Parametric analysis and optimization for a combined power and refrigeration cycle

A combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycle. This combined cycle uses a binary ammonia–water mixture as the working fluid and produces both power output and refrigeration output simultaneously with only one heat source. A parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle. It is shown that heat source temperature, environment temperature, refrigeration temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. A parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The optimized exergy efficiency is 43.06% under the given condition.     

Parametric analysis for a new combined power and ejector–absorption refrigeration cycle

A new combined power and ejector–absorption refrigeration cycle is proposed, which combines the Rankine cycle and the ejector–absorption refrigeration cycle, and could produce both power output and refrigeration output simultaneously. This combined cycle, which originates from the cycle proposed by authors previously, introduces an ejector between the rectifier and the condenser, and provides a performance improvement without greatly increasing the complexity of the system. A parametric analysis is conducted to evaluate the effects of the key thermodynamic parameters on the cycle performance. It is shown that heat source temperature, condenser temperature, evaporator temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. It is evident that the ejector can improve the performance of the combined cycle proposed by authors previously.     

Study on a solar-driven ejection absorption refrigeration cycle

This paper deals with a solar-driven ejection absorption refrigeration (EAR) cycle with reabsorption of the strong solution and pressure boost of the weak solution. The physical model is described and the corresponding thermodynamic calculation is performed with the working pair NH₃–LiNO₃. It is demonstrated that the EAR cycle has obvious advantages as compared with the conventional absorption refrigeration cycle: (1) the controllable high absorption pressure allows for substantially high coefficients of performance by the action of a liquid–gas ejector in which the low-pressure refrigerant vapour is injected and pressurized as a result of the ejection of high-pressure solution; (2) internal steady operation can be realized for refrigeration cycles driven by unsteady heat sources, especially for solar energy, by adjusting the power input consumed by solution pumps under the condition of economical and reasonable utilization of electric energy. © 1998 John Wiley & Sons, Ltd.     

Analysis of a combined power and cooling cycle for low‐grade heat sources

This paper presents a parametric analysis of a combined power/cooling cycle, which combines the Rankine and absorption refrigeration cycles, uses ammonia–water mixture as the working fluid and produces power and refrigeration, while power is the primary goal. This cycle, also known as the Goswami Cycle, can be used as a bottoming cycle using waste heat from a conventional power cycle or as an independent cycle using low‐temperature sources such as geothermal and solar energy. Optimum operating conditions were found for a range of ammonia concentration in the basic solution, isentropic turbine efficiency and boiler pressure. It is shown that the cycle can be optimized for net work, cooling output, effective first law and exergy efficiencies. The effect of rectification cooling source (external and internal) on the cycle output was investigated, and it was found that an internal rectification cooling source always produces higher efficiencies. When ammonia vapor is superheated after the rectification process, cycle efficiencies increase but cooling output decreases. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermoeconomic analysis of SOFC-GT-VARS-ORC combined power and cooling system

The integration of the gas turbine cycle and organic Rankine cycle with the solid oxide fuel cell for power generation is quite prevalent. However, the need is also felt for systems capable of providing power with cooling. Therefore, it is proposed to integrate solid oxide fuel cell with gas turbine cycle, vapour absorption refrigeration system and organic Rankine cycle through the heat available with fluid in the cycle. Here intercooled and reheat gas turbine cycle is integrated with solid oxide fuel cell. Heat rejected in intercooling is used in vapour absorption refrigeration system for cooling. This paper presents thermoeconomic analysis. Results show that the combination of solid oxide fuel cell-gas turbine-vapour absorption refrigeration system-organic Rankine cycle yields increase in efficiency to 68.79% as compared to 58.88% from combined solid oxide fuel cell-gas turbine cycle. The cost of electricity per unit power output is found as 1939.93 $/kW.     

高炉余能余热驱动的内可逆闭式布雷顿热电冷联产装置火用经济性能分析

用有限时间热力学理论研究恒温热源条件下由一个内可逆闭式布雷顿热机循环和一个内可逆四热源吸收式制冷循环组成的高炉余能余热驱动的热电冷联产装置的火用经济性能,导出热电冷联产装置的利润率和火用效率与压气机压比的关系。利用数值计算,分析热电比和吸收式制冷循环总放热量在吸收器和冷凝器之间的分配率对利润率与火用效率关系的影响,并研究联产装置各种参数对最大利润率及相应火用效率特性的影响。     

Modeling and experimentation of a novel pressurized CHP system with water extraction

A novel cooling and power cycle is proposed, which combines a semi‐closed cycle gas turbine called the high‐pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). This combined HPRTE/VARS cycle is capable of producing power, water and refrigeration effect for external loads. In a previous study, the combined cycle was modeled using zero‐dimensional steady‐state thermodynamics, with specified values of polytrophic efficiencies and pressure drops for the turbo‐machinery and heat exchangers. In this study, a modified version of the combined HPRTE/VARS cycle is experimentally investigated for the demonstration of the combined cycle concept and for the model validation. This modified HPRTE has two water‐cooled heat exchangers instead of the absorption refrigeration system. The model of the original combined HPRTE/VARS cycle was modified to simulate the performance of the modified HPRTE cycle. Temperatures, pressure, mass flow rates and other overall cycle parameters obtained from the computer model are compared with the corresponding experimental values of the modified cycle. The agreement between the values is found to be within acceptable limits. In addition, the uncertainty analysis of the experimental data is undertaken to find the uncertainty in the final output variables: thermal efficiency and non‐dimensional water extraction parameter. Copyright © 2008 John Wiley & Sons, Ltd.     

Geothermal energy use in hydrogen liquefaction

We propose the use of geothermal energy for hydrogen liquefaction, and investigate three possible cases for accomplishing such a task including (1) using geothermal output work as the input for a liquefaction cycle; (2) using geothermal heat in an absorption refrigeration process to precool the gas before the gas is liquefied in a liquefaction cycle; and (3) using part of the geothermal heat for absorption refrigeration to precool the gas and part of the geothermal heat to produce work and use it in a liquefaction cycle (i.e., cogeneration). A binary geothermal power plant is considered for power production while the precooled Linde–Hampson cycle is considered for hydrogen liquefaction. A liquid geothermal resource is considered and both ideal (i.e., reversible) and non-ideal (e.g., irreversible) system operations are analyzed. A procedure for such an investigation is developed and appropriate performance parameters are defined. Also, the effects of geothermal water temperature and gas precooling temperature on system performance parameters are studied. The results show that there is a significant amount of energy savings potential in the liquefaction work requirement as a result of precooling the gas in a geothermal absorption cooling system. Using geothermal energy in a cogeneration scheme (power production and absorption cooling) also provides significant advantages over the use of geothermal energy for power production only.     

A combined power and ejector refrigeration cycle for low temperature heat sources

A combined power and ejector refrigeration cycle for low temperature heat sources is under investigation in this paper. The proposed cycle combines the organic Rankine cycle and the ejector refrigeration cycle. The ejector is driven by the exhausts from the turbine to produce power and refrigeration simultaneously. A simulation was carried out to analyze the cycle performance using R245fa as the working fluid. A thermal efficiency of 34.1%, an effective efficiency of 18.7% and an exergy efficiency of 56.8% can be obtained at a generating temperature of 395 K, a condensing temperature of 298 K and an evaporating temperature of 280 K. Simulation results show that the proposed cycle has a big potential to produce refrigeration and most exergy losses take place in the ejector.     

A finite time analysis of combined Carnot driving and cooling cycles optimised for maximum refrigeration effect with applications to absorption refrigeration systems

A finite time analysis of an ideal refrigeration cycle with the objective of maximising refrigeration effect has been performed. The optimised refrigeration cycle has then been combined with an optimised power cycle to produce a combined cycle. The general matching requirements of the two cycles are discussed. The cycles are then combined in a specific way such that they become a model for an ideal absorption refrigeration cycle. The influence of the design parameters on the performance of the combined cycle is analysed. The performance of an experimental absorption unit is compared with the predictions made by the analysis.     

Theoretical and experimental investigation of an ammonia–water power and refrigeration thermodynamic cycle

A combined thermal power and cooling cycle proposed by Goswami is under intensive investigation, both theoretically and experimentally. The proposed cycle combines the Rankine and absorption refrigeration cycles, using a binary ammonia–water mixture as the working fluid. This cycle can be used as a bottoming cycle using waste heat from a conventional power cycle or an independent cycle using low temperature sources such as geothermal and solar energy. Initial parametric studies of the cycle showed the potential for the cycle to be optimized for first or second law efficiency, as well as work or cooling output. For a solar heat source, optimization of the second law efficiency is most appropriate, since the spent heat source fluid is recycled through the solar collectors. The optimization results verified that the cycle could be optimized using the generalized reduced gradient method. Theoretical results were extended to include realistic irreversibilities in the cycle, in preparation for the experimental study. An experimental system was constructed to demonstrate the feasibility of the cycle and to compare the experimental results with the theoretical simulation. Results showed that the vapor generation and absorption condensation processes work experimentally. The potential for combined turbine work and refrigeration output was evidenced in operating the system. Analysis of losses showed where improvements could be made, in preparation for further testing over a broader range of operating parameters.     

Analysis of power and cooling cogeneration using ammonia-water mixture

Development of innovative thermodynamic cycles is important for the efficient utilization of low-temperature heat sources such as solar, geothermal and waste heat sources. This paper presents a parametric analysis of a combined power/cooling cycle, which combines the Rankine and absorption refrigeration cycles, uses ammonia-water mixture as the working fluid and produces power and cooling simultaneously. This cycle, also known as the Goswami Cycle, can be used as a bottoming cycle using waste heat from a conventional power cycle or as an independent cycle using solar or geothermal energy. A thermodynamic study of power and cooling cogeneration is presented. The performance of the cycle for a range of boiler pressures, ammonia concentrations and isentropic turbine efficiencies are studied to find out the sensitivities of net work, amount of cooling and effective efficiencies. The roles of rectifier and superheater on the cycle performance are investigated. The cycle heat source temperature is varied between 90-170 °C and the maximum effective first law and exergy efficiencies for an absorber temperature of 30 °C are calculated as 20% and 72%, respectively. The turbine exit quality of the cycle for different boiler exit scenarios shows that turbine exit quality decreases when the absorber temperature decreases.     

Thermo-environmental analysis of a new molten carbonate fuel cell-based tri-generation plant using stirling engine,generator absorber exchanger and vapour absorption refrigeration: A comparative study

This study aims to present a novel tri-generation plant consisting of a molten carbonate fuel cell (MCFC) unit coupled with a Stirling engine (SE), a heat recovery steam generator (HRSG), and two types of absorption refrigeration cycles (ARCs), i.e., Generator Absorber eXchanger (GAX) and Vapour Absorption Refrigeration (VAR). The proposed system is evaluated from energy, exergy, as well as environmental impact (3E) points of view. To carry out the parametric study, three sub-models are also introduced for the whole system. The sub-model (1) investigates the solo MCFC with the new configuration. In the sub-model (2), the SE and HRSG are added to boost the power generation and overall system efficiency through employing the heat wasted in the sub-model (1). In the last sub-model, for cooling purposes, the surplus heat of MCFC is reutilized using an absorption refrigeration cycle. Besides, to make a comparative study between GAX and VAR systems, the sub-model (3) is classified into two different schemes: (a) with a VAR cycle, and (b) with a GAX cycle. The results reveal that the exergy efficiency and CO₂ emissions of the sub-models (1), (2), and (3) are 48.04%, 51.24%, 52.35% (VAR cycle), 52.12% (GAX cycle), 0.388 t/MWh, 0.364 t/MWh, 0.357 t/MWh (VAR cycle), and 0.358 t/MWh (GAX cycle), respectively. Either with GAX or VAR cycle, the proposed system indicates an acceptable standard of functionality in thermodynamic and environmental perspectives.     

Choice of absorbent-refrigerant mixtures

Twenty-six absorbent—refrigerant combinations, holding good promise as fluid systems, have been considered for single stage absorption air conditioning system. These fluids have been compared on the basis of solution characteristics, life expectancy characteristics and refrigeration cycle characteristics. The mass flow rates of rich and poor solutions per ton of refrigeration capacity and the coefficient of performance (CP) were compared for an evaporator temperature of 5°C, absorber and condenser temperatures of 35°C and a generator temperature of 120°C (low grade energy sources). More than half of the waste energy available in industry happens to be at a temperatures below 200°C. Other types of low grade thermal energy such as solar energy and geothermal energy can be used in operating vapour absorption refrigeration and air-conditioning systems.     

Irreversible four-temperature-level absorption refrigerator

A refrigeration cycle is modeled as a demonstration of an irreversible absorption refrigeration cycle. This four-temperature-level model takes into account the heat resistance, heat leakage, and irreversibilities due to internal dissipation of the working fluid. The fundamental optimal relationships between: (1) the coefficient of performance (COP) and the cooling load; (2) the maximum COP and the corresponding cooling load; and (3) the maximum cooling load and the corresponding COP of the cycle, all coupled to constant-temperature heat reservoirs, are derived by using finite-time thermodynamics. The optimal distribution relationships of the heat-transfer surface areas are also presented. Moreover, the effects of the cycle parameters on the COP and the cooling load of the cycle are studied by detailed numerical examples. The results obtained herein are useful for optimal design and performance improvement of absorption refrigeration cycles.     

Experimental investigation of integrated refrigeration system (IRS) with gas engine,compression chiller and absorption chiller

An integrated refrigeration system (IRS) with a gas engine, a vapor-compression chiller and an absorption chiller is set up and tested. The vapor-compression refrigeration cycle is operated directly by the gas engine. The waste heat from the gas engine operates the absorption refrigeration cycle, which provides additional cooling. The performance of the IRS is described. The cooling capacity of the IRS is about 596 kW, and primary energy ratio (PER) reaches 1.84 at air-conditioning rated conditions. The refrigerating capacity of the prototype increased and PER of prototype decreased with the increase of the gas engine speed. The gas engine speed was preferably regulated at part load condition in order to operate the prototype at high-energy efficiency. The refrigerating capacity and PER of the prototype increased with the increase of the outlet temperature of chilled water or the decrease of the inlet temperature of cooling water. The integrated refrigeration chiller in this work saves running costs as compared to the conventional refrigeration system by using the waste heat.     

Computer modeling and parametric study of a double effect generation absorption refrigeration cycle

This paper presents as assessment based on steady-state thermodynamic analysis and computer modeling of a double effect generation absorption refrigeration cycle for solar air-conditioning. The system consists of a second effect generator between the generator and condenser of the single effect absorption cycle and two solution heat exchangers between the absorber and the two generators. A numerical computer modeling of a water LiBr system based on the solution of simultaneous heat, mass and material balance equations for various components of the system has been carried out. The influences of component temperatures and heat exchanger effectiveness on the cooling coefficients of performance and component heat transfer rates have been investigated to obtain optimum operating conditions for the proposed air-conditioning system. Further, the single and double effect absorption cycles are compared with each other as well as with an ideal absorption cycle operating over the same range of temperatures.     

Modeling and optimization of a novel pressurized CHP system with water extraction and refrigeration

A novel cooling, heat, and power (CHP) system has been proposed that features a semi-closed Brayton cycle with pressurized recuperation, integrated with a vapor absorption refrigeration system (VARS). The semi-closed Brayton cycle is called the high-pressure regenerative turbine engine (HPRTE). The VARS interacts with the HPRTE power cycle through heat exchange in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount that depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for the inlet air to the high-pressure compressor, water extraction, and for an external cooling load. The computer model of the combined HPRTE/VARS cycle predicts that with steam blade cooling and a medium-sized engine, the cycle will have a thermal efficiency of 49% for a turbine inlet temperature of 1400°C. This thermal efficiency, is in addition to the large external cooling load, generated in the combined cycle, which is 13% of the net work output. In addition, it also produces up to 1.4 kg of water for each kg of fuel consumed, depending upon the fuel type. When the combined HPRTE/VARS cycle is optimized for maximum thermal efficiency, the optimum occurs for a broad range of operating conditions. Details of the multivariate optimization procedure and results are presented in this paper. Copyright © 2008 John Wiley & Sons, Ltd.     

地热驱动氨水吸收式动力/制冷复合循环参数优化分析

针对中低品位地热驱动的氨水吸收式动力/制冷复合循环的热力学性能展开分析与优化,在Kalina循环的基础上利用氨水变温蒸发的特性,将正向动力子过程与逆向制冷子过程耦合,对外实现动力与冷量的联供。本文对影响复合循环热力性能的工质对浓度x_w/x_b、氨水发生温度（露点温度）t₁₄、循环倍率K以及分流比n四个重要参数展开了分析优化。研究表明,在x_w/x_b=0.50/0.32、t₁₄=180℃、K=2.80和n=0.505的优化工况下,复合循环的热效率和?效率分别可达19.38%和59.77%,较氨水动力循环分别高出3.71%和4.74%,较水蒸气朗肯循环分别高出8.54%和35.81%。     

Solar Powered Cascading Cogeneration Cycle with ORC and Adsorption Technology for Electricity and Refrigeration

As a renewable source, solar energy has received more and more attention in recent years. Solar energy can readily provide heat efficiently within the temperature range of 70–100°C. For the utilization of this energy source, a cascading cycle was designed and was discussed. An organic Rankine cycle (ORC) and an adsorption refrigeration cycle were combined to provide the first- and second-stage energy conversion cycle, respectively. In the analysis, R600 was used as the working fluid for the ORC and a silica gel–water working pair was analyzed for the adsorption refrigeration cycle. The energy efficiency for electrical generation and refrigeration, as well as the exergy efficiency of the cascading cycle, was assessed. For an environmental temperature of 30°C and a refrigeration temperature of 12°C, the results showed that typically 1 kW of electricity and 6.3 kW of refrigeration could be generated from approximately 15 kW heating power. The electricity generation efficiency was between 0.1 and 0.15, while the refrigeration coefficient of performance was approximately 0.8. The exergy efficiency was found to be between 0.84 and 0.89 and between 0.32 and 0.46 for the single ORC and adsorption refrigeration cycle, respectively. The overall exergy efficiency was between 0.56 and 0.74.