Enhancement of the co-gasification reactivity of biomass and coal with the introduction of calcium-based additives

The alkali metals in biomass are the fundamental basis for the synergistic effect observed during co-gasification. However, coal minerals can deactivate these alkali metals by forming non-catalytic compounds, thus inhibiting their catalytic effect. The co-gasification of wheat straw and Jincheng anthracite coal was investigated in a fixed-bed reactor at 900–1000 °C under steam atmosphere. Results indicated the presence of a synergistic effect with an undesirable potassium deactivation. Calcium-based additives were introduced to mitigate the deactivation phenomenon. The effects of additive species, quantities and loading methods on co-gasification reactivity were explored. The introduction of calcium-based additives resulted in a higher content of water-soluble K, an increase in surface area and a more robust amorphous structure in the co-pyrolysis char. The optimal addition of 5 wt% Ca(Ac)2 almost doubled the gasification rate and decreased the activation energy of the co-pyrolysis char from 143.42 kJ/mol to 110.67 kJ/mol. Besides, the S-MRPM (shifted modified random pore model) can effectively predict the gasification of wheat straw char and co-pyrolysis char, while the RPM (random pore mode) described well the gasification of Jincheng anthracite coal char and the co-pyrolysis char with Ca(Ac)2.