Modelling of a Combined Biomass Clc Combustion and Renewable-Energy-Based Methane Production System for CO2 Utilization

In this work, an innovative process layout to promote the integration among the chemical looping combustion of biomass, solar hydrogen, and carbon methanation is proposed and numerically investigated. The core of the layout consists of a multiple interconnected fluidized bed system (MFB) equipped with a two-stage fuel reactor (t-FR), a riser used as Air Reactor (AR), a cyclone, a L-valve return leg, and a loop-seal. The two-stage FR is based on the concept presented in a previous work, where two bubbling beds were placed in series with respect to both gaseous and solids streams in order to overcome the limitations of a single-stage fuel reactor (poor char conversion, slip of unburnt volatiles, extensive elutriation of char fines). In the first stage, where fuel and fresh oxygen carrier (OC) from the AR enter, the solid carbon combustion took place. Volatile combustion occurs mainly in the second stage, where the partly reduced OC is present. An internal riser connects the two stages, thus allowing the solids to move from the first reactor to the other. The t-FR showed the best performances in terms of combustion efficiency, volatile matter and char conversion, carbon-to-CO2 conversion efficiency and loss of elutriated carbon for all the operating conditions investigated in. Solids from the second stage go through the loop-seal into the AR where the oxidation capability of the OC is restored. A cyclone collects the regenerated OC that is sent through the L-valve to the first stage of the t-FR. At the exit of the second stage, water and fines were separated from flue gas. This latter is partly conveyed to a methanation unit in order to react with a hydrogen stream coming from an-electrolysis cells (EC) array, while the remnant is recycled to FR.