Absorption of HCl and SO{sub 2} from humidified flue gas with calcium silicate solids

Journal Article · Sat Apr 01 04:00:00 EST 2000 · Industrial and Engineering Chemistry Research

DOI:https://doi.org/10.1021/ie990493k· OSTI ID:20062648

Chisholm, P N; Rochelle, G T

The absorption of HCl and SO{sub 2} with calcium silicate was studied in a bench-scale, fixed-bed reactor at 120 C. From 0 to 3.5% relative humidity (RH), an increase in relative humidity increased sorbent utilization by reaction with HCl. From 3.5 to 19% RH, final sorbent loading by HCl was constant at 1.4 mol/mol of Ca{sup 2+}. The absorption rate of HCl was first-order in HCl concentration from 250 to 3,250 ppm. When calcium silicate was exposed to HCl and SO{sub 2} simultaneously in the absence of O{sub 2} or NO{sub 2}, no SO{sub 2} remained loaded with the solids at the end of an experiment. Any SO{sub 2} that was absorbed was eventually emitted from the solids in favor of increased HCl absorption. The addition of O{sub 2} to the simulated flue gas caused improved SO{sub 2} adsorption but had little effect on HCl absorption. A dramatic increase in final SO{sub 2} loading and a decrease in final HCl loading was observed with NO{sub 2} was added to the gas stream. Adding 50 ppm NO{sub 2} increased SO{sub 2} loading from 0 to 0.73 mol/mol of Ca{sup 2+} and decreased HCl loading from 1.4 to 0.61 mol/mol of Ca{sup 2+}. In the presence of NO{sub 2}, increasing the SO{sub 2}/HCl inlet ratio increased final SO{sub 2} loading and decreased final HCl loading. In experiments without HCl from 90 to 150 C, it was found that a low concentration of NO{sub 2} increased final SO{sub 2} loading more at higher temperatures. The experimental data from the fixed bed were modeled using a modification of the shrinking core model. Flux equations and estimated parameters were then used to predict the performance of HCl and SO{sub 2} absorption by calcium silicate on the surface of a bag filter. The predictions suggested that, at reasonable gas conditions in the absence of SO{sub 2}, HCl penetration through the bag filter can be reduced below 20%. With simulated municipal waste combustion flue gas (low SO{sub 2}/HCI ratio) with 50 ppm NO{sub 2}, HCl and SO{sub 2} penetration can be reduced to less than 5%. At coal-fired boiler conditions (high SO{sub 2}/HCl ratio) with 50 ppm NO{sub 2}, HCl penetration can be reduced to 2% while SO{sub 2} penetration was predicted to be 40%.

• Research Organization: Univ. of Texas, Austin, TX (US)
• OSTI ID: 20062648
• Journal Information: Industrial and Engineering Chemistry Research, Journal Name: Industrial and Engineering Chemistry Research Journal Issue: 4 Vol. 39; ISSN IECRED; ISSN 0888-5885
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
ADSORPTION
CALCIUM SILICATES
COAL
DECHLORINATION
DESULFURIZATION
FLUE GAS
HYDROCHLORIC ACID
MATHEMATICAL MODELS
SULFUR DIOXIDE