“混合冷剂预冷+膨胀机制冷+双气过冷”乙烷回收工艺  

Ethane recovery process with"mixed refrigerant precooling+expander cooling+double gas overcooling"

作　　者：邱鹏 常志波 刘子兵 黄昌猛 李建刚 周小虎 QIU Peng;CHANG Zhibo;LIU Zibing;HUANG Changmeng;LI Jiangang;ZHOU Xiaohu(PetroChina Changqing Engineering Design Co.,Ltd.,Xi'an,Shaanxi 710001,China;PetroChina Changqing Oilfield Company,Yulin,Shaanxi 719000,China)

机构地区：[1]中国石油长庆工程设计有限公司 [2]中国石油长庆(榆林)油田有限公司

出　　处：《天然气工业》2021年第5期121-126,共6页Natural Gas Industry

基　　金：中国石油天然气股份有限公司重大科技专项“长庆油田5000万吨持续高效稳产关键技术研究与应用”(编号:2016E-0513)。

摘　　要：天然气中所含的乙烷、丙烷等重烃组分是优质的化工原料,具有很高的附加值。从天然气中回收乙烷需要采用深冷分离技术,而鄂尔多斯盆地上古生界气藏天然气因气质较贫、压力低且含有较多二氧化碳等原因,导致天然气露点温度低且在低温下容易发生干冰冻堵。为此,研发了“混合冷剂预冷+膨胀机制冷+双气过冷”的乙烷回收工艺技术,通过对该工艺流程进行模拟计算,分析了影响干冰生成和乙烷回收率的主要工艺参数。研究结果表明:①降低低温分离器操作温度以及增加脱甲烷塔顶回流量可以减小脱甲烷塔顶部物流中二氧化碳的浓度,从而降低干冰生成温度,提高脱甲烷塔防止干冰冻堵的能力;②膨胀机出口气进入脱甲烷塔的最佳位置在第14层理论板,此时乙烷回收率为95.7%,继续下移进料位置,乙烷回收率几乎不变反而会增加设备投资;③乙烷回收率随过冷原料气比例增加而升高,当过冷原料气比例超过20%后,乙烷回收率变化不大;④乙烷回收率随产品天然气回流量的增加而升高,适宜的回流量为3000 kmol/h,超过该值之后乙烷回收率的增幅变缓,而天然气增压功率却持续增加。Heavy hydrocarbon components contained in natural gas(e.g.ethane and propane)are high-quality chemical raw materials and their addition value is higher.Cryogenic separation technology is generally adopted to recover ethane from natural gas.However,the natural gas produced from the Upper Paleozoic gas reservoirs of Ordos Basin is characterized by low ethane content,low pressure and high carbon dioxide concentration,so it has low dew point temperature and tends to form dry ice blockage at low temperatures.To solve these problems,this paper develops a new ethane recovery technology,namely"mixed refrigerant for precooling+expander for refrigeration+dual gas for subcooling".Then,this technological process is simulated and calculated,and the main process parameters affecting the formation of dry ice and the ethane recovery are analyzed.And the following results were obtained.First,by decreasing the operation temperature of low temperature separator and increasing the reflux rate at the top of the demethanizer,the carbon dioxide concentration of the fluid at the top of the demethanizer can be reduced,which leads to the reduction of the formation temperature of dry ice.As a result,the demethanizer's capacity of preventing dry ice blockage is improved.Second,the optimum position for the expander outlet stream to enter the demethanizer is on the 14th theoretical plate,where the ethane recovery is up to 95.7%.And if the feed position is moved downwards further,the ethane recovery is basically unchanged while the equipment investment is increased.Third,the ethane recovery increases with the increase of the subcooled raw gas ratio,but when the ratio exceeds 20%,it has little effect on the ethane recovery.Fourth,the ethane recovery increases as the reflux rate of product natural gas increases.And the optimum reflux rate is 3000 kmol/h,beyond which,the increase amplitude of ethane recovery slows down whereas the gas compression power increases continuously.

关 键 词：鄂尔多斯盆地 上古生界气藏 天然气 乙烷 深冷分离 混合冷剂 二氧化碳 干冰 

分 类 号：TQ221.12[化学工程—有机化工]