Design and Analysis of a Single-Stage Transonic Centrifugal Turbine for organic Rankine cycle(ORC)

The recovery of low temperature heat sources is a hot topic in the world.The ORC system can effectively use the low temperature heat source.As its main output device,the performance of the turbine is very important.The single stage transonic turbine has the characteristics of small size and large output power.In this paper,the complete design process of a transonic centrifugal turbine with R245fa in low working temperature condition is introduced.At the design conditions,the shaft power and the wheel efficiency of the centrifugal turbine can reach 1.12 MW and 83.61%,respectively.In addition,a thermodynamic ORC cycle is presented and the off-design conditions of the turbine and its influence on the system are studied in detail.The results obtained in the present work show that the single-stage transonic centrifugal turbine can be regarded as a potential choice to be applied in small scale ORC systems.     

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.     

Design and testing of the Organic Rankine Cycle

We propose a new type of environmentally friendly system called the “Organic Rankine Cycle” (ORC) in which low-grade heat sources are utilized. This system combines a circulated thermosyphon with a turbine system. The working fluid used in this study is an organic substance which has a low boiling point and a low latent heat for using low-grade heat sources. A numerical simulation model of the ORC is made in order to estimate its optimum operating conditions. An experimental apparatus is also made in this study. From the numerical simulation, it is suggested that HCFC-123 gives higher turbine power than water which is a conventional working fluid, and operating conditions where saturated vapor at the turbine inlet would give the best performance. From the experimental results, HCFC-123 improves the cycle performance drastically. In addition, the turbine made for trial use in this study gives good performance.     

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.     

跨临界-亚临界复叠式有机朗肯循环性能分析

热源温度高于473.15 K时,复叠式有机朗肯循环(organic Rankine cycle,ORC)可避免高温下工质热分解、膨胀比过大等缺点,相对单级ORC更具优势。跨临界循环相较常规亚临界具有更高的吸热压力及更好的热源匹配性,其与复叠式ORC耦合有望获得更优的热力性能。因此,构建了跨临界-亚临界复叠式ORC(TSORC),以473.15~573.15 K工业烟气为热源,针对5组工质,探究了吸热压力、冷凝压力对系统热力性能的影响,优化系统参数以获得最大净输出功;并与常规亚临界-亚临界复叠式ORC(SSORC)进行对比。结果表明:TSORC相对SSORC可有效增大系统净输出功,最多可提高23.9%;但当热源温度低于"等值热源温度"时,SSORC的输出功反而更大;以R1233zd-R1234ze(E)为工质的TSORC具有最大净输出功。     

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.     

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.     

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。     

Working fluids for low-temperature heat source

The performance of different working fluids to recover low-temperature heat source is studied. A simple Rankine cycle with subcritical configuration is considered. This work is to screen working fluids based on power production capability and component (heat exchanger and turbine) size requirements. Working fluids considered are R134a, R123, R227ea, R245fa, R290, and n-pentane. Energy balance is carried out to predict operating conditions of the process. Outputs of energy balance are used as input for exergy analysis and components (heat exchanger and turbine) design. The heat exchanger is divided into small intervals so that logarithmic mean temperature difference (LMTD) method is applicable. R227ea gives highest power for heat source temperature range of 80–160 °C and R245fa produces the highest in the range of 160–200 °C. There is optimal pressure where the heat exchanger surface area is minimum. This optimal pressure changes with heat source temperature and working fluid used. The least heat exchanger area required at constant power rating is found when the working fluid is n-pentane. At lower heat source temperature (80 °C), the maximum power output and minimum heat exchanger surface area for different working fluids is comparable.     

Energy and exergy‐based working fluid selection for organic Rankine cycle recovering waste heat from high temperature solid oxide fuel cell and gas turbine hybrid systems

This paper performed a comparative analysis of organic Rankine cycle (ORC) using different working fluids, in order to recover waste heat from a solid oxide fuel cell‐gas turbine hybrid power cycle. Depending on operating parameters, criteria for the choice of the working fluid were identified. Results reveal that due to a significant temperature glide of the exhaust gas, the actual ORC cycle thermal efficiency strongly depends on the turbine inlet temperature, exhaust gas temperature, and fluid's critical point temperature. When exhaust gas temperature varies in the range of 500 K to 600 K, R123 is preferred among the nine dry typical organic fluids because of the highest and most stabilized mean thermal efficiency under wide operating conditions and its reasonable condensing pressure and turbine outlet specific volume, which in turn results in a feasible ORC cycle for practical concerns. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance analysis of organic Rankine cycle based on location of heat transfer pinch point in evaporator

The location of heat transfer pinch point in evaporator is the base of determining operating parameters of organic Rankine cycle (ORC). The physical mathematical model seeking the location of pinch point is established, by which, the temperature variations both of heat source and working fluid with UA can be obtained. Taking heat source with inlet temperature of 160 °C as example, the matching potentials between heat source and working fluid are revealed for subcritical and supercritical cycles with the determined temperature difference of pinch point. Thermal efficiency, exergy efficiency, work output per unit area and maximum work outputs are compared and analyzed based on the locations of heat transfer pinch point either. The results indicate that supercritical ORC has a better performance in thermal efficiency, exergy efficiency and work output while outlet temperature of heat source is low. Otherwise, subcritical performs better. Small heat transfer coefficient results in low value of work output per unit area for supercritical ORC. Introduction of IHX may reduce the optimal evaporating pressure, which has a great influence on heat source outlet temperature and superheat degree. The analysis may benefit the selection of operating parameters and control strategy of ORC.     

Optimization of low temperature solar thermal electric generation with Organic Rankine Cycle in different areas

The presented low temperature solar thermal electric generation system mainly consists of compound parabolic concentrators (CPC) and the Organic Rankine Cycle (ORC) working with HCFC-123. A novel design is proposed to reduce heat transfer irreversibility between conduction oil and HCFC-123 in the heat exchangers while maintaining the stability of electricity output. Mathematical formulations are developed to study the heat transfer and energy conversion processes and the numerical simulation is carried out based on distributed parameters. Annual performances of the proposed system in different areas of Canberra, Singapore, Bombay, Lhasa, Sacramento and Berlin are simulated. The influences of the collector tilt angle adjustment, the connection between the heat exchangers and the CPC collectors, and the ORC evaporation temperature on the system performance are investigated. The results indicate that the three factors have a major impact on the annual electricity output and should be the key points of optimization. And the optimized system shows that: (1) The annual received direct irradiance can be significantly increased by two or three times optimal adjustments even when the CPC concentration ratio is smaller than 3.0. (2) Compared with the traditional single-stage collectors, two-stage collectors connected with the heat exchangers by two thermal oil cycles can improve the collector efficiency by 8.1–20.9% in the simultaneous processes of heat collection and power generation. (3) On the use of the market available collectors the optimal ORC evaporation temperatures in most of the simulated areas are around 120 °C.     

低品位热能驱动有机朗肯循环的变工况特性

构建有机朗肯循环变工况分析模型,研究热源条件对系统变工况性能的影响规律。结果表明:随着热源温度升高,系统的最佳蒸发压力线性增大,而涡旋膨胀机的等熵效率逐渐减小。相比额定工况,热源温度变化-30.0K与30.0K时,净输出功率变化了-32.4%与18.4%,热效率降低了4.0%与11.4%,热回收效率变化幅度分别为-9.8%及8.9%;当热源温度从423增大至483K时,系统不可逆损失的变化率为-37.1%与45.5%,火用效率的变化率为6.7%与-17.5%。相比热源流量,热源温度对系统变工况性能的影响更大。     

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。     

Performance of irreversible Meletis–Georgiou vane rotary engine cycle with variable specific heats of working fluid

An irreversible cycle model of Meletis–Georgiou (MG) engine consisting of an isochoric heating branch, isochoric and isobaric cooling branches, two non-isentropic compression and two non-isentropic expansion branches and with heat transfer loss, internal irreversibility and the linear relation between specific heat of the working fluid and its temperature is established by using the theory of finite time thermodynamics. The analytical relations of the work output versus compression ratio, the efficiency versus compression ratio, as well as the work output versus efficiency are obtained by using numerical examples. The results show that the work output versus the efficiency characteristic of the irreversible MG cycle is a loop-shaped curve which is consistent with the general heat engine performance, and the cycle model considering the internal irreversibility and linear relation between specific heats of the working fluid and its temperature is closer to practice than the endo-reversible model with constant specific heats of the working fluid.     

Thermodynamic analysis and optimization of a solar-driven regenerative organic Rankine cycle (ORC) based on flat-plate solar collectors

This paper presents a regenerative organic Rankine cycle (ORC) to utilize the solar energy over a low temperature range. Flat-plate solar collectors are used to collect the solar radiation for their low costs. A thermal storage system is employed to store the collected solar energy and provide continuous power output when solar radiation is insufficient. A daily average efficiency is defined to evaluate the system performance exactly instead of instantaneous efficiency. By establishing mathematical models to simulate the system under steady-state conditions, parametric analysis is conducted to examine the effects of some thermodynamic parameters on the system performance using different working fluids. The system is also optimized with the daily average efficiency as its objective function by means of genetic algorithm under the given conditions. The results indicate that under the actual constraints, increasing turbine inlet pressure and temperature or lowering the turbine back pressure could improve the system performance. The parametric optimization also implies that a higher turbine inlet temperature with saturated vapor state could obtain the better system performance. Compared with other working fluids, R245fa and R123 are the most suitable working fluids for the system due to their high system performance and low operation pressure.     

1MW有机朗肯循环系统及轴流透平设计

基于自行开发的有机朗肯循环(ORC)系统热力计算软件设计了1 MW ORC系统.考虑到有机朗肯循环系统的特点,介绍了适合于该系统工况参数的有机工质轴流透平的设计过程.随后分析比较了应用于ORC系统的向心透平、螺杆膨胀机及轴流透平的不同特点,总结了轴流透平应用于该功率等级ORC系统的主要优点.最后,针对ORC系统设计了采用R123为工质的1 MW轴流透平,在CFD数值模拟的基础上进行了通流的优化和通流结构设计.     

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。     

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.     

Energy utilisation in a combined geothermal and organic Rankine power cycles

This study involves the design of a single flash cycle which comprises a separator, steam turbine, condenser and pump combined with Organic Rankine Cycle (ORC). The ORC has a three-stage heat exchanger. The mass flow rate of the organic fluid varies depending on the type of organic fluid. The system is heated by geothermal water. The effect of changing the geothermal water temperature [200–260°C] on performance parameters including the power output and overall efficiency has been studied. Four working fluids (n-Butane, Isobutane, R11 and R123) were chosen depending on their properties. The results show that a drop in the source temperature (T₁) by 10% will result in 9.7% and 25.3% drop in overall efficiency and net power output for Isobutane. Also, Isobutane has a drop of 4.2% in both; overall efficiency and net power output for a 10% drop in pressure ratio (r_p). R11 shows the highest overall efficiency and net power output (18.76% and 24.887 MW) respectively at the design point.