Abstract: A method for improving utilization of limestone in a sodium-limestone double alkali flue gas desulfurization process. Spent alkaline absorber solution, containing sodium sulfite and sodium bisulfite, is diverted for regeneration treatment in a series of stirred tank reactors, where it is contacted with the limestone regenerating agent. Dilute slurry from the last reactor is concentrated in a thickener, and the concentrated underflow slurry from the thickener is then treated further in an after-reactor circuit. Since the thickener underflow slurry contains residual unreacted limestone, the slurry is contacted with a side stream of spent alkaline absorber solution in the after-reactor circuit to promote further reaction of residual limestone before the solids are separated and discarded.

Abstract: YUtilization of a soda-type dry sorbent in a dry injection flue gas desulfurization process is increased, without sacrifice in the SO.sub.2 removal efficiency, by reinjecting a portion of the sorbent collected in the baghouse filter back into the hot flue gas stream along with fresh sorbent; the recycled sorbent is optionally cooled below the bag filter temperature prior to its reinjection.

Abstract: A flue gas desulfurization method for efficiently removing sulfur oxides from a gas stream with an aqueous sodium sulfite- and sodium bisulfite-containing absorption solution, in which absorber effluent solution at a pH of from 5.8 to 6.6 and having an active sodium concentration of from 0.5 M to 0.9 M is regenerated with sufficient ground limestone to yield a treated solution with a higher pH of from 6.3 to 7.0 and whose bisulfite concentration is reduced by from 35 to 70%.