Pyrolysis-Bridged Hybrid Power Systems and Their Application for

Article pubs.acs.org/EF

Pyrolysis-Bridged Hybrid Power Systems and Their Application for Thermal Power Plants Yuzhe Li,†,‡ Chuigang Fan,† and Wenli Song*,† †

State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China ‡ University of Chinese Academy of Sciences, Beijing 100049, China ABSTRACT: A hybrid power system based on coal pyrolysis and steam integration is proposed to improve the performance of power plants. The most outstanding features of the system are a pyrolysis process integrated with a circulating fluidized bed boiler and power generation by the steam integration. The model of the hybrid power system is set up by THERMOFLEX software and Aspen Plus. Results show that the thermal efficiency of pyrolysis process can achieve values of 90%−95%, and the majority of the energy used by the pyrolysis is consumed during the drying and quench processes. Compared with a conventional steam cycle power system, the gross electric efficiency and thermal efficiency of the new system are increased by 1.9% and 5.1%, respectively. Energy and exergy analyses are presented to study the performance differences of two systems. Exergy destruction of the boiler with steam integration is decreased in the new system. Exergy destruction of gas turbines is lower than that of the boiler. Although additional exergy loss occurs in the pyrolyzer and heat recovery steam generator, the overall exergy loss of the new system is less than that of the conventional system. combustor. The pyrolyzer could be a moving bed, a fluidized bed, or a downer. For the fossil fuel power generation system, there are two general systems: a natural gas combined system and a coal-fired steam system. Based on coal topping technology, a pyrolysisbridged hybrid power system (an IPE system) is proposed for improving thermal efficiency of coal-fired power plant. The IPE system has the features of two thermal systems, and through the steam integration, the two systems are coupled in the IPE system. This study aims at modeling the hybrid power system, and predicting its performance. Exergy analysis is also carried out for the performance assessment of the system.

1. INTRODUCTION Solid carbonaceous fuels have been predicted to remain as one of the most important energy sources for many decades.1,2 There is an increasing need to improve the conversion efficiency of coal, with respect to the continuous growth of economy and environmental awareness. New technologies have been developed to improve power generating efficiency and reduce pollutant emissions from coal utilization, and coal pyrolysis are seen to be one of them.3 Coal pyrolysis refers to the devolatilization of coal in an inert atmosphere.4,5 The products of pyrolysis are pyrolysis gas, tar, and char.6 A great deal of interesting work based on coal pyrolysis have been done using different equipment (e.g., fixed bed,7 fluidized bed,8 or downer bed9). Typical technologies include Luigi-Ruhrgas (L-R), COED, TOSCOAL, ETCH175,10 and DG.11 Only L-R technology is commercially operated now, while the use of the others has been stopped for technical or economic reasons.12 The performances of advanced power systems based on pyrolysis have been evaluated. Foster Wheeler Development Corporation developed a pyrolysis power system in which the electric efficiency and capacity were increased from 33.6% to 39.2%.13 In Italy, an integrated pyrolysis system was launched, including the preliminary numerical simulation and pilot operation.14 Cen et al. proposed a poly-generation system integrating pyrolysis technology with a circulating fluidized bed (CFB) boiler for the simultaneous production of gas, tar, electricity, and steam.15 A poly-generation process, called coal topping, was previously proposed by the Institute of Process Engineering (IPE) at the Chinese Academy of Sciences for the coproduction of pyrolysis gas, tar, and heat. The process system was composed of a pyrolyzer, a gas−solid separator, and a riser © 2014 American Chemical Society

2. IPE SYSTEM DESCRIPTION The key units of the IPE system including pyrolysis and power islands are shown in Figure 1. In the pyrolysis island, the coal pyrolysis unit is integrated with a CFB boiler. Coal is mixed with the circulating hot ash from the CFB boiler, and pyrolyzed, resulting in pyrolysis gas, tar, and char. The char and tar are combusted in the CFB boiler for steam production. The pyrolysis gas, after purification, is fired in a gas turbine for power generation. The heat of gas turbine exhaust is recuperated by a heat recovery steam generator (HRSG) to produce steam with low parameters. The steam is directly integrated with the CFB boiler’s steam system and superheated. Then, the superheated steam is fed into the steam turbine for power generation. The steam exhaust from steam turbine is condensed in the condenser and feedwater is pumped into the boiler and HRSG. Received: July 12, 2014 Revised: September 17, 2014 Published: September 17, 2014 6531

dx.doi.org/10.1021/ef5015742 | Energy Fuels 2014, 28, 6531−6539

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Figure 1. Flow diagram of the Institute of Process Engineering (IPE) system.

The thermal efficiency of pyrolysis can reach 90%−95%, as shown in Table 1. The thermal efficiency is higher than other

parameters, resulting in an increase in the power generating efficiency.

Table 1. Typical Technologies for Coal Pyrolysis

3. APPLICATION OF THE IPE SYSTEM 3.1. Thermal Power Plant. An existing coal-fired thermal power plant is going to be retrofitted for increasing the power supply. The layout of the existing plant is shown in Figure 2. It is capable of supplying 50 MWe of electricity to the grid and 180 MWth of heat for the surrounding industries and district heating. There are three 130 ton/h steam CFB boilers. The steam parameter of the CFB boiler is 9.8 MPa/540 °C without reheat, and the flow rate of steam can meet the demand of two 25 MWe condensing steam turbines with extraction for heating. The main parameters of thermal power plant are tabulated in Table 2. 3.2. Retrofitted Plant. Two schemes are selected to retrofit the existing plant (shown in Table 3). One of them is a new steam turbine generating set is added to the existing steam cycle system (CSC system). Alternatively, pyrolysis bridged hybrid

pyrolysis process

heat carrier

combustion mode

L-R COED

char gas

ETCH175 DG IPE

char

char in riser char in circulating fluidized bed char in riser

char ash

char in riser char in CFB boiler

operating temperature (°C)

thermal efficiency (%)

500 315−815

87−89 90

700

83−87

550−600 600−700

88 90−95

pyrolysis technologies, because of integration with the CFB boiler. The hot char from the pyrolyzer is fed into the CFB boiler without sensible heat loss, and the combustion efficiency is improved. The steam integration can enhance the steam

Figure 2. Flow diagram of the existing plant. 6532


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of exhaust from gas turbine is recovered by a HRSG to produce steam at 312 °C. The steam is fed into the existing CFB boiler’s drums. All of the steam is continuously superheated to 535 °C in the CFB boilers, and then injected to the steam turbines for power generation. In the above two schemes, the thermoelectric ratio is decreased from 3.6 to 2.3 while the heat output remains unchanged.

Table 2. Design Parameters of the Existing Thermal Power Plant thermal power plant

value

gross electric efficiency (LHV) thermal efficiency (LHV) thermoelectric ratio steam turbine isentropic efficiency steam turbine inlet pressure steam turbine inlet temperature condenser pressure steam flow rate exhaust temperature

16.9% 76.7% 3.6 78.3% 8.3 MPa 535 °C 0.005 MPa 373 t/h 140 °C

4. PROCESS SIMULATION The details of modeling of CSC and IPE system are given in this section. A fully flexible software, THERMOFLEX, which is widely employed in modeling study of power system.16,17 However, there is not a pyrolysis module in the software, which brings simulating IPE system difficulties. Hence, Aspen Plus is used to calculate the heat loss due to coal pyrolysis, and the results of heat loss are manually assigned to the heat exchange modules in the THERMOFLEX to finish the entire simulation. The lignite is selected as the raw material. The typical properties of the coal are listed in Table 4. The main assumptions taken for the simulation process for power systems are as follows: • the standard ambient conditions used by the literature18 • fixed extraction heat output (180 MWth) • boiler efficiency (91%) • pinch point of HRSG in the IPE system (10 °C) • no energy loss in removing acid gas 4.1. CSC System Simulation. The flowsheet of the CSC system is shown in Figure 3. New units are shown in the box bounded by dashed lines. A new 130 ton/h steam CFB boiler is added to meet the steam demand of a new 30 MWe condensing steam turbine. In the model, the increased steam consumption is provided by adjusting the mass flow rate of new boiler. The inlet of new steam turbine is connected to the steam outlet of the boiler. The boiler feedwater is pumped into the economizer. The parameters of main streams in Figure 3 are presented in Table 5.

Table 3. Design Schemes of Two Power Systems thermal scheme

new equipment

fuel

conventional steam cycle (CSC) system

• adding a steam turbine • adding a steam boiler

boiler: coal

pyrolysis-bridged hybrid power system (IPE system)

• adding a pyrolyzer • adding a gas turbine • adding a HRSG

boiler: char and tar gas turbine: pyrolysis gas

power system (IPE system) is applied to the project. The layouts of the CSC system and the IPE system are shown in Figures 3 and 4. A 30 MWe condensing steam turbine and a 130 ton/h steam CFB boiler are added to the plant to be retrofitted by the CSC system. The steam produced by the new CFB boiler is fed into the new steam turbine for power generation. The other retrofitted scheme by the IPE system is equipped with a 30 MWe gas turbine, a HRSG, and a pyrolyzer. The pyrolyzer can deal with 60 ton-coal/h, and the production of pyrolysis gas can meet the demand of the gas turbine. The heat

Figure 3. Flow diagram of the CSC system. 6533


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Figure 4. Flow diagram of the IPE system.

Table 4. Proximate and Ultimate Analysis of Coal Samplea Proximate Analysis (wt %, arb)

Ultimate Analysis (wt %, dafc)

coal sample

moisture, M

ash, A

volatiles, V

fixed carbon, FC

C

H

N

S

O

lower heating value, LHV (MJ/kg)

lignite

20

5.92

33.68

40.4

74.51

5.83

1.94

0.65

17.06

22.5

a

b

c

Data taken from ref 11. As-received basis. Dry-ash-free basis.

Table 5. Parameters of Main Streams in the CSC System stream

G (kg/s)

pressure, P (bar)

temperature, T (°C)

stream

G (kg/s)

pressure, P (bar)


1 2 3 4 5 6 7 8 9 10

43.75 60.08 22.22 33.33 11.10 13.88 43.81 61.39 13.25 17.74

88.30 88.30 13.00 39.00 0.05 0.05 105.20 105.20 7.70 7.87

534.30 534.30 312.00 445.00 32.54 32.54 218.80 217.80 28.61 33.49

11 12 13 14 15 16 17 18 19 20

22.22 33.33 17.67 97.28 97.28 211.25 32.28 32.28 22.73 27.25

13.00 14.14 1.01 1.01 1.01 1.01 88.30 105.2 0.04 28.49

80.48 104.40 15.00 15.00 15.00 144.4 534.30 218.00 28.10 28.49

Figure 5. Calculation flow sheet of coal pyrolysis process.

4.2. IPE System Simulation. 4.2.1. Pyrolysis Island. The schematic diagram used to simulate the pyrolysis island is

shown in Figure 5. The supplementary parts include a fuel dryer, a decomposer, a gas−solid separator, a heat exchanger, 6534


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and a boiler. The wet coal first enters the DRYER module, where the moisture content of coal is reduced. The dry coal is directed into the pyrolyzer (DECOMP), which is represented as the RYIELD reactor. In this case, coal is converted to pyrolysis products by specifying the yield distribution. The RYIELD module is useful when reaction stoichiometry and kinetics are unknown, and yield distribution data of correlations are available. According to the published experimental results,11 the pyrolysis products yields of dry coal (8% moisture content) for char, tar, gas, and water are 60.9, 6.0, 21.4, and 11.7 wt %, respectively. Since the composition of tar is very complex, tar is generally assumed to be a simple hydrocarbon, such as C14H10.19 To better represent the characteristics of tar, Cen et al. chose five different compounds.15 However, the oxygen content is low in their work. To fill the gap, six compounds are chosen in this work: phenol, benzoic acid, hexadecane, quinolone, naphthalene, and dibenzothiophene. The reaction heat of coal pyrolysis is considered, and designed, to be 837 kJ/kg devolatilization of coal.20 The considered heat dissipation for the pyrolysis island is supposed to be, constantly, 2% of the heat from the boiler to the pyrolyzer. The outlet temperature of pyrolysis products is set to 600 °C. The pyrolysis products are split into two streams. One stream entering into the combustion module (BOILER) is the residue of pyrolysis (char and ash), and the other stream fed into the CLEANUP module consists of gas, tar, and water. The RGIBBS reactor is selected to represent the BOILER module, and the minimization of the Gibbs free energy approach is carried out such as the approach is used by Cohce et al.21 The temperature of volatiles is reduced to 25 °C in the CLEANUP module, and sensible heat of volatiles is removed from the system. Since the connection of the pyrolyzer and boiler is dual-reactor design, it is difficult to complete convergence for circulating ash between two reactors. To solve the problem, the heat calculation of pyrolysis process is simplified in the Aspen Plus. The circulating ash to the pyrolyzer is replaced by a stream of heat flow, which provides the needed heat of pyrolysis. It is assumed that the needed heat of pyrolysis island includes pyrolysis reaction heat, the sensible heat loss of volatiles and heat dissipation. The heat loss of pyrolysis is manually assigned to the heat exchange module of power island in the THERMOFLEX. The efficiency of the overall system is calculated in the THERMOFLEX considering the heat loss of pyrolysis. 4.2.2. Power Island. The IPE system for power generation is illustrated in Figure 4. New modules are added in the box bounded by dashed lines, where fuels are divided into gas, tar, and char. The heat loss of pyrolysis obtained from Aspen Plus is assigned by the HEAT ADDER modules in the THERMOFLEX. The fuel streams are heated up to 600 °C before leaving the HEAT ADDER. The volatiles are cooled to 25 °C in the SCRUBBER modules. The gas turbine chosen from GT module library is another key unit. The main parameters of gas turbine are summarized in Table 6. The burner of gas turbine had to be designed according to the compositions of pyrolysis gas. In this paper, the efficiency of gas turbine based on the Thermoflex’s GT library was assigned to 39.9% LHV. The parameters of main streams in Figure 4 are presented in Table 7.

Table 6. Parameters of the Gas Turbine

η=

gas turbine

value

pressure ratio turbine inlet temperature turbine exhaust temperature gen power LHV efficiency

23.3 ∼1241 °C 500 °C 30 MW 39.9%

(Q char + Q tar + Q gas + Q reco) Q coal Q rh + Q sh + Q diss

=1−

Q coal

(1)

where Qchar represents the LHV of char, Qtar represents the LHV of tar, Qgas represents the LHV of gas, Qreco represents recovered sensible heat, Qcoal represents the LHV of coal, Qrh represents the pyrolysis reaction heat, Qsh represents sensible heat loss, and Qdiss represents the pyrolysis heat dissipation. Energy and exergy balances are carried out to evaluate the performances of the CSC and IPE systems, and the analysis method has also been reported and well-described by Rosen and Scott.22 Referencing 0 °C and 0.103 MPa as the ground state, energy and exergy balances can be written as21,23 Q̇ − Ẇ =

∑ ṁ ihi − ∑ ṁ jhj i

j

(2)

∑ ṁ iexi = ∑ ṁ jhj + Eẋ D i

(3)

j

where the subscripts i and j refer to streams entering and leaving the control volume, respectively. Here, ex is the exergy rate and Ė xD is the total exergy destruction. The exergy rate of a stream of substance (neglecting the potential and kinetic parts) can be expressed in terms of the sum of specific physical and chemical exergy:24 ex = ex ph + ex ch

(4)

The specific physical exergy can be defined as ex ph = (h − h0) − T0(S − S0)

(5)

In addition, the specific chemical exergy of pyrolysis gas can be written as follows: ex ch =

∑ xi(exich − RT ln xi) i

(6)

Here, x is the molar fraction and exch is the standard chemical exergy of component i. The specific chemical exergy of the coal is calculated as follows:25 ⎡ ⎛H⎞ ⎛O⎞ ch = LHV⎢1.0064 + 0.1519⎜ ⎟ + 0.0616⎜ ⎟ excoal ⎝C⎠ ⎝C⎠ ⎣ ⎛ N ⎞⎤ + 0.0429⎜ ⎟⎥ ⎝ C ⎠⎦

5. ANALYSIS METHOD In order to evaluate the energy use of the pyrolysis process, the thermal efficiency of the pyrolysis island is defined in eq 1:

(7)

LHV is the lower heating value of coal, and C, H, O, N represent the mass fraction of the carbon, hydrogen, oxygen, and nitrogen on a dry basis. 6535


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Table 7. Parameters of Main Streams in the IPE System stream

G (kg/s)

pressure, P (bar)


stream

G (kg/s)

pressure, P (bar)


1 2 3 4 5 6 7 8 9 10

43.75 60.08 22.22 33.33 13.16 16.17 36.97 53.86 13.89 13.89

88.30 88.30 13.00 39.00 0.05 0.05 104.30 104.30 104.10 102.00

535.00 535.00 312.00 445.00 32.54 32.54 221.80 217.80 34.78 312.50

11 12 13 14 15 16 17 18 19 20

22.22 33.33 11.00 2.73 75.33 75.33 158.83 82.53 83.47 83.47

13.00 14.14 1.01 1.01 1.01 1.01 1.01 1.01 1.03 1.01

80.48 104.40 25.00 25.00 15.00 15.00 133.40 15.00 505.20 120.80

The exergy efficiency (α) of the power system is calculated by eq 8, and the corresponding exergy loss coefficient (ε) is applied in the subsequent analysis. α=

Eẋ out Eẋ in

ε=1−α=

(8)

Eẋ D ̇ E in

(9)

To evaluate the exergy losses for the individual units, such as the boiler, the steam turbine, and the condenser, the significance (κ) and the loss contribution (λ) are introduced.26 κ=

Eẋ i Eẋ total

λ = εκ

Figure 6. Effects of moisture content on pyrolysis island performance (pyrolysis at 600 °C).

(10) (11)

content of dry coal is 8%, the effects of recovered sensible heat of the volatiles are illustrated in Figure 7. As the amount of

The significance is defined as the ratio of the feed exergy of unit i to the total incoming exergy of the system. Multiplying the significance by the loss coefficients gives the loss contribution (λ). The loss of individual units in the two systems is weighted according to their significance in the entire plant. In this way, the loss contribution can be calculated for each individual unit, relative to the entire plant.

6. RESULTS AND DISCUSSIONS 6.1. Thermal Efficiency of Pyrolysis Island. The moisture content is a negative factor in the pyrolysis process. The published results proved that the moisture content of coal negatively affected energy utilization during the pyrolysis process.27 The energy consumption of the pyrolysis island is directly related to the moisture content of coal. Removal of the water from the coal prior to pyrolysis reduces the sensible heat loss during the quench. As shown in Figure 6, as the moisture content of coal decreased, the energy consumption of the pyrolysis island decreased, even though the drying unit requires increasing energy consumption. The common method of coal drying can remove ∼60% of the moisture.28 In this case, it is reasonable that the moisture content of the lignite is decreased from 20% to 8% through coal drying. The thermal efficiency of the pyrolysis island can attain 94.3%, considering the completely sensible heat loss of the pyrolysis volatiles at the temperature of 600 °C. The amount of recovered sensible heat affects the thermal efficiency of pyrolysis island. It is possible that the sensible heat of hot char can be completely utilized through being put into the boiler, while that of high-temperature volatiles is partly recovered in the heat exchanger. Assuming the moisture

Figure 7. Effects of recovered sensible heat of the volatiles on pyrolysis island performance (pyrolysis at 600 °C).

recovered sensible heat increased, energy consumption of the pyrolysis island decreased. The results point out that, through 30% heat recovery, the thermal efficiency of pyrolysis island is increased by 1.0%, and up to 95.3%. In this working condition, the temperature of volatiles is decreased from 600 °C to 360 °C. The published results showed the heat exchanger fouling does not occurred when temperature is above 360 °C.27 So the fouling in the heat exchanger can be avoided. By means of an energy balance calculation for the typical pyrolysis process, energy flows of pyrolysis island are shown in 6536


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Figure 8. Energy flow of the coal pyrolysis island process.

The differences of thermal performance affected by the thermodynamic system are analyzed through energy and exergy distribution of these units. Energy and exergy analyses of the two systems are shown in Figure 9. It is known that energy loss mainly occurs in the condenser, which contributes more than half of energy loss.23 Condensation heat loss (27%) in the CSC system is increased when the flow rate of steam exhaust is increased, because of the installation of a new steam turbine. In the IPE system, condensation heat loss (17%) only comes from two existing steam turbines. Although the IPE system adds a pyrolysis unit, its pyrolysis loss (5%) is less than the condensation heat loss. There is ∼2% energy loss in the gas turbine side, because most of the exhaust heat is recovered by the HRSG. Overall exergy efficiencies of two systems are 35% and 37%, respectively. Thus, over 60% of the feeding exergy is lost in two systems. The largest exergy loss occurs in the boiler, as exergy analysis results of the coal-fired boiler are performed.29,30 The exergy loss in the boiler particularly results from the irreversibility of fuel combustion and heat transfer to the working fluid, and lost with exhaust gases emissions. The percentage of boiler exergy loss in the IPE system is 13.5% lower than that of CSC system. Additional exergy loss occurred in the gas turbine (7%) and pyrolysis unit (5%). Exergy loss in the condenser is thermodynamically insignificant, because of its low quality. For a better understanding of the differences of exergy distributions between both systems, the exergy losses of the individual units are shown in Figures 10 and 11. There is a 1.2% decline in the boiler’s loss coefficient (ε) in the IPE system, because of steam integration. The significance (κ) of the boiler reduces to 85% in the IPE system. Multiplying the value by the boiler’s loss coefficient of 50% gives a loss contribution of 42% (λ). With pyrolysis, 20% of the incoming exergy in fuel feed is assigned to the gas turbine, where the loss coefficient is 35%, and loss contribution in the gas turbine is significantly lower than that of the boiler. Although there also exists exergy loss in the pyrolyzer and HRSG, the overall exergy loss of the IPE system is lower than that of the CSC system. It is anticipated that a greater exergy ratio for the gas turbine can bring less overall exergy loss in the IPE system and, hence, increase the exergy efficiency of the system.

Figure 8. The energy of coal (1293 GJ) is input to the pyrolysis island, where coal is dried and pyrolyzed. It is observed that 61 GJ of energy are lost during pyrolysis. Energy loss comes from three units. The amounts of energy consumed by the dryer and the pyrolyzer are 20 GJ and 16 GJ, respectively; 25 GJ of heat are discharged from the cleanup unit. 6.2. Performances of Two Systems. Performance results of CSC and IPE system are given in Table 8. The thermal Table 8. Performance Results of CSC and IPE System Value parameter

CSC system

IPE system

gross electric efficiency (LHV) net electric efficiency (LHV) thermal efficiency fuel input steam turbine power gas turbine power heat output thermoelectric ratio

20.9% 18.7% 65.9% 379 MW 80 MW

22.8% 20.3% 71.0% 352 MW 50 MW 30 MW 180 MW 2.3

180 MW 2.3

performances are better in the IPE system with 95.3% pyrolysis thermal efficiency than those of CSC system. Gross electric efficiency and plant thermal efficiency of IPE system are 1.9% and 5.1% higher than those of CSC system, respectively, with the same electricity (80 MW) and heat (180 MW) output. The IPE system saves 27 MW fuel input, i.e., a reduction in coal input of 4.6 ton/h. A technical and economic evaluation study is carried out for the small power plant with IPE system (shown in Table 9). The results show that the internal rate of return is 12.87%, which could be accepted for commercial application. Table 9. Economic Results of the IPE system item

value in the IPE system

fixed capital cost (10 $/yr) interest during installation (106 $/yr) total capital cost (106 $/yr) annual output value (106 $/yr) annual profit (106 $/yr) internal rate of return (%) simple payback period (yr) 6

88.24 5.73 93.97 59.39 11.88 12.87 8.15 6537


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Figure 9. Energy and exergy distribution of the CSC and IPE systems.

7. CONCLUSIONS A pyrolysis-bridged hybrid power system (IPE system) with coal pyrolysis and steam integration, has been proposed to improve the performance of coal-fired thermal power plants. The pyrolysis process integrated with a circulating fluidized bed boiler can achieve a thermal efficiency of 90%−95%. The study shows that energy for pyrolysis process is consumed mainly in the drying and cleanup operations. Prior to pyrolysis, reducing the moisture content of coal benefits the overall system performance. Compared with the 80 MWe conventional steam cycle system, the gross electric efficiency and thermal efficiency of the IPE system is 1.9% higher and 5.1% higher, respectively. Energy and exergy analyses for the two systems show that energy loss mainly occurs in the condenser, while exergy destruction mainly occurs in the boiler. Exergy analyses indicate that the exergy loss coefficient of the boiler in IPE system is decreased because of steam integration. The exergy loss coefficient of gas turbine is significantly lower than that of the boiler. The overall exergy loss of the IPE system is lower than that of CSC system.

Figure 10. Exergetic figure for the units of the CSC system.

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AUTHOR INFORMATION

Corresponding Author

*Fax: +86-10-82544817. E-mail address: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The financial support from Strategic Priority Research Program of Chinese Academy of Sciences (No. XDA07010200) is gratefully acknowledged.

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NOMENCLATURE

Abbreviations

Figure 11. Exergetic figure for the units of the IPE system.

IPE = pyrolysis-bridged hybrid power system CSC = conventional steam cycle 6538


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(20) Yu, H.; Lu, w.; Xu, S.; Guo, M. J. China Univ. Sci. Technol. 1998, 28, 351−355. (21) Cohce, M. K.; Dincer, I.; Rosen, M. A. Bioresour. Technol. 2011, 102, 8466−8474. (22) Rosen, M. A.; Scott, D. S. Int. J. Hydrogen Energy 2003, 28, 1307−1313. (23) Ameri, M.; Ahmadi, P.; Hamidi, A. Int. J. Energy Res. 2009, 33, 499−512. (24) Ameri, M.; Ahmadi, P.; Khanmohammadi, S. Int. J. Energy Res. 2008, 32, 175−183. (25) Zhu, M. Exergy Analysis of the Energy System; Tsinghua University Publications: Beijing, 1988. (26) Kunze, C.; Riedl, K.; Spliethoff, H. Energy 2011, 36, 1480−1487. (27) Yi, Q.; Feng, J.; Lu, B.; Deng, J.; Yu, C.; Li, W. Energy Fuels 2013, 27, 4523−4533. (28) Miknis, F. P.; Netzel, D. A.; Turner, T. F.; Wallace, J. C.; Butcher, C. H. Energy Fuels 1996, 10, 631−640. (29) Yang, Y.; Wang, L.; Dong, C.; Xu, G.; Morosuk, T.; Tsatsaronis, G. Appl. Energy 2013, 112, 1087−1099. (30) Regulagadda, P.; Dincer, I.; Naterer, G. Appl. Therm. Eng. 2010, 30, 970−976.

GT = gas turbine HRSG = heat recovery steam generator PR = pressure ratio LHV = lower heating value Variables

Q̇ = rate of heat transfer Ẇ = power Ė x = exergy rate Ė xD = exergy destruction rate h = enthalpy S = entropy ṁ = mass rate ex = specific exergy x = volume fraction

Greek Symbols

η = thermal efficiency α = exergy efficiency ε = loss coefficient κ = significance λ = loss contribution Superscripts

ph = physical ch = chemical Subscripts

th = thermal e = electricity i = entering stream j = leaving stream

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REFERENCES

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