Thermodynamic and dynamic analysis of a hybrid PEMFC-ORC combined heat and power (CHP) system
Xinyu LuBanghua DuWenchao ZhuYang YangChangjun XieZhengkai TuBo ZhaoLeiqi ZhangJié SongZhanfeng Deng
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Keywords:
Exergy efficiency
Organic Rankine Cycle
Electrical efficiency
From the characteristics of waste heat in exhaust,cooling water and lubricant,a new thermodynamic cycle for waste heat recovery of vehicle engines was proposed. The present system consists of two cycles,organic Rankine cycle (ORC) for recovering the waste heat in high-temperature exhaust and lubricant and Kalina cycle for recovering the waste heat in low-temperature cooling water. Based on P-R equation of state,the thermodynamic performance of the cycle was theoretically calculated with a self-written computing program. Then the overall performance of the cycle with different organic working fluids was analyzed individually. Compared with the conventional cycle configuration used for only recovering the exhaust heat,the present cycle has higher waste heat recovery efficiency. The overall efficiency of the cycle with cyclopentane and R113 is 20.83% and 16.51%,respectively.
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Eight kinds of cycle media in organic Rankine cycle(ORC) were compared during the thermodynamic process.Considering the systemic,reliable and environmental factors,R245fa was the optimum selection for ORC.For the application of Cummins heavy duty vehicle engine,the power generation system with the waste heat recovery was designed.Recovering the heat from charge air,tail pipe gas and exhaust gas,the power generation was realized.The efficiency of waste heat recovery in the system was 10.4%.
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The organic Rankine cycle (ORC) system, which recovers the engine waste heat, can improve the energy utilization of the engine. This paper analyzed basic ORC and superheat ORC using R123 as working fluid, respectively. The results show that superheating the working fluid cannot gain the output power or improve the system efficiency effectively, while increase the irreversible loss of the system. Meanwhile superheat ORC system induces that the engine waste heat cannot utilize fully. So superheat ORC system is not fit for the engine waste heat.
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The utilization of waste heat for heat recovery technologies in process sites has been widely known in improving the site energy saving and energy efficiency. The Total Site Heat Integration (TSHI) methodologies have been established over time to assist the integration of heat recovery technologies in process sites with a centralized utility system, which is also known as Total Site (TS). One the earliest application of TSHI concept in waste heat recovery is through steam turbine using the popular Willan’s line approach. The TSHI methodologies later were extended to integrate with wide range of heat recovery technologies in many literature, whereby Organic Rankine Cycle (ORC) has been reported to be the one of the beneficial options for heat recovery. In general, the medium to high temperature waste heat is recovered via condensing/backpressure steam turbine, whereas ORC is targeted for recovering the low temperature waste heat. However, it is known that condensing turbine is also able to generate power by condensing low grade steam to sub-ambient pressure, which is comparable with ORC integration. In this work, the integration of ORC and condensing turbine are considered for a multiple-process system to recover intermediate temperature waste heat through utility system. This study presents a numerical methodology to investigate the performance analysis of integration of ORC and condensing turbine in process sites for recovering waste heat from a centralized utility system. A modified retrofit case study is used to demonstrate the effectiveness application of the proposed methodology. The performance of ORC and condensing steam turbine are evaluated with the plant total utility costing as the objective function.
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Large potential exists in recovering waste heat from paper industry processes and machinery. If the overall energy efficiency would be increased, it could lead to significant fuel savings and greenhouse gas emission reduction. The organic Rankine cycle (ORC) system is a very strong candidate for converting low-grade waste heat into power. However, there is a lot of water vapor containing latent heat in the exhaust gases from the drying process in the paper industry. Thus, the aim of this research work is to increase the efficiency of the ORC system by recovering not only the sensible heat but also the latent heat from the exhaust gases in the paper drying process. In order to recover the latent heat from the moist exhaust gases, one idea of this article is to introduce a direct contact condensing unit into the ORC system. The performance of ORC system with the direct contact condensing unit was analyzed by using the CHEMCAD software. A case study was conducted based on data of the exhaust gases from a tissue production / drying machine. Latent heat will be recovered when the evaporating temperature of the ORC working fluid is lower than the dew point of the water vapor in the exhaust gases. The results showed that the available heat load was increased when the evaporating temperature was reduced. Furthermore, a performance comparison of the ORC systems with and without the direct contact condensing unit was carried out in the case study as well. The results showed that the ORC system with the direct contact condensing unit not only could recover latent heat from the water vapor in the exhaust gases but also could have a small size and small volume evaporator in the ORC system.
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Organic Rankine Cycle (ORC) is an effective technology for low-grade waste heat power generation. In this paper, the thermal-dynamic performance of ORC system, in which low-temperature waste heat (from 40–140°C) is used as heat source, was evaluated with software RefProp8.0. The result indicates that in the range of low temperature, the working fluids like R601, R601a, R600a, R141b, R245fa and R245ca have better thermal performance. Furthermore, pilot-scale experiment using R245fa as working fluid was conducted, which validated the operation of the system for low-grade waste heat recovery. Finally, the economic feasibility of ORC has been analyzed for an ORC system using the waste heat from quenching water of blast furnace slag (80°C). According to the analysis, the project is reasonable in economy because the recovery period of investment is less than 4.2 years and environment-friendly since the CO2 emissions can be reduced by almost 43650.68t annually.
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Under the environment that the International Maritime Organization (IMO) will have stricter requirements for ship energy conservation and emission reduction, the use of organic Rankine cycle (ORC) technology to recover ship waste heat for power generation is one of the most promising methods. According to the grade characteristics and distribution characteristics of ship waste heat under different working conditions, this paper theoretically evaluates the feasibility of recovering exhaust gas waste heat, scavenge air cooling waste heat, and jacket cooling water waste heat, and summarizes the application status of using ORC technology to recover ship waste heat. It is proposed that ORC using multiple heat sources to recover is the future development trend. However, the safety of the applicable working fluid, lower actual efficiency, and longer input payback period are still bottlenecks that limit the application of ORC technology on ships. At the same time, for the subsequent in-depth research of ORC technology to recover ship waste heat for power generation, this paper uses a scroll expander as the core part to build an ORC system experimental bench for recovering ship waste heat. R245fa is used as the circulating working fluid. The 120 °C -150 °C high-temperature steam generated by the electric steam boiler and the 70 °C -90 °C hot water generated by the hot water device are used to simulate the exhaust gas waste heat and jacket cooling water waste heat of the marine diesel engine, respectively. The preliminary test results show that the basic ORC system can produce the maximum net output power of 526 W with heat source of 90 °C and hence the bench can work in order.
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