以LNG为冷源的跨临界有机工质联合循环发电系统工质选择与参数分析

Working fluid selection and parameter analysis of combined transcritical power generation system using LNG as the cold source

为提高液化天然气的利用效率,构建以液化天然气为冷源的跨临界有机朗肯循环-布雷顿循环联合发电系统.综合考虑工质的热物性和安全性等因素,筛选出10种综合性能较好的有机工质进行分析,并研究关键热力参数对工质流量、蒸汽轮机输出功、热效率和火用效率的影响.结果表明:提高蒸汽轮机入口压力和温度,降低冷凝温度可提高系统的火用效率;在给定运行工况下,工质临界温度越高,则系统性能越好;具有最高临界温度的有机工质R245fa的综合性能最好,系统的热效率和火用效率分别可达到53.07%和33.59%;冷凝器的火用损失占系统总火用损失的主要部分,因此减少该部件的不可逆损失是提高系统能量利用效率的关键.

In order to improve the utilization efficiency of the LNG cold energy,a transcritical organic Rankine-Brayton combined cycle was proposed in this paper which using LNG as the cold source.10 working fluids were selected based on the thermotphysical properties and safety level of the working fluids.Parametric analysis was performed to study the effects of key factors on mass flow rate,turbine power outputs,thermal efficiency and exergy efficiency.Results show that increasing the turbine inlet pressure and temperature or decreasing the condensation temperature will rises system exergy efficiency greatly.Under the given operating conditions,the higher critical temperature of working fluid,the better the system performance we will get.In this paper,R245 fa could achieve the best thermal efficiency and exergy efficiency of 53.07% and 33.59%,respectively.Condenser accounts for the largest part of exergy destruction.Hence,reducing the exergy destruction in condenser is the most effective way to improve the exergy efficiency.