Effect of Sodium Carbonate Additive on the Reaction of SO sub 2 /O sub 2 Mixtures with Carbonate Rocks

摘要

A detailed investigation of the interaction of sodium carbonate with limestones during calcination and sulfation has been performed. Laboratory results show that the presence of the salt induces structural rearrangements in the stones. The interaction of salt and stone produces a weakly volatile liquid that increases the ionic diffusion and mobility of the system, enhancing decarbonation, enhancing recrystallization of CaO and CaSO sub 4 , and providing a fluid medium favorable to reaction with SO sub 2 /O sub 2 mixtures. Verification of the effect of Na sub 2 CO sub 3 additive in a larger-scale process development unit is also reported. Sodium carbonate, when used as a mineralizing additive in fluidized-bed coal combustion, promotes the capture of sulfur dioxide by limestone. Sulfation of 50% of the CaO in the material to CaSO sub 4 can be achieved, which is a significant improvement over the average 30% sulfation of limestones under these conditions with additive absent. Sodium carbonate has a dramatic effect on the pore distribution of the calcined material, even at low concentrations. However, impurities in the natural stones reduce the effectiveness of the salt additive (1) by compound formation with the salt, and (2) by physical interference with recrystallization and pore growth. Liquid salt is present during sulfation, ensuring rapid sulfation of the CaO by promoting pore growth and increased gaseous diffusion, as well as providing a liquid medium for the reaction of dissolved gases and solids. (ERA citation 04:054064)