INTERNATIONAL JOURNAL OF ENERGY RESEARCH
Int. J. Energy Res. 2011; 35:909–922
Published online 27 July 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/er.1748
Evaluation of solar aided thermal power generationwith various power plants
Qin Yan1, Eric Hu2,�,y, Yongping Yang1,z,y and Rongrong Zhai1
1School of Energy Power and Mechanical Engineering, Beijing Key Laboratory of Energy Safety and Clean Utilization, North China
Electric Power University, Beijing 102206, People’s Republic of China2School of Mechanical Engineering, The University of Adelaide, Adelaide SA5005, Australia
SUMMARY
Solar aided power generation (SAPG) is an efficient way to make use of low or medium temperature solar heat forpower generation purposes. The so-called SAPG is actually ‘piggy back’ solar energy on the conventional fuel firedpower plant. Therefore, its solar-to-electricity efficiency depends on the power plant it is associated with. In thepaper, the developed SAPG model has been used to study the energy and economic benefits of the SAPG with 200and 300MW typical, 600MW subcritical, 600MW supercritical, and 600 and 1000MW ultra-supercritical fuelpower units separately. The solar heat in the temperature range from 260 to 901C is integrated with above-mentioned power units to replace the extraction steam (to preheat the feedwater) in power boosting and fuel-savingoperating modes. The results indicate that the benefits of SAPG are different for different steam extracted positionsand different power plants. Generally, the larger the power plant, the higher the solar benefit if the same level solaris integrated. Copyright r 2010 John Wiley & Sons, Ltd.
KEY WORDS
solar aided thermal power generation; solar energy to electricity efficiency; coal consumption rate
Correspondence
*Eric Hu, School of Mechanical Engineering, The University of Adelaide, Adelaide SA5005, Australia.yE-mail: [email protected] Yang, School of Energy Power and Mechanical Engineering, Beijing Key Laboratory of Energy Safety and Clean Utilization,
North China Electric Power University, Beijing 102206, People’s Republic of China.yE-mail: [email protected]
Received 3 January 2010; Revised 12 May 2010; Accepted 15 May 2010
1. INTRODUCTION
Solar energy is one of the clean and renewable green
resources, but its intermittent and low intensity nature,
thus low efficiency, constrain its application or increase
the costs significantly [1]. Therefore, the conventional
coal or gas-fired power plants are still dominant way to
generate base load electricity in the world for decades
to come [2,3], despite the pollution, green house gas
emission, and fossil fuel resource reduction draw more
and more critique to the conventional power plants [4].
Although the new designed ultra-supercritical coal-
fired plants have improved efficiencies to nearly
50% [5], they still cannot generate ‘green’ electricity
as solar and wind powers do. The conventional power
industry is under huge pressure with the forthcoming
renewable energy targets and carbon taxes set by
various governments. A real technical revolution is
needed to help the power industry to become cleaner
than before. Solar energy aided power [6] or equipment
[7] have been noticed and done some groping research
works in the whole world.
In this paper, solar thermal energy below 3001C (as
low as 901C) was assumed to be integrated with dif-
ferent capacities coal-fired power plants separately
(200 and 300MW typical, 600MW subcritical,
600MW supercritical and 600 and 1000MW ultra-
supercritical power units). In the integrations, steam
extractions from steam turbines are replaced by the
thermal oil from solar collectors to heat feedwater in
the thermal oil heater in both power boosting and fuel-
saving operating modes. The energy and economic
benefits after integration will be analyzed and dis-
cussed based on the developed models. The model will
Copyright r 2010 John Wiley & Sons, Ltd.
include steam turbine stages model, condenser model,
feedwater heater model, water mixer model, boiler
model, evaluating model and so on.
2. SYSTEM DESCRIPTION
2.1. Coal-fired power plant
Coal-fired power plants have been used for more than
one hundred years. In a typical regenerative and
reheating Rankine steam system, the boiler is com-
posed of furnace, drum, risers, superheaters, feedwater
heaters and economizer [8]. The combustion of coal
takes place in the boiler. The unsaturated feed-water
from condenser enters boiler after going through low-
pressure feedwater heaters and a deaerator, and then
enters high-pressure feedwater heaters. The super-
heated steam from the boiler enters the high-pressure
turbine to expand i.e. generate power, after reheated in
the boiler. The steam expands further through inter-
mediate pressure and lower pressure stages of the
turbine. At the end, the final exhaust steam is
condensed in the condenser. To increase the thermal
efficiency of the cycle, i.e. increasing the average heat
input temperature, parts of the steam is extracted at
the different locations of the turbine to pre-heat the
feedwater in the feedwater heaters. The deaerator is
actually an open type water heater in which steam mix
with the feedwater to preheat the feedwater and
remove the oxygen and other incoagulable gas from
the water. The feedwater heaters are typical shell-and-
tube closed type heaters.
2.2. Solar collector systems
There are two basic types of solar collectors, focusing
and non-focusing. Solar tower, solar dish and para-
bolic trough are three kinds of typical focusing
collectors. Linear parabolic concentrators in parabolic
trough type are used to focus sunlight to the receiver
running along the focal line of the collector. The solar
energy is absorbed by the heat transfer working fluid,
such as heat transfer oil or water/steam [9]. The
parabolic trough collector is typical medium tempera-
ture type, which can generate temperature up to 5001C.
Solar tower and solar dish are point focusing types;
they can generate higher temperature solar fluid. The
highest temperatures the solar tower can generate are
nearly 10001C [10]. If the focusing collectors are used
in a typical solar alone power station, the peak
thermal-electricity efficiency is about 20% [10,11].
A typical commercial medium temperature focusing
parabolic trough collector system is LS-2 in U.S.,
manufactured by LUZ Company. The collector system
has been used for the generation for the past two
decades. Table I lists the main parameters of the
system.
The vacuum tube and flat plate are non-focusing
type of collectors. Compared with focusing type col-
lectors, their investment costs are lower and almost
maintenance free, as the sun tracking system is not
required. However, a typical vacuum tube collector
with the selective coating can generate heat at maximal
temperature about 2001C, and a flat plat solar collector
can generate to 1001C [14].
2.3. Solar aided thermal power generation(SAPG)
Almost all combustion-based steam power plants are
running regenerative Rankine cycle thermodynami-
cally, in which part of the steam is bled-off/extracted
from the turbine to be used to pre-heat the boiler
feedwater from about 401C (from the condenser) to
3001C (to the boiler) [15]. By doing this, the overall
cycle thermal efficiency is increased, but the power
generated per unit steam passing through boiler is
reduced. In the SAPG, the bled-off steam is partly or
totally replaced by solar heat carried by heat transfer
fluid to preheat the feedwater, as shown in Figure 1.
Therefore, the saved bled-off steam continues to
expand in the turbine, to generate power. In Figure 1,
if the solar input cannot satisfy the demand to heat all
the distributed feedwater in cloudy days, the valves 1
and 2 can be adjusted to distribute part of the
feedwater to be heat by solar thermal oil. The ratio
of water flow through steam heater or thermal oil
heater is decided by sun radiation condition and
feedwater flow rate. In the nighttime, the valve 1 will
be opened and valve 2 closed, then the extracted steam
can heat the feedwater in original heater again. The
operating mode is back to conventional working
condition without integration.
Therefore, the advantages of the SAPG include:
(1) various temperature levels of solar heat can be in-
tegrated into various stages of the feedwater heaters;
(2) the solar to electricity conversion rate, i.e. efficiency
that is the power generated by the saved bled-off steam
to the solar heat input, is no longer limited by the
temperature of solar fluid as the solar does not directly
generate power; (3) the solar collectors using thermal
oil as the heat carrier can be used and (4) the benefit to
power station can come from either additional power
Table I. The system main parameters of the LS-2 system [12,13].
Name Parameters Value Unit
Solar collectors Length of single collector 47.1 m
Width of single collector 5 m
Area of single collector 235 m2
Focal length of the collector 1.84 m
Focal ratio of the collector 71 —
Absorber external diameter 70 mm
Envelope external diameter 115 mm
Evaluation of solar aided thermal power generationQ. Yan et al.
Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
910
generation with the same fuel consumption i.e. solar
boosting mode, or fuel and emission reduction while
keeping the same generating capacity i.e. fuel-saving
mode, shown in Figure 2. But in power boosting op-
erating mode, the output power exceeds the rated load
to reduce coal-fired energy consumption rate. In gen-
eral, the maximum safe power output (so-called
T-MCR working condition for a steam turbine) is
much higher than rated load, but the energy con-
sumption rate in the above working condition is also
much higher than in rated working condition. For
example, the maximum safe load for a 600MW unit is
about 645MW or much larger, 200MW unit has about
220MW maximum load.
3. MODELING AND VALIDATION OFCOAL-FIRED POWER SYSTEM
The mathematic simulation model to understand the
efficiencies of SAPG with various coal or gas fired
power plants has been developed and validated by their
designed values. Power units are grouped into sub-
critical, supercritical and ultra-supercritical according
to their designed steam parameters. The critical status
of water is 22.115MPa and 374.151C in thermody-
namics [5]. In a subcritical power plant, the steam
pressure and temperature from the boiler is lower than
the critical condition. If the steam’s parameters are
higher than the critical condition, but less than 25MPa
and 5931C, it is called supercritical. The ultra-super-
critical is defined as pressure higher than 25MPa and
temperature higher than 5931C [15,16]. Increasing
steam parameters to supercritical or ultra-supercritical
can get higher cycle efficiency and lower pollution
emission rate [17].
200 and 300MW subcritical units were the main
generating units in China before 2005. The perfor-
mance parameters of typical subcritical 200, 300
and 600MW, supercritical 600MW and ultra-super-
critical 600 and 1000MW are listed in Table II. The
steam and water flow and thermal system parameters
of a typical 600MW supercritical plant are drawn in
Figure 3. Other units’ descriptions are listed in
Table III.
The serial numbers in Table III are noted in
Figure 3. They are all important parameters to de-
scribe and evaluate a thermal system. The ‘—’ of
200MW unit means the vacant parameter, because the
selected 200MW unit only sets two high-pressure
feedwater heaters.
Steam
Heater
1
2Feedwater
Thermal oil heater
Solar collector
Oilpump
Figure 1. Schematic scheme of solar thermal energy replacing
one of bled-off steams.
0Power boosting mode
Pow
er o
utpu
t
Pow
er o
utpu
t
Fuel saving mode
Fuel
Fuel
Solar
Solar
2412 420(Hours)186 12 (Hours)186
Figure 2. Two operation modes of SAPG.
Evaluation of solar aided thermal power generation Q. Yan et al.
911Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
Table II. The main designed values of the selected units in 100% load.
Parameters Units
200 MW
subcritical
300 MW
subcritical
600 MW
subcritical
600 MW
supercritical
600 MW ultra
supercritical
1000 MW ultra
supercritical
Manufacturer — Beizhong — Hitachi Shangqi Shangqi Hitachi
Capacity MW 201.36 308.404 600 600 600 1000
Main steam parameters MPa 16.18 17.0 17.0 24.2 25.0 25.0
/1C 530 537 538 566 600 600
/1C 530 537 538 566 600 600
Feedwater flow rate t h�1 590.00 935.00 1810.383 1655.897 1598.77 2733.434
Condenser P kPa 5.4 5.5 5.41 4.9 4.9 4.5/5.7
Feedwater temp. 1C 246.13 268.84 271/5 273.8 283.7 294.8
Heat con. rate kJ kWh�1 7985.2 8005.71 7888.31 7517 7408 7354
Steam con. rate kg kWh�1 2.930 3.032 3.017 2.758 2.663 2.734
A C
D
E F G H
G.CHTR1HTR2HTR3HTR4HTR6HTR8
HTR5
273.8
1199.7
205.6
889.4
253.8
1104.5
211.2
903.2
180.2
779.0
137.8
580.4
99.98
419.0
105.5
442.5
86.36
361.6
56.51
236.5
80.80
338.3
50.95
213.2
39.19
164.1
33.63
140.8 99.04
415.0
32.54
136.3
174.9
741.1
To boiler
32.54
2346.9Boiler
HP IP LP LPIP
600.315 MW
B C DGH
301.2
2965.9
566.0
3598.8
--
3185.7
HTR7
185.7
788.5
248.3
1080.4
566.0
3396.0 24.2 MPa 1655.897 t/h
A
B
3.585 MPa
F E
0.919 MPa
5.688
3050.4
101.549
A3.863
2965.9
143.375
B1.747
3375.3
59.844
C0.891
3187.3
77.739
D0.3668
2972.0
81.237
E0.1117
2730.3
40.622
F0.05466
2616.3
60.499
G0.01481
2474.7
33.821
H--
--
1.499
I
I
Temperature C
Enthalpy kJ /kg
Pressure MPa
Enthalpy kJ /kg
Flow t/h
(1)
(2)(3)(4)(5)
(6)
(7)
(8)(9)
(10)
Figure 3. Steam and water flow and thermal system parameters of a 600 MW supercritical unit.
Table III. System parameters of other selected units.
1 2 3 4 5 6 7 8 9 10
Parameters MW 1C 1C 1C 1C 1C 1C 1C 1C 1C
200 MW subcritical 201.36 36.45 77.20 103.92 123.32 143.55 164.61 193.07 — 246.13
300 MW subcritical 308.40 35.69 83.12 103.34 124.52 145.75 169.23 198.31 242.25 268.83
600 MW subcritical 600.00 34.90 77.50 100.00 118.10 157.70 183.50 202.10 246.80 271.50
600 MW ultra-supercritical 600.27 33.67 53.97 74.09 94.89 134.80 171.00 207.80 248.40 283.00
1000 MW ultra-supercritical 1000.00 36.00 84.90 108.10 132.50 154.70 182.30 216.40 258.60 294.80
Evaluation of solar aided thermal power generationQ. Yan et al.
Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
912
As introduced before, an integrated thermal system
model is consisted of steam turbine stages model,
condenser model, feedwater heater model, water mixer
model, boiler model, evaluating model and so on. The
basic descriptions of the submodels are provided below.
3.1. Steam turbine stages model
The ideal process in a steam turbine stages is an
isentropic process in thermodynamical concept, sin 5
sout. Therefore, the ideal outlet steam specific enthalpy
hout can be calculated or found from steam tables when
the Pout and sout are known [18].
The ideal specific enthalpy change in the stages is:
Dh ¼ hin � hout ð1Þ
The real specific enthalpy change is:
Dh0 ¼ estage � Dh ¼ hin � h0out ð2Þ
where estage is the isentropic efficiency of the stages, %.
The real power output is:
Wout ¼ Fin � Dh0 ð3Þ
The real outlet steam enthalpy is:
h0out ¼ hin � Dh0 ð4Þ
The inlet steam flow rate entering next stages is the
difference of inlet flow of this stages and extraction
flow Fex. All the units of above enthalpies are kJ kg�1.
3.2. Condenser model
Condenser is one of the main equipments for maintaining
steam turbine backpressure. Its working performance
affects the units’ characters directly. In theory, the
condenser can be divided to pipe and shell sides,
according to its heat transfer principle. In pipe side,
cooling water is heated by condensed steam. The cooling
effect is decided by water flow rate, pipe structure and so
on. The shell side is consisted of steam section, condensed
water section and non-condensing gas section [19].
(1) Steam mass in shell side
d
dtMs ¼
XFsin �
XFsout ð5Þ
where Fsin is inlet steam mass, kg h�1; Fsout is outlet
steam mass, kg h�1.
(2) Air mass in shell side
d
dtMa ¼
XFain �
XFaout ð6Þ
where Fain is inlet air mass, kg h�1; Faout is outlet air
mass, kg h�1.
(3) Condensed steam mass
The vacuum in condenser is caused by condensed
steam, and its condensing effect also affects con-
denser’s working conditions. The condensed steam
mass is calculated by energy conversation.
Fc ¼as � Au � ðTs � TcÞ
Hs �Hcwð7Þ
where as is the condensing heat transfer efficiency
(W (m21C)�1), Au is the heat transfer area in shell side
(m2), Ts is the average temperature in condenser (1C),
Tc is the temperature of cooling water (1C) Hs is the
average steam enthalpy in condenser (kJ kg�1), Hcw is
the saturated water enthalpy in condenser (kJ kg�1).
(4) Partial steam pressure in shell side
State equation for ideal gas is applied for steam,
Ps � V ¼Ms � Rs � ðTs1273Þ. The partial differential of
the equation is
Ps ¼ P0s1dMsRs � ðTs1273Þ
Vð8Þ
where Ps is partial steam pressure in condenser (MPa),
P0s is the partial steam pressure at previous calculating
time (MPa), Rs is steam gas constant (J (kgK)�1), V is
the condenser’s volume (m3).
(5) Partial air pressure in shell side
As described in steam pressure, the partial air pres-
sure in shell side is
Pa ¼ P0a1dMaRa � ðTa1273Þ
Vð9Þ
where Ma is air mass in condenser (kg h�1), Pa is
partial air pressure in shell side (MPa), P0a is the partial
air pressure at previous calculating time (MPa), Ra is
air gas constant (J (kgK)�1).
(6) Pressure in shell side
The total pressure in shell side is the sum of partial
steam and air pressures.
P ¼ Ps1Pa ð10Þ
(7) Cooling water outlet temperature
According to energy balance in condenser,
McwCwd
dtT11T2
2
� �¼ Qc �DwCwðT2 � T1Þ ð11Þ
where T1 and T2 are cooling water inlet and outlet
temperature (1C), Qc is absorbed heat by cooling water
(kJ), Dw is cooling water mass flow rate (kg h�1), Cw is
cooling water thermal capacity (kJ (kg 1C)�1), Mcw is
the kept cooling water in condenser (kg).
3.3. Feedwater heater model
Feedwater heaters are typical close heaters, the feed-
water is heated by extracted steam from steam turbine.
The heater can be sorted into higher-pressure and
lower-pressure heaters, according to the inlet steam
parameters. The heater consists of steam side and air
side in shell side, and the pipe side is feedwater side.
The main mathematic descriptions are
(1) Average steam enthalpy in steam side
The average steam enthalpy in feedwater heaters is
calculated by energy and mass balance principles.
Hsteama ¼Fsteam �Hsteam1
PF �Hc
Fsteam1P
Fð12Þ
where Hsteama is the average steam enthalpy (kJ kg�1),
Fsteam and Hsteam are mass flow rate and enthalpy of
Evaluation of solar aided thermal power generation Q. Yan et al.
913Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
extracted steam (kg h�1 and kJ kg�1),P
F �Hc is total
vaporized steam energy (kJ).
(2) Condensed steam mass in steam side
Fcon ¼Kcon � F0:8
win � ð1� foulÞHsteama �Hcw
�Twin � Twout
2ð13Þ
where Kcon is heat transfer efficiency in feedwater side
(W (m21C)�1), Fwin is feedwater mass flow rate
(kg h�1), foul is fouling factor in feedwater side, Hcw is
saturated feedwater enthalpy in special pressure
(kJ kg�1), Twin and Twout are inlet and outlet feedwater
temperature (1C).
(3) Feedwater heater pressure
The total pressure of heater is the sum of partial
steam pressure and air pressure.
Pr ¼ Prs1Pra ð14Þ
(4) Outlet feedwater temperature
The outlet temperature of heated feedwater by ab-
sorbed condensed steam can be calculated by the fol-
lowing equation.
dcw �Mw � ðTwin1TwoutÞ
dt¼ Fwin � cw � ðTwin � TwoutÞ1Fcon � ðHsteam �HcwÞ
ð15Þ
where cw is water specific heat capacity (kJ (kg 1C)�1),
Mw is water mass in pipe side (kg h�1).
3.4. Deaerator model
Deaerator in coal-fired power plant is used for
removing oxygen in feedwater, by heating water to
saturated state. Oxygen in feedwater can corrupt
steel equipments and harm safety and economic
characters. In this study, the deaerator is only an
open water-steam heater. So the basic heat balance
equation is
where Hwater is outlet feedwater enthalpy (kJ kg�1),
Hsteam and Fsteam are enthalpy and mass flow rate of
extracted steam (kJ kg�1 and kg h�1), Hfeedwater and
Ffeedwater are feedwater enthalpy and mass flow rate
from lower-pressure heaters (kJ kg�1 and kg h�1),
Hdrain and Fdrain are drain water enthalpy and mass
flow rate from higher-pressure heaters (kJ kg�1
and kg h�1), Hother and Fother are enthalpy and
mass flow rate of other inlet water or steam (kJ kg�1
and kg h�1).
3.5. Boiler model
Boiler is the main equipment in thermal power plants
to combust fuel to heat water or steam. Boiler is the
energy resource for an integrated thermal circle. Its
main characteristic parameters are superheated and
reheated steam temperature, pressure, flow rate and
fuel consumption rate. As described in deaerator
model, boiler is considered as a ‘black box’ with input
and output parameters of temperature, enthalpy, mass
flow rate and pressure.
The standard coal consumption rate can be calcu-
lated by energy balance principle.
where Mscoal is the standard coal consumption rate
(kg h�1), Hmsteam and Fmsteam are enthalpy and mass
flow rate of main steam (kJ kg�1 and kg h�1), Hmwater
is main feedwater enthalpy (kJ kg�1), Hrsteamout and
Frsteamout are outlet enthalpy and mass flow rate of
reheated steam (kJ kg�1 and kg h�1), Hrsteamin is inlet
reheated steam enthalpy (kJ kg�1), qscoal is standard
coal thermal value (kJ kg�1).
3.6. System evaluating model
The benefits in terms of efficiency and fuel saving of
various levels of solar heat in various power stations
are modeled in this study. To evaluate the benefit or
the efficiency of the solar heat utilization, the solar to
power efficiency (Zse) and solar percentage (psolar) in
the above solar aided thermal power generation is
defined as follows:
Zse ¼DWe
Qsolar� DQboiler� 100% ð18Þ
psolar ¼Qsolar
Qboiler1Qsolar� 100% ð19Þ
where DWe is the increased power output after the
solar replacement (kW), Qsolar is the solar heat
transferred into the feedwater heater (kW), DQboiler is
the possible change of the thermal energy load in boiler
after replacement, e.g. boiler reheating load would
increase if the replaced bled-off is before re-heating
(kW). The other impacts after the solar integration,
e.g. the minor changes of pumps work for steam
and oil are not included in the calculation. ‘7’ in
Equation (18) means the changed boiler heat demands,
it is ‘1’ if the integration adds boiler heat load, but ‘�’when decreasing boiler heat load.
Mscoal ¼ðHmsteam �HmwaterÞ � Fmsteam1ðHrsteamout �HrsteaminÞ � Frsteamout
qscoalð17Þ
Hwater ¼Hsteam � Fsteam1Hfeedwater � Ffeedwater1Hdrain � Fdrain1Hother � Fother
Fsteam1Ffeedwater1Fdrain1Fotherð16Þ
Evaluation of solar aided thermal power generationQ. Yan et al.
Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
914
Other criteria used in the study are specific steam
consumption rate, heat consumption rate and standard
coal consumption rate, which are defined as below:
Specific steam consumption rate is the mass of steam
(passing trough boiler) for per kWh electrical power
generated (kg kWh�1) defined as
d ¼D
Wð20Þ
where D is boiler steam flow rate (kg h�1), W is elec-
trical energy output the plant (kWhh�1).
Heat consumption rate is the per kWh fuel heat
consumption, for per kWh electrical power generated
(kJ kWh�1) defined as
q ¼Q
Wð21Þ
where Q is the total heat load in boiler per hour (kJh�1).
Standard coal consumption rate (generating coal
consumption rate) is standard coal consumption for
per kWh (g kWh�1) defined as
b ¼M
Wð22Þ
where M is the coal consumption (per hour) converted
to the standard coal (29 298 kJ kg�1), in kg h�1.
The feedwater heating system of the selected
200MW subcritical unit is more complex than others,
with the additional five drain water heat exchangers
and two water mixers. The thermodynamic submodels
developed for the conventional power plant can accu-
rately simulate the performance of the power plants.
The main sub models will be connected and debugged
according to the real steam and water flow direction.
Then, all the modeled power plants are validated with
simulated and designed values in Table IV.
The advantages of the supercritical and ultra-su-
percritical units are clear. The selected six units are
typical in steam flow and structure. Therefore, other
similar unit in capacity has analogous characters. The
error percentages in Table IV indicate the great pre-
cision between the designed and simulated results. The
main error source is the neglected parts of gland lea-
kages and make-up water flows, especially for 200MW
subcritical unit with more water mixing and hybrid. In
general, the total model precision can satisfy project
modeling demands.
4. ANALYSIS OF SOLAR AIDEDTHERMAL POWER SYSTEM
As discussed above, the purpose of extracted steam
from turbine is to preheat the feedwater, thus reducing
the heat demand in boiler resulting the higher cycle
efficiency. However, the steam passing the turbine
and power generated are reduced due to the extraction.
In the SAPG system, the solar heat carried by thermal
oil is to replace the extraction steam to preheat
the feedwater while the saved steam is allowed to
continue through the turbine to generate power. In the
system, medium temperature solar heat less than
3001C, from non-concentration types of solar collec-
tors, can be used to generate power through saved
extraction steam because the highest and lowest
temperatures required for feedwater heaters are less
than 260 and 901C respectively in normal power
stations. The assumed temperature differences between
thermal oil and feedwater demands are all about 151C
here. The differences are normal in industry and they
are easy to achieve.
Table IV. Comparison between simulated and designed values.
Parameters Units
200 MW
subcritical
300 MW
subcritical
600 MW
subcritical
600 MW
supercritical
600 MW ultra-
supercritical
1000 MW ultra-
supercritical
Output power DV� MW 201.36 308.404 600 600.315 600.274 1000.000
SV�� MW 200.24 308.673 600.00 600.314 600.271 1000.163
(error) (%) (0.56) (0.087) (0) (0) (0.005) (0.02)
Feedwater temperature DV 1C 246.13 268.83 271.5 273.8 283.00 294.80
SV 1C 245.58 269.08 271.45 275.93 284.55 294.77
(error) (%) (0.22) (0.093) (0.015) (0.78) (0.55) (0.01)
Steam consumption rate DV kg kWh�1 2.930 3.032 3.017 2.758 2.663 2.734
SV kg kWh�1 2.946 3.031 3.017 2.758 2.663 2.733
(error) (%) (0.55) (0.033) (0) (0) (0) (0.04)
Heat consumption rate DV kJ kWh�1 7985.20 8005.71 7888.31 7517 7408.00 7354.00
SV kJ kWh�1 8072.04 8010.67 7897.99 7533.88 7388.74 7330.37
(error) (%) (0.01) (0.062) (0.12) (0.22) (0.26) (0.32)
Coal consumption rate DV g kWh�1 272.83 273.53 269.52 256.83 253.11 251.26
SV g kWh�1 275.79 273.70 269.85 257.41 252.45 250.45
(error) (%) (0.01) (0.062) (0.12) (0.22) (0.26) (0.32)
�DV, designed value; ��SV, simulated values.
Evaluation of solar aided thermal power generation Q. Yan et al.
915Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
4.1. 200 MW subcritical unit
As described in Table II, the solar heat can be used to
replace the steams entering the first high-pressure
heater (HTR7), the second high-pressure heater
(HTR6), the first low-pressure heater (HTR4) and
the last low-pressure heater (HTR1), which are at 260,
215, 160 and 901C, respectively. And the temperature
difference between feedwater demand and the solar
thermal oil temperature of HTR7 is 141C, with outlet
feedwater temperature 2461C; HTR6 is 201C, HTR4
171C and HTR1 131C. The results for integrating solar
into the 200MW subcritical power unit are shown in
Table V. Four replacements are operated in power
boosting and fuel-saving modes to analyze separately.
In Table V, four cases of solar replacements are si-
mulated and analyzed in two operating modes. In the
case of replacing HTR7 steam, the coal consumption
rate in power boosting mode is reduced by 20 g kWh�1,
while increasing 20MW power output. But it is not
recommended to long-term running in this mode due
to safety limitation unless the unit is retrofitted. In fuel-
saving mode, the coal consumption rate is reduced by
18 g kWh�1 in the replacing HTR7 case, while main-
taining the base load 200MW. In the case of replacing
HTR4, the original steam entering HTR4 is 13.28 t h�1
extraction steam mixed with 3.65 t h�1 gland leakage
steam, after extraction steam is replaced by solar heat;
the gland leakage steam now enters the next heater
HTR3. The 901C solar heat can also achieve reduced
coal consumption rate by about 3 g kWh�1.
4.2. 300 MW subcritical unit
The results for integrating solar energy into the
300MW subcritical power unit are shown in Table VI.
Compared with the results in Table V, there are
slight differences, because of the different steam
parameters and heat demands. It should be noted that
the power generation efficiency of 901C thermal oil
from solar energy is higher as 13.65%, which is very
difficult for any solar (alone) thermal power generating
systems to achieve in industry.
4.3. 600 MW subcritical unit
For the 600MW subcritical unit in Table III, the
second high-pressure heater (HTR7), the third high-
pressure heater (HTR6), the second low-pressure
heater (HTR3) and the first low-pressure heater
(HTR1) are selected to be replaced by 260, 215, 160
and 901C thermal oil in both power boosting and fuel-
saving operating modes. The results are listed in
Table VII.
It seems that the benefits of the larger power gen-
eration unit with solar aiding are more obvious than 200
and 300MW units listed above. The solar heat (at
2601C) to electricity efficiency is 40%. When replacing
the first high-pressure HTR7, the gland leakage steam
10 mixing with extraction 8 is moved to mix with steam
9 to enter into the gland steam heater G.C., the feed-
water temperature from G.C. will have a few increasing.
4.4. 600 MW supercritical unit
The thermal balance diagram of a 600MW super-
critical unit is shown in Table III, which has the similar
structure to the 600MW subcritical one. The solar
thermal oil is used to replace the second high-pressure
heater HTR7 at 2601C, the third high-pressure heater
HTR6 at 2151C, the forth low-pressure heater HTR4
at 1601C and the second low-pressure heater HTR2 at
901C separately. The simulation results are shown in
Table VIII.
In Table VIII, the greater reduction of heat (coal)
consumption rates indicates that the solar integration
Table V. Comparisons of the 200 MW subcritical unit in different replacements.
Replacing HTR7
steam
Replacing HTR6
steam
Replacing HTR4
steam
Replacing HTR1
steam
Schemes
Parameters Units
Base
case
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Oil temp.demand 1C — 260 260 215 215 160 160 90 90
Feedwater temp. 1C 245.58 245.52 245.54 249.85 251.09 245.54 246.08 245.58 246.92
Feedwater flow t h�1 589.99 589.99 541.69 589.99 577.89 589.99 584.30 589.99 584.60
Condenser flow t h�1 434.39 496.37 448.07 453.49 441.39 447.67 441.98 434.39 429.00
Output power MW 200.24 219.72 200.12 205.02 200.12 202.55 200.24 202.40 200.21
Coal con. t h�1 55.17 56.19 51.58 54.79 53.54 55.17 54.58 55.17 54.54
Heat con. rate kJ kWh�1 8072.04 7492.55 7551.45 7829.59 7838.07 7890.53 7986.14 7985.85 7980.73
Steam con. rate kg kWh�1 2.946 2.685 2.707 2.878 2.888 2.913 2.918 2.915 2.920
Coal con. rate g kWh�1 275.79 256.00 258.01 267.51 267.80 272.67 272.86 272.85 272.68
Input solar heat MW 0 46.88 37.53 23.56 21.60 10.34 9.05 21.14 20.85
Solar to power eff % 0 36.58 — 25.48 — 22.33 — 10.65 —
Solar percentage % 0 10.25 8.94 5.28 4.96 2.30 2.04 4.71 4.70
Evaluation of solar aided thermal power generationQ. Yan et al.
Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
916
has greater advantage in the supercritical plant. The
solar-to-electricity efficiency is also higher than that in
the subcritical unit in Table VI, but the solar heat
demand is also increasing.
4.5. 600 MW ultra-supercritical unit
The thermal balance diagram of a 600MW ultra-
supercritical unit is given in Table III. The solar
heat at the same temperature levels (as previous
cases) is integrated. The simulated benefits in terms
of power boosting and fuel saving are listed in
Table IX.
In the ultra-supercritical unit, the extracted steam in
low-pressure heaters are all from low-pressure stages of
the turbine with lower steam quality. Therefore, the
benefits of using solar to replace the extracted steam
are limited when compared with the above 600 and
300MW sub or supercritical units.
4.6. 1000 MW ultra-supercritical unit
The 1000MW ultra-supercritical unit modeled is a
product of Hitachi, in Table III. Solar heat was
integrated into the third high-pressure heater (HTR6),
the third and forth low-pressure heaters (HTR4 6 and
HTR3) and the last heater (HTR1).
From Table X it can be seen that for the 1000MW
ultra-supercritical unit, the benefits, i.e. the reduced
energy consumption rate and solar-to-electricity effi-
ciency, are smaller than that in the supercritical units.
But the average coal consumption rate difference be-
tween ultra-supercritical and subcritical units are all
about 15 g kWh�1, with great energy-saving potential.
Table VI. Comparisons of the 300 MW subcritical unit in different replacements.
Replacing
HTR7 steam
Replacing
HTR6 steam
Replacing
HTR4 steam
Replacing
HTR1 steam
Schemes
Parameters Units
Base
case
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Oil temp.demand 1C — 260 260 215 215 160 160 90 90
Feedwater temp. 1C 269.08 269.08 270.96 269.24 270.51 269.08 270.53 269.08 270.96
Feedwater flow t h�1 935.64 935.64 874.54 933.25 915.40 935.64 924.14 935.64 926.14
Condenser flow t h�1 735.34 815.23 754.13 767.79 749.94 735.34 723.84 735.34 725.84
Output power MW 308.67 334.31 308.65 316.16 308.67 313.51 308.68 312.65 308.66
Coal con. t h�1 84.40 85.77 79.88 84.15 82.33 84.40 83.13 84.40 83.26
Heat con. Rate kJ kWh�1 8010.67 7516.78 7582.65 7798.26 7814.69 7887.13 7890.50 7908.74 7902.78
Steam con. Rate kg kWh�1 3.013 2.799 2.833 2.952 2.966 2.984 2.994 2.993 3.001
Coal con. rate g kWh�1 273.70 256.82 259.07 266.44 267.00 269.48 269.59 270.22 270.01
Input solar heat MW 0 59.54 44.03 31.12 27.62 19.38 17.88 29.15 28.76
Solar to power eff % 0 36.24 — 24.08 — 22.79 — 13.65 —
Solar percentage % 0 8.53 6.77 4.54 4.12 2.82 2.64 4.24 4.24
Table VII. Comparisons of the 600 MW subcritical unit in different replacements.
Replacing HTR7
steam
Replacing HTR6
steam
Replacing HTR3
steam
Replacing HTR1
steam
Schemes
Parameters Units
Base
case
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Oil temp. demand 1C — 260 260 215 215 160 160 90 90
Feedwater temp. 1C 271.45 271.45 273.26 271.45 272.37 271.45 272.56 271.45 273.07
Feedwater flow t h�1 1810.38 1810.383 1687.143 1810.383 1784.413 1810.383 1796.223 1810.383 1794.903
Condenser flow t h�1 1444.55 1603.416 1480.176 1517.789 1458.778 1444.548 1430.388 1444.548 1429.068
Output power MW 600.00 652.89 600.00 611.15 600.00 606.08 600.00 606.64 600.00
Coal con. t h�1 161.74 164.40 152.66 161.75 159.12 161.75 160.15 161.75 159.89
Heat con. Rate kJ kWh�1 7897.99 7377.45 7454.62 7754.00 7769.79 7818.80 7820.00 7811.51 7807.32
Steam con. Rate kg kWh�1 3.017 2.773 2.812 2.962 2.974 2.987 2.994 2.984 2.992
Coal con. Rate g kWh�1 269.85 252.06 254.70 264.93 265.47 267.14 267.18 266.89 266.75
Input solar heat MW 0 109.96 78.87 35.77 30.69 37.68 36.62 53.33 53.25
Solar to power eff % 0 40.26 — 31.16 — 16.13 — 12.46 —
Solar percentage % 0 8.23 6.36 2.72 2.37 2.87 2.81 4.06 4.10
Evaluation of solar aided thermal power generation Q. Yan et al.
917Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
Table VIII. Comparisons of the 600 MW supercritical unit in different replacements.
Replacing
HTR7 steam
Replacing
HTR6 steam
Replacing
HTR4 steam
Replacing
HTR2 steam
Schemes
Parameters Units
Base
case
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Oil temp. demand 1C — 260 260 215 215 160 160 90 90
Feedwater temp. 1C 275.93 275.66 277.81 275.76 277.15 275.81 278.42 275.89 277.20
Feedwater flow t h�1 1655.895 1665.273 1548.732 1655.895 1618.715 1655.895 1624.595 1655.895 1644.915
Condenser flow t h�1 1273.388 1426.141 1309.600 1333.232 1296.052 1273.388 1242.088 1273.388 1262.408
Output power MW 600.314 654.70 600.317 617.50 600.147 614.721 600.115 605.213 600.090
Coal con. t h�1 154.37 158.43 146.76 154.40 150.50 154.39 150.75 154.38 153.00
Heat con. Rate kJ kWh�1 7533.88 7089.88 7162.35 7325.83 7346.95 7358.49 7359.89 7473.28 7469.78
Steam con. rate kg kWh�1 2.758 2.544 2.580 2.682 2.697 2.694 2.707 2.736 2.741
Coal con. Rate g kWh�1 257.41 242.24 244.71 250.30 251.02 251.42 251.46 255.34 252.22
Input solar heat MW 0 102.00 72.50 56.12 48.73 59.61 55.92 36.75 36.25
Solar to power eff % 0 41.22 — 30.94 — 23.27 — 12.75 —
Solar percentage % 0 7.91 6.07 4.44 3.98 4.72 4.56 2.91 2.91
Table IX. Comparisons of the 600 MW ultra-supercritical unit in different replacements.
Replacing
HTR7 steam
Replacing
HTR6 steam
Replacing
HTR4 steam
Replacing
HTR2 steam
Schemes
Parameters Units
Base
case
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Oil temp. demand 1C — 260 260 215 215 160 160 90 90
Feedwater temp. 1C 284.55 284.55 286.722 284.55 286.43 284.55 287.14 284.55 285.24
Feedwater flow t h�1 1598.772 1598.772 1505.912 1598.722 1556.912 1598.772 1570.532 1598.771 1593.429
Condenser flow t h�1 1206.641 1332.717 1239.857 1275.251 1233.391 1206641 1178.401 1206.641 1201.299
Output power MW 600.271 645.512 600.279 620.655 600.265 614.028 600.272 602.866 600.264
Coal con. t h�1 151.38 154.18 144.63 151.38 146.85 151.38 148.01 151.38 150.70
Heat con. rate kJ kWh�1 7388.74 6997.83 7058.90 7146.07 7167.73 7223.20 7223.84 7356.93 7355.21
Steam con.rate kg kWh�1 2.663 2.477 2.509 2.576 2.594 2.604 2.616 2.652 2.655
Coal con. Rate g kWh�1 252.45 239.09 241.18 244.16 244.90 246.79 246.81 251.38 251.30
Input solar heat MW 0 104.30 79.19 72.81 63.49 55.67 52.79 28.63 28.48
Solar to power eff % 0 35.61 — 28.00 — 24.71 — 9.06 —
Solar percentage % 0 8.31 6.71 5.91 5.31 4.50 4.38 2.32 2.31
Table X. Comparisons of the 1000 MW ultra-supercritical unit in different replacements.
Replacing
HTR6 steam
Replacing
HTR4 steam
Replacing
HTR3 steam
Replacing
HTR1 steam
Schemes
Parameters Units
Base
case
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Power
boosting
Fuel
saving
Oil temp. demand 1C — 260 260 215 215 160 160 90 90
Feedwater temp. 1C 294.77 294.76 296.57 294.77 296.47 294.77 296.49 294.77 296.94
Feedwater flow t h�1 2733.434 2733.434 2664.434 2733.434 2699.234 2733.434 2703.834 2733.434 2705.655
Condenser flow t h�1 2076.699 2184.318 2115.318 2076.699 2042.499 2076.699 2047.099 2076.699 2048.920
Output power MW 1000.163 1033.53 1000.038 1016.701 1000.102 1014.407 1000.04 1013.606 1000.123
Coal con. t h�1 250.24 250.24 242.95 250.24 246.29 250.24 246.72 250.24 246.70
Heat con. Rate kJ kWh�1 7330.37 7093.76 7117.74 7211.14 7215.07 7227.45 7228.06 7233.16 7227.04
Steam con. Rate kg kWh�1 2.733 2.645 2.664 2.689 2.699 2.695 2.704 2.697 2.705
Coal con. rate g kWh�1 250.45 242.37 243.19 246.38 246.51 246.94 246.96 247.13 246.92
Input solar heat MW 0 106.57 91.73 55.77 51.32 66.26 63.68 119.45 117.82
Solar to power eff % 0 31.31 — 29.65 — 21.50 — 11.25 —
Solar percentage % 0 5.24 4.64 2.74 2.56 3.38 3.17 5.87 5.87
Evaluation of solar aided thermal power generationQ. Yan et al.
Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
918
5. THERMAL AND ECONOMICBENEFIT ANALYSIS
The solar-to-electricity (power) efficiency, the reduced
fuel consumption rate and solar percentage are selected
to compare the merits of solar integration among
various power plants in power boosting and fuel-
saving modes. The results of solar-to-electricity effi-
ciencies for all six different units in same solar
temperatures in power boosting operating mode are
shown in Figure 4.
Table XI shows the reduced coal consumption rate
breduced and the solar percentage psolar in different in-
tegrations in fuel-saving operating modes. It can be
seen that generally, the higher the solar heat tem-
perature, more significant the benefits for the same
unit. But the rates of input solar heat in different steam
extraction structures and parameters are changed with
different units. Input solar heat under 901C for
1000MW unit is much more than the 2601C working
condition, but the other units are the opposite. The
reason for the difference of 1000MW unit is that the
designed increased temperature (heat demand) of the
replaced lower-pressure heater is higher than others.
To show the comparison of solar integration clearly,
the results of three 600MW units all in power boosting
operating models are shown in Figure 5. Apparently,
subcritical and supercritical power plants are more
beneficial for solar integration, especially for low
temperature solar heat, compared with ultra-super-
critical plants. The solar percentages for replacing
2151C extracted stream in the 600MW ultra-super-
critical unit is higher than subcritical and supercritical
units, but the reduced coal consumption rate is less
than the two units. Meanwhile, the coal consumption
rates in fuel-saving operating mode will increase a bit
when compared with the power boosting mode.
For some integrating modes, especially in replacing
the higher pressure extraction steam, if the power out-
put exceeds the long-term safe limitation in power
boosting mode, then the integration system could adjust
valves 1 and 2 in Figure 1 to decrease the power output
05
1015202530354045
90 160 215 260
200MW sub critical unit 300MW sub critical unit
600MW sub critical unit 600MW super critical unit
600MW ultra supercritical unit 1000MW ultra supercritical unit
Solar Thermal Oil Temperature ( C)
Sola
r to
ele
ctri
city
eff
icie
ncy
(%)
1-
4-
12 3 4
56
2-
5-
3-
6-
1
2
3
4 56
12
3 45 6 6
5
43
21
Figure 4. Comparison analysis of the solar to electricity
efficiencies (in power boosting mode).
Tab
leX
I.C
om
parison
analy
sis
of
the
reduced
coalconsum
ption
rate
sand
sola
rperc
enta
ges
(In
fuelsavin
gm
ode).
200
MW
subcriticalunit
300
MW
subcriticalunit
600
MW
subcriticalunit
600
MW
superc
riticalunit
600
MW
ultra
-superc
ritical
unit
1000
MW
ultra
-superc
ritical
unit
Para
mete
rsb
reduced
psola
r(Q
sola
r)b
reduced
psola
r(Q
sola
r)b
reduced
psola
rb
reduced
psola
rb
reduced
psola
rb
reduced
psola
r
Therm
aloil
tem
pera
ture
gkW
h�
1%
(MW
)g
kW
h�
1%
(MW
)g
kW
h�
1%
(MW
)g
kW
h�
1%
(MW
)g
kW
h�
1%
(MW
)g
kW
h�
1%
(MW
)
901C
3.1
14.7
3.6
94.2
43.1
04.1
5.1
92.9
11.1
52.3
13.5
35.8
7
(20.8
5)
(28.7
6)
(53.2
5)
(36.2
5)
(28.4
8)
(117.8
2)
1601C
2.9
32.0
44.1
12.6
42.6
72.8
15.9
54.5
65.6
44.3
83.4
93.1
7
(9.0
5)
(17.8
8)
(36.6
2)
(55.9
2)
(52.7
9)
(63.6
8)
2151C
7.9
94.9
66.7
04.1
24.3
82.3
76.3
93.9
87.5
55.3
13.9
42.5
6
(21.6
0)
(27.6
2)
(30.6
9)
(48.7
3)
(63.4
9)
(51.3
2)
2601C
17.8
88.9
414.6
36.7
715.1
56.3
612.7
06.0
711.2
76.7
17.2
64.6
4
(37.5
3)
(44.0
3)
(78.8
7)
(72.5
0)
(79.1
9)
(91.7
3)
Evaluation of solar aided thermal power generation Q. Yan et al.
919Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
or change to fuel-saving operating mode. In other ways,
if the weather condition often changes, adjusting system
will work frequently. In order to avoid the parameter
fluctuating, a small heat storage system can be set to
stabilize the temperature changes between solar col-
lector and thermal oil heater. But the installed heat
storage system will increase investment cost apparently.
In addition, the solar heat demands in fuel-saving mode
is smaller than the power boosting mode for same re-
placement in Tables V–X. But the reduced coal con-
sumption rates are also a little small compared with the
power boosting operating mode. Meanwhile, the units
operated in fuel-saving mode are much safer, because
the power output is always below the rated load.
In economic analysis, the capital cost for the typical
parabolic trough solar collector system (maximum
temperature below 3501C) is about 2000 h kW�1 in
international market [20], less than 1500 h kW�1 in
China. But the coal price is about 55–80 h t�1 in China.
Therefore, the payback period of the integration is
acceptable, especially under the encouraged policy
from the government. For example, in China, the
prices of electricity output from sustainable energy
(including solar energy, wind energy and so on) are
much higher than the conventional coal-fired power
plants. The potential carbon tax will also accelerate the
process of energy-saving reform. The benefits of the
SAPG are much more observable in the future.
In addition, the above-mentioned integrating modes
studied only the effect and benefits of replacing single
feedwater heater. If the solar collector system can af-
ford enough heat demands to satisfy replacing two or
more heaters, the benefits will be more remarkable.
6. CONCLUSIONS
In this paper, using SAPG concept [21], i.e. integrating
solar heat at various temperature levels of 260, 215,
160 and 901C in the 200MW typical, 300 and 600MW
subcritical, 600MW supercritical and 600 and
1000MW ultra-supercritical power plants are modeled.
Thus their benefits in terms of integrated with solar
energy to preheat the feedwater both in power
boosting and fuel-saving models are studied and
compared.
The results indicate that the SAPG technique can
achieve higher solar (to power) efficiency compared to
the solar alone power plant and is more suitable to be
adopted in subcritical and supercritical plants than in
ultra-supercritical plants. The solar energy can play a
significant (up to 20%) and ecumenically competitive
role in providing base load power generation once the
SAPG principle. Therefore, the SAPG is proved the-
oretically to be the most efficient way to make use of
solar energy especially at low-to-medium temperature
ranges for power generation purposes.
NOMENCLATURE
SAPG 5 solar aided power generation
P 5 pressure (MPa)
temp. 5 temperature (1C)
con. 5 consumption
sin 5 inlet steam entropy (kJ kg�1)
sout 5 outlet steam entropy (kJ kg�1)
hin 5 inlet steam-specific enthalpy (kJkg�1)
hout 5 ideal outlet steam-specific enthalpy
(kJ kg�1)
h0out 5 real outlet steam-specific enthalpy
(kJ kg�1)
Dh 5 ideal enthalpy change (kJ kg�1)
Dh0
5 real enthalpy change (kJ kg�1)
estage 5 the isentropic efficiency of the stages
(%)
Fin 5 inlet steam mass flow rate (kg h�1)
Wout 5 real power output (kW)
0
5
10
15
20
25
30
35
40
45
90 160 215 260
600MW sub critical unit solar to electricity eff. 600MW sub critical unit solar percentage
600MW 600MW super critical unit solar percentage
600MWultra super critical unit solar to electricity eff. 600MWultra super critical unit solar percentage
Solar Thermal Oil Temperature(oC)
Sola
r to
ele
ctri
city
eff
icie
ncy
(%)
/Sol
ar p
erce
ntag
e (%
)
super critical unit solar to electricity eff.
1-
2-
3-
1
1
1
1
2
2
2
2
3
33
3
a-
b-
c-
a b c ab c
ab c
a b c
Figure 5. Solar to electricity efficiencies and solar percentages in 600 MW power boosting operating modes.
Evaluation of solar aided thermal power generationQ. Yan et al.
Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
920
Fex 5 steam extraction flow rate (kg h�1)
Ms 5 steam mass in shell side of the
condenser (kg h�1)
Fsin 5 inlet steam mass of the condenser
(kg h�1)
Fsout 5 outlet steam mass of the condenser
(kg h�1)
Ma 5 air mass in shell side of the con-
denser (kg h�1)
Fain 5 inlet air mass of the condenser
(kg h�1)
Faout 5 outlet air mass of the condenser
(kg h�1)
Fc 5 condensed steam mass of the con-
denser (kg h�1)
as 5 the condensing heat transfer effi-
ciency (W (m21C)�1)
Au 5 the heat transfer area in shell side
(m2)
Ts 5 the average temperature in conden-
ser (1C)
Tc 5 the temperature of cooling water
(1C)
Hs 5 the average steam enthalpy in con-
denser (kJ kg�1)
Hcw 5 the saturated water enthalpy in con-
denser (kJ kg�1)
Ps 5 partial steam pressure in condenser
(MPa)
P0s 5 partial steam pressure at previous
calculating time (MPa)
Rs 5 steam gas constant (J (kgK)�1)
V 5 condenser’s volume (m3)
Ma 5 air mass in condenser (kg h�1)
Pa 5 partial air pressure in shell side of the
condenser (MPa)
P0a 5 partial air pressure at previous cal-
culating time (MPa)
Ra 5 air gas constant (J (kgK)�1)
P 5 pressure in shell side of the conden-
ser (MPa)
Mcw 5 the kept cooling water in condenser
(kg)
Cw 5 cooling water thermal capacity
(kJ (kg 1C)�1)
Dw 5 cooling water mass flow rate (kg h�1)
Qc 5 absorbed heat by cooling water (kJ)
T1 5 cooling water inlet temperature (1C)
T2 5 cooling water outlet temperature (1C)
Hsteama 5 the average steam enthalpy (kJ kg�1)
Fsteam 5mass flow rate of extracted steam
(kg h�1)
Hsteam 5 enthalpy of extracted steam (kJ kg�1)PF �Hc 5 total vaporized steam energy (kJ)
Fcon 5 condensed steam mass in steam side
of the feedwater heater (kg h�1)
Kcon 5 heat transfer efficiency in feedwater
side (W (m21C)�1)
Fwin 5 feedwater mass flow rate (kg h�1)
foul 5Fouling factor in feedwater side
Hcw 5 saturated feedwater enthalpy in spe-
cial pressure (kJ kg�1)
Twin 5 inlet feedwater temperature (1C)
Twout 5 outlet feedwater temperature (1C)
Pr 5 feedwater heater pressure (MPa)
Pr,s 5 partial steam pressure of the feed-
water heater (MPa)
Pra 5 partial air pressure of the feedwater
heater (MPa)
Twin 5 inlet temperature of heated feed-
water (1C)
Twout 5 outlet temperature of heated feed-
water (1C)
cw 5water specific heat capacity
(kJ (kg 1C)�1)
Mw 5water mass in pipe side of the heater
(kg h�1)
Hwater 5 outlet feedwater enthalpy (kJ kg�1)
Hsteam 5 enthalpy of extracted steam (kJ kg�1)
Fsteam 5mass flow rate of extracted steam
(kg h�1)
Hfeedwater 5 feedwater enthalpy from lower-pres-
sure heaters (kJ kg�1)
Ffeedwater 5 feedeater mass flow rate from lower-
pressure heaters (kg h�1)
Hdrain 5 drain water enthalpy from higher-
pressure heaters (kJ kg�1)
Fdrain 5 drain water mass flow rate from
higher-pressure heaters (kg h�1)
Hother 5 enthalpy of other inlet water or
steam (kJ kg�1)
Fother 5mass flow rate of other inlet water or
steam (kg h�1)
Mscoal 5 the standard coal consumption rate
(kg h�1)
Hmsteam 5 enthalpy and mass flow rate of main
steam (kJ kg�1)
Fmsteam 5mass flow rate of main steam
(kg h�1)
Hmwater 5main feedwater enthalpy (kJ kg�1)
Hrsteamout 5 outlet enthalpy of reheated steam
(kJ kg�1)
Frsteamout 5 outlet mass flow rate of reheated
steam (kg h�1)
Hrsteamin 5 inlet reheated steam enthalpy
(kJ kg�1)
qscoal 5 standard coal thermal value (kJ kg�1)
Zse 5 the solar to power efficiency (%)
psolar 5 the solar percentage (%)
DWe 5 the increased power output after the
solar replacement (kW)
Qsolar 5 the solar heat transferred into the
feedwater heater (kW)
DQboiler 5 the possible change of the thermal
energy load in boiler after replace-
ment (kW)
Evaluation of solar aided thermal power generation Q. Yan et al.
921Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.
DOI: 10.1002/er
d 5 specific steam consumption rate
(kg kWh�1)
D 5 boiler steam flow rate (kg h�1)
W 5 electrical energy output the plant
(kWhh�1)
q 5 heat consumption rate (kJ kWh�1)
Q 5 the total heat load in boiler per hour
(kJ h�1)
b 5 standard coal consumption rate
(g kWh�1)
M 5 the coal consumption (per hour)
converted to the standard coal
(29 298 kJ kg�1) (kg h�1)
breduced 5 the reduced coal consumption rate
(kg kWh�1)
DV 5 designed value
SV 5 simulated values
ACKNOWLEDGEMENTS
We are grateful for the project (No. 2009CB219801),funding from National Basic Research Program ofChina-973 program, and China National NaturalScience Fund Project (No. 50776028) to support theresearch.
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