天然气液化中重烃和氮气脱除工艺优化研究

Optimization of heavy hydrocarbons and nitrogen removal process in natural gas liquefaction

设计了一种天然气液化中重烃和氮气脱除的工艺流程,考察了原料气预冷温度、脱重烃塔回流温度对重烃脱除的影响,同时分析了脱氮塔下部进料比率、脱氮塔操作压力和脱氮塔进料位置对氮气脱除的影响。研究结果表明:原料气预冷温度和脱重烃塔回流温度降低均有利于原料气中重烃的脱除;脱氮塔下部进料量增加和脱氮塔操作压力的降低有利于LNG产品中氮气的脱除。经过优化后的工艺操作条件为:原料气预冷温度为-30℃,脱重烃塔回流温度为-66℃,脱氮塔下部进料比率为7.8%,脱氮塔操作压力为290kPa,脱氮塔中部进料位置为第6块理论板。在此条件下,对N2和C5+的摩尔分数分别为3.1157%和0.0214%的进料气,得到的LNG产品中N2摩尔分数为1.48%,脱除的氮气中烃摩尔分数为4.37%,LNG收率达到98.22%。

A process for removing heavy hydrocarbons and nitrogen from natural gas to meet LNG production requirement was designed. The effects of feed gas precooling temperature and column reflux temperature on heavy hydrocarbon removal, and the impact of the proportion of feed at the bottom of the denitrification column, column operating pressure and feeding location on nitrogen removal were also investigated. The results show that the lower temperatures of feed gas precooling and de-heavy hydrocarbon column reflux are beneficial to the removal of heavy hydrocarbons in the feed gas, and the higher bottom feed flowrate and lower operating pressure of the denitrification column can improve the removal of nitrogen in the LNG product. When N2 and C5+ mole fractions in feed gas were 3.1157% and 0.0214%, respectively, LNG yield reached up to 98.22% with 1.48% nitrogen and4.37% methane in disposed nitrogen under the optimized operation condition: feed precooling temperature of-30℃, column reflux temperature of-66℃, proportion of feed at column bottom of 7.8%, denitrogen column operating pressure of 290 kPa and feeding in the middle of denitrification column at the location of sixth stage.