Flue gas desulphurisation process - uses absorption in limestone slurry, producing gypsum in different grades and treating effluent internally

摘要

Flue gas desulphurisation process comprises: (a) cooling and dedusting; (b) contacting with a limestone slurry, to remove SOx by absorption; (c) adjustment of pH of the slurry, now contg. Ca(HSO3)2 and CaSO3 produced in step (b); (d) contacting the slurry with an O2-contg. gas, giving gypsum (e) concentrating the gypsum slurry; (f) adjusting the concn. of the conc. gypsum slurry; (g) centrifugally sepg. gypsum from its slurry; and (h) treating the effluent discharged from step (a). An alternative process differs only in that slurry from step (b) is fed to step (a), for reaction of excess limestone with SOx. Pref. in step (c), the pH is pref. adjusted to 4-5 by H2SO4 addn. In step (d), O2 is added at 1.5-3.0 times the theoretically required rate. The concn. of gypsum in the conc. slurry is pref. 15-25%. The gypsum concn. in step (b), arising from fine particles escaping removal in step (g) and then being returned to step (b), is 5% or more.