Techno-Economics Optimization of H2 and CO2 Compression for Renewable Energy Storage and Power-to-Gas Applications

The decarbonization of the industrial sector is imperative to achieve a sustainable future. Carbon capture and storage technologies are the leading options, but lately the use of CO2 is also being considered as a very attractive alternative that approaches a circular economy. In this regard, power to gas is a promising option to take advantage of renewable H-2 by converting it, together with the captured CO2, into renewable gases, in particular renewable methane. As renewable energy production, or the mismatch between renewable production and consumption, is not constant, it is essential to store renewable H-2 or CO2 to properly run a methanation installation and produce renewable gas. This work analyses and optimizes the system layout and storage pressure and presents an annual cost (including CAPEX and OPEX) minimization. Results show the proper compression stages need to achieve the storage pressure that minimizes the system cost. This pressure is just below the supercritical pressure for CO2 and at lower pressures for H-2, around 67 bar. This last quantity is in agreement with the usual pressures to store and distribute natural gas. Moreover, the H-2 storage costs are higher than that of CO2, even with lower mass quantities; this is due to the lower H-2 density compared with CO2. Finally, it is concluded that the compressor costs are the most relevant costs for CO2 compression, but the storage tank costs are the most relevant in the case of H-2.