Kinetic analysis on CO2 sequestration from flue gas through direct aqueous mineral carbonation of circulating fluidized bed combustion fly ash

In this work, the suitability of fly ash from 600 MW circulating fluidized bed boiler for CO2 sequestration through direct aqueous route was evaluated. The circulating fluidized bed combustion fly ash exhibited favorable carbon capture characteristics with a maximum CO2 sequestration capacity of 0.128 g CO2/g CFA and a corresponding carbonation efficiency of 78.17 %. A modified shrinking core model incorporated gaseous CO2 dissolution and time-dependent effective coefficient of internal diffusion was proposed to determine the gas-liquid-solid carbonation kinetics. The key kinetic parameters were assessed as a function of various carbonation conditions including reaction temperature, solid-liquid (S/L) ratio, energy input and superficial gas velocity. The mass diffusion through the liquid film near the gas-liquid interface was the rate-controlling step during the initial period of time, while diffusion through the expanded passivation layer constituted the controlling mechanism at the final stage. The model provides a more accurate representation of the gas-liquid-solid carbonation process and can be generalized to describe the carbonation of other solid wastes of interest.