Power-To-Gas Concepts Integrated with Biomethane Production through Gasification of Forest Residues: Economic Evaluation

Biomethane is an attractive transportation fuel due to an increase in demand of biofuels. Biomass gasification is a well-known technology used to produce biomethane from renewable feedstock, for instance, forest residues. The challenge with a high capital cost of gasification can be compromised by increasing the process efficiency, enhancing the yield of product biomethane, and operating in a larger plant scale. Power-to-gas technology is one of propitious solutions to help facilitating the biomass gasification by increasing the yield of biomethane while reducing the capital cost of CO2 separation units and CO2 emissions. To investigate the process integration possibility and the economic performances of biomass gasification integrated with power-to-gas technology, four different process designs, regarding the injection and ejection procedures of CO2 and H2, were evaluated in this study. The economic evaluation included total capital cost investment, production cost in terms of the levelized cost of fuel, and gross profit. The economic performances of different process designs, including the conventional base case for a stand-alone gasification plant, were compared, and the most preferable design was also suggested. The electrolysis technologies, alkaline and polymer electrolyte membrane (PEM) electrolysers, were compared in each configuration as well. According to the results, the process configurations integrated with alkaline electrolysis is relatively cheaper than PEM electrolysis, therefore, the process configurations integrated with alkaline electrolysis were only in focus. The overall economic evaluation shows that a process configuration, designed to feed H2 so that a complete conversion of CO2 can be achieved, is preferable due to its relatively low production cost and high profit. Although the configuration designed to increase process flexibility by recycling unreacted CO2 back to the Sabatier inlet stream requires less total capital investment, the annual levelized cost of fuel of the former configuration is lower. By operating the former process configuration, the plant will potentially obtain 3 times more profit, compared to the conventional gasification, and the CO2 emissions per unit of produced biomethane can also be minimized since a higher amount of biomethane (biofuel) can be obtained when using a similar quantity of utilized biomass