基于热源耦合ORC ANN模型的循环性能预测及工质优选

基于已建立的有机朗肯循环(ORC) 人工神经网络(ANN)模型,将其与热源进行耦合,从而在不同烟气工况下对ORC进行循环性能预测及工质优选。为了分析与热源耦合的ORC ANN模型精度,基于初选的10种工质,比较了该模型与REFPROP软件对基本ORC和回热ORC的计算结果,比较结果表明：该ORC ANN模型对大部分循环参数的平均相对偏差都小于5%。在此基础上,针对不同烟气热源温度（523.15,488.15和453.15 K）,以最大净输出功为目标,分别优化循环的蒸发温度,优化结果显示：3种热源温度对应的最佳工质分别为R1336mzz(Z),R600a和R236fa。     

换热器压降对ORC发电系统的影响

在考虑换热器压降及散热损失的情况下建立中低温地热驱动的有机朗肯循环(ORC)发电系统模型并通过500 kW示范工程进行验证。模型选取5种有机工质,研究换热器压降在不同热源温度、蒸发温度和冷凝温度下对系统性能的影响。研究结果表明随着热源温度以及蒸发温度的升高,压降对系统净发电量以及净发电效率的影响逐渐降低,但随着冷凝温度的升高,压降对系统净发电量的影响逐渐升高。其中,采用R227ea的系统受换热器压降影响最小,采用R123的系统受影响最大。     

Using the condenser effluent from a nuclear power plant for Ocean Thermal Energy Conversion (OTEC)

There has been increasing interest in clean energy over past few years. Ocean Thermal Energy Conversion (OTEC) power plants have been examined as a viable option for supplying clean energy. This paper evaluated the thermodynamic performance of the OTEC power system. Computer simulation programs were developed under the same conditions but with various working fluids for a closed system, a regeneration system, an open system, a Kalina system, and a hybrid system. The results showed that the regeneration system using R125 showed a 0.17 to 1.56% increase in system efficiency. Moreover, the system can generate electricity when the difference in temperature between the warm and cold seawater inlet temperatures is greater than 15 °C. In addition, the system efficiency of OTEC power plants using the condenser effluent from a nuclear power plant instead of surface water was increased by approximately 2%.     

基于动态透平效率的有机朗肯循环性能分析及优化

常规有机朗肯循环(ORC)中透平效率多假设为定值,而实际上透平效率因工质种类和运行参数的不同而有较大差异。因此,采用向心透平效率计算模型,将动态透平效率与ORC系统耦合,分析透平效率随蒸发温度与冷凝温度的变化规律,比较固定透平效率与动态透平效率ORC系统热效率的差异。综合考虑热力性与经济性,采用多目标优化算法,对固定透平效率与动态透平效率ORC系统进行工质筛选及参数优化,并对优化结果进行分析比较。结果表明:透平效率随蒸发温度的下降或者冷凝温度升高而增大;不同工质及不同蒸发冷凝温度条件下,透平效率差异较大,最大达0.148。固定透平效率ORC系统与动态透平效率ORC系统的热效率随蒸发温度的变化规律有较大差异,尤其在高蒸发温度区间更为明显。对于固定透平效率ORC系统,R245ca和R236ea为最佳工质;而对于动态透平效率ORC系统,R114为最佳工质。在引入动态透平效率前后,各工质的最佳蒸发温度与最佳冷凝温度也有较大变化。     

余热驱动的有机朗肯循环-复叠式制冷系统?分析

针对余热的有效利用,建立了有机朗肯循环-复叠式制冷系统的热力学模型,其中:有机朗肯循环系统分别采用R123、R1234ze、R245fa、R600a、RC318、R141b等六种工质;复叠式制冷系统分别采用R22/R23、R404/R23、R290/R744、R717/R744等四种工质对。选择系统?效率作为性能评价指标,运用热力学第二定律研究系统运行参数对系统?效率的影响,分析了系统各部件的?损失,并指出了能量利用的薄弱环节,提出了有效提高系统性能的建议,为系统的优化提供参考。结果表明,对系统?效率而言,R141b和R717/R744是最佳工质。系统主要部件按?损失大小依次为凝汽器、膨胀机、高温级冷凝器、发生器、高温级压缩机、低温级蒸发器、蒸发冷凝器。尽可能提高压缩机的等熵效率,优化设计换热器的结构,减小传热温差,才能减少不可逆损失,提高换热器的?效率。     

Thermo-economic analysis and optimization of a combined Organic Rankine Cycle (ORC) system with LNG cold energy and waste heat recovery of dual-fuel marine engine

A combined Organic Rankine Cycle (ORC) system with liquefied nature gas (LNG) cold energy and dual-fuel (DF) marine engine waste heat utilization was proposed. Engine exhaust gas and engine jacket cooling water were adopted as parallel heat sources. Thermo-economic analyses of the proposed system with 32 working fluids combinations were performed. Two objective functions covering thermal efficiencies and economic index were employed for performance evaluation. Afterward, the effects of operation pressure on the objective functions were investigated. Finally, the optimal conditions were obtained from the Pareto front with the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) method. The results show that the proposed ORC system has better energy recovery performances than the parallel ORC system. R1150-R600a-R290, R1150-R601a-R600a, and R170-R601-R290 are determined as the three most promising working fluids combinations. Under optimized conditions, the output power range is 199.97 to 218.51 kW, the energy efficiency range is 13.64% to 15.62%, and the exergy efficiency range is 25.29% to 27.3%. The payback period ranges from 8.36 to 8.74 years. The working fluids selection helps to reduce the exergy destruction of intermediate heat exchanger, which could be up to 30.59%.     

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.     

A study of organic working fluids on system efficiency of an ORC using low-grade energy sources

Rankine cycles using organic fluids (as categorized into three groups: wet, dry, and isentropic fluids) as working fluids in converting low-grade energy are investigated in this study. The main purpose is to identify suitable working fluids which may yield high system efficiencies in an organic Rankine cycle (ORC) system. Efficiencies of ORC systems are calculated based on an assumption that the inlet condition of the working fluid entering turbine is in saturated vapor phase. Parameters under investigation are turbine inlet temperature, turbine inlet pressure, condenser exit temperature, turbine exit quality, overall irrversibility, and system efficiency. The low-grade energy source can be obtained from a solar pond or/and an ocean thermal energy conversion (OTEC) system. Results indicate that wet fluids with very steep saturated vapor curves in T-s diagram have a better overall performance in energy conversion efficiencies than that of dry fluids. It can also be shown that all the working fluids have a similar behavior of the efficiency-condenser exit temperature relationship. Furthermore, an appropriate combination of solar energy and an ORC system with a higher turbine inlet temperature and a lower condenser temperature (as operated deeply under sea level) would provide an economically feasible and environment-friendly renewable energy conversion system.     

Assessment of blends of CO2 with butane and isobutane as working fluids for heat pump applications

In the present study, blends R744/R600 and R744/R600a are being proposed as working fluids in heat pumps for medium and high temperature heating applications. COP based performances have been evaluated for zeotropic mixtures of both working fluid pairs for various compositions and compared against that of pure working fluids. Effect of internal heat exchanger on blend based system performance is also presented and finally heat transfer issues in evaporation and condensation are discussed. Results show that due to gliding temperature during evaporation and condensation, the zeotropic blends, instead of pure counterparts, can be employed very effectively in heat pumps for variable temperature or simultaneous cooling and heating applications (e.g., dairy plants) at conventional high side pressure. The blend R744/R600a can be the best alternative refrigerant to R114 for high temperature heating due to superior COP (more than twice) over R600 and R600a and eliminating the requirement of extremely high side pressure of R744 systems.     

混合工质组分对ORC系统性能影响实验研究

针对低品位热能的特点,利用搭建的有机物朗肯循环(ORC)系统实验装置,对采用不同组分混合工质R600a/R601a的ORC系统性能进行实验研究,获得系统和部件特性随组分的变化规律。实验结果表明:随着混合工质中的R600a组分的增大膨胀比减小,下降幅度为38.4%,涡旋膨胀机效率受R600a组分变化的影响较小,在60%附近上下波动;净发电功率、工质吸热量和蒸发过程温度滑移量都随着R600a组分的增大先增大后减小,在R600a组分为0.4处,混合工质具有最大的净发电功率、吸热量和温度滑移量,净输出功率比纯R601a高出25%。这说明非等温相变特性可以使混合工质的吸热过程更好地与热源流体的放热过程相匹配,从而提高热能利用率,增加发电功率。     

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.     

分离式热管在不同高度差下传热性能的实验研究

本文以翅片管换热器作为蒸发端和冷凝端,R600a为循环工质,进行了分离式热管的实验研究。着重就不同的工作温度、不同冷凝端与蒸发端的高度差对分离式热管的传热性能的影响进行了研究。实验表明,在冷凝端进风温度恒定为16．55℃时,蒸发端进风温度低于60℃时,以R600a为工质的分离式热管的传热量曲线近似于二次曲线,蒸发端进风温度高于60℃时,其传热量曲线近似于一条直线。随着蒸发器与冷凝器的高度差的增大,分离式热管的传热能力得到提高。高度差为1m的分离式热管比高度差为0．8m的传热能力平均提高9．57％。     

Experimental investigation on the performance of ORC power system using zeotropic mixture R601a/R600a

An experimental study on the practical performance of organic Rankine cycle (ORC) system using zeotropic mixture is performed by using a small scale ORC power generation experimental setup. R601a/R600a is selected as the working fluid. The effects of mixture composition, heat source temperature, and working fluid flow rate on the performance of ORC system are investigated. The experimental results indicate that the net power output first increases and then decreases as the R600a concentration increases. The optimal mixture composition with the maximum net power output is 0.6/0.4 (mass fraction) at the heat source temperature of 115°C. The net power output of R601a/R600a (0.6/0.4) is higher than that of R601a by 25%, indicating that the performance of ORC system can be clearly improved by using the zeotropic mixture. For a fixed working fluid flow rate, both net power output and thermal efficiency first decrease slowly and then drop sharply with the decrease of the heat source temperature. The appropriate superheat degree of R601a/R600a is in the range of 15 to 20°C when the heat source temperature has a small variation. In addition, the optimal working fluid volume flow rates yielding the maximum net power output are obtained for different compositions of R601a/R600a. The experimental results in the study can be of great significance for the design and operation of ORC power system using zeotropic mixture. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance analyses and improvement guidelines for organic Rankine cycles using R600a/R601a mixtures driven by heat sources of 100°C to 200°C

R600a/R601a mixtures are promising to be widely used in organic Rankine cycle (ORC) systems and also can promote the popularization of ORC technology. While, most of existing studies on ORC systems using R600a/R601a mixtures are based on certain heat source temperatures (generally below 150°C) and saturated vapor at the evaporator outlet. Variations in the optimal mixture composition and superheat degree of R600a/R601a mixtures with increasing heat source temperature remain indeterminate thus far, especially for heat sources above 150°C. Suitable approaches to further improve the system thermodynamic performance are also unclear. This study carried out a systematized analysis for subcritical ORC systems using R600a/R601a mixtures driven by heat sources of 100°C to 200°C, based on the first and second law analysis methods. Guidelines for selections of optimal mixture composition and cycle parameters were provided. Characteristics of exergy loss distribution were revealed to point out the crucial process to further improve the system thermodynamic performance. Results show that the effects of critical parameters on the selections of optimal mixture composition and evaporation pressure become remarkable for heat sources above approximately 160°C. A minimum superheat degree is optimal for heat sources below 170°C, whereas the optimal superheat degree may increase with increasing heat source temperature and R600a mass fraction for heat sources above 170°C. Moreover, reducing the exergy losses in the heat absorption process, turbine, and condenser is vital to further increase the heat‐work conversion efficiency for heat sources of approximately 100°C to 160°C, 170°C to 190°C, and 200°C, respectively.     

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。     

有出口温度限制的热源亚临界有机朗肯循环最佳回热度定量准则的研究

我国的余热资源和可再生能源丰富,但部分余热资源和可再生能源分布比较分散,并存在温度和能量密度均较低的问题。基于传统能源转化技术,利用温度较低的余热资源和能量密度较低的可再生能源进行发电,会降低余热资源和可再生能源的热功转换效率。有机朗肯循环(ORC)系统可以有效利用低温热能进行发电。对于不同温度和形式的热源,采用合适的工质和循环工况,可以提高ORC系统的发电效率。有出口温度限制的热源是一种较为常见的热源形式,在ORC系统中增加回热装置可能会进一步提高热力循环对该类热源的利用效率。因此,文章针对有温度出口限制的热源,建立了亚临界ORC计算分析模型,选取了干流体和等熵流体作为循环工质,以热源回收?效率作为ORC系统的循环性能评价指标,系统地比较了不同回热度条件下ORC系统的循环性能。文章系统地分析了回热流程对ORC系统循环性能的影响规律,并将计算结果进行理论关联,首次建立了依据冷源和热源条件直接选取最佳回热度的定量准则。     

Experimental research on geothermal heat pump system with non-azeotropic working fluids

The subject of the paper is how to solve the problem of heating in some areas and making the best of geothermal waste water through heat pump. Now the biggest barrier is to find proper working fluids, which can work in the condition of 80–100 °C as condensation temperature and 25–35 °C as evaporation temperature, and at the same time keep the highest pressure in the system under 2500 kPa. Experimental results show that new working fluids R123/R290 (50/50 by mass %) and R123/R290/R600a (40/50/10 by mass %) will meet the requirement of the new working condition. The coefficient of performance of the geothermal heat pump system using the working fluids is above 3.0 with condensation temperature above 80 °C and condensation pressures below 2500 kPa. In the end of the paper, some improvements are proposed for the purpose of better performance. In the paper, the thermodynamic properties of mixtures are calculated with REFPROP 6.1.     

Performance analysis of an Organic Rankine Cycle with superheating under different heat source temperature conditions

This paper presents an analysis of non-regenerative Organic Rankine Cycle (ORC), based on the parametric optimization, using R-12, R-123, R-134a and R-717 as working fluids superheated at constant pressure. A computer programme has been developed to parametrically optimize and compare the system and second law efficiency, irreversibility of the system, availability ratio, work output, mass flow rate with increase in turbine inlet temperature (TIT) under different heat source temperature conditions. The calculated results reveal that R-123 produces the maximum efficiencies and turbine work output with minimum irreversibility for employed constant as well as variable heat source temperature conditions. Hence, selection of a non-regenerative ORC during superheating using R-123 as working fluid appears to be a choice system for converting low-grade heat to power.     

基于采用分液冷凝有机闪蒸循环分液干度分析及优化

分液冷凝是一种新兴的强化传热方法,可以显著提高冷凝传热系数。将分液冷凝应用于有机闪蒸循环(OFC),采用R227ea、R236ea、R245fa、R600、R601、R600a、R601a、R1234ze和R1234yf为循环工质,分别研究了进口干度、分液干度、冷却水温升和质流密度对冷凝器换热面积的影响。研究结果表明:当进口干度较大时,换热面积会随着分液干度的增大而先减小后增大;当分液干度较小时,分液干度越接近进口干度换热面积越小。采用分液冷凝后的冷凝器换热面积相对不分液时减少13.2%~55.3%,且相对减少量随着进口干度的增大而减小。     

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.