükség van-e sebességkorlátozásra a szakaszon). A vezetéknélküli szenzorhálózatok gyakran nehezen megközelíthető vagy veszélyes környezetben üzemelnek, ami megnehezíti vagy ellehetetleníti karbantartásukat. Ennek megfelelően az ilyen rendszerek fontos tulajdonságai a hibatűrés, az önszerveződés és az öngyógyulás. A szenzoregységek autonóm módon, dinamikusan hozzák létre és konfigurálják a hálózat topológiáját, alkalmazkodva a pillanatnyi körülményekhez. Az egységek nagy része általában akkumulátoros tápellátású, és hosszú élettartamra tervezett (hónapok vagy akár évek), ezért az egységek alacson fogyasztása létfontosságú. Mivel tápkábelekre nincs szükség, a rendszer telepítése is könnyebb, robosztussága nagyobb. Mindezen tulajdonságok rendkívül előnyösek egy a vasúti nyílt pályán üzemelő rendszer számára. 3. Az eRTM rendszer Az eRTM (evopro Rail Temperature Monitoring) az evopro Innovation Kft. által fejlesztett vezetéknélküli sínhőmérséklet monitorozó rendszer. A rendszer elemei a sínre szerelt szenzormodulok, a méréseket gyűjtő köztponti gateway egység, az adatbázisszerver és a kliens alkalmazások. A rendszer architektúrája a 2. ábrán látható. A következő alfejezetek részletesen is bemutatják az egyes komponenseket. 3.1 A szenzorok és az eSCTR kártya A szenzor modulok az evopro általános célú, flexibilis és bővíthető, vezetéknélküli szenzor- és interfészkártyáján, az eSCTR-en alapulnak [5]. Az eSCTR kártya legfontosabb elemei egy Texas Instruments MSP430 mikrokontroller és egy Digi International XBee rádiómodul. Az MSP430 mikrokontroller számos analóg és digitális I/O csatornával és sokféle interfész egységgel rendelkezik (pl. UART, SPI, I2C), ami különféle kommunikációs módszerek és protokollok széles skálájának alkalmazását teszi lehetővé (pl. RS-232, RS-485, 1-wire, stb.). Az XBee egység rádiós elérhetőséget biztosít az eSCTR kártya számára. A modul a 868MHz-es ISM sávban működik, és a Digi egyedi protokollját használja, mely pont-pont, pont-multipont és mesh jellegű kommunikációt is támogat. Mindezek segítségével az eSCTR modulok különböző topológiájú vezetéknélküli hálózatokat építhetnek föl (mint például a 2. ábrán látható lineáris és csillag topológiák). Az eSCTR kártya flexibilis architektúrája által könnyen adaptálható különböző alkalmazásokhoz. A kártyának két fő felhasználási lehetősége van. Az egyik esetben az eSCTR vezetéknélküli interfészkártyaként viselkedve lehetőséget ad arra, hogy bizonyos


eszközök (pl. PLC-k) valamilyen standard protokoll alkalmazása mellett rádiósan,

szenzor 868MHz ISM

vezetéknélküli hálózat lineáris topológiával

kliensek

GPRS szerver HTTPS

SMS riasztás gateway

vezetéknélküli hálózat csillag topológiával

2. ábra: eRTM rendszer különféle hálózati topológiákkal

kommunikációs kábelek nélkül kapcsolódhassanak össze, ami nagyon előnyös lehet például ipari környezetben. Ebben az esetben a kívánt protokollt (pl. Modbus) az eSCTR kártya valósítja meg valamelyik standard interfész egysége segítségével. Az ezen a csatornán vett kommunikációs csomagokat az eszköz továbbítja a rádiós oldalra és fordítva. A második felhasználási lehetőség során az eSCTR vezetéknélküli szenzorkártyaként működik. Ilyenkor a kártya egy környezeti paramétert monitoroz egy szenzorral, ami valamelyik analóg bemenetére vagy interfész egységére van kötve, a mérési eredményt pedig egy központi adatgyűjtő egységnek rádión küldi tovább. Az eRTM rendszer esetében az eSCTR kártya vezetéknélküli szenzoregységként van alkalmazva (második eset). A hőmérsékletmérés egy termisztorral valósul meg, ami az MSP430-as egy analóg bemenetére van csatlakoztatva. A termisztor a sínen egy zsákfuratba van beragasztva, mely a síngerinc semleges szála mentén helyezkedik el. A szenzoregység periodikusan méri a hőmérsékletet, az idő fennmaradó részében viszont készenléti üzemmódban marad (mind az MSP430, mind az XBee modul alacsony fogyasztású/alvó módban működik) a kis átlagos fogyasztás és a hosszú akkumulátor élettartam érdekében. Az adatokat a modul rádiósan továbbítja a gateway egységnek. 3.2 Gateway egység


A gateway modul egy egykártyás számítógépen alapul, rendelkezik továbbá egy XBee egységgel és egy GPRS kommunikációra szolgáló celluláris modemmel. Az XBee modul egy központi nyelő (adatgyűjtő) pontként működik a vezetéknélküli szenzorhálózat számára. A gateway megkapja a szenzoroktól a mért hőmérsékletértékeket, és GPRS kapcsolaton keresztül továbbítja azokat a szervernek. A GPRS csatorna sávszélessége meglehetősen alacsony, de az alkalmazás igényeinek tökéletesen megfelel, hisz a küldendő adatmennyiség is minimális. A gateway egység hálózati táplálású, és egy a vasúti pálya melletti oszlopra szerelt szekrényben helyezkedhet el. 3.3 Szerver Az eRTM rendszer harmadik eleme a szerver alkalmazás, mely megkapja a gatewaytől a mérési adatokat, letárolja őket egy adatbázisban és hozzáférést biztosít az adatok kiértékeléséhez. Ezen kívül riasztás küldésére is képes SMS-ben vagy e-mail-ben, hogyha a mért hőmérséklet értékek elérnek bizonyos előre megadott határértékeket. 3.4 Kliens alkalmazások Az eRTM rendszer részei azok a különböző kliens alkalmazások, melyek számos platformon futtathatók (standard PC, okostelefon, tablet, stb.), és amik a szerveren tárolt adatok különböző vetületeit jeleníthetik meg a célfelhasználó igényeitől függően. Ezen nézetek mutathatják az aktuális hőmérséklet értékeket, riasztásokat és szélsőséges értékeket, az elmúlt néhány óra/nap mérési adatait, vagy például hosszútávú trendeket és statisztikai adatokat. 4. A tesztüzem eredményei Tatabánya közelében a Magyar Államvasutak pályaszakaszán egy pilot rendszer lett telepítve, ami nagyjából 400 napot üzemelt 2010 augusztus – 2011 január, illetve 2011 április – 2011 november között. A pilot rendszer felépítését és elrendezését a 3. ábra mutatja. A rendszer három szenzoregységet tartalmazott, melyek egymástól néhány száz méterre, különböző geográfiai adottságokkal rendelkező mérési pontokon lettek elhelyezve. Szenzor1 egy magas sziklafal mellett lett a sínre szerelve, míg szenzor2 és szenzor3 nyílt területen helyezkedtek el. A gateway egység egy oszlopra lett szerelve szenzor2 közvetlen közelében. É gateway

szenzor2

szenzor1

SZIKLAFAL

150m

D

5m

szenzor3

200m

3. ábra: eRTM pilot rendszer


A mérési eredmények jól tükrözik a három szenzoregység környezetének mikroklímájában meglévő különbségeket. A 4. ábra példaképp mutatja három egymást követő nyári napon a regisztrált sínhőmérséklet értékeket 1 óra felbontással. Az első két (vélhetően felhőtlen) napon hasonló minta figyelhető meg. A délelőtt folyamán a hőmérséklet értékek egyszerre emelkednek. A maximális hőmérséklet nagyjából 45°C volt, amit szenzor2 és szenzor3 13:30-kor mért. A szenzor1 által mért sínhőmérséklet ugyanakkor 12:30 után csökkenni kezd (a sziklafal rávetülő árnyéka miatt), és 5-15°Ckal alatta marad a másik két ponton mért sínhőmérsékletnek a délután folyamán. A harmadik napon ugyanakkor mindhárom szenzor hirtelen hőmérsékletesést regisztrált 12:30 után, valószínűsíthetően a gyülekező felhők miatt.

Hőmérséklet [°C]

Mért hőmérséklet értékek 2011. 07. 16-18 között 50 40 30

szenzor1

20

szenzor2

10

szenzor3

0

2011.07.16 00:00

2011.07.16 12:00

2011.07.17 00:00

2011.07.17 12:00

2011.07.18 00:00

2011.07.18 12:00

2011.07.19 00:00

Dátum

4. ábra: Mérési adatok (példa)

Az 1. táblázat a szenzorok által valaha mért minimális és maximális hőmérséklet értékeket mutatja. A legnagyobb és legkisebb hőmérséklet 55,4°C és -17,13°C volt, melyet szenzor3 illetve szenzor2 mért 2011. 08. 24-én és 2010. 12. 19-én. A 2. táblázat azon órák számát mutatja (az összes, kb. 9600 óra közül), amikor a mérési pontok hőmérséklete szélsőséges intervallumokba esett. Szenzor1 a várakozásoknak megfelelően lényegesen kevesebb extrém meleg órát regisztrált, mint szenzor2 és szenzor3. A 3. táblázat a szenzorok közt páronként tapasztalt legnagyobb hőmérsékletkülönbségeket foglalja össze. A legnagyobb különbségek tipikusan tavasszal és ősszel fordultak elő. Figyelembe véve a szenzorok távolságát is a legnagyobb mért hőmérséklet gradiens 17,7°C volt kb. 150m-en (szenzor1 és szenzor2 között). Mindezen adatok azért fontosak, mert alátámasztják, hogy a lokális geográfiai adottságoknak köszönhetően meglehetősen kis távolságban is ki tudnak alakulni nagy hőmérsékletkülönbségek a sínben. Ennek pontos ismeretében megalapozottabb döntések hozhatók meg a sebességkorlátozások kiterjedésének meghatározásakor. Legmagasabb észlelt hőmérséklet Legalacsonyabb észlelt hőmérséklet

érték dátum érték dátum

szenzor1 53,45°C 2011. 07. 09 13:30 -16°C 2010. 12. 19 05:30

szenzor2 54,18°C 2011. 08. 24 13:30 -17,13°C 2010. 12. 19 05:30

szenzor3 55,4°C 2011. 08. 24 13:30 -15,08°C 2010. 12. 17 00:30

1. táblázat: Legmagasabb és legalacsonyabb hőmérséklet értékek

40°C fölött 45°C fölött

szenzor1 262 óra 64 óra




50°C fölött 0°C alatt -5°C alatt -10°C alatt

5 óra 1045 óra 265 óra 35 óra



2. táblázat: Szélsőséges hőmérséklet intervallumokba eső órák száma Szenzorpár (szenzorx vs. szenzory) szenzor2 vs. szenzor1 szenzor3 vs. szenzor1 szenzor3 vs. szenzor2

MAX+ MAXMAX+ MAXMAX+ MAX-

Hőmérsékletkülönbség (Tszenzorx – Tszenzory = ΔT) 47,9 – 30,2 = 17,7°C 3,9 – 11,4 = -7,5°C 44,6 – 22,6 = 22°C 24,8 – 43,4 = -18,6°C 31.2 – 12.1 = 19,1°C 23,8 – 40,5 = -16,7°C

Dátum 2011. 09. 13 13:30 2011. 11. 12 10:30 2011. 10. 03 13:30 2011. 04. 20 14:30 2011. 10. 17 12:30 2011. 05. 17 14:30

3. táblázat: Legnagyobb hőmérsékletkülönbségek

5. Összefoglalás A sínhőmérséklet valósidejű monitorozása a hézagnélküli vágányok potenciális kivetődésének elkerülésével és a sebességkorlátozásokra vonatkozó döntések támogatásával növelheti a vasúti a közlekedés biztonságát és minőségét. A cikk az eRTM rendszert mutatta be, ami az evopro Innovation Kft. által fejlesztett vezetéknélküli sínhőmérséklet monitorozó rendszer. A rendszer az evopro általános célú vezetéknélküli szenzor és interfész kártyáját, az eSCTR kártyát alkalmazó vezetéknélküli szenzorhálózatra alapul. A szenzorok a sínre vannak szerelve, ahol termisztorok segítségével periodikusan mérik a sín hőmérsékletét. A hőmérséklet értékeket egy gateway egység gyűjti össze és továbbítja GPRS csatornán a szervernek. A rendszer különböző kliens alkalmazásokat is tartalmaz, amelyek a hőmérsékletek valósidejű követése mellett statisztikai analízisre is lehetőséget adnak. A cikkben egy pilot rendszer is bemutatásra került, ami több, mint egy évig üzemelt a Magyar Államvasutak pályaszakaszán Tatabánya közelében. A mért hőmérséklet adatok jól tükrözik a pilot rendszer környezetének lokális geográfiai adottságait, és alátámasztják a valós idejű sínhőmérséklet monitorozás alkalmazhatóságát és előnyeit. Elérhetőségek:

[1] [2] [3] [4] [5]

PECHAN Imre, evopro Innovation Kft., H-1116 Budapest, Hauszmann Alajos u. 2, Magyarország. Telefon: +361-2793970. E-mail: [email protected].

Coenraad Esveld: Modern Railway Track (Second Edition), 2001, MRT-Productions. Matthew Ryan: Rail temperature study (A report produced for Rail Safety and Standards Board, RSSB), 2005 június. Geoff V Merret and Yen Kheng Tan (szerkesztők): Wireless sensor networks: application-centric design, 2010, InTech. Bharath Sundararaman, Ugo Buy and Ajay D. Kshemkalyani: Clock synchronization for wireless sensor networks: a survey. Ad Hoc Networks 3 (2005), 281-323. old. Pechan Imre: eSCTR – A vezetéknélküli szenzor- és interfészkártya, Folyamatirányító Rendszerek XVII. Találkozó, 2011 október, Miskolc-Lillafüred.


eRTM – Wireless Rail Temperature Monitoring System IMRE PECHAN, ZSOLT SZEPESSY evopro Innovation Kft. Budapest, Hauszmann Alajos u. 2, Hungary, H-1116

SUMMARY Monitoring rail temperature real-time can significantly contribute to railway transportation safety. Wireless sensor networks offer an effective solution for measuring temperature at different locations along the rail. The eRTM system is a wireless rail temperature monitoring system developed by evopro Innovation Kft., which consists of wireless sensor nodes mounted on the rail, a central gateway module collecting measurement results, a database server and client applications. The pilot system operated during a oneyear test period on the track of Hungarian State Railways (MÁV) near Tatabánya.

1. Motivation There is a growing demand for increasing the safety and quality of railway transportation by applying the newest achievements of industrial measurement, embedded system and telecommunication technologies. Temperature is an important parameter of the rail, which needs to be continuously measured or estimated for ensuring transportation safety. Most modern railway tracks consist of continuous welded rails (CWR), which require much less maintenance than traditional, non-welded tracks due to the absence of joints. In case of CWRs, rail sections are welded together for kilometres; longitudinal and lateral stability is provided by sleepers, clips and the ballast. The temperature at which CWR has no stress is called neutral temperature and its value is usually around 25°C. If the actual temperature is higher or lower than this value, compressive or tensile stress arises in the rail, which might lead to rail deformation and buckling under severe conditions [1]. In order to prevent potential buckling, speed restrictions may need to be put in place according to the actual rail temperature. In practice, however, temperature is often determined with ad-hoc measurements or it is estimated based on expected weather conditions. By monitoring rail temperature continuously more reasonable decisions can be made when imposing speed restrictions. A real-time rail temperature monitoring system may have many advantages and application possibilities such as: - increasing transportation safety and protecting railway infrastructure by preventing buckling and vehicle derailment - choosing the duration and geographical location of speed restrictions and the corresponding speed limits more effectively for avoiding unnecessary restrictions, thus increasing the quality of railway transportation - assisting or automating the control of railroad switch heating during winter for power saving purposes


-

supporting maintenance planning and scheduling by predicting rail defects and failures in connection with temperature variation - investigating the unique local microclimate of the track, which can be especially useful near bridges, tunnels and other structures The aim of this paper is to introduce eRTM, the wireless, real-time rail temperature monitoring system, which was developed by evopro Innovation Kft. for the purposes mentioned above. 2. Background 2.1 Rail thermal model The main goal of rail temperature measurement is to detect temperature levels which may result in dangerous deformation or buckling. Temperature inside a real rail depends on all the three spatial coordinates and time; however, a reasonable simplification is to treat it constant along a cross-section of the rail. In case of this model the independent variables are the linear position along the rail (x) and time (t), the dependent variable is temperature (T): T = f(x, t).

(1)

Rail can be treated as a dynamic thermal system (Figure 1). Heat is transferred between the rail and its environment with radiation, conduction and convection depending mainly on current weather conditions. Heat transferred by radiation is influenced by sunlight and cloudiness. Convection depends on air temperature, humidity, wind strength, etc. Heat conduction is determined by the temperature difference along the rail which can arise due to the different environmental conditions. Thermal capacity of the rail is also an important parameter representing the energy storing capability of the casting. Theoretically, if the space and time dependent function of every environmental parameter (boundary conditions) as well as initial temperature distribution are known, temperature function of the rail (f in Equation 1) can be determined. Obviously, this cannot be achieved in practice; measuring every single environmental parameter is not possible. The feasible solution is to measure rail temperature at discrete points, which still may allow creating a simplified, lumped element thermal model a posteriori. radiation

conduction

reflexion

convection radiation

heat capacity

conduction Figure 1: Thermal model of rail


x [m]

2.2 Temperature measurement Choosing suitable method and tools for rail temperature measurement is crucial to ensure reliable results. The appropriate measurement point on the rail as well as the applied sensor type must be selected with respect to both measurement accuracy and field conditions. It should also be taken into account that the primary goal of measurement is to detect when the stress arising in the rail due to rising temperature reaches a dangerous level. There is an RSSB study available addressing rail thermal behaviour [2]. The study describes experiments which involved heating a 90cm test rail and measuring its temperature at several different points with different tools. Expansion of the rail was measured with LVDT sensors. Based on the expanded length and the thermal expansion coefficient, the theoretical “bulk” temperature of the test rail was determined and compared to the temperature values detected at the different measurement points. Bulk temperature is the integral of the temperature throughout the rail. Since the temperature of a rail section is generally not constant, real expansion (or stress) is determined by bulk temperature. Although this value cannot be measured, it can be approximated with discrete measurements quite accurately according to the study. Both surface and internal temperatures of the rail head, web and foot were measured, from which the web was judged to be the best location for temperature measurement due to its more rapid and consistent behaviour during tests. If web surface temperature is known, bulk temperature can be calculated as: TBULK = 0.999*TWEB + 2.09,

(2)

which was determined with linear regression based on experiment results [2]. As it was mentioned, the applied sensor type has also a big impact on measurement quality. Possible temperature sensor types that are widely used for temperature measurement are as follows: - digital thermometer (silicon bandgap temperature sensor) - thermistor - thermocouple - optical (infrared) thermometer The accuracy of thermocouples is quite limited. Optical thermometers are used usually if a non-contact device is needed. Considering the required measurement accuracy (below 1°C), the wide measurement range (-40…+70°C) and environmental conditions, thermistors and digital thermometers are the best choice. If the sensor needs to be placed in a drilled hole, thermistor is superior due to easier physical mounting. 2.3 Wireless sensor networks Due to the fast development of low-cost, low-power sensors, microcontrollers and wireless technology, wireless sensor networks (WSN) [3, 4] became more and more widespread in recent years. WSNs have nowadays many application areas such as environmental monitoring, building automation and intelligent home, process control, healthcare and ambient assisted living, surveillance, military and scientific experiments. WSNs have a lot of features that make them suitable also for the given purpose; that is, for monitoring temperature continuously at different locations along a rail section.


WSNs consist of spatially distributed autonomous sensor nodes which communicate with each other via a wireless medium in order to perform a task co-operatively. As it was mentioned, a typical task is the distributed monitoring of a physical parameter of the environment (e. g. temperature). The basic operation principle of such a system is data fusion, which means that data from each sensor node is collected and processed to produce a single meaningful result (such as generating the current temperature distribution of the rail based on the temperature of discrete points, or determining if speed restrictions are required). The network is often deployed in inaccessible, dangerous or hostile environment making system maintenance difficult or impossible. As a consequence, important features of wireless sensor networks are fault tolerance, selforganization and self-healing; the sensor nodes build up and configure the topology of the network autonomously and dynamically, according to the current conditions. Usually, the majority or all of the nodes are battery powered, and they are intended to work for a long period of time (couple of months or years); that is why low power consumption of the nodes is of great importance. Moreover, lack of cables increases robustness and makes system deployment easier. All of these features are very advantageous for a system operating in a harsh environment such as a railway track. 3. The eRTM system The eRTM (evopro Rail Temperature Monitoring) system is a wireless railway temperature monitoring and logging system developed by evopro Innovation Kft. The system consists of wireless sensor nodes mounted on the rail, a central gateway module collecting measurement results, a database server and client applications. The system architecture can be seen on Figure 2. The following subsections introduce the system components in details. 3.1 Sensor nodes and the eSCTR card The sensor nodes are based on evopro’s eSCTR card, which is a general-purpose, flexible, extendable wireless sensor and interface card [5]. The eSCTR card includes a Texas Instruments MSP430 mixed-signal microcontroller and a Digi International XBee radio module. The MSP430 microcontroller has several analogue and digital I/O channels and interface units (e. g. UART, SPI, I2C), which allow using a wide range of communication methods and protocols (RS-232, RS-485, 1-wire, etc.). The XBee module provides wireless connectivity for the eSCTR card. It works in the 868MHz ISM radio channel and uses Digi’s proprietary protocol supporting point-to-point, point-tomultipoint and mesh-based communication. This allows the eSCTR modules to form a wireless network applying various network topologies (such as the star and linear topologies shown on Figure 2.). The eSCTR card has a flexible architecture that can be easily adapted to different applications. There are two basic use cases. In the first use case eSCTR works as a wireless interface card that allows connecting devices (e. g. PLCs) with a standard protocol wirelessly without any communication cables, which can be very advantageous in an industrial environment. In this case the desired protocol (e. g. Modbus) is implemented by the eSCTR using one of the standard interface units of the MSP430; communication packets received on this interface are forwarded wirelessly and vice versa. In the second use case eSCTR is a wireless sensor card; it monitors a parameter with a sensor attached to one of its analogue inputs or interface units, and sends measurement results wirelessly to a central device.


In case of the eRTM system the eSCTR card is used as a wireless sensor node (second use case). Temperature measurement is performed with a thermistor connected to an analogue input of the MSP430. The thermistor is placed in a blind hole that is drilled in the rail web at the neutral axis. The sensor node performs temperature

sensor 868MHz ISM

wireless network with linear topology

clients GPRS server HTTPS

SMS Alarm gateway

wireless network with star topology

Figure 2: eRTM system with different WSN topologies

measurement periodically but remains idle in the remaining time (by keeping both the MSP430 and the XBee modules in low power/sleep mode) to ensure low average power consumption and long battery life. Temperature data are sent via the wireless network to the gateway module. 3.2 Gateway The gateway module is based on a single-board computer (SBC); in addition, it includes an XBee module and a cellular modem for GPRS communication. The XBee module operates as a central sink node for the wireless sensor network. The gateway receives the measured temperature values from the sensors and forwards them to the server via GPRS. Bandwidth of the GPRS channel is quite low but suits the application needs since the amount of data is minimal. The gateway module is mains powered; it can reside in a cabinet mounted on a railway column next to the track. 3.3 Server


The third component of eRTM system is a server application which receives the measurement data from the gateway, stores them in a database and allows accessing them for evaluation. It can also send alert messages with SMS or e-mail in case the measured temperature values reach certain pre-defined limits. 3.4 Client applications The eRTM system includes different client applications, which can run on various platforms (standard PC, smartphone, tablet, etc.). Applications can provide different views of the data stored on the server depending on the needs of the intended user. These views can show the current temperature values, alert events and extremities, measurement data of the last few hours/days, as well as long-term trends or statistical data. 4. Test operation results A pilot system was deployed near Tatabánya on the track of Hungarian State Railways (MÁV) and operated about 400 days between August 2010 – January 2011 and April 2011 – November 2011. Figure 3 shows the pilot system configuration and layout. The system included three sensor nodes placed a few hundred meters away from each other at locations with different geographical features; sensor1 was installed next to a tall cliff, sensor2 and sensor3 at an open area. The gateway module was mounted on a column next to sensor2. N gateway

sensor2

sensor1

CLIFF

S

5m

sensor3

200m

150m

Figure 3: eRTM pilot system

Measurement results reflect the different microclimates of the three sensor locations clearly. As an example, Figure 4 shows the registered rail temperature values at the measurement points on three consecutive summer days with 1h resolution. On the first two (probably cloudless) days similar pattern can be observed. The temperature values

Temperature [°C]

Measured temperature between 16-18. 07. 2011 50 40 30

Sensor1

20

Sensor2

10

Sensor3

0

16.07.2011 00:00

16.07.2011 12:00

17.07.2011 00:00

17.07.2011 12:00

18.07.2011 00:00

18.07.2011 12:00

Date 18th International T H E R M O Conference

Figure 4: Example temperature records

19.07.2011 00:00

rise in unison at each sensor in the morning. The peak temperature registered by sensor2 and sensor3 is about 45°C at 13:30. Rail temperature at sensor1, however, starts falling after 12:30 due to the cliff shadow, and is 5-15°C lower than the other ones in the afternoon. On the third day, each sensor registered a rapid temperature drop after 12:30, probably caused by gathering clouds. Table 1 summarizes the maximal and minimal temperature values registered by the sensors. Highest and lowest temperature was 55,4°C and -17,13°C, measured by sensor3 on 24. 08. 2011 and sensor2 on 19. 12. 2010, respectively. Table 2 shows the total number of hours when the temperature of the measurement points fell in extreme intervals (out of the full operation time of cca. 9600 hours). Sensor1 registered much less extremely warm hours than sensor2 and sensor3, as expected. Table 3 summarizes the highest temperature differences detected between the sensors pairwise. Typically, the highest differences occurred in spring and autumn. Considering also the distance between the sensor positions, the highest temperature gradient detected was 17,7°C on about 150m (between sensor1 and sensor2). These values are relevant since they confirm that quite high differences can occur in temperature even within short distances due to local geographical conditions. By exploiting this knowledge, more reasonable decisions could be made regarding the accurate geographical location of speed restrictions. Highest temperature detected Lowest temperature detected

value date value date

sensor1 53,45°C 09. 07. 2011 13:30 -16°C 19. 12. 2010 05:30

sensor2 54,18°C 24. 08. 2011 13:30 -17,13°C 19. 12. 2010 05:30

sensor3 55,4°C 24. 08. 2011 13:30 -15,08°C 17. 12. 2010 00:30

Table 1: Highest and lowest temperature values sensor1 262 hours 64 hours 5 hours 1045 hours 265 hours 35 hours

above 40°C above 45°C above 50°C below 0°C below -5°C below -10°C

sensor2 461 hours 172 hours 30 hours 1032 hours 266 hours 35 hours

sensor3 516 hours 242 hours 41 hours 946 hours 195 hours 23 hours

Table 2: Number of hours in extreme intervals Compared sensors (sensorx vs. sensory) sensor2 vs. sensor1 sensor3 vs. sensor1 sensor3 vs. sensor2

MAX+ MAXMAX+ MAXMAX+ MAX-

Temperature difference (Tsensorx – Tsensory = ΔT) 47,9 – 30,2 = 17,7°C 3,9 – 11,4 = -7,5°C 44,6 – 22,6 = 22°C 24,8 – 43,4 = -18,6°C 31.2 – 12.1 = 19,1°C 23,8 – 40,5 = -16,7°C

Date 13. 09. 2011 13:30 12. 11. 2011 10:30 03. 10. 2011 13:30 20. 04. 2011 14:30 17. 10. 2011 12:30 17. 05. 2011 14:30

Table 3: Highest temperature differences

5. Summary Monitoring rail temperature real-time can increase railway transportation safety and quality by preventing potential buckling of continuous welded rails and assisting decision making regarding speed restrictions. Wireless sensor networks are often applied in 18th International T H E R M O Conference

harsh environments for environmental monitoring tasks. The paper presented eRTM, a wireless rail temperature monitoring system developed by evopro Innovation Kft. The system is based on a wireless sensor network utilizing the eSCTR card, evopro’s general-purpose wireless sensor and interface card. The sensor nodes are mounted on the rail and perform thermistor-based temperature measurement periodically. Temperature values are collected and forwarded by a gateway module to a server via GPRS. The system includes different client applications enabling real-time temperature monitoring as well as statistical analysis. A pilot system was also introduced, which operated more than a year on the track of Hungarian State Railways (MÁV) near Tatabánya. Temperature recordings reflect the local geographical conditions of the pilot system plainly and confirm the usability and advantages of real-time rail temperature monitoring. Contact details:

[1] [2] [3] [4] [5]

Imre PECHAN, evopro Innovation Kft., H-1116 Budapest, Hauszmann Alajos u. 2, Hungary. Phone: +361-279-3970. Email: [email protected].

Coenraad Esveld: Modern Railway Track (Second Edition), 2001, MRT-Productions. Matthew Ryan: Rail temperature study (A report produced for Rail Safety and Standards Board, RSSB), June 2005. Geoff V Merret and Yen Kheng Tan (editors): Wireless sensor networks: application-centric design, 2010, InTech. Bharath Sundararaman, Ugo Buy and Ajay D. Kshemkalyani: Clock synchronization for wireless sensor networks: a survey. Ad Hoc Networks 3 (2005), pp. 281-323. Imre Pechan: eSCTR – The wireless sensor & interface card, Distributed Control Systems 17th Meeting, October 2011, Miskolc-Lillafüred.


Investigation of Thermal Behavior and Kinetic Parameters of Biochars Produced from Biomass Samples HANZADE HAYKIRI-ACMA (Prof.Dr.)*, SERDAR YAMAN (Prof.Dr.) Istanbul Technical University Istanbul Technical University, Chemical and Metallurgical Engineering Faculty, Chemical Engineering Department, 34469, Maslak, Istanbul, Turkey

SUMMARY Thermal behavior and kinetic parameters of biochars produced from biomass samples such as sunflower stalk and stove (SS), apricot stone (AS), and hybrid poplar (HP) were investigated using thermogravimetry under oxidation conditions. Also, macromolecular ingredients in biomass including holocellulose (cellulose+hemicellulosics) and lignin were isolated from the parent samples by chemical isolation methods, and then they were also investigated under the same conditions. The obtained data were used for the approximation methods of Coats-Redfern, Horowitz-Metzger, Dharwadker, ZsakoZsako, and Borchardt-Daniels to determine the kinetic properties.

1. INTRODUCTION Renewable energy from biomass is regarded as a sustainable, environmentally friendly and economical energy source. However, many types of biomass species have undesirable fuel characteristics including low calorific value, high moisture content, and low density [1]. Because of such concerns, it is not generally preferable to burn biomass directly. Instead, some conversion techniques such as carbonization, liquefaction, pyrolysis or gasification have been widely applied to evaluate the biomass energy efficiently [2]. In order to develop a better understanding of such thermal processes, kinetic parameters that determine the characteristics of the relevant reactions during transformations must be taken into account. For this reason, the present study aims to investigate the burning of the pyrolytic biochars in association with the study of the kinetic parameters. Some biomass samples such as sunflower stalk and stove, apricot stone, and hybrid poplar were used in this study. 2. METHODS 2.1. Sample Identification, Biochar Production, and Burning Experiments All the biomass samples are Turkish origin and they have very high potentials to use in energy sector. For experiments, the biomass samples were first allowed to stay in open 18th International T H E R M O Conference

containers in laboratory for one week to get air-dried samples, and then representative samples were taken. Proximate analyses of the samples were carried out according to ASTM standards. Macromolecular ingredients in biomass such as extractives-free bulk, holocellulose (cellulosics + hemicellulosics), and lignin were isolated chemically. For this purpose, ASTM D1105 standard was first applied to obtain the extractives-free bulk by removal of extractives through extraction with solutions of benzene and ethyl alcohol. The extractives-free bulk was then further proceeded to determine the contents of holocellulose and lignin. Mixtures of NaClO2, acetic acid, and water were employed to specify the holocellulose content, while the lignin content was determined by the method of van Soest [3] in which extractives-free bulk was treated with 72 vol.% sulphuric acid. Biomass samples were subjected to pyrolysis conditions in a horizontal tube furnace up to four different final temperatures of 150, 318, 370, and 600°C under nitrogen flow, for which the heating rate was fixed at 10°C/min, and also a hold time of 10 min was allowed at the final temperature. The residues (biochars) obtained after pyrolysis were collected and stored under nitrogen for subsequent burning experiments in a thermogravimetric analyser from which the kinetic data was derived. Non-isothermal burning profiles were obtained by TA Instruments SDT Q600 model thermal analyzer. For this, 10 mg of biochars were heated from ambient to 600ºC with a heating rate of 10ºC/min under dry air flow, and sufficient hold times were allowed at the final temperature to attain a fixed sample weight. In this way, the burning data was obtained from DTG (Derivative Thermogravimetric Analysis) burning profiles. 2.2. Integral Methods Used in Calculations of Kinetic Parameters The kinetic part of this study based on the usage of the data from the DTG burning profiles, and the kinetic parameters were determined by using a computer program that employs the approximation methods of Coats-Redfern, Horowitz-Metzger, Dharwadker, Zsako-Zsako, and Borchardt-Daniels. 2.2.1. Coats-Redfern (CR) Method For such a reaction given below [4, 5]; aA(k) ↔ bB(k) + cC(g) In Coats-Redfern method, decomposition rate of compound A is as follows: where n is degree of reaction Upon integration and linearization, this equation yields:


2.2.2. Horowitz-Metzger (HM) Method The term ‘reference temperature, Ts’ is defined as the temperature at variation point of TG graph, while variation point is maximum value of the slope of the curve. is defined as a variable that changes depending on reference temperature and ambient temperature, T:

The conversion at variation occurs (αs) determines the degree of reaction and when 1-αs=1/e, the degree of reaction is equal to 1 [5]. The reaction kinetic for n=1 is:

When ln[-ln(1-α)] is plotted versus

, the intercept becomes C and slope becomes

2.2.3. Zsako-Zsako (ZZ) Method In Zsako-Zsako’s method, change in the weight or in conversion can be expressed as a function of temperature:

After integration of the last equation:

where g(α) is integral of conversion function expressed as:

P(x) is an exponential integral and when U is used in spite of E/RT [5]


2.2.4. Borchardt-Daniels (BD) Method Boorchartd & Daniels Method is a kinetic-analyze method that uses the data obtained from linear heating rate in order to calculate reaction order (n), heat of reaction (ΔH) and activation energy (Ea). This method is based on general rate expression of n. order reactions:

where α is relative conversion, k(T) is rate constant at T (1/min), n is reaction order. ΔHT is the heat of reaction at T, ΔH0 is total heat of reaction and rate expression is defined as follow:

where E is activation energy (J/mol), Z is Arrhenius frequency factor (1/min), R is gas constant (8,413 J/molK). Finally:

3. RESULTS AND DISCUSSION Proximate analysis results of the parent samples and their isolated ingredients are given in Table 1. It is seen that the main biomass samples contain great amounts of volatiles matter, while the highest value belongs to apricot stone. Fixed carbon contents are comparable, and they change relatively in a narrow range. The ash content of sunflower stalk and stoker is disproportionally higher than those of the other samples. On the other hand, compared to the main samples, the isolated lignins are rich in fixed carbon and poor in volatiles. Table 1. Proximate Analysis Results of the Parent Samples Main Sample Moisture 8.90 Volatiles 76.13 F.Carbon 11.72 Ash 3.25 Ext. : Extractives-free

Hybrid Poplar (HP) Ext. Holoc.

Lignin

5.61 7.70 18.50 83.04 75.21 49.68 9.65 14.89 27.87 1.70 2.20 3.95 Holoc. : Holocellulose

Sunflower Stalk and Stover (SS) Main Ext. Holoc. Lignin Sample 8.06 10.76 9.67 12.53 73.67 72.20 71.07 42.09 9.00 11.58 12.45 14.14 9.27 5.46 6.81 31.24 F.Carbon : Fixed Carbon

Main Sample 3.70 82.55 12.36 1.39

Apricot Stone (AS) Ext. Holoc. 5.91 75.38 17.96 0.75

5.58 74.99 17.81 1.62

Lignin 12.70 58.49 26.13 2.68

Table 2 represents the proximate analysis results of biochars obtained at 600°C as well as their isolated ingredients. 18th International T H E R M O Conference

Table 2. Proximate Analysis Results of the Biochars Obtained at 600°C

Moisture Volatiles F.Carbon Ash

Main Sample 4.52 13.57 76.64 9.27

Hybrid Poplar (HP) Ext. Holoc. 4.49 16.63 69.13 9.75

7.35 15.57 68.50 8.58

Lignin 5.05 10.04 71.42 13.49

Sunflower Stalk and Stover (SS) Main Ext. Holoc. Lignin Sample 7.32 4.20 6.01 3.16 28.58 26.36 25.03 12.88 39.36 59.69 40.79 71.08 24.74 9.73 28.17 13.49

Main Sample 5.76 12.89 75.89 5.46

Apricot Stone (AS) Ext. Holoc. 6.29 11.87 78.14 3.70

6.23 13.50 77.93 2.34

Lignin 2.65 9.39 80.45 7.51

It can be said that the applied carbonization process from which the biochars are produced caused some changes in biomass structure in such a way that the contents of volatiles reduced considerably while the contents of fixed carbon increased. Besides, since the ash forming mineral matter became concentrated in biochars, the ash contents showed serious increases. In order to determine the temperatures of pyrolysis processes to obtain biochars, a preliminary experiment was carried out in the thermal analyzer under nitrogen flow. In Figure 1, pyrolytic behavior of hybrid poplar (HP) is shown, and some information about the release of moisture, initiation of devolatilization, maximum volatile matter release, and the end of devolatilization can be determined basing on this DTG curve.

Figure 1. DTG Curve for Pyrolysis of Hybrid Poplar’s Main Sample


Figure 2. DTG curve obtained from combustion of main sample of HP Combustion of HP indicates that the combustion process takes place in two main regions in which burning of volatiles and burning of fixed carbon occur, respectively. Moreover, it can be said that the combustion process is almost ended at around 700°C. Basing on the combustion data, kinetic parameters have been determined for every biomass samples. However, only the results for HP biomass could be included in this paper. Table 3 gives the kinetic parameters for the main sample of HP. Table 3. Kinetic Parameters for Main Sample of HP


The DTG curve was separated into several temperature regions in order to calculate kinetic parameters. When the results of HM and DK methods are analyzed, it is seen that chemical kinetic controlled combustion process (Fn 0) occurs. Moreover Ea and log A value decreases as the temperature range increases. In ZZ method kinetic model is B2 and Ea value increases as the temperature range increases. It is observed that kinetic parameters differ from each other due to calculation methods. Therefore, temperature dependence of kinetic parameters should be considered within the methods. Four different temperature values were determined considering release of moisture, the beginning of volatile matter release, maximum volatile matter release, and end temperature. These temperatures are 210, 354, 400 and 600ºC. The kinetic parameters of the biochars obtained at these temperatures are tabulated in the Tables 4-7. Table 4. Kinetic Parameters for Main Sample of HP Charred at 210°C

The kinetic parameters of combustion for the biochar obtained at 210°C showed that according to HM and DK methods, the mechanism is controlled by chemical kinetics (with models Fn 2/3 and Fn 0). On the other hand, CR and ZZ methods predicted that as the temperature increases kinetic models changes from D2 into B4 and B3, respectively. Meanwhile, activation energy changes between the 2.21 kJ/mol and 142.35 kJ/mol that is rather a wide range. The kinetic parameters calculated for the biochars produced at temperatures of 354 and 400°C indicated that CR method proposes the suitability of D2 kinetic model. Furthermore, activation energies varied between the 29.94 kJ/mol and 87.92 kJ/mol for 354ºC and between 26.47 kJ/mol and 138.16kJ/mol for 400ºC.


Table 5. Kinetic Parameters for Main sample of HP Charred at 354°C

Table 6. Kinetic Parameters for Main Sample of HP Charred at 400°C

Table 7. Kinetic Parameters for Main Sample of HP Charred at 600°C


As to the biochar produced at 600°C, according to HM and DK methods, it can be concluded that there exist kinetic model changes from Fn 0 into Fn 3 as the temperature increases. Whereas, CR and ZZ methods indicate that kinetic model changes from D2 into Fn 3 as the temperature increases. Activation energy takes the values between 21.61 kJ/mol and 144.62 kJ/mol. Activation energies that were calculated from B&D method are higher than those from other four methods due to the fact that calculations of B&D method base only on exothermic reactions. Generally, kinetic parameters calculated by using B&D method increases as the temperature increases. Results are given in Table 8. Table 8. Kinetic Parameters for Main Sample and Charred Samples of HP Calculated by Using B&D Method

4. CONCLUSION In this study, the kinetic parameters of combustion process have been investigated considering separation of the DTG burning profiles into several temperature intervals. Biomass materials have been tested from this point of view. Moreover, biochars obtained from carbonization of biomass at different temperatures showed different combustion characteristics. That is, activation energies, frequency factors, and the degree of reaction are highly affected from the carbonization temperature.


REFERENCES [1] Klass D.L., Biomass for Renewable Energy, Fuels, and Chemicals, Academic Press, San Diego, 1998. [2] Basu P., Biomass Gasification and Pyrolysis, Practical Design and Theory, Elsevier, Oxford, 2010. [3] Van Soest P.J., Use of Detergents in the Analysis of Fibrous Feeds. II. A Rapid Method for the Determination of Fiber and Lignin, J. Assoc. Offic. Anal. Chem. 46, 829835, 1963. [4] Lu C., Song W., Lin W., Kinetics of Biomass Catalytic Pyrolysis. Biotechnology Advances, 27, 583-587, 2009. [5] Acma H., Effects of Mineral Matter on Properties of Coal, Ph.D. Thesis, Istanbul Technical University, 1999.


Complex Diagnostics of the Cutting Process of Metal Composite Materials, using Thermo Camera Dr. Ferenc DÖMÖTÖR1 Senior Lecturer – Zoltán WELTSCH2 Lecturer BME Budapest University of Technology and Economics Faculty of Transportation Engineering and Vehicle Engineering Department of Automobiles and Vehicle Manufacturing H-1111 Budapest, Stoczek Street 4, Hungary

SUMMARY Some years ago in the department of the authors at the BME University in Budapest a research project on complex diagnostics of the cutting process of metal composite structures has been launched. The purpose of the research work, serving as a basis of our current article, was the investigation of the thermal, vibration etc. processes occurring during the cutting of metal-composite materials. When this kind of material is being cut, then the tool is contacted by different materials, and influenced by different parameters of cutting. The purpose of our job was to monitor the changes of those parameters (geometry, surface roughness, etc.), and to find the limits of toleration, when the technology had to be changed. This paper provides a report on the recently achieved results on this research work. This time the results, obtained by the thermo camera are emphasized. KEY WORDS: metal composite structures, complex diagnostics, cutting process of machine tools, vibration measurements, thermo vision

1. Introduction A research project on complex diagnostics of the cutting process of metal composite structures has been launched some years ago (2004-2006) in the department of the authors at the BME University in Budapest, Hungary. The purpose of the original job was to find optimal conditions for the cutting of magnesium based hybrid materials, and to find optimal tools (optimal edge geometry) for dry cutting these combinations of materials. The results of this project were published in several papers [03], [04], [05], [06] and PhD Thesis [01] as well. After the initial success it seemed to be advisable to continue the job and involve other methods as well. This paper provides a report on the recently achieved results. 2. Thermo pictures of milling The first attempt of our research work was to identify the thermal process, and to find out distribution of the temperature during milling, as a function of time and space. For this at the beginning a simple thermo camera of type WUHAN Guide IR928 was used. The main parameters of the camera: amorf silicon micro bolometer detector, pixel: 320 x 240, spectrum: 8 – 14 micrometer, temperature range: -20˚C, + 1500˚C. The tested system is shown on the Fig. 1. while the picture, taken by the thermo camera can be seem on the Fig. 2.


Fig.1. The tested system

Fig. 2. Thermal picture of the milling tool

3. Simulation of milling by turning The second series of our project was a simulation of milling by turning. This has been carried out on the lathe, located in our laboratory. The main parameters of the process were as follows: - rotational speed of the spindle: n = 530/min, - feed: 0.1 mm/rotation, - depth of cut: 0.5 mm. The tested specimens can be seen on the Fig. 3. They consist of a cylinder, made of aluminium alloy, and a thorn, made of steel/bronze, as shown on the Fig. 4. For this measurement of thermal imaging an AGEMA THV LWB-880 type camera was used, switched to line scanning mode. In order to protect the liquid N2 cooled MCT detector, a specially coated IR mirror was used. As a result of this it was possible to monitor the process, i.e. not only static pictures were taken, but the process also as the function of time was monitored. The optical fine adjustment of the camera (i.e. adjusting the plane of the scanning) had been carried out by a special geodetic tool.

Fig. 3. The tested specimens

Fig. 4. – Geometry of the specimen


As a result of the investigation it was found, that: the unique, high frequency, non-contact method is suitable to describe the high speed thermodynamic process, – the heat load in the investigated cutting environment is influenced not only by the chemical composition, and the parameters of the cutting process (speed, feed rate, depth of cutting, etc.), and the tool geometry, but also the heat convection of the chips, - the temperature of the tool itself is changing periodically, and proportionally to the rotational speed of the lathe (workpiece). -

thermo camera MCT detector cross support

plane of sensitivity

trigger

Fig. 5. – Installation of the thermo camera 4. Results of the Tool Temperature Measurements Recently a new thermo camera of type Flir Sc325 has been purchased by our department. The main parameters of it were as follows: 25˚x18.8˚ field of view, 0.4 m minimum focus distance, 60 Hz image frequency, un-cooled microbolometer type detector, 320 x 240 pixel IR resolution, 12 ms detector time constant. The process was same as in the case, described chapter 3, and also the specimens of the previous measurement series have been used. (Fig. 3. and Fig. 4.)


Fig. 6. ~ 5 turns of the workpiece Based on the measurement it was found, that: – The so called non contact, high frequency measurement is capable to describe the high speed thermodynamic processes. – The heat load of the tool in the vicinity of the tested cutting area is influenced by the chemical composition of the workpiece, the cutting parameters (rotational speed, depth of cut, feed rate, cooling, etc.), the geometry of the selected tool, and the heat transfer. – In the case of the tested SD11+AZ91 hybrid material it has to be emphasized, that the temperature of the cutting tool will be reduced periodically, when going through the Mg alloy, having a higher thermal capacity.


Fig. 7.

Fig. 8.

Arrangement of the testing equipment

Picture, taken by the high speed camera

Unfortunately, the resolution of the camera is not very high for this task, but as a conclusion of the measurement, it was observed, that the tool temperature is changing in harmony with the rotational speed.

Fig. 9. – Temperature of the tool, as a function of time The authors wish to express their thanks to the NKTH (National Bureau of Research and Technology, Budapest) for their support by the project „K+F Munkaero_09”. The content of this project is connected to the Quality Oriented Strategy of Education and Research on the BME University”. The project has been supported by the program of ÚMFT TÁMOP-4.2.1/B-09/01KMR-2010-0002.


Literature [01] Ozsvath, P.: Optimum solution for the metal cutting of Mg based, hybrid materials, PhD Dissertation (in Hungarian), BME Budapest University of Technology and Economics, Fac. of Transport, Dept. of Vehicle Manuf. and Repair, Bp., Hungary, 2009. [02] Takacs, J. (edited by): Modern Technologies in the transition of surface features, Műegyetemi Kiadó, Budapest, Hungary, 2004, ISBN 963 420 789 8 [03] Szmejkal, A.–Ozsvath, P.-Takacs J.: Dry cutting of Mg based hybrid materials (in Hungarian), Gepgyartas XLVII, 2007/2-3., HU ISSN 0016-8580 pp.: 41-46; [04] Ozsvath, P. - Takacs, J.: Investigation of Hard-Soft Boundaries of Mg based Hybrid Materials, Materials Eng. Vol. 15, 2008, No. 2a, ISSN 1335-0803, pp.15-22. [05] Ozsvath, P. - Szmejkal, A. – Takacs, J.: Dry milling of Mg based hybrid materials, Per. Polytechn. Transp. Eng., Budapest, 2008. 36 1-2, HU ISSN 0303-7800, pp.73-78. [06] Ozsváth, P. - Szmejkal, A.- Takacs, J.: Milling of AZ91 and AlSi12 using different edge geometries of CVD diamond thick film, International Journal of APPLIED MECHANICS AND ENGINEERING, 2010 Volume 15 Number 2, ISSN 1425-1655, University Press, Zielona Gora, Poland pp.335-342. ; [07]

Nagy, I. et al.: Techn. Diagnostics II. (Thermography), ISBN 978-963-06-0808

Contact details:

Dr. Ferenc DÖMÖTÖR, Budapest University of Technology and Economics (BME), Faculty of Transportation Engineering and Vehicle Engineering, Department of Automobiles and Vehicle Manufacturing, H-1111 Budapest, Stoczek Street 4., Hungary, Phone/fax: +361-463-1827, E-mail: [email protected]


THERMAL ENERGY STORAGE USING PHASE CHANGE MATERIALS: A REVIEW SANJAYKUMAR A. BORIKAR1, MAYURI WANDHARE2 1

Department of Mechanical Engineering, Kavikulguru Institute Of Technology and Science, Ramtek,RTM Nagpur University, Dist.-Nagpur ( Maharashtra), INDIA Mailing Address: Q.no. R3/3 KITS Campus, KITS Ramtek, Dist.- Nagpur (Maharashtra state), INDIA, PIN-441106 2

Heat Power Engineering, Kavikulguru Institute Of Technology and Science, Ramtek,RTM Nagpur University, Dist.-Nagpur ( Maharashtra), INDIA

Abstract Solar water heater provides an alternative solution for warming water for household as well as industrial applications. It is commonly used in recent days. One of the areas of concern in using solar water heater is that it can not provide warm water during early morning and at night time; to receive hot water from solar water heater storage of some amount of thermal energy is required and then utilize that energy in later part. Phase change materials (PCM’s) provides the means (medium) for storing the thermal energy associated with the warm water at day time and make it possible to retrieve for heating water ( at ambient temperature) during night or morning. The present work has been undertaken to study the feasibility of storing solar energy using phase change materials (PCMs) and utilizing this energy to heat water for domestic applications during early morning and night time. This ensures that the hot water is available throughout the day. The storage system consists of two heat-absorbing units, one of them is a solar water heater and the other a heat storage unit consists of PCM. They can be used for equalization of day & night temperature. Current study dealt with CaCl26H2O as PCM for storing the thermal energy from hat water during day time. The proposed solar water heater with thermal storage is designed to obtain the temperature of 600C at off time because the water heater has an ability to heat the water up to 1080C. Key words: Thermal energy storage, Phase change materials, solar energy, latent heat, sensible heat. 1. INTRODUCTION Thermal energy storage can be sensible heat storage (SHS) or latent heat storage (LHS). To store same heat energy the size requirement of storage media in LHS is smaller than SHT system. The latent heat thermal energy storage (LHTES) method is mainly used in airconditioning due to its high storage capacity during phase transition of substance (PCM) at constant temperature. The selection of the heat storage material (PCM) in the LHTES depends on its thermal efficiency because a solar energy application requires an efficient thermal storage. When substance melts or solidifies the large amount of thermal (heat) energy released or absorbed by the substance (PCM). PCM’s simply bridge the gap between energy availability and energy use. Therefore it has the potential to achieve considerable environment as well as economical benefits for many heating and cooling application [14]. In Sensible heat storage the thermal energy is stored by raising the heat from the solid or liquid (temperature varies as heat released) without changing its phase. The amount of heat stored 18th International T H E R M O Conference

depends on the specific heat of the medium, the temperature change and the amount of storage material [1]. The amount heat stored is given by; Or In Latent heat storage the heat absorption or release occurs when a storage material undergoes a phase change from solid to liquid or liquid to gas or vice versa[1]. The storage capacity of the LHS system with a PCM medium is given by

Fig.1 represents the capacity of the materials to store the thermal energy which provide the base for selection of the phase change material for storage application of heat. It shows the increase of internal energy when energy in the form of heat is added to the material.

Fig. 1 Temperature – time diagram for the heating of a substance [11] Change of phase of material (substance) from solid to vapour the heat contents of the substance increases continuously. The amount of heat gain by the substance is given by; [11]

2. STORAGE MEDIA (PCM’S) Phase Change Material (PCM) is a substance with a high heat of fusion melts and solidify at certain temperature, also capable of storing or releasing large amounts of heat while changing the phase. Phase change materials are latent heat storage substance in which the energy is being store during the process of change of state. When phase change materials attends the phase change temperature they absorbs large amount of energy and release the heat while regaining its old state [11]. 2.1 Requirements for phase change materials (PCM’s) 1. Release and absorb large amounts of energy when freezing and melting : PCM requires to have a large latent heat of fusion and to be as dense as possible[14] 18th International T H E R M O Conference

2. Have a fixed and clearly determined phase change temperature (freeze/melt point): The PCM needs to freeze and melt cleanly over as small a temperature range as possible. Water is ideal in this respect, since it freezes and melts at exactly 0°C (32°F). However many PCMs freeze or melt over a range of several degrees, and will often have a melting point that is slightly higher or lower than the freezing point. This phenomenon is known as hysteresis[14] 3. Remain stable and unchanged over many freeze/melt cycles: PCMs are usually used many times over, and often have an operational lifespan of many years in which they will be subjected to thousands of freeze/melt cycles. It is very important that the PCM is not prone to chemical or physical degradation over time which will the energy storage capability of the PCM. 4. Non-hazardous: PCMs are often used in applications whereby they could come in contact with people, for example in food cooling or heating applications, or in building temperature maintenance. For this reason they should be safe 5. Economical: It doesn't matter how well a substance can perform as a PCM if is prohibitively expensive. PCMs can range in price from very cheap (e.g. water) to very expensive (e.g. pure linear Hydrocarbons). If cost outweighs the benefits obtained using the PCM, its use will be very limited. 6. High thermal conductivity: Both solid and liquid phases in order to assist the charging and discharging energy of the storage system. 7. Small volume change on phase transformation and low vapor pressure at operating Temperature in order to reduce the containment problem. 8. High rate of crystal growth: The system can meet demand of heat recovery from the storage system. 9. Complete reversible freeze/melt cycle. 10. No corrosiveness to the construction materials. 11. Non-toxic, non-flammable and non-explosive material for safety. 2.2Classification of PCM The PCMs are generally divided into three main groups: organic, inorganic and eutectics of organic and inorganic compounds. There are a large number of organic and inorganic chemical materials, which can be identified as PCM from the point of view of melting temperature and latent heat of fusion.

Fig. 2 Classifications of Phase change materials [1] 2.2.1. Inorganic PCM’s These materials are salt hydrates, the phase change properties of these materials are shown in Table1.These PCMs have some attractive properties including high latent heat values, 18th International T H E R M O Conference

they are not flammable and their high water content means that they are inexpensive and readily available. However, their unsuitable characteristics have led to the investigation of organic PCMs for this purpose. These include corrosiveness; instability, improper re-solidification, and a tendency to super cool. Table-1 Inorganic Salt hydrate PCMs (thermal properties) [14] Phase change material KF 4H2O (Potassium fluoride tetra Hydrate) Mn(NO3)26H2O (Manganese nitrate Hexhydrate) CaCl26H2O (Calcium chloride Hex hydrate) CaBr26H2O (Calcium bromide Hex hydrate) Li NO36H2O (Lithium nitrate Hex hydrate) Na2SO410H2O (Sodium sulphate decahydrate) Na2CO310H2O (Sodium carbonate) Na2HPO412H2O (Sodium Orthophosphate Zn (NO3)26H2O (Zinc nitrate Hex hydrate)

Melting point (0C) 18.5 25.8 29.0 30.2 30.0 32.4 34.2 35.5 36.2

Heat of fusion (KJ/kg) 231 125.9 190.8 115.5 296 254 146.9 265 246.5

Table-1 show the melting point and heat of fusion of various inorganic salts hydrate PCM’s, which are essential for selection of these PCM’s for heat storage applications. Low heat of fusion and melting point near to room temperature is good for heat storage in solar water heater. 2.2.2 Organic PCM’s They are more chemically stable than inorganic substances, they melt congruently and super cooling does not pose as a significant problem. However, these organic materials do have their quota of unsuitable properties such as they are flammable and they may generate harmful fumes on combustion. Other problems, which can arise in a minority of cases, are a reaction with the products of hydration in concrete, thermal oxidative ageing, odour and an appreciable volume change. Table 2- Organic Salt hydrate PCMs (typical values) [14] Phase change material CH3 (CH2)16COO(CH2)3CH3 (Butyl tearate) CH3 (CH2)11OH (dodecanol) CH3 (CH2)12OH (tetradecanol) CH3 (CH2) n(CH3) Paraffin 45% CH3(CH2)8COOH 55% CH3(CH2)10COOH 45/55 (capric-lauric CH3(CH2)12COOC3H7 (Propyl palmitat)

Meltin Heat of g Point fusion (0C) (KJ/kg 19 140 26 200 38 205 20-60 200 21 143 19 186

Table-1 show the melting point and heat of fusion of various organic salts hydrate PCM’s, which are essential for selection of these PCM’s for heat storage applications. Low heat of fusion and melting point near to room temperature is good for heat storage in solar water heater. 2.2.3. Eutectics Eutectics are mixtures of two or more salts which have definite melting–freezing points. Their behavior is analogous to congruent melting salt hydrates and has great potential for 18th International T H E R M O Conference

thermal energy storage application. A large number of eutectics of inorganic and organic compounds have been reported, and they can be classified as inorganic eutectics, organic eutectics and organic–inorganic eutectics. Table-3 Inorganic eutectics with potential use as PCM [13] Phase Change Material 66.6% CaCl2 ~ 6H2O+33.3% MgCl2 ~ 6H2O 48% CaCl2+4.3% NaCl+0.4% KCl+47.3 ~ H2O 61.5 % Mg(NO3)2 ~ 6H2O + 38.5 % NH4NO3

Melting Point Temperature (0C) 25 26.8

Heat of fusion (KJ/kg) 127 188

52

125.5

449 31.5 30

---226 200.5

11.8% NaF+54.3% KF+26.6%LiF+7.3%MgF2 60% Na(CH3COO) ~ 3H2O +40% CO(NH2)

Table-4 Organic eutectics with potential use as PCM [13] Phase change material 37.5% Urea+63.5 acetamide 67.1% Napthalene+32.9% benzoic acid Lauric–capric acid Lauric–palmitic acid Lauric–stearic acid

Melting Point temp. (0C) 53 67 18 33 34

Heat of fusion (KJ/kg) ---123.4 120 145 150

Table-3 and table-4 comprises of specific properties of inorganic and organic eutectics phase change materials. 2.2.4 Selection of PCM Selection of PCM’s depends on the thermal properties of materials such as, melting point (range of 250C -700C), heat of fusion (range of 111 -195 KJ/kg), freezing point. Also some physical and chemical properties are considered while selecting the PCM’s for storage applications such as corrosiveness, flammability, size of storage, thermal conductivity, toxicity, vapour pressure etc. CaCl2.6h2O (calcium chloride hexa- hydrate) is most suitable for climatic conditions of Nagpur city; it is easily available, economical, non-toxic, non-dangerous, non-corrosive, and chemically stable. It has limited changes in density to avoid problems with the storage tank, low vapour pressure, favorable phase equilibrium. 3. DISCUSSION ON PREVIOUS RESULTS A TES tank containing latent heat storage material is constructed to analyze the performance of LHS system. It consists of the cylindrical TES tank, which holds the PCM in a packed bed of cylindrical aluminium capsules, solar flat plate collector, flow meter, temperature indicator and circulating pump. The stainless steel TES tank has a capacity of 48 liters, capable of supplying water for a family of four. With an internal diameter of 360mm and a height of 460mm, it houses the PCM capsules and allows for heat transfer between the capsules and the HTF. It contains two plenum chambers on the top and the bottom of the tank and a flow distributor is provided on the top of the tank to maintain a uniform flow of HTF. The tank is insulated with 50mm of glass wool and is provided with an aluminum cladding [3] [4]. 18th International T H E R M O Conference

The PCM is encapsulated in Aluminium cylinders of internal diameter 34mm and height 110mm, with wall thickness 2mm. Each cylinder contains 75gm of PCM by wt. The cylinders are packed in layers one over the other, with every two layers separated by a wire mesh to enhance the rigidity of the setup. The setup consisted of 4 layers of cylinders.[3,4] It is considered that, on an average, the family would require 60 liters of heated water for their daily needs. This energy is stored as a mixture of sensible and latent heat of PCM and sensible heat of water within the TES tank. We assume that the PCM store two-thirds of the energy while the remaining is stored as sensible heat of water. RTDs are provided at four different locations of the storage tank and inside four PCM capsules to measure temperature changes for every 2 layers of the PCM capsules, with an accuracy of ±0.3°C. The flow rate of the HTF through the system is measured using a Rota meter. The PCM used is industrial grade granulated paraffin wax with a melting point range of 58-61°C and water is used as both the HTF and the SHS material. The temperatures of the PCM and the HTF are continuously recorded at different locations (8 RTD inputs). Solar radiation is measured using a Pyranometer The TES tank is connected to a solar flat plate collector of 2 m2 area and the PCM capsules in the TES tank are surrounded by water. During the experiment, the HTF inlet varies in accordance with solar radiation During the charging process the HTF is circulated through the TES tank and the solar collector unit continuously. The HTF absorbs solar energy sensibly, and exchanges this heat with the PCM in the PCM storage tank, which is initially at room temperature. The PCM slowly gets heated, sensibly at first, until it reaches its melting point temperature. As the charging proceeds, energy storage as Latent heat is achieved as the Paraffin wax melts at constant temperature (59±2°C). After complete melting is achieved, further heat addition from the HTF causes the PCM to superheat, thereby again storing heat sensibly. The charging process continues till the PCM and the HTF attain thermal equilibrium. Temperatures of the PCM and HTF at the different locations are recorded at intervals of 10 minutes. The PCM is charged through the day, whenever hot water is not demanded by the user. The discharging process used is termed as batch wise process. In this method, a certain quantity of hot water is withdrawn from the TES tank and mixed with cold water to obtain a nominal temperature of 45 ± 0.5°C for direct use and the tank is refilled with cold water to maintain a constant amount of water in tank. This is then repeated for intervals of 10 minutes, in which time transfer of energy from the PCM would have occurred. This procedure is continued till PCM reaches a temperature of 45°C. REFERENCES [1] Atul Sharma, V.V.Tyagi, C.R.Chen, D.Buddhi, “Review on thermal energy storage with phase change material and applications”. Review and sustainable energy review 13(2009) 318-345 [2] Anant Shukla, D. Buddhi, R.L. Sawhney “ Solar water heaters with phase change material thermal energy storage medium” Renewable and Sustainable Energy Reviews, Volume 13, Issue 8, October 2009, Pp 2119-2125 [3] S.A.Vijay Padmaraju 1, M.Viginesh 1, N.Nallusamy ,Comparitive study of sensible and latent heat storage systems integrated with solar water heating unit. [4] Vikram D1, Kaushik S1, Prashanth V1, Nallusamy N2, An Improvement in the Solar Water Heating Systems using Phase Change Materials.


[5] Shahidul I. Khan* and M. Obaidullah “Fundamental of Solar Water Heaters” Director, Centre for Energy Studies [6] A.A. Dehghan, A. Barzegar “Thermal performance behavior of domestic hot water solar storage tank during consumption operation” [7] I.M. Michaelides, P.C. Eleftheriou” Experimental investigation of performance boundaries of solar water heating system” [8] Francis de Winter & Associates “Optimum Designs for Solar Water Heating Equipment for the Single Family Home” [9] Abdul Jabbar N. Khalifa, Ayad T. Mustafa and Farhan A. Khammas “ Experimental study of temperature stratification in a thermal storage tank in the static mode for different aspect ratios” ARPN Journal of Engineering and Applied Sciences, Volume. 6, no. 2, February 2011,pages53-60 [10] M. A. Islam, M. A. R. Khan and M. A. R. Sarkar “Performance of a Two-Phase Solar Collector in Water Heating” Journal of Energy & Environment 4 (2005): pages 117 – 123 [11] M. Fatih Demirbas “Thermal Energy Storage and Phase Change Materials: An Overview” [12] Halime Paksoy, Selma Yilmaz, Ozgul GOK, Metin O. Yilmaz, 2Muhsin Mazma, Hunay Evliya , “Thermal Energy Storage For More Efficient Domestic Appliances’’ [13] Souad Babay, Hamza Bouguettaia*, Djamel Bechki, Slimane Boughali, Bachir Bouchekima And Hocine Mahcene, “Review On Thermal Energy Storage Systems.’’ [14] Nitin .D. Patil, S. R. Karale, “Design and Analysis of Phase Change Material based thermal energy storage for active building cooling: a Review” International Journal of Engineering Science and Technology (IJEST) NOMENCLATURE Cap Average specific heat between Ti and Tf (J/kg K) Clp average specific heat between Tm and Tf (J/kg K) Cp specific heat (J/kg K) Csp average specific heat between Ti and Tm (kJ/kg K) T temperature (0C) Tf final temperature (0C) Ti initial temperature (0C) Tm melting temperature (0C) m mass of heat storage medium (kg) Q quantity of heat stored (J) ∆hm heat of fusion per unit mass (J/kg) am fraction melted


A Proposal to Maintain Proper Indoor Air Quality in Forced Ventilated Spaces GYÖNGYIKE O. TIMÁR Budapest Széher út 18/A 1. SUMMARY Changes of actual load often lead to trouble with the operation of the ventilation system. The design data are no longer correct if, for any reason, the actual load has permanently changed during the usage. The proposed ventilating system maintains the most commonly developed harmful gaseous contaminant content below the permissible level in spaces with forced ventilation. Sensors are mounted in every room, in a given height. By following the demand, the supplied fresh air volume matches the momentary load. Thus, possible health hazards can be mitigated and acceptable life- and working conditions can be maintained in these spaces. The requested indoor air quality is assured in any ventilated space without disturbing the air supply to other spaces. One of the main advantages of this system is that no energy is wasted for the handling of any excess air when the system load is below the design load

2. PURPOSE OF THE STUDY 2.1 Theory People exhale 12-30 l/h carbon dioxide1, depending on their activity. In practice, this average of carbon dioxide is considered to determine fresh air demand per person. According to the customary proportional control formula, the fresh air demand due to respiration is in directly proportional to the exhaled quantity of carbon dioxide, and inversely proportional to the difference between the carbon dioxide concentration limit and that of the outside air, namely: Vs = K/(kper - kout)

[m3/h]

(1)

Where Vs is the fresh air quantity [m3/h], K is the generated air contamination quantity [mg/h], kper is the permitted level of the contaminant in the room [ mg/m3], and kout is the average content of air contaminant in the outside air [mg/m3]. Thus, the calculated amount of fresh air dilutes the room's air in a way that the level of carbon dioxide contamination remains below the permitted concentration. This approximate fresh air volume depends on the difference of carbon dioxide content between the inside and outside air. The outside air's carbon dioxide content (kout) is considered an average, constant volume. The inside air's carbon dioxide content (kper) is considered to be the permitted level of carbon dioxide in the inside air, and is supposed to be constant too. 2.2 Experiences Experience shows that there are differences between the design and the real load of forced ventilating systems. The following factors might be listed as the most common reasons for these inconsistencies. The customer is not aware of the exact load, the number of people, and the equipment heat load in the spaces at the time of design. The load, the number of people or the equipment heat load changes considerably during operation of the ventilation system. The layout of the space is altered resulting in changes in volume and air flow, or the function of the space is changed. These variations cannot be predicted. However, it is not possible to mitigate the effect of load distribution changes during operation. Moreover, in normal usage, different types of gaseous contaminants enter the air, which may be hazardous to health. The constant inhalation of contaminated indoor air might lead to discomfort or to harmful physiological effects. 2.3 Perception Often the number of people within the ventilated space changes over a long period of time. Such changes often lead to inadequate performance of the ventilation system or to energy waste. To the contrary to the mentioned theory, the amount of actual CO2 concentration is often higher than theoretical concentration, kper within the ventilated space during operation. There are no means to limit its content by using the temperature


based control. Under overload conditions the generated CO2 content might reach or even surpass the permitted limit, and remain on this higher level. Moreover, under part load condition considerable energy is wasted because of handling unnecessary air volume. Such performance anomalies can be diminished or eliminated by augmenting the ventilation system with appropriate controls. 2.4 Practice According to accepted practice or standard, the air quality is appropriate in a workplace if the carbon monoxide content is below 30-35 ppm during 30 minutes. Also, there are recommendations2 for suitable air quality below 1 000 ppm CO2. Fresh air supply is requested if the concentration of one of the contaminant exceeds these values. There are professional recommendations proposing the fresh air demand in function of satisfactory between 4-10 l/s, occupant for spaces where occupants are the only source of pollution in non-smoking environment3. While other recommendations4 propose the maintenance of the CO2 content within certain limits in function of air quality as ‘low, adequate, medium, high’ room air quality, in the ventilated spaces. In addition to the requirements in connection with thermodynamic properties of circulating air, for example temperature and humidity, there are requirements5 with regards to its chemical composition. During normal usage, different types of gaseous contaminants enter the air, that are hazardous to health. Most common of these contaminants are carbon dioxide and carbon monoxide. Carbon monoxide, especially common where people are smoking, is a poisonous gas. Carbon dioxide used as the most common indicator of indoor air quality, is not poisonous but in prolonged excess concentration might lead to oxygen deprivation. Since both of these contaminant gases are colorless and odorless, the occupants are not aware of their presence. They affect the occupants to varying degrees, depending on their individual susceptibility, particularly their alertness and effectiveness. According to estimates office workers, for example, spend nearly 90% of their lives indoors. Offices can be regarded as “continuous operation”, where people stay mostly at one location. In a workplace, supplied solely with forced ventilation, occupants usually have no means to let fresh air enter the room or leave it to get fresh air when they experience discomfort. It can assume that the individual’s performance depends both, on the surrounding conditions and on their own capability. The office environment along with the suitable indoor air quality is an important part of this surrounding. There was a case, when ingenious occupants placed paper stripes in front of air diffusers in order to check ventilation. This way proves whether the fan was in operation, but gave no information about the rate or the quality of the supplied air. The complaints experienced by occupants in forced ventilated buildings are listed among „sick building” symptoms. Different studies have been conducted regarding these symptoms as well as the effects of high CO2 concentration in indoor air. For example, a questionnaire was completed for 4000 occupants of different ages concerning their experiences with interior conditions. More than 60% of them considered the ventilating and the air conditioning system as the most disturbing effect on their general state of health6. Some important arguments should also be discussed. The insufficiencies and the effect on occupants of any inadequate ventilation system can be compared with that of other building supplies. When a central heating’s efficacy is poor, the indoor air temperature might be lower than the designed value. The usage of sanitary appliances takes longer than usual, when for any reason there is trouble in the water supply. Cooking might take more time, when the quantity or the quality of the gas is not sufficient, and similar inconveniences might occur when the warm water supply is not proper. It can be noticed that poor operation of the other building supplies does not cause but inconveniences for occupants, mostly wasting their time and testing their patience. Despite of this, the forced ventilation is one among these services that might have direct harm to occupants. The insufficient operation of a ventilation system’s probable harmful effect on occupants can not be measured directly. Still, the aforementioned symptoms might be observed. That is the reason why it is beneficial to continually regulate the required indoor air quality in ventilated spaces beyond the regular inspection of the ventilation system7. There exist recommendations, for example, to measure CO2 content during operation of the ventilation system. Also, professional literature proposes different techniques to decrease building energy demand. Some of these propositions are: to replace existing windows and doors with energy efficient ones; to apply different energy saving methods; to regularly test the ventilating and air conditioning systems’ efficacy; and to maintain the ventilating system properly. In order to assure the designed or required characteristics, it is proposed to use an independent firm to set and maintain the building services including ventilation. 2.5 Major energy waste It is known, that energy consumption of buildings requires about 40 % of the entire energy demand. According to estimations, ventilation and air conditioning energy requirement is nearly 35-40% of the building total energy need. A significant amount of energy is wasted under part load conditions during the operation of a ventilating system. That is, without proper control, this energy is consumed unnecessarily in heating, cooling, and transporting the air difference between the designed and the actual load.


3. METHODS 3.1 Objective To implement the above, an extended air supply system with an additional control system is needed as well as appropriate changes in the air duct system. The task, the objective of the study, is twofold: prevent the probable harmful effects on occupants' health in spaces with forced ventilation as well as to operate the ventilating system in an energy efficient way8. It is important to keep the gaseous contaminants below permitted concentration limits, especially where forced ventilation is the only source of air supply. In such systems, there is no mixing of fresh air through natural circulation. Thus, the constant inhalation of contaminated indoor air can lead to discomfort and possibly to harmful physiological effects. The increased concentration of this kind of contamination is usually can not be perceived by senses, but it can be continuously and reliably measured by appropriate instrumentation. Controlling the contamination, e.g. the CO2 content, should be adequate to assure required fresh air quantity to suit overload conditions. Regarding under load conditions, this proposed control system effectively avoids any energy waste. 3.2 The proposal The goal of the air supply system is the maintenance of optimal environment and of optimal energy consumption for varying load conditions. The proposed, extended ventilation system tracks the actual load and supplies the necessary supplemental fresh air without disturbing the air supply to other spaces. The benefit of this system is that the required air quantity is supplied to follow the load but no energy is wasted for the heating and cooling of spaces where the system load is below the design load. 3.3 Description The ventilation system's control is based on the variation of the concentration of harmful gaseous contaminants, supplying only the required fresh air volume to the space. Energy efficient operation is assured by supplying only the required fraction of the nominal air volume under part load conditions, and handling the increased air volume when the system load increases. It has to be stressed that this system is only one of numerous solutions. The proposed system will prevent the above mentioned harmful physiological effects when individual spaces are loaded beyond the design load. The duct system will supply additional fresh air to limit the concentrations of harmful contaminants. In case of under-utilization, the energy of the heating, cooling and the transportation of the excess air can be spared. The proposed ventilating system allows for different levels of supply into several independent spaces simultaneously. The duct system supply and return should be separated by spaces or by extension of given areas. Motor driven dampers are in every supply and return branch air duct, while the necessary control devices are mounted in the main air duct. The main difference from traditional ventilation systems is not only the usage of supplemental equipment, but also in the selection and the sizing of elements of the main system. The basis of the sizing is no longer a specific air volume, but a range of air volumes. During sizing, both the lowest and the highest load limits need to be considered. The suggested contamination based control system does not substitute the control system based on the customarily controlled temperature and humidity. The appropriate air quality in the ventilated spaces can be assured by coordinated operation of the two control systems. 3.4 Energy saving appliance, the novelty of the proposed ventilating system The ventilated room’s air volume controlling valve closes when the fresh air demand drops below the designed volume. Then it is necessary to retrieve the actual surplus air, otherwise there might arise unwanted air circulation. The air might even enter to other spaces disturbing these spaces’ ventilation. A new feature of this system is the collector duct. This ‘third’ duct collects from each supplied room the actual superfluous air along the main air duct transporting it back ahead of the fan. By using this arrangement no energy is wasted for heating and cooling the air difference between the designed and that of the required or diminished air volume. 3.5 The proposed arrangement The proposed additional fresh air supply can be assured by installing supplemental equipment. These are parts of design, of mounting, and of operation. The ventilating system’s main parts are slightly oversized; the air handling unit, the main air duct, the air inlet and outlet devices are typically selected for 120% load. The supplemental equipment consists of: a collector duct to transport back ahead of the fan the actual superfluous air volume, air volume sensor, pressure sensor, air volume controlling device in the room's branch air duct, inlet and outlet grids supplied with controlling device, check valve in the air duct transporting the surplus air. For further energy efficiency a fan of smaller capacity for the long term diminished load is recommended. The additional control system monitors and keeps the most frequently developed gas contaminants, the quantity of carbon monoxide and carbon dioxide of the indoor air below the harmful limit. It measures the concentration of these contaminants at given time-intervals. Whenever requested, it displays the monitored quantity, and it registers the data. The gas sensor measures the contamination level, and


depending on the measured value, opens or closes the room’s air volume control device. This latter actuation is followed by the fresh air intake louver and fan adjustment. The system raises an alarm signal if the contamination level surpasses the permitted limit longer than a permitted time period. The gas sensors are mounted at a given height in every room. The supplementary fresh air quantity depends on the measured concentrations. It is obvious that this arrangement can be used to control any other gas concentration or even several gas concentrations simultaneously. In this case the gas sensors should be appropriate to the developing contamination. The air supply volume suits the ‘worst case’ scenario when different types of gaseous contaminations are controlled in a space. The layout of the ventilation system is shown in Figure 1.

Figure 1. System Layout In Figure 1. V shows the fan's nominal load [m3/h]. Check valves are indicated in the surplus and in the supply air branch ducts. The path for additional fresh air should be assured during operation. During periods of low loads, the third, collector duct transports the excess, already handled air to the fan inlet. Thus, the fan is operating continuously with 100% air volume, working at highest efficiency. The advantage of this system is that only the required air quantity is supplied, and no energy is wasted for the heating and cooling the air volume difference. The smaller fans indicated on Figure 1. provided for extended periods, potentially several days, of low load conditions. By monitoring the frequency of the intervention of the auxiliary equipment, the building operator can establish whether the load in the destination room is within the ventilating system design limits.

3.51 Operation The following discussion comprises the typical situations that might occur during furnishing the fresh air based on demand. There might be the designed or normal operation, under- and over-ventilation according to the variation in actual load. These are the following: Situation 1.


This is normal operation, under the designed conditions. The CO2 sensors average reading including the supply air CO2 content, is 1000 ppm. The room’s air volume controlling devices and the fresh air inlet louver are adjusted to deliver Vnom air volume. The supply 1. and exhaust 1. fans are working. The supplementary smaller fans are off. The air valves of supply 2. fan, and exhaust 2. fan and the motor driven damper of the collector duct are closed. Situation 2. The load in the space exceeds the design conditions, therefore, there is need for supplemental air. The CO2 sensor’s average reading exceeds 1000 ppm. The high limit of the air flow has arbitrarily been chosen at 1,2 Vnom. The air supply control devices and the fresh air louver are adjusted to supply up to1,2 Vnom air. The pressure sensor in the main air duct indicates decreased pressure. The supply 1. fan and exhaust 1.fan are working. The supplementary smaller fans are off. The air valves of supply 2. fan, and exhaust 2. fan and the motor driven damper of the collector duct are closed. Situation 3. The load in the space is under the design conditions, therefore, only a fraction of Vnom is needed. The low limit of the air volume is 0,2 Vnom. The rooms’ air volume controlling device closes, until the CO2 sensors indicate 1000 ppm. The fresh air inlet louver is adjusted, closed proportionally. The pressure sensor in the main air duct indicates pressure elevation. Supply 1. fan and exhaust 1.fan are working, the supplied air is diminishing up to 0,6 Vnom air volume. These fans stop transportation below 0,6 Vnom air volume. The return duct’s damper is open. Supply 2. and exhaust 2. additional fans’ dampers are closed, these fans are off. Supply 2. fan and exhaust 2. fan are working, when the request for fresh air drops below 0,6 Vnom up to 0,2 Vnom. The air valves of supply 2. fan and exhaust 2.fan, and the damper of the collector duct are now open. 4. SAVINGS The next example shows the theoretically possible energy savings of air heating, cooling and transportation under part load conditions in a ventilated office space. The number of occupants is consecutively 80, 60, 40, 20, 10. The ventilating fresh air quantity is 10 l/s,p /36m3/h,p/. Winter conditions are the next. Outside air: temperature to = -15 oC, density: r=1,205 kg/m3. Inside air: temperature ti = +20 oC, specific heat cp20=1,013 kJ/kgK. Summer conditions are as follows. Outside air: temperature to = +32 oC, humidity f=40 %, enthalpy io=62,5 kJ/kg. Supplied air: temperature tsupply = +18 oC, humidity f=55 %, enthalpy isupply=34 kJ/kg. Air duct and air handling unit pressure drop Dp= 900 Pa. Fan type: HPD. 4.1 Heating ================================================================ Occupants number

Proportion of operation

Fresh air demand

Heating capacity S A V I N G S requirement

---------------------------------------------------------------------------------------------------------------[%] [m3/h] [kg/s] [kW] [kW] [%] ---------------------------------------------------------------------------------------------------------------80 100 2880 0,96 34 60

75

2160

0,72

22,5

8,5

25

40

50

1440

0,48

17

17

50

20

25

720

0,24

8,5

25,5

75

10 12, 360 0,12 4,2 29,8 87,5 ----------------------------------------------------------------------------------------------------------------Table 1. Heating theoretically possible savings


4.2 Cooling =============================================================== Occupants Proportion of Fresh air Cooling capacity S A V I N G S number operation demand requirement --------------------------------------------------------------------------------------------------------------[%] [m3/h] [kg/s] [kW] [kW] [%] ---------------------------------------------------------------------------------------------------------------80 100 2880 0,96 27 60

75

2160

0,72

20, 3

6,7

25

40

50

1440

0,48

13,5

13,5

50

20

25

720

0,24

6,8

20,2

75

10 12,5 360 0,12 4,3 23,6 87,5 ----------------------------------------------------------------------------------------------------------------Table 2. Cooling theoretically possible savings

4.3 Transportation =========================================================== Occupants Proportion Fresh Fan Energy savings number of operation air V h Pm -------------------------------------------------------------------------------------------------------[%] [kW] [kW] [%] [p] [%] [m3/h] Type -------------------------------------------------------------------------------------------------------80 100 2880 HPD250 73 1,1 60

75

2160 HPD250 70

0,65

0,45

41

40

50

1440 HPD200 62

0,56

0,54

51

20 25 720 HPD200 62 0,4 0,7 64 ------------------------------------------------------------------------------------------------------Table 3.

Transportation theoretically possible energy savings

Under part load conditions there is possibility to save considerable amounts of operating energy with the assistance of the collector duct. This energy saving can be increased with the usage of smaller fans for long time part load conditions. Since the minimum air supply is Vmin =0,2 Vnom, there is the possibility of sparing up higher than to 80% of cooling and heating energy. This saving refers solely to the secondary energy consumption, and it diminishes the ventilation system’s operation fees. Regarding the aforementioned proportions, the energy saving might reach more than 30 % of the building total energy demand. The primary energy consumption’s accompanied reduction is an additional saving that decreases the total energy demand of the ventilating and air conditioning system, thus the whole building’s energy requirement.

5. CONCLUSIONS The proposed ventilating system’s advantages are: - proper life- and working conditions can be maintained in the ventilated space - appropriate indoor air quality can be assured in any distinct room with varying load, without disturbing other space's ventilation - the possible health hazard effect of gaseous contaminants to people is prevented - demand controlled ventilation can be assured in every spaces - between certain limit, sufficient amount of fresh air can be supplied to any ventilated room - none of the parts or element of the ventilating system is operating unnecessarily; - the cooling, heating or transporting energy of the momentary superfluous air can be saved; - the additional control system monitors and keeps the most frequently developed gas contaminant, the quantity of carbon dioxide of the indoor air, below the harmful limit.


- occupants are continuously informed of the momentary air quality; - occupants and operator are warned when indoor air quality is unacceptable in any space; - by applying it, the required supplemental fresh air can be supplied while minimizing the energy demand of the ventilating system and, consequently, the operating costs. This arrangement requires slightly larger duct, grids or possible air handling unit, and an additional control. All of these augment the value of the ventilation system. The supplemental elements displayed on Figure 1. are readily available on the market. It can be easily proved that these are one-time expenses that will be recovered not only in the enhanced efficiency of the people working in the ventilated spaces, but also, in energy savings. Depending on architectural conditions, it can be installed in existing ventilating systems too. Although the control system can be developed according to the description, its efficiency can only be proved after successful experimental testing, by an installed and reliable working system.

NOMENCLATURE Vnom nominal fresh air demand, 100%, m3/h Vmin minimal supplied fresh air, m3/h supplied fresh air quantity [m3/h] Vs K generated air contamination quantity [mg/h] permitted level of the contaminant in the ventilated space [ mg/m3] kper kout average content of air contaminant in the outside air [mg/m3]. CO2 carbon dioxide sensor M-D1 room air volume controlling device M-L fresh air intake louver M O/C On/Off motor driven switch Dp pressure switch P pressure sensor Av air flow sensor

REFERENCES 1 Épületgépészet 2000 Alapismeretek, Table 13.4, p.344. Épületgépészeti Kiadó Kft., Budapest, Hungary 2000 2 ANSI/ASHRAE 62-1989 (1990). Ventilation for Acceptable Indoor Air Quality., Atlanta GA. 3 CEN CR -1752:1998 Ventilation for Building-Design Criteria for Indoor Environment Table 2. p.11. 4 EN 13779:2007 Ventilation for non-residential buildings. Performance requirements for ventilation and room-conditioning systems Annex “A” Table 10 5 EÜM-SZCSM /Hungarian Norm/ (2000). 25/2000 (IX.30.) About the chemical Safety of Work Places Budapest, Hungary 6 Bánhidi, L. Kajtár, L. (2000) Komfort elmélet p. 207. Technical University, Budapest, Hungary. 7 MSZ EN 15239: 2007, /Hungarian Norm/ MSZ EN 15240: 2007 Ventilation for buildings – Energy performance of buildings – Guidelines for inspection of air-conditioning systems 8 Timár, Gy. Energiatakarékos szellőző berendezések 1-2 Magyar Installateur, Vol. 17. pp.34, 36-37 December 2007, Vol. 18. January- February 2008.


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