First and second law analysis of solar operated combined Rankine and ejector refrigeration cycle

A combined Rankine and ejector refrigeration cycle is proposed for the production of power and refrigeration output using duratherm 600 oil as the heat transfer fluid. Thermodynamic analysis has been done to observe the effect of parameters on the performance of the combined cycle. The effect of various parameters asthe turbine inlet pressure, evaporator temperature, condenser temperature, extraction ratio and direct normal radiation per unit area on the performance of the cycle have significant effects on the net power output, refrigeration output, first law efficiency and second law efficiency. It is also observed that the maximum irreversibility occurs in central receiver as 52.5% followed by 25% in the heliostat, 5.3% in the heat recovery vapor generator, 2.6% in the ejector, and 1.6% in the turbine and around 1.1% in the other components of the cycle. The second law efficiency of the solar operated combined Rankine and ejector refrigeration cycle is 11.90% which is much lower than its first law efficiency of 14.81%.     

Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

This paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s^?1. One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger. Copyright © 2006 John Wiley & Sons, Ltd.     

分液冷凝有机朗肯循环系统R245fa/HFOs工质选择研究

有机朗肯循环是中低品位热能高效利用的有效技术之一,分液冷凝有机朗肯循环（LSCORC）是基于分液冷凝传热强化的新型热力循环。为寻找新型环保替代工质,建立LSCORC系统的热力学模型,以最大化净输出功为目标,重点考虑了雅各布数、冷热源换热匹配对系统性能的影响,对R245fa/HFOs工质进行了对比筛选。结果表明：工质的雅各布数越大,其净输出功越小;在基础工况下,R245fa/R1336mzz(Z)的热力性能及热经济性表现最佳;当热源参数变化时,雅各布数较小工质的性能表现普遍优于雅各布数较大的工质组合;当冷源参数变化时,在分液冷凝器两个流程中温度滑移和冷源温升匹配越好的工质组合,其系统净输出功越大。     

An iterative method for modelling the air‐cooled organic Rankine cycle geothermal power plant

This work presents an iterative method for modelling the effect of ambient air temperature on the air‐cooled organic Rankine cycle. The ambient temperature affects the condenser performance, and hence the performance of the whole cycle, in two ways. First, changing the equilibrium pressure inside the condenser, the turbine outlet pressure and the turbine pressure ratio vary. Since the turbine pressure ratio is a major parameter in determining the power generated by a turbine, the plant output is directly affected. Second, changing the condenser outlet temperature with ambient temperature, the pump inlet and outlet conditions are changed. Thus, the vapourizer equilibrium temperature and pressure are influenced. The developed method iteratively seeks the equilibrium conditions for both the condenser and vapourizer. Two case studies based on a real plant performance have been carried out to demonstrate the validity of the method. The developed method demonstrates robustness and converges regardless of the initial conditions allowed by the physical properties of the working fluid. This method is effective for cycles that use saturated vapour as well as superheated vapour under static or dynamic conditions with appropriate initial conditions and constraints. The developed method may be applied to any Rankine cycle with closed cycle operation. Copyright © 2010 John Wiley & Sons, Ltd.     

Formulation and analysis of the heat pipe turbine for production of power from renewable sources

The heat pipe turbine or thermosyphon Rankine engine is a new concept for power generation using solar, geothermal or other available low grade heat sources. The basis of the engine is the thermosyphon cycle, with its excellent heat and mass transfer characteristics, modified to incorporate a turbine in the adiabatic region. The basic configuration is a closed vertical cylinder functioning as an evaporator, an insulated section and a condenser. The turbine is placed in the upper end between the insulated section and condenser section, and a plate is installed to separate the high pressure region from the low pressure region in the condenser. Conversion of enthalpy to kinetic energy is achieved through the nozzles. The mechanical energy developed by the turbine can be converted to electrical energy by direct coupling to an electrical generator.This paper describes the development of the heat pipe turbine from concept to reality, a series of development steps taken to optimise the design and manufacture. Also in this paper, attempts have been made to provide relationships for the developed power in terms of the geometric and thermodynamic parameters and to discuss limitations on the efficiencies of these turbines.     

R245fa有机朗肯循环余热发电系统火用分析

以低品位热能驱动的有机朗肯循环发电系统,是实现将低品位热能转变为电能,进而提高热力系统总体热效率,降低污染排放的有效途径之一。本文建立了低品位热能发电系统火用分析模型,对以R245fa为工质的温度低于383.15 K的低品位热能有机朗肯循环余热发电系统进行了火用分析,得到了各环节的能量转换效率并确定了对系统性能影响最大的环节;通过改变蒸发器和冷凝器的压降和传热系数值,分析了主要换热设备的设计和运行性能参数对系统火用效率、热效率和发电量的影响趋势,提出了低品位热能发电系统的优化方向。     

Multi-objective optimization design of condenser in an organic Rankine cycle for low grade waste heat recovery using evolutionary algorithm

The optimum design of a condenser is significant in an organic Rankine cycle to achieve higher waste heat utilization efficiency. Based on the mathematical model of a condenser using plate heat exchanger (PHE), some key geometric parameters on the total heat transfer surface area and pressure drop of the condenser are examined. In order to obtain geometric parameters of a plate heat exchanger, a multi-objective optimization of the condenser in organic Rankine cycle is conducted to achieve the optimal geometry design. The total heat transfer surface area and pressure drop are selected as two objective functions to minimize both total heat transfer surface area and pressure drop under the constant heat transfer rate and LMTD conditions. The plate width, plate length and plant distance are selected as the decision variables. Non-dominated sorting generic algorithm-II (NSGA-II) which is an effective multi-objective optimization method is employed to solve this multi-objective optimization design of PHE. The results show that an increase in channel distance or plate width increases the total heat transfer surface area and decreases pressure drop in the condenser. It is noted that the plate length of PHE has a positive effect on the optimization design of PHE. By multi-objective optimization design of the PHE, a Pareto optimal point curve is obtained, which shows that a decrease in total heat transfer surface area of a condenser can increase the pressure drop through the condenser.     

How to select regenerative configurations of CO2 transcritical Rankine cycle based on the temperature matching analysis

CO₂ transcritical Rankine cycle is regarded as a potential technology for internal combustion engines waste heat recovery, and its regenerative configurations present great prospect to increase the power output capacity. This paper proposed different regenerator layout configurations based on the temperature matching analysis, including low temperature regenerative transcritical Rankine cycle (LR-TRC), high temperature regenerative transcritical Rankine cycle (HR-TRC), dual regenerative transcritical Rankine cycle (DR-TRC) and split dual regenerative transcritical Rankine cycle (SR-TRC). Afterward, the thermodynamics, electricity production cost (EPC) and miniaturization performance are implemented. The results show that regenerative configurations have an effect on improving net power output and SR-TRC obtained optimal value of net power output. For the perspective of economic performance, the greatest value is obtained for HR-TRC among four regenerative configurations. As for the miniaturization performance, the total heat transfer area increment of LR-TRC is the lowest. The comparative analysis results offer guidance for selecting optimal regenerative configurations.     

Experimental investigation of a combined ejector-absorption refrigerator

This paper describes an experimental study of a novel heat-operated refrigeration cycle, ‘combined ejector-absorption refrigeration cycle’. In this novel cycle, an ejector was placed between a generator and a condenser of a conventional single-effect absorption refrigerator. The high-pressure vapour refrigerant produced in the generator section was used as the motive fluid for the ejector which entrained low-pressure refrigerant vapour from the evaporator and discharged it to the condenser. This was shown to significantly increase the cooling capacity and COP of the novel refrigerator above that of a conventional absorption unit with little increase in system complexity. © 1998 John Wiley & Sons, Ltd.     

Simulation of performance of intermediate fluid vaporizer under wide operation conditions

The intermediate fluid vaporizer (IFV) is a typical vaporizer of liquefied natural gas (LNG), which in general consists of three shell-and-tube heat exchangers (an evaporator, a condenser, and a thermolator). LNG is heated by seawater and the intermediate fluid in these heat exchangers. A one-dimensional heat transfer model for IFV is established in this paper in order to investigate the influences of structure and operation parameters on the heat transfer performance. In the rated condition, it is suggested to reduce tube diameters appropriately to get a large total heat transfer coefficient and increase the tube number to ensure the sufficient heat transfer area. According to simulation results, although the IFV capacity is much larger than the simplified-IFV (SIFV) capacity, the mode of SIFV could be recommended in some low-load cases as well. In some cases at high loads exceeding the capacity of a single IFV, it is better to add an AAV or an SCV operating to the IFV than just to increase the mass flow rate of seawater in the IFV in LNG receiving terminals.     

Design and Optimization of a Full-Generation System for Marine LNG Cold Energy Cascade Utilization

This paper took a 100,000 DWT LNG fuel powered ship as the research object.Based on the idea of"temperature matching,cascade utilization"and combined with the application conditions of the ship,a horizontal three-level nested Rankine cycle full-generation system which combined the high-temperature waste heat of the main engine flue gas with the low-temperature cold energy of LNG was proposed in this paper.Furthermore,based on the analysis and selection of the parameters which had high sensitivity to the system performance,the parameters of the proposed system were optimized by using the genetic algorithm.After optimization,the exergy efficiency of the marine LNG gasification cold energy cascade utilization power generation system can reach 48.06%,and the thermal efficiency can reach 35.56%.In addition,this paper took LNG net power generation as the performance index,and compared it with the typical LNG cold energy utilization power generation system in this field.The results showed that the unit mass flow LNG power generation of the system proposed in this paper was the largest,reaching 457.41 k W.     

温差发电和动力装置联合回收液化天然气冷能

对液化天然气(LNG)冷能的回收,提出了温差发电器与动力装置联合的回收系统,对系统的各个状态 参数和转化能量及其效率进行了分析计算。计算显示甲烷在天然气中的摩尔含量会显著地影响功量的输出,但 对系统的效率影响不大。系统对LNG最大可用能的回收效率可达29％。     

On site experimental evaluation of a low-temperature solar organic Rankine cycle system for RO desalination

The paper presents the on site experimental evaluation of the performance of a low-temperature solar organic Rankine cycle system (SORC) for reverse osmosis (RO) desalination. This work is a research step forward to the experimental evaluation of the SORC under laboratory conditions, where the system was tested using an electric brake as load and an electric thermal heater as heat supply. The difference is that solar collectors have been applied as heat supply and there has been a realistic investigation of the performance of the system under the conditions implied by solar energy. The thermal energy produced by the solar collectors’ array evaporates the refrigerant HFC-134a in the pre-heater-evaporator surfaces of the Rankine engine. The superheated vapour is then driven to the expander, where the generated mechanical work produced from expansion drives the high-pressure pump of the RO desalination unit. The superheated vapour at the expander’s outlet is directed to the condenser and condensates. Finally, the saturated liquid at the condenser outlet is pressurized by a positive displacement pump and the thermodynamic cycle is repeated. A special energy recovery system of Axial Pistons Pumps (APP) has been integrated into the RO unit to minimise the specific energy consumption. The results prove that the above concept is technically feasible and continuous operation is achieved under the intermittent availability of solar energy. However, considerably low efficiency has been observed, in comparison with the results taken under controlled thermal load. Nevertheless, it becomes apparent that further optimisation work is required to improve the system efficiency. The research work has been done within the framework of COOP-CT-2003-507997 contract, partly financed by EC.     

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.     

Modelling of organic Rankine cycle system and heat exchanger components

Numerical models of a standard organic Rankine cycle (ORC) system and the heat exchangers comprising the system are developed as a design tool platform for a flexible design. The objective is design of an efficient, cost-effective ORC power plant that can effectively exploit low-grade industrial waste heat or low to medium-temperature geothermal fluid. Typical heat exchanger configurations were modelled, including the circular finned-tube evaporator, air-cooled condenser, and flat-plate preheater. A published ORC configuration and process conditions from experiments are used for the thermodynamic cycle analysis in order to validate of the system model. Heat transfer correlations and friction factors are described for the modelling of the heat exchangers. The simulation results of the ORC system provide the design requirements for the heat exchangers. Geometric specifications and performance of the heat exchangers are determined by iterative simulations.     

Thermodynamic analysis of a new double-pressure condensation power generation system recovering LNG cold energy for hydrogen production

Cold energy during the LNG regasification process is usually applied for power generation, but the electricity demand varies with the time. Therefore, a thought that transforming electrical energy into hydrogen energy by PEM electrolyzer is put forward to adjust the adaptability of power output to electricity demand. This paper proposes a new double-pressure condensation Rankine cycle integrated with PEM electrolyzer for hydrogen production. In this system, seawater is used as the heat source, and binary mixed working fluids are applied. Meanwhile, multi-stream heat exchanger is introduced to improve the irreversibility of heat transfer between LNG and working fluid. The key system parameters, including seawater temperature, the first-stage condensation temperature, the second-stage condensation temperature, and outlet temperature of LNG, are studied to clarify their effects on net power generation, hydrogen production rate and energy efficiency. Furthermore, the hydrogen production rate is as the objective function, these parameters are optimized by genetic algorithm. Results show that seawater temperature has positive impact on the net power output and hydrogen production rate. The first-stage condensation temperature, the second-stage condensation temperature, and outlet temperature of LNG have diverse effects on the system performance. Under the optimal working conditions, when the LNG regasification pressure are 600, 2500, 3000 and 7000 kPa, the increasing rate for optimized net power output, hydrogen production rate and energy efficiency are more than 11.68%, 11.67% and 8.88%, respectively. The cost of hydrogen production with the proposed system varies from 1.93 $/kg H2 to 2.88 $/kg H2 when LNG regasification pressure changes from 600 kPa to 7000 kPa.     

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.     

跨临界-亚临界复叠式有机朗肯循环性能分析

热源温度高于473.15 K时,复叠式有机朗肯循环(organic Rankine cycle,ORC)可避免高温下工质热分解、膨胀比过大等缺点,相对单级ORC更具优势.跨临界循环相较常规亚临界具有更高的吸热压力及更好的热源匹配性,其与复叠式ORC耦合有望获得更优的热力性能.因此,构建了跨临界-亚临界复叠式ORC(TS...     

Preliminary analysis of compound systems based on high temperature fuel cell, gas turbine and Organic Rankine Cycle

This article presents a novel proposal for complex hybrid systems comprising high temperature fuel cells and thermal engines. In this case, the system is composed by a molten carbonate fuel cell with cascaded hot air turbine and Organic Rankine Cycle (ORC), a layout that is based on subsequent waste heat recovery for additional power production. The work will credit that it is possible to achieve 60% efficiency even if the fuel cell operates at atmospheric pressure.The first part of the analysis focuses on selecting the working fluid of the Organic Rankine Cycle. After a thermodynamic optimisation, toluene turns out to be the most efficient fluid in terms of cycle performance. However, it is also detected that the performance of the heat recovery vapour generator is equally important, what makes R245fa be the most interesting fluid due to its balanced thermal and HRVG efficiencies that yield the highest global bottoming cycle efficiency. When this fluid is employed in the compound system, conservative operating conditions permit achieving 60% global system efficiency, therefore accomplishing the initial objective set up in the work.A simultaneous optimisation of gas turbine (pressure ratio) and ORC (live vapour pressure) is then presented, to check if the previous results are improved or if the fluid of choice must be replaced. Eventually, even if system performance improves for some fluids, it is concluded that (i) R245fa is the most efficient fluid and (ii) the operating conditions considered in the previous analysis are still valid.The work concludes with an assessment about safety-related aspects of using hydrocarbons in the system. Flammability is studied, showing that R245fa is the most interesting fluid also in this regard due to its inert behaviour, as opposed to the other fluids under consideration all of which are highly flammable.     

超临界有机朗肯循环低温余热发电系统的分析

当采用朗肯循环方式回收低温余热（350℃以下）的动力时,不宜采用水作工质,而使用一些低沸点有机物的有机朗肯循环（ORCs）,则能获得较高的能量转换效率。有机朗肯循环可分为亚临界条件下的动力循环与超临界条件下的动力循环,超临界条件下的动力循环在热端换热器中（余热加热蒸汽发生器）能获得较好的温度匹配和较高的[火用]效率。