Impact of unequal depth arrangement on heat extraction performance of middle-deep borehole heat exchanger array

doi:10.16085/j.issn.1000-6613.2024-2041

Abstract

Abstract:

In order to study the influence of different arrangement forms and well pipe spacing of coaxial casing type deep borehole heat exchangers (DBHEs) on the heat extraction performance, under the condition of equal total buried pipe length, COMSOL Multiphysics 6.2 was used for numerical simulation for equal depth arrangement and unequal depth arrangement. The heat extraction effects of three arrangement modes of well pipe cross-line arrangement, well pipe rectangular arrangement and well pipe circular arrangement after 20 years of operation were compared and analyzed. The results indicated there were some differences in the influence of different well pipe arrangements of DBHEs on the heat extraction performance, whether it was equal depth arrangements or unequal depth layout. The cross-line arrangement showed the least decline in outlet water temperature and heat extraction capacity, followed by the rectangular arrangement, while the circular arrangement exhibited the greatest decline. By strategically removing some boreholes in the "cold accumulation" region, the heat extraction capacity of the DBHEs could be effectively enhanced in both equal depth and unequal depth setups. Compared to the equal depth setup, the unequal depth setup with an improved planar design could increase the heat extraction rate by up to 24.59% for the rectangular arrangement, 24.36% for the cross-line arrangement, and only 13.04% for the circular arrangement. The results of this study have certain theoretical guiding significance for the design of pipe arrays.

Key words: middle-deep geothermal energy, pipe array, layout form, unequal depth, heat conduction, numerical simulation

摘要：

为研究同轴套管式地埋管换热器管群（DBHEs）的不同布置形式及井管间距对管群取热性能的影响规律，在总埋管长度相等的条件下，针对等深布置和非等深布置情况，使用COMSOL Multiphysics 6.2进行数值模拟，分别对比分析了井管交叉线形排列、井管矩形排列和井管圆形排列3种井管排列方式的管群运行20年后的取热效果。结果表明：无论是等深布置还是非等深布置，DBHE的不同井管布置形式对地埋管取热性能的影响存在一定差异。交叉线形排列时各地埋管出口水温和取热功率衰减最小，其次为矩形排列，圆形排列方式衰减最大。根据“冷堆积”区域范围有针对性地移除部分井管，在等深布置和非等深布置情况下均可有效提升管群的取热能力。与等深布置相比，改进平面布置后的非等深布置，矩形排列取热量提升率可达24.59%，交叉线形排列提升率可达24.36%，而圆形排列仅为13.04%。本文研究结果对于管群设计具有一定的理论指导意义。

关键词: 中深层地热, 管群, 布置形式, 非等深, 热传导, 数值模拟

CLC Number:

TK529

ZHANG Qiqiang, WANG Ye, LIU Hengjian, ZHANG Luyu, LU Zhi, HENG Zixin. Impact of unequal depth arrangement on heat extraction performance of middle-deep borehole heat exchanger array[J]. Chemical Industry and Engineering Progress, 2025, 44(12): 6859-6871.

张期强, 王烨, 刘亨坚, 张露予, 鲁贽, 恒子欣. 中深层地热管群非等深布置对取热性能的影响[J]. 化工进展, 2025, 44(12): 6859-6871.

Figures/Tables 22

References 25

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参数	数值
井深度/m	880
外管外径/cm	17.78
外管壁厚/cm	0.90
内管外径/cm	8.90
内管壁厚/cm	1.92
循环流量/m³·h^-1	4.8
外管热导率/W·m^-1·K^-1	46.1
内管热导率/W·m^-1·K^-1	0.02
地层热导率/W·m^-1·K^-1	1.60
地层比热容/ kJ·kg^-1·K^-1	0.87
地层密度/kg·m^-3	3050
入口温度/℃	30

参数	数值
井深度/m	880
外管外径/cm	17.78
外管壁厚/cm	0.90
内管外径/cm	8.90
内管壁厚/cm	1.92
循环流量/m³·h^-1	4.8
外管热导率/W·m^-1·K^-1	46.1
内管热导率/W·m^-1·K^-1	0.02
地层热导率/W·m^-1·K^-1	1.60
地层比热容/ kJ·kg^-1·K^-1	0.87
地层密度/kg·m^-3	3050
入口温度/℃	30

案例	布置方案	具体布置形式	取热量提升率
Case1	基础布置	等深布置（M1、M2和M3）	矩形排列更优，提升率为23.22%
Case1	改进布置	等深布置移除部分埋管（M1-1、M2-1和M3-1）	矩形排列更优，提升率为23.22%
Case2	基础布置	等深布置（M1、M2和M3）	α=80°时，交叉线形排列最优，提升率为2.79%
Case2	改进布置	非等深布置（M1-2、M2-2和M3-2）	α=80°时，交叉线形排列最优，提升率为2.79%
Case3	基础布置	等深布置（M1、M2和M3）	α=80°时，矩形排列最优，提升率为24.59%
Case3	改进布置	非等深布置移除部分埋管（M1-3、M2-3和M3-3）	α=80°时，矩形排列最优，提升率为24.59%
Case4	基础布置	等深布置移除部分埋管（M1-1、M2-1和M3-1）	α=80°时，矩形排列最优，提升率为1.11%
Case4	改进布置	非等深布置移除部分埋管（M1-3、M2-3和M3-3）	α=80°时，矩形排列最优，提升率为1.11%
Case5	基础布置	非等深布置（M1-2、M2-2和M3-2）	α=45°时，矩形排列最优，提升率为23.6%
Case5	改进布置	非等深布置移除部分埋管（M1-3、M2-3和M3-3）	α=45°时，矩形排列最优，提升率为23.6%

案例	布置方案	具体布置形式	取热量提升率
Case1	基础布置	等深布置（M1、M2和M3）	矩形排列更优，提升率为23.22%
Case1	改进布置	等深布置移除部分埋管（M1-1、M2-1和M3-1）	矩形排列更优，提升率为23.22%
Case2	基础布置	等深布置（M1、M2和M3）	α=80°时，交叉线形排列最优，提升率为2.79%
Case2	改进布置	非等深布置（M1-2、M2-2和M3-2）	α=80°时，交叉线形排列最优，提升率为2.79%
Case3	基础布置	等深布置（M1、M2和M3）	α=80°时，矩形排列最优，提升率为24.59%
Case3	改进布置	非等深布置移除部分埋管（M1-3、M2-3和M3-3）	α=80°时，矩形排列最优，提升率为24.59%
Case4	基础布置	等深布置移除部分埋管（M1-1、M2-1和M3-1）	α=80°时，矩形排列最优，提升率为1.11%
Case4	改进布置	非等深布置移除部分埋管（M1-3、M2-3和M3-3）	α=80°时，矩形排列最优，提升率为1.11%
Case5	基础布置	非等深布置（M1-2、M2-2和M3-2）	α=45°时，矩形排列最优，提升率为23.6%
Case5	改进布置	非等深布置移除部分埋管（M1-3、M2-3和M3-3）	α=45°时，矩形排列最优，提升率为23.6%