Increasing Compressed Gas Energy Storage Density Using CO2-N2 Gas Mixture

This paper demonstrates a new method by which the energy storage density of compressed air systems is increased by 56.8% by changing the composition of the compressed gas to include a condensable component. A higher storage density of 7.33 MJ/m(3) is possible using a mixture of 88% CO2 and 12% N-2 compared to 4.67 MJ/m(3) using pure N-2. This ratio of gases representing an optimum mixture was determined through computer simulations that considered a variety of different proportions from pure CO2 to pure N-2. The computer simulations are based on a thermodynamic equilibrium model that predicts the mixture composition as a function of volume and pressure under progressive compression to ultimately identify the optimal mixture composition (88% CO2 + 12% N-2). The model and simulations predict that the optimal gas mixture attains a higher energy storage density than using either of the pure gases.