Conceptual assessment of sustainable methane production from oxycombustion CO2 capture in waste-to-energy power plants

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The worldwide deployment of renewable energy is growing exponentially. However, its intermittency limits its impact on the yearly energy contribution to the grid. Thus, coal remains the largest source of electricity generation in the world. Developing negative emissions technologies, such as Bioenergy with Carbon Capture and Utilization (BECCU), is a promising pathway. This study focuses on integrating waste biomass oxycombustion and a power-to-methane system. A proton exchange membrane electrolysis driven by photovoltaic solar energy is considered to produce hydrogen and oxygen, which is used for oxy-waste combustion in a sub-critical steam power cycle. Depending on the operation strategy, a certain amount of additional O2 would be required, produced by a cryogenic distillation air separation process. At the exit of the boiler, the almost pure CO2 stream is further purified, compressed, and sent to the methanation reactor. A quasi-stationary model of the entire plant is developed to simulate different operation conditions and assess the integration efficiency. The results show an excellent integration of the whole plant, with a yearly average efficiency penalty associated with the CO2 avoided of 6 % points. Since waste biomass is used as fuel, the system provides −610 kg CO2/MWh emissions compared to biomass plants without CO2 capture. Results from a yearly detailed techno-economic analysis show an average levelized cost of electricity of 199.56 €/MWh and an average green methane production cost of around 110.12 €/MWh. These yearly results involve a CO2 capture cost of about 65.66 €/ton CO2, which justify the potential interest in the proposed system for new and retrofitted biomass power plants.