MODEL FOR THE SULFIDATION OF CALCINED LIMESTONE AND ITS USE IN REACTOR MODELS

A mathematical model describing the sulfidation of a single calcined l imestone particle was developed and experimentally verified This model , which includes no fitting parameters, assumes a calcined limestone p article to consist of spherical grains of various sizes that react wit h H2S according to the classic shrinking-core model. The initial size distribution of the grains is derived from mercury porosimetry. The tr ansport of H2S through the bidisperse limestone particle is calculated based on the random-pore model of Wakao and Smith, which distinguishe s macropore and micropore zones. Knudsen diffusivity inside the microp ore zones is calculated according to the dusty-gas approach. The singl e-particle model delivers the value of a new defined utilization facto r, which includes effects of external mass-transfer limitation, pore-d iffusion limitation, and grain-size distribution on particle reactivit y. A correlation derived for a single batch of calcined limestone expl icitly expresses this utilization factor. as a function of conversion and relevant process parameters. This correlation can be easily incorp orated into reactor models, as shown for an existing model describing the capture of H2S by a fluidized bed of calcined limestone particles.