一种新型跨临界CO2冷电联供系统热力分析

提出一种新型跨临界二氧化碳（trans-critical carbon dioxide,TCO₂）再压缩循环和喷射器制冷循环耦合的冷电联供系统。该系统在输出电能的同时,利用低品位热能驱动喷射器工作输出冷量。以输出电量1 MW为设计目标,对比冷电联供系统和再压缩发电系统的性能,研究联供系统各部件（火用）损和主要热力参数对其性能的影响。结果表明：联供系统利用CO₂余热驱动喷射器输出冷量,循环热效率高于单一再压缩系统;加热器（火用）损所占比例最大,回热器次之;透平进口温度、压力和背压对联供系统工质流量、循环效率、输出功率、加热器功率、压缩机耗功及喷射器制冷量等参数影响较大;而冷凝温度和蒸发温度仅对制冷循环制冷量影响较大。在设定条件下,联供系统的循环热效率和（火用）效率可分别达到46.99%和47.21%。     

Investigation on gradient thermal cycle for power and refrigeration cogeneration

In order to improve energy utilization efficiency of low grade heat, a novel gradient thermal cycle for power and refrigeration cogeneration is proposed. The cycle is cascaded with two stages based on different thermal driven temperature. The first stage is pumpless Organic Rankine Cycle (PRC) while the second stage is two-stage sorption refrigerator. R245fa is selected as the working fluid of PRC, whereas CaCl₂-BaCl₂-NH₃ working pair is chosen for two-stage sorption refrigerator. Different heat source temperatures from 80°C to 95°C are adopted for analysis and comparison. Results indicate that the highest average power output and cooling effect are able to reach 204 W and 0.91 kW under the condition of 95°C heat source temperature and 10°C refrigeration temperature. For different heat source temperatures, total energy and exergy efficiency of the gradient thermal cycle for power and refrigeration cogeneration range from 9.49% to 9.9% and 10.9% to 11.8%, respectively. For gradient thermal cycle exergy efficiency of heat utilization ranges from 24% to 18.8% which is 126.5% and 70.9% higher than the PRC and two-stage sorption refrigerator, respectively, when the heat source temperature is 80°C.     

Exergy analysis of gas turbine trigeneration system for combined production of power heat and refrigeration

A conceptual trigeneration system is proposed based on the conventional gas turbine cycle for the high temperature heat addition while adopting the heat recovery steam generator for process heat and vapor absorption refrigeration for the cold production. Combined first and second law approach is applied and computational analysis is performed to investigate the effects of overall pressure ratio, turbine inlet temperature, pressure drop in combustor and heat recovery steam generator, and evaporator temperature on the exergy destruction in each component, first law efficiency, electrical to thermal energy ratio, and second law efficiency of the system. Thermodynamic analysis indicates that exergy destruction in combustion chamber and HRSG is significantly affected by the pressure ratio and turbine inlet temperature, and not at all affected by pressure drop and evaporator temperature. The process heat pressure and evaporator temperature causes significant exergy destruction in various components of vapor absorption refrigeration cycle and HRSG. It also indicates that maximum exergy is destroyed during the combustion and steam generation process; which represents over 80% of the total exergy destruction in the overall system. The first law efficiency, electrical to thermal energy ratio and second law efficiency of the trigeneration, cogeneration, and gas turbine cycle significantly varies with the change in overall pressure ratio and turbine inlet temperature, but the change in pressure drop, process heat pressure, and evaporator temperature shows small variations in these parameters. Decision makers should find the methodology contained in this paper useful in the comparison and selection of advanced heat recovery systems.     

A theoretical study on a novel combined power and ejector refrigeration cycle

A new combined power and refrigeration cycle is proposed for the cogeneration, which combines the Rankine cycle and the ejector refrigeration cycle by adding an extraction turbine between heat recovery vapor generator (HRVG) and ejector. This combined cycle could produce both power output and refrigeration output simultaneously, and could be driven by the flue gas from gas turbine or engine, solar energy, geothermal energy and industrial waste heats. Parametric analysis and exergy analysis are conducted to examine the effects of thermodynamic parameters on the performance and exergy destruction in each component for the combined cycle. The results show that the condenser temperature, the evaporator temperature, the turbine inlet pressure, the turbine extraction pressure and extraction ratio have significant effects on the turbine power output, refrigeration output, exergy efficiency and exergy destruction in each component in the combined cycle. It is also shown that the biggest exergy destruction occurs in the heat recovery vapor generator, followed by the ejector and turbine.     

A theoretical study on a novel solar based integrated system for simultaneous production of cooling and heating

An integrated system for simultaneous production of triple-effect cooling and single stage heating is proposed in this paper to harness low grade solar energy. The proposed system combines the heliostat field with a central receiver and the ejector-absorption cycle with the shaft power driven transcritical CO₂ cycle. A parametric study based on first and second laws of thermodynamics is carried out to ascertain the effect of varying the exit temperature of duratherm oil, turbine inlet pressure, and evaporators temperature on the energy and exergy output as well as on the energy and exergy efficiencies of the system. The results obtained indicate that major source of exergy destruction is the central receiver where 52.5% of the inlet solar heat exergy is lost followed by the heliostat where 25% of the inlet exergy is destroyed. The energy and exergy efficiencies of the integrated system vary from 32% to 39% and 2.5%–4.0%, respectively, with a rise in the hot oil outlet temperature from 160 °C–180 °C. It is further shown that increase in evaporator temperature of transcritical CO₂ cycle from −20 °C to 0 °C increases the energy efficiency from 27.45% to 43.27% and exergy efficiency from 2.51% to 2.97%, respectively. The results clearly show how the variation in the values of hot oil outlet temperature, turbine inlet pressure, and the evaporator temperature of transcritical CO2 cycle strongly influences the attainable performance of the integrated system.     

Investigation of an ammonia-water combined power and cooling system driven by the jacket water and exhaust gas heat of an internal combustion engine

An ammonia-water combined power and cooling system is proposed and investigated in this work, in which the waste heat contained in the jacket water and exhaust gas of an internal combustion engine can be recovered efficiently to generate power and cooling energy simultaneously. The proposed system was simulated, and its thermodynamic performance in the base case was calculated based on waste heat data from an actual gas engine with a rated power output of 300 kW. The equivalent heat-to-power efficiency of the combined system is 19.76%, and the total equivalent power output is as high as 92.86 kW. The exergy efficiency of the combined system reaches 33.69%. The effects of the turbine inlet pressure, generation pressure in the reboiler, exhaust gas temperature and cooling water temperature were studied to provide guidance for the system design. The results of an economic analysis indicate that the proposed system has good economic benefit.     

Methodology for thermal design of novel combined refrigeration/power binary fluid systems

Refrigeration cogeneration systems which generate power alongside with cooling improve energy utilization significantly, because such systems offer a more reasonable arrangement of energy and exergy “flows” within the system, which results in lower fuel consumption as compared to the separate generation of power and cooling or heating. This paper proposes several novel systems of that type, based on ammonia–water working fluid. Importantly, general principles for integration of refrigeration and power systems to produce better energy and exergy efficiencies are summarized, based primarily on the reduction of exergy destruction. The proposed plants analyzed here operate in a fully-integrated combined cycle mode with ammonia–water Rankine cycle(s) and an ammonia refrigeration cycle, interconnected by absorption, separation and heat transfer processes. It was found that the cogeneration systems have good performance, with energy and exergy efficiencies of 28% and 55–60%, respectively, for the base-case studied (at maximum heat input temperature of 450 °C). That efficiency is, by itself, excellent for cogeneration cycles using heat sources at these temperatures, with the exergy efficiency comparable to that of nuclear power plants. When using exhaust heat from topping gas turbine power plants, the total plant energy efficiency can rise to the remarkable value of about 57%. The hardware proposed for use is conventional and commercially available; no hardware additional to that needed in conventional power and absorption cycles is needed.     

低温热源有机工质带叶片盘式透平设计及性能分析

Tesla盘式透平是一种以流体边界层摩擦力带动转子旋转的非传统透平,具有结构简单、成本低廉、工质适应性好等优点,尤其适用于低品位热源余热回收系统。但由于其特有的做功方式,盘式透平的运行转矩与效率均远低于常规透平形式,这也是制约其商业应用的主要因素。在传统盘式透平的相邻盘片间增加导流叶片,并针对增加叶片后的透平结构进行了数学建模以及计算流体力学（computational fluid dynamics,CFD）验证。CFD验证表明,所建立的数学模型能够计算流体通道内的流体速度场、压力场分布,并能够预测透平效率在不同工况下的变化趋势。针对余热回收有机朗肯循环（organic rankine cycle,ORC）系统,利用所建立的数学模型,使用不同有机工质进行计算并进行对比。结果表明,在使用不同种类工质做功时,增加叶片均可以大幅提升盘式透平转矩与效率。     

液化天然气(LNG)冷能用于斯特林发动机和燃气轮机的联合系统研究

利用LNG冷能具有较好的节能潜力和经济效益,通过流程的创新设计,提出了一种将LNG冷能用于燃气轮机和斯特林发动机的联合系统。基于热力学第一、第二定律,对联合系统进行热力学分析,结果表明:在环境温度35℃条件下,联合系统的输出功率为5715.48kW,热效率为31.62%,效率为43.65%;相比燃气轮机系统和直接冷却进气系统,联合系统的输出功率分别提高了7.84%和0.78%,热效率分别提高了3.16%和1.18%,效率分别提高了4.23%和1.63%。联合系统在不同环境温度下,可将燃气轮机的进气温度降低10℃左右,系统的输出功率和效率随着进气温度的降低均有所提高。     

Exergy analysis of a thermal power plant using a modeling approach

The objective of this article is to perform exergy analysis for thermal power plants based on the simulation software Aspen Plus. In this study, the main sections of the system including the boiler and the steam turbine are modeled using the Aspen Plus software. Exergy analysis of the modeled system is studied to obtain the energy loss distribution of the system. The influences of various operating conditions on the exergy efficiency of the system are investigated including combustion temperature, excess air coefficient, steam temperature, and steam pressure. The results show that exergy loss mainly occurs in the boiler and the steam turbine. The major sources of irreversibility are combustion and the internal thermal energy exchange in the boiler. The high-pressure turbine has the lowest exergy efficiency in the steam turbine; however, it assumes the largest work output, accounting for 37.08%. Therefore, reducing the irreversible loss in the boiler and improving the performance of the high-pressure turbine are the requirements for improving the system.     

利用燃气轮机烟气余热的复合有机朗肯循环系统优化分析

本文针对燃气轮机烟气余热设计了一种复合有机朗肯循环系统,对其进行了详细的热力学分析,以某燃驱压气站烟气条件(400℃,26 kg/s)为例,以系统净输出功为目标,利用Matlab和Refprop 9. 0选择了13种工质,并确定了系统最优工况。结果表明,甲苯、R141b、丙酮分别作为3个子系统的工质时,系统可实现最大净输出功为1 587 k W,热效率和火用效率分别可达20. 26%和42. 68%,比单级循环可实现的最大净输出功高23. 33%。对系统各部件进行火用损失分析,发现蒸发器火用损失最大,并提出了改进方案。     

Thermal and exergoeconomic analysis of a novel solar driven combined power and ejector refrigeration (CPER) system

In the present study, a novel solar driven combined power and ejector refrigeration system (CPER) of 50 kW power capacity composed of an ORC (organic Rankine cycle) and an ejector refrigeration system is investigated. Solar driven CPER system is composed of two main cycles: collector cycle and refrigeration cycle. The collector cycle is made of a U-tube ETC and circulation pump and the ejector refrigeration cycle consists of generator, turbine, ejector, heat exchanger, condenser, evaporator, expansion valve, and pump. Thermodynamic performance of the proposed CPER system is evaluated and a thermo-economic analysis is conducted using the SPECO (specific exergy costing) method. A parametric study showed the effects of condenser temperature, evaporator temperature, generator pressure, turbine back pressure and turbine extraction ratio. The genetic algorithm optimization analysis is conducted which shows 25.5% improvement in thermal energy, 21.27% in exergy efficiency, and 7.76% reduction in the total cost of the CPER system. The results reveal that the performance of the CPER system is considerably improved at higher temperatures of generator and evaporator.     

First and second law investigation of waste heat based combined power and ejector-absorption refrigeration cycle

In the proposed cogeneration cycle, a LiBr-H₂O absorption refrigeration system is employed to the combined power and ejector refrigeration system which uses R141b as a working fluid. Estimates for irreversibilities of individual components of the cycle lead to possible measures for performance improvement. Results of exergy distribution of waste heat in the cycle show that around 53.6% of the total input exergy is destroyed due to irreversibilities in the components, 22.7% is available as a useful exergy output, and 23.7% is exhaust exergy lost to the environment, whereas energy distribution shows 44% is exhaust energy and 19.7% is useful energy output. Results also show that proposed cogeneration cycle yields much better thermal and exergy efficiencies than the previously investigated combined power and ejector cooling cycle. Current investigation clearly show that the second law analysis is quantitatively visualizes losses within a cycle and gives clear trends for optimization.     

新Kalina循环系统（KCS）34的热力学分析

本文提出新Kalina循环即一次抽汽回热式KCS34和分级抽汽回热式KCS34,根据热力学第一定律和第二定律,利用EES软件仿真模拟对该循环进行热力性能分析,并与基本KCS34进行相同条件下的性能对比,研究了抽汽压力、透平进口压力和透平进口温度变化对一次抽汽回热式KCS34性能的影响。研究结果表明：额定工况下,一次抽汽回热式KCS34的热效率为12.33%,比基本KCS34高0.35%;效率为46.07%,比基本KCS34高1.35%。且与一次抽汽回热式KCS34相比,分级抽汽回热式KCS34热效率高0.13%,效率高0.49%。另外,抽汽压力增加,一次抽汽回热式KCS34发电量和效率逐渐降低,热效率在10bar时达到最大;随着透平进口压力增加,一次抽汽回热式KCS34热效率逐渐增加,发电量和效率在30.79 bar时达到最大;随着透平进口温度增加,一次抽汽回热式KCS34热效率逐渐、发电量和效率都增大。     

基于非共沸工质的喷射式功冷并供循环㶲经济性分析

从热力学第一、二定律和经济性的角度，对一种新型的基于非共沸工质的喷射式功冷并供循环进行热经济性分析。并在此基础上对循环进行参数分析，研究工质组分比、蒸发温度、冷凝温度、膨胀机膨胀比、蒸汽发生器出口温度5个关键参数对循环热效率、㶲效率和资金成本率的影响。最后，以㶲效率最大化和成本率最小化为目标优化函数，采用NSGA-II算法得出帕累托最优解系，并使用TOPSIS方法进行决策，得出最优决策点，即㶲效率为0.131 9，资金成本率为1.94×10^-5美元/s。     

有机朗肯循环模拟及涡旋式膨胀机的性能研究

近些年来,太阳能作为一种可再生能源受到了广泛的关注。其中利用太阳能集热器实现100℃以下高效的热量回收,是一种普遍且有效的太阳能利用方式。采用有机朗肯循环与100℃的低温热源相结合进行发电,目前也逐渐受到了研究人员的关注。考虑到膨胀机是有机朗肯循环的核心部件,本文选择了R600制冷剂作为ORC系统的工质,对其进行了计算以及热力学性能分析。同时搭建了利用压缩空气来驱动的涡旋式膨胀机性能研究的实验台。从ORC的理论分析得,当热源温度为78~97℃,环境温度为30℃,可以获得0.7~1kW的电量,效率为0.84~0.89。利用压缩空气模拟R600,当温度从75℃变化到95℃,对应的压力从0.8MPa变化到1.2MPa,膨胀机出口压力控制在0.28MPa,等熵效率维持在0.7左右。膨胀机的功电转化效率随着膨胀机理想输出功的增加而降低。     

两级双效溴化锂制冷-热泵复合循环

在热电冷联产系统中,溴化锂吸收式制冷机在制冷过程中排放了大量的废热,这些废热品味低,难以直接回收利用。在此提出了两级双效溴化锂制冷-热泵复合循环,该循环具有冷凝温度较高的特点,便于直接回收冷凝排放热。系统以背压汽轮机的背压蒸汽为热源,制冷的同时利用循环所排出的废热加热锅炉补充水至较高温度。以具有相同功效的双效溴冷机与单效溴化锂热泵联合运行作为对比循环,制冷-热泵复合循环系统省去了一台蒸发器与冷凝器,减少了两个换热温差,并且通过热力计算、能量分析和分析表明,该循环的能量利用率与效率均有很大的提高,效率比对比循环提高了45%。     

Molecular Entropy, Thermal Efficiency, and Designing of Working Fluids for Organic Rankine Cycles

A shortage of fossil energy sources boosts the utilization of renewable energy. Among numerous novel techniques, recovering energy from low-grade heat sources through power generation via organic Rankine cycles (ORCs) is one of the focuses. Properties of working fluids are crucial for the ORC’s performance. Many studies have been done to select proper working fluids or to design new working fluids. However, no researcher has systematically investigated the relationship between molecular structures and thermal efficiencies of various working fluids for an ideal ORC. This paper has investigated the interrelations of molecular structures, molecular entropies, and thermal efficiencies of various working fluids for an ideal ORC. By calculating thermal efficiencies and molecular entropies, we find that the molecular entropy is the most appropriate thermophysical property of a working fluid to determine how much energy can be converted into work and how much cannot in a system. Generally speaking, working fluids with low entropies will generally have high thermal efficiency for an ideal ORC. Based on this understanding, the direct interrelations of molecular structures and entropies provide an explicit interrelation between molecular structures and thermal efficiencies, and thus provide an insightful direction for molecular design of novel working fluids for ORCs.     

过冷度对地热发电非共沸工质有机朗肯循环热力性能的影响

有机朗肯循环（organic Rankine cycle,ORC）是利用中低温地热能（< 150℃）发电的主要途径,在实际运行中,非共沸工质往往会冷凝至过冷状态。分析了冷凝过冷度对非共沸工质ORC热力性能的影响,建立了ORC、内回热（internal heat exchanger,IHE）ORC的热力学模型,以净输出功最大为目标函数优化了工质的蒸发压力,并开展了系统的㶲分析。结果表明：过冷度影响了工质与冷源换热流体间的温度匹配特性,受夹点温差的限制,随着过冷度的增加,工质的冷凝压力上升;过冷度亦改变了预热器和蒸发器的热量分摊,随着过冷度的增加,最佳蒸发压力亦上升。混合工质异丁烷/异戊烷的质量配比为0.4：0.6时,净输出功受过冷度的影响最大,当过冷度为2℃时,净输出功下降了4.36%。IHE回收膨胀机排汽的余热,提高了预热器入口温度,可提高过冷ORC系统净输出功0.55%。过冷度增大了冷凝器的㶲损失;采用内回热冷凝器的㶲损失降低了24.7%。