Process for treating combustion gases

Details Process for treating combustion gases Process for treating combustion gases

C - Chemistry, Metallurgy

01

B

23/349

C01B 17/00 (2006.01) B01D 53/50 (2006.01)

Patent

CA 1107037

ABSTRACT OF THE DISCLOSURE A process is provided for the removal of sulphur dioxide from a combustion gas stream containing said SO2 and particulate solids including flyash, in a wet scrubber having an aqueous slurry-containing sump zone. The process includes the first steps of: (a) passing the gas stream through the wet scrubber to effect SO2 removal. The second step is (b) separ- ately and directly injecting a calcium-containing reactant into the wet scrubber to mix with the aqueous slurry in the sump zone to form, inter alia, calcium sulphite and calcium sulphate, the slurry having a pH maintained in the range of approximately 6.0 to 8.5. The third step is (c)discharging at least a portion of the slurry from the wet scrubber. The fourth step is (d) bleeding off a portion of the discharged slurry to maintain a controlled quantity of slurry having a solids content of ap- proximately 5 to 40% by weight, of which at least approximately 5 to 25% comprises flyash. The fifth step is (e) recycling the flyash containing controlled quantity of slurry to the wet scrubber, and contacting the controlled quantity of slurry with the aqueous slurry to provide nucleation sites for the formation of calcium sulphite and calcium suphate crystals. The final step is (f) co-precipitating calcium sulphite and calcium sul- phate crystals on the flyash, thereby maintaining a substantially unsaturated calcium sulphate level in the aqueous slurry, and thus minimizing scale deposition on the surfaces of the wet scrubber. This procedure purifies combustion gases by reducing emissions of sulphur dioxide and particulate material. The process avoids the necessity of reaction mix tanks, and elaborate wash systems.

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