燃气轮机废热利用的新型动力系统热力学分析

基于能量等级回收和梯级利用的原则,构建了一种燃气轮机废热利用的新型动力系统。该系统主要由燃气轮机布雷顿循环(GTC)、再压缩式超临界CO₂布雷顿循环(S-CO₂)、朗肯循环(RC)、有机朗肯循环(ORC)和有机闪蒸循环(OFC)组成。该动力系统不仅克服了单个子循环热量回收范围窄的局限性,而且通过回热的方式实现了能量的梯级利用,进而提高了系统效率。通过Aspen HYSYS软件对构建的动力系统及各子循环分别进行模拟仿真,进一步研究了工况参数对系统的影响。与现有文献中的数据对比表明,该动力系统中各子循环均得到较好的验证。在相同工况条件下,文献中动力系统净功率为48 592.84 kW,热效率和火用效率分别为42.41%和62.02%,而本研究系统净功率为50 040.46 kW,热效率和火用效率分别达到43.673%和73.593%。因此,该新型动力系统具有较好的能源利用效果。     

The exergy of the ocean thermal resource and analysis of second-law efficiencies of idealized ocean thermal energy conversion power cycles

We develop a fomula here to compute the maximum amount of work which can be extracted from a given combined mass of warm and cold ocean water (a quantity called the exergy of the ocean thermal resource). We then compare the second-law efficiencies of various proposed ocean thermal energy conversion power cycles to determine which best utilizes the exergy of the ocean thermal resource. The second-law efficiencies of the multicomponent working fluid cycle, the Beck cycle, and the open and closed single- and multiple-stage Rankine cycles are compared. These types of OTEC power plants are analyzed in a consistent manner, which assumes that all deviations from a plant making use of all the exergy (one with a second-law efficiency of 100%) occur because of irreversible transfer of heat across a finite temperature difference. Conversion of thermal energy to other forms is assumed to occur reversibly. The comparison of second-law efficiencies of various OTEC power cycles shows that the multistage Rankine open cycle with just three stages has the potential of best using the exergy of the ocean thermal resource.     

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power is proposed and analyzed in this paper. Unlike a conventional organic Rankine cycle, a supercritical Rankine cycle does not go through the two-phase region during the heating process. By adopting zeotropic mixtures as the working fluids, the condensation process also happens non-isothermally. Both of these features create a potential for reducing the irreversibilities and improving the system efficiency. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle can achieve thermal efficiencies of 10.8-13.4% with the cycle high temperature of 393 K-473 K as compared to 9.7-10.1% for the organic Rankine cycle, which is an improvement of 10-30% over the organic Rankine cycle. When including the heating and condensation processes in the system, the system exergy efficiency is 38.6% for the proposed supercritical Rankine cycle as compared to 24.1% for the organic Rankine cycle.     

Energetic and exergetic analysis of CO2- and R32-based transcritical Rankine cycles for low-grade heat conversion

Transcritical Rankine cycles using refrigerant R32 (CH₂F₂) and carbon dioxide (CO₂) as the working fluids are studied for the conversion of low-grade heat into mechanical power. Compared to CO₂, R32 has higher thermal conductivity and condenses easily. The energy and exergy analyses of the cycle with these two fluids shows that the R32-based transcritical Rankine cycle can achieve 12.6–18.7% higher thermal efficiency and works at much lower pressures. An analysis of the exergy destruction and losses as well as the exergy efficiency optimization of the transcritical Rankine cycle is conducted. Based on the analysis, an “ideal” working fluid for the transcritical Rankine cycle is conceived, and ideas are proposed to design working fluids that can approach the properties of an “ideal” working fluid.     

基于液态金属朗肯循环的空间双模式核热推进系统性能分析

随着深空探测技术的进步,空间核动力越来越成为载人航天任务的理想选择,将双模式空间核动力推进系统应用于航天推进系统已成为一种新的趋势。基于空间核能液态金属朗肯循环,提出一种新型的双模式核热推进系统,并对该推进系统发电模式下的液态金属朗肯循环进行了性能分析。利用能量分析和?分析的方法对双模式核热推进系统下的朗肯循环进行热力计算,得出各部件的能量损失和?损,找出损失最大的部件并分析原因,取不同的空间环境温度研究其对?损和?效率的影响,为系统的进一步优化提供理论依据。     

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。     

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.     

A new power/cooling cogeneration system using R1234ze(E)/ionic liquid working fluid

A novel power/cooling system integrated with organic Rankine cycle and absorption-compression refrigeration cycle was proposed in order to realize the cascade utilization of low-grade energy. In the proposed system, R1234ze(E) (trans-1,3,3,3-tetrafluoropropene) is used as the working fluid for the organic Rankine cycle subsystem and the binary mixtures of R1234ze(E) with three ionic liquids [HMIM][BF₄], [EMIM][BF₄] and [OMIM][BF₄] are used as working fluid for absorption-compression refrigeration cycle subsystem due to their superior environmental protection property and physicochemical property. Moreover, in order to recover the heat of the exhaust gas from turbine in organic Rankine cycle subsystem, the exhaust gas is mixed with R1234ze(E)/ionic liquid solution directly in desorber, while the heat of refrigerant from desorber is recovered to reduce the heat load of condenser. The proposed system has much higher energy and exergy efficiency and lower heat load of condenser than reference system. Under specific conditions, increases of 0.24 and 0.07 in thermal efficiency and exergy efficiency of reference system can be achieved. The effect of distribution ratio, expansion ratio, heat source temperature, condensation temperature, generation temperature, evaporation temperature and compression ratio were analyzed for better design in actual application.     

Thermodynamic analysis of a multigeneration system using solid oxide cells for renewable power-to-X conversion

A hybrid renewable-based integrated energy system for power-to-X conversion is designed and analyzed. The system produces several valuable commodities: Hydrogen, electricity, heat, ammonia, urea, and synthetic natural gas (SNG). Hydrogen is produced and stored for power generation from solar energy by utilizing solid oxide electrolyzers and fuel cells. Ammonia, urea, and synthetic natural gas are produced to mitigate hydrogen transportation and storage complexities and act as energy carriers or valuable chemical products. The system is analyzed from a thermodynamic perspective, the exergy destruction rates are compared, and the effects of different parameters are evaluated. The overall system's energy efficiency is 56%, while the exergy efficiency is 14%. The highest exergy destruction occurs in the Rankine cycle with 48 MW. The mass flow rates of the produced chemicals are 0.064, 0.088, and 0.048 kg/s for ammonia, urea, and SNG, respectively.     

低温地热发电有机朗肯循环的优化

采用(火用)分析方法及PR状态方程,建立了低温地热发电有机朗肯循环的工质优选及主要参数优化热力学方法.比较计算了以10种干流体有机工质为循环工质的低温地热发电有机朗肯循环的输出功率、(火用)效率及其余主要热力性能.结果表明,低温地热发电有机朗肯循环的性能极大地受工质的物性及蒸发温度的影响.总体来看,随着工质临界温度的升...     

Performance investigation in modified and improved augmented power generation Kalina cycle using Python

In the generation of electricity and cogeneration, Kalina cycle is considered as one of the competitors to organic Rankine cycle. With the simplicity and identical components of the binary mixture, Kalina system makes it more prominent to get developed and implemented as well with its environmental friendly associate. This work proposes a new improved Kalina cycle system to convert the natural source from sun to useful work. The proposed system utilizes heat source suitable to medium temperature heat applications. The proposed cycle have 2 units of solar collector, favoring an additional heat recovery and higher performance. Solar hot source temperature and pressure are 190°C and 45 bar with additional flow to the turbine of 1.15 kg/s. Energy and second law analysis have considered in evaluating the performance of the proposed plant. The energy analysis shows minimum value of net power, energy efficiency and plant efficiency as 241 kW, 15.5% and 5.7. The exergy analysis defines that, to the proposed cycle, the exergy efficiency initializes at 77% with more exergy destruction at turbine with 31%. With the parametric analysis, the system is amended to have the maximum values of energy and exergy performances as 18.5%, 7.1% and 85%. The parametric study identifies the optimum value of the inlet temperature and pressure of the pump and turbine.     

Performance assessment and optimization of a biomass-based solid oxide fuel cell and micro gas turbine system integrated with an organic Rankine cycle

Rice straw is a potential energy source for power generation. Here, a biomass-based combined heat and power plant integrating a downdraft gasifier, a solid oxide fuel cell, a micro gas turbine and an organic Rankine cycle is investigated. Energy, exergy, and economic analyses and multi-objective optimization of the proposed system are performed. A parametric analysis is carried out to understand the effects on system performance and cost of varying key parameters: current density, fuel utilization factor, operating pressure, pinch point temperature, recuperator effectiveness and compressors isentropic efficiency. The results show that current density plays the most important role in achieving a tradeoff between system exergy efficiency and cost rate. Also, it is observed that the highest exergy destruction occurs in the gasifier, so improving the performance of this component can considerably reduce the system irreversibility. At the optimum point, the system generates 329 kW of electricity and 56 kW of heating with an exergy efficiency of 35.1% and a cost rate of 10.2 $/h. The capability of this system for using Iran rice straw produced in one year is evaluated as a case study, and it is shown that the proposed system can generate 6660 GWh electrical energy and 1140 GWh thermal energy.     

SECOND LAW ANALYSIS OF A SOLAR THERMAL POWER SYSTEM

This communication presents second law analysis based on exergy concept for a solar thermal power system. Basic energy and exergy analysis for the system components (viz. parabolic trough collector/receiver and Rankine heat engine etc.) are carried out for evaluating the energy and exergy losses as well as exergetic efficiency for typical solar thermal power system under given operating conditions. Relevant energy flow and exergy flow diagrams are drawn to show the various thermodynamic and thermal losses. It is found that the main energy loss takes place at the condenser of the heat engine part whereas the exergy analysis shows that the collector-receiver assembly is the part where the losses are maximum. The analysis and results can be used for evaluating the component irreversibilities which can also explain the deviation between the actual efficiency and ideal efficiency of solar thermal power system.     

Exergy analysis,parametric analysis and optimization for a novel combined power and ejector refrigeration cycle

A new combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the ejector refrigeration cycle. This combined cycle produces both power output and refrigeration output simultaneously. It can be driven by the flue gas of gas turbine or engine, solar energy, geothermal energy and industrial waste heats. An exergy analysis is performed to guide the thermodynamic improvement for this cycle. And a parametric analysis is conducted to evaluate the effects of the key thermodynamic parameters on the performance of the combined cycle. In addition, a parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The results show that the biggest exergy loss due to the irreversibility occurs in heat addition processes, and the ejector causes the next largest exergy loss. It is also shown that the turbine inlet pressure, the turbine back pressure, the condenser temperature and the evaporator temperature have significant effects on the turbine power output, refrigeration output and exergy efficiency of the combined cycle. The optimized exergy efficiency is 27.10% under the given condition.     

Exergy analysis of micro-organic Rankine power cycles for a small scale solar driven reverse osmosis desalination system

Exergy analysis of micro-organic Rankine heat engines is performed to identify the most suitable engine for driving a small scale reverse osmosis desalination system. Three modified engines derived from simple Rankine engine using regeneration (incorporation of regenerator or feedliquid heaters) are analyzed through a novel approach, called exergy-topological method based on the combination of exergy flow graphs, exergy loss graphs, and thermoeconomic graphs. For the investigations, three working fluids are considered: R134a, R245fa and R600. The incorporated devices produce different results with different fluids. Exergy destruction throughout the systems operating with R134a was quantified and illustrated using exergy diagrams. The sites with greater exergy destruction include turbine, evaporator and feedliquid heaters. The most critical components include evaporator, turbine and mixing units. A regenerative heat exchanger has positive effects only when the engine operates with dry fluids; feedliquid heaters improve the degree of thermodynamic perfection of the system but lead to loss in exergetic efficiency. Although, different modifications produce better energy conversion and less exergy destroyed, the improvements are not significant enough and subsequent modifications of the simple Rankine engine cannot be considered as economically profitable for heat source temperature below 100 °C. As illustration, a regenerator increases the system’s energy efficiency by 7%, the degree of thermodynamic perfection by 3.5% while the exergetic efficiency is unchanged in comparison with the simple Rankine cycle, with R600 as working fluid. The impacts of heat source temperature and pinch point temperature difference on engine’s performance are also examined. Finally, results demonstrate that energy analysis combined with the mathematical graph theory is a powerful tool in performance assessments of Rankine based power systems and permits meaningful comparison of different regenerative effects based on their contribution to systems improvements.     

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.     

Performance analysis of a waste‐heat‐powered thermodynamic cycle for multieffect refrigeration

A multieffect refrigeration system that is based on a waste‐heat‐driven organic Rankine cycle that could produce refrigeration output of different magnitudes at different levels of temperature is presented. The proposed system is integration of combined ejector–absorption refrigeration cycle and ejector expansion Joule–Thomson (EJT) cooling cycle that can meet the requirements of air‐conditioning, refrigeration, and cryogenic cooling simultaneously at the expense of industrial waste heat. The variation of the parameters that affect the system performance such as industrial waste heat temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector refrigeration cycle (ERC) and EJT cycles was examined, respectively. It was found that refrigeration output and thermal efficiency of the multieffect cycle decrease considerably with the increase in industrial waste heat temperature, while its exergy efficiency varies marginally. A thermal efficiency value of 22.5% and exergy efficiency value of 8.6% were obtained at an industrial waste heat temperature of 210°C, a turbine inlet pressure of 1.3 MPa, and ejector evaporator temperature of 268 K. Both refrigeration output and thermal efficiency increase with the increase in turbine inlet pressure and ERC evaporator temperature. Change in EJT cycle evaporator temperature shows a little impact on both thermal and exergy efficiency values of the multieffect cycle. Analysis of the results clearly shows that the proposed cycle has an effective potential for cooling production through exploitation of lost energy from the industry. Copyright © 2014 John Wiley & Sons, Ltd.     

Energy,exergy and exergo-environmental impact assessment of a solid oxide fuel cell coupled with absorption chiller & cascaded closed loop ORC for multi-generation

A novel solid oxide fuel cell (SOFC) multigeneration system fueled by biogas derived from agricultural waste (maize silage) is designed and analyzed from the view point of energy and exergy analysis. The system is proposed in order to limit the greenhouse gas emissions as it uses a renewable energy source as a fuel. Electricity, domestic hot water, hydrogen and cooling load are produced simultaneously by the system. The system includes a solid oxide fuel cell; which is the primary mover, a biogas digester subsystem, a cascaded closed loop organic Rankine cycle, a single effect LiBr-water absorption refrigeration cycle, and a proton exchange membrane electrolyzer subsystem. The proposed cascaded closed-loop ORC cycle is considered as one of the advanced heat recovery technologies that significantly improve thermal efficiency of integrated systems. The thermal performance of the proposed system is observed to be higher in comparison to the simple ORC and the recuperated ORC cycles. The integration of a splitter to govern the flue gas separation ratio is also introduced in this study to cater for particular needs/demands. The separation ratio can be used to vary the cooling load or the additional power supplied by the ORC to the system. It is deduced that net electrical power, cooling load, heating capacity of the domestic hot water and total energy and exergy efficiency are 789.7 kW, 317.3 kW, 65.75 kW, 69.86% and 47.4% respectively under integral design conditions. Using a parametric approach, the effects of main parameters on the output of the device are analyzed. Current density is an important parameter for system performance. Increasing the current density leads to increased power produced by the system, decreased exergy efficiency in the system and increased energy efficiency. After-burner, air and fuel heat exchangers are observed to have the highest exergy destruction rates. Lower current density values are desirable for better exergy-based sustainability from the exergetic environmental impact assessment. Higher current density values have negative effect on the environment.     

4E analysis of efficient waste heat recovery from SOFC using APC: An effort to reach maximum efficiency and minimum emission through an application of grey wolf optimization

This article presents an innovative combined heat and power system comprising a solid oxide fuel cell (SOFC), a heat recovery unit, and a lithium bromide absorption power cycle (APC). The energy, exergy, economic, and environmental perspectives of the proposed system are compared against the same configuration using an organic Rankine cycle (ORC), recovering the waste heat of the SOFC. A multi-criteria optimization based on the Grey Wolf approach is applied to each system to specify the best operation conditions having the exergy efficiency and total cost rate as the objectives. Furthermore, a parametric investigation is conducted to assess the effects of changing the decision variables on the systems proficiencies. The results indicate that although the ORC-based cycle is economically very slightly superior, the integration of the SOFC with the APC offers a much higher exergy efficiency due to the better temperature matching between the working fluid and heat source. Optimization can increase the exergy efficiencies of the SOFC-ORC and the SOFC-APC systems by about 13.8% and 14.7% while reducing the total cost rate by 11.2 $/h and 11.0 $/h, respectively, compared to the base system. Environmental analysis results reveal that APC use leads to a lower emission of 2.8 kg/MWh.     

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.