Interpretation of the sulfation rate of CaO, MgO, and ZnO with SO₂ and SO₃

Abstract

Published models for gas‐solid reactions have been used with certain modifications to interpret sulfation data for CaO, MgO, and ZnO with SO2 and SO3. None of the models evaluated gave an adequate interpretation for high solid conversions, which were found to exceed 90% in some cases. Such high conversions are inconsistent with the current models, and a new mechanism must be postulated to explain the reaction after the solid product theoretically fills the initial pores of the particle. An important factor in successfully interpreting the experimental data is the distributed nature of the pore sizes within the solid particle.

Identification of CaSO4 formed by reaction of CaO and SO2

“…For Ca (OH), that develops its theoretical porosity during dehydration to CaO, its theoretical porosity, t, is Thus, the maximum expected conversion for Ca(OH), is 56.3% and for CaCO, is 69.6%. While this Z value helps to account for some of the excesses of the X,values noted experimentally (Kocaefe et al, 1987;Gullett et al, 1988), it does not fully account for reaction levels (up to 90% conversion) observed by Borgwardt and Bruce (1986). Nonetheless, the magnitude of the density change will have a significant effect upon sulfation models that incorporate reaction limitations based upon pore filling or blocking.…”

“…This leads to a product/reactant expansion ratio, z = vCaSo,/VCaO 7 of 52.2/16.9, or 3.09. Use of this particular handbook value (Weast, 1968) of density (or its associated Z value) has continued in subsequent papers (Hartman and Coughlin, 1976;Ramachandran and Smith, 1977;Hartman et al, 1978;Bhatia and Perlmutter, 1981; Sotirchos and Yu, 1985;Reyes and Jensen, 1987;Borgwardt et al, 1987;Kocaefe et al, 1987;Simons and Garman, 1986;Yu and Sotirchos, 1987). One instance (Hartman and Trnka, 1980) is noted where the value of 2.97 g/cm3 (45.8 cm3/mol) has been used, cited from an unidentified *Correspondence concerning this paper should be addressed to B. K. Gullett handbook.…”

Modeling of calcium-based sorbent reactions with sulfur dioxide

“…Sulfation model used was the PSS model introduced by Lindner 2 and further described in the literature. [2][3][4][5] The model assumes that a sorbent particle consists of small non-porous spherical grains in contact with m other grains ( Fig. 1 are the same and have radius r 0 .…”

“…The simplest of them are shrinking unreacted core models, such as the one described by Borgwardt. 1 More complex and computationally demanding models are the partially sintered spheres model (PSSM), 2-5 the pore model, 2,3 the network model 2,3 and their variations. The PSSM and pore models have a certain 550 TOMANOVIĆ et al level of similarity, both observing the particle structure during reactions and highly depending on particle transformation over time.…”

“…Several models are available in literature. [2][3][4][5]8,[10][11][12][13][14] The most used sorbents are calcium-based, i.e., CaCO 3 and Ca(OH) 2 , due to their availability and good reactivity with sulfur oxides under combustion conditions. Reactions of particles consist of calcination, sintering and sulfation.…”