煤层气深冷液化多级脱水工艺

A multi-stage dehydration process for CBM liquefaction

煤层气从地下抽采出后,经过湿法脱碳工艺段,导致含有大量的液态水和气态水。在利用煤层气制取LNG工艺中,必须对煤层气进行深度脱水,使煤层气在进入冷箱液化之前的露点达到-70℃,以防止煤层气进入冷箱后其中的水结冰堵塞换热器。多级脱水工艺采用机械脱水、降温脱水和变温吸附(TSA)脱水联合工艺。机械脱水脱出煤层气中的液态水,降温脱水利用氟利昂预冷机组脱出大部分饱和气态水,TSA采用复合床层吸附剂(氧化铝和分子筛)进行深度脱水。利用吸附剂在不同压力和温度下吸附容量差异和选择吸附的特性,脱除煤层气中剩余的气态水及CO_2以满足LNG液化单元要求。TSA脱水由2台干燥塔交替工作。当一台干燥塔在吸附时,另外一台干燥塔利用氮气进行置换吹扫、热吹和冷吹,实现再生。多级脱水工艺针对不同的含水量每级采用不同的脱水原理,使整个工艺流程能耗降低,最终含水量达到设计要求。在贵州盘江煤层气提纯制LNG项目中,成功应用多级脱水工艺,取得良好的经济效益。

After coalbed methane(CBM)is extracted from the ground,it passes through a wet decarburization stage,which results in it containing a large amount of liquid water and gaseous water.Using such CBM to produce LNG,a deep dehydration of it must be carried out to achieve a dew point of-70益before liquefying it into the cold box to prevent the water from freezing and blocking heat exchanger after it enters the cold box.The multi-stage dehydration process uses a combination of mechanical dehydration,condensing dehydration and temperature swing adsorption(TSA)dehydration.Mechanical dehydration removes liquid water from CBM;condensing dehydration uses Freon precooling unit to remove most of the saturated gaseous water;and TSA uses composite bed adsorbent(alumina and molecular sieve)for deep dehydration.The adsorption capacity difference and the selective adsorption characteristics of the adsorbent at different pressures and temperatures are utilized to remove the remaining gaseous water and CO2 in the CBM to meet the requirements of the LNG liquefaction unit.TSA dehydration is alternately operated by two drying towers.When one drying tower is adsorbed,another drying tower uses nitrogen for displacement purging,hot blowing and cold blowing to achieve regeneration.The multi-stage dehydration process uses different dehydration principles for each stage of different water content,so that the energy consumption of the whole process is reduced,and the final water content meets the design requirements.In the LNG project of CBM purification in Panjiang,Guizhou,the multi-stage dehydration process has been successfully applied and good economic benefits have been achieved.