燃气内燃机冷热电三联供性能分析

针对分布式能源系统,计算分析燃气内燃机冷热电联产系统的热力性能以及经济性能,讨论冷热电联产系统对比单独发电或制热制冷的优劣。以总能利用率为基础,结合?效率,对燃气冷热电三联供系统进行性能分析,并与常规的单产系统进行对比;并分析了三联供系统的初期投资及运营费用对成本回收的影响。     

内燃机分布式冷热电联供技术应用及发展趋势

分布式冷热电联产技术符合"温度对口,梯级利用"的科学用能原则,是实现节能减排的重要途径。以内燃机为动力装置的冷热电联产系统在国内外已有一定的应用,但在单元技术和系统集成技术上仍处于较低水平,系统节能率较低。新一代内燃机分布式冷热电联产技术通过吸收式除湿技术、升温型热泵技术等对内燃机缸套水低温余热进行更为有效的利用,使系统节能率上升至25%以上。本文介绍了内燃机分布式冷热电联产技术的研究现状和应用现状,对新一代内燃机分布式冷热电联产技术应用的发展趋势进行了系统分析。     

分布式冷热电联产系统的能量梯级利用率新准则

分布式冷热电联产系统评价准则对系统集成开拓与设计优化至关重要,传统的热效率、火用效率等难以全面科学地评估多供能系统性能特性,也不适于作为联产系统设计优化的目标函数。文章概述了目前常用的评价准则及其存在问题,基于热力学基本方程和联产系统的本质特征,提出了能量梯级利用率的评价准则。新准则从发电、制冷及供热等过程耗用能量的品位和生产产品的品质等来全面权衡不同能量转换利用过程的本质差异,并借助权重系数来综合量化描述。还结合实际的联产系统算例,对新准则和原有的评价准则进行比较分析。研究表明,该准则应用简便、合理、准确,为冷热电联产系统集成开拓与设计优化提供了一个更好的新准则。     

冷热电联产系统与微型燃气轮机

以发展冷热电联产系统为能源配置方向和以微型燃气轮机为重要发电方式，是第二代能源系统建设的需要，对平衡城市的能源结构、提高能源使用效率、促进环境保护具有现实而长远的意义。文章论述了冷热电联产系统与微型燃气轮机的特点与发展前景。     

冷热电联产系统新评价准则研究

从冷热电联产系统能量梯级利用的本质特征提出了能量梯级利用率的评价准则.该准则由发电、制冷与供热的能量利用率分别乘以不同的权重系数后累加得到.先确定比较的基准点,然后采用层次分析的方法得出基准点各能量利用率的权重系数.对基准点权重系数根据冷热产品温度及环境温度进行修正可得到其它情况的权重系数值.结合实际的联产系统算例,给出了这种评价准则的使用方法,并与原有的评价准则进行分析对比.结果表明,该评价准则具有合理性,可作为冷热电联产系统评价比较的实用方法.     

分布式供能的发展与系统构成

随着社会的发展和生活水平的提高,分布式供能系统的发展正呈现出新的变化趋势.介绍了当今分布式供能系统的发展状况以及系统的构成.除了传统模式的多样化发展,燃料电池技术和可再生能源技术的应用也受到了关注.介绍了以燃气轮机和内燃机为主要设备的冷热电联产系统的应用模式,而以燃料电池为主要设备的冷热电联产系统因发电效率高而受到越来...     

化工动力多联产系统评价准则问题研究综述

多联产系统评价准则对系统集成开拓与设计优化至关重要。传统的热力学性能指标难以全面科学地评估多能源输入、多功能的联产系统性能特性,也不适合作为系统设计优化的目标函数。文章概述了系统热效率、效率及折合性能指标等目前常用的评价准则及其存在问题;概述了采用相对节能率时的通常做法和存在问题以及对它的改进;概述了经济效率和经济系数以及能量综合梯级利用率等新评价准则的研究进展;还介绍了联产系统全工况评价准则的探讨研究等。     

基于燃气轮机循环的冷热电联产系统对比分析

本文以燃气轮机作为发电装置,分别采用简单循环与回热循环,提出天然气冷热电联产系统两套方案.利用数值分析方法,对比分析各方案的系统效率与经济性指标.分析表明:基于回热循环的燃气轮机联产系统在经济效益和能源利用效率方面,相比简单循环联产系统都有十分明显的优势.     

带冷凝除湿的湿空气透平热电联产系统

建议了一种新的基于加湿和冷凝除湿混合循环的湿空气透平热电联产系统,可提高城市热电联产系统的发电和能源利用效率,实现燃料和热源的多样性,降低主机投资和装置回收周期。利用直接式除湿器进一步回收潜热和改善系统。基于节点能量平衡的热力性能分析方法,揭示了关键参数对系统性能影响的特性规律。分析表明:借助联合应用加湿和除湿过程,系统主机的优化压缩比可以低选,发电和热电效率相应提高,有利于实用、经济、环保地实现分布式热电联产节能工程。     

沼气与液化石油气热电联产试验对比研究

通过搭建小型实验平台,对基于燃气内燃机的热电联产系统在不同燃料下的机组性能和系统性能进行了探究。通过测得的发电功率和燃气流量计算出燃气发电机在不同负荷下的发电效率和燃烧功率,进而计算出不同燃料下热电联产系统的系统总效率并加以比较。试验结果表明,燃气内燃机组的发电效率和系统总效率随着电负荷的增大而增大;使用沼气作为燃料时,系统总效率最高可达到46.96%,高于使用液化石油气作为燃料时的系统总效率;用电负荷是影响系统各种效率的主要因素之一。     

联合循环热电冷三联供系统的热经济性分析

燃气—蒸汽联合循环的热电冷三联供系统是一种崭新的能量供应系统,它实现了能量的梯级利用。本文在联合循环的热电冷三联供系统基础上,从总热效率、效率和经济效率三个方面并结合具体实例对系统进行了热经济性计算和分析。     

Thermodynamic performance comparison of SOFC-MGT-CCHP systems coupled with two different solar methane steam reforming processes

Multi-energy complementary distributed energy system integrated with renewable energy is at the forefront of energy sustainable development and is an important way to achieve energy conservation and emission reduction. A comparative analysis of solid oxide fuel cell (SOFC)-micro gas turbine (MGT)-combined cooling, heating and power (CCHP) systems coupled with two solar methane steam reforming processes is presented in terms of energy, exergy, environmental and economic performances in this paper. The first is to couple with the traditional solar methane steam reforming process. Then the produced hydrogen-rich syngas is directly sent into the SOFC anode to produce electricity. The second is to couple with the medium-temperature solar methane membrane separation and reforming process. The produced pure hydrogen enters the SOFC anode to generate electricity, and the remaining small amount of fuel gas enters the afterburner to increase the exhaust gas enthalpy. Both systems transfer the low-grade solar energy to high-grade hydrogen, and then orderly release energy in the systems. The research results show that the solar thermochemical efficiency, energy efficiency and exergy efficiency of the second system reach 52.20%, 77.97% and 57.29%, respectively, 19.05%, 7.51% and 3.63% higher than those of the first system, respectively. Exergy analysis results indicate that both the solar heat collection process and the SOFC electrochemical process have larger exergy destruction. The levelized cost of products of the first system is about 0.0735$/h that is lower than that of the second system. And these two new systems have less environmental impact, with specific CO₂ emissions of 236.98 g/kWh and 249.89 g/kWh, respectively.     

Exergetic performance evaluation of a combined heat and power (CHP) system in Turkey

This study deals with the exergetic performance assessment of a combined heat and power (CHP) system installed in Eskisehir city of Turkey. Quantitative exergy balance for each component and the whole CHP system was considered, while exergy consumptions in the system were determined. The performance characteristics of this CHP system were evaluated using exergy analysis method. The exergetic efficiency of the CHP system was accounted for 38.16% with 49 880 kW as electrical products. The exergy consumption occurred in this system amounted to 80 833.67 kW. The ways of improving the exergy efficiency of this system were also analysed. As a result of these, a simple way of increasing the exergy efficiency of the available CHP system was suggested that the valves‐I–III and the MPSC could be replaced by a 3500 kW‐intermediate pressure steam turbine (IPST). If the IPST is installed to the CHP system (called the modified CHP (MCHP) system), the exergetic efficiency of the MCHP system is calculated to be 40.75% with 53 269.53 kW as electrical products. The exergy consumption is found to be 77 444.14 kW in the MCHP system. Copyright © 2006 John Wiley & Sons, Ltd.     

Optimal design and 4E assessment of typical combined cooling,heating and power systems considering the effects of energy price fluctuation

Although as an advanced energy utilization approach, the performance of combined cooling, heating, and power (CCHP) system is susceptible to its configuration and operation strategy. Energy price will also affect the system performance indirectly by influencing the system's design scheme. In this paper, a linear programming (LP) based optimization model is formulated to obtain the optimal design scheme that minimizes the annual total cost of typical CCHP systems, and a comprehensive assessment framework involving economic, energy, exergy, and ecological (4E) aspects is established to assess the system performance roundly. Taking a CCHP project in Xian, China as the specific case, the design and assessment of the CCHP system are completed and sensitivity analyses for two steps, namely configuration design step and operation strategy design step, are carried out to explore the impacts of energy price fluctuation on the design scheme and performance of the system. In this process, the coupling relationship between the purchase price of natural gas and electricity are considered, and as a special form of energy price, the effects of the feed‐in tariff are also discussed. The results show that the performance of the CCHP system is superior to the separate generation (SG) system in 4E aspects, reducing the running and maintenance cost, primary energy consumption, and greenhouse gas emissions by 18.63%, 24.77%, and 31.88%, respectively, and promoting the exergy efficiency by 30.87%. The feed‐in tariff lower than or equal to the electricity price will have positive effects on the overall performance of the CCHP system, and a lower natural gas price and a higher electricity price are benefit for playing the advantages of the system.     

Thermodynamic and economic assessment of a PEMFC-based micro-CCHP system integrated with geothermal-assisted methanol reforming

A micro-combined cooling heating and power (CCHP) system integrated with geothermal-assisted methanol reforming and incorporating a proton exchange membrane fuel cell (PEMFC) stack is presented. The novel CCHP system consists of a geothermal-based methanol steam reforming subsystem, PEMFC, micro gas turbine and lithium bromide (LiBr) absorption chiller. Geothermal energy is used as a heat source to drive methanol steam reforming to produce hydrogen. The unreacted methanol and hydrogen are efficiently utilized via the gas turbine and PEMFC to generate electricity, respectively. For thermodynamic and economic analysis, the effects of the thermodynamic parameters (geothermal temperature and molar ratio of water to methanol) and economic factors (such as methanol price, hydrogen price and service life) on the proposed system performance are investigated. The results indicate that the ExUF (exergy utilization factor the exergy utilization factor), TPES (trigeneration primary energy saving) and energy efficiency of the novel system can be reached at 8.8%, 47.24% and 66.3%, respectively; the levelized cost of energy is 0.0422 $/kWh, and the annual total cost saving ratio can be reached at 20.9%, compared with the conventional system. The novel system achieves thermodynamic and economic potential, and provides an alternative and promising way for efficiently utilizing abundant geothermal energy and methanol resources.     

Thermodynamic analysis of a new combined cooling, heat and power system driven by solid oxide fuel cell based on ammonia-water mixture

Although a solid oxide fuel cell combined with a gas turbine (SOFC-GT) has good performance, the temperature of exhaust from gas turbine is still relatively high. In order to recover the waste heat of exhaust from the SOFC-GT to enhance energy conversion efficiency as well as to reduce the emissions of greenhouse gases and pollutants, in this study a new combined cooling, heat and power (CCHP) system driven by the SOFC is proposed to perform the trigeneration by using ammonia-water mixture to recover the waste heat of exhaust from the SOFC-GT. The CCHP system, whose main fuel is methane, can generate electricity, cooling effect and heat effect simultaneously. The overall system performance has been evaluated by mathematical models and thermodynamic laws. A parametric analysis is also conducted to examine the effects of some key thermodynamic parameters on the system performance. Results indicate that the overall energy conversion efficiency exceeds 80% under the given conditions, and it is also found that the increasing the fuel flow rate can improve overall energy conversion efficiency, even though both the SOFC efficiency and electricity efficiency decrease. Moreover, with an increased compressor pressure ratio, the SOFC efficiency, electricity efficiency and overall energy conversion efficiency all increase. Ammonia concentration and pressure entering ammonia-water turbine can also affect the CCHP system performance.     

Development of an integrated gasifier-solid oxide fuel cell test system: A detailed system study

A detailed system study on an integrated gasifier-SOFC test system which is being constructed for combined heat and power (CHP) application is presented. The performance of the system is evaluated using thermodynamic calculations. The system includes a fixed bed gasifier and a 5 kW SOFC CHP system. Two kinds of gas cleaning systems, a combined high and low temperature gas cleaning system and a high temperature gas cleaning system, are considered to connect the gasifier and the SOFC system. A complete model of the gasifier-SOFC system with these two gas cleaning systems is built and evaluated in terms of energy and exergy efficiencies. A sensitivity study is carried out to check system responses to different working parameters. The results of this work show that the electrical efficiencies of the gasifier-SOFC CHP systems with different gas cleaning systems are almost the same whereas the gasifier-SOFC CHP systems with the high temperature gas cleaning system offers higher heat efficiency for both energy and exergy.     

Analysis of a gas turbine and steam turbine combined cycle with liquefied hydrogen as fuel

The performances of a combined cycle driven by the liquid hydrogen are discussed. The cycle consists of a gas turbine with a pre-cooler system and a steam turbine heated by the exhaust energy of gas turbine. The liquid hydrogen has not only chemical but cryogenic exergy. The latter is about 10% of the total exergy and is converted to the useful work through the pre-cooling system and an auxiliary hydrogen turbine. The specific output and thermal efficiency of the combined cycle are much higher than those of a simple cycle gas turbine, but in order to operate the combined cycle successfully, it is necessary to check the pinch point which may take place in the boiling process which is heated by the exhaust energy of the gas turbine.     

Typical off-design analytical performances of internal combustion engine cogeneration

Based on experimental data, typical off-design characteristic curves with corresponding formulas of internal combustion engine (ICE) are summarized and investigated. In combination with analytical solution of single-pressure heat recovery steam generator (HRSG) and influence of ambient pressure on combined heat and power (CHP) system, off-design operation regularities of ICE cogeneration are analyzed. The approach temperature difference ΔT _a, relative steam production and superheated steam temperature decrease with the decrease in engine load. The total energy efficiency, equivalent exergy efficiency and economic exergy efficiency first increase and then decrease. Therefore, there exists an optimum value, corresponding to ICE best efficiency operating condition. It is worth emphasizing that ΔT _a is likely to be negative in low load condition with high design steam parameter and low ICE design exhaust gas temperature. Compared with single shaft gas turbine cogeneration, ΔT _a in ICE cogeneration is more likely to be negative. The main reason for this is that the gas turbine has an increased exhaust gas flow with the decrease in load; while ICE is on the contrary. Moreover, ICE power output and efficiency decrease with the decrease in ambient pressure. Hence, approach temperature difference, relative steam production and superheated steam temperature decrease rapidly while the cogeneration efficiencies decrease slightly. It is necessary to consider the influence of ambient conditions, especially the optimization of ICE performances at different places, on cogeneration performances.     

A linear programming optimization model for optimal operation strategy design and sizing of the CCHP systems

Combined cooling, heat, and power (CCHP) system offers numerous potential advantages for the supply of energy to residential buildings in the sense of improved energy efficiency and reduced environmental burdens. To realize the potential for being more beneficial, however, such systems must reduce total costs relative to conventional systems. In this study, a linear programming optimization model was presented for optimum planning and sizing of CCHP systems. The purpose of the model is to give the design of the CCHP system by considering electrical chiller and absorption chiller simultaneously in economic viewpoint. A numerical study was conducted in Tehran to evaluate the CCHP system model. The linear programming (LP) model determines the optimal sizes of the CCHP equipment by considering capital cost of the system. It showed that by considering electricity buyback, the optimum size of the electrical chiller decrease and the optimum size of the combined heat and power (CHP) unit and the absorption chiller increase dramatically with respect to without electricity buyback. Also, the LP model determines the optimal operation strategy of the system by neglecting capital cost. The optimally operated CCHP system encompassing electrical and absorption chiller could result in an 18% decrease in operating cost when compared to a CHP system encompassing electrical chiller only. Without electricity buyback, the profitability of CCHP was 23%, while with electricity buyback, profitability became 39%. Furthermore, a sensitivity analysis was conducted to show how the important parameters affect the entire system performance.