Thermodynamic Assessment of the Novel Concept of the Energy Storage System Using Compressed Carbon Dioxide, Methanation and Hydrogen Generator

The main aim of this paper is to characterize the concept of a novel energy storage system, based on compressed CO2 storage installation, that uses an infrastructure of depleted coal mines to provide required volume of tanks, and, additionally, hydrogen generators, and a methanation installation to generate synthetic natural gas that can be used within the system or taken out of it, e.g., to a gas grid. A detailed mathematical model of the proposed solution was built using own codes and Aspen Plus software. Thermodynamic evaluation, aiming at determining parameters, composition and streams in all the most important nodes of the system for the nominal point and when changing a defined decision variable δ (in the range from 0.1 to 0.9) was made. The evaluation was made based on the storage efficiency, volume of the tanks and flows of energy within the system. The storage efficiency in the nominal point reached 45.08%, but was changing in the range from 35.06% (for δ = 0.1) to 63.93% (for δ = 0.9). For the nominal value of δ, equal to 0.5, volume of the low-pressure tank (LPT) was equal to 132,869 m3 , while of the high pressure tank (HPT) to 1219 m3 . When changing δ these volumes were changing from 101,900 m3 to 190,878 m3 (for LPT), and from 935 to 1751 m3 (for HPT), respectively. Detailed results are presented in the paper and indicate high storage potential of the proposed solution in regions with underground mine infrastructure.