低含氦天然气提氦联产LNG工艺设计与分析

Process design and analysis of extracting helium from low helium natural gas and co-producing LNG

天然气分离法是氦气工业化生产的主要途径,但中国多数气田的天然气氦含量(物质的量分数,下同)较低,超95%的氦气依赖进口。针对低含氦(小于0.5%)天然气,提出了一种低温高压浓缩、天然气液化、低温精馏提氦相结合的提氦工艺方案。以某乙烷回收处理厂为例(原料气进料温度为50℃、进料压力为5.8 MPa、处理量为1000×10^(4)m^(3)/d),利用HYSYS软件对低含氦天然气提氦联产液化天然气(LNG)工艺方案进行了模拟。在控制氦气浓缩倍数为19.15的前提下,对低温高压提浓装置进行了关键参数分析,同时研究了工艺流程对原料气中CO_(2)和氮气含量的适应性。结果表明,提浓塔压力过高会导致塔底氦气损失量增加,压力过低会导致外输气压缩机功率增加,针对原料气设置合理的塔压为3.8 MPa;提浓塔塔板数的增加会使氦气回收率增加,但当塔板数大于16块时,氦气回收率增加不明显;原料气中CO_(2)含量低于2%时,提浓塔不会形成CO_(2)冻堵物;原料气氮气含量高于0.5%时,需对塔顶气进行脱氮处理,以达到LNG生产的质量标准。

Natural gas separation is the main way for industrial production of helium,but the low helium content(mole fraction,the same as below) of natural gas in most gas fields in China causes that more than 95%of helium in China depends on imports.Aiming at the natural gas with low helium content(less than 0.5%),a process scheme of extracting helium by combining low temperature and high pressure concentration,natural gas liquefaction and low temperature rectification was put forward.Take an ethane recovery plant(feed gas temperature is 50℃,feed pressure is 5.8 MPa,treatment capacity is 1000×10^(4)m^(3)/d) as an example,the process scheme of extracting helium from low helium natural gas and co-producing liquified natural gas(LNG) was simulated by Aspen HYSYS software.On the premise of controlling the helium concentration multiple to 19.15,the key parameters of the low-temperature and high-pressure concentration device were analyzed,and the adaptability of the process flow to the content of CO_(2) and nitrogen in the feed gas was studied.It is found that too high pressure in the concentration tower will lead to an increase in helium loss at the bottom of the tower,and too low pressure will lead to an increase in the power of the export gas compressor,so a reasonable tower pressure of3.8 MPa is set for this feed gas.The increase of the tray number in the concentration tower will increase the helium recovery rate,but the increase of helium recovery rate is not obvious when the tray number is greater than 16.When the CO_(2) content of the feed gas is lower than 2%,the concentration tower will not form CO_(2) frozen blockage.When the nitrogen content of feed gas is higher than 0.5%,it is necessary to denitrify the overhead gas to meet the quality standard of LNG production.