A study of the concomitant calcination and sulfation reactions of calcium carbonate and sulfur dioxide.

摘要

A structural pore propagation model has been developed to describe microscopic pore evolution from the thermal decomposition reaction of a single calcium carbonate sphere. This model depicts a uniform distribution of equal sized pores growing from the surface of the sphere toward its center while CO{dollar}sb2{dollar} is evolved from the pore bottom. The chemical reaction at the interface, as well as heat transfer from the surroundings to the decomposing sphere and transport of CO{dollar}sb2{dollar} from the pore bottom to the bulk gas, are included in the model.; The pore propagation model has been expanded for the concomitant calcination and sulfation reactions which occur when raw limestone particles are used in a dry flue gas desulfurization system. The model allows the sulfation reaction product to deposit along the pore wall during and after the course of the calcination reaction. The model takes into consideration the SO{dollar}sb2{dollar} transport from the bulk gas into the pore as well as the solid state diffusion through the product layer and the difference in the molar volume of the solid reactant and product.; The simulation of the calcination reaction confirms the experimental observations indicating slower calcination rates at higher background CO{dollar}sb2{dollar} pressures, mainly due to internal unsteady-state buildup of CO{dollar}sb2{dollar} in the pore. The effect of the background CO{dollar}sb2{dollar} pressure is significantly more prominent in the smaller particles.; The model shows the strong effect of the CO{dollar}sb2{dollar} accumulation in the pore during the calcination reaction on the extent of the sulfation reaction which depends on the SO{dollar}sb2{dollar} concentration in the pore space. This effect is more distinguished in larger particles and/or at lower reaction temperature where the calcination reaction is relatively slow compared to the sulfation reaction.