Heat exchanger network arrangement and multi-level matching characteristic of air separation system using LNG cold energy

doi:10.11949/j.issn.0438-1157.20150693

Abstract

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

摘要：

分析了常见的基于空分系统的液化天然气(LNG)冷能利用方式,依据LNG冷能的能谱特点及空分系统运行安全性的特殊要求提出较优的冷能利用方案;针对不同压力等级工况提出LNG与N₂的换热网络布置方案,对提出的4种LNG-N₂换热网络分别进行了流程模拟,并与传统空分系统和已有的LNG冷能利用空分系统进行了比较,结果表明:新的LNG换热网络能有效降低空分系统的单位液态产品能耗,采用LNG-N₂双高压方案时为0.217 kW·h·kg^-1,若对LNG出口压力没有限制则采用LNG-N₂双低压方案可进一步降低能耗至0.176 kW·h·kg^-1,相比已有的LNG冷能利用空分系统能耗分别降低了15.9%和31.8%;同时研究了LNG冷能的多能级换热匹配性能,分析了当N₂压力不变时LNG压力变动对各个方案换热均匀性的影响。研究结果可为不同工况下选择合适的LNG换热压力提供参考。

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

CLC Number:

TQ028

ZHENG Jieyu, LI Guangpeng, LI Yanzhong, SI Biao, YANG Yujie. Heat exchanger network arrangement and multi-level matching characteristic of air separation system using LNG cold energy[J]. CIESC Journal, 2015, 66(S2): 76-84.

郑捷宇, 李广鹏, 厉彦忠, 司标, 杨宇杰. 利用LNG冷能的空分系统换热网络布置及多能级匹配性能[J]. 化工学报, 2015, 66(S2): 76-84.

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