Thermal characteristics of supercritical CO₂ gas turbine cycle integrated with renewable methanol generation system

Energy storage is crucial for reducing the imbalance between energy demand and generation and thus an important asset for increasing the share of renewable energy. This work proposes an integrated energy system that stores excess renewable electrical energy by producing renewable methanol and generates electrical energy in a supercritical CO₂ gas turbine system. Hereby, the supercritical CO₂ gas turbine is an essential component of the integrated energy system, allowing self-sufficiency and high round-trip efficiency.

To assess the thermal characteristics of supercritical CO₂ gas turbines, a thermodynamic model is developed in MATLAB/CoolProp, with a focus on the following aspects: heat recuperation with pinch analysis, thermodynamic properties of CO₂ including the variations in the critical region, thermodynamic properties of the CO₂/H₂O mixture and condensation of water by cooling below the saturation temperature for the partial pressure of water in the mixture. A multi-parameter analysis shows the influence of various operating conditions, such as (i) compressor outlet pressure, (ii) gas turbine inlet temperature, (iii) regenerator temperature difference, (iv) compressor isentropic efficiency, (v) gas turbine isentropic efficiency, and (vi) pressure drop in heat exchangers.

The results of the investigation show that high thermal efficiency of the supercritical CO₂ gas turbine (above 60 %) can be achieved. Hereby, the low compression work near the critical point, operation at high temperature and high pressure, and effective heat recuperation in the cycle are essential to achieve this high efficiency. The mass and energy flow balances of the integrated energy system lead to self-sufficiency and high round-trip efficiency (37 %).