Applied Thermal Engineering 73 (2014) 49e63

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Applied Thermal Engineering

journal homepage: www.elsevier.com/locate/apthermeng

Energy and exergy analysis of a super critical thermal power plant at

various load conditions under constant and pure sliding pressure
operation
Sairam Adibhatla a, *, S.C. Kaushik b
a
Power Management Institute, NTPC Ltd, Sector-16A, Noida, Uttar Pradesh 201301, India
b
Centre for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India

h i g h l i g h t s

Sliding pressure operation is better than constant pressure operation at part loads.

This is due to reduced throttling losses at part load operation.

A large reduction in rate of exergy destruction at part loads has been observed for turbine.

The feed pump power input reduces by 42.5% for a 660 MWe unit at 60% of rated load.

a r t i c l e i n f o a b s t r a c t

Article history: The objective of this paper is to perform an energetic and exergetic analysis on a 660 MWe coal fired
Received 19 April 2014 supercritical thermal power plant at 100%, 80% and 60% of normal continuous rating (NCR) conditions
Accepted 10 July 2014 under constant pressure as well as pure sliding pressure operation and to highlight the benefits of the
Available online 17 July 2014
latter over the former. The energetic input, energetic output, exergetic input, exergetic output, energetic
and exergetic efficiencies of various components of the supercritical thermal power plant are estimated
Keywords:
at 660 MWe, 528 MWe and 396 MWe load under both constant pressure as well as pure sliding pressure
Exergy destruction
operation. Also the energy losses and exergy destruction in various components of a power plant i.e.
Normal continuous rating
Energetic efficiency
Boiler, high pressure turbine (HPT), intermediate pressure turbine (IPT), low pressure turbine (LPT),
Exergetic efficiency condenser, gland steam coolers, condensate extraction pumps, low pressure heaters (LPH), drip pumps
Constant pressure operation (DP), deaerator (D), boiler feed pump (BFP) and high pressure heaters (HPH) have been calculated. The
Sliding pressure operation results have shown that the boiler has the maximum rate of exergy destruction than any other
component in the power plant. After the boiler, turbine has the maximum rate of exergy destruction than
any other component of the power plant. The study reveals that there is a significant reduction in the rate
of exergy destruction at part load conditions for the turbine in case of sliding pressure operation in
comparison to constant pressure operation. The rate of exergy destruction in the turbine at 100%, 80%
and 60% of NCR conditions is 49.16 MW/43.22 MW/43.92 MW for constant pressure operation and
47.66 MW/37.88 MW/28.94 MW respectively. The BFP power input reduces by 9.39%, 21.52% and 42.5%
respectively at 100%, 80% and 60% of NCR conditions if the unit runs in sliding pressure mode compared
to constant pressure mode.
© 2014 Elsevier Ltd. All rights reserved.

1. Introduction power generation industry. The advent of supercritical once

through units with higher cycle efficiencies has made it possible
Economic power generation with lowest possible fuel con- to minimise the cost of power generation considerably. Besides
sumption is the main challenge for all the engineers working in this, in Indian scenario, the highly varying grid frequencies due to
large supply-demand imbalance at times force the generators to
reduce their station loads to much below their declared capa-
bilities resulting into lower plant efficiencies. This necessitates
* Corresponding author. Tel.: þ91 9650995313.
E-mail addresses: adibhatla2@rediffmail.com, asairam02@gmail.com
units with better part load efficiency towards achieving economic
(S. Adibhatla). power generation. Unlike drum type units, once through

http://dx.doi.org/10.1016/j.applthermaleng.2014.07.030
1359-4311/© 2014 Elsevier Ltd. All rights reserved.
50 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63

subcritical and supercritical units are suitable for sliding pressure reference environmental state on the exergy analysis and found
operation. that for a moderate change in the reference state, no significant
In a constant pressure operation, all control valves of high changes occurred in the performance of the major components [8].
pressure turbine (HPT) are operated simultaneously by same In this paper, energy and exergy analysis of a 660 MWe bitu-
amount. The main steam pressure is held constant at rated condi- minous coal fired, once through supercritical power plant has been
tion for all turbine loads. The turbine output increases as the con- carried out at different load conditions. The load conditions chosen
trol valves are opened. This operation is also referred to as throttle are 660 MWe, 528 MWe and 396 MWe respectively corresponding
control of steam turbines. At part loads, the control valves of HPT to 100%, 80% and 60% of normal continuous rating (NCR). This
are throttled by a large amount to match the reduced flow analysis has been separately carried out for constant and pure
requirement of the steam turbine. As throttling is a highly irre- sliding pressure operating conditions and the results have been
versible process, throttle control at part loads increases the entropy compared. An attempt has been made to develop a model using
generation. Hence a significant amount of useful energy (exergy) is engineering equation solver (EES) software [9] for performing en-
destructed at part loads in constant pressure operation. As the main ergy and exergy analysis.
steam pressure is held constant at rated condition for all turbine
loads, boiler feed pumps (BFP) have to operate at their design 2. System description of 660 MWe coal fired supercritical
pressures irrespective of the turbine loading. power plant
In pure or natural sliding pressure operation, the steam flow is
controlled by varying the steam generator pressure with control Nowadays, due to higher cycle efficiencies, the supercritical
valves of HPT in fixed position. In this flow control method, the once through units are being preferred over the conventional sub
control valves of HPT are typically wide open. The steam flow to the critical drum type units. Besides higher cycle efficiencies, super-
turbine is controlled by the pressure of the steam generator. Main critical units are better suited for sliding pressure operation with
steam pressure is controlled by the steam generator firing rate. As quick response to load changes and shorter start up time. In this
the main steam pressure required for part load operation of the paper, we are considering the analysis of a coal fired 660 MWe
turbine is less, the BFP's need not required to develop design supercritical once through thermal power plant based on modified
pressure. This reduces the BFP power consumption considerably. Rankine cycle with all methods of efficiency improvement tech-
Energy and exergy analysis based on first and second law of niques like lowering the condenser pressure, superheating the
thermodynamics is a very powerful tool in analysing the thermal steam to high temperatures, increasing the boiler pressure,
systems. It can be applied to thermal power plants to quantify the reheating and regenerative feed water heating.
sources of inefficiency, to find out the location, type and true A continuous mass flow diagram for one unit of supercritical
magnitude of exergy destruction. Moreover, another important once through power plant modelled in this paper includes the main
issue for improving the existing system is the origin of the exergy components such as high pressure turbine (HPT), intermediate
loss. Hence, a clear picture, instead of only the magnitude of exergy pressure turbine (IPT), low pressure turbines (LPT), a boiler (B),
loss in each section, is required [1]. condensate extraction pumps (CEP), boiler feed pumps (BFP), drip
Several researchers have already done a good amount of work in pumps(DP), low pressure heaters (LPH) and high pressure heaters
the area of energy and exergy analysis of thermal power plants. (HPH), a deaerator (D), a generator (G) as shown in Fig. 1.
However, the literature on energy and exergy analysis reveals a lack The boiler of this power plant produces super-heated steam at a
of clear information on application of these techniques for power pressure of 251 bar and temperature of 813.15 K at super heater
plants operating under sliding pressure at different load conditions. outlet at a steam flow rate of 561.19 kg/s. There is a single reheat at a
It seems that there is no literature which clearly highlights the temperature of 838.15 K. Reheating of cold reheat (CRH) steam is in
benefits of sliding pressure over the constant pressure operation. place to avoid high moisture content at the last stages of LPT. A
Ameri et al. have done energy, exergy and exergoeconomic concept of heater above reheat point (HARP) is employed in the
analysis of a 250 MW thermal power plant operating in Iran. They cycle wherein the extraction is taken from the last stages of HPT for
have estimated the exergy destruction in various components of feed water regeneration in the last high pressure heater. This is in
power plant by varying the ambient temperature. They have also place for improving the economiser inlet feed water temperature.
calculated the cost of exergy destruction for each component of the The fuel used is Indian bituminous coal which has a higher
power plant [2]. calorific value (HCV) of 13, 817 kJ/kg. The detailed proximate and
Kaushik et al. have explained the detailed methodology of per- ultimate analysis of the fuel used is shown in Tables 1 and 2
forming the energy and exergy analysis on major components of a respectively.
thermal power plant and came to the conclusion that boiler is the
main component where a major amount of exergy destruction
takes place [3]. 2.1. Energetic analysis
Datta et al. have presented exergy analysis of a coal based
thermal power plant by splitting up the entire plant cycle into three In an open flow system, there are three types of energy transfer
zones for the analysis [4]. Ganapathy et al. have determined the across the control surface namely, work transfer, heat transfer and
energy losses and exergy losses of the individual components of the energy associated with mass transfer. The first law of thermody-
lignite fired thermal power plant [5]. Hasti et al. have carried out namics when applied to steady flow process of an open system is
exergy analysis on an ultra-supercritical lignite fired power plant given below:
and found out the exergy destruction in various components of the " # " #
X Ci2 Co2
power plant [6]. _
Q k þ m_ hi þ þ gZi ¼ m_ ho þ þ gZo þ W_ (1)
Reddy et al. have done a detailed exergetic analysis and per- 2 2
formance evaluation of a parabolic trough concentrating solar
thermal power plant [7]. Aljundi has studied energy and exergy Where Q_ k the heat transfer flux to the system from source at
analysis of Al-Hossien power plant in Jordan and showed that the temperature Tk, W_ is the net work developed by the system, C is the
maximum exergy destruction occurs in the boiler (77%) followed by bulk velocity of the working fluid, Z is the altitude of the stream
the turbine (13%). He has also discussed the effect of varying the above the sea level, g is the acceleration due to gravity.
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 51

Fig. 1. Simplified schematic view of 660 MWe coal fired supercritical thermal power plant.

2.1.1. The mass balance for the boiler is given as _

W _ 2 ðh2  h3 Þ þ ðm_ 2  m_ 3 Þðh3  h4 Þ  E_ L;HPT
HPT ¼ m (7)

Where E_ L;HPT and W_ HPT are the rate of energy loss and work output
m_ 42 þ m_ 5 ¼ m_ 1 þ m_ 6 (2)
of the HPT respectively.
The energy balance for the boiler/combustion is given as: This gives:

0 ¼ Q_ k  m_ 1 ðh1  h42 Þ  m_ 6 ðh6  h5 Þ  E_ L;B (3) E_ L;HPT ¼ m_ 2 ðh2  h3 Þ þ ðm_ 2  m_ 3 Þðh3  h4 Þ  W_ HPT (8)

The first law efficiency of HPT is expressed as:

E_ L;HPT W _ HPT
hI;HPT ¼ 1  ¼ (9)
m_ 2 ðh2  h3 Þ þ ðm_ 2  m_ 3 Þðh3  h4 Þ m_ 2 ðh2  h3 Þ þ ðm_ 2  m_ 3 Þðh3  h4 Þ

where m_ 1 is the mass flow rate of feed water entering the boiler, m_ 6
is the mass flow rate of steam entering the reheater and E_ L;B is the
energy loss rate in the boiler Table 1
Proximate analysis of the coal used for the study.

E_ L;B ¼ Q_ k  m_ 1 ðh1  h42 Þ  m_ 6 ðh6  h5 Þ (4) Parameter Percentage of constituent

Total moisture 12
The first law efficiency for the boiler is defined as:
Volatile matter 21
Fixed carbon 24
E_ L;B m_ 1 ðh1  h42 Þ þ m_ 6 ðh6  h5 Þ Ash 43
hI;B ¼ 1  ¼ (5)
Q_
k Q_ k

where Q_ k the rate of heat transfer to the boiler from source at Table 2
Ultimate analysis of coal used for the study.
temperature Tk
Parameter Percentage of constituent

Carbon 34.46
2.1.2. The mass balance for HPT is given as Hydrogen 2.43
Nitrogen 0.69
Oxygen 6.64
Sulphur 0.45
m_ 2 ¼ m_ 3 þ m_ 4 (6) Ash 43
Moisture 12
The energy balance for the HPT is given as:
 52 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63

2.1.3. The mass balance for the IPT is given as

2.1.5. The mass balance for each one of the condenser-1/2 is given
as

m_ 6 ¼ m_ 7 þ m_ 8 þ m_ 9 þ m_ 10 þ m_ 11 þ m_ 12 (10)
m_ 18 ¼ m_ 16 þ 0:5*m_ 23 þ 0:5*m_ 21 (18)
The energy balance for the IPT is given as

W_ IPT ¼ m_ ðh  h7 Þ þ ðm_  m_ 7 Þðh7  h Þ þ ðm_  m_ 7  m_ Þðh  h Þ þ ðm_  m_ 7  m_  m_ Þðh  h Þ

6 6 6 8 6 8 8 9 6 8 9 9 10

þðm_  m_ 7  m_  m_  m_ Þðh  h Þ þ ðm_  m_ 7  m_  m_  m_  m_ Þðh  h Þ  E_ L;IPT

6 8 9 10 10 11 6 8 9 10 11 11 12 (11)

:WhereE_ L;IPT and W_ IPT are the rate of energy loss and work output The energy for each one of the Condenser-1/2 is given as:
of the IPT respectively.
This gives:

EL;IPT ¼ m_ 6 ðh6  h7 Þ þ ðm_ 6  m_ 7 Þðh7  h8 Þ þ ðm_ 6  m_ 7  m_ 8 Þðh8  h9 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9 Þðh9  h10 Þ

þðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10 Þðh10  h11 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10  m_ 11 Þðh11  h12 Þ  W_ IPT (12)

The first law efficiency of IPT is expressed as:

E_ L;IPT
hI;IPT ¼ 1 
m6 ðh6  h7 Þ þ ðm6  m7 Þðh7  h8 Þ þ ðm6  m7  m_ 8 Þðh8  h9 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9 Þðh9  h10 Þ
_ _ _ _ _
þðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10 Þðh10  h11 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10  m_ 11 Þðh11  h12 Þ
W _ IPT
¼
m_ 6 ðh6  h7 Þ þ ðm_ 6  m_ 7 Þðh7  h8 Þ þ ðm_ 6  m_ 7  m_ 8 Þðh8  h9 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9 Þðh9  h10 Þ
þðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10 Þðh10  h11 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10  m_ 11 Þðh11  h12 Þ (13)

2.1.4. The mass balance for the LPT-1/2 is given as

m_ 16 h16 þ 0:5*m_ 23 h23 þ 0:5*m_ 21 h21  Q_ Cond ¼ m_ 18 h18 þ E_ L;Cond
m_ 13 ¼ m_ 14 þ m_ 15 þ m_ 16 (14) (19)
The energy balance for the LPT-1/2 is given as:
Where Q_ Cond and E_ L;Cond are heat rejected to circulating water and
W_ LPT¼ m_ ðh  h Þ þ ðm_  m_ Þðh  h Þ rate of energy loss in the condenser respectively.
13 13 14 13 14 14 15
This gives:
þðm_  m_  m_ Þðh  h Þ  E_ L;LPT
13 14 15 15 16 (15)
E_ L;Cond ¼ m_ 16 h16 þ 0:5*m_ 23 h23 þ 0:5*m_ 21 h21  m_ 18 h18  Q_ Cond
Where E_ L;LPT and W_ LPT are the rate of energy loss and work output
(20)
of the LPT respectively.
This gives: The first law efficiency of the condenser is expressed as:

E_ L;LPT¼ m_ 13 ðh13  h14 Þ þ ðm_ 13  m_ 14 Þðh14  h15 Þ

E_ L;Cond
þðm_ 13  m_ 14  m_ 15 Þðh15  h16 Þ  W_ LPT (16) hI;Cond ¼ 1 
m16 h16 þ 0:5*m23 h23 þ 0:5*m_ 21 h21  m_ 18 h18
_ _
The first law efficiency of LPT-1/2 is expressed as: (21)

E_ L;LPT
hI;LPT ¼ 1 
m_ 13 ðh13  h14 Þ þ ðm_ 13  m_ 14 Þðh14  h15 Þ þ ðm_ 13  m_ 14  m_ 15 Þðh15  h16 Þ
W _ LPT
¼ (17)
m_ 13 ðh13  h14 Þ þ ðm_ 13  m_ 14 Þðh14  h15 Þ þ ðm_ 13  m_ 14  m_ 15 Þðh15  h16 Þ
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 53

2.1.6. The mass balance for the condensate extraction pump (CEP) is
given as E_ L;D ¼ m_ 9a h9a þ m_ 30 h30 þ m_ 35 h35  m_ 33a h33a (33)

m_ 18 ¼ m_ 19 (22) where E_ L;D is the rate of energy loss in the deaerator

The first law of efficiency of deaerator is expressed as:

E_ L;D m_ 33a h33a

hI;D ¼ 1  ¼ (34)
m_ 9a h9a þ m_ 30 h30 þ m_ 35 h35 m_ 9a h9a þ m_ 30 h30 þ m_ 35 h35

The energy balance for the condensate extraction pump (CEP) is 2.1.10. The mass balance for the HPH-8 is given as
given as:

E_ L;CEP ¼ m_ 19 ðh18  h19 Þ þ W_

CEP (23) m_ 37 ¼ m_ 39 (35)

where E_ L;CEP and W_

CEP are rate of energy loss and work input to CEP m_ 3a ¼ m_ 38 (36)
respectively.
The first law efficiency of the CEP is expressed as: The energy balance for HPH-8 is given as:

E_ L;CEP m_ 19 ðh19  h18 Þ E_ L;HPH8 ¼ m_ 3a ðh3a  h38 Þ  m_ 37 ðh39  h37 Þ (37)

hI;CEP ¼ 1  ¼ (24)
W _ W_
Where E_ L;HPH8 is the rate of energy loss in the HPH-8.
CEP CEP

The first law of efficiency of HPH-8 is expressed as:

2.1.7. The mass balance for BFP is given as
E_ L;HPH8
hI;HPH8 ¼ 1  (38)
m_ 3a ðh3a  h38 Þ
m_ 33a ¼ m_ 33 (25)
2.2. Exergetic analysis
The energy balance for the BFP is given as:

E_ L;BFP ¼ m_ 33 ðh33a  h33 Þ þ W_ BFP (26) 2.2.1. The exergy balance for the combustion is given as

where E_ L;BFP and W_ BFP are rate of energy loss and work input to BFP
r h  
X i
respectively. 0¼ mj _ p  T0 S_gen
_ f þa  mj (39)
The first law efficiency of the CEP is expressed as: k¼1

E_ L;BFP m_ 33 ðh33  h33a Þ where m_ f þa , is the sum of the mass of coal, air,m_ p is the mass of the
hI;BFP ¼ 1  ¼ (27) products of combustion and S_gen is the associated entropy
W _ BFP W_ BFP
generation.
Exergy of the coal, flue gas and hot products are explained in
2.1.8. The mass balance for LPH-1 is given as Kotas (1984).
The Exergetic efficiency is defined as:

m_ 15a ¼ m_ 23 (28) T0 S_gen _ p

mj
hII;Comb ¼ 1  ¼ (40)
_ f þa mj
mj _ f þa
m_ 20 ¼ m_ 22 (29)
2.2.2. The exergy flow equation for the high temperature heat
The energy balance for LPH-1 is given as:
transfer becomes
E_ L;LPH1 ¼ m_ 15a ðh15a  h22 Þ  m_ 20 ðh22  h20 Þ (30)
0 ¼ m_ p ðji  j0 Þ  m_ 42 ðj1  j42 Þ  m_ 6 ðj6  j4 Þ
WhereE_ L;LPH1 is the rate of energy loss in the LPH-1
The first law of efficiency of LPH-1 is expressed as: m_ ðj  j Þ  T S_gen
air b a 0 (41)

E_ L;LPH1
hI;LPH1 ¼ 1  (31)
m_ 15a ðh15a  h22 Þ 2.2.3. Th exergy balance for HPT is

2.1.9. The mass balance for the deaerator (D) is given as W_ _ 2 ðj2  j3 Þ þ ðm_ 2  m_ 3 Þðj3  j4 Þ  T0 S_gen
HPT ¼ m (42)

I_d;HPT ¼ T0 S_gen ¼ T0 ½m_ 2 ðs3  s2 Þ þ ðm_ 2  m_ 3 Þðs4  s3 Þ (43)

m_ 33a ¼ m_ 30 þ m_ 35 þ m_ 9a (32)
The energy balance for the deaerator (D) is given as: where I_d;HPT is the rate of exergy destruction in the HPT
54 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63

The second law efficiency for HPT can be expressed as: 2.2.6. The exergy balance for the condenser is

I_d;HPT
hII;HPT ¼ 1 
m_ 2 ðj2  j3 Þ þ ðm_ 2  m_ 3 Þðj3  j4 Þ
W_ HPT I_d;Cond ¼ m_ 16 j16 þ 0:5*m_ 15 j15 þ 0:5*m_ 21 j21  m_ 18 j18
¼ (44)
m_ 2 ðj2  j3 Þ þ ðm_ 2  m_ 3 Þðj3  j4 Þ n 
X 
T0 _
 1 Qk (52)
Tk
k¼1

2.2.4. The exergy balance for IPT is where the rate of exergy destruction in the condenser is I_d;Cond

W_ IPT ¼ m_ ðj  j Þ þ ðm_  m_ 7 Þðj  j Þ þ ðm_  m_ 7  m_ Þðj  j Þ þ ðm_  m_ 7  m_  m_ Þðj  j Þ

6 6 7 6 7 8 6 8 8 9 6 8 9 9 10

þðm  m  m  m  m Þðj  j Þ þ ðm  m  m  m  m  m Þðj  j Þ  T S_gen

_ _6 _ 7 _ 8 _ 9 10 10_ _
11 _ _
6 _ 7 _ 8 9 10 11 11 12 0 (45)

where k is the number of heat sources with which the condenser

is exchanging heat. Here k ¼ 1 and Q_ k becomes Q_ Cond .

_ _
W d;IPT ¼ ExIIPT  T0 Sgen (46) The second law efficiency for the condenser can be expressed as:

I_d;IPT ¼ T0 S_gen ¼ T0 ½m_ 6 ðs7  s6 Þ þ ðm_ 6  m_ 7 Þðs8  s7 Þ þ ðm_ 6  m_ 7  m_ 8 Þðs9  s8 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9 Þðs10  s9 Þ
þðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10 Þðs11  s10 Þ þ ðm_ 6  m_ 7  m_ 8  m_ 9  m_ 10  m_ 11 Þðs12  s11 Þ (47)

where the rate of exergy destruction in the IPT is I_d;IPT I_d;Cond

hII;Cond ¼ 1 
The second law efficiency for the IPT can be expressed as: m_ 16 j16 þ 0:5*m_ 15 j15 þ 0:5*m_ 21 j21  m_ 18 j18
(53)
I_d;IPT W_
IPT
hII;IPT ¼1 ¼ (48)
ExIIPT ExIIPT 2.2.7. The exergy balance for the CEP is

I_d;CEP ¼ T0 S_gen ¼ m_ 19 ðj18  j19 Þ þ W_ _ 19 T0 ðs19  s18 Þ

CEP ¼ m
2.2.5. The exergy balance for LPT is
(54)

W_ LPT ¼ m_ ðj  j Þ þ ðm_  m_ Þðj  j Þ

13 13 14 13 14 14 15
where the rate of exergy destruction in the CEP is I_d;CEP
The second law efficiency for the CEP can be expressed as:
þðm_ 13  m_ 14  m_ 15 Þðj15  j16 Þ  T0 S_gen (49)
I_d;CEP m_ ðj  j19 Þ
hII;CEP ¼ 1  ¼ 19 18 (55)
W _ W_
CEP CEP
I_d;LPT ¼ T0 S_gen ¼ T0 ½m_ 13 ðs14  s13 Þ þ ðm_ 13  m_ 14 Þðs15  s14 Þ
2.2.8. The exergy balance for the BFP is
þðm_ 13  m_ 14  m_ 15 Þðs16  s15 Þ (50)

I_d;BFP ¼ T0 S_gen ¼ m_ 33 ðj33a  j33 Þ þ W_ _ 33 T0 ðs33  s33a Þ

BFP ¼ m

where the rate of exergy destruction in the LPT isI_d;LPT (56)

The second law efficiency for the LPT can be expressed as:

I_d;LPT
hII;LPT ¼ 1 
m13 ðj13  j14 Þ þ ðm13  m14 Þðj14  j15 Þ þ ðm_ 13  m_ 14  m_ 15 Þðj15  j16 Þ
_ _ _
W_
LPT
¼ (51)
m_ 13 ðj13  j14 Þ þ ðm_ 13  m_ 14 Þðj14  j15 Þ þ ðm_ 13  m_ 14  m_ 15 Þðj15  j16 Þ
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 55
Table 3
Flow stream data of 660 MWe supercritical power plant at unit load of 660 MWe, 528 MWe and 396 MWe under constant pressure operation.

Stream Id Mass flow rate, kg/sec Temperature, K Pressure, bar Fluid

100% 80% 60% 100% 80% 60% 100% 80% 60% 100% 80% 60%

1B 562.2 435.7 327.6 813.1 813.1 813.1 248.5 248.5 248.5 Steam Steam Steam
1 562.2 435.7 327.6 810.1 810.1 810.1 242.2 242.2 242.2 Steam Steam Steam
2 562.2 435.7 327.6 805.1 787.0 766.5 229.2 183.0 138.1 Steam Steam Steam
3 40.78 27.02 17.63 625.6 599.5 584.7 71.02 55.51 42.32 Steam Steam Steam
3a 40.78 27.02 17.63 622.4 596.6 582.3 67.47 52.73 40.21 Steam Steam Steam
4 49.21 35.52 24.26 571.9 550.0 537.4 47.07 37.36 28.68 Steam Steam Steam
4a 49.21 35.52 24.26 568.8 547.2 535.0 44.72 35.50 27.25 Steam Steam Steam
5 467.0 368.7 281.8 571.9 550.0 537.4 47.07 37.36 28.68 Steam Steam Steam
6 467.0 368.7 281.8 838.2 838.2 838.2 42.36 33.63 25.81 Steam Steam Steam
7 21.92 16.34 11.50 743.5 744.7 745.4 22.4 17.88 13.77 Steam Steam Steam
7i 21.92 16.34 11.50 488.7 477.4 465.1 21.28 16.99 13.08 Steam Steam Steam
7a 21.92 16.34 11.50 742.9 744.2 745.1 21.28 16.99 13.08 Steam Steam Steam
8 27.22 20.38 15.88 742.0 743.5 744.5 19.71 15.74 12.11 Steam Steam Steam
9 14.50 10.78 7.808 655.0 656.8 658.1 12.08 9.679 7.473 Steam Steam Steam
9a 16.17 12.11 8.833 647.4 647.4 648.0 11.12 8.904 6.874 Steam Steam Steam
10 20.89 15.53 11.11 573.0 575.2 577.0 6.453 5.188 4.021 Steam Steam Steam
10a 22.70 16.98 12.23 574.5 575.4 576.4 6.129 4.923 3.815 Steam Steam Steam
11 31.63 23.97 17.44 487.7 490.1 492.1 3.069 2.481 1.922 Steam Steam Steam
11a 31.63 23.97 17.44 487.4 489.8 491.9 2.913 2.354 1.834 Steam Steam Steam
12 350.9 281.7 218.0 487.7 490.1 492.1 3.069 2.481 1.922 Steam Steam Steam
13 175.7 141.2 109.5 487.6 490.0 492.0 3.02 2.442 1.902 Steam Steam Steam
14 13.16 9.922 7.083 360.9 355.4 353.5 0.6443 0.520 0.407 Steam Steam Steam
14a 13.21 9.922 7.083 359.6 354.1 353.3 0.6119 0.493 0.386 Steam Steam Steam
15 9.650 5.128 1.833 340.1 335.6 331.0 0.2726 0.224 0.180 Steam Steam Steam
15a 9.650 5.128 1.833 338.9 334.5 329.9 0.2589 0.213 0.172 Steam Steam Steam
16 164.3 133.7 105.0 319.5 319.5 319.5 0.103 0.103 0.103 Steam Steam Steam
17 1.325 1.311 1.297 534.3 531.8 0.9512 0.951 0.951 Steam Steam Steam
18 183.4 147.1 114.5 319.5 319.5 319.5 0.103 0.103 0.103 Water Water Water
19 366.6 294.0 228.8 320.1 320.1 320.1 31.12 26.01 21.95 Water Water Water
20 366.6 293.9 228.8 321.6 321.9 322.4 30.63 25.69 21.76 Water Water Water
21 0.8917 0.878 0.864 371.4 371.4 371.4 0.9512 0.951 0.951 Water Water Water
22 366.6 293.9 228.8 335.9 331.5 327.0 21.77 17.55 14.12 Water Water Water
23 9.650 5.128 1.833 338.9 334.5 330.3 0.2589 0.213 0.172 Water Water Water
24 366.6 293.9 228.8 356.2 351.2 345.2 21.29 17.24 13.93 Water Water Water
25 434.1 344.8 265.6 357.1 351.6 345.6 21.29 17.24 13.93 Water Water Water
26a 67.54 50.87 36.75 359.6 354.1 348.2 0.6119 0.493 0.386 Water Water Water
26 67.54 50.87 36.75 359.9 354.4 348.4 21.29 17.24 13.93 Water Water Water
27 54.33 40.95 29.66 367.1 361.6 355.6 2.913 2.354 1.834 Water Water Water
28 434.1 344.8 265.6 402.7 395.6 387.6 18.8 15.67 13.00 Water Water Water
29 22.7 16.98 12.23 412.7 405.6 397.6 6.129 4.923 3.815 Water Water Water
30 434.1 344.8 265.6 432.9 424.5 415.2 16.32 14.10 12.07 Water Water Water
33a 562.2 435.8 327.6 e e e 11.12 8.904 6.874 Water Water Water
33 562.2 435.8 327.6 463.2 453.0 442.0 305.7 283.8 279.9 Water Water Water
34 562.2 435.8 327.6 486.7 475.4 463.0 305.7 283.8 279.9 Water Water Water
35 111.9 78.88 53.39 488.7 477.4 465.1 21.28 16.99 13.08 Water Water Water
36 89.99 62.54 41.89 530.2 516.6 501.8 44.72 35.50 27.25 Water Water Water
37 562.2 435.8 327.6 528.2 514.5 499.7 300.2 276.2 268.7 Water Water Water
38 40.78 27.02 17.63 556.5 540.5 523.8 67.47 52.73 40.21 Water Water Water
39 562.2 435.8 327.6 556.7 539.8 523.0 294.8 268.7 257.9 Water Water Water
40 55.56 43.05 32.39 556.7 539.8 523.0 294.8 268.7 257.9 Water Water Water
41 55.56 43.05 32.39 597.5 584.0 565.5 294.8 268.7 257.9 Water Water Water
42 562.2 435.8 327.6 559.5 558.7 526.3 294.8 268.7 257.9 Water Water Water

where the rate of exergy destruction in the BFP isI_d;BFP 2.2.10. The exergy balance for the LPH-1 is
The second law efficiency for the BFP can be expressed as:

I_d;BFP m_ ðj  j33 Þ I_d;D ¼ m_ 15a ðj15a  j23 Þ  m_ 20 ðj22  j20 Þ (60)

hII;BFP ¼ 1  ¼ 33 33a (57)
_
W BFP W _ BFP
where the rate of exergy destruction in the LPH-1is I_d;LPH1
The second law efficiency for the LPH-1 can be expressed as:

2.2.9. The exergy balance for the deaerator is I_d;LPH1

hII;LPH1 ¼ 1  (61)
m_ 15a ðj15a  j23 Þ
I_d;D ¼ T0 S_gen ¼ m_ 9a j9a þ m_ 30 j30 þ m_ 35 j35  m_ 33a j33a (58)

where the rate of exergy destruction in the deaerator isI_d;D 2.2.11. The exergy balance for the HPH-8 is
The second law efficiency for the deaerator can be expressed as:

I_d;HPH8 ¼ m_ 3a ðj3a  j38 Þ  m_ 37 ðj39  j37 Þ (62)

I_d;D
hII;D ¼1 (59)
m_ 9a j9a þ m_ 30 j30 þ m_ 35 j35 where the rate of exergy destruction in the HPH-8isI_d;HPH8
56 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63

Table 4
Results of energetic analysis of 660 MWe power plant at unit load of 660 MWe, 528 MWe and 396 MWe under constant pressure operation.

Component Energetic power input Energetic power output, Energetic power loss Energetic efficiency

MW MW MW %

100% 80% of 60% of 100% of 80% of 60% of 100% of NCR 80% of 60% of 100% of 80% of 60% of
of NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR

Combustion 1693 1367 1050 1693 1367 1050 0 0 0 100 100 100
Heat transfer 1693 1367 1050 1461 1185 912.2 232.0 182.0 137.8 86.30 86.69 86.88
Boiler 1693 1367 1050 1461 1185 912.2 232.0 182.0 137.8 86.30 86.69 86.88
HPT 206.1 173.7 130.9 206.1 173.7 130.9 0 0 0 100 100 100
IPT 292.7 232.6 178.5 292.7 232.6 178.5 0 0 0 100 100 100
LPT-1 85.26 65.38 47.12 85.26 65.38 47.12 0 0 0 100 100 100
LPT-2 85.26 65.38 47.12 85.26 65.38 47.12 0 0 0 100 100 100
Turbinea 669.3 537.0 403.6 669.3 537.0 403.6 0 0 0 100 100 100
Cond-1 395.5 325.8 260.0 35.61 28.56 22.23 96.23 86.29 79.60 73.26 70.96 66.52
Cond-2 395.5 325.8 260.0 35.61 28.56 22.23 96.23 86.29 79.60 73.26 70.96 66.52
CEP 2.200 1.760 1.320 1.811 1.322 0.948 0.389 0.438 0.372 82.32 75.11 71.82
GSC 3.603 3.561 2.344 2.358 2.234 2.257 1.245 1.327 0.087 65.45 62.74 96.29
LPH-1 21.63 11.63 4.207 21.59 11.62 4.183 0.040 0.010 0.024 99.82 99.91 99.43
LPH-2 31.77 24.11 17.44 31.73 23.89 17.31 0.040 0.220 0.130 99.87 99.09 99.25
LPH-3 83.50 63.84 46.86 83.26 63.49 46.79 0.240 0.350 0.070 99.71 99.45 99.85
LPH-4 56.21 42.66 31.19 56.05 42.48 31.17 0.160 0.180 0.020 99.72 99.58 99.94
Drip pump 0.250 0.175 0.110 0.209 0.130 0.070 0.040 0.050 0.035 83.56 72.23 67.43
Deaerator 448.3 327.4 230.9 440.5 322.9 227.4 7.800 4.500 3.500 98.26 98.63 98.48
BFP 21.91 15.92 11.92 21.71 15.73 11.72 0.200 0.190 0.200 99.09 98.81 98.32
DSH 13.15 10.02 7.216 13.13 10.02 7.155 0.020 0 0.061 99.85 100.0 99.15
HPH-6 58.86 42.79 29.68 58.82 42.45 29.61 0.040 0.340 0.070 99.93 99.21 99.76
HPH-7 94.63 68.90 48.44 94.45 68.41 48.43 0.180 0.490 0.010 99.81 99.29 99.98
HPH-8 72.02 49.03 33.41 71.98 48.86 33.34 0.040 0.170 0.070 99.94 99.65 99.79
Plant (Gross) 1703 1367 1050 669.3 537.1 403.6 1033 829.9 646.4 39.30 39.29 38.44
Plant (Net) 1703 1367 1050 659.9 528.1 396.1 1043 838.9 653.9 38.75 38.63 37.72
a
Expansion in all turbine sections is assumed as isentropic.

The second law efficiency for the HPH-8 can be expressed as: under constant pressure operation. For modelling purpose, boiler is
divided into two zones. One is the combustion zone and second one
I_d;HPH8 is the heat transfer zone. The methodology as explained by Kotas
hII;HPH8 ¼ 1  (63)
m_ 3a ðj3a  j38 Þ [10] has been followed for modelling of boiler.
Fig. 2 shows the variation of energetic efficiency of all major
power plant components at 660 MWe, 528 MWe and 396 MWe unit
load under constant pressure operation.
3. Energetic and exergetic analysis of the plant under The energetic efficiencies of combustion zone of the boiler at
constant pressure operation unit load of 660 MWe, 528 MWe and 396 MWe under constant
pressure operation are 100% thru out the load range. So it can be
Initially, energetic and exergetic analysis have been performed concluded that there is no energy loss during the combustion
under constant pressure operation at 660 MWe, 528 MWe and process.
396 MWe unit load. The streams data corresponding to 660 MWe, The energetic efficiencies of heat transfer zone of the boiler at
528 MWe and 396 MWe load under constant pressure operation 660 MW, 528 MW and 396 MW load under constant pressure
are shown in Table 3. operation are 86.30%, 86.69% and 86.88% respectively. It shows that
Table 4 shows the result of energetic analysis of 660 MWe su- there is a significant energy loss during the heat exchange between
percritical power plant at 660 MWe, 528 MWe and 396 MWe load flue gasses and working fluid receiving heat.

120.00

100.00
660 MWe
Energy efficiency, (%)

80.00
528 MWe
396 MW
60.00

40.00

20.00

0.00

Fig. 2. Energetic efficiency of major power plant components at unit load of 660 MWe, 528 MWe and 396 MWe, under constant pressure operation.
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 57

Table 5
Results of exergetic analysis of 660 MWe power plant at an unit load of 660 MWe, 528 MWe and 396 MWe under constant pressure operation.

Component Exergetic power input Exergetic power output, Rate of exergy destruction Exergetic efficiency

MW MW MW %

100% of 80% of 60% of 100% of 80% of 60% of 100% of 80% of 60% of 100% of 80% of 60% of
NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR

Combustion 1850 1498 1150 1193 965.4 741.3 657 532.6 408.7 64.49 64.45 64.46
Heat transfer 1193 965.4 741.3 744.2 603.8 471.3 448.8 361.6 270.0 62.38 62.54 63.58
Boiler 1850 1498 1150 744.2 603.8 471.3 1105 894.2 678.7 40.23 40.31 40.98
HPT 221.6 190.9 154.3 206.1 173.7 130.9 15.50 17.20 23.40 93.01 90.99 84.83
IPT 307.8 244.4 187.7 292.7 232.6 178.5 15.10 11.80 9.200 95.09 95.17 95.10
LPT-1 94.54 72.49 52.78 85.26 65.38 47.12 9.280 7.110 5.660 90.18 90.19 89.28
LPT-2 94.54 72.49 52.78 85.26 65.38 47.12 9.280 7.110 5.660 90.18 90.19 89.28
Turbine 718.4 580.2 447.5 669.3 537.0 403.6 49.16 43.22 43.92 93.16 92.55 90.19
Cond-1 24.28 20.03 16.02 17.63 14.10 10.58 6.653 5.931 5.448 72.60 70.39 66.00
Cond-2 24.28 20.03 16.02 17.63 14.10 10.58 6.653 5.931 5.448 72.60 70.39 66.00
CEP 2.200 1.760 1.320 1.582 1.245 0.906 0.618 0.515 0.413 71.91 70.74 68.70
GSC 0.748 0.735 0.439 0.152 0.152 0.158 0.596 0.583 0.280 20.32 20.63 36.13
LPH-1 2.572 1.265 0.405 1.690 0.794 0.179 0.882 0.471 0.225 65.71 62.74 44.27
LPH-2 5.446 3.823 2.515 4.389 3.003 1.942 1.057 0.820 0.573 80.59 78.55 77.22
LPH-3 22.12 16.19 11.25 17.75 12.71 8.684 4.370 3.480 2.566 80.24 78.51 77.19
LPH-4 18.04 13.22 9.229 15.93 11.52 7.990 2.110 1.700 1.239 88.30 87.14 86.57
Drip pump 0.250 0.175 0.110 0.197 0.142 0.090 0.055 0.032 0.019 78.60 81.37 81.99
Deaerator 80.47 54.44 35.80 74.15 51.28 33.49 6.320 3.160 2.310 92.15 94.20 93.55
BFP 22.82 15.92 11.92 20.69 14.34 10.64 2.130 1.580 1.280 90.67 90.08 89.26
DSH 6.554 5.011 3.572 6.247 4.691 3.223 0.307 0.320 0.349 95.32 93.61 90.23
HPH-6 24.01 16.43 10.86 22.16 15.31 10.10 1.850 1.120 0.760 92.29 93.18 93.00
HPH-7 46.35 29.27 19.74 43.00 27.00 18.08 3.350 2.270 1.660 92.77 92.24 91.59
HPH-8 34.66 22.11 14.49 32.97 20.90 13.53 1.690 1.210 0.960 95.12 94.53 93.37
Plant (Gross) 1850 1498 1150 669.3 537.0 403.6 1180 960.9 746.3 36.18 35.85 35.10
Plant (Net) 1850 1498 1150 660 528.1 396.1 1190 969.9 753.9 35.68 35.25 34.44

Table 5 shows the results of exergetic analysis of 660 MWe su- The rate of exergy destruction of overall turbine at a unit load of
percritical power plant at unit load of 660 MWe, 528 MWe and 660 MWe, 528 MWe and 396 MWe, under constant pressure
396 MWe, under constant pressure operation. operation is 42.3 MW, 29 MW and 23.2 MW respectively. Also the
The rate of exergy destruction/Exergetic power loss for the entire result shows that the turbine is the second major component
boiler (including combustion and heat transfer zones) at a unit load having maximum rate of exergy destruction than any other
of 660 MWe, 528 MWe and 396 MWe, under constant pressure component in a power plant after the boiler. The exergetic effi-
operation is 1105.8 MW, 894.2 MW and 678.7 MW respectively. The ciency of the overall boiler at unit load of 660 MWe, 528 MWe and
result clearly shows that the boiler has the maximum exergy 396 MWe, under constant pressure operation is 40.23%, 40.31% and
destruction rate than any other component in the power plant. 40.88% respectively.
The net turbine power output is obtained by deducting me- It shows that the exergetic efficiency of the boiler almost
chanical losses, generator losses and auxiliary power consumption remains the same when unit load is reduced from design (full)
from gross turbine power output. load.
The variation in the rate of exergy destruction for major power Similarly, the exergetic efficiency of the overall turbine at a unit
plant components at unit load of 660 MWe, 528 MWe and load of 660 MWe, 528 MWe and 396 MWe under constant pressure
396 MWe, under constant pressure operation is shown in Fig. 3. operation is 93.16%, 92.55% and 90.19% respectively indicating that

Fig. 3. Rate of exergy destruction of various power plant components at unit load of 660 MWe, 528 MWe and 396 MWe, under constant pressure operation.
 100.00
90.00

%
80.00 660 MW CP
528 MW CP

Exerge c efficiency
70.00
60.00 396 MW CP
50.00
40.00
30.00
20.00
10.00
0.00

Fig. 4. Exergetic efficiency of all major power plant components at unit load of 660 MWe, 528 MWe and 396 MWe under constant pressure operation.

Table 6
Flow stream data of 660 MWe supercritical power plant at a unit load of 660 MWe, 528 MWe and 396 MWe under pure sliding pressure operation.

Stream Id Mass flow rate, kg/sec Temperature, K Pressure, bar Fluid

100% 80% 60% 100% 80% 60% 100% 80% 60% 100% 80% 60%

1B 563.3 439.8 325.6 813.15 813.15 813.15 242.2 196.3 151.4 Steam Steam Steam
1 563.3 439.8 325.6 810.15 810.15 810.15 229.2 183.0 138.1 Steam Steam Steam
2 563.3 439.8 325.6 810.15 810.20 810.20 229.2 183.0 138.1 Steam Steam Steam
3 41.56 29.45 19.36 633.25 636.70 640.70 71.52 57.36 43.58 Steam Steam Steam
3a 41.56 29.45 19.36 630.15 634.20 638.80 67.94 54.49 41.40 Steam Steam Steam
4 48.83 34.37 22.59 578.25 581.40 585.40 47.17 37.76 28.65 Steam Steam Steam
4a 48.83 34.37 22.59 575.25 578.90 583.40 44.82 35.87 27.21 Steam Steam Steam
5 467.8 371.9 280.6 578.25 581.40 585.40 47.17 37.76 28.65 Steam Steam Steam
6 467.8 371.9 280.6 838.15 838.20 838.20 42.45 33.98 25.78 Steam Steam Steam
7 22.21 17.40 12.53 743.75 745.90 747.70 22.48 18.18 13.92 Steam Steam Steam
7i 22.21 17.40 12.53 743.05 745.40 747.30 21.35 17.28 13.22 Steam Steam Steam
7a 22.21 17.40 12.53 488.85 478.30 465.60 21.35 17.28 13.22 Steam Steam Steam
8 26.22 16.75 10.58 742.25 744.70 746.70 19.78 16.00 12.25 Steam Steam Steam
9 14.53 10.93 7.778 655.25 657.90 660.20 12.13 9.846 7.561 Steam Steam Steam
9a 16.20 12.23 8.747 648.45 652.50 656.10 11.16 9.052 6.953 Steam Steam Steam
10 20.94 15.73 11.06 573.25 576.20 578.90 6.472 5.276 4.070 Steam Steam Steam
10a 22.73 17.13 12.11 575.65 580.40 584.90 6.149 5.011 3.864 Steam Steam Steam
11 31.68 24.16 17.27 487.85 491.00 494.00 3.079 2.520 1.952 Steam Steam Steam
11a 31.68 24.16 17.27 487.55 490.80 493.80 2.922 2.393 1.853 Steam Steam Steam
12 352.2 287.0 221.3 487.85 491.00 494.00 3.079 2.520 1.952 Steam Steam Steam
13 176.4 143.7 110.8 487.75 490.90 493.90 3.030 2.481 1.922 Steam Steam Steam
14 13.20 10.01 7.036 360.99 355.90 354.90 0.6463 0.529 0.413 Steam Steam Steam
14a 13.25 10.01 7.036 359.66 354.60 354.70 0.6139 0.502 0.392 Steam Steam Steam
15 9.669 5.356 1.867 340.05 336.00 331.20 0.2726 0.228 0.182 Steam Steam Steam
15a 9.669 5.356 1.867 338.89 334.80 330.20 0.2589 0.216 0.174 Steam Steam Steam
16 164.9 136.0 106.4 319.51 319.50 319.50 0.103 0.103 0.103 Steam Steam Steam
17 1.322 1.306 1.289 535.95 539.10 541.20 0.9512 0.951 0.951 Steam Steam Steam
18 183.4 147.7 113.2 319.51 319.50 319.50 0.103 0.103 0.103 Water Water Water
19 366.9 295.2 226.2 320.05 320.20 320.20 31.17 26.20 21.97 Water Water Water
20 366.9 295.1 225.2 321.61 321.90 322.50 30.68 25.89 21.77 Water Water Water
21 0.891 0.872 0.856 371.36 371.40 371.40 0.9512 0.951 0.951 Water Water Water
22 366.9 295.1 225.2 335.92 331.90 327.20 21.82 17.73 14.15 Water Water Water
23 9.669 5.356 1.867 338.92 334.90 330.20 0.2589 0.216 0.174 Water Water Water
24 366.9 295.1 225.2 357.20 352.10 346.00 21.34 17.42 13.96 Water Water Water
25 434.5 346.4 261.6 357.20 352.10 346.00 21.34 17.42 13.96 Water Water Water
26a 67.66 51.29 36.41 359.66 354.60 348.50 0.6139 0.502 0.392 Water Water Water
26 67.66 51.29 36.41 360.02 354.90 348.70 21.34 17.42 13.96 Water Water Water
27 54.41 41.28 29.38 367.20 362.10 356.00 2.922 2.393 1.853 Water Water Water
28 434.5 346.4 261.6 402.85 396.20 388.10 18.85 15.84 13.06 Water Water Water
29 22.73 17.13 12.11 412.85 406.20 398.10 6.149 5.011 3.864 Water Water Water
30 434.5 346.4 261.6 433.15 425.40 415.90 16.36 14.25 12.15 Water Water Water
33a 563.3 439.9 325.6 e e e 11.16 9.052 6.953 Water Water Water
33 563.3 439.9 325.6 463.05 452.60 440.70 291.9 220.6 168.1 Water Water Water
34 563.3 439.9 325.6 486.85 476.30 463.60 291.9 220.6 168.1 Water Water Water
35 112.6 81.21 54.48 488.85 478.30 465.60 21.35 17.28 13.22 Water Water Water
36 90.39 63.82 41.95 530.35 517.20 501.70 44.82 35.87 27.21 Water Water Water
37 563.3 439.9 325.6 528.35 515.20 499.70 286.6 214.7 161.4 Water Water Water
38 41.56 29.45 19.36 556.95 542.60 525.60 67.94 54.49 41.4 Water Water Water
39 563.3 439.9 325.6 557.45 543.40 526.70 281.5 208.9 154.9 Water Water Water
40 55.64 43.44 32.17 557.45 543.40 526.70 281.5 208.9 154.9 Water Water Water
41 55.64 43.44 32.17 598.15 584.20 563.20 281.5 208.9 154.9 Water Water Water
42 563.3 439.9 325.6 560.35 546.60 530.10 281.5 208.9 154.9 Water Water Water
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 59

Table 7
Results of energetic analysis of 660 MWe power plant at unit load of 660 MWe, 528 MWe and 396 MWe under pure sliding pressure operation.

Component Energetic power input Energetic power output, Energetic power loss Energetic efficiency

MW MW MW %

100% of 80% of 60% of 100% of 80% of 60% of 100% of 80% of 60% of NCR 100% of 80% of 60% of
NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR

Combustion 1695 1363 1046 1695 1363 1046 0 0 0 100 100 100
Heat transfer 1695 1363 1046 1462 1182 908.8 233.0 181.4 137.2 86.25 86.69 86.88
Boiler 1695 1363 1046 1462 1182 908.8 233.0 181.4 137.2 86.25 86.69 86.88
HPT 204.8 166.8 128.2 204.8 166.8 128.2 0 0 0 100 100 100
IPT 293.4 235.4 178.8 293.4 235.4 178.8 0 0 0 100 100 100
LPT-1 85.66 66.71 48.01 85.66 66.71 48.01 0 0 0 100 100 100
LPT-2 85.66 66.71 48.01 85.66 66.71 48.01 0 0 0 100 100 100
Turbinea 669.5 535.6 403.0 669.5 535.6 403.0 0 0 0 100 100 100
Cond-1 396.9 331.1 263.4 35.61 28.67 21.98 97.68 91.56 83.21 72.96 69.73 65.53
Cond-2 396.9 331.1 263.4 35.61 28.67 21.98 97.68 91.56 83.21 72.96 69.73 65.53
CEP 2.200 1.760 1.320 1.816 1.332 0.937 0.384 0.428 0.382 82.55 75.68 71.02
GSC 2.420 3.565 3.527 2.361 2.243 2.092 0.059 1.322 1.435 97.56 62.92 59.31
LPH-1 21.67 12.14 4.288 21.64 12.12 4.271 0.030 0.02 0.017 99.86 99.84 99.60
LPH-2 31.87 24.32 17.32 31.63 24.27 17.25 0.240 0.05 0.070 99.25 99.79 99.60
LPH-3 83.66 64.35 46.45 83.22 64.33 46.29 0.440 0.02 0.160 99.47 99.97 99.66
LPH-4 56.35 43.14 31.07 55.93 43.12 30.96 0.420 0.02 0.110 99.25 99.95 99.65
Drip pump 0.250 0.175 0.110 0.215 0.129 0.070 0.035 0.045 0.039 85.96 74.23 63.84
Deaerator 449.3 332.9 230.1 441.7 327.2 226.7 7.600 5.700 3.400 98.31 98.29 98.52
BFP 20.99 12.39 7.038 20.77 12.26 6.875 0.220 0.130 0.163 98.95 98.95 97.68
DSH 13.33 10.70 7.916 13.23 10.65 7.903 0.100 0.050 0.013 99.25 99.53 99.84
HPH-6 59.45 44.94 31.59 59.13 44.80 31.46 0.320 0.140 0.13 99.46 99.69 99.59
HPH-7 95.02 70.17 48.41 94.69 69.76 48.31 0.330 0.410 0.10 99.65 99.42 99.79
HPH-8 74.28 56.09 39.30 73.91 55.58 39.00 0.370 0.510 0.30 99.50 99.09 99.24
Plant (Gross) 1695 1363 1046 669.5 535.5 403.1 1025 827.5 642.9 39.50 39.29 38.54
Plant (Net) 1695 1363 1046 660 528.1 396.0 1035 834.9 650 38.94 38.75 37.86
a
Expansion in all turbine sections is assumed as isentropic.

the exergetic efficiency has a declining trend with decreasing unit The exergetic efficiencies of the overall plant (net) at a unit load
load. This is because of continuous increase in throttling losses with of 660 MWe, 528 MWe and 396 MWe under constant pressure
decreasing load. operation are 35.68%, 35.25% and 34.44% respectively. The net
Fig. 4 shows the variation in the exergetic efficiency of all major turbine power output is obtained by deducting mechanical losses,
power plant components at a unit load of 660 MWe, 528 MWe and generator losses and auxiliary power consumption from gross
396 MWe under constant pressure operation. The exergetic effi- turbine power output.
ciencies of combustion zone of the boiler at unit load of 660 MWe,
528 MWe and 396 MWe under constant pressure operation are 4. Energetic and exergetic analysis of plant under pure sliding
64.49%, 64.45% and 64.46% respectively. pressure operation
The exergetic efficiencies of heat transfer zone of the boiler
at unit load of 660 MWe, 528 MWe and 396 MWe under The stream data corresponding to a unit load of 660 MWe,
constant pressure operation are 62.38%, 62.54% and 63.58% 528 MWe and 396 MWe under pure sliding pressure operation is
respectively. shown in Table 6.

120.00

100.00
Energe c Efficiency %

80.00
660 MW SP

60.00 528 MW SP
396 MW SP
40.00

20.00

0.00

Fig. 5. Energetic efficiency of all major power plant components at a unit load of 660 MWe, 528 MWe and 396 MWe under pure sliding pressure operation.
60 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63

Table 8
Results of exergetic analysis of 660 MWe power plant at an unit load of 660 MWe, 528 MWe and 396 MWe under pure sliding pressure operation.

Component Exergetic power input Exergetic power output, Rate of exergy destruction Exergetic efficiency

MW MW MW %

100% of 80% of 60% of 100% of 80% of 60% of 100% of 80% of 60% of 100% of 80% of 60% of
NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR NCR

Combustion 1856 1493 1146 1196 962.4 738.6 660 530.6 407 64.44 64.46 64.4
Heat Transfer 1196 962.4 738.6 745.5 597.1 452.8 450.5 365.3 286 62.33 62.04 61.3
Boiler 1856 1493 1146 745.5 597.1 452.8 1110 895.9 693 40.17 39.99 39.5
HPT 218.7 178 137.1 204.8 166.8 128.7 13.9 11.2 8.4 93.64 93.71 93.8
IPT 308.5 247.4 187.9 293.4 235.4 178.8 15.1 12 9.1 95.11 95.15 95.1
LPT-1 94.99 74.05 53.73 85.66 66.71 48.01 9.33 7.34 5.72 90.18 90.09 89.3
LPT-2 94.99 74.05 53.73 85.66 66.71 48.01 9.33 7.34 5.72 90.18 90.09 89.3
Turbine 717.1 573.5 432.4 669.5 535.6 403.5 47.66 37.88 28.94 93.35 93.39 93.3
Cond-1 24.54 20.36 16.23 17.63 14.1 10.58 6.918 6.258 5.65 71.81 69.26 65.1
Cond-2 24.54 20.36 16.23 17.63 14.1 10.58 6.918 6.258 5.65 71.81 69.26 65.1
CEP 2.2 1.76 1.32 1.579 1.244 0.911 0.621 0.516 0.408 71.77 70.68 69.0
GSC 0.454 0.740 0.733 0.150 0.151 0.160 0.304 0.589 0.573 33.03 20.45 21.8
LPH-1 2.608 1.33 0.415 1.712 0.841 0.191 0.896 0.488 0.224 65.64 63.30 46.0
LPH-2 5.471 3.882 2.514 4.368 3.081 1.953 1.103 0.801 0.561 79.84 79.37 77.6
LPH-3 22.23 16.39 11.18 17.79 12.97 8.626 4.44 3.42 2.554 80.03 79.13 77.1
LPH-4 18.17 13.44 9.255 15.92 11.76 7.968 2.25 1.68 1.287 87.62 87.50 86.0
Drip pump 0.25 0.175 0.11 0.192 0.140 0.11 0.058 0.034 0.016 76.76 80.51 84.8
Deaerator 79.52 55.78 35.92 74.7 52.21 33.5 4.82 3.57 2.42 93.94 93.60 93.2
BFP 20.99 12.39 7.038 19.06 11.15 6.302 1.93 1.24 0.736 90.81 89.99 89.5
DSH 6.726 5.357 3.926 6.373 5.011 3.6 0.353 0.346 0.326 94.75 93.54 91.7
HPH-6 23.78 17.29 11.57 22.00 16.05 10.72 1.78 1.24 0.85 92.51 92.83 92.6
HPH-7 41.92 30.01 19.91 38.64 27.46 18.16 3.28 2.55 1.75 92.18 91.50 91.2
HPH-8 34.85 25.61 17.32 32.77 23.85 16.05 2.08 1.76 1.27 94.03 93.13 92.6
Plant (Gross) 1856 1493 1146 669.5 535.5 403.6 1186 957.5 742.4 36.07 35.87 35.2
Plant (Net) 1856 1493 1146 660 528.1 396.1 1196 964.9 749.9 35.56 35.37 34.5

Table 7 shows the results of energetic analysis of a 660 MWe The net turbine power output is obtained by deducting me-
supercritical power plant at a unit load of 660 MWe, 528 MWe and chanical losses, generator losses and auxiliary power consumption
396 MWe under pure sliding pressure operation. Fig. 5 shows the from gross turbine power output.
variation in the energetic efficiency of all major power plant com- Table 8 shows the results of exergetic analysis of 660 MWe
ponents at a unit load of 660 MWe, 528 MWe and 396 MWe under supercritical power plant at a unit load of 660 MWe,
pure sliding pressure operation. The energetic efficiencies of com- 528 MWe and 396 MWe under pure sliding pressure operation.
bustion zone of the boiler at a unit load of 660 MWe, 528 MWe and The rate of exergy destruction/Exergetic power loss for the entire
396 MWe under pure sliding pressure operation is 100% boiler (including combustion and heat transfer zones) at a unit
throughout the load range. So it can be concluded that there is no load of 660 MWe, 528 MWe and 396 MWe under pure sliding
energy loss during the combustion process. The energy losses in the pressure operation is 1110.5 MW, 895.9 MW and 693.2 MW
overall boiler at a unit load of 660 MWe, 528 MWe and 396 MWe respectively.
under pure sliding pressure operation are 233 MW/181.4 MW/ The results clearly show that the boiler has the maximum
137.2 MW respectively. The entire energy loss in the boiler is exergy destruction rate than any other component in the power
attributed to the heat transfer process taking place between the plant. The variation in the rate of exergy destruction for major
flue gasses and working fluid receiving heat. power plant components at a unit load of 660 MWe, 528 MWe and

700.0
660.0
650.0
600.0
530.6
Rate of Exergy Destruc on (MW)

550.0
500.0
450.5
450.0
407.4
400.0 365.3
350.0 660 MW SP
300.0 285.8 528 MW SP
250.0 396 MW SP
200.0
150.0
100.0
47.7 37.9
50.0 28.9
13.8 12.5 11.3 16.2 12.3 8.8
1.9 1.2 0.7
0.0
Combus on Heat Transfer Overall Condensers BFP Heaters
Turbine

Fig. 6. Rate of exergy destruction of various power plant components at a unit load of 660 MWe, 528 MWe and 396 MWe under pure sliding pressure operation.
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 61

100.00
90.00

Exerge c Efficiency %
80.00
70.00
60.00
50.00
40.00
30.00 660 MW CP
20.00 528 MW CP
10.00 396 MW CP
0.00

Fig. 7. Exergetic efficiency of all major power plant components at a unit load of 660 MWe, 528 MWe and 396 MWe under pure sliding pressure operation.

396 MWe under pure sliding pressure operation is shown in Fig. 6. 528 MWe and 396 MWe under pure sliding pressure operation is
The rate of exergy destruction of overall turbine at 100%, 80% and 40.17%, 39.99% and 39.51% respectively as shown in Fig. 7.
60% of NCR conditions is 47.66 MW, 37.88 MW and 28.94 MW It shows that the exergetic efficiency of the boiler decreases
respectively. The result shows that the turbine is the second major when unit load is reduced from design (full) load.
component having the maximum rate of exergy destruction than Similarly, the exergetic efficiency of the overall turbine at a unit
any other component in a power plant after the boiler. The exer- load of 660 MWe, 528 MWe and 396 MWe under pure sliding
getic efficiency of the overall boiler at a unit load of 660 MWe, pressure operation is 93.35%, 93.39% and 93.31% respectively

60
Rate of Exergy Destruc on in the Turbine,

49.16
50 47.66
43.22 43.92

40 37.88
MW

28.94 C.P
30
S.P
20

10

0
660 MW 528 MW 396 MW

Fig. 8. Comparison of rate of exergy destruction for Turbine at a unit load of 660 MWe, 528 MWe and 396 MWe between constant and pure sliding pressure operation.

1200
1105.8 1110.5
Rate of exergy destruc on in the boiler, MW

1000
894.2 895.9

800
678.7 693.2

600 CP
SP

400

200

0
660 MW 528 MW 396 MW

Fig. 9. Comparison of rate of exergy destruction for boiler at a unit load of 660 MWe, 528 MWe and 396 MWe between constant pressure and pure sliding pressure operation.
62 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63

2.5

Rate of Exergy Destruc on in BFP, MW

2.13
1.93
2
1.58
1.5
1.24 1.28 CP
SP
1
0.736

0.5

0
660 MW 528 MW 396 MW

Fig. 10. Comparison of rate of exergy destruction for the BFP at a unit load of 660 MWe, 528 MWe and 396 MWe between constant and pure sliding pressure operation.

21.91
20.97
BFP Power Input, MW

15.92

12.39 CP
11.92
SP

7.038

660 MW 528 MW 396 MW

Fig. 11. Comparison of BFP power input at 660 MWe, 528 MWe and 396 MWe load conditions between constant and pure sliding pressure operation.

indicating that the exergetic efficiency almost remains the same rated load if the unit runs in sliding pressure mode compared to
irrespective of the unit load. constant pressure mode operation. The BFP power input at
660 MWe, 528 MWe and 396 MWe load conditions under constant
and pure sliding pressure operation is shown in Fig. 11.
5. Comparison of results of energetic and exergetic analysis
between constant pressure and pure sliding pressure
6. Conclusions
operation
Undoubtedly, sliding pressure operation of the unit at part
Compared to constant pressure operation, in pure sliding pres-
loads has several benefits. These benefits include significant
sure operation, the exergy destruction associated with the throt-
reduction in the BFP power consumption, reduction in exergy
tling of turbine control valves can be avoided leading to reduced
destruction associated with control valve throttling leading to
exergy destruction of the turbine.
improved exergetic efficiency of all turbine sections and exergy
This is evident from the significant reduction in the rate of
destruction in BFP. Hence sliding pressure operation is suitable
exergy destruction of turbine as shown in Fig. 8.
for once through units and thus a better way of operating at part
The rate of exergy destruction of boiler at 660 MWe, 528 MWe
load conditions.
and 396 MWe load conditions under constant pressure and pure
sliding pressure operation is shown in Fig. 9.
It is observed that no significant reduction in exergy destruction Acknowledgements
took place because during sliding pressure operation, both the
superheater outlet and economiser inlet pressure have reduced. The authors are greatly acknowledging the valuable support
The rate of exergy destruction of BFP at a unit load of 660 MWe, provided by NTPC Ltd., India.
528 MWe and 396 MWe under constant and pure sliding pressure
operation is shown in Fig. 10. Nomenclature
It is observed that a huge reduction in exergy destruction has
taken place during sliding pressure operation. As the throttle B boiler
pressure required to be maintained in sliding pressure operation HPT high pressure turbine
for the same unit load is much lower, the rate of exergy IPT intermediate pressure turbine
destruction in the BFP and the BFP power input reduces LPT low pressure turbine
drastically. COND condenser
The BFP power input reduces by 9.39%, 21.52% and 42.5% CEP condensate extraction pump
respectively for a 660 MWe supercritical unit at 100%, 80% and 60% GSC gland steam cooler
 S. Adibhatla, S.C. Kaushik / Applied Thermal Engineering 73 (2014) 49e63 63

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