SURFACE AREA FORMATION IN DRY FGD SORBENTS

Dry flue gas desulfurization (DFGD) technologies are being developed which require sorbents with high specific surface areas capable of large sulfur dioxide uptake. Specifically, novel methods of controlling S0₂ in a fiuidized bed absorber are being studied which will have the capability of isothermal operation at optimum temperature for S0₂ uptake with alkaline sorbents. This paper reports on a study of surface area development with respect to time for three sorbent materials (pure calcium carbonate, dolomitic limestone and pressure hydrated dolomitic limestone) undergoing thermal decomposition in the temperature range of 600-850°C (1100-1550°F). Two of these sorbents (calcium carbonate and dolomitic limestone) confirm observations made by others of a lag time between recrystalization of the product from the reactant and the development of the maximum surface area. A model is presented which predicts the surface area development by accounting for the surface area generated by thermal decomposition and the surface area lost due to sintering. The parameters necessary for the model were obtained from the experimental data. The ability of the model to predict the surface area change with respect to time is shown to be good for the conditions tested.