Study of the efficiency of a gas turbine on CO₂ for the use of secondary heat of mining enterprises

Abstract The mining industry has significant sources of secondary thermal resources with low temperatures of 35°C- 80°C. For their use in the production of additional electricity, it is proposed to use a gas turbine that operates on carbon dioxide (freon R-744) and implements the Rankine cycle. Known detailed tables and model equations for carbon dioxide describe its thermophysical properties. However, they are very complex and challenging to access for inspection. Therefore, this article aims to develop simple analytical expressions for the thermophysical parameters of R-744 for temperatures of 3°C- 80ºC and use them to study effective operation modes of a gas turbine for the use of secondary heat resources of mining enterprises. Mathematical modelling methods, theories of approximation of functions, fundamental laws of gas dynamics and technical thermodynamics were used to achieve the goal. The study resolved the issue of selecting an effective turbine operating mode based on the level of thermodynamic efficiency based on general thermodynamic laws. It was shown that reducing the cooling temperature of R-744 in the condenser from 20°C to 5°C due to the use of mine water increases the thermodynamic efficiency of the Rankine cycle almost twice.