Performance of a horizontal square-spiral-type backfill heat exchanger in a deep mine and its coupled heat pump system
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摘要: 深部礦井蘊藏著大量地熱資源，功能性充填體技術將深部采礦和深部地熱開采相結合，實現礦產和地熱資源開發共贏，是延長深部礦山壽命的重要舉措。本文在分析了國內外充填礦井通過埋管提取地熱資源現狀基礎上，提出了一種水平方螺旋形埋管充填體換熱器（Square-spiral-type backfill heat exchangers，S-S BHE）。考慮到地下水滲流對礦井埋管充填體換熱器（Backfill heat exchangers，BHE）取熱影響顯著但前期研究相對不足，利用COMSOL軟件建立了三維非穩態BHE熱滲耦合模型并驗證了其可靠性。在此基礎上，建立了埋管充填體換熱器耦合熱泵（Backfill heat exchangers coupled heat pump，BHECHP）數學模型及四個綜合評價指標。首先，在相同幾何條件和物理條件下，對比分析了S-S BHE與兩種典型蛇形BHE的性能，結果表明：S-S BHE的綜合評價指標均優于蛇形BHE，且在較高滲流條件下優勢更加顯著。其次，研究了管內流速、管間距、滲流速度和入口水溫對S-S BHE及其耦合熱泵特性的影響規律，研究發現：管內流速和滲流速度對綜合評價指標的影響最為顯著，管內流速越高，單位管長平均換熱功率越高，但制熱季節能效明顯降低。分析認為管內流速存在0.4～0.6 m·s–1的最優區間，此時管內循環水流動處于從過渡區向旺盛湍流轉變。滲流速度在小于10–6 m·s–1時的影響可以忽略不計，在10–6～10–5 m·s–1的常見滲流范圍內，綜合評價指標均呈線性遞增的趨勢。最后，對方螺旋形埋管充填體換熱器耦合熱泵（Square-spiral-type backfill heat exchangers coupled heat pump，S-S BHECHP）進行了生態評價。通過與傳統供暖方式對比發現：采用S-S BHECHP的供暖方式具有顯著的節能降碳效果，一次能源消費和碳排放量比蓄熱式電鍋爐、燃煤鍋爐和空氣源熱泵相應降低了83.39%、61.57%和56.84%。本研究結果展示了方螺旋形BHE和BHECHP的優良性能，為蓄熱儲能式功能性充填在深部礦井的應用與探索提供了理論指導。Abstract: Geothermal resources are abundant in deep mines. Functional backfill technology combines deep mining and deep geothermal mining to achieve a win-win situation for mineral and geothermal resource development and is an important measure for extending the life of deep mines. In this paper, on the basis of an analysis of the research status of geothermal resource extraction through tubes embedded in backfill bodies in mines, a horizontal square-spiral-type backfill heat exchangers (S-S BHE) is proposed. Considering the significant influence of groundwater advection on the heat extraction of backfill heat exchangers (BHE) in mines and the relative scarcity of previous studies, a verified three-dimensional unsteady BHE model coupling heat transfer and seepage are established using COMSOL software. Based on this model, a mathematical model of the backfill heat exchanger coupled heat pump (BHECHP), and four comprehensive evaluation indicators are established. Firstly, the performance of the S-S BHE is compared with that of two typical serpentine BHEs under the same geometric and physical conditions. The results show that the S-S BHE performs better than the two serpentine BHEs across the board, and the advantage is more substantial under situations of higher permeability flow. Secondly, the characteristics of the S-S BHE and its coupled heat pump are examined in relation to the in-tube flow rate, tube spacing, seepage velocity, and inlet water temperature. The in-tube flow rate and seepage velocity are found to have the most significant effects on the comprehensive evaluation indicators. The average heat transfer power per unit of tube length increases with flow rate, but the heating seasonal performance factor (HSPF) decreases obviously. The analysis revealed an optimum interval of 0.4–0.6 m·s?1 for the flow rate in the tube, where the flow of circulating water in the tube is in transition from the transition zone to the fully turbulent flow zone. The effect of seepage velocity is negligible at less than 10–6 m·s?1, and all comprehensive evaluation indicators present linearly increasing trends in the usual seepage range of 10–6 to 10–5 m·s?1. Finally, an ecological evaluation of the S-S BHECHP was conducted. A comparison with traditional heating methods reveals that the heating method using S-S BHECHP has a significant energy saving and carbon reduction effect. The primary energy consumption and carbon emissions of the S-S BHECHP are reduced by 83.39%, 61.57%, and 56.84% compared to the regenerative electric boiler, coal-fired boiler, and air-source heat pump, respectively. The findings of this study show how well the S-S BHE and the S-S BHECHP performance, and they also provide some theoretical recommendations for the application and exploration of heat storage/energy storage functional backfill in deep mines.
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圖 2 S-S BHE物理模型與網格劃分. (a) 3D物理模型; (b) 方螺旋管布置; (c) 物理模型網格劃分
Figure 2. Physical modeling and meshing of a horizontal S-S BHE: (a) 3D physical model; (b) square-spiral-type tube arrangement; (c) meshing of the physical model
圖 3 數學模型獨立性驗證. (a) 網格獨立性驗證; (b) 時間步長獨立性驗證
Figure 3. Mathematical model independence verification: (a) grid independence verification; (b) time-step independence verification
圖 4 模型準確性驗證. (a)模擬值與文獻實驗值對比; (b)模擬值與實驗值之間的偏差
Figure 4. Model accuracy validation: (a) comparison of simulation values with experimental values from the literature; (b) deviation between simulation and experimental values
圖 5 典型蛇形管布置示意圖. (a) L-S BHE; (b) T-S BHE
Figure 5. Schematic diagram of two typical serpentine tube arrangements: (a) L-S BHE; (b) T-S BHE
圖 6 120 d供熱期內單位管長平均換熱功率在不同滲流條件下隨管內流速的變化
Figure 6. Variations in the average heat transfer power per unit tube length with the flow rate in the tube at different groundwater advection conditions during a 120-day heating period
圖 7 120 d供熱期內平均換熱效能在不同滲流條件下隨管內流速的變化
Figure 7. Variations in the average heat transfer efficiency with the flow rate in the tube at different groundwater advection conditions during a 120-day heating period
圖 8 不同管內流速下出口水溫隨運行時間的變化
Figure 8. Variations in the outlet water temperature with the operating time at different flow rates in the tube
圖 9 不同管內流速下單位管長換熱功率隨運行時間的變化
Figure 9. Variations in the heat transfer power per unit tube length with the operating time at different flow rates in the tube
圖 10 平均出口水溫和單位管長平均換熱功率隨管內流速的變化
Figure 10. Variations in the average outlet water temperature and the average heat transfer power per unit tube length with the flow rate in the tube
圖 11 制熱季節能效和平均換熱效能隨管內流速的變化
Figure 11. Variations in the HSPF and the average heat transfer efficiency with the flow rate in the tube
圖 12 不同管間距下出口水溫隨運行時間的變化
Figure 12. Variations in the outlet water temperature with the operating time at different tube spacings
圖 13 不同管間距下單位管長換熱功率隨運行時間的變化
Figure 13. Variations in the heat transfer power per unit tube length with the operating time at different tube spacings
圖 14 平均出口水溫和單位管長平均換熱功率隨管間距的變化
Figure 14. Variations in the average outlet water temperature and the average heat transfer power per unit tube length with tube spacing
圖 15 制熱季節能效和平均換熱效能隨管間距的變化
Figure 15. Variations in the HSPF and the average heat transfer efficiency with tube spacing
圖 16 不同滲流條件下出口水溫隨運行時間的變化
Figure 16. Variations in the outlet water temperature with the operating time at different groundwater advection conditions
圖 17 不同滲流速度下單位管長換熱功率隨運行時間的變化
Figure 17. Variations in the heat transfer power per unit tube length with the operating time at different groundwater advection conditions
圖 18 平均出口水溫和平均單位管長換熱功率隨滲流速度的變化
Figure 18. Variations in the average outlet water temperature and the average heat transfer power per unit tube length with the seepage velocity
圖 19 制熱季節能效和平均換熱效能隨滲流速度的變化
Figure 19. Variations in the HSPF and the average heat transfer efficiency with the seepage velocity
圖 20 不同進口水溫時出口水溫隨運行時間的變化
Figure 20. Variations in the outlet water temperature with the operating time at different inlet temperatures
圖 21 不同進口水溫時單位管長換熱功率隨運行時間的變化
Figure 21. Variations in the heat transfer power per unit tube length with the operating time at different inlet temperatures
圖 22 平均出口水溫和單位管長平均換熱功率隨入口水溫的變化
Figure 22. Variations in the average outlet water temperature and the average heat transfer power per unit tube length with the inlet temperature
圖 23 制熱季節能效和平均換熱效能隨入口水溫的變化
Figure 23. Variations in the HSPF and the average heat transfer efficiency with the inlet temperature
圖 24 四種供熱方式的單位供熱面積年標準煤耗量和單位供熱面積年碳排放量
Figure 24. Annual standard coal consumption and annual carbon emissions per unit heating area for the four heating methods
表 1 模型幾何條件
Table 1. Model geometric conditions
Type Parameters Value Default value Backfill body Lb × Wb × Hb (Length × width × height) 30 m × 12 m × 4 m — Surrounding rock Lr × Wr × Hr (Length × width × height) 30 m × 6 m × 4 m — Embedded tube di (Inner diameter of the tube） 20–50 mm 25 mm S (Tube spacing) 1–2 m 1.0 m h (Height of embedded tube position) 2 m — 
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久色视频表 2 模型物理條件
Table 2. Model physical conditions
Type Density / (kg·m?3) Specific heat / (J·kg?1·K?1) Thermal conductivity / (W·m?1·K–1) Porosity / % Permeability / m2 Circulating water/groundwater 998 4187 0.6 — — Embedded copper tubes 8500 393.6 110 — — Backfill body 1709 1235 0.6 30 0.04 Surrounding rock 2400 2000 2.5 25 0.03
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