Experimental measurements of the reaction of sulfur dioxide and oxygen with limestones have demonstrated substantial influence of the geologic origin of the stone, its porosity and particle size, gaseous concentration of sulfur dioxide, and temperature on the course of reaction and the conversion (that is, the degree of utilization of the limestone content of the particles as a sorbent for sulfur dioxide). A mathematical model including intraparticle transport and chemical reaction within the particles (grain theory) has been developed to simulate this sulfur dioxide sorption reaction.

cp = product concentration in electrodialysis, equiv/m3 c, = reference concentration, equiv/m3; for electrodial-A simple structural model has been developed and used to correlate experimental results for the reaction of porous particles of limestone with SOn and oxygen in flue gas at high temperature. The model incorporates parameters such as the porosity of the natural rock, its true theoretical density, the content of calcium carbonate, and its conversion to sulfate. The agreement between the model and the experiments implies that the reaction is strongly influenced by reduction in porosity caused by the sulfation reaction, with both the reaction rate and the porosity becoming very small at conversions of about 50%. The pore-size distributions of unsulfated calcines and sulfated samples are remarkably different.The pores with radius larger than 3980 A are probably responsible for the high capacity of limestone to react with Son. Incomplete conversion of calcium oxide results from the strong diffusional resistance developed in the interior of the particles owing to reduction in porosity as the reaction proceeds.

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