CO2 Plume Geothermal (CPG) Systems for Combined Heat and Power Production: an Evaluation of Various Plant Configurations

Abstract

CO2 Plume Geothermal (CPG) systems are a promising concept for utilising petrothermal resources in the context of a future carbon capture utilisation and sequestration economy. Petrothermal geothermal energy has a tremendous worldwide potential for decarbonising both the power and heating sectors. This paper investigates three potential CPG configurations for combined heating and power generation (CHP). The present work examines scenarios with reservoir depths of 4 km and 5 km, as well as required district heating system (DHS) supply temperatures of 70°C and 90°C. The results reveal that a two-staged serial CHP concept eventuates in the highest achievable net power output. For a thermosiphon system, the relative net power reduction by the CHP option compared with a sole power generation system is significantly lower than for a pumped system. The net power reduction for pumped systems lies between 62.6% and 22.9%. For a thermosiphon system with a depth of 5 km and a required DHS supply temperature of 70°C, the achievable net power by the most beneficial CHP option is even 9.2% higher than for sole power generation systems. The second law efficiency for the sole power generation concepts are in a range between 33.0% and 43.0%. The second law efficiency can increase up to 63.0% in the case of a CHP application. Thus, the combined heat and power generation can significantly increase the overall second law efficiency of a CPG system. The evaluation of the achievable revenues demonstrates that a CHP application might improve the economic performance of both thermosiphon and pumped CPG systems. However, the minimum heat revenue required for compensating the power reduction increases with higher electricity revenues. In summary, the results of this work provide valuable insights for the potential development of CPG systems for CHP applications and their economic feasibility.