Abstract: To a coal-fired furnace that uses electrostatic precipitation or a mechanical collector to collect fly ash, a mix of magnesia-alumina or magnesia-talc is added above the fireball (2600.degree.-3300.degree. F.). The additive increases the mean particle size of the fly ash and reduces its surface resistivity, thereby causing improved collection in the electrostatic precipitators or mechanical collector. Fine particulates containing heavy metals tend to be agglomerated; thus the invention permits recovery of substantial amounts of heavy metal contaminants that would otherwise be lost as stack emission.

Abstract: An additive, e. g., MgO.Mg silicate, is injected into the flue gas stream of a coal-or oil-fired furnace, at 2300-1700 deg. F., thereby reducing accumulation of sulfuric acid on the air heater inlet and outlet.