Medium-Low-Enthalpy Geothermal Power-Electricity Generation at Gonghe Basin, Qinghai Province
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摘要: 青海省是我国地热资源相对丰富的地区, 但其主要地热能开发利用方式长期以来为效率较低的直接利用.以青海东北部地热异常明显的共和盆地为典型研究区, 依据前期地热地质调查和地球物理工作成果, 在盆地北部施工了终孔深度为1 852 m的DR2井, 获取了温度达84.2 ℃的地热流体.在此基础上, 建立了青海省首个试验地热发电站, 设计年平均净发电量为114 kW.与利用高温地热流体发电的西藏羊八井地热电站不同, 青海共和试验地热电站是青藏高原利用中低温地热流体发电的典范, 有望为青海省能源结构优化做出开拓性贡献.总体来看, 共和盆地地热流体温度较高、水量丰富、具有较大的发电潜力, 但在开发利用过程中也应注意结垢问题.Abstract: Qinghai Province is characterized by relatively abundant geothermal resources in China, but geothermal energy utilization has been suffering from low efficiency due to the dominant direct use over a long period. Taking Gonghe Basin located in northeastern Qinghai as the study area, we explore the issue in this paper on the basis of the previous geothermal geological and geophysical investigations. A borehole (DR2) with a depth of 1 852 m in the north part of the basin is drilled and geothermal fluid with a temperature up to 84.2 ℃ can be extracted from DR2, based on which the first geothermal power plant in Qinghai with an annual net electricity generation capacity of 114 kW is established. Different from the Yangbajing geothermal power plant in Tibet where high-temperature geothermal fluids are exploited for electricity generation, the Gonghe pilot power plant in Qinghai is a typical example of middle-low-enthalpy geothermal power generation, which leads the optimization of energy structure in Qinghai Province. In general, the geothermal fluids from Gonghe are featured with comparatively high temperatures and discharge rates, and therefore have a great potential for power generation. However, scaling may occur during the exploitation of Gonghe geothermal fluid in view of its chemical composition, which should be addressed in the process.
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图 1 共和地质简图及DR2井位(据薛建球等, 2013)
Fig. 1. Simplified geological map of Gonghe Basin and location of Well DR2
图 2 DR2井地温(a)和地温梯度(b)随深度变化曲线
Fig. 2. Plots of well temperature (a) and geothermal gradient (b) versus depth for Well DR2
图 3 螺杆膨胀机发电流程
Fig. 3. A flow chart showing the process of electricity generation by screw expander
表 1 DR2生产井地热水的化学组成
Table 1. Chemical composition of geothermal water sample from Well DR2
分析项目(μg/L) 分析项目(μg/L) 分析项目(μg/L) 分析项目(μg/L) Al3+ nd. F- 3.56 Ag 0.453 Li 9 060 As 0.621 HCO3- 604 Au 0.154 Rb 122 B 26.4 CO32- 2.42 Ba 0.066 Cs 686 Ca2+ 45.7 Cl- 678 Be nd. Sb 12.81 K+ 12.1 NO3- nd. Cd 0.003 Mg2+ 1.82 SO42- 135.6 Co nd. Na+ 576.5 Cr nd. Sr 1.46 Cu nd. Zn2+ 0.04 Ni 0.011 Fe(总) nd. NH4+ 0.59 Pb 0.044 Hg nd. Fe2+ 0.02 Se 0.012 Sn 0.12 SiO2 58.2 Mn nd. V 0.11 CO2 15.4 H2S nd. 注: pH为7.69；温度为84.2 ℃. 
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表 2 20~90 ℃范围内DR2井地热水对方解石的饱和指数
Table 2. Saturation indices of the geothermal water extracted from DR2 with respect to calcite over a temperature range of 20-90 ℃
温度(℃) 20 30 40 50 60 70 80 90 饱和指数 0.736 0.787 0.851 0.929 1.008 1.093 1.183 1.276
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