低温热能有机物发电系统热力分析

首先介绍了ORC循环工质的热力学和一些性质,指出工质应满足压力、干湿性以及环保等方面的要求,然后以R123、R21和R245fa工质为例给出了热源温度低于:100℃情况下ORC发电系统的热力学模型分析,比较了不同工质下系统工作参数对ORC性能的影响规律,并且指出工质R245fa是综合考虑环保、热力性能等因素下的较好的选择.     

非共沸工质与纯工质在ORC系统中的特性比较研究

工质的特性是影响ORC(有机朗肯循环)系统性能的重要因素之一。建立了65~100℃低温地热水有机朗肯循环发电系统数学模型,将R245fa分别与R601a和R227ea以不同比例混合作为ORC系统的工质,比较了非共沸混合物和纯物质两类工质对ORC系统循环净功、热效率和火用效率的影响。研究结果表明:无论是纯工质还是非共沸工质,系统的循环净功、热效率和火用效率都随着热源温度的升高而增大。工质在相变过程中是否存在温度滑移,是影响ORC系统性能的重要因素之一。在65~100℃的热源条件下,综合考虑3个评价指标,当R245fa配比为0.1~0.7时,R245fa/R601a混合物的循环净功、热效率和火用效率分别提升0.012~2.48 k W、0.005%~1.15%和0.08%~10.7%;当R245fa配比为0.5~0.9时,R245fa/R227ea混合物的循环净功、热效率和火用效率分别提升0.049~4.25 k W、0.057%~1.75%和0.21%~16.1%。     

R1234yf有机朗肯循环系统热力学性能研究

为提高有机朗肯循环（Organic Rankine Cycle, ORC）在中低温地热发电领域的效率,本文以R1234yf为工质,依据热力学第一定律与第二定律分析了系统单位质量热水净发电功率和系统?效率,并与目前应用广泛的R245fa工质进行了性能对比。研究结果表明,存在最佳蒸发温度和最佳冷凝温度,使得ORC发电系统单位质量热水净发电功率、?效率最大。对于热源温度为110℃ ~ 150℃的ORC发电系统,R1234yf对应的最大系统单位质量热水净发电功率和最大?效率均大于R245fa     

中低温热水发电系统循环参数和工质的选择

针对热源为80～150℃热水的有机朗肯循环（ORC）发电系统,以发电功率和效率为评价指标,分别分析了以R134a、R123和R245fa三种工质为循环介质时的系统,确定了最佳循环参数和工质。一般来说,最佳蒸发温度对应着最大的输出电功,且随着热流体温度的升高而升高;当热源温度大于120℃时,R134a的系统不存在最佳蒸发温度,此时输出电功随着蒸发温度的升高而增大。对于80～135℃的热水,工质R245fa的发电功率最大;当热水温度超过135℃时,工质R134a的发电功率最大。工质R245fa的发电效率始终是最大的。     

采用不同工质的高温复合热泵开水器特性研究

热泵开水器具有较高的能源利用效率,是公共场所电加热开水装置的理想替代品。从提高能源效率和一机两用的角度,构建了一种高温复合热泵开水器系统。建立了系统热力学模型,选R236fa、R245fa、R365mfc、R245ca、RC318和R236ea等6种较高临界温度的制冷工质,通过能量分析和[火用]分析的方法,探讨了不同制冷工质对高温复合热泵开水器系统性能的影响。研究结果表明:R245fa作为工质的高温复合热泵开水器系统具有最佳的性能,而以RC318作为工质的系统性能最差。在给定工况下,R245fa作为工质系统制热性能系数(COP_h)为2.47,而其制冷性能系数(COP_c)为3.37,[火用]损失和[火用]效率分别为9.47 kW和49.07%;与R245fa相比,RC318作为工质系统的总能耗增加了39.53%。     

不同工况下非共沸混合工质有机朗肯循环系统性能研究

采用MATLAB软件模拟非共沸混合工质在不同冷热源条件下对有机朗肯循环(ORC)系统性能的影响。选取R245fa/R1234ze和R245fa/R600a作为混合工质,热源温度取120和200℃,分别在冷凝露点温度为40℃和冷却水温升为5,10,15℃的工况条件下,利用热力学第一定律和火积理论对系统性能进行分析。结果表明：热源温度为200℃时,R245fa, R1234ze和R600a系统净输出功率分别为89.83,61.87和77.74 kW,使用R245fa系统性能优于其混合工质;热源温度为120℃、固定冷凝露点温度时,混合工质R245fa/R600a(90%∶10%)净输出功率比R245fa和R600a分别提高了27.6%和27%,R245fa/R1234ze(60%∶40%)净输出功率比R245fa和R600a分别提高了26%和20.5%;火积耗散和单位面积做功量与净输出功率变化相反,提高冷却水温升时,增大了系统火积耗散,且流向环境中的火积耗散在总火积耗散中占比增大,导致系统的传热不可逆损失增加。     

低温蒸汽_太阳能双热源ORC发电系统热力性能分析

为充分回收矿藏热采过程尾端低温蒸汽余热,提出一种通过利用太阳能热量补充预热器中热源显热以缩小换热温差的新型低温蒸汽-太阳能双热源ORC发电系统。根据热力学第一、第二定律,建立其热力学模型,编制计算程序并进行了热力性能分析及比较。计算结果表明:采用热源补助可有效减小换热温差,进而显著提升系统热力性能。当采用R245fa作为循环工质时,与基本的ORC系统相比,选择冷端温差较小的预热器可使双热源系统火用效率显著增加;在预热器冷端温差为30 K、两系统分别采用5种不同循环工质时,双热源ORC系统的热力性能均高于基本ORC系统,且以R236fa为工质的双热源ORC系统热力性能最佳。     

超_亚临界ORC联合发电系统热力性能分析

本研究在单纯超临界、亚临界的ORC(有机朗肯循环)发电系统基础上,提出一种新型超临界、亚临界ORC联合发电系统,并建立其理论模型。通过编制计算机程序,分别对单纯超临界、亚临界ORC以及新型联合发电系统的热力性能进行比较。结果表明:采用R143a、R245fa作为联合系统的两循环区工质,当依次单独改变超临界、亚临界区蒸发压力时,各循环区质量流量变化与单纯超临界、亚临界ORC相似。前者随蒸发压力的增大而逐渐递增,后者则呈相反变化趋势,联合发电系统的热力性能均优于单纯超临界、亚临界ORC。同时随两循环区蒸发压力的增大而不断提高,但增幅减小,且提高超临界区蒸发压力可使系统热力性能最佳。采用R134a、R245fa作为系统两循环区有机工质,可使联合发电系统火用损失达到最小。     

新型梯级换热有机朗肯循环系统热力性能分析

为了充分提高低品位能源利用过程中的回收利用率,降低热源排放温度,本研究提出一种基于热源分流的新型梯级换热、梯级发电的有机朗肯循环系统。系统以地热水为热源,分析了在给定热源工况时,蒸发温度对系统性能的影响以及在不同热源工况下,采用R123、R245fa及R152a3种工质互相组合时,系统性能的变化规律。结果表明,梯级ORC(有机朗肯循环)存在最佳蒸发温度,且其性能优于单级ORC循环,在T_g=373 K时,其输出功增加59.12 k W。随热源工况变化,两级循环中最佳工质分别变化,若两级循环均在亚临界区工作,则一级循环工质临界温度越低、二级循环工质临界温度越高系统性能越好;若两级循环中存在近临界运行工况,则应选择可使系统在近临界下运行工质。根据不同运行工况,合理选择最佳工质,对提高该梯级换热ORC系统性能具有重要意义。     

喷射器对地热有机朗肯循环发电系统性能的影响

为了缓解由于冷凝温度较高带来的高背压问题,提出一种带喷射器的ORC(有机朗肯循环)发电系统。针对373 K地热热源,分析了不同工质及冷凝温度下,喷射器对系统性能的影响,并将其在有/无分流2种工况下进行比较。结果表明:采用喷射装置可提高系统性能,存在一最佳升压比a使系统性能最大,其中ORC-分流喷射系统ORC-喷射系统ORC系统,若以R245fa为工质,在Tc=298 K时,经分流喷射的系统较喷射ORC及ORC系统火用效率分别高出1.89%和6.43%。工质临界温度越高,采用喷射装置对系统性能提高越大,通过分流可以削弱工质对喷射装置的影响,使其更接近ORC系统的工质表现规律:R236faR114R245faR152a。当系统冷凝温度较高时,采用喷射装置具有重要意义。     

不同工质对太阳能有机朗肯循环系统性能的影响

循环工质的特性是影响有机朗肯循环系统性能的重要因素之一,在不同的蒸发温度条件下,选取R600、R600a、R245fa、R236fa、R236ea、R601、R601a、RC318及R227ea共9种有机工质,基于热力学第一定律和第二定律对其热力循环特性进行了计算分析,并对各有机工质的蒸发压力、热效率、功比和不可逆损失等进行了比较.结果表明：R245fa作为太阳能低温热发电朗肯循环系统的循环工质具有较高的热效率和效率,并且产生的系统总不可逆损失较小,是一种较理想的有机工质;其次,R236fa和R236ea作为系统循环工质也具有较为良好的性能.     

Material Compatibility of Hexamethyldisiloxane as Organic Rankine Cycle Working Fluids at High Temperatures

The organic Rankine cycle(ORC)is a promising technology for industrial waste heat recovery and renewable energy utilization.High temperature ORCs have attracted particular interest because of their high thermal efficiencies and outputs.The material compatibility of working fluid is a significant limitation for the working fluid selection and system design for high temperature ORCs.This work presents a method for studying the material compatibility of ORC working fluids based on the calculated conditions of the ORCs and matching of components,temperatures,and materials.Hexamethyldisiloxane(MM)was chosen as the test fluid.The experimental results show that 304 stainless steel has better compatibility with MM than copper as the material of evaporators.Fluoric rubber is not a suitable sealing material for high temperature ORCs with MM as the working fluids because of the bad compatibility.Mineral oil has better compatibility with MM than polyol ester(POE)lubricant as the lubricant for the fluid pump.     

低温余热有机朗肯循环发电系统工质选择

对有机朗肯循环系统工质的优化选择已逐渐从单一优化目标向多目标发展,但所选的优化目标及优化方法普遍存在主观性较强的问题.针对上述问题,从环保性、安全性等方面对工质进行初选,得到了R123、R245fa、R245ca和R601等9种工质,然后采用主成分分析法对工质的热效率、循环净功和不可逆损失等7个热力性能指标进行了分析计算,得到了两个较为客观的综合评价指标,并在不同蒸发温度下对工质的综合热力性能进行了分析.结果表明:R601做功能力较强,综合效率较高,是该循环系统较为理想的工质.     

Energetic and exergetic analysis of waste heat recovery from a microturbine using organic Rankine cycles

This article examines the exhaust waste heat recovery potential of a microturbine (MT) using an organic Rankine cycle (ORC). Possible improvements in electric and exergy efficiencies as well as specific emissions by recovering waste heat from the MT exhaust gases are determined. Different dry organic working fluids are considered during the evaluation (R113, R123, R245fa, and R236fa). In general, it has been found that the use of an ORC to recover waste heat from MTs improves the combined electric and exergy efficiencies for all the evaluated fluids, obtaining increases of an average of 27% when the ORC was operated using R113 as the working fluid. It has also been found that higher ORC evaporator effectiveness values correspond to lower pinch point temperature differences and higher exergy efficiencies. Three different MT sizes were evaluated, and the results indicate that the energetic and exergetic performance as well as the reduction of specific emissions of a combined MT‐ORC is better for small MT power outputs than for larger MTs. This article also shows how the electric efficiency can be used to ascertain under which circumstances the use of a combined MT‐ORC will result in better cost, primary energy consumption, or emission reduction when compared with buying electricity directly from electric utilities. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of dry hydrocarbons and critical point temperature on the efficiencies of organic Rankine cycle

Higher efficiencies and optimal utilization of geothermal energy require a careful selection of the working fluid in organic Rankine cycles (ORC). The objectives of this study are to analyze and explain the effect of using alternative dry fluids on the efficiencies of the ORC and compare them with other refrigerants. In addition, the effect of the critical temperature on the thermal and exergetic efficiencies will also be determined. Results showed that iso-pentane is a good replacement for R-113, while neo-pentane outperformed C₅F₁₂. In addition, n-butane showed better efficiency than RC-318, R-236fa, and R-245fa. The best working fluid in the studied system was n-hexane, while R-227ea was the worst. It was also found that efficiencies correlate with the critical temperature of the working fluid where a strong functionality was noticed in the studied range. The contribution of the evaporator to the total exergy destruction was the most relevant, while the pump contribution was marginal. It is concluded that thermodynamically, hydrocarbons are superior to some refrigerants and could be the next generation working fluids for geothermal or waste heat recovery systems.     

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.     

有机工质低温余热发电系统多目标优化设计

针对现有有机朗肯循环单目标优化设计的局限性,从热力性、经济性等多方面对有机工质低温余热发电系统进行多目标优化设计.以系统效率最大和总投资费用最小为目标函数,选取透平进口温度、透平进口压力、余热锅炉节点温差、接近点温差和冷凝器端差等5个关键热力参数作为决策变量,利用非支配解排序遗传算法(NSGA-II)分别对采用R123、R245fa和异丁烷的有机工质余热发电系统进行多目标优化,获得不同工质的多目标优化的最优解集(Pareto最优前沿),并采用理想点辅助法从最优解集中选择出最优解及相应的系统最佳热力参数组合.结果表明:在给定余热条件下,从热力性能和经济性两方面考虑,R245fa是最优的有机工质,从多目标优化的最优解集中选择出的最佳效率为10.37%,最小总投资费用为455.84万元.     

分级抽汽回热式太阳能低温有机朗肯循环系统的热力性能分析

研究了分级抽汽回热式太阳能低温有机朗肯循环系统的热力性能。以R600和R245fa作为循环工质,利用热力学第一定律和第二定律,在不同的蒸发温度和膨胀比的条件下,对分级抽汽回热式系统和基本有机朗肯循环系统的热力性能变化进行比较和分析,指出分级抽汽回热式系统的热效率和效率更高,产生的不可逆损失更小,具有更优越的性能。     

Comparison of a Basic Organic Rankine Cycle and a Parallel Double-Evaporator Organic Rankine Cycle

ABSTRACT

The applications of zeotropic mixtures and multi-evaporator systems are two viable options to improve the performance of the organic Rankine cycle (ORC). This paper conducts the thermo-economic comparison of a basic ORC with R245fa/R600a and a parallel double-evaporator organic Rankine cycle (PDORC) with R245fa. Four indicators are used to evaluate the system performance: net power, cycle efficiency, area of heat exchangers, and area of heat exchangers per net power output. Submodels of condensers and evaporators are established specially for pure organic fluids and zeotropic mixtures. The performance optimization using genetic algorithm is conducted to compare the two systems quantitatively. The optimization indicates a zeotropic mixture is more profitable than a pure work fluid in a basic ORC with a worthy additional investment of heat exchanger. Though PDORC can increase net power obviously, it would decrease the thermo-economic performance of ORC.