Dry absorption of HCL and SO2 with hydrated lime from humidified flue gas

The simultaneous absorption of HCl and SO2 by hydrated lime in a fixed-bed reactor has been studied at conditions simulating humidified flue gas dry s crubbing. At 120 degrees C, an increase in relative humidity from 0% to 19% increased HCl removal and sorbent utilization. At 19% relative humidity (R H), the final loading of hydrated lime was 1.64 mol of HCl/mol of Ca2+. Fro m 250 to 1000 ppm HCl, HCl removal was first order in HCl concentration. Wh en SO2 was added to the feed gas, the total utilization of the sorbent by H Cl and SO2 was not a function of gas concentration with 250-1000 ppm HCl an d 0-2000 ppm SO2. However, the fraction of the hydrated lime converted by S OB increased as the SO2/HCl feed ratio increased. With oxygen present in th e feed, more SO2 was absorbed. Adding 150 ppm NO2 to the gas stream increas ed the final SO2 loading from 0.06 to 0.17 mol of SO2/mol of Ca2+. As the r eactivity of SO2 and NO2 increased, the reactivity of HCl decreased slightl y as a result of the competition for alkalinity with the other acid gases. The data were modeled using semiempirical flux equations based on a modifie d shrinking core model. Results from the parameter estimation were used to predict the absorption of HCl and SO2 on the surface of a bag filter. The p redictions indicated that, with a humidified flue gas and 50% sorbent utili zation, less than 20% HCl penetration is possible. However, even at the con ditions with the greatest SO2 absorption (250 ppm HCl, 150 ppm NO2, and 2.5 % O-2), 90% SO2 penetration is predicted at 50% sorbent utilization.