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Vapors of alkali metal compounds can be removed from coal combustion and gasification flue gases using high-temperature aluminosilicate sorbents. The fundamentals of alkali adsorption on kaolinite, bauxite, and emathlite are compared and analyzed both experimentally and through theoretical modeling. The results show that the process is not a simple physical condensation, but a complex combination of diffusion and reaction. The kinetics of adsorption on these sorbents have similarities: the process is diffusion-influenced, the rate decreases with time, and there is a final saturation limit. There are, however, differences in reaction mechanisms leading to potentially different applications for each sorbent. In adsorbing alkali chloride vapors, kaolinite and emathlite release all the chlorine back to the gas phase while bauxite retains some of the chlorine. Moreover, the products of reaction with emathlite have a melting point significantly lower than those for kaolinite and bauxite. Therefore, emathlite is more suitable for lower-temperature sorption systems downstream of the combustors / gasifiers, while kaolinite and bauxite are suitable as in-sito additives.

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Monolith catalyst reactors are used for controlling emissions of automotive and industrial pollutants. Various external mass transfer correlations are available for small-pitch catalysts typical of automotive applications; however, little information is available for catalysts having larger pitch and length that are more typical of power plant applications. The present paper proposes a new correlation Sh = 2.696[1 + 0.139ScRe(d/L)]0.81 based on data for the mass transfer limited performance for the CO oxidation reaction in square-channeled titania−silica honeycomb catalysts. The correlation is suitable for describing the performance of square-channeled honeycomb catalysts used for the selective catalytic removal of nitric oxide from power plant effluents. The differences between the present correlation and other literature correlations are discussed.