Energy conversion processes for the use of geothermal heat - Final report
The study deals with theoretical as well as with practical aspects of the conversion of geothermal heat to electricity. The report is divided into three parts: • Part I: General study • Part II: Practical experience: planning & operation of geothermal power plants • Part III: Methodology for the optimal integration of energy conversion system in geothermal power plants. In the first part the specific properties and characteristics of geothermal resources as heat sources are discussed. Both, EGS as well as deep aquifer resources are considered. Furthermore a general survey of conversion processes is presented with special emphasis on thermo-electric conversion. The various conversion processes are evaluated with respect to their possibilities and limits for future application in geothermal power plants. The second part deals with practical aspects related to planning, construction and operation of geothermal power plants. The first chapter includes the technical basics, in particular relevant site specific conditions, drilling techniques, thermal water or brine quality, and requirement for materials to be used for the relevant system components. In the second chapter planning procedures of both sub- surface and surface installation including state-ofthe- art power conversion systems is discussed. In the third chapter aspects of operation and maintenance are treated and the last part includes some basic information on costs and economics. The third part of the report presents the methodology and results for the optimal valorization of the thermodynamic potential contained in deep geothermal fields. A pinchanalysis approach is applied to choose suitable conversion systems to be integrated into constrained geothermal processes. The optimal integration of the geothermal conversion system is achieved by the use of a multi-objective optimization technique including thermodynamic and economic objectives. Three case studies have been carried out: the EGS projects DHM Basel and GGP Geneva, and the aquifer project Lavey-les-bains. The results relate the trade-offs between installation costs and efficiency, and give the expected heat and electricity services delivered for the corresponding optimal systems. The selected methodology has been successfully validated with data from existing ORC plants, only minor differences between modeling results and measured values have been observed. The results presented for the three case studies are a valuable basis for further development of the actual projects as well as for new developments.