关键词: 液化天然气, 冷能回收, 空分系统, 换热网络, 流程模拟, 过程控制, 系统工程, 数值分析

Abstract:

The common liquefied natural gas(LNG)cold energy utilization methods based on air separation system were analyzed and on the basis of varing character of LNG cold energy and safety requirement for air separation sytem,a better LNG cold energy utilization scheme was proposed;in line with the principe of scientific use of energy,4 kinds of LNG-N₂ heat exchanger network arrangement schemes were proposed aiming at solving the problem of designing a series of heat exchanger network system of high power efficiency at various operation pressure.All the proposed scheme were simulated and the results showed that the new schemes tend to yield more liquid products compared to conventional air separation unit using no LNG and the prior art of that using LNG cold energy.The high pressure(HP)LNG +HP N₂ scheme ends up with the unit liquid product power consumption of 0.217 kW·h·kg^-1 and if LNG outlet pressure is not limited,the power consumption can be further decreased to 0.176 kW·h·kg^-1 by using scheme 4,which is 15.9% and 31.8% less than that of the prior art,respectively.The arithmetic mean temperature difference(AMTD)was choosen as the indicator of the uniformity of heat exchange.The variation rules of AMTD along with LNG pressure also suggested that scheme 2 with low pressure(LP)N₂+LP LNG was with the best uniformity of heat exchange,and some other suggestions were made for determination of a suitable pressure under different working conditions.

Key words: liquefied natural gas, cold energy recovery, air separation system, heat exchanger network, flowsheet simulation, process control, system engineering, numerical analysis