基于LNG气化分段模型的低温动力循环火用分析

构建LNG低温朗肯循环发电系统是冷能利用的主要方式之一。为了提高LNG冷能回收效率，根据LNG气化特性，笔者提出了冷能的分段利用模型，并采用火用分析的方法对低温朗肯循环各环节的火用损失进行了分析，得出如下结论：①LNG气化曲线存在较为明显的分段规律，为建立高效的冷能发电循环提供了基础；②LNG低温朗肯循环发电系统的火用损失主要集中在换热设备当中，因而系统的优化重点应放在对于换热设备尤其是冷凝器的优化上，减少平均换热温差能有效降低换热器的传热不可逆损失；③对LNG按不同温度段进行回收利用，构建梯级循环发电系统，能有效减小循环冷火用损失，提高LNG冷能回收效率。根据LNG气化特性构建的梯级循环流程较单极循环流程而言，总的冷火用损失显著减少，冷火用利用效率提高了16.2%。

Exergy analysis of the model on a LNG cryogenic power generation system based on the Rankine cascading cycle

To build up a LNG cryogenic power generation system by use of the Rankine cycle is one of the most popular cold energy utilization ways. In order to improve the recovery ratio of LNG cold energy, we presented a model of cryogenic energy utilization by the cascading cycles, and conducted the exergy analysis on the exergy loss at each level of the cascading cryogenic Rankine cycle. We conclude that (1)there is obvious sectional difference from in the gasification curves, providing a robust foundation for building up a high efficiency cold energy power generation cycle, (2)the exergy loss in this Rankine cycle occurs mainly on the heat exchanging facilities, so the optimization of the system should focus on the heat exchanging facilities, especially the condenser to reduce the average temperature difference of heat transfer and cut down the irreversible exergy loss in heat exchangers, and (3)a cascading cycle for the power generation system is built up to make full use of the LNG by different levels of temperature, in this way, the exergy loss in this cycle will be decreased effectively and the recovery rate of LNG cold energy will be improved. Compared with a simple single level cycle, this cascading cycle built on the gasification features of LNG significantly reduces the total exergy loss in the whole process with the efficiency of exergy utilization being increased by 16.2%.