Modelling of gas conversion with an analytical reactor model for biomass chemical looping combustion (bio-CLC) of solid fuels

Artikel i vetenskaplig tidskrift, 2022

Manganese ores are promising oxygen carriers for chemical looping combustion (CLC), due to their high reactivity with combustible gases. In this work, a manganese ore called EB (Elwaleed B, originating from Egypt) is studied for its reaction rate with CH4, CO and H2 and the data are used in an analytically solved reactor model. The reactivity of fresh and three used EB samples from previous operation in a 10 kWth pilot was examined in a batch fluidized bed reactor with CH4 and syngas (50%CO + 50%H2). In comparison with other manganese ores, the EB ore has a lower rate of reaction with CH4, while showing a significantly higher reactivity with syngas. Nevertheless, this manganese ore always presents a better conversion of CH4 and syngas than the benchmark ilmenite. Mass-based reaction rate constants were obtained using a pseudo first-order reaction mechanism: 1.1·10-4 m3/(kg·s) for CH4, 6.6·10-3 m3/(kg·s) for CO and 7.5·10-3 m3/(kg·s) for H2. These rate constants were used in an analytical reactor model to further investigate results from previous operation in the 10 kWth unit. According to the analytical model, in the 10 kWth operation, 98% of the char in the biomass fuels was gasified before leaving the fuel reactor, while the char gasification products (CO and H2) have a 90% contact efficiency with the bed material. On the contrary, the volatiles have a much lower contact efficiency with the oxygen carrier bed, i.e. 20%, leading to low conversion of volatiles released. Thus, the results emphasize the importance of improving the contact between volatiles and bed material in order to promote combustion performance in the CLC process.