基于Aspen Plus的小型含氧煤层气液化工艺分析

Analysis of small-scale oxygen-contained coalbed methane gas liquefaction process based on Aspen Plus

针对某一典型含氧煤层气气源,构建了适用于小型液化装置的丙烷预冷氮-甲烷膨胀液化精馏工艺,并采用Aspen Plus对该流程进行建模及分析。以流程比功耗、甲烷回收率为评价指标,分别研究了制冷剂高压压力PN2和低压压力PN7对流程比功耗的影响。结果表明,在PN2为3.8MPa,P_(N7)为0.3MPa时,比功耗为0.513k Wh·Nm^3,甲烷回收率为93.42%,LNG产品纯度接近100%。结合爆炸极限计算表明,含氧煤层气在压缩、冷却、液化及节流过程中,甲烷浓度均高于爆炸上限,操作安全性较高,而精馏塔顶部甲烷浓度变化会穿越爆炸上下限区间,基于此,采用原料气低压初脱氧的方式来控制精馏塔顶部氧气含量。分析结果表明,对当粗脱氧后进入压缩机的煤层气含氧量低于2.4mol%时,流程操作安全可靠。

A small scale oxygen - contained coal bed methane liquefaction process adopting nitrogen - methane expansion with propane pre - cooling was proposed and simulated by Aspen Plus software. The specific power consumption and the efficiency of methane recovery were listed as the evaluation factors. The influence of the refrigerant higher pressure PN2 and the refrigerant lower pressure PN7 on the specific power consumption was conducted. The results showed that the specific power consumption was 0.513kWh· Nm^3 ,the methane recovery efficiency was 93.42%, and the purity of LNG was near 100% when the PN2 was 3. 8MPa and PN7 was 0.3MPa, respectively. The flammability limits were analyzed, and the results indicated that no flammable haz- ards existed in the process of oxygen - contained methane compression, cooling, liquefaction and throttling, while the flammabili- ty was founded in the top of the distillation column. Based on these analyses, a method which the oxygen contained in the coal bed methane was first removed from the raw gas was adopted to ensure the safety of the whole process. The results showed that when the content of oxygen in the raw gas was below 2.4 mol%, the operation safety of the whole process was eligible.