Heat pump enhanced gas turbine cogeneration

A significant fraction of the gaseous fuel supplied to industry will be used in medium- and small-size cogeneration plants. In this paper, a gas turbine and a gas engine of about 800 kW power output are compared at full and part load operation. When low-temperature heat (e.g., for space heating) is produced, the higher exhaust losses of the gas turbine yield a lower system efficiency, particularly at part load. A scheme is proposed to recover the exhaust gas energy by cooling to a temperature near ambient. The system features a heat pump to raise the recovered heat temperature to a usable level and an organic Rankine cycle (ORC) engine to drive the heat pump. The ORC engine uses the high-temperature fraction of the heat recovered from the exhaust. The data for the ORC engine are derived from an actual experimental engine. The performance is calculated for the system at full load.     

高温燃料电池_燃气轮机混合发电系统性能分析

针对 高温燃料电池系统的高效率、环保性以及排气废热的巨大利用潜能,将其与燃气轮机组成混合装置进行发电是未来分布式发电的一种极有前景的方案。文中对高温燃料电池及混合循环系统作了简介,并对两种典型的高温燃料电池－燃气轮机混合循环发电系统进行了性能分析,这将为我国高温燃料电池－燃气轮机混合循环系统的研制提供参考。     

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。     

冷热电三联供系统的优化研究

冷热电联供系统主要应用于大型集中性供能系统中。作为分布式能源的一种,冷热电联供系统具有节约能源、改善环境、提高电力综合效益的优势。一般情况下,三联供系统是以天然气为燃料带动燃气轮机、微燃机或内燃机发电机等燃气发电设备运行,产生的电力供应用户的电力需求,系统发电后排出的余热通过余热回收利用设备(余热锅炉或者余热直燃机等)向用户供热、供冷。通过这种方式提高整个系统的一次能源利用率,实现能源的梯级利用,还可以提供并网电力作能源互补,经济收益和效率均得以提升。研究较为常见的燃气轮机中的一种蒸汽型吸收式冷热电联产系统,对不同配置方式和运行方式进行横向与纵向交叉比较,以完成系统优化研究。     

Stirling based fuel cell hybrid systems: An alternative for molten carbonate fuel cells

This paper presents a new design for high temperature fuel cell and bottoming thermal engine hybrid systems. Now, instead of the commonly used gas turbine engine, an externally fired - Stirling - piston engine is used, showing outstanding performance when compared to previous designs.Firstly, a comparison between three thermal cycles potentially usable for recovering waste heat from the cell is presented, concluding the interest of the Stirling engine against other solutions used in the past.Secondly, the interest shown in the previous section is confirmed when the complete hybrid system is analyzed. Advantages are not only related to pure thermal and electrochemical parameters like specific power or overall efficiency. Additionally, further benefits can be obtained from the atmospheric operation of the fuel cell and the possibility to disconnect the bottoming engine from the cell to operate the latter on stand alone mode. This analysis includes on design and off design operation.     

内燃机和燃气轮机在发电领域的比较

从油耗、温度、部分负荷以及海拔高度对原动机的影响等方面 ,对内燃机和燃汽轮机的功率与效率进行了比较。实践证明 ,在上述条件下 ,内燃机比燃气轮机更优越 ,同时受燃料价格波动影响也较小。     

Theory and experimental validation of cross-flow micro-channel heat exchanger module with reference to high Mach aircraft gas turbine engines

This study explores the design, analysis, and performance assessment of a new class of heat exchangers intended for high Mach aircraft gas turbine engines. Because the compressor air that is used to cool turbine blades and other components in a high Mach engine is itself too hot, aircraft fuel is needed to precool the compressor air, cooling is achieved with a new heat exchanger. The heat exchanger consists of a large number of miniature, closely-spaced modules. Within each module, the fuel flows through a series of parallel micro-channels, while the air flows externally over rows of short, straight fins perpendicular to the direction of fuel flow. A theoretical model was developed to predict the thermal performance of the module for various operating conditions. To confirm the accuracy of the model, a single module was constructed and tested using water to simulate the aircraft fuel. The theoretical model was used to predict the air temperature drop, water temperature rise, and heat transfer rate for each fluid stream. Comparisons between theory and experiment show good overall agreement in exit temperatures and heat transfer rates. This study shows the theoretical model is a reliable tool for predicting the performance of heat exchanger modules under actual fuel and air turbine engine conditions and for the design of aircraft heat exchangers of different sizes and design envelopes.     

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.     

A computational study on the combustion of hydrogen/methane blended fuels for a micro gas turbines

To understand the combustion performance of using hydrogen/methane blended fuels for a micro gas turbine that was originally designed as a natural gas fueled engine, the combustion characteristics of a can combustor has been modeled and the effects of hydrogen addition were investigated. The simulations were performed with three-dimensional compressible k-ε turbulent flow model and presumed probability density function for chemical reaction. The combustion and emission characteristics with a variable volumetric fraction of hydrogen from 0% to 90% were studied. As hydrogen is substituted for methane at a fixed fuel injection velocity, the flame temperatures become higher, but lower fuel flow rate and heat input at higher hydrogen substitution percentages cause a power shortage. To apply the blended fuels at a constant fuel flow rate, the flame temperatures are increased with increasing hydrogen percentages. This will benefit the performance of gas turbine, but the cooling and the NO_x emissions are the primary concerns. While fixing a certain heat input to the engine with blended fuels, wider but shorter flames at higher hydrogen percentages are found, but the substantial increase of CO emission indicates a decrease in combustion efficiency. Further modifications including fuel injection and cooling strategies are needed for the micro gas turbine engine with hydrogen/methane blended fuel as an alternative.     

Performance characteristics of a low heat rejection diesel engine operating with biodiesel

Vegetable oils are a promising alternative among the different diesel fuel alternatives. However, the high viscosity, poor volatility and cold flow characteristics of vegetable oils can cause some problems such as injector coking, severe engine deposits, filter gumming, piston ring sticking and thickening of lubrication oil from long-term use in diesel engines. These problems can be eliminated or minimized by transesterification of the vegetable oils to form monoesters. These monoesters are known as biodiesel. The important advantages of biodiesel are lower exhaust gas emissions and its biodegradability and renewability compared with petroleum-based diesel fuel. Although the transesterification improves the fuel properties of vegetable oil, the viscosity and volatility of biodiesel are still worse than that of petroleum diesel fuel. The energy of the biodiesel can be released more efficiently with the concept of low heat rejection (LHR) engine. The aim of this study is to apply LHR engine for improving engine performance when biodiesel is used as an alternative fuel. For this purpose, a turbocharged direct injection (DI) diesel engine was converted to a LHR engine and the effects of biodiesel (produced from sunflower oil) usage in the LHR engine on its performance characteristics have been investigated experimentally. The results showed that specific fuel consumption and the brake thermal efficiency were improved and exhaust gas temperature before the turbine inlet was increased for both fuels in the LHR engine.     

Energy consumption by multi-stage flash and reverse osmosis desalters

Kuwait and most of the Gulf countries, depend mainly on desalted water from the sea for satisfying their fresh water needs. These countries are using the multi-stage flash (MSF) desalting system, as the ‘work horse’ for their water production. This system is less efficient in energy consumption as compared to the reverse osmosis (RO) system. Moreover, large units based on the MSF system have to be combined with steam or gas turbines power plants for better utilization of steam supplied to the MSF units at moderately low temperature and pressure (as compared to steam produced by large steam generators). The value and the cost of the thermal energy supplied to the MSF desalting system depends on the method of supplying this energy. This steam can be supplied directly from a fuel operated boiler or heat recovery steam generator associated with a gas turbine. It can also be supplied from the exhaust of a steam back pressure turbine or bled from condensed extraction steam turbine at a pressure suitable for the desalting process. Any energy comparison should be based on simple criteria, either how much fuel energy is consumed to produce this energy or how much mechanical energy is needed per unit product. The energy consumed in the light of the practice used in most Gulf countries are discussed here. In this study, reference desalting and power plants are used for comparison purposes. This study shows that shifting from MSF desalting system to the RO system can save up to 66% of the fuel energy used to desalt seawater.     

Simulation of the operation of a gas turbine installation of a thermal power plant with a hydrogen fuel production system

The growth in demand for the production of heat and electricity requires an increase in fuel consumption by power equipment. At the moment, the most demanded thermal equipment for construction and modernization is gas turbine units. Gas turbines can burn a variety of fuels (natural gas, synthesis gas, methane), but the main fuel is natural gas of various compositions. The use of alternative fuels makes it possible to reduce CO₂ and NO_x emissions during the operation of a gas turbine. Under conditions of operation of thermal power plants at the wholesale power market, it becomes probable that combined cycle power units, designed to carry base load, will start to operate in variable modes. Variable operation modes lead to a decrease in the efficiency of power equipment. One way to minimize or eliminate equipment unloading is to install an electrolysis unit to produce hydrogen.In this article the technology of “Power to gas” production with the necessary pressure at the outlet of 30 kgf/cm² (this pressure is necessary for stable operation of the fuel preparation system of the gas turbine) is considered. High cost of hydrogen fuel during production affects the final cost of heat and electric energy, therefore it is necessary to burn hydrogen in mixture with natural gas. Burning a mixture of 5% hydrogen fuel and 95% natural gas requires minimal changes in the design of the gas turbine, it is necessary to supplement the fuel preparation system (install a cleaning system, compression for hydrogen fuel). In addition, the produced hydrogen can be stored, transported to the consumer. For the possibility of combustion of a mixture of natural gas and hydrogen fuel in a gas turbine the methodology of calculation of thermodynamic properties of working bodies developed by a team of authors under the guidance of Academician RAS (the Russian Academy of Sciences) V.E. Alemasov has been adapted, resulting in a program that allows to obtain an adequate mathematical model of the gas turbine. The permissible range of the working body temperature is limited to 3000 K. This paper presents the developed all-mode mathematical model of a gas turbine.On the basis of mathematical modeling of a gas turbine, a change in the main energy and environmental characteristics is shown depending on the composition of the fuel gas. Adding 5% hydrogen to natural gas has little effect on the gas turbine air treatment system, the flow rate remains virtually unchanged. CO₂ emissions decrease, but there is an increase in the amount of H₂O in the turbine exhaust gases.     

Thermodynamic analysis and experimental validation of multi-composition ammonia liquor absorption engine cycle for power generation

Energy conservation, utilization, and effective integration are of utmost importance for future sustenance. Accordingly, this work focuses on the generation of power from the low-grade temperature below 150°C . A proposed novel multi-composition ammonia liquor absorption engine (MALAE) power cycle can be used toward the above purpose by supplying renewable energy obtained from low concentration type solar collectors. Proposed MALAE power cycle minimizes heal loss due to heat recovery and uses high purity NH₃ vapors to expand through the isentropic turbine. MALAE power system is modeled and simulated using NH₃-H₂O as a working fluid for a reboiler temperature of 115°C . The purpose of this work is to simulate the proposed MALAE power cycle with the distillation column and two solution heat exchanger (SHE). MALAE modeling and simulation is accomplished in SCILAB software. The simulation outcome is validated with the pilot-scale 5 kW experimental setup and validation showed ±5% deviation. A comparison of MALAE cycle with published cycles signifies higher efficiency of MALAE cycle toward the utilization of low-grade energy from a temperature range of 100°C to 150°C . Finally, detailed parametric analysis of MALAE cycle efficiency is presented in terms of number of plates, distillation pressure and vapor flowrate, absorber temperature, pressure partial condenser temperature, and heat loads.     

Economie d'énergie en trigénération

Trigeneration is defined as the production of three useful forms of energy—heat, cold and power—from a primary source of energy such as natural gas or oil. For instance, trigeneration systems typically produce electrical power via a reciprocating engine or gas turbine and recover a large percentage of the heat energy retained in the lubricating oil, exhaust gas and coolant water systems to maximize the utilization of the primary fuel. The heat produced can be totally or partially used to fuel absorption refrigerators. Therefore, trigeneration systems enjoy an inherently high efficiency and have the potential to significantly reduce the energy-related operation costs of facilities. In this paper, we describe a model of characterization of trigeneration systems trough the condition of primary energy saving and the quality index, compared to the separate production of heat, cold and power. The study highlights the importance of the choice of the separate production reference system on the level of primary energy saving and emissions reduction.     

高原环境重型车用柴油机热负荷性能分析

以高原修正的广安博之喷雾模型为基础,建立具有环境适应性的某特种车辆柴油机缸内燃烧与冷却系统传热耦合模型。海拔3 700m的实车试验表明:模型最大误差在4.3%以内。在不改变发动机部件的前提下,通过调整柴油机供油提前角和最大循环供油量,可改善高原运行时特种车辆柴油机的热负荷。试验结果表明:在海拔4 000m时,供油提前角提前4°CA可使涡前温度最高下降30℃,活塞表面温度最高下降15℃,且表面温度场分布稍有改善,但缸内温度峰值上升20℃;在满足任务工况功率需求的基础上,供油量调整螺钉拧入角度为255°时,热负荷参数满足发动机控制参数要求。     

Modelling of aluminum-fuelled power plant with steam-hydrogen enthalpy utilization

Present paper is devoted to the modelling of aluminum-fuelled power plants which employ an aluminum-water reactor for hydrogen and heat production. We considered two new schemes for power plants with aluminum-water reactors producing high-temperature steam-hydrogen mixture: a power plant with a steam-hydrogen turbine, condenser and air-hydrogen fuel cell and a power plant with a steam-hydrogen turbine, combustion chamber and steam-gas turbine. Parameters of the aluminum-water reactor described in the paper correspond to those of the recently developed and tested aluminum-water reactor: pressure – 15 MPa, temperature – 600 K, steam to hydrogen mass ratio – 40. It was shown that the electrical efficiency can be increased from 12% to 25–30% for the power plant with an air-hydrogen fuel cell and to 18–25% for that with a combustion chamber and steam-gas turbine. The total efficiency of such power plants can reach 80%. Moreover, the efficiency of aluminum-fuelled power plants can be further increased by heat regeneration or heat transfer to the secondary circuit. The proposed calculation method provides high accuracy and can be used to predict the performance of power plants with aluminum-water reactors under different operation conditions. In general, the proposed method can be used to simulate utilization of the enthalpy of high-temperature steam-hydrogen mixture from various sources.     

A polygeneration process concept for HCCI-engines – Modeling product gas purification and exergy losses

This modeling study addresses the question, whether HCCI piston engines can be used as chemical reactors in a polygeneration process. In this context, a combustion engine is used to produce hydrogen by partial oxidation in the engine and the further auxiliary units assure the purification of hydrogen. Several aspects were addressed during the development of the process regarding fresh-gas- and exhaust gas-treatment and energy integration. The fresh gas preheating for methane ignition was achieved by recirculation of hot exhaust gas, which also contributed to a high flexibility towards power-, heat- and hydrogen-output. Exergetic efficiencies, process-outputs and fuel consumption were calculated and compared for different operation points. Exergetic efficiencies of up to 80% were achievable and this high efficiency leads to reduced fuel consumption, with up to 40% fuel savings compared to the separated production of power, heat and hydrogen. Power and heat flow of the process can be adjusted very flexibly and the ratio can be varied within a factor of two within the investigated operating conditions.     

Development of a hybrid compressed gas engine/PEFC power system using the dissociation expansion characteristics of gas hydrate

The pressure of dissociation and expansion of a gas hydrate can fully power a compression gas engine with a temperature change from 0 °C to 10 °C. The use of green energy (high temperature) and simple refrigeration (low temperature) can easily provide this temperature difference. The dissociation characteristics of a hydrate can be used to develop a clean and efficient hydrate actuator (HA). In this paper, we examine the operation of a hybrid power system consisting of an HA engine and a proton-exchange membrane fuel cell (PEFC), using an example application of an individual house in Sapporo, Japan. A power-generation system that uses the exhaust heat of a PEFC and the cold energy of a heat pump to dissociate and recombine a hydrate is proposed. The results of this analysis indicate that the average electricity production efficiency on a representative day may reach 60.5%. This technique of using the dissociation expansion characteristics of a gas hydrate for power-generation deserves further attention in the search for clean energy.     

Study of molten carbonate fuel cell—microturbine hybrid power cycles

The interaction realized by fuel cell—microturbine hybrids derive primarily from using the rejected thermal energy and combustion of residual fuel from a fuel cell in driving the gas turbine. This leveraging of thermal energy makes the high temperature molten carbonate fuel cells (MCFCs) ideal candidates for hybrid systems. Use of a recuperator contributes to thermal efficiency by transferring heat from the gas turbine exhaust to the fuel and air used in the system.Traditional control design approaches, consider a fixed operating point in the hope that the resulting controller is robust enough to stabilize the system for different operating conditions. On the other hand, adaptive control incorporates the time-varying dynamical properties of the model (a new value of gas composition) and considers the disturbances acting at the plant (load power variation).     

Experimental study of combustion performances and emissions of a spark ignition cogeneration engine operating in lean conditions using different fuels

This work presents an experimental study describing a six-cylinder spark ignition engine running with a lean equivalence ratio, high compression ratio, ignition delay and used in a cogeneration system (heat and electricity production). Three types of fuels; natural gas, pure methane and methane/hydrogen blend (85% CH₄ and 15% H₂ by volume), were used for comparison purposes. Each fuel has been investigated at 1500 rpm and for various engine loads fixed by electrical power output conditions. CO, CO₂, HC, and NOx emissions values, and exhaust gas temperature were measured. The effect of fuel composition on engine characteristics has been studied. The results show, that the hydrogen addition increased HC emissions (around 18%), as well as performance, whilst it reduced NO_x (around 31%), exhaust gas temperature, CO and CO₂.