Process Design of the Biogas Upgrading to Biomethane Using Green Hydrogen

Abstract

In recent years there was an increase in the use of renewable energy resources but there are still technological limits regarding the not constant power productivity. To face this problem, a possibility is to convert the surplus of renewable electricity into chemical energy producing hydrogen through electrolysis. The main drawback of this solution is that hydrogen is still hardly usable and so a good choice could be to convert this fuel into a more common one, such as methane. This work aims to carry out a techno-economic analysis of an upgrade section for a biogas plant to convert CO2 into biomethane. The used methodology consists in sizing the methanation reactor considering kinetic and catalyst effectiveness, membrane separation and simulating the whole process changing operating conditions such as temperature and pressure. The results of this study show that methanation can be extremely efficient in terms of energy consumption and carbon conversion. The methane production cost without accounting for hydrogen cost is between 0.15-0.19 €/kg, the same cost range as commercial natural gas. This value mainly depends on the capital and operating cost of the compression system. However, by including the high cost of hydrogen obtained by electrolysis, equal to 5 €/kg, this process is not economically feasible. On the other hand, by exploiting the surplus of renewable energy production, the cost of green hydrogen is expected to radically decrease shortly.