DEVELOPMENT OF AN ADVANCED MONITORING APPLICATION FOR GEOTHERMAL POWER PLANTS WITH AN ORGANIC RANKINE CYCLE

Renewable power generation technologies are becoming increasingly important. One of these technologies is electricity production with an Organic Rankine Cycle supplied by the heat of deep hydro-geothermal plants. They produce electrical power with a high annual full load hour percentage and comparatively low CO₂ emissions. However, since the geothermal plants are operated with air-cooled condensers as well as scaling affects the performance of the electrical submersible pump and thus the lifted thermal water flow rate, the generated gross electrical power is strongly fluctuating. Therefore, the process parameters of the main components heat exchanger, turbine and condenser of an Organic Rankine Cycle as part of a geothermal plant are highly variable, both in terms of diurnal and seasonal fluctuations. Monitoring an Organic Rankine Cycle is therefore associated with special challenges for geothermal power plant operators. For advanced monitoring of the operation of the main components heat exchanger, turbine and condenser of geothermal power plants, a methodology with developed analytical and empirical simulation models is presented in this paper. For a shell-and-tube evaporator of a reference geothermal power plant in the South Bavarian Molasse Basin with a two-stage Organic Rankine Cycle, an equation-based simulation model for the calculation of the thermal resistance due to scaling and fouling in the thermal brine circuit is shown. The analysis of more than three years of operation of the shell-and-tube evaporator in the high-temperature circuit of an ORC reference geothermal plant shows a minimal thermal resistance due to scaling and fouling for the whole period, which indicates that scaling and fouling did not have a strong influence on heat transfer. Furthermore, empirical simulation models based on linear regression developed for the turbines of the reference geothermal power plant with a two-stage Organic Rankine Cycle are presented. The isentropic turbine efficiency is determined with a two-dimensional polynomial function of the simulation model, whose regression coefficients are calculated numerically. For this purpose, operational data from a three-year period of the reference geothermal power plant with a two-stage Organic Rankine Cycle in the south of Munich (Germany) were preprocessed and used. Polynomial functions of various degrees and different objective functions for the numerical computation of regression coefficients are examined. Regression models for three years of operation of the investigated geothermal plant were computed and compared with each other. The same methodology as for monitoring the operation of the turbines is applied to monitor the performance of the air condenser of a geothermal power plant. In addition, results of applying this methodology by retro perspective analysis of the operational data of the reference geothermal power plant are processed, which show no negative changes in the operation of the turbines and air-cooled condensers in both circuits of the ORC reference geothermal power plant. A software application is presented, developed with the MATLAB^® App Designer that integrates the developed methodology and the simulation models of the main components. For realtime operation monitoring, the current process parameters of the main components of the Organic Rankine Cycle of the reference geothermal power plant can be specified, which are evaluated comparatively with the calculated key performance indicator values of the empirical models of each operation year or of the analytical models. Thus, the developed software tool facilitates operators to easily and precisely monitor the operation of the main components of an Organic Rankine Cycle of their geothermal power plant.