Optimization of the irreversible Stirling heat engine

The effects of inefficiencies in the compression, expansion and regeneration processes on engine performance have been evaluated theoretically for a Stirling heat engine operating in a closed regenerative thermodynamic cycle. The irreversible cycle has been optimized by using the maximum power density technique. Maximized power and maximized power density are obtained for different n_ex, τ, α_c, α_h, η_c, η_ex and η_reg values. The maximum efficiencies have been found very close to the values corresponding to the maximum power density conditions but far from the values at maximum power. It has been found that the engines designed by considering the maximum power density have high efficiencies and small sizes under the same prescribed conditions. Copyright © 1999 John Wiley & Sons, Ltd.     

Modeling and optimization of a novel pressurized CHP system with water extraction and refrigeration

A novel cooling, heat, and power (CHP) system has been proposed that features a semi-closed Brayton cycle with pressurized recuperation, integrated with a vapor absorption refrigeration system (VARS). The semi-closed Brayton cycle is called the high-pressure regenerative turbine engine (HPRTE). The VARS interacts with the HPRTE power cycle through heat exchange in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount that depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for the inlet air to the high-pressure compressor, water extraction, and for an external cooling load. The computer model of the combined HPRTE/VARS cycle predicts that with steam blade cooling and a medium-sized engine, the cycle will have a thermal efficiency of 49% for a turbine inlet temperature of 1400°C. This thermal efficiency, is in addition to the large external cooling load, generated in the combined cycle, which is 13% of the net work output. In addition, it also produces up to 1.4 kg of water for each kg of fuel consumed, depending upon the fuel type. When the combined HPRTE/VARS cycle is optimized for maximum thermal efficiency, the optimum occurs for a broad range of operating conditions. Details of the multivariate optimization procedure and results are presented in this paper. Copyright © 2008 John Wiley & Sons, Ltd.     

Modeling and experimentation of a novel pressurized CHP system with water extraction

A novel cooling and power cycle is proposed, which combines a semi‐closed cycle gas turbine called the high‐pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). This combined HPRTE/VARS cycle is capable of producing power, water and refrigeration effect for external loads. In a previous study, the combined cycle was modeled using zero‐dimensional steady‐state thermodynamics, with specified values of polytrophic efficiencies and pressure drops for the turbo‐machinery and heat exchangers. In this study, a modified version of the combined HPRTE/VARS cycle is experimentally investigated for the demonstration of the combined cycle concept and for the model validation. This modified HPRTE has two water‐cooled heat exchangers instead of the absorption refrigeration system. The model of the original combined HPRTE/VARS cycle was modified to simulate the performance of the modified HPRTE cycle. Temperatures, pressure, mass flow rates and other overall cycle parameters obtained from the computer model are compared with the corresponding experimental values of the modified cycle. The agreement between the values is found to be within acceptable limits. In addition, the uncertainty analysis of the experimental data is undertaken to find the uncertainty in the final output variables: thermal efficiency and non‐dimensional water extraction parameter. Copyright © 2008 John Wiley & Sons, Ltd.     

Finite time thermodynamic analysis of an irreversible regenerative closed cycle brayton heat engine

This communication presents the parametric study of an irreversible regenerative Brayton cycle with nonisentropic compression and expansion processes for finite heat capacitance rates of external reservoirs. The power output of the cycle is maximized with respect to the working fluid temperatures and the expressions for maximum power output and the corresponding thermal efficiency are obtained. The effect of the effectiveness of the various heat exchangers and the efficiencies of the turbine and compressor, the reservoir temperature ratio and the heat capacitance rate of heating and cooling fluids and the cycle working fluid on the power output and the corresponding thermal efficiency has been studied. It is seen the effect of cold side effectiveness is more pronounced for the power output while the effect of regenerative effectiveness is more pronounced for the thermal efficiency. It is found that the effect of turbine efficiency is more than the compressor efficiency on the performance of these cycles. It is also found that the effect of sink-side heat capacitance rate is more pronounced than the heat capacitance rate on the source side and the heat capacitance rate of the working fluid.     

燃气-超临界CO2联合循环发电系统

  [目的]  燃气轮机排气温度高,可增加底循环,利用排气的余热发电,从而提高燃料总的能量利用率。鉴于超临界CO₂循环热效率高,并且具有系统简单、结构紧凑、运行灵活等潜在优势,可与燃气轮机组成新型的燃气-超临界CO₂联合循环。  [方法]  为了充分利用燃气轮机排气余热,提出在简单回热超临界CO₂循环的基础上,再嵌套一个简单回热循环的布置方式,并以PG9351(FA)型燃气轮机为例,对其热效率进行了计算分析。同时,在系统中增加余热利用装置,可将剩余热量用于供热、转换为冷量或发电。  [结果]  结果表明:对于选定的燃气轮机,超临界CO₂循环最高温度可达约600 ℃,循环发电效率约32%,获得余热温度为170 ℃以上,余热热量占燃气轮机排气热量9%,联合循环发电效率约54%。  [结论]  燃气-超临界CO₂联合循环发电系统具有较高的热效率,并且保留部分较高品位的余热,可进一步用于电厂运行。     

氢燃联合循环中两种回热网络的优化与比较

氢气－燃气透平联合循环中燃气透平排气的热容大于压缩空气的热容,且远大于氢气的热容。先将燃气透平的排气分流成二股并分别预热空气和氢气,再合流并加热温氢的回热网络,与燃气透平的先预热压缩空气、再热预氢的回热网络比较,有效地提高了气透平的进气温度,从而增大了联合循环的比输出功,提高了联合循环的热效率和降低了燃料氢的耗量。本文用过程能量组合方法对两回热网络进行了优化分析,并定量比较了采用两种优化后的回热网     

Efficient use of energy by utilizing gas turbine combined systems

The gas turbine engine is characterized by its relatively low capital cost compared with steam power plants. It has environmental advantages and short construction lead time. However, conventional industrial engines have lower efficiencies especially at part load. One of the technologies adopted nowadays for improvement is the “combined cycle”. Hence, it is expected that the combined cycle continues to gain acceptance throughout the world as a reliable, flexible and efficient base load power generation plant. In this article, 12 research investigations, carried out by the author and associates during the last 10 years are briefly reviewed. These cover 12 gas turbine systems which would contribute towards efficient use of energy. They entail fundamental studies in addition to applications of combined systems in industry including: the closed gas turbine cycle; the organic Rankine cycle; repowering; integrated power and refrigeration; cryogenic power; liquefied natural gas (LNG) gasification; and inlet air cooling.     

Analysis of the stirling heat engine at maximum power conditions

The Stirling heat engine operating in a closed regenerative thermodynamic cycle is analyzed. Polytropic processes are used for the power and displacement pistons. Following regeneration, the maximum power density and efficiency are found and the compression ratio at maximum power density is determined.     

Performance analysis and comparison of an Atkinson cycle coupled to variable temperature heat reservoirs under maximum power and maximum power density conditions

In this paper, performance analysis and comparison based on the maximum power and maximum power density conditions have been conducted for an Atkinson cycle coupled to variable temperature heat reservoirs. The Atkinson cycle is internally reversible but externally irreversible, since there is external irreversibility of heat transfer during the processes of constant volume heat addition and constant pressure heat rejection. This study is based purely on classical thermodynamic analysis methodology. It should be especially emphasized that all the results and conclusions are based on classical thermodynamics. The power density, defined as the ratio of power output to maximum specific volume in the cycle, is taken as the optimization objective because it considers the effects of engine size as related to investment cost. The results show that an engine design based on maximum power density with constant effectiveness of the hot and cold side heat exchangers or constant inlet temperature ratio of the heat reservoirs will have smaller size but higher efficiency, compression ratio, expansion ratio and maximum temperature than one based on maximum power. From the view points of engine size and thermal efficiency, an engine design based on maximum power density is better than one based on maximum power conditions. However, due to the higher compression ratio and maximum temperature in the cycle, an engine design based on maximum power density conditions requires tougher materials for engine construction than one based on maximum power conditions.     

Thermodynamical,economical and environmental evaluation of high efficiency gas turbine cogeneration systems

The paper evaluates the thermodynamical, economical and environmental characteristics of a cogeneration system composed of a gas turbine and a waste heat boiler (system A). Two other systems for increasing power generating efficiency are also evaluated, namely systems B and C, which are constructed by incorporating a regenerative cycle and a dual fluid cycle, respectively, into system A. It has been estimated that system C satisfies an environmental constraint that the nitrogen oxide density exhausted should be less than 100 parts in 10⁶, and that systems A and B also satisfy this constraint if a small amount of steam is injected into the combustor. The power generating efficiencies of systems A and B, in this case, and that of system C have been estimated to be 33.5%, 38.5% and 41.2%, respectively; i.e. the efficiencies of systems B and C can be improved noticeably compared with that of system A. The economics of these systems have also been evaluated based on the value of a profit index, and the systems are all estimated to be economically viable under the conditions assumed. As a result, it has been shown that it is possible to construct cogeneration systems with satisfactory characteristics of both environmental protection and profitability if system A is used in districts where the heat demand is large, system C in districts where the heat demand is small, and system B in districts with intermediate heat demand.     

Exergy analysis,parametric analysis and optimization for a novel combined power and ejector refrigeration cycle

A new combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the ejector refrigeration cycle. This combined cycle produces both power output and refrigeration output simultaneously. It can be driven by the flue gas of gas turbine or engine, solar energy, geothermal energy and industrial waste heats. An exergy analysis is performed to guide the thermodynamic improvement for this cycle. And a parametric analysis is conducted to evaluate the effects of the key thermodynamic parameters on the performance of the combined cycle. In addition, a parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The results show that the biggest exergy loss due to the irreversibility occurs in heat addition processes, and the ejector causes the next largest exergy loss. It is also shown that the turbine inlet pressure, the turbine back pressure, the condenser temperature and the evaporator temperature have significant effects on the turbine power output, refrigeration output and exergy efficiency of the combined cycle. The optimized exergy efficiency is 27.10% under the given condition.     

Power generation with gas turbine systems and combined heat and power

This article gives an overview of power generation with gas turbine and combined heat and power (CHP) systems. It also presents the European Union strategy for developing gas turbines and CHP systems. Ways to improve the performance of the several types of gas turbine cycle will be a major objective in the coming years. The targets are combined cycle efficiencies above 60% industrial gas turbine system efficiencies of at least 50% and small gas turbines efficiencies above 35% and designs for the use of fuels with less than 25% heating value of that of natural gas. The main CHP targets are the reduction of the overall costs and the development of above 40 kW biomass-fired systems.     

Development of a gas turbine performance analysis program and its application

A general-purpose performance prediction program, which can simulate various types of gas turbine such as simple, recuperative, and reheat cycle engines, has been developed. A stage-stacking method has been adopted for the compressor, and a stage-by-stage model including blade cooling has been used for the turbine. The combustor model has the capability of dealing with various types of gaseous fuels. The program has been validated through simulation of various commercial gas turbines. The simulated design performance has been in good agreement with reference data for all of the gas turbines. The average deviations of the predicted performance parameters (power output, thermal efficiency, and turbine exhaust temperature) were less than 0.5% in the design simulations. The accuracy of the simulation of off-design operation was also good. The maximum root mean square deviations of the predicted off-design performance parameters from the reference data were 0.22% and 0.44% for the two simple cycle engines, 0.22% for the recuperative cycle engine, and 0.21% for the reheat cycle engine. Both the design and off-design simulations confirmed that the component models and the program structure are quite reliable for the performance prediction of various types of gas turbine cycle over a wide range of operations.     

Carbon Dioxide as Working Fluids in Transcritical Rankine Cycle for Diesel Engine Multiple Waste Heat Recovery in Comparison to Hydrocarbons

In consideration of the high-temperature characteristic of engine's waste heat and stricter environmental regulations, natural substance, including CO_2 and hydrocarbons, have been treated as promising working fluid for diesel engine waste heat recovery due to its environment friendly and excellent physical and chemical properties. This paper presented a comprehensive performance analysis on transcritical Rankine cycles for diesel engine multiple waste heat recovery using hydrocarbons and CO_2 as working fluid. The optimal turbine inlet pressures corresponding to maximum net power output, maximum exergy efficiency and minimum electricity production cost(EPC) were obtained. The effect of working fluid on these optimal pressures has been discussed. For fluids with low critical temperature, the optimal pressure corresponding to maximum net power output is lower than the one for maximum exergy efficiency, while the opposite results can be found for fluid with high critical temperature. Then, the effect of various working fluid properties in transcritical cycle performance is discussed. Comparison results show that CO_2 obtains only more power output than Ethane, Propane and Propene, but CO_2 is capable of absorbing more energy from engine coolant and regeneration heat with comparable total heat transfer areas and has an advantage in turbine size, particularly for hydrocarbons with high critical temperature.     

有无后冷器的微燃气轮机HAT循环性能比较

基于某80kW微燃气轮机回热循环改造工作,比较了有后冷器和无后冷器的HAT(Humid Air Turbine)循环性能和需要增加的换热器面积。研究结果表明,对于所研究的微燃气轮机,有、无后冷器的HAT循环系统折合效率和折合输出功相当,与有后冷器的HAT循环相比,无后冷器的HAT循环湿化器更高,体积更大,但是由于省掉了后冷器,其总换热面积(后冷器、湿化器、省煤器换热面积之和)更小,即意味着其投资更低,且无后冷器的HAT循环系统结构更简单,将使系统更加紧凑且控制更容易。     

Regenerative steam-injection gas-turbine systems

There is a demand for developments of the distributed energy system using a small-scale gas turbine. The steam injection configuration can improve the thermal efficiency of simple and regenerative gas-turbine cycles. In this paper, the performance characteristics of two types of regenerative steam-injection gas-turbine (RSTIG) systems are analyzed and they are compared with the performances of the simple, regenerative, water injection and steam injected gas-turbine (STIG) cycles. The thermal efficiencies of the RSTIG systems are higher than those of the regenerative, water injection and STIG systems and the specific power is larger than that of the regenerative cycle. The optimum pressure-ratio for maximum efficiency of the RSTIG systems is relatively low. Furthermore, the steam-injection configuration can be applied in the flexible heat-and-power cogeneration system and the total efficiency of the RSTIG cogeneration system reaches more than 70% (HHV).     

Influence of multiple irreversible losses on the performance of a molten carbonate fuel cell-gas turbine hybrid system

In this study, a new molten carbonate fuel cell-gas turbine hybrid system, which consists of a fuel cell, three heat exchangers, a compressor, and a turbine, is established. The multiple irreversible losses existing in real hybrid systems are taken into account by the models of a molten carbonate fuel cell and an open Brayton cycle with a regenerative process. Expressions for the power outputs and efficiencies of the subsystems and hybrid system are derived. The maximum power output and efficiency of the hybrid system are numerically calculated. It is found that compared with a single molten carbonate fuel cell, both the power output and efficiency of the hybrid system are greatly enhanced. The general performance characteristics of the hybrid system are evaluated and the optimal criteria of the main performance parameters are determined. The effects of key irreversibilities on the performance of the hybrid system are investigated in detail. It is found that the use of a regenerator in the gas turbine can availably improve the power output and efficiency of the system. The results obtained here are significant and may be directly used to discuss the optimal performance of the hybrid system in special cases.     

Exergetic evaluation of methods for improving power generation efficiency of a gas turbine cogeneration system

A cogeneration system generating both heat and power for district heating and cooling is required to be more efficient to improve its economy. In this paper, three typical methods for improving the power generation efficiency of a gas turbine cogeneration system are evaluated by examining exergy flow at various points of the system. The three methods investigated are: (a) to raise turbine inlet temperature, (b) to incorporate a regenerative cycle, and (c) to introduce a dual-fluid cycle. Exergy flows at various points of each cogeneration system have been evaluated. It has been shown through quantitve analyses of exergy flows (1) what kind of energy loss of the system can be reduced by introducing each efficiency-improving method, (2) that the method of incorporating a regenerative cycle is highly useful in improving exergy efficiency of the cogeneration system. © 1997 by John Wiley & Sons, Ltd.     

退役航空涡扇发动机地面应用的有效途径之一_再热燃气_蒸汽联合循环

本文探讨以退役航空涡扇发动机作为燃气发生器,内函的燃气与外函的空气相掺混。经再热燃烧室加热后进入动力涡轮作功,并且应用余热锅炉回收－部分排气余热,产生蒸汽,驱动汽轮机作功所组成的再热热气－蒸汽联合循环。通过计算实例说明该循环具有输出功率大,循环效率具有相当大的提高等特点。     

GA-based design-point performance adaptation and its comparison with ICM-based approach

Accurate performance simulation and estimation of gas turbine engines is very useful for gas turbine manufacturers and users alike and such a simulation normally starts from its design-point. When some of the engine component parameters for an existing engine are not available, they must be estimated in order that the performance analysis can be started. Therefore, the simulated design-point performance of an engine may be slightly different from its actual performance. In this paper, a Genetic Algorithm (GA) based non-linear gas turbine design-point performance adaptation approach has been presented to best estimate the unknown component parameters and match available design-point engine performance. In the approach, the component parameters may be compressor pressure ratios and efficiencies, turbine entry temperature, turbine efficiencies, engine mass flow rate, cooling flows, by-pass ratio, etc. The engine performance parameters may be thrust and SFC for aero engines, shaft power and thermal efficiency for industrial engines, gas path pressures and temperatures, etc. To select the most appropriate to-be-adapted component parameters, a sensitivity analysis is used to analyze the sensitivity of all potential component parameters against the engine performance parameters. The adaptation approach has been applied to an industrial gas turbine engine to test the effectiveness of the approach. The approach has also been compared with a non-linear Influence Coefficient Matrix (ICM) based adaptation method and the advantages and disadvantages of the two adaptation methods have been compared with each other. The application shows that the sensitivity analysis is very useful in the selection of the to-be-adapted component parameters and the GA-based adaptation approach is able to produce good quality engine models at design-point. Compared with the non-linear ICM-based method, the GA-based performance adaptation method is more robust but slower in computation and relatively less accurate.