Enhanced geothermal systems distinguish themselves among other technologies that utilize renewable energy sources by their possibility of the partial sequestration of carbon dioxide (CO2). Thus, CO2 in its supercritical form in such units may be considered as better working fluid for heat transfer than conventionally used water. The main goal of the study was to perform the techno-economic analysis of different configurations of supercritical carbon dioxide-enhanced geothermal systems (sCO2-EGSs). The energy performance as well as economic evaluation including heat and power generation, capital and operational expenditures, and levelized cost of electricity and heat were investigated based on the results of mathematical modeling and process simulations. The results indicated that sCO2 mass flow rates and injection temperature have a significant impact on energetic results and also cost estimation. In relation to financial assessment, the highest levelized cost of electricity was obtained for the indirect sCO2 cycle (219.5 EUR/MWh) mainly due to the lower electricity production (in comparison with systems using Organic Rankine Cycle) and high investment costs. Both energy and economic assessments in this study provide a systematic approach to compare the sCO2-EGS variants.
In this study, turbine modelling of a geothermal sourced organic Rankine cycle (ORC) power plant is aimed. Thermodynamic model of the plant is constructed with the help of design and off-design plant data from an existing two-cycle power plant in southwestern Anatolia. Utilizing statistical analysis tools such as maximum likelihood estimation and probability distribution, plant variables are obtained within their standard deviations. Stodola curves and probability calculations demonstrate that both turbines are most likely to have two stages. Average losses are 2.3 MW and 1.2 MW from Turbine-I and Turbine-II respectively throughout the different seasons. After the determination of losses, overall turbine efficiencies demonstrate a reverse trend with increasing reduced mass flow rate. This may be associated with the increased choking of the turbine. Correlations estimate rather fixed efficiency values at off-design conditions (84% for Turbine-I and 77% for Turbine-II); that is an expected outcome since these correlations are influenced mainly by the design isentropic efficiency, which is a constant value. On the other hand, these correlations are most likely to be proposed for non-choking conditions which are invalid for off-design conditions of existing ORC turbines. Datapoint dispersion in Turbine-II does not demonstrate a strong correlation with physical constraints such as -pressure ratio and reduced mass flow rate- as it does for Turbine-I; this phenomenon may need further attention for future work.
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