Impacts of pressure, temperature, and CO2 fraction on performance of CO2-circulated geothermal power plants

Although CO 2 behaviors in porous subsurface formations have been extensively investigated during decades of CO 2 -enhanced oil recovery and CO 2 sequestration practices, very limited efforts have been focused on the associated CO 2 -circulated geothermal power plant on the surface. This study aims to contribute to this field by numerically evaluating such a power plant dealing with produced binary fluid mixture (CO 2 , water) under various conditions. The proposed power plant consisting of a separator, a turbine, and a cooler is numerically simulated using the ASPEN Plus® process modeling software. The pressure, temperature, CO 2 mass fraction of the produced fluids, and turbine outlet/inlet pressure ratio are sampled 50 times in a 4D parameter space constrained by their ranges, which are specified according to typical geothermal reservoir conditions in North Oman. Each input sample is fed into the separator and turbine model in the ASPEN software, and a set of performance metrics are obtained from the model outputs. Based on the 50 pairs of input-output data, response surfaces of outputs in response to input parameters are developed to surrogate ASPEN models. The fast, data-driven response surface models are efficiently applied to global sensitivity analysis and performance evaluations for both separator and turbine units. Results show the separator performance is controlled by the temperature. The efficiency is higher in lower temperatures, and sharply reduced above 140°C. The turbine, however, is affected by both the temperature and pressure drop. The output power is increased from 100 to 600 kW with inlet temperature increasing from 60 to 200°C and ratio of pressure drop decreasing from 65 to 35%. The developed response surface models can quickly predict power output given a set of geothermal fluid condition.