KINETICS OF FLUE-GAS DESULFURIZATION AT LOW-TEMPERATURES - FLY-ASH CALCIUM-(3 1) SORBENT BEHAVIOR/

The reaction rate equation for the flue gas desulphurization at low te mperatures using fly ash/calcium sorbents has been determined in a fix ed-bed reactor in the range of SO2 concentration, 2000 less than or eq ual to C less than or equal to 5500 (ppmv), temperature 52 less than o r equal to T less than or equal to 67 degrees C and relative humidity 0.40 less than or equal to RH less than or equal to 0.90, working at c onditions prevailing in the exhaust gases of coal-fired plants. The ki netic models discrimination procedure leads to a reaction rate express ion based on the SO2 adsorption on a nonideal surface as the rate-cont rolling step, in terms of an exponential influence of the calcium conv ersion in the reaction sate. The influence of the SO2 concentration in the gas phase has been described by a partial-reaction order equal to 1. Concerning the temperature influence, the kinetic constant does no t depend on this variable, which can be explained by a sorption equili brium step previous to the reaction, the observed kinetic constant bei ng an apparent parameter. The relative humidity has been concluded to be the most relevant variable, with a significant influence on the kin etic behaviour of the sorbent, which can be described by the fitting o f the parameter which accounts for the nonideal solid surface to the r elative humidity. From the obtained conclusions, an appropriate kineti c model based on three parameters has been proposed for the kinetic de scription of the desulphurization reaction under study, i.e. when a so rbent based on a fly ash-Ca(OH)(2) mixture 3/1 is used in the process. (C) 1997 Elsevier Science Ltd.