太阳能-地热能混合式发电系统的性能评价

Performance Evaluation of a Hybrid Solar-geothermal Power Generation System

混合式发电系统是可再生能源高效利用的主要技术,能流的匹配特性是提高系统发电稳定性和效率的关键。围绕西藏当雄地区的太阳能和地热能资源特征,提出太阳能加热地热水产生高压蒸汽协同地热饱和蒸汽驱动汽轮机发电,而低温地热水驱动有机朗肯循环的混合式发电系统。构建了系统的热力学模型,分析了设计工况下系统的热力性能,探究了地热水温度、流量和太阳能辐射强度(direct normal irradiance,DNI)对系统性能的影响。提出系统全工况运行策略,探讨系统在典型日不同时段的热力性能表现。结果表明:系统的净输出功率和热效率随DNI的增加而上升,但是系统(火用)效率下降。设计工况系统的热效率为14.66%;系统(火用)效率为27.52%,太阳能集热器(火用)损失达45.4%。夏季和秋季典型日储热时段,高、低压汽轮机载荷因子分别高于0.94和0.95。当系统仅由地热能驱动时,热效率降低至12.08%。该研究可为太阳能与地热能混合式发电系统的设计和运行提供参考。

A hybrid power generation system is a key measure to utilizing renewable energies efficiently.The matching characteristics of the energy flows are the basis for improving stability and efficiency of a hybrid power generation system.A hybrid solar-geothermal power generation system is proposed for the Tibetan region in this work.The steam turbine is driven by high pressure steam generated by solar energy and saturated steam separated from geothermal fluid.And the organic Rankine cycle is driven by low temperature saturated geothermal water.The thermodynamic model of the system is constructed,the thermal performance of the system under the design conditions is analyzed,and the influence of geothermal water temperature,mass flow rate and direct normal irradiance(DNI)on the system performance is explored.The system operation strategy under all operating conditions is proposed,and the thermal performance of the system in different periods of typical days is discussed.The results show that the net output power and thermal efficiency of the system is increased with the increase of DNI,but the system efficiency is decreased.The thermal efficiency of the system for the design condition is 14.66%and the exergy efficiency is 27.52%.The maximum exergy losses occur in the solar collector accounting for 45.4%of the exergy input.During the typical daily heat storage period in summer and autumn,the load factors of high and low pressure steam turbines are higher than 0.94 and 0.95,respectively.When the system is only driven by geothermal energy,the thermal efficiency is decreased to 12.08%.This work can provide reference for the design and operation of hybrid solar-geothermal power generation systems.