用低沸点工质的朗肯循环(ORC)方法回收低位工业余热

我国的中低温余热发电技术尚不很成熟。本文介绍以低沸点的有机物 (正戊烷N - pantane)作为工质来回收废气余热、汽化进入汽轮机膨胀作功 ,带动发电机发电的有机朗肯循环 (ORC)余热发电技术 ,对于低位工业余热及地热能的开发 ,都有重要的参考价值。     

内燃机余热驱动的储热式有机朗肯循环试验研究

为了提高尾气余热利用率并削弱热源波动对有机朗肯循环的影响,提出了一种集成相变储热换热器的有机朗肯循环（organic Rankine cycle,ORC）系统,利用相变材料削弱尾气余热波动并储存热量。搭建了内燃机尾气余热直接驱动的储热式有机朗肯循环试验台架,开展了内燃机稳态工况和阶跃变工况下储热式有机朗肯循环的热力学性能和动态性能试验研究。结果表明,内燃机稳态工况下尾气平均温度和平均流量为342℃和0.142kg/s,蒸发压力为0.75MPa条件下储热式ORC系统平均输出功率约3.43kW,平均热效率可达到12.7%,平均尾气余热回收率可达40.1%。内燃机阶跃工况下,工质出口温度、蒸发压力和过热度均呈现快速下降的趋势。试验结果还表明储热式ORC具备完全抵御发动机工况小幅波动的能力。在发动机工况阶跃变化比例过大时,储热换热器可以实现对尾气的补热,从而延长储热式ORC的安全工作时间。     

我国太阳能有机朗肯循环研究现状

太阳能具有易转化为低温热源的特性,而有机朗肯循环是利用低温热源或工业余热发电的理想方式,两者相结合形成基于太阳能的有机朗肯循环发电技术。综述了我国光热太阳能发电技术和市场现状以及针对有机朗肯循环的研究现状。经分析发现,目前研究中理论分析或计算机模拟较多,缺乏实际应用的验证。论述了有机朗肯循环工质的选择、循环性能分析方法以及所面临的问题和改善方法。     

有机朗肯循环回收直接空冷机组排气余热系统的热力性能研究

空冷机组汽机排汽热损失巨大,而有机朗肯循环是利用中低温热源的重要技术之一。提出采用有机朗肯循环回收空冷机组汽轮机排汽余热的技术方案,建立空冷机组和有机朗肯循环的物理模型,编制有机朗肯循环回收空冷机组汽轮机排汽余热技术的模拟程序,并将模拟计算结果与厂家提供的某型号有机朗肯循环机组的性能数据进行对比。以内蒙古锡林郭勒盟某典型600 MW机组为对象,探究汽机乏汽温度、环境温度、ORC机组过热度等关键参数变化对系统热力性能的影响规律。结果表明,ORC机组净出功和ORC机组热效率随着汽机乏汽温度的升高而增大,而随着环境温度和ORC机组过热度的增大而减小。     

ORC系统热力性能计算程序开发

在有机朗肯循环(ORC)系统设计理论基础上,结合Matlab 2010a平台及REFPROP(工质物性)8.0数据库,编写了低品位余热发电ORC系统热力性能的计算程序。参照实例的设计参数,运用该程序进行了ORC系统的设计,并将程序运算结果与实际运行参数进行了对比。结果表明,该程序具有工质筛选、系统循环热力计算以及设备初步选型等应用功能,且运算结果准确。     

有机朗肯循环系统回收低温余热的优势

当前国内传统余热发电系统都是利用水蒸气的朗肯循环。举例分析了目前我国低温余热回收状况,进而通过和传统水蒸气余热发电系统的对比,阐述了有机朗肯循环(ORC)在回收低温余热领域的优势以及国内外实际应用情况。最后提出了对于国内发展ORC余热发电系统的建议。     

电石炉烟气余热回收双回路ORC系统性能分析

有机朗肯循环(ORC)系统在回收余热方面具有较大优势.本文采用双回路有机朗肯循环(DORC)系统回收电石炉烟气余热.对比了不同工质组合、不同循环结构下,高温循环的蒸发温度与冷凝温度对系统输出功率、效率和发电成本的影响.结果表明:与基础DORC相比,回热式DORC系统性能更佳,其中以甲醇与R123工质组合的系统净功率与效率最大,水作为高温循环工质在无回热的基础DORC系统中经济性优势明显.恒定热源条件下增大高温循环蒸发温度,对所有工质组合下同性能均有明显改善,增大高温循环冷凝温度则降低系统性能.     

利用烟气余热的有机朗肯循环与苦咸水淡化联合系统

针对沿海和西北内陆地区淡水紧缺和工业烟气余热的排放问题,设计了一种有机朗肯循环与苦咸水淡化的联合系统对工业烟气余热进行有效回收,以生产淡水和电能。该联合系统将闪蒸法与有机朗肯循环进行有机结合,通过变参数法计算采用戊烷作为工质的有机朗肯循环的循环效率,确定该系统运行的最佳参数,并与水工质朗肯循环进行对比,证明了联合系统的优越性。     

亚临界有机朗肯循环系统的热经济分析与优化

以系统发电成本(electricity production cost,EPC)为评价指标,对用于回收工业锅炉烟气余热的有机朗肯循环(ORC)系统进行了热经济分析与优化。结果表明,随着蒸发器和冷凝器节点温差的增大,系统发电成本先减小、再增大,即存在一组最优的蒸发器和冷凝器节点温差使发电成本最小。分别以纯工质R245fa和R236ea、非共沸混合工质R141b/RC318和乙烷/丁烷为循环工质,得到了最小发电成本时有机朗肯循环系统的最优工作参数,以及对应的系统净输出功、热效率和火用效率。     

基于有机朗肯循环低温余热利用研究

文章应用PR方程编制了有机工质热物性计算程序,对多种有机工质的朗肯循环进行了热力计算,研究了各主要参数对朗肯循环性能影响的规律。在给定余热条件下,采用模拟退火算法对循环的主要参数进行优化,得出了整个循环在净输出功率最大时的最优参数值,并比较了以R236fa为工质的有机朗肯循环和常规朗肯循环的对外做功能力。     

Review of the Working Fluid Thermal Stability for Organic Rankine Cycles

The organic Rankine cycle(ORC) is an efficient power generation technology and has been widely used for renewable energy utilization and industrial waste heat recovery. Thermal stability is a significant property of ORC working fluids and is the primary limitation for working fluid selection and system design. This paper presents a review of the working fluid thermal stability for ORCs, including an analysis of the main theoretical method for thermal stability, a summary of the main experimental method for thermal stability, a summary of the decomposition experimental results for working fluids, and a discussion of the decomposition influence on ORC systems. Further research trends of thermal stability are also discussed in this paper.     

有机工质余热发电技术的研究进展及其应用前景

工业余热、太阳能热、地热、生物质能、海洋温差等都是低品位热源,有机朗肯循环(ORC)可以有效提高低品位热源的利用效率。提高ORC效率的关键是根据应用对象的特点选择合适的有机工质,国内外学者对各种领域内应用的ORC工质进行了大量深入的工作,并且取得很多成果,我国低温余热资源十分丰富,而能源利用率却不高,采用ORC提高能源回收以及利用率,在我国各行各业在都有着广阔的应用前景。     

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...     

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.     

A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery

The organic rankine cycle (ORC) as a bottoming cycle¹ to convert low-grade waste heat into useful work has been widely investigated for many years. The CO₂ transcritical power cycle, on the other hand, is scarcely treated in the open literature. A CO₂ transcritical power cycle (CO₂ TPC) shows a higher potential than an ORC when taking the behavior of the heat source and the heat transfer between heat source and working fluid in the main heat exchanger into account. This is mainly due to better temperature glide matching between heat source and working fluid. The CO₂ cycle also shows no pinch limitation in the heat exchanger. This study treats the performance of the CO₂ transcritical power cycle utilizing energy from low-grade waste heat to produce useful work in comparison to an ORC using R123 as working fluid.Due to the temperature gradients for the heat source and heat sink the thermodynamic mean temperature has been used as a reference temperature when comparing both cycles. The thermodynamic models have been developed in EES² The relative efficiencies have been calculated for both cycles. The results obtained show that when utilizing the low-grade waste heat with the same thermodynamic mean heat rejection temperature, a transcritical carbon dioxide power system gives a slightly higher power output than the organic rankine cycle.     

Effect of working fluids on organic Rankine cycle for waste heat recovery

This study presents an analysis of the performance of organic Rankine cycle (ORC) subjected to the influence of working fluids. The effects of various working fluids on the thermal efficiency and on the total heat-recovery efficiency have been investigated. It is found that the presence of hydrogen bond in certain molecules such as water, ammonia, and ethanol may result in wet fluid conditions due to larger vaporizing enthalpy, and is regarded as inappropriate for ORC systems. The calculated results reveal that the thermal efficiency for various working fluids is a weak function of the critical temperature. The maximum value of the total heat-recovery efficiency occurs at the appropriate evaporating temperature between the inlet temperature of waste heat and the condensing temperature. In addition, the maximum value of total heat-recovery efficiency increases with the increase of the inlet temperature of the waste heat source and decreases it by using working fluids having lower critical temperature. Analytical results using a constant waste heat temperature or based on thermal efficiency may result in considerable deviation of system design relative to the varying temperature conditions of the actual waste heat recovery and is regarded as inappropriate.     

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.     

Thermo-economic analysis of using an organic Rankine cycle for heat recovery from both the cell stack and reformer in a PEMFC for power generation

Distributed power generation is gaining attention as a solution for the transmission loss and site selection in centralized power generation. Polymer-electrolyte membrane fuel cells (PEMFCs) are suitable as a distributed power source for residential areas because of their high efficiency and low environmental impact. This study proposes a combined power generation system for recovering waste heat from both the cell stack and the reformer of a PEMFC by applying an organic Rankine cycle (ORC). The best working fluid with the highest ORC power output (i.e., the highest combined system efficiency) was identified through a parametric study of different working fluids. An economic analysis was also performed for different working fluids, waste heat sources, and types of system operation. The results show that the installation cost of the ORC can be recovered within the fuel cell's lifetime in all design cases. Greater cumulative profit can be generated by maintaining the same power output as the stand-alone PEMFC system for greater efficiency than when increasing the power output to sell surplus power. The results demonstrate that the optimal heat recovery from the PEMFC system is both thermodynamically and economically beneficial.