Method of treating spent pulping liquor in a fluidized bed reactor

A method of treating a material which is spent liquor from a pulping process which contains sodium compounds and the organic components in said material to be treated are carbon-containing combustibles, which comprises the steps of:

• (a) subjecting said material to combustion in a single fluidized bed reactor and recovering flue gases which have entrained hot solid particles;
• (b) introducing said flue gases and entrained hot solid particles from step (a) into a dust separator to remove the hot solid particles entrained in the flue gases;
• (c) introducing said hot solid particles free from the flue gases from step (b) into a prereactor and mixing therewith said material to preheat whereby a preheated material is obtained;
• (d) introducing said preheated material from step (c) together with said hot solid particles from step (b) into said fluidized bed reactor, subjecting the preheated material in the presence of said hot particles to combustion therein to obtain flue gases;
• (e) introducing the flue gases from step (d) into said dust separator to separate hot solid particles which are recycled in step (c) and wherein the spent liquor is mixed in step (c) with alumina hydrate, the alumina hydrate reacts partially with the sodium in the spent liquor to form sodium aluminate, the hot solid particles removed from the fluidized bed reactor from step (b) contain sodium aluminate and at least a portion of the sodium aluminate-containing hot solid particles removed from the flue gases coming from the fluidized bed reactor is added to the spent liquor in step (c).