基于潜热比的低温余热蒸汽联合回热有机朗肯循环系统最佳工质筛选

为充分回收矿藏热采尾端低温余热蒸汽,提高能源利用率,建立以低温蒸汽为热源的抽汽-乏汽联合回热有机朗肯循环(ORC)系统,选取6种不同临界温度的干湿工质,提出以工质潜热比σr评价蒸发器火用损及系统热力性能的标准,在热力学第一、第二定律基础上,通过编制程序分析不同蒸发温度T11、热源温度Tg下工质对系统的影响,确定最佳工况点,选择最佳工质。结果表明:随工质临界温度Tc增大,其潜热比σr较大,系统热力性能较高,且热源温度愈高,不同工质间热力性能差距愈大;对于蒸汽热源,工质在低于临界温度25K左右的热源下工作可获得最大热力性能;增加联合回热有助于提高系统热力性能,对于各工质有R236fa>R123>R152a,当Tg=413.15K时,若系统采用R236fa作为工质,系统较ORC系统净输出功高出1455kW。

抽汽-乏汽联合回热对低温蒸汽ORC系统热力性能影响

为充分回收矿藏热采过程中尾端的低温蒸汽余热,根据热力学第一、第二定律,在单独抽汽回热、单独乏汽回热系统的基础上,提出一种新型抽汽-乏汽联合回热系统,并建立以低温蒸汽为热源的抽汽-乏汽联合回热理论模型。通过编制计算程序分别对带抽汽回热的ORC循环、乏汽回热ORC循环以及联合回热ORC循环的热力学性能进行了分析,并与无回热ORC循环的性能进行了比较。结果表明:3种回热循环的热效率、净输出功以及火用效率均随蒸发压力升高而升高,其中联合回热循环的热力性能最高,分别能达到11.37%、7 593 kW及51.9%,比相同工况下的无回热ORC循环分别增高百分比为19.6%、12.5%及15.1%;对于单位功耗火用损,各循环则表现为随蒸发压力的升高而逐渐递减,且有联合回热循环的单位功耗火用损<抽汽回热<乏汽回热<无回热ORC循环,在蒸发温度为105℃时,对应单位功耗火用损分别为0.91、0.95、1.06及1.22;同时,在相同抽汽压力下,联合回热循环的抽气系数α小于单独抽汽回热循环,工质质量流量基本相同,联合回热循环具有更好的热力性能。

低温蒸汽联合回热ORC系统变工况热效率的优化

为研究变工况下抽汽-乏汽联合回热系统的热力性能,建立热源与冷源变化的联合回热系统模型,对不同抽汽压力、不同回热器效能下系统热力性能随热源温度T_g与冷源温度T_0变化的规律进行分析,并在变工况下对不同回热循环系统的热力性能进行比较。结果表明:在不同抽汽压力与回热器效能下,系统净输出功、热效率均随热源温度升高不断增加,效率存在一最佳值;系统各热力性能随冷源温度增加则不断降低;在变工况下,当热源温度较高或冷源温度较低时增加抽汽回热、乏汽回热效果显著,在热源温度T_g=140℃,冷源温度T_0=10℃时,其热效率分别比其他三种循环(抽汽回热系统、乏汽回热系统、无回热系统)高1.03%、1.13%及2.78%,同时,热源与冷源温度增加,最佳抽汽压力增大,反之降低。

Performance Improvement of Combined Cycle Power Plant Based on the Optimization of the Bottom Cycle and Heat Recuperation

Many F class gas turbine combined cycle （GTCC） power plants are built in China at present because of less emission and high efficiency. It is of great interest to investigate the efficiency improvement of GTCC plant. A combined cycle with three-pressure reheat heat recovery steam generator （HRSG） is selected for study in this paper. In order to maximize the GTCC efficiency, the optimization of the HRSG operating parameters is performed. The operating parameters are determined by means of a thermodynamic analysis, i.e. the minimization of exergy losses. The influence of HRSG inlet gas temperature on the steam bottoming cycle efficiency is discussed. The result shows that increasing the HRSG inlet temperature has less improvement to steam cycle efficiency when it is over 590℃. Partial gas to gas recuperation in the topping cycle is studied. Joining HRSG optimization with the use of gas to gas heat recuperation, the combined plant efficiency can rise up to 59.05% at base load. In addition, the part load performance of the GTCC power plant gets much better. The efficiency is increased by 2.11% at 75% load and by 4.17% at 50% load.

Analysis of an electricity-cooling cogeneration system for waste heat recovery of gaseous fuel engines

Waste heat recovery(WHR)is one of the most useful ways to improve the efficiency of internal combustion engines,and an electricity-cooling cogeneration system(ECCS)based on Rankin-absorption refrigeration combined cycle for the WHR of gaseous fuel engines is proposed in the paper.This system can avoid wasting the heat in condenser so that the efficiency of the whole WHR system improves,but the condensing temperature of Rankin cycle(RC)must increase in order to use absorption refrigeration system,which leads to the decrease of RC output power.Therefore,the relationship between the profit of absorption refrigeration system and the loss of RC in this combined system is the mainly studied content in the paper.Because the energy quality of cooling and electricity are different,cooling power in absorption refrigeration is converted to corresponding electrical power consumed by electric cooling system,which is defined as equivalent electrical power.With this method,the effects of some important operation parameters on the performance of the ECCS are researched,and the equivalent efficiency,exergy efficiency and primary energy rate are compared in the paper.