METHODS FOR PRODUCING PULP AND TREATING BLACK LIQUOR

摘要

A method is provided for treating black liquor particularly derived from nonwood pulp, by heating with an alkaline earth metal oxide in a toroidal fluidised bed reactor (304) at a temperature of above 650°C. The method may be used alone or as part of a method of converting graminaceous raw material to pulp for paper or board, said method comprising (a) digesting (12) said raw material with a white liquor based on sodium hydroxide and further comprising calcium hydroxide in an amount effective to substantially convert silica of said raw material to calcium silicate; (b) recovering (14) pulp and black liquor substantially free of uncombined silica; (c) heating the black liquor in a fluidized bed reactor (304) containing calcium oxide for catalysing conversion of organic content of said black liquor to gas and for providing recovered solids including sodium values of said white liquor and calcium oxide; and regenerating said white liquor using said recovered solids. The use of the above mentioned white liquor permits treatment of wheat straw, rice straw and other high-silica materials (9) without resulting in a black liquor that is difficult to treat.