Method of removing sulfur dioxide and other toxic and noxious components from flue gases

A method of removing sulfur dioxide from fly ash containing flue gas of a fossil fuel combustion, comprising the steps of:

• (a) dry desulfurizing said flue gas by contacting same during said combustion with a finely divided particulate absorbent consisting essentially of calcium hydroxide, oxide or carbonate and thereafter separating dry solids, including said absorbent, reaction products of sulfur dioxide with said absorbent and fly ash from the flue gas;
• (b) milling at least some of the dry solids separated from the flue gas in step (a)
• (c) treating at least some of the dry solids separatd from the flue gas in step (a) with steam
• (d) wet scrubbing at least part of said flue gas following the dry desulfrurization in step (a) with an aqueous scrubbing liquid containing water and a secondary absorbent, said secondary absorbent being at least part of the dry solids separated from the flue gas in step (a) and milled and treated in steps (b) and (c);
• (e) introducing a previously unused quantity of said finely divided particulate absorbent into the scrubbing liquid in step (b) whereby a gypsum-containing sludge is formed in said scrubbing liguid upon collection thereof subsequent to wet scrubbing;
• and
• (f) recovering a gypsum-containing sludge from said scrubbing liquid after the wet scrubbing in step (b) for use as a structural material.