Carbon Utilization Through Power to Gas and Oxyfuel Combustion Hybridization with Recycled CO2: Design and Preliminary Results

Abstract

Power-to-gas (PtG) is one of the most promising energy storage technologies. PtG converts surplus (renewable) electricity into synthetic natural gas by combining H2 from water electrolysis with CO2 through methanation reaction. This technology has been proposed for carbon utilization using captured CO2 to produce a ‘CO2 neutral’ natural gas. It allows the temporal displacement (storage) in the use of renewable energy. In theory, the interconnection between the electric and gas grids leads to higher flexibility of the global energy supply. This work presents the design, construction and testing of a methanation reactor at laboratory scale (1-5 kW of hydrogen input) to make use of the CO2 produced in oxy-fuel combustion. Experimental installation includes a mixer of CO2 and H2 flows coming from bottles, an electrical heater to obtain the temperature needed for the reactor catalyst operation, around 350oC, a fixed bed tubular reactor filled with Ruthenium based catalyst, an air-cooling jacket for the reactor, a flue gas cooler and water condenser, and several points for the gas analyser, thermocouples and pressure difference devices. In the next set of experimental tests a second catalytic reactor, after the flue gases water condensation, will be included to increase the extent of methanation reaction. The objective is to characterize the experimental production of synthetic methane under different temperatures, ranging 300-400oC, and pressures, ranging 1 bara-2bara. The work also includes the evaluation of the methane conversion rates under different CO2 stream impurities (CO and H2O). These impurities are related to the expected flue gas composition that comes from a burner working under oxy-fuel conditions. First results to be presented comprise the design of the lab-scale system together with the economic itemization of the installation and preliminary experimental results of methanation reactor.