Abstract: Calcium carbonate scaling is inhibited in a multi-stage alkaline waste liquor evaporation plant in a chemical cellulose pulp mill having a bleaching plant. Calcium-containing effluent from the bleaching plant is treated together with alkaline waste liquor in the evaporation plant. A portion of the alkaline waste liquor of the evaporation plant is supplied to the bleaching effluent to increase the carbonate content of the effluent. Then the bleaching effluent is heated to 110-160° C. by direct contact with a heating medium (e.g. steam, or secondary vapor) and maintained in a retention tank for a period of about 1-20 minutes to reduce the amount of dissolved calcium in the effluent. Finally the heat-treated bleaching effluent is evaporated with the alkaline waste liquor in the evaporation plant, with minimized scaling.

Abstract: A falling film evaporator includes a shell with a number of heat transfer elements within the shell. Each heat transfer element has two opposed essentially rectangular plates joined together along upright sides and along seams substantially parallel to the upright sides. The seams form with each other, and the upright sides, a number of vertical flow channels through which steam (heating fluid) flows in the interior of the heat transfer elements to evaporate evaporable liquid flowing downwardly in a film over the outer surfaces of the heat transfer plates.

Abstract: A process and apparatus provide for the evaporation of spent liquors in several stages, and recovery of volatile substances from spent liquors of organic solvent pulping processes. The recovery system for volatiles is integrated with the evaporation of spent liquors. Heating condensation is carried out in each evaporator effect on several heat surfaces separated from each other. Pure water, vapor condensate, or steam may be injected to the warmer side of an evaporator effect in order to increase the condensing temperature of the vapor. The volatiles are typically alcohols (methanol and/or ethanol) used as the cooking liquor in organic solvent pulping.