中深层相变取热系统中携液问题的数值研究  

Numerical study on liquid carrying problem in the middle-deep phase change heat extraction system

作　　者：张梁[1] 赵通 梁政[1] 郑继禹 ZHANG Liang;ZHAO Tong;LIANG Zheng;ZHENG JiYu(School of Mechanical Engineering,Southwest Petroleum University,Chengdu 610500,China)

机构地区：[1]西南石油大学机电工程学院,成都610500

出　　处：《地球物理学进展》2023年第1期110-121,共12页Progress in Geophysics

基　　金：干热岩地热资源开发方案设计及热流固耦合机理研究(2020JDRC0088)资助。

摘　　要：针对中深层相变取热系统存在的携液问题,通过数值方法,研究了液态CO_(2)在蒸发段的相变过程,分析了产生携液问题的原因,同时分析了进口流速、管内压力、热储层温度对蒸发率和携带率的影响.结果表明:管内液体呈液滴状分布在管中,一部分液滴随气体携带出系统,另一部分液滴回落井底形成液池.管内气体温度从井底到出口先升高后下降.气体压力相差较小,但在6~8 m的管段存在较高压力.积液质量随时间增长逐渐稳定,但被携带出去的液体质量将不断升高.蒸发段的取热效率和出口温度在系统运行初期存在峰值.通过研究,采用较低的入口流速,能够明显改善携液情况.当热储层温度为105℃时,进口流速为0.05 m/s和0.45 m/s,管内压力应当分别控制在6.7 MPa和4.7 MPa,对改善蒸发和携液情况更有利.当管内压力为3.7 MPa时,进口流速为0.05 m/s和0.45 m/s,携液问题最小时的井底温度分别为145℃和125℃.At present,the research and transformation of ultra-long thermosiphon to extract middle-deep geothermal energy mainly focused on the overall heat extraction performance research.But there are fewer articles about the evaporation section.In this paper,a middle-deep phase change heat extraction system is proposed based on the ultra-long thermosiphon and the problem of liquid carrying in the evaporation section is studied.The phase transition process of the liquid CO_(2) at the evaporation section is studied by numerical methods and the reasons for the problem of liquid carrying are analyzed.At the same time,the effects of inlet flow rates,pressure in the tube,and temperature of the thermal reservoir on the evaporation rate and the carrying rate are analyzed.The results show that liquid CO_(2) is distributed in the pipe in the form of droplets.Some droplets are carried out of the system with the CO_(2) vapor,and the other part of the droplets fall back to the bottom of the tube to form a liquid pool.The gas temperature in the tube increases and then decreases from the bottom of the tube to the outlet.The pressure difference in tube is very small,and there is a high pressure in the tube section of 6~8 m.The peak value of heat extraction efficiency and outlet temperature exists in the early stage of system operation.The mass of liquid accumulation in the tube is stable with time,but the mass of liquid carried by the gas will increase continuously.Through the study,the problem of carrying liquid can be reduced by adopting a lower inlet velocity.When the temperature of the thermal reservoir is 105℃,the inlet flow rate is 0.05 m/s and 0.45 m/s,and the pressure in the tube should be controlled at 6.7 MPa and 4.7 MPa.It is beneficial to improve the evaporation rate and reduce the carrying rate.The inlet flow rate is 0.05 m/s and 0.45 m/s at the pressure of 3.7 MPa,and the temperatures are 145℃ and 125℃ at the minimum of the fluid carrying problem.

关 键 词：地热能 CO_(2) 携液 相变 VOF模型 

分 类 号：P314[天文地球—固体地球物理学]