含氧煤层气液化流程安全性分析与措施

Security analysis and measures for the liquefaction process of oxygen-bearing coal-bed methane

矿下抽采的煤层气由于混有空气而在液化中存在爆炸危险。通过将HYSYS对常规液化分离流程的模拟结果与爆炸极限理论相结合进行分析计算得出:爆炸危险主要集中在冷凝终了处和精馏塔顶部。进而提出降低压缩机出口压力或提高最终冷凝温度;严格控制精馏塔塔顶气相CH4含量在爆炸上限之上,塔顶气用N2惰化后再与液氮逆流接触以进一步回收CH4。计算表明,当N2注入比达0.6(摩尔比),气相CH4含量曲线将绕过临界点进入安全区。采取措施后CH4有较高收率且液化流程安全性得以提高。

There is a risk of explosion during purifying the coal-bed methane coming from underground drainage,for the reason that the gas contains oxygen.In this paper,the results of simulation with HYSYS and the flammability limit theory were combined together to analyze the security of whole process.The results showed that the explosion hazard concentrated at the end of the condensation and on the top of rectification tower.The measure to reduce the compressor outlet pressure or raise the final condensation temperature was proposed.What′s more,the security measure was proposed to control the methane content of rectification tower gas above the upper limit of the explosion strictly,and then the inerting gas with nitrogen contacts with liquid nitrogen upstream for further recovery of CH4.The results indicate that when the value of nitrogen injection ratio is greater than 0.6（mole ratio）,there is no danger of explosion in liquefaction process,and both methane yield and process safety are improved greatly in this way.