Exergy-energy analysis of full repowering of a steam power plant

doi:10.1007/s11708-014-0342-6

Front. Energy

2015, Vol. 9

Issue (1) : 54-67 https://doi.org/10.1007/s11708-014-0342-6

RESEARCH ARTICLE

Exergy-energy analysis of full repowering of a steam power plant

S. NIKBAKHT NASERABAD, K. MOBINI(

), A. MEHRPANAHI, M. R. ALIGOODARZ

Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran 7591618439, Iran

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Abstract

A 320 MW old steam power plant has been chosen for repowering in this paper. Considering the technical conditions and working life of the power plant, the full repowering method has been selected from different repowering methods. The power plant repowering has been analyzed for three different feed water flow rates: a flow rate equal to the flow rate at the condenser exit in the original plant when it works at nominal load, a flow rate at maximum load, and a flow rate when all the extractions are blocked. For each flow rates, two types of gas turbines have been examined: V94.2 and V94.3A. The effect of a duct burner has then been investigated in each of the above six cases. Steam is produced by a double-pressure heat recovery steam generator (HRSG) with reheat which obtains its required heat from the exhaust gases coming from the gas turbines. The results obtained from modeling and analyzing the energy-exergy of the original steam power plant and the repowered power plant indicate that the maximum efficiency of the repowered power plant is 52.04%. This maximum efficiency occurs when utilizing two V94.3A gas turbines without duct burner in the steam flow rate of the nominal load.

Keywords full repowering exergy analysis V94.2 and V94.3A gas turbines double-pressure HRSG duct burner Bandarabbas steam power plant efficiency

Corresponding Author(s): K. MOBINI

Just Accepted Date: 04 December 2014 Issue Date: 02 March 2015

Cite this article:

S. NIKBAKHT NASERABAD,K. MOBINI,A. MEHRPANAHI, et al. Exergy-energy analysis of full repowering of a steam power plant[J]. Front. Energy, 2015, 9(1): 54-67.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-014-0342-6
https://academic.hep.com.cn/fie/EN/Y2015/V9/I1/54

Fig.1 Schematic diagram of Bandarabbas steam power plant

Fig.2 Schematic diagram of repowered cycle

Tab.1 Analysis of natural gas

Tab.2 Results of modeling of the steam power plant showing the properties of water/steam at different points (Fig. 1)

Tab.3 Comparison of the result obtained from modeling and data of the power plant

Fig.3 Definition of pinch and approach temperature differences

Tab.4 Comparison of the results obtained from modeling and the existing data from two available gas turbines

Fig.4 Comparison of exhaust loss and total power for different repowering scenario

Type of gas turbine	Situation of repowering	Numbers of gas turbine	Duct burner	k	y	?T_pinch,_hp/K	?T_pinch,_lp/K	?T_pinch,_Dea/K	T_gt,_out,_HRSG/K	$E ˙ g,out,HRSG PH$	$E ˙ g,out,HRSG CH$	$η exergy$ $/ %$	New ST power/MW	Total power/ MW
V94.3A	Nominal	2	Exists	1.0	0.88	15.58	55.56	72.54	420.6	23.3713	14.1825	51.04	289.2	875.2
		2	Deleted	1.0	0.83	5.230	35.54	51.48	399.3	16.3331	14.1403	52.04	280.0	866.0
		3	Exists	1.0	0.88	98.78	192.5	219.4	583.3	158.823	21.2526	45.87	289.2	1168
		3	Deleted	1.0	0.88	82.02	175.3	202.1	565.9	142.398	21.2104	46.81	289.2	1168
	Overload	2	Exists	1.2	—	—	—	—	—	—	—	—	—	—
		2	Deleted	1.2	—	—	—	—	—	—	—	—	—	—
		3	Exists	1.2	0.88	64.93	133.4	160.2	517.8	100.831	21.2526	47.94	342.0	1221
		3	Deleted	1.2	0.88	48.01	116.0	142.6	500.1	86.8514	21.2104	48.92	342.0	1221
	Extraction deletion	2	Exists	1.37	—	—	—	—	—	—	—	—	—	—
		2	Deleted	1.37	—	—	—	—	—	—	—	—	—	—
		3	Exists	1.37	0.88	36.24	83.98	109.1	461.3	59.2849	21.2526	49.56	383.3	1262
		3	Deleted	1.37	0.88	19.20	66.32	91.34	443.3	47.9138	21.2104	50.57	383.3	1262
V94.2	Nominal	4	Exists	1.00	0.83	5.100	95.02	120.9	486.1	88.4272	18.7023	42.19	269.4	929.4
		4	Deleted	1.00	0.72	5.031	84.63	107.0	472.3	77.0860	18.6747	42.28	249.9	909.9
		5	Exists	1.00	0.88	27.48	142.4	173.3	544.3	177.918	23.3910	40.21	277.2	1102
		5	Deleted	1.00	0.88	10.80	125.4	156.2	527.1	156.677	23.3434	40.97	277.2	1102
	Overload	4	Exists	1.20	0.69	5.260	52.85	75.15	434.6	49.4961	18.7023	43.19	291.5	951.5
		4	Deleted	1.20	0.60	5.153	41.98	61.36	420.7	40.5653	18.6747	43.27	271.2	931.2
		5	Exists	1.20	0.86	5.149	96.88	128.8	495.1	120.140	23.3910	41.93	324.4	1149
		5	Deleted	1.20	0.77	5.103	88.60	117.5	483.8	108.063	23.3434	42.06	306.3	1131
	Extraction deletion	4	Exists	1.37	0.57	13.64	20.56	38.76	393.1	25.1567	18.7023	43.65	301.6	961.6
		4	Deleted	1.37	−	−	−	−	−	−	−	−	−	−
		5	Exists	1.37	0.75	5.062	68.08	97.03	459.4	83.8888	23.3910	42.65	344.0	1169
		5	Deleted	1.37	0.67	5.177	59.61	85.83	448.1	73.4947	23.3434	42.76	325.2	1150

Results obtained from modeling of the repowered power plant at different conditions

Fig.5 Diagram of temperature versus total heat absorbed by steam along HRSG

Fig.6 Absorption at different HRSG components

Fig.7 Effect of fuel consumption in duct burner on total power and exergy efficiency

Fig.8 Effect of y and k parameters on exhaust gas temperature

Fig.9 Effect of y and k parameters on exergy efficiency

Fig.10 Effect of y and k parameters on repowered power plant net work

Fig.11 Effect of exhaust temperature on total power and exergy efficiency

C_pa	Specific heat/(kJ·kg⁻¹·K⁻¹)
Comp	Compressor
$Δ T$	Temperature difference/K
$η$	Efficiency/%
$E ˙$	Exergy rate/kW
ex,e	Specific exergy/(kJ·kg⁻¹)
FA	Ratio of fuel to air
$γ a$	Air specific heat rate
$γ f$	Fuel exergy grade function/%
$γ g$	Gas specific heat rate
h	Enthalpy/(kJ·kg⁻¹)
HP	High pressure
IP	Intermediate pressure
LHV	lower heating value/(kJ·kg⁻¹)
LP	Low Pressure
$m ˙$	Mass flow rate/(kg·s⁻¹)
N	Numbers of gas turbine
P	Pressure/bar
$Q ˙$	Heat transfer rate/kW
R	Universal constant of gases
r_p	Pressure ratio
s	Entropy
T	Temperature/K
$W ˙$	Power/kW
Subscripts
a	Air
app	Approach
Comp	Compressor
Cch	Combustion chamber
Cond	Condensor
DB, db	Duct burner
Dea	Deaerator
eco	Economizer
eva	Evaporator
f	Fuel
g	Gas
GT,gt	Gas turbine
Ise	Isentropic
l	Loss
p	Pinch
pp	Power plant
pre	Pre heater
RC	Repowered cycle
St	Steam turbine
Sup	Super heater
t	Turbine
tot	Total
0	Dead state
Superscripts
PH	Physical exergy
Physical exergy	Chemical exergy
KN	Kinetic exergy
PT	Potential exergy

Notations

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