天然气提氦联产LNG新工艺特性及适应性分析

Characteristics and adaptability analysis of a new process of natural gas helium extraction combined with LNG production

关键词:  提氦联产LNG  特性  适应性  优化  综合能耗 

Key words:  helium extraction combined with LNG production  characteristics  adaptability  optimization  comprehensive energy consumption

摘要:

目的 为降低利用单一低温法从天然气中提氦的工艺设备投资及能量损耗,提出一种新型天然气提氦联产LNG工艺。方法 以国内某气田低含氦原料气数据为基础,对该新工艺的特性及适应性进行了模拟分析,并通过遗传算法对混合制冷剂制冷循环进行了优化。结果 ①通过特性分析可知,节流前温度越低、节流压力越高,闪蒸罐对氦气的浓缩作用越好,同时可生产摩尔分数达到99.9%的高纯氮气产品,并自产液氮产品；②新工艺对原料气中氮气、氦气纯度变化及原料气压力均有很强的适应性,原料气压力越高、氮气和氦气纯度越低,压缩机轴功率越低；③通过特性及适应性分析、混合制冷剂制冷工艺参数优化可得闪蒸罐节流前温度为-150 ℃,节流压力为350 kPa,提氦塔压力为3 200 kPa,脱氮塔和提氦塔塔板数均为12块,混合制冷剂压缩机一级和二级最优增压压力分别为1 341 kPa和2 767 kPa,混合制冷剂循环量为1 722.7 kmol/h,压缩机总轴功率为3 765 kW,冷却水用量为6 474 t/d,综合能耗及单位能耗分别为1 097 216.00 MJ/d、3.66 MJ/m³。结论 该新型工艺的氦气回收率超过98%,粗氦摩尔分数高于70%,且可自产制冷剂,并得到高纯氮气和液氮产品,对原料气气质条件适应性好。 

Abstract:

Objective In order to reduce the equipment investment and energy loss of extracting helium from natural gas by using a single low-temperature method, a new natural gas helium extraction combined with LNG production process is provided. Methods Based on the data of low helium feed gas from a domestic gas field, the characteristics and adaptability of this new process have been simulated and analyzed, and the refrigeration cycle of the mixed refrigerant has been optimized by genetic algorithm. Results (1) Characteristic analysis shows that the lower the temperature before throttling and the higher the throttling pressure, the better the concentration effect of the flash tank on helium gas. At the same time, nitrogen products with a purity of 99.9 mol% can be produced, and liquid nitrogen products can be produced by itself; (2) The new process has strong adaptability to changes in nitrogen and helium content in the feed gas, as well as the pressure of the feed gas. The higher the feed gas pressure and the lower the nitrogen and helium content, the lower the compressor shaft power; (3) Through analysis of characteristics and adaptability, as well as optimization of mixed refrigerant refrigeration process parameters, it can be obtained that the temperature before throttling in the flash tank is -150 ℃, the throttling pressure is 350 kPa, the pressure of the helium extraction tower is 3 200 kPa, the number of plates in both the denitrification and helium extraction towers is 12,the optimal boost pressures for the first and second stages of the mixed refrigerant compressor are 1 341 kPa and 2 767 kPa, respectively, and the circulation rate of the mixed refrigerant is 1 722.67 kmol/h,the total compressor shaft power is 3 765 kW, the cooling water consumption is 6 474 t/d, the comprehensive energy consumption and unit energy consumption are 1 097 216.00 MJ/d and 3.66 MJ/m³, respectively. Conclusion sThe helium recovery rate is more than 98%, and the crude helium purity is higher than 70 mol% for the new process. It can produce refrigerants by itself and obtain high-purity nitrogen and liquid nitrogen products, and has good adaptability to the gas quality conditions of the feed gas.