Design and Thermoeconomic Evaluation of a Waste Plant With an Integrated CO2 Chemical Sequestration System for CH4 Production

Object of this paper is the modelling, process design and simulation of a waste incineration plant integrated with a novel CO2 chemical sequestration system for CH4 production. The main components of the proposed system are: the incineration plant (whose operational data are considered known here), a Sabatier reactor for CH4 production, a post-combustion monoethanolamine (MEA) chemical absorption unit and a H2O electrolyser. Carbon dioxide captured from the waste plant stack gases and hydrogen from water electrolysis feed the Sabatier chemical reactor in a temperature range of 250–450°C. Through the exothermic methanation reaction (CO2 + 4H2 = CH4 + 2H2O + Heat), methane is produced with a conversion yield of 90–95%. Through a perm-selective membrane, hot steam can be extracted from the reactor and recycled to cover about 40% of the MEA regenerating re-boiler duty. The methanation of CO2 is an established carbon capture technique, profitably suitable for waste plants. When the produced methane is burned, the CO2 absorbed in the process returns to the environment, enacting in a global sense a quasi-zero-emissions cycle. The possible integration of the electrolyser with renewable-generated electricity has been investigated to evaluate the storage capacity of electrical energy as “renewable methane”, which from a technical point of view is more suitable than hydrogen to be stored, burned or sent into natural gas pipelines. A thermo-economic analysis is presented to evaluate the exergetic performance of the proposed system and the final cost of products.