Suppression of fine ash formation in pulverized coal flames. Quarterly technical progress report No. 11, April 1, 1995--June 30, 1995

Previous work has shown that pulverized bituminous coals that were treated by coal cleaning (via froth flotation) or aerodynamic sizing exhibited altered aerosol emission characteristics. Specifically, the emissions of aerosol for the cleaned and sized coals increased by as much as one order of magnitude. The goals of the present program are to: (1) perform measurements on carefully characterized coals to identify the means by which the coal treatment increases aerosol yields; (2) investigate means by which coal cleaning can be done in a way that will not increase aerosol yields; and (3) identify whether this mechanism can be used to reduce aerosol yields from systems burning straight coal. The current experimental series focuses on the use of artificial char to study sodium vaporization and aerosol formation associated with dispersed sodium and mineral inclusions. Artificial char has the advantage over natural coal in that the composition can be precisely controlled, such that the influences of specific mineral composition and content can be investigated. The study showed: the addition of calcite had no effect of the aerosol yield; increased amounts of pyrite did not lead to increased residual ash formation; in spite of the increase in mineral content, the yield of aerosol on the backup filter did not correlate with the amount of added minerals; and the general trend was for reduced aerosol yields as the amount of bentonite increased which suggested that the bentonite was effective at complexing sodium and reducing its overall vaporization