Municipal solid waste thermochemical conversion to substitute natural gas: Comparative techno-economic analysis between updraft gasification and chemical looping

A comparative techno-economic analysis has been performed on two innovative pathways for municipal solid waste (100 t/h) thermochemical processing to substitute natural gas. The first pathway is based on updraft gasification with bottom hydrogen oxy-combustion and ashes melting, the second on autothermal chemical looping hydrogen production with Fe2O3/SiC oxygen carrier. Catalytic methanation in a series of adiabatic fixed bed reactors has been implemented and substitute natural gas quality has been evaluated based on the Italian legislation. Although the updraft gasification process shows higher substitute natural gas productivity (16.3 t/h vs 13.7 t/h), better system energy efficiency (42 % vs 35 %) and energy intensity (125 vs 141 GJ/t), the levelized cost of substitute natural gas is more competitive in the chemical looping configuration due to the lower capital expenditure. Product prices of 2.26 €/kg and 1.76 €/kg have been calculated for updraft gasification and chemical looping, respectively, assuming 8 % discount rate, 80 % capacity factor, and 90 €/MWh electricity cost. Sensitivity analyses indicate that, among other parameters, the plant capacity factor and the electric power cost have a relevant impact on the final product cost. Additionally, both pathways are shown to be economically competitive with substitute natural gas production from H2O electrolysis and CO2 capture/purchase. Finally, actions to reach competitivity with fossil natural gas for industrial uses are qualitatively discussed.