ANALYSIS OF A BRAZILIAN THERMAL PLANT OPERATION APPLYING ENERGETIC AND EXERGETIC BALANCES

Fraga, M. M. C.; Campos, B. L. de O.; Lisboa, M. S.; Almeida, T. B. de; Costa, A. O. S. da; Lins, V. de F. C.

doi:10.1590/0104-6632.20180354s20170425

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Thermodynamics • Braz. J. Chem. Eng. 35 (4) • Dec 2018 • https://doi.org/10.1590/0104-6632.20180354s20170425 copy

ANALYSIS OF A BRAZILIAN THERMAL PLANT OPERATION APPLYING ENERGETIC AND EXERGETIC BALANCES

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

When the level of water reservoirs from Brazilian hydroelectric stations is low, additional thermal plants are turned on to complement the power of the national electric system. The fuels used in these plants are generally natural gas, fuel oil and coal. The objective of this work is to analyze energetically and exergetically a fuel oil thermal plant in operation in Brazil. Real industrial data were used in this analysis. The calculated total work of the turbine is 120.73 MW, which is close to the real value of 120 MW. The cycle energetic efficiency is 36.8% and the exergetic efficiency is 34.4%. The highest exergy destruction was found to be in the boiler (177.11 MW), followed by the high pressure turbine (13.37 MW), due to larger irreversibilities in the processes of these equipment. The exergetic analysis functioned as a complement to the energetic analysis, pointing out where the greatest irreversibilities and improvement potential are: in the boiler.

Key words:
Electrical power generation; Efficiency; Exergy destruction

i	T (K)	P (MPa)	$\dot{m}$ (kg·s^-1)
1	319.15	0.0474	-
2	-	1.965	-
3	343.15	-	-
4	378.15	-	-
5	424.15	0.494	114.72
6	428.15	15.988	-
7	463.15	-	-
8	508.15	-	-
9	-	15.302	-
10	526.65	-	-
11	-	14.909	-
12	804.15	13.635	-
13	802.65	12.948	-
14	688.65	3.329	-
16	810.65	-	-
19	-	0.0114	-
20	-	-	2.78

Extraction	P (MPa)
I	0.0474
II	0.131
III	0.592
IV	1.376
V	3.239

Components	Mass fraction
Carbon	0.8493
Hydrogen	0.1029
Sulfur	0.0412
Nitrogen	0.0033
Oxygen	0.0033

Substance	Property	Value
Fuel oil	Lower heating value (LHV)	40166.4 kJ·kg^-1
	Mass flow rate	7.917 kg·s^-1
	Input temperature	413.15 K
	Heat capacity	2.303kJ·kg^-1.K^-1
Air	Input temperature	313.15 K
	Oxygen excess	30%
Flue gas	Output temperature	426.15 K

i	T (K)	P(MPa)	m(kg·s^-1)	s (kJ·kg^-1·K^-1)	h (kJ·kg^-1)	ex (kJ·kg^-1)
1	319.15	0.0474	92.20	0.652	192.65	2.90
2	320.15	1.965	92.20	0.664	198.50	5.10
3	343.15	1.965	92.20	0.954	294.60	14.77
4	378.15	1.965	92.20	1.362	441.58	40.16
5	424.15	0.489	114.72	1.852	636.57	88.93
6	428.15	15.988	114.72	1.875	663.31	108.76
7	463.15	15.988	114.72	2.215	814.59	158.79
8	508.15	15.988	114.72	2.630	1016.20	236.59
9	508.15	15.302	111.94	2.631	1016.04	236.04
10	526.65	14.909	111.94	2.825	1102.65	272.47
11	614.81	14.909	111.94	5.317	2613.45	1032.70
12	804.15	13.635	114.72	6.518	3414.30	1475.50
13	802.65	12.948	114.72	6.544	3417.74	1471.10
14	688.65	3.239	114.72	6.935	3263.00	1199.80
15	688.65	3.239	104.37	6.935	3263.00	1199.80
16	810.65	3.239	104.37	7.305	3539.07	1365.80
17	810.65	3.239	104.37	7.305	3539.07	1365.80
18	-	-	92.20	-	-	-
19	321.5	0.0114	83.55	7.632	2436.88	165.84
20	508.15	15.988	2.78	2.630	1016.20	236.59
I	353.14	0.047	2.89	7.611	2642.99	378.27
II	437.65	0.131	5.76	7.554	2803.37	555.63
III	592.65	0.592	6.02	7.450	3102.80	886.06
IV	695.15	1.376	6.16	7.382	3305.79	1109.40
V	688.65	3.239	10.35	6.935	3263.00	1199.80
A	511.31	3.239	10.35	2.685	1028.73	232.75
B	467.40	1.376	16.51	2.276	826.55	152.44
C	380.43	0.131	5.76	1.389	449.84	40.41
D	353.14	0.047	8.64	1.075	334.90	18.87

Equipment	w (kJ·kg^-1)	$\dot{W}$ (MW)	η_En	η_Ex	${\dot{I}}_{d}$ (MW)
High Pressure Turbine (HPT)	154.74	17.75	1	0.570	13.37
Medium & Low Pressure Turbine (MPT/LPT)	986.63	102.98	1	0.918	9.264
Condenser Extraction Pump (CEP)	5.85	0.539	1	0.376	0.336
Boiler Feeding Pump (BFP)	26.74	3.07	1	0.742	0.792

Authors	Fuel	Net power output (MW)	Energy efficiency (%)	Exergy efficiency (%)
Ontario Power Generation – Lakeview (1969), apud Rosen and Dincer (2003)Rosen, M.A. and Dincer, I., Exergoeconomic analysis of power plants operating on various fuels. Applied Thermal Engineering, 23(6), 643–658 (2003).	Coal	307	35.5	33.2
Ontario Power Generation - Lennox (1970), apud Rosen and Dincer (2003)Rosen, M.A. and Dincer, I., Exergoeconomic analysis of power plants operating on various fuels. Applied Thermal Engineering, 23(6), 643–658 (2003).	Oil	512	37.0	34.8
Ontario Power Generation – Bruce B (1990), apud Rosen and Dincer (2003)Rosen, M.A. and Dincer, I., Exergoeconomic analysis of power plants operating on various fuels. Applied Thermal Engineering, 23(6), 643–658 (2003).	Uranium	842	31.0	31.0
Ontario Power Generation - Nanticoke, apud Rosen and Dincer (2003)Rosen, M.A. and Dincer, I., Exergoeconomic analysis of power plants operating on various fuels. Applied Thermal Engineering, 23(6), 643–658 (2003).	Coal	500	37.4	35.8
Aljundi (2009)Aljundi, I.H., Energy and exergy analysis of a steam power plant in Jordan. Applied Thermal Engineering, 29(2–3), 324–328 (2009).. Available at: http://dx.doi.org/10.1016/j.applthermaleng.2008.02.029. http://dx.doi.org/10.1016/j.applthermale...	Heavy fuel oil	396	26	25
Regulagadda et al. (2010)Regulagadda, P., Dincer, I. and Naterer, G.F., Exergy analysis of a thermal power plant with measured boiler and turbine losses. Applied Thermal Engineering, 30(8–9), 970–976 (2010). Available at: http://dx.doi.org/10.1016/j.applthermaleng.2010.01.008. http://dx.doi.org/10.1016/j.applthermale...	Coal	32	27.5	23.17
Adibhatla and Kaushik (2014)Adibhatla, S., and Kaushik, S.C., Energy and exergy analysis of a super critical thermal power plant at various load conditions under constant and pure sliding pressure operation. Applied Thermal Engineering, 73(1), 49–63 (2014). Available at: http://dx.doi.org/10.1016/j.applthermaleng.2014.07.030. http://dx.doi.org/10.1016/j.applthermale...	Coal	660	38.94	35.56

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[1] Corresponding author: brunolacerdaoc@gmail.com

Correction factor (β)	1.069
Chemical exergy (exchem)	42941.75 kJ·kg^-1
Thermo-mechanical exergy (extm)	40.85 kJ·kg^-1
Fuel exergy (exf)	42982.60 kJ·kg^-1

Heat rate input in the boiler ( ${\dot{Q}}_{B}$ )	303.95 MW
Energetic efficiency (η_B,En)	0.956
Exergetic efficiency (η_B,Ex)	0.469
Exergy destruction ( ${\dot{I}}_{d}$ )	177.11 MW

Heat rate input in the boiler ( ${\dot{Q}}_{B}$ )	303.95 MW
Heat rejected in the condenser ( ${\dot{Q}}_{C}$ )	187.51 MW
${\dot{Q}}_{B} - {\dot{Q}}_{C}$	116.43 MW
Gross power output ( ${\dot{W}}_{g}$ )	120.73 MW
Net power output ( ${\dot{W}}_{e}$ )	117.12 MW
Carnot efficiency (η_Carnot)	0.639
Energy efficiency (η_En)	0.368
Exergy efficiency (η_Ex)	0.344