Techno-economic analysis of integrated processes for the decarbonization of a waste-to-energy plant

This work aims at providing a deeper insight into different possible solutions for the decarbonization of existing power plants as support for the achievement of the goals planned by the European Commission 2030 strategy for climate and energy framework. In particular, the study is focused on the conversion of carbon dioxide contained inside the exhausts of a waste-to-energy plant, into valuable products. Two different solutions are addressed: -The Power-to-gas pathway to produce synthetic natural gas (SNG) from the captured CO2 and the H2 produced by electrolysis -The CO2 capture and storage pathway (CCS) for the sequestration of CO2 and its storage in liquid form. Firstly, the results of the annual simulations from a previous study on the power-to-gas were adapted and rescaled to the two systems to obtain material and energetic flows. With these results, a detailed analysis of the energy consumption is implemented to evaluate some environmental and energetic parameters along with a preliminary sizing of the two systems. Secondly, a detailed economic analysis is performed to understand the feasibility of the two plants. The results of the energy and economic analysis show that the two solutions analysed are technically feasible, thus allowing to avoid the emissions of 7740 t/y of CO2. The electrolysis section is the critical part of the entire power-to-gas plant with an electric consumption of 82.69 GWhel/y. This is reflected in the total cost of the plant and, thus, on the levelized cost of the SNG produced of 1.77 €/Nm3 in a realistic scenario: this value is much higher than the actual price of natural gas (0.61 €/Nm3). To reduce the cost for the annual electric consumption, it is necessary to use the energy surplus coming from renewable energy sources as much as possible, so that the cost to produce SNG can reach acceptable values. For the CCS solution, the fundamental part is represented by the thermal energy fed to the reboiler. Two different configurations for the waste-to-energy plant are considered for the solvent regeneration: a CHP layout and the use of an electric heater. Despite the CAPEX is lower for the full-electric configuration, the CHP pathway is preferable because it leads to a lower value of the levelized cost of the liquid CO2 produced (83.77 €/t). This result is in line with the market values of liquid CO2 both for the bulk conditions (i.e. for food and beverage) and for the retail market (i.e. technical gases for laboratory). In conclusion, although these plants still have evident technological and economic limitations, the development of even more efficient processes can accelerate the route towards a faster energy transition, thus contributing to the mitigation of climate change down the line.