Process for converting sulfitic solutions by means of ammonium bisulfate with SO2 production

Claim 1

A process for converting an ammonium sulfite solution to sulfur dioxide, which comprises the continuous steps of: (a) reacting said ammonium sulfite solution with a stream of an aqueous ammonium bisulfate solution as defined in step (d), in order to evolve sulfur dioxide and convert the ammonium bisulfate in said solution to ammonium sulfate, (b) discharging said evolved sulfur dioxide, (c) decomposing said ammonium sulfate by heating to gaseous ammonia and molten ammonium bisulfate, discharging said gaseous ammonia, and overflowing said molten ammonium bisulfate, (d) maintaining an aqueous ammonium bisulfate solution in a reserve tank and passing a first fraction thereof to step (a) as said stream of an aqueous ammonium bisulfate solution and a second fraction thereof to a mixing zone, (e) admixing the overflowed molten ammonium bisulfate of step (c) with the second fraction of step (d) in said mixing zone and recycling the resultant mixture to said reserve tank, the ratio by weight of said second fraction to said overflowed molten ammonium bisulfate in said mixing zone being higher than 5:1 (f) adding water to the aqueous ammonium bisulfate solution in order to maintain a substantially constant ammonium bisulfate concentration in said mixing zone and so as to compensate for the supply of molten ammonium bisulfate to the mixing zone.