北极多年冻土区埋地输气管道周边温度场数值分析

Numerical Analysis of Temperature Field Around Buried Gas Pipeline in Arctic Permafrost Regions

以北极规划输气管道工程为依托,建立埋地管道与冻土热交换相互作用数值计算模型,探究了埋地管道在连续多年冻土区、非连续多年冻土区和季节冻土区内,按照不同操作温度(5、-1和-5℃)运行情况下管道周围冻土温度演化过程。计算结果表明:同一区域不同管温对冻土上限值影响差异较大,尤其是在非连续多年冻土区,无论管道是正温输送还是负温输送,由于管道的运营,极大地影响了冻土上限值。5℃正温管道将导致冻土上限下降1~3倍管径;-1℃和-5℃负温管道将有助于提高冻土人为上限。建议在连续多年冻土区管道采用-1℃输送温度;在非连续多年冻土区冬季采用-1℃输送温度,夏季可以是正温,接近环境大气温度,但全年输气平均温度要小于0℃;在季节冻土区,若按照负温输送,反而容易引起管基土冻胀,建议输气温度不作特别控制,与温带地区管道类似,正温输送。希望能够为北极多年冻土区天然气管道建设提供新的思路。

Based on one planned arctic gas pipeline project which will cross continuous,discontinuous and sporadic permafrost zones and zones of seasonal frost from north to south,with 5℃,-1℃and-5℃settings of gas-flow in buried pipeline,a geothermal model for the interactions between pipeline and permafrost was established to investigate the thermal effect of pipelines on the freezing and thawing of soil around pipeline and thermal stability of permafrost by using a commercially available finite-element program for numerical analysis.The results show that different pipeline gas flow temperatures influence the permafrost table greatly.Especially in discontinuous permafrost zones the permafrost table is influenced in both positive temperature and negative temperature.The warm(+5℃)gas pipeline could lower permafrost table by about 1 to 3 times of pipe diameter and aggravate the degradation of permafrost around pipeline;The cold(-1℃)and chilled(-5℃)gas pipeline can effectively raise the permafrost table and maintain the thermal stability of frozen soil,but the temperature of soils under the chilled(-5℃)pipeline decreases obviously,which may lead to frost heave hazards.In terms of thermal stability around pipeline,it is advised that a transporting temperature of gas flow as -1℃ should be adopted in continuous permafrost zone all year round which causes only little disturbance to the permafrost environment;in discontinuous permafrost zone pipeline could operate above freezing in the summer months with the station discharge temperature trending the ambient air temperature,but the discharge temperature must be maintained as -1℃ throughout the winter months;in zone of seasonal frost the cold(-1℃)and chilled(-5℃)pipeline may cause frost heave,therefore pipeline should run in positive temperature without extra temperature cooling control.Finally,the initial framework solutions are proposed in hope of supplementing existing gas transporting process theory and identifying new approaches for gas pipeline in northern and upland permafrost regions.