Performance investigation of a combined MCFC system

This study investigates the performance of a combined industrial molten carbonate fuel cell (MCFC) system, including a turbo expander, which was recently installed by Enbridge Inc. in Toronto, Canada. It entails a comprehensive thermodynamic analysis regarding energy and exergy calculations, subject to varying operating conditions. Furthermore, a simplified and novel method is used for a cost analysis to assess the amortization of the system. The results from the base case study suggest that an overall energy efficiency as high as 60% is achievable while fuel cell stack energy and exergy efficiencies of 50.6% and 49.3%, respectively, are reached. The cost analysis indicates that the amortization of the system may take up to 15 years of operational time, depending on the price of electricity and natural gas. However, carbon offsets may make a paramount contribution to the overall savings and economic viability of future combined MCFC systems.     

A novel MCFC hybrid power generation process using solar parabolic dish thermal energy

In this paper, a novel molten carbonate fuel cell hybrid power generation process with using solar parabolic dish thermal energy is proposed. The process contains MCFC, Oxy-fuel and Rankine power generation cycles. The Rankine power generation cycles utilized various types of working fluid to emphasize taking advantage of the cycles in different thermodynamic conditions. The required hot and cold energies are provided from solar dish parabolic thermal hot and liquefied natural gas (LNG) cold energies, respectively. The carbon dioxide (CO₂) from MCFC effluent stream is captured from the process at liquid state. The process total heat integrated and in this regards, no need to any hot and cold external sources with the net electrical power generation. The energy and exergy analysis are conducted to determine the approaches to improve the process performance. This integrated structure consumed 2.30 × 10⁶ kg h⁻¹ of air and 2.67 × 10⁶ kg h⁻¹ of LNG to generate 292597 kW of net power. The products of this integrated structure are 6.25 × 10⁴ kg h⁻¹ of condensates, 183 kg h⁻¹ of water vapor, 2.20 × 10⁶ kg h⁻¹ of MCFC effluent stream, 2.60 × 10⁶ kg h⁻¹ of natural gas and 1.10 × 10⁵ kg h⁻¹ of CO₂ in liquid state. The presented new integrated structure has overall thermal efficiency of 73.14% and total exergy efficiency of 63.19%. Also, sensitivity analysis is performed for determination of the process key parameters which affected the process operating performance.     

Energetic and exergetic analysis of a biomass-fueled CCHP system integrated with proton exchange membrane fuel cell

As a high-efficiency and eco-friendly way of energy conversion, fuel cell has received much attention in recent years. A novel residential combined cooling, heating and power (CCHP) system, consisting of a biomass gasifier, a proton exchange membrane fuel cell (PEMFC) stack, an absorption chiller and auxiliary equipment, is proposed. Based on the established thermodynamic models, the effects of operating parameters, biomass materials type and moisture content on the system performance are closely investigated. Overall system performance is then compared under four different operating modes. From the viewpoints of energy utilization and CO₂ emissions, the CCHP mode has the best performance with corresponding energy efficiency of 57.41% and CO₂ emission index of 0.516 ton/MWh. Exergy analysis results suggest that the optimization and transformation on the gasifier and PEMFC stack should be encouraged. Energy and exergy assessments in this research provide pragmatic guidance to the performance improvement of the integrated CCHP systems with PEMFC. This research also achieves a reasonable combination of efficient cogeneration, green hydrogen production and full recovery of low grade waste heat.     

Thermodynamic analysis of a tri-generation system based on micro-gas turbine with a steam ejector refrigeration system

In the present work, performance of new configuration of Micro-gas turbine cogeneration and tri-generation systems, with a steam ejector refrigeration system and Heat recovery Steam Generator (HRSG) are studied. A micro-gas turbine cycle produces 200 KW power and exhaust gases of this micro-gas turbine are recovered in an HRSG. The main part of saturated steam in HRSG is used through a steam ejector refrigeration system to produce cooling in summer. In winter, this part of saturated steam is used to produce heating. In the first part of this paper, performance evaluation of this system with respect to Energy Utilization Factor (EUF), Fuel Energy Saving Ratio (FESR), thermal efficiency, pinch point temperature difference, net power to evaporator cooling load and power to heat ratio is carried out. It has been shown that by using the present cogeneration system, one can save fuel consumption from about 23% in summer up to 33% in winter in comparison with separate generation of heating, cooling and electricity.     

Performance analysis of a CCHP system based on SOFC/GT/CO2 cycle and ORC with LNG cold energy utilization

An innovative CCHP system based on SOFC/GT/CO₂ cycle and the organic Rankine cycle (ORC) with LNG cold energy utilization is proposed to achieve cascade energy utilization and carbon dioxide capture. The mathematical models are developed and the system performance is analyzed using the energy and exergy methods. The results illustrate that the comprehensive energy utilization, the net power generation and the overall exergy efficiencies of the system can reach about 79.48%, 79.81% and 62.29%, respectively, while the power generation efficiency of the SOFC is 50.96% and the CO₂ capture rate of the proposed CCHP system is 79.2 kg/h under the given conditions. It shows that the proposed CCHP system can reach a high energy utilization efficiency with near zero emissions. The influence of some key parameters, such as the fuel utilization factor, the air-fuel ratio, the oxygen concentration in the cathode feed and the compression ratio of the SCO₂ turbine on the performance of the entire system is studied.     

Energy management strategy and capacity optimization for CCHP system integrated with electric-thermal hybrid energy storage system

In order to improve the comprehensive energy utilization rate of combined cooling, heating, and power (CCHP) system, a hybrid energy storage system (HESS) is proposed in this paper consisting of electric and thermal energy storage systems. And the overall optimization design and operation of CCHP system with HESS are the main problems to be solved in application. Therefore, the topology and the energy flow model of CCHP system with HESS are established and analyzed according to the energy conversion characteristics of the component equipment. Moreover, combined with five evaluative restrictions for HESS system, a rule-based energy management strategy is designed to realize the decoupling regulation of electric energy and thermal energy in CCHP system. On this basis, a multi-objective optimization model is studied by taking the indicators of annual cost ratio, the primary energy consumption ratio, and loss energy ratio, and then the capacity parameters are optimized by particle swarm optimization algorithm (PSOA). Finally, a case is carried out to compare the energy allocation situations and capacity optimization results between CCHP system with HESS and CCHP system with single thermal energy storage system (ST). Results show that the capacity of ICE is reduced by 34%, and the annual cost and the primary energy consumption are saved about 7.69% and 18.47%, respectively, demonstrating that HESS has better optimization effect and applicable for small-scale CCHP system.     

Enhanced generation of hydrogen,power, and heat with a novel integrated photoelectrochemical system

Hydrogen is an essential component of power-to-gas technologies that are needed for a complete transition to renewable energy systems. Although hydrogen has zero GHG emissions at the end-use point, its production could become an issue if non-renewable, and pollutant energy and material resources are used in this step. Therefore, a crucial step for the fully developed hydrogen economy is to find alternative hydrogen production methods that are clean, efficient, affordable, and reliable. With this motivation, in this study, an integrated and continuous type of hydrogen production system is designed, developed, and investigated. This system has three components. There is a solar spectral splitting device (Unit I), which splits the incoming solar energy into two parts. Photons with longer wavelength is sent to the photovoltaic thermal hybrid solar collector, PV/T, (Unit II) and used for combined heat and power generation. Then the remaining part is transferred to the novel hybrid photoelectrochemical-chloralkali reactor (Unit III) for simultaneous H₂, Cl₂, and NaOH production. This system has only one energy input, which is the solar irradiation and five outputs, namely H₂, Cl₂, NaOH, heat, and electricity. Unlike most of the studies in the literature, this system does not use only PV or only a photoelectrochemical reactor. With this approach, solar energy utilization is maximized, and the wasted portion is minimized. By selecting PV/T rather than PV, the performance of the panels is maximized because recovering the by-product heat as a system output in addition to electricity, and the PV/T has less waste and higher efficiency. The present reactor does not use any additional electron donors, so the wastewater discharge is only depleted NaCl solution, which makes the system significantly cleaner than the ones available in the literature. The specific aim of this study is to demonstrate the optimum operating parameters to reach the maximum achievable production rates and efficiencies while keeping the exergy destruction as little as possible. In this study, there are four case studies, and in each case study, one decision variable is optimized to get the desired performance results. Within the selected operating parameter range, all performance criteria (except exergy destruction) are normalized and ranked for proper comparison. The maximum production rates and efficiencies with the least possible exergy destruction are observed at the operating temperature of 30 °C. At 30 °C, 4.18 g/h H₂, 127.55 g/h Cl₂, 151 W electricity, and 716 W heat are produced with an exergy destruction rate of 95.74 W and 78% and 30% energy and exergy efficiencies, respectively.     

Second law-based thermodynamic analysis of water-lithium bromide absorption refrigeration system

In this study, the first and the second law of thermodynamics are used to analyze the performance of a single-stage water-lithium bromide absorption refrigeration system (ARS) when some working parameters are varied. A mathematical model based on the exergy method is introduced to evaluate the system performance, exergy loss of each component and total exergy loss of all the system components. Parameters connected with performance of the cycle–circulation ratio (CR), coefficient of performance (COP), Carnot coefficient of performance (COP_c), exergetic efficiency (ξ) and efficiency ratio (τ)–are calculated from the thermodynamic properties of the working fluids at various operating conditions. Using the developed model, the effect of main system temperatures on the performance parameters of the system, irreversibilities in the thermal process and non-dimensional exergy loss of each component are analyzed in detail. The results show that the performance of the ARS increases with increasing generator and evaporator temperatures, but decreases with increasing condenser and absorber temperatures. Exergy losses in the expansion valves, pump and heat exchangers, especially refrigerant heat exchanger, are small compared to other components. The highest exergy loss occurs in the generator regardless of operating conditions, which therefore makes the generator the most important component of the cycle.     

Performance evaluation of a radiant floor cooling system integrated with dehumidified ventilation

The radiant floor cooling system can be used as an alternative to all-air cooling systems, using the existing Ondol system (a radiant floor heating system) in Korea to save energy and maintain indoor thermal comfort. Unfortunately, a radiant floor cooling system may cause condensation on the floor surface under hot and humid conditions during the cooling season. In addition, the radiant floor system does not respond quickly to internal load changes due to the thermal storage effect of the concrete mass, which is usually present in radiant floor cooling systems.This study proposes a radiant floor cooling system integrated with dehumidified ventilation, which cools and dehumidifies the outdoor air entering through the cooling coil in the ventilator by lowering the dew-point temperature to prevent condensation on the floor surface. Furthermore, outdoor reset control was used to modulate the temperature of chilled water supplied to the radiant floor, and indoor temperature feedback control was then used to respond to the internal load changes.To evaluate the performance of the radiant floor cooling system integrated with dehumidified ventilation, both a physical experiment in a laboratory setting and TRNSYS simulation for an apartment in Korea have been conducted. As a result, it was found that the proposed system was not only able to solve the problem of condensation on a floor surface but also to control the indoor thermal environment within the acceptable range of comfort. Furthermore, the proposed system improved the responsiveness to internal load changes.     

Energy,exergy and thermoeconomic analysis of a combined cooling,heating and power (CCHP) system with gas turbine prime mover

In this paper energy, exergy and thermoeconomic analysis of a combined cooling, heating and power (CCHP) system has been performed. Applying the first and second laws of thermodynamics and economic analysis, simultaneously, has made a powerful tool for the analysis of energy systems such as CCHP systems. The system integrates air compressor, combustion chamber, gas turbine, dual pressure heat recovery steam generator (HRSG) and absorption chiller to produce cooling, heating and power. In fact, the first and second laws of thermodynamics are combined with thermoeconomic approaches. Next, computational analysis is performed to investigate the effects of below items on the fuel consumption, values of cooling, heating and net power output, the first and second laws efficiencies, exergy destruction in each of the components and total cost of the system. These items include the following: air compressor pressure ratio, turbine inlet temperature, pinch temperatures in dual pressure HRSG, pressure of steam that enters the generator of absorption chiller and process steam pressure. Decision makers may find the methodology explained in this paper very useful for comparison and selection of CCHP systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Modeling the performance of MCFC for various fuel and oxidant compositions

100 cm² molten carbonate fuel cells (MCFC) was used for testing the fuel and oxidant composition influence on MCFC performance as a temperature function.     

Performance evaluation of a geothermal based integrated system for power,hydrogen and heat generation

In the present study, an integrated system is proposed and thermodynamically analyzed to reduce greenhouse gas (GHG) emissions while improving overall system performance. The integrated system is comprised of a supercritical carbon dioxide (CO₂) Rankine cycle cascaded by an Organic (R600) Rankine cycle, an electrolyzer, and a heat recovery system. It is designed to utilize a medium-to-high temperature geothermal energy source for power and hydrogen production, and thermal energy utilization for space heating. Therefore, parametric studies for the supercritical CO₂ cycle, the Organic (R600) cycle, and the overall system are conducted. In addition, the effect of various operational conditions, such as geothermal source, ambient and cooling water temperatures on the performance of each cycle and the integrated system, is illustrated. It is found that increasing geothermal source temperature results in slight increases of the exergetic efficiency of the overall system. The energy efficiencies of the CO₂ and Organic Rankine cycles do not considerably vary with source temperature changes. The decay of the cooling water temperature leads to a decrease in the overall system exergetic efficiency. The system configuration, which is introduced, is capable of producing about 180 kg/h for the geothermal source of mass flow rate of 40 kg/s and a temperature of 473 K.     

天然气冷热电联供系统在某商场建筑中的应用分析

简要介绍天然气冷热电联供系统的国内外研究动态,从系统的优化配置、运行策略和性能分析几个方面列举一些对该领域有突出贡献的专家学者及其研究成果。针对一个典型的商场建筑冷热电联供系统进行性能分析,并将其与传统的供能方式进行了比较。     

微燃机冷热电联供系统(CCHP)的建模及仿真研究

本文用matlab中simulink和人工神经网络为工具,分别建立了微燃机和烟气型溴化锂吸收式机组模型,以全年时间环境温度为变化条件,微燃机全工况下得到CCHP系统仿真结果,为以后优化运行打下基础。     

Thermodynamic analysis of a novel integrated system operating with gas turbine,s-CO2 and t-CO2 power systems for hydrogen production and storage

In this paper, a proposal for a novel integrated Brayton cycle, supercritical plant, trans critical plant and organic Rankine cycle-based power systems for multi-generation applications are presented and analyzed thermodynamically. The plant can generate power, heating-cooling for residential applications, and hydrogen simultaneously from a single energy source. Both energetic and exergetic analyses are conducted on this multi-generation plant and its subsystems in order to evaluate and compare them thermodynamically, in terms of their useful product capabilities. The energetic and exergetic effectiveness of the multi-generation system are computed as 44.69% and 42.03%, respectively. After that, a parametric study on each of the subsystems of the proposed combined system is given in order to provide a deeper understanding of the working of these subsystems under different states. Lastly, environmental impact assessments are provided to raise environmental concerns for several operating conditions. For the base working condition, the results illustrate that the proposed plant has 0.5961, 0.0442, 0.6265 and 1.678 of exergo-environmental impact factor, exergy sustainability index, exergy stability factor and sustainability index, respectively.     

Development and analysis of a novel biomass-based integrated system for multigeneration with hydrogen production

Energy and exergy analyses of an integrated system based on anaerobic digestion (AD) of sewage sludge from wastewater treatment plant (WWTP) for multi-generation are investigated in this study. The multigeneration system is operated by the biogas produced from digestion process. The useful outputs of this system are power, freshwater, heat, and hydrogen while there are some heat recoveries within the system for improving efficiency. An open-air Brayton cycle, as well as organic Rankine cycle (ORC) with R-245fa as working fluid, are employed for power generation. Also, desalination is performed using the waste heat of power generation unit through a parallel/cross multi-effect desalination (MED) system for water purification. Moreover, a proton exchange membrane (PEM) electrolyzer is used for electrochemical hydrogen production option in the case of excess electricity generation. The heating process is performed via the rejected heat of the ORC's working fluid. The production rates for products including the power, freshwater, hydrogen, and hot water are obtained as 1102 kW, 0.94 kg/s, 0.347 kg/h, and 1.82 kg/s, respectively, in the base case conditions. Besides, the overall energy and exergy efficiencies of 63.6% and 40% are obtained for the developed system, respectively.     

Energy and exergy performance assessment of a novel solar-based integrated system with hydrogen production

In this study, a new solar power assisted multigeneration system designed and thermodynamically analyzed. In this system, it is designed to perform heating, cooling, drying, hydrogen and power generation with a single energy input. The proposed study consists of seven sub-parts which are namely parabolic dish solar collector, Rankine cycle, organic Rankine cycle, PEM-electrolyzer, double effect absorption cooling, dryer and heat pump. The effects of varying reference temperature, solar irradiation, input and output pressure of high-pressure turbine and pinch point temperature heat recovery steam generator are investigated on the energetic and exergetic performance of integration system. Thermodynamic analysis result outputs show that the energy and exergy performance of overall study are computed as 48.19% and 43.57%, respectively. Moreover, the highest rate of irreversibility has the parabolic dish collector with 24,750 kW, while the lowest rate of irreversibility is calculated as 5745 kW in dryer. In addition, the main contribution of this study is that the solar-assisted multi-generation systems have good potential in terms of energy and exergy efficiency.     

Advanced exergetic evaluation of refrigeration machines using different working fluids

Splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts has many advantages for the detailed analysis of energy conversion systems. Endogenous is the exergy destruction obtained when all other system components are ideal and the component being considered operates with its real efficiency. The difference between total and endogenous exergy destruction is the exogenous exergy destruction caused within the component being considered by the irreversibilities in the remaining components and the structure of the overall system. Unavoidable is the part of exergy destruction within one system component that cannot be eliminated even if the best available technology in the near future would be applied. The avoidable exergy destruction is the difference between total and unavoidable exergy destruction. These concepts enhance an exergy analysis and assist in improving the quality of the conclusions obtained from this analysis. The paper presents the combined application of both concepts to vapor-compression refrigeration machines using different one-component working fluids (R125, R134a, R22 and R717) as well as azeotropic (R500) and zeotropic (R407C) mixtures. The purpose of the paper is not to evaluate these working fluids, some of which cannot be used in future, but to demonstrate the effect of different material properties on the results of advanced exergy analysis.     

Transient thermodynamic analysis of a novel integrated ammonia production,storage and hydrogen production system

A transient thermodynamic analysis is reported of a novel chemical hydrogen storage system using energy and exergy approaches. The hydrogen is stored chemically in ammonia using the proposed hydrogen storage system and recovered via the electrochemical decomposition of ammonia through an ammonia electrolyzer. The proposed hydrogen storage system is based on a novel subzero ammonia production reactor. A single stage refrigeration system maintains the ammonia production reactor at a temperature of −10 °C. The energy and exergy efficiencies of the proposed system are 85.6% and 85.3% respectively. The proposed system consumes 34.0 kJ of work through the process of storing 1 mol of hydrogen and recovering it using the ammonia electrolyzer. The system is simulated for filling 30,000 L of ammonia at a pressure of 5 bar, and the system was able to store 7500 kg of ammonia in a liquid state (1% vapor) in 1500 s. The system consumes nearly 45.3 GJ of energy to store the 7500 kg of ammonia and to decompose it to reproduce the stored hydrogen during the discharge phase.     

An exergy analysis of a solar-driven ejector refrigeration system

Exergy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m², an evaporator temperature of 10 °C, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 °C as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 °C.