柴油机工况对中温有机朗肯循环性能影响的模拟

根据某重型车用柴油机的试验数据,选用两种不同的排气状态作为设计点,分别设计了两套中温有机朗肯循环余热回收系统.通过理论计算,对比了两套系统的工质蒸发率、各节点温度、系统效率及输出功率等参数随排气温度变化的规律,并主要针对第2套设计方案系统研究了排气流量、排气温度等参数对中温朗肯循环系统效率的影响.结果表明:选择中高工况...     

变工况下有机朗肯循环发电特性的实验研究

有机朗肯循环是利用中低温热源的重要技术之一。基于R245fa为工质的低温热源驱动有机朗肯循环发电系统,通过改变电加热器功率来研究其在变工况下的发电特性。结果表明：热源热量变化12%时,系统最大净发电量为7.8 kW,发电效率为8.7%;系统最小净发电量为6.9 kW,发电效率为8.26%;系统重新达到稳定状态的时间为35 ~ 45 min,相同时间内,系统对热源温度降低的响应更迅速而对热源温度升高的响应速度较慢;在此热源的改变条件下系统仍能稳定运行。     

有机朗肯循环低品位能回收技术

有机朗肯循环是回收低品位能的有效途径,对有机朗肯循环的工质、膨胀机等关键技术及实际应用情况进行了介绍。     

太阳能驱动有机朗肯循环的工质比较

针对太阳能热水和其它低品位热能的动力利用,研究了工作在100℃供热温度和30℃冷凝温度之间的有机朗肯循环工质的优化选择,以满足较高的循环效率、较大的机械能输出、较小的排气量需求等要求。工质模型采用RKS状态方程,针对R22在-30～95℃温度区间内,计算结果与ASHRAE20-2005数据比较,除液相密度外,其它的热力学参数计算绝对误差小于5%,满足工程模拟要求。利用RKS模型,文中分析了19种有机工质的动力循环参数,发现工质R11的热力学性能系数最高。结合GWP和ODP环境指标,发现R142b、Rc318与R600适合于低温朗肯循环。     

内燃机尾气余热驱动有机朗肯蒸汽压缩制冷循环的研究

设计了以内燃机尾气余热为热源驱动的有机朗肯蒸气压缩制冷循环系统。根据热力学定律,建立了循环系统的数学模型,提出了尾气换热夹点确定方法。以Matlab和Refprop软件为工具,研究了有机朗肯循环(organic Rankine cycle,ORC)各换热器负荷、做功量、热效率分别随蒸发压力、冷凝温度的变化关系,并确定了最优工质。研究了蒸汽压缩制冷循环(vapor compression refrigeration,VCR)各换热器负荷、制冷系数分别随蒸发温度、冷凝温度的变化关系。由于压缩比的限制,确定了多种制冷工质在不同冷凝温度下的最低蒸发温度,结合相关标准中所规定的各型冷藏车蒸发温度的范围,确定了各型冷藏车的可选制冷剂。研究了与可选工质对应的制冷系数随蒸发温度的变化关系,从而确定最优工质。计算了各型冷藏车在采用最优制冷剂时,在最严苛工况下的制冷量、制冷系数及综合系数。     

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。     

超临界二氧化碳布雷顿/有机朗肯循环联合系统的热力学特性

针对再压缩式超临界二氧化碳布雷顿发电循环(S-CO_2),将有机朗肯循环(ORC)作为底循环用于回收系统余热,建立了S-CO_2/ORC联合循环。采用Aspen Plus建立分析模型,根据顶循环余热温度范围和安全环保要求,选取R245fa作为ORC系统工质,分析透平进口温度、透平进口压力及分流比对循环效率的影响,并通过分析耗能设备的功率变化找到影响系统效率变化的因素。结果表明:通过顶循环低温余热的回收利用,系统热效率提高4%以上;增大透平进口温度可提高顶循环的热效率,但对底循环热效率的影响较小;随着顶循环透平进口压力的增大,顶循环热效率增加而底循环热效率下降;在透平入口温度680℃、入口压力280 MPa的条件下,存在最优的再压缩循环分流比0.66使得联合循环热效率最高;使用ORC底循环回收顶循环余热,最高可以将系统热效率从50.3%提高到53.7%,联合系统可以获得6.7%的效率提升。     

低温余热有机朗肯循环发电系统热经济性分析

针对工业中排放的低温烟气,建立有机朗肯循环发电系统的热经济分析模型,分析蒸发压力、热源温度及蒸发器最小传热温差对系统经济性能的影响。分析结果表明:热源温度为140℃,循环采用R123的经济性最佳,相应的发电成本与动态投资回收期分别为0.142元(/kW.h)与3.68年。余热发电系统存在一个经济性最高的蒸发压力,不同工质对应的最佳蒸发压力也不同。蒸发器内最小传热温差为15℃时,系统的经济性较好。烟气温度在100～180℃时,系统采用R123的投资回收期最短,而烟气温度高于180℃时,R141b的经济性更高;不宜采用有机朗肯循环发电技术回收温度低于100℃的低温烟气。     

基于有机朗肯循环的APU余热回收系统性能分析

为有效利用飞机辅助动力装置（Auxitlary Power Unit , APU）排气余热,基于有机朗肯循环（Organic Rankine Cycle, ORC）发电系统,构建了APU余热回收系统。系统以APU排气余热为输入,驱动ORC做功,输出电能,为机载设备提供二次能源。结合工程热力学原理,建立系统热力学模型,并通过Matlab编程对余热回收系统进行了仿真计算及性能分析。仿真结果表明,系统功率及效率随飞行马赫数增加而降低;APU余热回收系统在飞机低音速飞行时有良好的性能;马赫数小于1时,系统功率在12 kW以上,效率在11%以上,耗气率低于0.0262 kg/kJ。     

有机朗肯循环工质的热稳定性分析

利用化学反应的热力学性质,以正戊烷为工质,从理论上分析计算正戊烷在375℃的中温环境中的分解产物,从而为分析系统性能的影响提供理论依据。     

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.     

烟气驱动复叠式非共沸工质有机朗肯循环系统㶲分析

通过构建复叠式非共沸工质有机朗肯循环系统模型,并采用■分析方法,研究了系统■效率随工质摩尔组分的变化规律以及不同摩尔组分下,系统各部件■损失分布情况。研究结果表明:受蒸发器泡点温度与高温级蒸发器夹点位置影响,当高温级循环工质环戊烷摩尔分数为0.8,低温级循环工质异丁烷摩尔分数为0.1时,系统■效率取得最大值48.56%,比采用纯工质时相对提高了3.83%;且采用非共沸工质后,排烟损失、高温级蒸发器■损失、低温级冷凝器■损失均有显著降低。     

Heat exchanger network design of an organic Rankine cycle integrated waste heat recovery system of a marine vessel using pinch point analysis

The coexistence of different kinds of waste heat sources on marine vessels with various temperature ranges increases the need for an optimal heat exchanger network (HEN) design for the heat collection process to reduce the unutilizable heat that needs to be discharged to overboard. The optimal HEN design has not been taken into consideration by using pinch point analysis in previous studies of marine organic Rankine cycle (ORC) systems that utilize from different kinds of waste heat sources. The objective of the study is to determine the optimal HEN design for an ORC integrated waste heat recovery system of a marine vessel by utilizing the pinch point analysis to improve the overall energy efficiency. Lubricating oil, high-temperature cooling water and scavenge air of the main engine, and the exhaust gas emitted from the boiler plant were identified as the major waste heat sources of a reference container ship. A heat collection stream, in which thermal oil is used as the heat transfer fluid that transfers the collected heat to an ORC system, was proposed. The pinch point analysis showed that the optimum waste heat recovery could be gained by separating the scavenge air cooler into three stages and the lubricating oil cooler into two stages. The results of the parametric study for the varying evaporator inlet pressure between 1000 and 3000 kPa showed that R1234ze(Z) yields the best performance among nine different organic working fluids with the thermal efficiency and exergy efficiency of 15.24% and 86.47% for the ORC system, respectively. For the proposed configuration, the unavailable waste heat that cannot be transferred to thermal oil was found as 23.71%, 16.56%, 13.17%, and 7.81% of the total waste heat produced by the heat sources, and also 8.24%, 9.80%, 11.55%, and 12.93% of the net power output produced by the main engine can be recovered for 25%, 50%, 76%, and 100% maximum continuous rating (MCR), respectively.     

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。     

Parametric optimisation of the organic Rankine cycle for power generation from low-grade waste heat

This research work deals with the optimisation of controllable parameters of the organic Rankine cycle (ORC) run by waste heat. Performance measures have been evaluated for different waste heat temperatures, condenser temperatures, refrigerants and mass flow rate. The design of experiment was performed on the L9 orthogonal array of Taguchi's method. Three performance measures such as thermal efficiency, exergy destruction rate and the work output were used for the assessment and optimisation of the cycle. An optimum combination of parameters obtained by Taguchi's method is compared with analytical results. The comparison suggests that the variance of results is within the desired level of confidence. Individual effect of parameters on the performance of ORC is also estimated using analysis of variance. Turbine inlet temperature has large effects on efficiency and work output. Mass flow rate of the refrigerant has the largest effect on the exergy destruction rate.     

Experimental investigation of a scroll expander for an organic Rankine cycle

This paper presents experimental investigation of the performance of an organic Rankine cycle (ORC) with scroll expander which utilizes renewable, process and waste heats. An ORC test bench is built with a scroll expander‐generator unit modified from a refrigeration compressor‐electrical drive unit. A detailed experimental investigation within the test bench is performed with the organic working fluid R134a. The results show that scroll expander can effectively be used in low‐power ORC to generate mechanical work or electricity from low‐temperature thermal sources (e.g. 80–200 °C, respectively). The experiments are performed under fixed intake conditions into the expander. The pressure ratio and the load connected to the expander‐generator unit were varied. It is found that an optimum pressure ratio and an optimum angular speed co‐exist. When operating optimally, the expander's isentropic efficiency is the highest. The optimum angular speed is around 171 rad/s which corresponds to a generated voltage of 18.6 V. The optimum pressure ratio is about 4. The isentropic efficiency at optimum operation is found in the range of 0.5 to 0.64, depending on the intake conditions. The volumetric efficiency overpasses 0.9 at optimum operation and degrades significantly if the load is increased over the optimum load. A regenerative ORC equipped with the studied expender‐generator unit that operates under 120 °C heat source and has an air cooled condenser generates 920 W net power with efficiencies of 8.5% energetically and 35% exergetically. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimum design criteria for an Organic Rankine cycle using low-temperature geothermal heat sources

A cost-effective optimum design criterion for Organic Rankine power cycles utilizing low-temperature geothermal heat sources is presented. The ratio of the total heat exchanger area to net power output is used as the objective function and was optimized using the steepest descent method. Evaporation and condensation temperatures, geothermal and cooling water velocities are varied in the optimization method. The optimum cycle performance is evaluated and compared for working fluids that include ammonia, HCFC123, n-Pentane and PF5050. The optimization method converges to a unique solution for specific values of evaporation and condensation temperatures and geothermal and cooling water velocities. The choice of working fluid can be greatly affect the objective function which is a measure of power plant cost and in some instances the difference could be more than twice. Ammonia has minimum objective function and maximum geothermal water utilization, but not necessarily maximum cycle efficiency. Exergy analysis shows that efficiency of the ammonia cycle has been largely compromised in the optimization process than that of other working fluids. The fluids, HCFC 123 and n-Pentane, have better performance than PF 5050, although the latter has most preferable physical and chemical characteristics compared to other fluids considered.     

Parametric optimization and performance analysis of a waste heat recovery system using Organic Rankine Cycle

Parametric optimization and performance analysis of a waste heat recovery system based on Organic Rankine Cycle, using R-12, R-123 and R-134a as working fluids for power generation have been studied. The cycles are compared with heat source as waste heat of flue gas at 140 °C and 312 Kg/s/unit mass flow rate at the exhaust of ID fans for 4 × 210 MW, NTPC Ltd. Kahalgaon, India. Optimization of turbine inlet pressure for maximum work and efficiencies of the system along the saturated vapour line and isobaric superheating at different pressures has been carried out for the selected fluids. The results show that R-123 has the maximum work output and efficiencies among all the selected fluids. The Carnot efficiency for R-123 at corrected pressure evaluated under similar conditions is close to the actual efficiency. It can generate 19.09 MW with a mass flow rate of 341.16 Kg/s having a pinch point of 5 °C, First law efficiency of 25.30% and the Second law efficiency of 64.40%. Hence selection of an Organic Rankine Cycle with R-123 as working fluid appears to be a choice system for utilizing low-grade heat sources for power generation.     

Low‐grade heat‐driven Rankine cycle,a feasibility study

Conversion of low‐grade heat to high‐quality energy such as electricity using the Rankine cycle poses serious challenges. When such conversion is possible, it is invariably expensive or unacceptable due to environmental concerns associated with the working medium. The low‐grade heat can either be from exhaust systems or from solar radiation. Thus, the topic addresses a very useful subject, combining energy efficiency and renewable energy. Although high‐grade heat recovery and energy conversion is a mature technology widely covered by the literature, low‐grade energy conversion, especially using thermodynamic cycles, has not been sufficiently addressed to date. This paper addresses the feasibility of a low‐grade heat‐driven Rankine cycle to produce power using a scroll expander, a low toxicity, low flammability, and ozone‐neutral working fluid. A cost benefit analysis of the recommended system shows that it is a viable option for solar power generation, at about one‐third the cost of a comparable photovoltaic system. Copyright © 2008 John Wiley & Sons, Ltd.