地热单井连续和间歇供暖性能

Performance of a geothermal single well for continuous and intermittent heating

目前国内的地热单井供暖(SWGH)工程实践遇到了单井换热量小和投资回收期长的问题.再加上SWGH的运行数据在公开场合没有报道,导致很多企业家不了解其性能,限制了SWGH的快速推广.本文建立了SWGH取热和热恢复过程的数学模型,分析了间歇和连续运行工况下取热温度和功率的变化以及岩石温度场的衰减和恢复.研究结果表明:连续供暖整个供暖季平均出口温度和取热功率分别为18.16℃和635.68 kW.出口温度和取热功率在前两周剧烈减小,两周后逐渐趋于稳定.由于岩石导热系数小、热阻大,连续取热导致岩石温度降低,越靠近井壁,岩石温降越大.非供暖季的热恢复是保障地热单井连续出力的有效手段.由于有热恢复时间,间歇供暖能部分克服岩石导热系数小的难题,大幅提高单井取热功率.间歇供暖的平均取热功率为920.21 kW,比连续供暖提高44.76%.由于总取热量小于连续供暖,间歇供暖工况下岩石温度场的衰减及恢复均好于连续供暖.3000 m的地热井,连续和间歇运行工况下的静态投资回收期分别为6.18和4.37年.因此,采用间歇供暖模式,将会促进SWGH的快速推广,可为我国北方雾霾的解决做出巨大的贡献.

Single-well geothermal heating(SWGH)is well accepted by some enterprises,and some projects have been implemented in China.However,many problems have been encountered in the actual projects,the most prominent of which are low heat transfer and the long payback period for SWGH.In addition,there are few papers or reports that provide operating data for SWGH,which results in a lack of knowledge on its performance and limits its rapid promotion.In this paper,a mathematical model for the heat transfer and recovery of SWGH is established and the outlet temperature,extracted heat power,and rock temperature field are analyzed for continuous and intermittent heating.The simulated results show that the average outlet temperature and extracted heat power for continuous heating are 18.16°C and 635.68 kW,respectively.The outlet temperature and extracted heat power sharply decrease in the first two weeks,and then the rate of decrease slows gradually.The rock temperature decreases because it is cooled by the injection water,and the rocks closest to the well wall have the greatest temperature drop.The maximum rock temperature difference is only 4°C after the heat recovery period,which means that heat recovery is the most effective means of maintaining the sustainability of SWGH.Intermittent heating can improve the extracted heat power due to the heat recovery of rock.The average extracted heat power under intermittent heating is 920.21 kW,and it increases by 284.53 kW with a percentage change of 44.76%compared with continuous heating.Owing to less heat extracted from the rock,the attenuation and recovery of the rock temperature field under intermittent heating is better than that under continuous heating.The static payback periods for continuous and intermittent heating are 6.18 and 4.37 years,respectively,if the cost of drilling and well completion for a depth of 3000 m is 2.1 million RMB.They will be 5.08 and 3.69 years,respectively,if the cost of drilling and well completion is reduced to 1.5 million RMB.