Behavior of sulfur and chlorine in coal during combustion and boiler corrosion. Final technical report, 1 September, 1992--31 August, 1993

The goals of this project are to investigate the behavior of sulfur and chlorine during pyrolysis and combustion of Illinois coals, the chemistry and mineralogy of boiler deposits, the effects of combustion gases on boiler materials, and remedial measures to reduce the sulfur and chlorine compounds in combustion gases. Replicate determinations of chlorine and sulfur evolution during coal pyrolysis-gas combustion were conducted using a pyrolysis apparatus in conjunction with a quadrupole gas analyzer. HCl is the only gaseous chlorine species measured in combustion gases. Pyrolysis of coal IBC-109 spiked with NaCl solution shows a strong peak of HCl evolution above 700C. The absence of this peak during pyrolysis of Illinois coal indicates that little chlorine in Illinois coal occurs in the NaCl form. Evolution of sulfur during coal pyrolysis was studied; the sulfur evolution profile may be explained by the sulfur forms in coal. To determine the fate of sulfur and chlorine during combustion, a set of six samples of boiler deposits from superheater and reheater tubes of an Illinois power plant was investigated. Scanning electron microscopy shows microscopic calcium sulfate droplets on cenospheres. Superheater deposits are high in mullite, hematite, and cristobalite, whereas a reheater deposit is enriched inmore » anhydrite. The chlorine content is very low, indicating that most of the chlorine in the feed coal is lost as volatile HCl during he combustion process. The profiles of SO{sub 2} released during combustion experiments at 825 C indicate that calcium hydroxide added to the coal has a significant effect on reducing the SO{sub 2} vapors in combustion gases.« less