Roasting of minerals, esp. gypsum, in multistorey furnace - which is divided into low temp. calcining zone and high temp. calcining zone with separate inlets and outlets

摘要

Gypsum is pref. fed into the top end of a furnace divided into two zones, viz. an upper zone using low calcining temp., and lower zone using high calcining temp. At least part of the gypsum is removed after travelling through the upper zone. Crude gypsum may also be fed directly into top end of lower zone. Two types of roasted gypsum of obtd. are pref. fed into a mixer. Pref. furnace has two outlets for roasted gypsum, one outlet being located at the bottom end of each zone. Alternatively, mixing of two types of roasted gypsum occurs in lower, high temp. calcining zone. Lump gypsum and/or plaster gypsum can be made with a precise degree of calcining.