Possibilities of removing H2S from gas from gasification of biomass Ing. Pavel Machač, CSc, Dr. Ing. Vladislav Krystl, Ing. Sergej Skoblja, Ing. Petr Chalupa Institute of Chemical Technology Prague Technická 5, 166 28 Praha 6 – Dejvice, Czech Republic, Department of Gas, Coke and Air protection.
[email protected] ∗ Department of Inorganic Technology Vysoká Škola Chemicko Technologická v Praze, Ústav plynárenství, koksochemie a ochrany ovzduší Technická 5, 166 28 Praha 6
Introduction ¾ The first research of removing H2S from energetical gas at high temperature by means of limestone or dolomite application was in the U.S.A in the early the eighties years of last century. ¾ This method should be used instead of classical procedure which use absorption as e single step. ¾ Typical concentration level of sulfane in raw pressure generator gas is about 0,6 – 0,8 % vol. ¾ Typical facilities for „O2 – steam“ gasification at pressure about 25 Bar is LURGI generator. Vysoká Škola Chemicko Technologická v Praze, Ústav plynárenství, koksochemie a ochrany ovzduší Technická 5, 166 28 Praha 6
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Introduction ¾ Applications of gas from gasification process as a fuel for FUEL CELL is researched at present. ¾ Raw gas contains tar, fly-ash, H2S, HCl, HF and other. ¾ In case of high temperature (800°C) FUEL CELL is calculated upon removing H2S to value 1 ppm (from 100 – 200 ppm), for HCl and HF to value 10 ppm. ¾ Using of limestone and dolomite was tested at high temperature.
Vysoká Škola Chemicko Technologická v Praze, Ústav plynárenství, koksochemie a ochrany ovzduší Technická 5, 166 28 Praha 6
Chemism of system H2S – CaO ¾ Bacic reaction is: CaO + H2S → CaS + H2O (CaO + MgO) + H2S → (CaS + MgO) + H2O (CaCO3 + MgO) + H2S → (CaS + MgO) + H2O + CO2 CaO and (CaCO3 + MgO) is calcinated limestone or dolomite. ¾CaS is product and can be regenerated: 2CaS + 3O2 = 2CaO + 2SO2 CaS + CO2 + H2O(g) = CaCO3 + H2S
(t) (t,p)
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Chemical composition of limestones Comp.
Limestone
%
Čertovy schody
Vrchlabí
Čížkovice
14,03
Krušné hory 3,23
Orlické hory 2,02
HejnáHydčice 6,36
SiO2
0,24
1,92
Al2O3
0,07
0,36
5,69
0,16
0,36
1,22
Fe2O3
0,13
0,16
1,51
0,85
0,22
0,32
CaO
55,19
52,90
43,67
26,92
37,72
45,23
MgO
0,45
1,14
0,62
20,11
13,64
5,22
Na2O
0,04
0,01
0,02
-
-
0,29
K2O
0,04
0,13
0,63
0,13
0.07
0,45
CO2
43,82
42,70
32,27
44,76
45,57
39,89
H2O
0,50
0,90
2,33
0,70
0,35
0,50
Vysoká Škola Chemicko Technologická v Praze, Ústav plynárenství, koksochemie a ochrany ovzduší Technická 5, 166 28 Praha 6
Thermodynamic of reaction CaO or (CaCO3) + H2S ¾ Eguilibrium of this chemisorption is positive from catching of H2S point of view at wide temperature range 600 to 1400°C. Eguilibrium is described by following equation: log
[ H 2 O] 1 = 3519,2 − 0,268 [H 2 S ] T
where T is absolute teperature [K] [H2O],[H2S] molar concentration
¾ Eguilibrium of system (CaCO3 + MgO) – H2S is positive at temperature over 800°C. From previous relation and from eguilibrium of calcinate reaction (CaCO3 = CaO + CO2) was deriveted equation: log([ H 2 O ][CO2 ]) •
P 5280,5 = 7,253 − 101,3[ H 2 S ] T
where P is pressure [kPa]
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Kinetics of CaO + H2S reaction ¾For: ¾ c is H2S concentration of gaseous phase i ¾ x is molar quantity of reactive CaO ¾ t is time ¾ there is relation: dx where K is speed constant − = Kxc
dt
dA dN − −E dt dt K = z • exp( 1, 2,3 ) RT
¾
Mechanism of adsorption was studied and time decreasing of no-converted CaO N and quantity of reaction capable CaO A and quantity of blocked CaO B and quantity of product G were measured. −
dN dt
−
dA dt
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Kinetics CaO + H2S reaction ¾ Reaction constant K has form : K = z • exp( E1,2,3 R
− E1, 2,3 RT
)
where z is exponential factor, dN − is activation energy of adsorption, desorption and chemical dt reaction, is gass constant
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Konversion - time dependence of CaO <=> CaS for limestone Čertovy schody
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Konversion - time dependence for
varied size of particles (t = 850°C)
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Apparatus for mmeasurement kinetics of systém CaO + H2S
Vysoká Škola Chemicko Technologická v Praze, Ústav plynárenství, koksochemie a ochrany ovzduší Technická 5, 166 28 Praha 6
Matematical models of process ¾ Validity of a few models for reaction heterogeneous systém solid matter – gas was verificated: Model according to Borgwardt r0 = Ks Sg CSO2 η r = r0 exp (-βx)
β x
where Ks is speed constant where Sg is specific surface of calcinate (CaO) where CSO2 is concentration of SO2 and η is factor of efficiency Is the so name sensitivity on sulfatation is conversion
Empirical formula from ÚTZCHT x = 1-exp[ -(t/t0)n]
x is conversion of CaO t is time t0,n are empirical parameters depend on SO2 concentration and size of particles
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Matematical models of process Model according to Pigford ∂C1 De 1 ∂ 2 ∂C1 S v r − ϑ = • 2• • Ds C R − ∂t ∂R ε τ R ∂R rϑ ϑ
R C1 De τ ε Sv r Ds
thickness of reaction product radius of spherical particle concentration SO2 at radius R equivalent diffusivity tortuousity porosity is specific surface of unit volume of particle is radius inside grain equvalent diffusivity of solid reaction components
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Comparison of models for limestone Čertovy schody at 800 °C ¾ For evalution of reaction CaO + SO2 models was find out that a very good results gives empirical formula and model by Borgwardt.
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Conclusion Knowledges obtained by means of research of process power gas dry desulphurisation can be apply for the use of gasification gas from biomass as a feed gas in the FUEL CELL.
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