STRUCTURAL TRANSFORMATIONS IN CA-BASED SORBENTS USED FOR SO2 EMISSIONCONTROL

Economizer temperature injection of Ca-based sorbents is an option for dry control of SO2-Emissions from coal-fired boilers. Their reactivit y with SO2 was found to be a function of their specific surface areas. In the course of this work, Ca(OH)2 sorbents with specific surface ar eas from 2 to 79 m2/g and porosities from 0.02 to 0.48 were produced f rom a number of commercial sources in a laboratory-scale hydrator by ' 'single'' or ''double'' hydration. Single hydration produced Ca(OH)2 f rom CaCO3-derived CaO with specific surface areas up to 17.3 m2/g and porosities up to 0.29. Double hydration produced Ca(OH)z from Ca(OH)z- derived CaO with specific surface areas up to 23 M2/g and porosities u p to 0.33. In both types of hydration, a significant correlation was o bserved between the measured specific surface area and porosity of the CaO and its hydration product. Ca(OH)2. Ca(OH)2 sorbents were calcine d in a flow reactor operated at 550-degrees-C and 1 s residence time t o simulate conditions encountered by the solids during economizer inje ction and to investigate their response to economizer temperature. A c orrelation could be found between structural properties of Ca(OH)2 and the product of its calcination in the flow reactor. Calcination of hi gher specific surface area/porosity Ca(OH)2 resulted in higher specifi c surface area/porosity CaO. Similar pore size distributions were meas ured for CaO produced from calcination of Ca(OH)2 with similar specifi c surface area, regardless of the source of Ca(OH)2. Based on the stru ctural response of Ca(OH)2 following 550-degrees-C and 1 s exposure in the flow reactor. Ca(OH)2 with a high specific surface area (55-60 m2 /g) and high porosity (approximately 0.40) is recommended for economiz er injection application.