Optimization of electrical power production from high temperature geothermal fields with respect to silica scaling problems

Abstract

Silica scaling is an obstacle in the use of geothermal fluid from high-temperature fields. The potential issue of silica deposition rises with increasing resource temperature. A single flash condensing system is the most common energy conversion system for utilizing geothermal fluid from high-temperature fields, mainly due to its smallest possibility of silica precipitation. This thesis investigates the possibility of optimizing the employment of geothermal fluid from high-temperature fields by using an alternative energy conversion system in place of a conventional single flash cycle with a condensing turbine. Thermodynamic and silica scaling calculations were modelled and simulated in Matlab for five different energy conversion systems in order to obtain the optimum specific power output for each power conversion system. The models include: a single flash and a double flash condensing system, a combination of a single flash condensing cycle and a binary cycle utilizing separated brine, a combination of a single flash back pressure cycle and a binary cycle utilizing the turbine exhaust steam, and a combination of a single flash back pressure cycle and a binary cycle utilizing both separated brine and exhaust steam. An economical analysis was also performed to find the total capital investment needed for different energy conversion systems at their optimum power output production. The specific power outputs and total capital investments for different power conversion systems were finally compared.

Results from the study show that the employment of geothermal fluid from a hightemperature field at a certain range of fluid enthalpy and resource temperature could be optimized by using the double flash system, the combination of a single flash condensing cycle and a binary cycle, or the combination of a single flash back pressure cycle and a binary cycle. These results can be used by a decision maker to identify the most appropriate energy conversion system for making use of geothermal fluid from hightemperature fields where silica scaling becomes a hindrance based on a given geothermal fluid enthalpy and resource temperature.