Magnesium bi:sulphite recovery from waste gas leaving lye boiler - esp. in cellulose mfr., by absorbing sulphur di:oxide in magnesium hydroxide soln. (OE 15.4.78)

摘要

The absorption of SO2 in the gas occurs in at least one magnesium sulphite (MS) stage and at least one magnesium bisulphite (MBS) stage. More MS is made than is required for the prodn. of bisulphite, and the excess (E) is removed as MS from the MBS system. Excess (E) corresponds with the difference of the amt. of S in the thick lye and the total bonded S in the tower acid. The MS removed is pref. employed for mfg. H2SO4; or is cracked by heating to obtain MgO recycled to the MBS stage and SO2 fed into the purified bisulphite soln. The MS is pref. cracked at 500-900 degrees C., possibly using some heat from the lye boiler. The MS is pref. dried before craking, which pref. occurs in a stream of SO2, and the resulting SO2 is pref. liquefied. Used in the prodn. of cellulose, using a completely closed circuit for the chemicals, and to produce a digestion acid contg. any desired amt. of SO2 in soln.