Patent ID: 6063352
Filing Date: 2000-05-16
Classification: B01D,C01C

Abstract:
A method of removing sulfur dioxide from a flue gas, comprising the steps of:(a) passing a flue gas containing sulfur dioxide upwardly through at least one scrubbing zone of a scrubber in counterflow to a scrubbing liquid introduced at an upper portion of said zone and discharged from said scrubber at a lower portion of said zone;(b) providing a scrubbing-liquid recirculation path between said lower portion of said zone and said upper portion thereof;(c) branching at least a part of said scrubbing liquid discharged from said scrubber to an oxidation unit for oxidizing ammonium sulfite to ammonium sulfate in said part of said scrubbing liquid before returning said part branched through said oxidation unit to the scrubbing liquid;(d) adding aqueous ammonia solution to the scrubbing liquid in said path;(e) controlling steps (b), (c) and (d) so that the scrubbing liquid introduced to said zone at the upper portion thereof is a mixture of:(1) aqueous ammonia solution,(2) ammonium sulfite containing scrubbing liquid as discharged from said lower portion without intervening treatment, and(3) ammonium sulfate solution from said oxidation unit;(f) maintaining a mixing ratio of the ammonium sulfite and the ammonium sulfate in the scrubbing liquid introduced into said upper portion of said scrubbing zone at 15:1 to 3:1; and(g) adjusting a pH of the scrubbing liquid introduced to said zone at the upper portion thereof between pH 4.5 and pH 7 with aqueous ammonia solution.