封闭性采热模式在地热发电中的应用

Geothermal power generation is of significant importance in economic development and environmental protection. However, the open heat extraction mode widely adopted in existing geothermal power plants tends to cause problems, such as scaling and corrosion in power generation equipment, insufficient and fluctuating rate of circulation water flow, and high back power consumed by the station itself. Adopting a closed heat extraction mode, which separates the heat transfer medium from the geothermal reservoir, not only provides a radical cure to the above mentioned problems, but also promotes the flexibility in selecting heat transfer medium and designing heat transfer circulation. In this study, a combination of theoretical analysis and numerical simulation will be adopted to investigate how the single-phase-flow type and the vapor-liquid two-phase-flow type closed heat extraction modes impacting the key indicators such as power generation capacity, efficiency, and serving time of geothermal power stations，with focuses on the pattern and flow rate along with their control factors of the natural convection in geothermal reservoir as well as the kinematic, hydrodynamic and thermodynamic states along with their variations of heat transfer medium flowing in the circulation channels. Incorporated with the real data collected from the geothermal power stations at Yabajing (Tibet), Qianshan Oilfield (North China) and Soultz-sous-Forets (France), the long term performance of the closed heat extraction modes will be quantitatively predicted and compared with that of the open heat extraction mode. This study will provide scientific basis and key technological supports for optimal selection of heat extraction mode and optimal design of heat extraction system in future geothermal power generation practice.

地热发电对经济发展和环境保护都具有重要意义。然而，现有地热电站广泛采用的开放性采热模式易导致发电设备结垢与腐蚀、循环水流量不足与波动、电站自耗功率高等问题。采用传热工质与地热储层分离的封闭性采热模式，不但能根治上述问题，而且提升了选择传热工质和设计传热循环的灵活性。本项目拟采用理论分析与数值模拟相结合的方法，对单相流和气-液两相流两种封闭性采热模式如何影响地热发电功率、效率、寿命等关键指标进行研究，着重分析地热储层内自然对流的形态、流量及其控制因素以及传热工质在管道内循环流动过程中的运动学、流体动力学和热力学状态及其变化。本项目还将结合西藏羊八井、华北潜山油田与法国苏尔士地热电站的实际资料，定量预测封闭性采热模式的长期性能，并与开放性采热模式进行对比。本项目将为未来地热发电工程优选采热模式和优化采热系统设计提供科学基础和关键技术支持。

本项目采用理论分析与数值模拟相结合的方法研究封闭性采热模式在地热发电中的应用,为未来地热发电工程优选采热模式和优化采热系统设计提供科学基础和关键技术支持。基于经典边界层理论和混合长度湍流模型，推导出圆形管道内单相流和气-液两相流的摩擦因子和换热系数理论公式，从而为封闭性采热模式下选择传热工质和设计传热循环提供理论指导和计算工具。利用本研究推导的孔隙介质自然对流级数解，系统研究了地热储层内自然对流特征及其对地热储层几何、物性结构及物理条件的依赖关系，深入分析了热对流的结构和稳定性，得到了在不同储层几何形态下稳态解存在的瑞利数范围以及非稳态对流从周期性、准周期性运动到混沌运动的动力学途径，能够为设计和优化地热系统提供定量的依据。采用有限元模型系统分析了封闭性采热系统中水平井采热效率的关键控制因素，包括储层渗透率及其不均匀分布、储层高度与宽度、储层中水平井位置和传热工质温度的影响。结合西藏羊八井、华北潜山油田与法国苏尔士的实际资料，对封闭性采热模式下地热电站的长期性能进行了定量模拟，并与开放性采热模式进行了对比。