Thermodynamic performance study of the MR SOFC-HAT-CCHP system

international journal of hydrogen energy xxx (xxxx) xxx

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Thermodynamic performance study of the MR SOFC-HAT-CCHP system Hongbin Zhao a,b,*, Qinlong Hou a,b a b

College of Machinery and Transportation Engineering, China University of Petroleum, Beijing, 102249, PR China Beijing Key Laboratory of Process Fluid Filtration and Separation, Beijing, 102249, PR China

article info

abstract

Article history:

Based on Aspen Plus, a methanol reforming Solid Oxide Fuel Cell - Humid Air Turbine -

Received 11 August 2018

Combined cooling, heating and power (SOFC-HAT-CCHP) system based on solar methanol

Received in revised form

reforming is built in this paper, which combines (Solid Oxide Fuel Cell) SOFC with (Humid

21 November 2018

Air Turbine) HAT power generation system. This paper analyzes the performance of SOFC-

Accepted 18 December 2018

HAT-CCHP system, and reveals the affinity of complementary utilization of solar energy

Available online xxx

and chemical energy. This paper optimizes the integrated design of the system and con-

Keywords:

show that the total power efficiency of the method, the system total exergy efficiency and

Methanol reforming

the thermal efficiency are 57.2%, 63.0% and 87.1% respectively. The results show that the

Water recovery

introduction of HAT power generation system has increased the power generation and

SOFC-HAT-CCHP

reduced the coal consumption rate. Compared with simple methanol reforming (Solid

EUD

Oxide Fuel Cell - Gas Turbine - Combined cooling, heating and power) SOFC-GT-CCHP, the

structs a steady state model of the system's thermal calculation. The calculation results

introduction of HAT effectively improves the total power generation efficiency of the system and increases 4.1% points. The exergy efficiency of increased by 4.6% points. Compared to the reference system, the standard coal consumption rate of electricity generated by the new system decreased by 16.6 g/kWh and the power generation increased by 15.5 g/kWh. © 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Introduction With the rapid development of the economy in recent years, developing efficient solar energy utilization technology is one of the effective ways to solve the problem of human energy. Coal is in the dominant position in China's energy consumption, and the energy structure with coal as the main body has caused serious environmental pollution. From the year 2000e2030, the growth rate of global electricity demand reached 2.4%. Although China's total energy volume is large,

its per capita energy volume is small. The new generation of power generation will be the combined cycle of burning natural gas. Energy is the lifeblood of the country's economy, and our country has also begun to implement stricter standards for pollutant emissions. The contradiction between energy and environment forces people to save energy and reduce consumption, rationally make resources and improve efficiency. Achieving the full use of energy is also a guarantee for the economic development of each country. Conventional energy use will produce a lot of pollution, and improving the

* Corresponding author. College of machinery and transportation engineering, China University of Petroleum, Beijing, 102249, PR China. E-mail address: [email protected] (H. Zhao). https://doi.org/10.1016/j.ijhydene.2018.12.129 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Zhao H, Hou Q, Thermodynamic performance study of the MR SOFC-HAT-CCHP system, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.129

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efficiency of existing energy use has become the top priority of our country's development. The demand for electricity in our country is increasing. The efficient and clean thermal cycle is an important direction for development, and thermal power generation mainly depends on coal resources (see, e.g., Ref. [1]) today. The combination of distributed energy and large power grids is the main direction of future power market development (see, e.g., Ref. [2]). In China, distributed cogeneration system has begun to take shape. Among them, the energy utilization rate of the coproduction system of Guangzhou University City is as high as 70%e80%., HAN Zhonghe, etc. (see, e.g., Ref. [3]) in North China University of Electric Power established indicators of primary energy efficiency, initial investment in systems and NOx emissions. The results of the evaluation show that distributed energy has advantages in energy and environmental benefits. However, the economic benefits need to be further improved. JIANG Shu and others (see, e.g., Ref. [4]) analyzed distributed systems in terms of their thermodynamic properties, but there was less evaluation of the combined benefits. The distributed energy economy, energy consumption and environmental benefits were evaluated comprehensively by DONG Fugui and others (see, e.g., Ref. [5]). The operating equipment of the distributed energy system mainly includes gas turbines, HRSG, steam turbines, solar power generation devices and other auxiliary equipment. Among them, aviation modifications have accounted for 10%e 20% of the total gas turbine unit capacity (see, e.g., Ref. [6]) in recent years. Solar energy will play an important role in energy composition (see, e.g., Ref. [7]). Solar power generation is the main way of using solar energy, and it is the fastest growing new energy power generation method. China is one of the countries with the most abundant solar energy resources in the world (see, e.g., Ref. [8]), which makes that the potential of solar energy utilization technology in our country is enormous. The design of the indirect reforming reactor for solar energy driven methane reforming has a thermal storage function, which makes the absorbing solar system by concentrating light and the chemical reaction system relatively independently (see, e.g., Ref. [9]). European CoMETHy (Compact Multifuel-Energy to Hydrogen converter) and other projects use indirect reforming reactors with molten salt as the intermediate working material (see, e.g., Ref. [10]). Dynamic model of packed bed reactor (see, e.g., Ref. [11]) and heat transfer coupled with reaction dynamic model (see, e.g., Ref. [12]) have been experimentally verified after proposed. Japanese researchers such as Prof. Kodama developed a fluidized bed solar thermal chemical coal gasification reactor (see, e.g., Refs. [13,14]). It is found that the reaction area of fluidized bed reactor is narrow in the experiment. The researchers proposed an internal circulating fluidized bed reactor (see, e.g., Refs. [15,16]) to equalize the temperature inside the fluidized bed, and reduce inert gas consumption. The research team of Xi'an Jiaotong University has studied on supercritical water gasification of solar-powered biomass in tube heat exchanger with temperature of 873 K (see, e.g., Refs. [17,18]) and an operating pressure of 240 bar. The advantage of supercritical biomass water gasification is that the operating temperature is relatively low. The French PROMES-CNRS researchers studied the use of Ce1-xZrxO2 in the thermochemical

cycle without sintering (see, e.g., Ref. [19]). Researchers at the Sandia National Laboratory in the United States used the CR5 reactor for the thermal chemical cycle of Cerium oxide solar energy to produce synthetic gas (see, e.g., Ref. [20]), and the peak efficiency of the reactor reached 0.3%. LIU Qibin and other researchers (see, e.g., Ref. [21]) developed a 5 kW solar energy heating and thermochemical conversion integrated hydrogen production experimental platform. The evaluation methods commonly used to compare the energy utilization performance of CCHP systems include primary energy consumption saving (PES) (see, e.g., Refs. [22,23]), fuel consumption saving rate (FESR) (see, e.g., Ref. [24]), energy utilization efficiency (see, e.g., Ref. [25]), exergy analysis methods and PURPA efficiency method (see, e.g., Ref. [26]). Fuel Cells (FC) have relative high energy conversion efficiency. Among them, SOFC (Solid oxide fuel cell) has developed most rapidly. The Humid Air Turbine (HAT) cycle is known as the 21st century's extremely potential thermodynamic cycle. Solid oxide fuel cells are mainly composed of cathode, anode, electrolyte and connecting materials in the physical structure. About research on the influence of SOFC and its performance and parameters, the commonly used method is to establish a mathematical model, using MATLAB, Aspen Plus and other methods. In order to further optimize the SOFC-GT system, two structural improvement methods were tried by (see, e.g., Ref. [27]) Penyarat et al. based on the previous research. The effects of air inlet and outlet temperature on the performance of the system were studied by LI He of Dalian University of Technology (see, e.g., Ref. [28]). The results show that there is an optimal fuel and air utilization rate to make the highest system efficiency. The high temperature exhaust of SOFC can be used to solve the shortcomings of the lack of supply of HAT circulating heat source if the SOFC is combined with the HAT cycle. Our research on fuel cells began in the 1950s, and the study of SOFC began in 1971. The Chinese state has introduced relevant policies to encourage research on fuel cells. Some scientific research units, colleges and universities have studied on key materials preparation process and integrated generation system for SOFC (see, e.g., Ref. [29]) and other aspects of research and exploration have been conducted. Salha (see, e.g., Ref. [30]) studied energetic and exergetic parametric study of a SOFC-GT hybrid power plant and heat recovery systems are adopted to valorize the waste heat at the SOFC and GT exhausts. Numerical simulation using EES software is performed. Obtained results show that the integration of the SOFC enhances significantly the hybrid overall cycle efficiency. While the pre-reforming fraction, has a positive effect on the indicated parameters. MENG Qingshan (see, e.g., Ref. [31]) proposed a combined power generation system which is based on SOFC/GT and trans-critical carbon dioxide cycle. The proposed system performance is evaluated by thermodynamic laws. Results indicate that the SOFC, TRCC and overall system electrical efficiencies are 49.21%, 29.14% and 69.26% under the designed conditions. The entrance pressures of expansion machine in TRCC also affect the performance of the combined power generation system. In recent years, there has been a lot of research on HAT cycle (see, e.g., Refs. [32,33]). It has medium cooling, postcooling, and reheating, which improves the environmental protection performance of the cycle (see, e.g., Ref. [34]). The

Please cite this article as: Zhao H, Hou Q, Thermodynamic performance study of the MR SOFC-HAT-CCHP system, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.129

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principle of the HAT cycle was proposed by Professor Mori of Japan in 1983. It has higher partial load efficiency, better variable performance, and high cyclic efficiency than other combined cycles (see, e.g., Refs. [35,36]). The saturator is the core component of the HAT cycle. Katagiri et al. studied the control system of AHAT (Advanced HAT) in 2007 (see, e.g., Ref. [37]). With the development of the HAT cycle, it is urgent to grasp its dynamic characteristics and its operating laws. Dynamic simulation research has important significance (see, e.g., Ref. [38]). In the commercial operation of the HAT cycle, there is a mismatch between the compressor and the turbine which can lead to congestion of the compressor. The overall performance of HAT gas turbine was studied theoretically by WEI Chenyu (see, e.g., Ref. [39]) based on the test of HAT cycle sub-shaft gas turbine test. It is pointed out that the variation of humid air content at the outlet of the humidifier has a great influence on the performance of the HAT cycle GT. ZHAO Pan and others (see, e.g., Ref. [40]) established the CAES (Compressed air energy storage) - HAT system. They use compressed heat and turbine exhaust heat to heat circulating water, and the performance of the system is analyzed and optimized. Due to the large amount of water required for the HAT cycle, the efficiency of the power supply is reduced. In order to take advantage of the exhaust heat, WANG Jiaying et al. in Xi'an Jiaotong University (see, e.g., Ref. [41]) proposed a kind of CAES-HAT CHP system. The waste heat is used by grade and the thermodynamic analysis of the key parameters of the system is also carried out. Shanghai Jiaotong University constitutes the HAT cycle sub-shaft gas turbine demonstration test device by installing an air humidification system (see, e.g., Ref. [42]). The saturator model established by CHEN Jinwei and others (see, e.g., Ref. [43]) avoided the use of heat transfer and mass transfer coefficients, and the model has high accuracy. The original compressor and turbine characteristics are not suitable for the modified HAT cycle and a proposal for improvement has been made. Battery technology mainly includes solar cells, fuel cells, chemical cells and nuclear cells. Solar cells continue to make breakthroughs in materials and processes (see, e.g., Ref. [44]) and its conversion efficiency continues to increase (see, e.g., Ref. [45]). But its working principle limits the use of batteries in weak light, and the nuclear battery has a nuclear radiation risk. SOFC do not use precious metals as catalysts, which has many advantages such as modular assembly and near-zero pollution (see, e.g., Refs. [46e48]). The H2 is so expensive that methanol reforming for H2 can be a good choice for SOFC. Raziye (see, e.g., Ref. [49]) has done study of the performance of dry methane reforming in a microchannel reactor. His study shows that this type of reactor has many advantages in terms of performance, compactness, and economic concerns. In this study, a microchannel reactor was designed, its catalytic performance in dry methane reforming (DRM) was assessed, and the results were compared with those observed in a conventional fixed bed reactor. Methanol steam reforming on catalyst coating by cold gas dynamic spray is studied by WANG Guoqiang (see, e.g., Ref. [50]). The activity of CGDS (Coating by cold gas dynamic spray) was superior to that of the same catalyst of Tubular Reactor. The highest methanol conversion of 90.45% was achieved on CGDS Coating.

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This paper presents a new type of MR SOFC-HAT-CCHP (Methanol reforming Solid oxide fuel cell - Humid air turbineCombined cooling, heating and power) distributed energy system. In the new system, several heat exchangers in the HAT cycle system can realize the rational energy ladder utilization. The heat of gas turbine exhaust in the system can be used more rationally by heat exchanger added in HAT. Humid air turbine has realized the increase of work capacity, and the equipment is relatively simple compared with the gas-steam combined system. The waste heat of the system can be recovered by absorption heat pump and refrigeration system to get reasonable cascade utilization. Combining the first and second law of thermodynamics, the simulation calculation and analyses have been down of SOFC-GT-CCHP and SOFCHAT-CCHP. The thermal performance of new system under different fuel flow is better than that of conventional system. We've done a lot of works on the SOFC and various types of GT CCHP systems before (see, e.g., Refs. [51,52]), and related experimental platforms are also being built. This article is based on the tubular SOFC developed by Siemens Westinghouse Power (SWP). The MR SOFC-HAT-CCHP combined circulatory system was established. It will provide a theoretical basis for the further use of the SOFC-HAT combined circulatory system in the future. Relying on the National Natural Science Foundation, a new tri-generation system is proposed. Based on the first and second laws of thermodynamics, the performances of the two systems are compared. The systems are SOFC-GT-CCHP (Methanol reforming SOFC-GT-CCHP System) and SOFC-HAT-CCHP (Methanol reforming SOFC-HATCCHP System) respectively.

System description The flow charts of the two systems are shown in Figs.1 and 2.

SOFC-CCHP system for regular gas turbine cycle (SOFC-GTCCHP) In Fig. 1 of SOFC - GT - CCHP system, solar energy as heat source of methanol (Fig. 1, stream No. 1), after the reaction to generate hydrogen and carbon monoxide (Fig. 1, stream No. 4), further improved the pressure (Fig. 1, stream No. 5), and in turn, pass preheater2 (Fig. 1, stream No. 6), preheater1 (Fig. 1, stream No. 7). The mixed gas (Fig. 1, stream No. 8) is as a SOFC anode fuels. Compressed air (Fig. 1, stream No. 14) goes into the air preheater2, preheater1 (Fig. 1, stream No. 16), and then to the battery cathode. Gas (Fig. 1, stream No. 9) are divided, one part (Fig. 1, stream No. 10) is mixed with gas (Fig. 1, stream No. 6). Another part (Fig. 1, stream No. 11) and air (Fig. 1, stream No. 17) enter the afterburner and then the high-temperature gas (Fig. 1, stream No. 12) enters the GT for power output. GT exhaust (Fig. 1, stream No. 18) is used to preheat air. The stream (Fig. 1, stream No. 19) is as the heat source of AR and HE.

The new combined system (SOFC-HAT-CCHP) As shown in Fig. 2 about MR SOFC-HAT-CCHP system, methanol (Fig. 2, stream No. 1) absorbs the low temperature solar energy to generate hydrogen and carbon monoxide syngas

Please cite this article as: Zhao H, Hou Q, Thermodynamic performance study of the MR SOFC-HAT-CCHP system, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.129

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Fig. 1 e Flow diagram of SOFC-GT-CCHP.

Fig. 2 e Flow diagram of SOFC-HAT-CCHP.

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(Fig. 2, stream No. 4), pressurized syngas (Fig. 2, stream No. 5) after preheater 2 (Fig. 2, stream No. 6). Then mixed with return fuel (Fig. 2, stream No. 10) from anode (Fig. 2, stream No. 7), pre reformed (Fig. 2, stream No. 8) as anode fuel into the SOFC. In the HAT subsystem, air (Fig. 2, stream No. 12) is compressed by air compressor (Fig. 2, stream No. 13) and cooled in the cooler (Fig. 2, stream No. 14). Afterwards, it comes into humidifier to increase humidity, in which the compressed air contacts with hot water (Fig. 2, stream No. 18) coming from the top of the humidifier in countercurrent to exchange heat and quality, and a part of the hot water evaporates (Fig. 2, stream No. 21). At the same time, most of the cooled water (Fig. 2, stream No. 19) flows out of the bottom of the humidifier to mix with supplemental water (Fig. 2, stream No. 16) for recycling after preheated (Fig. 2, stream No. 20). After the humidified air (Fig. 2, stream No. 21) leaves from the humidifier, it is preheated by the preheater 1 (Fig. 2, stream No. 22), preheater 2 (Fig. 2, stream No. 23) and then it goes into SOFC to participate electrochemical reaction. The exhaust (Fig. 2, stream No. 25) from the afterburner drives the turbine to do power generation (Fig. 2, stream No. 26). Several heat exchangers are used in SOFC-HAT circulation system to realize rational step utilization of energy. The rational arrangement of cooler and preheater can realize the step utilization of energy well and provide favorable conditions for high efficiency of circulation system. The electrochemical reaction between fuel and air in SOFC is finally converted to AC (alternating current). Gas (Fig. 2, stream No. 9) are divided, one part (Fig. 2, stream No. 10) is mixed with gas (Fig. 2, stream No. 6). Another part (Fig. 2, stream No. 11) and air (Fig. 2, stream No. 24) enter the afterburner and then the hightemperature gas (Fig. 2, stream No. 25) enters the GT for power output. GT exhaust (Fig. 2, stream No. 26) is used to preheat air (27) and then preheat the water. The stream (Fig. 2, stream No. 28) is as the heat source of AR and HE.

Injected water recovery and recycling system In the system of Fig. 2, the CO2 (Fig. 2, stream No. 45) in the gas turbine exhaust of the SOFC-HAT-CCHP system can be directly discharged into the atmosphere. The vapor in the exhaust condenses into liquid water (Fig. 2, stream No. 30), some (Fig. 2, stream No. 45) of which is released into the atmosphere or used in other systems, and the other part (Fig. 2, stream No. 15) is injected into the humidifier by circulating pumps as a source of water (Fig. 2, stream No. 16) for the HAT cycle. The organic combination of HAT and SOFC- CCHP is realized through the recycling of water resources. Compared with the general HAT system, water resources are recycled.

Performance models of the integrated system The model of SOFC-HAT-CCHP is established by FORTRAN. The calculated process is embedded in the ASPEN PLUS in this paper. Aspen Plus contains 50 unit modules (see, e.g., Ref. [53]), which can build the system flow required by the users. Since the Aspen Plus model of other components in the new circulatory system is easy to establish, this section focuses on the Aspen Plus model of the humidifier and SOFC. The thermodynamic parameters are shown in Table 1 to establish mathematical model.

(1) After the introduction of SOFC power generation and HAT power generation systems, the state parameters of other nodes remain unchanged. (2) The gas is an ideal gas and is evenly distributed. (3) The SOFC operating temperature is the same as the exit temperature, regardless of the mass loss of the gas in each component. (4) The temperature at the entrance of the compressor is 25
C, and the compressor inlet pressure is 100 kPa.

SOFC system performance calculation model The reorganization reaction, chemical and electrochemical reactions in SOFC are as follows. Methanol reforming: CH4O/CO þ H2

(1)

Water-gas shift reaction: CO þ H2O ⇔ CO2þH2

(2)

Electrochemical reaction: 2H2þO2/2H2O

(3)

The current can be calculated as follows according to the formula below. 
I ¼ 2  nH2 þ nCO  F  Uf

(4)

The n is the molar flow of the fuel component. F ¼ 96485.33 c/mol. Uf ¼ 0:85. The current density ic (mA/cm2) is obtained as follows. ic ¼

I mcell Acell

(5)

The mcell presents the numbers of SOFC monomers in the battery and Acell is the active surface area of SOFC monomer, cm2. The actual voltage of SOFC is as follows. VSOFC ðVÞ ¼ Vr þ DVT þ DVa þ DVp þ DVc

(6)

Vr (V), VT (V),DVa (V), DVp (V),DVc (V) can be obtained by formulas (7e11). Vr ¼ 0:72988 þ 2:00014  104 ic  9:668  107 ic þ 2:626 2

 1010 ic

3

(7)

DVT ¼ 8  106  ðT  Tr Þ  ic DVa ¼ 0:172 log

pH2 =pH2 o ðpH2 =pH2 OÞr

   DVp ¼ 0:076 log p pr

(8)

(9)

(10)

Table 1 e Parameters of main design points. Atmospheric temperature (
C) Atmospheric pressure (MPa) Operating pressure of SOFC (MPa) Running temperature of SOFC (
C) CH4O flow (mol/s) Mass flow of AIR (kg/s) Solar heating temperature (
C)

25 0.1 0.4 900 0.45 0.311 300

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 .   pO2 DVc ¼ 0:092 log pO2

(11)

r

Tr is for reference to the system temperature, 1000
C. ðpH2 =pH2 O Þr is 0.15. The reference pressure pr ¼ 100 kpa. The reference of pO2 is ðpO2 Þr ¼ 0.164 (see Fig. 3). The model has been verified by coke oven gas as an example which proves the reliability of process simulation. The composition of methanol reforming gas is similar to that of coke oven gas. Table 2 shows the SOFC monomer model running parameters and operating conditions, by indirect method for the change trend of SOFC output voltage under different current density, and compared with the experimental results in literature (see, e.g., Ref. [54]), the result is shown in Fig. 4. The calculation result of indirect calculation is consistent with the experimental values. Compared the results of our model with the value in the literature, the results of the calculation of 120 kW straight abortion work is compared with those in the literature (see, e.g., Refs. [55,56]). The results were listed in Table 3. The calculation results are consistent with the literature data, and the model can be used to simulate the whole SOFC-CCHP composite system. About the methanol reforming, we took the following experiment for an example as the condition defined to

Fig. 3 e Comparison of the simulated results with experimental data to validate the model. (a) Flowchart of humidifier (b) Aspen Plus model of humidifier. Table 2 e Simulation parameters and operating conditions for the SOFC model. Parameters Geometry parameters Cell length (mm) Cell diameter (mm) Cell wall thickness (mm) Single cell active area (cm2) Composition of the gas Anode (%) Cathode (%) Operating conditions Operating temperature T (
C) Pressure of the SOFC p (bar) Fuel utilization factor Uf

Values 1500 22 2 834 H2 (89), H2O(11) O2 (21), N2 (79) 1000 1.08 0.85

Fig. 4 e Flowchart and Aspen Plus model of humidifier. (a) The variation of outlet wet-air temperature (b) The variation of outlet water temperature (c) The variation of outlet wet-air relative humidity (d) The variation of outlet wet-air specific humid.

certificate the validation of methanol calculated by ASPEN PLUS. Table 4 shows the comparison between the experimental results and the simulation results under the equilibrium state. By using ASPEN PLUS for chemical equilibrium calculation, the mass flow controller of methanol and deionized water was used to measure, and the average composition of methanol aqueous solution (methanol: water mass ratio ¼ 1:1) was used to determine the quantity of reactants. It can be seen that the measured concentration is quite consistent with the equilibrium calculation. The difference between the numerical values can be explained to a great extent by the slight difference between the actual methanol aqueous solution and the simulated data. This indicates that methanol can be converted into hydrogen effectively and the performance of the reformer is also good. Because the simulation is

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Table 3 e 120 kW direct current output of the SOFC model simulation results. Parameters

Ref. [55]

Ref. [56]

Indirect prediction

0.70 178 19 809

e 180 e 823

0.694 180 19.21 810

834 120 52

847 120 50

805 120.6 52.09

Voltage of SOFC (V) Current density (mA/cm2) Utility of air (%) Preformer outlet temperature (K) SOFC outlet temperature (K) Power output (kW) (%)

Table 4 e Measured (dry basis) reformate gas composition compared to equilibrium calculation. Measured

Equilibrium

Absolute error

68.59% 27.22% 0.72% 3.47%

72.47% 25.41% 1.14% 0.98%

3.88% 1.81% 0.42% 2.49%

H2 CO2 CO Others

calculated based on pure methanol, it is impossible to be 100% methanol in practice, but the proportion of methanol is higher than 99%, and the composition of methanol decomposition is not much different. While the difference of other components is relatively large, because the proportion is small and the absolute difference is not large. And the simulation is 100% perfectly balanced, and in practice and in practice it's dynamic, the composition of the reaction is related to residence time, just as close to the equilibrium as possible (see Table 5).

Performance evaluation indicators of the humidifier system The flowchart of the humidifier and its Aspen Plus model are shown in Fig. 4. In the picture, the solid line represents the logistics. Logistics 14 (Fig. 4, stream No. 14) is for air cooled by cooler, and the logistics 18 (Fig. 4, stream No. 18) is for hot water heated by the cooler from logistics 17 (Fig. 4, stream No. 17). The logistics 21 (Fig. 4, stream No. 21) is for the humid air

made in the humidifier, and the logistics 19 (Fig. 4, stream No. 19) is for the exit water. In the humidifier, hot water from the top comes in direct contact with low temperature air entering from the bottom, which is heated and humidified. Hot water is cooled and partially evaporated, while unevaporated water flows from the bottom of the humidifier as circulating water continues. The humidifier has two main functions: one is to increase the working mass flow, increase the specific work. The second is to reduce the circulating water temperature and recover the heat at low temperature to improve the thermal efficiency of the system (see, e.g., Ref. [57]). The thermal performance of humidifier is measured by the temperature of outlet humid air (T21), outlet water (T19) and the specific humidity of outlet humid air (d). Temperature in
C and specific humidity in g/kg dry air. d ¼ 622

4ps p  4ps

(12)

In the formula, 4 is the relative humidity of the air, ps is the separation pressure of water vapor in saturated humid air. p is the total pressure. Within 2 MPa, it can be approximated that the water vapor partition pressure and water vapor density in saturated air are independent of the humid air pressure. They depend only on the temperature of the humid air (T21). Humidifier outlet humid air temperature is (see, e.g., Ref. [58]) as follows. T21 ¼ T14 þ DT

(13)

In the formula, T14 is the air wet ball temperature entering the humidifier; DT is at least 4 K.

Performance evaluation indicators of the system SOFC power output is as follows in type (14): WSOFC ¼ hDA  VSOFC  ISOFC

(14)

DC-AC conversion efficiency is that hDA ¼ 0.92. SOFC power generation efficiency: hSOFC ¼

wSOFC qCH4  LHVCH4 O

(15)

The total power efficiency of the system: he ¼

Table 5 e Model validation of humidifier. Known Parameter

Unit

Value

C kg/s bar
C kg/s kg water/kg dry air
C

68 2.19 8.16 147 3.27 0.007 73




Inlet air temperature Inlet air flow rate Inlet air pressure Inlet water temperature Inlet water flow rate Inlet air specific humidity Outlet water temperature

Error analysis Output Parameter

Unit

Simulation value

Experimental value [59]

Relative error/%

Outlet air temperature Outlet air flow rate Outlet water flow rate




C

119.7

118

1.44

kg/s

2.594

2.57

0.93

kg/s

2.866

2.89

0.83

WSOFC þ WGT  WAC qCH4 O  LHVCH4 O

(16)

The thermal efficiency: ht ¼

wSOFC þ WGT  WAC þ QC þ QH qCH4 O  LHVCH4 O

(17)

System exergy efficiency: hexe ¼

ExSOFC þ ExGT  ExAC þ ExC þ ExH ExCH4 O þ ExSOLAR

(18)

Study on the performance of the key component d humidifier In this section, the model validation of the humidifier, thermal performance of the humidifier, influence of inlet air

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temperature on the thermal performance of the humidifier have been done. They are described as follows.

Model validation of the humidifier In this paper, the humidifier model is established in Aspen Plus. And according to the experimental data form the literature (see, e.g., Ref. [59]), the correction of the humidifier model is verified. The results of the Aspen Plus simulation of the humidifier show that: under the same import conditions, the relative errors of the humidifier outlet air temperature, the outlet air flow and the outlet water flow are all within 1.5%. It can meet the precision requirement for calculation.

Thermal performance of the humidifier The thermal performance of the humidifier is mainly measured by outlet humid air temperature, outlet water temperature, and outlet humid air specific humidity. Table 6 shows the thermal performance parameter of the humidifier under certain conditions.

Influence of inlet air temperature on the thermal performance of the humidifier Known condition: the theoretical plate number is 4; the operation pressure is 4 bar, the inlet water temperature is 100
C. The inlet water flow is 2.162 kg/s. Fig. 5(a) shows that the temperature of the humid air at the outlet varies with the increase of the inlet air flow at different inlet air temperatures. As you can see from the picture, the effect of inlet air temperature on outlet humid air temperature is not significant under different inlet air flows. The temperature of the outlet humid air dropped with the increase of inlet air flow. Fig. 5(b) shows that the temperature of outlet water changes with the increase of the inlet air flow at different inlet

Table 6 e Thermal performance parameters of humidifier under certain condition. (a) Input parameter Input Parameter Theoretical plate number Inlet water temperature Inlet water flow rate Inlet air temperature Inlet air flow rate Humidifier running pressure (b) Output Parameter Output Parameter Outlet humid air temperature Outlet humid air flow rate Outlet humid air relative humid Outlet water temperature Outlet water temperature flow rate Steam sub-pressure of saturated humid air Outlet humid air specific humidity

Symbol

Value

N T18 G18 T14 G14 p

4 100 2.162 70 0.311 0.4

Symbol

Value

T21 G21 RH T19 G19 ps d

98.7 0.368 0.398 85.1 2.105 0.4 186.283

Unit piece C kg/s
C kg/s MPa


Unit


C kg/s 1
C kg/s MPa g/kg dry air

air temperatures. As you can see from the picture, the temperature of the outlet water dropped accordingly with the increase inlet air flow when the air temperature of the inlet is fixed. When the air temperature of the inlet is 70
C, the outlet water temperature was reduced from 116.6
C to 81.7
C with the increase inlet air flow from 0.05 kg/s to 0.4 kg/s. The higher the inlet air temperature, the higher the temperature of the outlet water will be when the inlet air flow is constant. And the larger the inlet air flow, the larger the outlet water temperature increases will be with the increase of the inlet air temperature. When the inlet air flow is 0.2 kg/s, the outlet water temperature increased from 89.3
C to 90.5
C, only 1.2
C increased, as the inlet air temperature increased from 30
C to 90
C. When the inlet air flow is 0.4 kg/s, the outlet water temperature increased from 80.1
C to 82.4
C, 1.2
C increased, as the inlet air temperature increased from 30
C to 90
C. Fig. 5(c) shows that the outlet humid air relative humidity changes with increase of the inlet air flow at different inlet air temperatures. Inlet air temperature has little effect on the outlet humid air relative humidity under different inlet air flows. With the increase of inlet air flow, the relative humidity of the outlet humid air increases accordingly. Fig. 5(d) shows that specific humid of outlet humid air varies with the increase of inlet air flow at different inlet air temperatures. Inlet air temperature has little effect on the specific humid of outlet humid air under different inlet air flows. The specific humid of the outlet humid air is reduced accordingly with the increase of inlet air flow. In order to improve the thermal performance of the humidifier, it is also necessary to consider the reasonable matching of the operating pressure and the number of theoretical plates of the humidifier under the condition of mass balance and energy balance. It has been analyzed in previous studies and will not be discussed in detail here.

Results and discussions In the study of SOFC-HAT-CCHP system, the effects of fuel flow and fuel utilization on the total power of the system, the system power generation efficiency, the total thermal efficiency of the system, and the total system exergy efficiency were selected. The simulation conditions of the new system are shown in Table 7. Table 8 shows the thermodynamic parameters corresponding to each node of the new system. Table 9 is the thermodynamic parameters corresponding to each node of the reference system. In the tables, the component of CH4O þ H2O is 50% CH4O þ50% H2O in molar percent. The AIR is 79% N2 þ21% O2 in molar percent. The component of syngas and exhaust is determined by the inlet and the operation of the facility.

The effect of operating pressure on system performance SOFC operating pressure determines the GT production work and the pressure of the SOFC performance of the system is very important for the composite with GT. Battery operating pressure will affect the performance of the system, given in Figs. 6e8, in which the range of operating pressure is

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9

Fig. 5 e The variations of parameters of humidifier with inlet air flow at different inlet air temperature.

Table 7 e Conditions of simulation for the system. Items Component of reformed methanol Operating temperature Operating pressure Fuel flow rate Water injection Fuel utilization factor DC Active surface area Water injection inlet temperature Fuel inlet temperature Air inlet temperature Compressor adiabatic efficiency Turbine adiabatic efficiency S/C Heat loss of SOFC Afterburner efficiency Pressure loss of SOFC Efficiency of DC to AC Compressor mechanical efficiency Turbine mechanical efficiency The coefficient of AR

Values H2 (12.5%), CO(87.5%) 900
C 400 kPa 0.45 mol/s 0.029 kg/s 0.85 134 kW 96.1m2 (1152 cells) 25
C 25
C 25
C 0.9 0.9 2.5 2% 100% 0 0.92 0.99 0.99 0.7

0.1e0.8 MPa. Actual operating pressure depends on the material development SOFC. As shown in Fig. 6, the effect of the operating pressure on each voltage component in MD-SOFC is given. It is the same change trend with MR-SOFC. DVp and DVa are 0.728 V and 0.184 V. DVa and DVc decreased slowly from 0.00593 V to 0.00060 Ve0.00589 V and 0.00075 V. DVp increased from 0 V to 0.07 V. Fig. 7 is the effect of the operating pressure on the SOFC performance in MD-SOFC system. The variation trends of SOFC performance are the same as those in MR-SOFC. As the operating pressure increases from 0.1 MPa to 0.8 MPa, the SOFC output voltage increased from 0.55 V to 0.62 V. The current density keeps the constant of 230.40mA/cm2, slightly lower than that in the MR-SOFC. Fig. 8 is the effect of the operating pressure on SOFC AC power and system net power output in MD-SOFC system. The change trend of SOFC AC power and system net power is the same as that in MR-SOFC. WSOFC increased from 112.05 kW to 125.75 kW, hSOFC was increased from 32.48% to 36.45%. WNW decreased from 112.05 kW to 61.51 kW, he was decreased from 29.49% to 16.19%.

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Table 8 e Results of simulation for SOFC-HAT-CCHP system. Stream no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Flow rate

Pressure

Temperature

h

s

exe

kg/s

kPa

K

kJ/kg

kJ/(kg$K)

kJ/kg

Com ponents

0.014 0.014 0.014 0.014 0.014 0.014 0.062 0.062 0.08 0.048 0.033 0.311 0.311 0.311 0.029 0.029 0.634 0.634 0.606 0.606 0.340 0.340 0.340 0.322 0.354 0.354 0.354 0.354 0.354 0.354

100 100 100 100 400 400 400 400 400 400 400 100 400 400 100 400 400 400 400 400 400 400 400 400 400 100 100 100 100 100

298.1 336.9 573.1 473.1 722.6 500 957.9 983.6 1173.1 1173.4 1173.4 298.1 457.6 368.1 298.1 298.2 352.9 362.7 339.3 355.5 357.1 381.1 852.2 1173.2 1283.3 967.9 546.6 437.4. 374.6 313.1

7530.5 7254.1 2695.2 2971.6 2277.4 2897.3 7590.0 7590.0 9011.5 9011.5 9011.5 0.279 161.95 70.25 15972 15972 15723 15678 15785 15711 1180.2 1153.9 512.6 169.5 987.49 1408.3 1927.5 2053.6 2125.0 2423.2

7.788 6.942 5.083 4.553 4.650 3.626 2.157 2.161 1.27 1.27 1.27 0.151 0.187 0.04 9.32 9.32 8.56 8.43 8.74 8.52 0.18 0.109 0.809 1.192 1.331 1.38 0.679 0.422 0.246 0.658

5208.5 5184.2 4210.6 4329.0 3663.9 3978.3 8233.0 8234.1 9390.0 9390.0 9390.0 45.34 106.13 80.90 13193 13193 13172 13165 13181 13170 1026.4 1021.3 753.9 524.9 1384.3 1819.7 2130.0 2179.4 2198.3 2226.9

CH4O þ H2O Syngas Syngas Syngas Syngas Syngas Syngas Syngas Syngas Syngas Syngas AIR AIR AIR H 2O H 2O H 2O H 2O H 2O H 2O AIR þ H2O AIR þ H2O AIR þ H2O AIR þ H2O Exhaust Exhaust Exhaust Exhaust Exhaust Exhaust

h

s

exe

Components

Table 9 e Results of simulation for SOFC- GT -CCHP system. Stream no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Flow rate

Pressure

Temperature

kg/s

kPa

K

kJ/kg

kJ/(kg$K)

kJ/kg

0.014 0.014 0.014 0.014 0.014 0.014 0.062 0.062 0.08 0.048 0.033 0.325 0.311 0.311 0.311 0.311 0.293 0.325 0.325 0.325 0.325

100 100 100 100 400 400 400 400 400 400 400 400 100 400 400 400 400 100 100 100 100

298.1 336.9 573.1 473.1 722.6 500 957.9 983.6 1173.1 1173.4 1173.4 1302.1 298.1 457.6 484.1 793.1 1173.1 975.5 707.0 374.6 313.1

7530.5 7254.1 2695.2 2971.6 2277.4 2897.3 7590.0 7590.0 9011.5 9011.5 9011.5 45.8 0.279 161.95 189.4 519.8 958.3 452.1 767.8 1132.5 1261.9

7.788 6.942 5.083 4.553 4.650 3.626 2.157 2.161 1.27 1.27 1.27 1.391 0.151 0.187 0.246 0.772 1.204 1.438 1.060 0.366 1.548

5208.5 5184.2 4210.6 4329.0 3663.9 3978.3 8233.0 8234.1 9390.0 9390.0 9390.0 460.5 45.34 106.13 116.2 289.6 599.2 880.8 1083.9 1241.6 800.5

However, high operating pressure will result in high SOFC costs and gas turbine system costs. In actual industrial production, the SOFC system still has a long time to optimize the appropriate operating pressure.

CH4O þ H2O Syngas Syngas Syngas Syngas Syngas Syngas Syngas Syngas Syngas Syngas Exhaust AIR AIR AIR AIR AIR Exhaust Exhaust Exhaust Exhaust

The effect of current density on system performance In this section, the change of current density is realized by adjusting fuel flow rate and fuel utilization rate while keeping

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Fig. 6 e Effect of the operating pressure on voltages of the SOFC.

Fig. 7 e Effect of the operating pressure on performance of the SOFC.

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Fig. 9 e Effect of the current density on voltage and power of the SOFC stack (a).

utilization rate increases, the current density will increase accordingly, leading to increased polarization voltage and decreased SOFC voltage. It can be seen from Fig. 9 that the power of the fuel cell decreases with the increase of current density, which is because the current and voltage decrease, SOFC power decrease and battery efficiency decrease with the unchanged fuel utilization factor. As shown in Fig. 10, the change of current density is achieved by adjusting fuel flow rate. As the current density increased from 12.80 mA/cm2 to 64.02 mA/cm2, the battery voltage decreased from 0.768 V to 0.736 V, and the output power of the battery increased from 34.75 kW to 166.58 kW. As shown in Fig. 10, changes in current density can be achieved by adjusting fuel utilization. As the current density increased from 40.67 mA/cm2 to 64.39 mA/cm2, the battery voltage decreased from 0.755 V to 0.730 V, and the output power of the battery increased from 108.61 kW to 166.26 kW.

The effect of fuel flow on system performance The change of the fuel flow directly affects the change of battery current density so the change of the fuel flow will

Fig. 8 e Effect of the operating pressure on performance of electricity power of the SOFC. the effective area of the battery unchanged. Figs. 9 and 10 show the effect of current density changes on SOFC voltage and output power by adjusting fuel flow and fuel efficiency, respectively. When the effective area of the battery remains unchanged, SOFC electrode reaction area remains constant. However, as the fuel flow rate of the battery or the fuel

Fig. 10 e Effect of the current density on voltage and power of the SOFC stack (b).

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affect the performance parameters of the whole system. The effects of fuel flow on system performance are shown in Figs. 11e13. The study range of fuel flow from 0.1 to 0.55 mol/s. The higher fuel flow means that more chemical energy will be converted into electricity which produces more electricity. Fig. 11 is the influence of fuel flow on the system performance. As fuel flow increased from 0.1 to 0.55 mol/s, the output voltage of SOFC decreased from 0.74 to 0.54 V and the current density increased rapidly from 51.20 mA/cm2 to 281.60 mA/cm2. SOFC efficiency, total electrical efficiency and total thermal efficiency of the system are decreased from 43.69%, 60.49% and 89.20%e31.79%, 55.66% and 86.76%. Fig. 12 is the effect of fuel flow on SOFC AC power, HAT network and total power of the system. It can be seen from the diagram that the WSOFC ,WNetHAT and Ptotal respectively increased by 100.54 kW, 106.88 kW and 206.92 kW with the increase of the fuel flow, from 33.50 kW, 17.58 kW and 51.08 kW to 134.04 kW, 124.46 kW and 258.50 kW. With the fuel flow increases, the overall system power efficiency decreases although the system total power output increases. Due to the increase of air volume provided by the simulation system, WAC and WFC will be increased as fuel flow increases.

Fig. 11 e Effect of the fuel flow rate on current density, voltage of SOFC and efficiency.

Fig. 12 e Effect of the fuel flow rate on electricity power.

The ultimate product of the efficient SOFC-HAT-CCHP system is the simultaneous output of a certain amount of cooling, heating and power. The total electric power, refrigerating capacity and heat output in the system are increased in the same manner as shown in Fig. 13. With the increase of fuel flow, the total system power Ptotal , the heat supply QH and the refrigerant QC increased by 206.92 kW, 78.77 kW and 41.45 kW. As the fuel flow increases, the system's total energy supply increased by 327.65 kW. The increase of the total energy supply of the system is less than the increase of the ideal condition. The total thermal efficiency of the system decreases with the increase of fuel flow.

The effect of fuel utilization on system performance Fuel utilization factor ðUf Þ is an important parameter of the fuel cell system evaluation which has a significant impact on the performance of SOFC-HAT-CCHP system. Because of the balance of chemical reactions, the fuel that enters the SOFC is not completely transformed and it is why the afterburner in the system is set up. Figs. 14e16 shows the effect of Uf on SOFC-HAT-CCHP system, the Uf change interval is 0.60e0.95. Fig. 14 shows the effect of Uf on system performance and it can be seen from the figure that as Uf increases from 0.6 to 0.95, SOFC output voltage decreased from 0.656 V to 0.563 V and the current density increased rapidly from 162.63 mA/cm2 to 257.50 mA/cm2. The SOFC efficiency and total power efficiency of the system were respectively increased from 0.273 to 0.533 to the maximum 0.376 and 0.589. The total thermal efficiency of the system is basically unchanged, which is about 0.871. Fig. 15 shows the effect of Uf on the power of equipment in the system. It can be seen from the figure that when the fuel utilization factor changed from 0.60 to 0.95, WSOFC and Ptotal increased to a maximum of 129.8 kW and 224.0 kW from 94.4 kW to 202.5 kW, WNHAT were reduced from 108.1 kW to the minimum of 94.2 kW. The higher the fuel utilization factor, the higher the WSOFC (SOFC AC) output will be. As can be seen from the figure, total power Ptotal and WSOFC change for the same trend, with higher fuel utilization. The change trend of WNHAT is opposite to that of WSOFC .

Fig. 13 e Effect of the fuel flow rate on cooling, heating and power.

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Fig. 14 e Effect of the fuel utilization factor on performance of the system.

Fig. 16 e Effect of the fuel utilization factor on cooling, heating and power.

Table 10 e Energy analysis results for distributed energy system.

Energy input/kW Solar energy Methanol Energy output/kW Power Heating Cooling Energy loss/kW Others Refrigeration Ex-smo he /% ht /% m/(g/kWh)

SOFC-GT-CCHP

SOFC-HAT-CCHP

75.8 304.2

75.8 304.2

201.8 42.1 83.1

217.3 73.0 40.6

4.9 35.6 12.5 53.1 86.0 231.3

4.9 17.4 26.8 57.2 87.1 214.8

Fig. 15 e Effect of the fuel utilization factor on electricity power.

The total electric power, refrigerating capacity and heat output in the system are increased in the same manner as shown in Fig. 16. From the figure, it can be seen thatPtotal , QC and WSOFC have the same trend. The trend of QH and Ptotal are opposite. With the increase of Uf , the total system power Ptotal and the refrigerant QC increased from 202.5 kW to 34.0 kWe224.0 kW and 42.9 kW. The heat supply QH decreased from 95.4 kW to 64.3 kW.

Optimization of energy analysis Energy balance and thermal efficiency of the systems are shown in Table 10. In the system of SOFC-HAT-CCHP, solar energy and HAT cycle are introduced to effectively utilize the low temperature heat source and waste heat. The power generation efficiency of SOFC-GT-CCHP and SOFC-HAT-CCHP system are 53.1% and 57.2% respectively. The thermal efficiency of the two systems are 86.0% and 87.1% respectively. The standard coal consumption rates are 231.3 g/kWh and 214.8 g/kWh respectively.

Fig. 17 shows the total power output, refrigerating capacity and heat output of the two systems. It can be seen from the figure that in the range of 0.1e0.55 mol/s, the total power generation and heat supply of the SOFC-HAT-CCHP system is higher than that of SOFC-GT-CCHP. And it increases with the increase of fuel flow. The gap ranges from 2.80 to 18.43 kW and 8.19e39.95 kW respectively. As the fuel flow increases from 0.1 mol/s to 0.55 mol/s, the total power generation and heat supply of the new system increased from 51.1 kW to 15.9 kWe258.5 kW and 94.6 kW respectively. The total power generation and heat supply of the reference system increased from 48.3 kW to 7.7 kWe240.0 kW and 54.7 kW respectively. SOFC-HATCCHP system refrigeration is lower than SOFC-GT-CCHP, and it increases with the increase in fuel flow. The gap ranges from 2.80 to 18.43 kW. Fig. 18 shows the total power efficiency, total thermal efficiency and fuel consumption rate of the two systems. It can be seen from the figure that in the range of 0.1e0.55 mol/s, the total power efficiency of the SOFC-HAT-CCHP system is higher than that of SOFC-GT-CCHP. And the fuel consumption rate of

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Table 11 e Exergy analysis results for distributed energy system.

Fig. 17 e Effect of the fuel flow rate on cooling, heating and power of the two systems.

Exergy input/kW Solar energy Methanol Exergy output/kW Power Heating Cooling Exergy loss/kW SE FC SOFC GT Afterburner Ex-smo HTR hexe /%

SOFC-GT-CCHP

SOFC-HAT-CCHP

41.6 322.7

41.6 322.7

201.8 5.1 5.7

217.3 9.4 2.8

26.9 0.8 13.3 20.2 15.4 1.4 73.7 58.4

26.9 0.8 13.2 24.4 28.6 3.0 37.9 63.0

Fig. 19 e Exergy analysis of the SOFC-GT-CCHP. Fig. 18 e Effect of the fuel flow rate on performance of the two systems.

the new system is lower than that of the reference. Total thermal efficiency of the SOFC-HAT-CCHP system is higher.

Exergy analysis of the system Exergy balance and exergy efficiency of the two systems are shown in Table 11. The exergy efficiency of the new system is higher than that of SOFC-GT-CCHP and their exergy efficiency are of 63.0% and 58.4% respectively at the designed condition. Exergy loss in detailed and each part of the two systems in proportion to the total exergy loses are shown in Figs. 19 and 20. Major parts of exergy loss in SOFC-GT-CCHP system are respectively HTR 73.7 kW, SE 26.9 kW and GT 55.2 kW. The proportions to the total loss are respectively for 48.6%,17.7% and 13.3%. Major parts of exergy loss in SOFC-HAT-CCHP system are respectively HTR 37.9 kW, Afterburner 28.6 kW and SE 26.9 kW. The proportions to the total loss are respectively for 28.1%,21.2% and 20.0%.

Fig. 20 e Exergy analysis of the SOFC-HAT-CCHP. The power output of the SOFC-HAT-CCHP system increases compared with SOFC-GT-CCHP system. GT exhaust is further used to power generation. Exergy loss of exhaust gas is reduced much more to make less exergy loss of the system.

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Fig. 21 e Comparison of exergy loss of each subsystem. Fig. 23 e EUD analysis of SOFC-HAT-CCHP.

Conclusion

Fig. 22 e EUD analysis of SOFC-GT-CCHP.

The exergy losses of each subsystem in the two systems are shown in Fig. 21.

EUD analysis To further study the exergy loss, energy flow and energy level in both systems, overall exergy loss of every component of the system is presented more visually through the UED (Energy Utilization Diagram) diagram. The area between the energy donor (Aed) and the energy acceptor (Aea) can clearly indicate the loss of each component. Figs. 22 and 23 are EUD images of SOFC-GT-CCHP and SOFC-HAT-CCHP systems respectively. As shown in Fig. 16, the largest part of the loss is in the loss of heat transfer, SOFC and the afterburner. Other parts have relatively small losses, such as the compressor and GT. As shown in Fig. 23, the losses are relatively evenly distributed. Although the addition of humidifiers and heat exchangers have a relatively greater loss, the exergy loss of heat transfer, SOFC exergy loss and the loss of fuel in the afterburner were greatly reduced. And the loss of other parts is relatively small, such as compressor and GT.

Based on the first and second laws of thermodynamics, a new CCHP generation system (SOFC-HAT-CCHP) is proposed. The thermodynamic properties such as fuel flow and fuel utilization factor to the system are studied. Turns out, the total power efficiency, total exergy efficiency and total thermal efficiency in the new system are 57.19%, 63.00% and 87.09% respectively. More chemical energy can be converted into electricity when the fuel flow is from 0.1 to 0.55 mol/s. With the increase of current density, the voltage, SOFC efficiency and total electrical efficiency are decreased linearly. Fuel utilization factor is an important influence parameter and has a significant influence on system performance. Uf is 0.95 at the simulation condition. The efficiency of the SOFC, total power efficiency and total thermal efficiency in the new system are 37.60%, 58.95% and 87.16% respectively. Compared to just SOFC-GT-CCHP, the introduction of HAT system effectively increased the total power efficiency of the system by 4.1% points. The combining with HAT system can reduce coal consumption effectively, save fossil energy which is drying up and promote the development of renewable energy. At the same time, the exergy efficiency of the system increased by 4.6% points. Compared to SOFC-GT-CCHP, the standard coal consumption rate of SOFC-HAT-CCHP was reduced by 16.56 g/kWh, power output increased by 15.5 kW. The new system proposed in this paper is an effective energy utilization method. The power efficiency is greatly improved. In the new system, several heat exchangers in the HAT cycle system can realize the rational energy ladder utilization. The heat of gas turbine exhaust in the system can be used more rationally by heat exchanger added in HAT. Humid air turbine has realized the increase of work capacity, and the equipment is relatively simple compared with the gas-steam combined system. The waste heat of the system can be recovered by absorption heat pump and refrigeration system to get reasonable cascade utilization. We will continue to studies SOFC power systems for CCHP. To analyze the economical and exergy economical property, and the systems

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will be combined with CLC (Chemical Looping Combustion) to solve the problem of carbon accumulation.

Acknowledgments The Project supported by National Natural Science Foundation of China No. 51274224.

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.ijhydene.2018.12.129.

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Nomenclature Acell: The active area of one single cell AR: Absorption refrigeration CHP: Combined heating and power CCHP: Combined cooling, heating and power COP: Coefficient of performance EUD: Energy Utilization Diagram ENernst: Nernst voltage (V) Ex-smo: Exhaust smoke F: Faraday's constant (96485.33 c/mol) FC: Fuel compressor GT: Gas turbine HAT: Humid Air Turbine HC: Heater consumer HE: Heat exchanger HTR: Heat transfer and others I: Current of the SOFC (A) ic: Current density (mA/cm2) mcell: The total cell numbers MR: Methanol reforming SOFC-GT-CCHP: Methanol reforming SOFC-GT-CCHP System SOFC-HAT-CCHP: Methanol reforming SOFC-HAT-CCHP System P: Actual operating pressure of SOFC (MPa) pr: Reference pressure (kpa) PTC: Parabolic trough solar collector qCH4 O : The flow rate of the CH4 O (mol/s) RC: Refrigeration Consumer SE: Solar energy SC: Solar collector SOFC: Solid Oxide Fuel Cell T: Actual operating temperature of SOFC (
C) Tr : Reference temperature (
C) Uf : Fuel utilization factor DVa : The effect of flow composition in anode on SOFC voltage (V) DVc : The effect of flow composition in cathode on SOFC voltage (V) DVp : The effect of operating pressure on voltage (V) Vr : Reference voltage of SOFC (V) VSOFC : Voltage of SOFC by direct calculation (V) DVT : The effect of temperature on the voltage (V) WAC: Air compressor power consumption (kW) WGT: Power of gas turbine (kW) WSOFC: The AC power of cell stack (kW) WSP: Pump power consumption (kW) Greek letters h: Efficiency hact;a : Activation polarization of anode (V) hact;c : Activation polarization of cathode (V)

Please cite this article as: Zhao H, Hou Q, Thermodynamic performance study of the MR SOFC-HAT-CCHP system, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.129

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hohm : Ohmic polarization (V) hcon;a : Concentration polarization of anode (V) hcon;c : Concentration polarization of cathode (V) hDA : The efficiency of direct current converting to alternating current hSOFC : The efficiency of SOFC he : The total power efficiency of system

hexe : The total exergy efficiency of system Subscripts r: Reference system t: Total

Please cite this article as: Zhao H, Hou Q, Thermodynamic performance study of the MR SOFC-HAT-CCHP system, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.129