48
BAB III ANALISA DAN PERHITUNGAN COGENERATION PLANT
3.1.
Sampel data Perhitungan Heat Balance Cogeneration plant di PT “X” saya ambil data
selama 1 bulan pada bulan desember 2012 sebagai referensi, dengan sebelumnya mengambil sample Parameter dari beberapa macam beban sesaat yang diterima oleh Gas turbin yang juga terhubung pada HRSG. Tabel 3.1. Sample Parameter Gas Turbine
Load
TOp
Amb. Gas MWH temp Cons
R/H
Power Fuel Rate avg.
Heat Rate
Gas Energy
Elec. Energy Elect. Eff.
degC degC MWH Nm3 4.0 MW 519 26.0 96.0 36,720
H 24.00
MW (Nm³/kWh) kJ/kWh Btu/kWh kJ kJ 4.0 0.383 13,541 12,823 1,299,888,000 345,600,000 26.6%
3.9 MW 500
26.0 93.6
36,000
24.00
3.9
0.385
13,615
12,894 1,274,400,000 336,960,000 26.4%
3.8 MW 488
26.0 91.2
34,848
24.00
3.8
0.382
13,527
12,810 1,233,619,200 328,320,000 26.6%
3.7 MW 483
26.0 88.8
34,128
24.00
3.7
0.384
13,605
12,884 1,208,131,200 319,680,000 26.5%
3.6 MW 471
26.0 86.4
33,840
24.00
3.6
0.392
13,865
13,130 1,197,936,000 311,040,000 26.0%
3.5 MW 462
26.0 84.0
33,120
24.00
3.5
0.394
13,958
13,218 1,172,448,000 302,400,000 25.8%
3.4 MW 456
26.0 81.6
32,400
24.00
3.4
0.397
14,056
13,311 1,146,960,000 293,760,000 25.6%
3.3 MW 450
26.0 79.2
31,968
24.00
3.3
0.404
14,289
13,531 1,131,667,200 285,120,000 25.2%
3.2 MW 438
26.0 76.8
31,536
24.00
3.2
0.411
14,536
13,766 1,116,374,400 276,480,000 24.8%
3.1 MW 431
26.0 74.4
30,960
24.00
3.1
0.416
14,731
13,950 1,095,984,000 267,840,000 24.4%
3.0 MW 427
26.0 72.0
29,952
24.00
3.0
0.416
14,726
13,946 1,060,300,800 259,200,000 24.4%
Keterangan tabel :
1 Kwh
=
3600 kJ
Gas Fuel Energy
=
35400 kJ/Nm³
1 kJ
=
0.947 Btu
http://digilib.mercubuana.ac.id/
49
Elec .Energy X 100% Gas.Fuel .Energy
=
Elect. Eff.
Tabel 1 merupakan sampling data parameter gas turbin dari beban 3 MW sampai 4 MW, berikut ini adalah perhitungan dan analisa dengan mengambil sample load 3.5 MW.
Load 3.5 MW, total 1 hari adalah 3.5 MW x 24 h = 84 MWh (Output)
Gas flow 23 M3/Min, total konsumsi gas dalam 1 hari adalah 23 m3/Min x 60 x 24 = 33,120 Nm3 (Input)
Fuel rate =
Gas.consumption Elect . production
=
33,120 Nm3 84,000.kWh
=
0.394 Nm3/kWh
yang artinya untuk menghasilkan 1 kWh listrik memerlukan 0.394 Nm3 bahan bakar gas
Samakan nilai satuan input dan outputnya menjadi satuan kilojoule (kJ)
Electrical Energy
= 84 MWh x 3600 = 302,400,000 kJ
= 33,120 Nm3 x 35400 kJ/Nm3
Gas Fuel Energy
= 1,172,448,000 kJ
Electrical Efficiency
=
Elec .Energy X 100% Gas.Fuel .Energy
=
302,400,000.kJ X 100% 1,172,448,000.kJ
http://digilib.mercubuana.ac.id/
50
= 25.8 %
Sehingga di ketahui pada saat load gas turbin 3.5 MW di dapatkan nilai efiensinya sebesar 25.8 % dengan nilai fuel rate 0.394 Nm3/kWh Tabel 3.2. Sample Parameter HRSG
Feed Make Up Steam Steam Burner Stack feedwater Gas Steam Steam Make Up Cogen Eff. R/H Water Water Steam Energy Cons. prod. avg. water Energy (Elec. + Load Press. temp duct temp temp pressure Cons Cons Steam) Barg degC 4.0 MW 8.0 173
degC 533
degC 155
Barg 15
H 24.0
m3 0
Ton Ton/h 264.0 11.00
Ton 269
Ton 73
kJ 732,600,000
kJ 9,148,546
82.4%
3.9 MW 8.0
173
514
155
15
24.0
0
264.0 11.00
269
73
732,600,000
9,148,546
83.3%
3.8 MW 8.0
173
505
155
15
24.0
0
259.2 10.80
264
71
719,280,000
8,982,208
84.3%
3.7 MW 8.0
173
500
155
15
24.0
0
256.8 10.70
262
71
712,620,000
8,899,040
84.8%
3.6 MW 8.0
173
490
155
15
24.0
0
252.0 10.50
257
69
699,300,000
8,732,703
83.7%
3.5 MW 8.0
173
480
155
15
24.0
0
240.0 10.00
245
66
666,000,000
8,316,860
82.0%
3.4 MW 8.0
173
474
155
15
24.0
0
230.4
9.60
235
63
639,360,000
7,984,185
80.8%
3.3 MW 8.0
173
470
155
15
24.0
0
225.6
9.40
230
62
626,040,000
7,817,848
80.0%
3.2 MW 8.0
173
459
155
15
24.0
0
220.8
9.20
225
61
612,720,000
7,651,511
79.1%
3.1 MW 8.0
173
450
155
15
24.0
0
216.0
9.00
220
59
599,400,000
7,485,174
78.6%
3.0 MW 8.0
173
445
155
15
24.0
0
206.4
8.60
211
57
572,760,000
7,152,499
77.9%
Keterangan Tabel :
h Steam (8 bar - 173°C)
=
2775 kJ/kg
h Make Up Water (1 bar - 30°C)
=
125.83 kJ/kg
Cogen Eff.
=
Elec .Energy Steam.Energy
Gas.Fuel .Energy MakeUpWater.Energy
X 100%
Tabel 2 merupakan sampling data parameter HRSG dari beban Gas turbin 3 MW sampai 4 MW , berikut ini adalah perhitungan dan analisa dengan mengambil sample load 3.5 MW.
Pada saat load Gas turbin 3.5 MW dengan panas gas buang 480°C, HRSG dapat menghasilkan steam 10 ton/h dalam sehari total steam adalah 240 ton
http://digilib.mercubuana.ac.id/
51
Steam Energi pada tekanan 8 bar dan temperatur 173°C dalam 1 hari di dapat, Steam Energi = 240,000 kg (total steam) x 2775 kJ/kg (h steam) = 666,000,000 kJ
Make Up Water Energi pada tekanan 1 Bar dan Temperatur 30°C dalam 1 hari di dapat, Make Up Water = 66,000 kg (total Make up water) x 125.83 kJ/kg = 8,316,860 kJ
Karena semua factor cogen telah di dapatkan, maka cogen effisiensi dapat di cari menggunakan cara sebagai berikut, Cogen Eff. =
=
Elec .Energy Steam.Energy
Gas.Fuel .Energy MakeUpWater.Energy 302,400,000.kJ 666,000,000.kJ 1,172,448,000.kJ 8,316,860.kJ
X 100%
X 100%
= 82.0 %
Jadi pada saat load Gas turbin 3.5 MW di dapat electrical effisiensi 25.8 %, dengan Cogen effisiensi 82.0 %.
Dari kedua hasil diatas kita bisa mengetahui berapa nilai presentase keseluruhan dengan menggunakan Heat balance berikut. % Electicity
= Electrical Efficiency = 25.8 %
% Steam
= Cogen Efficiency – Electrical Efficiency = 82.0 % - 25.8 % = 56.2 %
% Exhaust loss
= 1 - Cogen Efficiency = 100 % - 82.0 % = 18 %
http://digilib.mercubuana.ac.id/
52
Maka dari perhitungan Heat balance Cogeneration dengan mengambil
Losses 18% Steam 56.2 %
Exhaust Gas 74.2%
Thermal Energy 100%
Elctricity 25.8%
sample pada load 3.5 MW di dapatkan hasil dengan ilustrasi seperti dibawah ini,
Gambar 3.1 : Heat Balance GT+HRSG Beban 3.5 MW 3.2.
Perhitungan dan analisa Dari referensi data parameter dan hasil produksi bulan desember 2012,
saya hanya mengambil data dimana saat HRSG tidak menggunakan gas tambahan atau supplementary firing agar analisanya lebih mudah karena hanya satu nilai gas fuel consumption (Q1) yang di masukkan. Perhitungan Heat balance pada Cogeneration plant PT “X” dapat di lihat dari tabel 3.3 Perhitungan & Analisa Heat Balance pada GT & HRSG. Data tersebut di ambil dari data operasional selama 1 bulan, tepatnya bulan desember 2012. Untuk lebih memahami tabel tersebut, bisa dilihat dari gambar dibawah ini.
http://digilib.mercubuana.ac.id/
53
Gambar 3.2 : Cogeneration Heat Balance flowchart Sumber : Siemens energy industrial gas turbine
http://digilib.mercubuana.ac.id/
54
Tabel 3.3. Perhitungan & Analisa Heat Balance pada GT & HRSG TOp
Amb. temp
MWH
Gas Cons
R/H
Power avg.
Fuel Rate
1-Dec
degC 442
degC 31.9
MWH 74.6
Nm3 29,962
H 24.0
MW 3.1
(Nm³/kWh) 0.402
2-Dec
429
29.3
73.3
30,859
24.0
3.1
3-Dec
442
29.4
75.0
30,733
24.0
5-Dec
436
30.4
73.6
30,054
6-Dec
434
30.0
73.7
8-Dec
447
31.3
9-Dec
441
12-Dec
Date
Heat Rate
Gas Energy
Elec. Energy
Elect. Eff.
kJ/kWh 14,224
Btu/kWh 13,470
kJ 1,060,654,800
kJ 268,452,000
25.3%
0.421
14,913
14,123
1,092,408,600
263,700,000
24.1%
3.1
0.410
14,500
13,732
1,087,948,200
270,108,000
24.8%
24.0
3.1
0.408
14,455
13,689
1,063,911,600
264,960,000
24.9%
31,441
24.0
3.1
0.427
15,104
14,303
1,113,011,400
265,284,000
23.8%
70.2
31,285
24.0
2.9
0.446
15,783
14,946
1,107,489,000
252,612,000
22.8%
28.1
76.4
31,255
24.0
3.2
0.409
14,482
13,714
1,106,427,000
275,040,000
24.9%
444
29.3
76.2
31,686
24.0
3.2
0.416
14,728
13,947
1,121,674,134
274,176,000
24.4%
13-Dec
416
30.3
68.7
30,185
24.0
2.9
0.440
15,563
14,738
1,068,557,496
247,176,000
23.1%
14-Dec
431
28.7
70.8
30,828
24.0
3.0
0.435
15,407
14,591
1,091,301,996
254,988,000
23.4%
15-Dec
424
31.0
70.1
30,858
24.0
2.9
0.440
15,588
14,761
1,092,375,678
252,288,000
23.1%
16-Dec
424
29.5
71.0
30,619
24.0
3.0
0.431
15,258
14,449
1,083,920,388
255,744,000
23.6%
17-Dec
430
29.0
72.0
31,171
24.0
3.0
0.433
15,322
14,510
1,103,462,250
259,272,000
23.5%
18-Dec
422
29.4
69.6
29,605
24.0
2.9
0.425
15,053
14,255
1,048,008,858
250,632,000
23.9%
19-Dec
421
30.4
70.4
29,898
24.0
2.9
0.425
15,038
14,241
1,058,391,678
253,368,000
23.9%
21-Dec
421
28.3
71.7
29,743
24.0
3.0
0.415
14,681
13,903
1,052,908,926
258,192,000
24.5%
22-Dec
416
28.5
69.0
30,559
24.0
2.9
0.443
15,685
14,854
1,081,798,512
248,292,000
23.0%
23-Dec
440
27.6
72.0
31,785
24.0
3.0
0.442
15,634
14,806
1,125,190,062
259,092,000
23.0%
30-Dec avg If 4.0 MW
417
29.4
69.76
29,221
24.0
2.9
0.419
14,828
14,042
1,034,406,054
251,136,000
24.3%
430 519
26.0
72.0 96.0
36,720
avg 24.00
3.0 4.0
0.383
13,541
12,823
1,299,888,000
345,600,000
23.9% 26.6%
If 3.9 MW
500
26.0
93.6
36,000
24.00
3.9
0.385
13,615
12,894
1,274,400,000
336,960,000
26.4%
If 3.8 MW
488
26.0
91.2
34,848
24.00
3.8
0.382
13,527
12,810
1,233,619,200
328,320,000
26.6%
If 3.7 MW
483
26.0
88.8
34,128
24.00
3.7
0.384
13,605
12,884
1,208,131,200
319,680,000
26.5%
If 3.6 MW
471
26.0
86.4
33,840
24.00
3.6
0.392
13,865
13,130
1,197,936,000
311,040,000
26.0%
If 3.5 MW
462
26.0
84.0
33,120
24.00
3.5
0.394
13,958
13,218
1,172,448,000
302,400,000
25.8%
If 3.4 MW
456
26.0
81.6
32,400
24.00
3.4
0.397
14,056
13,311
1,146,960,000
293,760,000
25.6%
If 3.3 MW
450
26.0
79.2
31,968
24.00
3.3
0.404
14,289
13,531
1,131,667,200
285,120,000
25.2%
If 3.2 MW
438
26.0
76.8
31,536
24.00
3.2
0.411
14,536
13,766
1,116,374,400
276,480,000
24.8%
If 3.1 MW
431
26.0
74.4
30,960
24.00
3.1
0.416
14,731
13,950
1,095,984,000
267,840,000
24.4%
If 3.0 MW
427
26.0
72.0
29,952
24.00
3.0
0.416
14,726
13,946
1,060,300,800
259,200,000
24.4%
http://digilib.mercubuana.ac.id/
55
Tabel 3.4. Perhitungan & Analisa Heat Balance pada GT & HRSG (lanjutan)
Date
Steam Steam Burner Stack feedwater Press. temp duct temp temp pressure
R/H
Gas Steam Cons. prod.
Steam avg.
Feed Make Up Water Water Steam Energy Cons Cons
Heat Balance Make Up Cogen Eff. water Energy (Elec. + Steam)
% of Elect.
% of Steam
% of Exhaust Gas
% of Losses
1-Dec
Barg 8.0
degC 173
degC 454
degC 156
Barg 15
H 24.0
m3 0
Ton 206
Ton/h 8.58
Ton 210
Ton 57
kJ 571,650,000
kJ 7,138,638
78.7%
25.3%
53.4%
74.7%
21.3%
2-Dec
8.0
172
451
155
15
24.0
0
208
8.67
212
57
577,200,000
7,207,945
76.5%
24.1%
52.3%
75.9%
23.5%
3-Dec
7.9
172
454
154
15
24.0
0
210
8.75
214
58
582,750,000
7,277,252
77.9%
24.8%
53.0%
75.2%
22.1%
5-Dec
7.8
172
439
153
15
23.93
0
213
8.90
217
59
591,075,000
7,381,213
79.9%
24.9%
55.0%
75.1%
20.1%
6-Dec
7.8
172
446
154
15
24.0
0
216
9.00
220
59
599,400,000
7,485,174
77.2%
23.8%
53.3%
76.2%
22.8%
8-Dec
8.1
165
461
153
15
24.0
0
200
8.33
204
55
555,000,000
6,930,716
72.5%
22.8%
49.7%
77.2%
27.5%
9-Dec
8.1
173
456
155
15
24.0
0
209
8.71
213
58
579,975,000
7,242,599
76.8%
24.9%
51.9%
75.1%
23.2%
12-Dec
7.9
172
457
153
15
24.0
0
218
9.08
222
60
604,950,000
7,554,481
77.9%
24.4%
53.4%
75.6%
22.1%
13-Dec
8.0
173
439
155
15
24.0
0
197
8.21
201
54
546,675,000
6,826,756
73.8%
23.1%
50.7%
76.9%
26.2%
14-Dec
8.3
173
440
155
15
24.0
0
211
8.79
215
58
585,525,000
7,311,906
76.5%
23.4%
53.1%
76.6%
23.5%
15-Dec
8.1
173
435
155
15
24.0
0
204
8.50
208
56
566,100,000
7,069,331
74.4%
23.1%
51.3%
76.9%
25.6%
16-Dec
7.8
172
445
152
15
24.0
0
205
8.54
209
56
568,875,000
7,103,984
75.6%
23.6%
52.0%
76.4%
24.4%
17-Dec
7.8
172
438
153
15
24.0
0
212
8.83
216
58
588,300,000
7,346,559
76.3%
23.5%
52.8%
76.5%
23.7%
18-Dec
8.0
173
438
155
15
24.0
0
196
8.17
200
54
543,900,000
6,792,102
75.3%
23.9%
51.4%
76.1%
24.7%
19-Dec
7.7
171
441
152
15
24.0
0
226
9.42
231
62
627,150,000
7,831,710
82.6%
23.9%
58.6%
76.1%
17.4%
21-Dec
8.1
174
443
153
15
24.0
0
207
8.63
211
57
574,425,000
7,173,291
78.5%
24.5%
54.0%
75.5%
21.5%
22-Dec
8.1
173
433
155
14
24.0
0
202
8.42
206
56
560,550,000
7,000,024
74.3%
23.0%
51.3%
77.0%
25.7%
23-Dec
8.0
173
449
154
15
24.0
0
204
8.50
208
56
566,100,000
7,069,331
72.9%
23.0%
49.9%
77.0%
27.1%
30-Dec
7.9
172
425
153
15
24.0
0
206
8.58
210
57
571,650,000
7,138,638
79.0%
24.3%
54.7%
75.7%
21.0%
76.7% 82.4%
23.9% 26.6%
52.7% 55.8%
76.1% 73.4%
23.3% 17.6%
If 4.0 MW
8.0
173
533
155
15
24.0
0
264.0
11.00
269
73
732,600,000
average 9,148,546
If 3.9 MW
8.0
173
514
155
15
24.0
0
264.0
11.00
269
73
732,600,000
9,148,546
83.3%
26.4%
56.9%
73.6%
16.7%
If 3.8 MW
8.0
173
505
155
15
24.0
0
259.2
10.80
264
71
719,280,000
8,982,208
84.3%
26.6%
57.7%
73.4%
15.7%
If 3.7 MW
8.0
173
500
155
15
24.0
0
256.8
10.70
262
71
712,620,000
8,899,040
84.8%
26.5%
58.4%
73.5%
15.2%
If 3.6 MW
8.0
173
490
155
15
24.0
0
252.0
10.50
257
69
699,300,000
8,732,703
83.7%
26.0%
57.8%
74.0%
16.3%
If 3.5 MW
8.0
173
480
155
15
24.0
0
240.0
10.00
245
66
666,000,000
8,316,860
82.0%
25.8%
56.2%
74.2%
18.0%
If 3.4 MW
8.0
173
474
155
15
24.0
0
230.4
9.60
235
63
639,360,000
7,984,185
80.8%
25.6%
55.2%
74.4%
19.2%
If 3.3 MW
8.0
173
470
155
15
24.0
0
225.6
9.40
230
62
626,040,000
7,817,848
80.0%
25.2%
54.8%
74.8%
20.0%
If 3.2 MW
8.0
173
459
155
15
24.0
0
220.8
9.20
225
61
612,720,000
7,651,511
79.1%
24.8%
54.3%
75.2%
20.9%
If 3.1 MW
8.0
173
450
155
15
24.0
0
216.0
9.00
220
59
599,400,000
7,485,174
78.6%
24.4%
54.2%
75.6%
21.4%
If 3.0 MW
8.0
173
445
155
15
24.0
0
206.4
8.60
211
57
572,760,000
7,152,499
77.9%
24.4%
53.5%
75.6%
22.1%
http://digilib.mercubuana.ac.id/
56
Dari tabel di atas maka Heat Balance bulan desember 2012 dengan power average 3.0 MW adalah : % of Electricity % of Steam % of Exhaust Gas % of Losses
= = = =
23.9 % 52.7 % 76.1 % 23.3 %
Steam 52.7 %
Exhaust Gas 76.1%
Losses 23.3%
Thermal Energy 100%
Elctricity 23.9%
Gambar 3.2 : Heat Balance GT+HRSG Desember 2012 Jika load Turbin dibuat konstan dengan average air intake 26°C, bisa dilihat dari tabel dan grafik berikut. Tabel 3.5. Heat balance Load Konstan LOAD (MW)
% of Elect.
% of Exhaust Gas
% of Steam
% of Losses
Cogen Eff
3.0
24.4%
75.6%
53.5%
22.1%
77.9%
3.1
24.4%
75.6%
54.2%
21.4%
78.6%
3.2
24.8%
75.2%
54.3%
20.9%
79.1%
3.3
25.2%
74.8%
54.8%
20.0%
80.0%
3.4
25.6%
74.4%
55.2%
19.2%
80.8%
3.5
25.8%
74.2%
56.2%
18.0%
82.0%
3.6
26.0%
74.0%
57.8%
16.3%
83.7%
3.7
26.5%
73.5%
58.4%
15.2%
84.8%
3.8
26.6%
73.4%
57.7%
15.7%
84.3%
3.9
26.4%
73.6%
56.9%
16.7%
83.3%
4.0
26.6%
73.4%
55.8%
17.6%
82.4%
http://digilib.mercubuana.ac.id/
57
Grafik 3.1. Perbandingan Load GT terhapap Effisiensi Cogen
Grafik 3.2. Heat balance Terhadap Load GT
Maka dari analisa di atas jika Load Gas Turbine dapat dioperasikan stabil pada 3.7 MW didapatkan cogen effisiensi maksimal 84.8 % dengan electrical
http://digilib.mercubuana.ac.id/
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effisiensi 26.5 %, steam effisiensi 58.4 % dan losses exhaust gas 15.2 %. Losses tersebut merupakan gas buang yang keluar pada stack, juga dari radiasi pada isolasi. Dari data performance SGT-100 Gas Turbine diketahui elec eff 31% dengan heat rate 11008 BTU/kWH karena intake air temp 15°C, sedangkan untuk Cogen tangerang intake air temp 24~29°C (avg/day 26°C) sehingga heat ratenya 12800~14000 Btu/kWH. Dari hasil analisa ini kita dapat berpedoman pada hukum pertama thermodinamika yang menjelaskan tentang konsep “Kekekalan Energi”.Energi tidak dapat diciptakan dan tidak dapat dimusnahkan, tetapi Energi dapat dirubah dari satu bentuk ke bentuk lainnya. Perubahan energi ini bisa di bagi menjadi 2, yaitu energi yang termanfaatkan dan ada yang terbuang percuma. Dan energi yang termanfaatkan itulah yang di sebut Exergy. Jadi dalam kasus ini bisa kita simpulkan bahwa dari 100% energi yang akan kita konversi hanya 84.8 % exergy maksimal yang kita peroleh. Sehingga walaupun energi itu kekal, kita harus tetap hemat energi.
http://digilib.mercubuana.ac.id/
