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AssigneesEco-Tec Limited, Pulp and Paper Research Institute of Canada
InventorsMichael Paleologou, Rokhsareh Thompson, Richard McKinnon Berry, Michael A. Sheedy, Craig J. Brown
Estimating the term…
Sodium chloride is removed from pulping chemicals used in a Kraft pulping process by the use of a snake-cage polyelectrolyte ion exchange resin, coupled with removal of sulfide prior to treatment, or treatment of chemicals which are already low in sulfide. In one aspect of the invention, dust is collected from exhaust gases produced in the black liquor recovery cycle and is dissolved in water to produce a solution containing sodium chloride and sodium sulfate. The solution is filtered to yield a solid product and a filtrate solution. The filtrate solution is fed to an ion exchange unit which removes chloride and produces a purified sodium sulfate product. The sodium chloride is removed from the ion exchange resin by water elution, and useful recovered chemicals are recycled to the recovery cycle of the Kraft process. In one embodiment, only a portion of the dust is dissolved so that the solid product produced by filtering is primarily sodium sulfate, and that sodium sulfate is recycled to the recovery cycle of the Kraft process. In another aspect of the invention, white liquor from the pulping process is treated directly after oxidizing sulfide to sulfate. After removal of sodium chloride in the ion exchange unit, the treated white liquor can be used as a source of sodium hydroxide for oxygen delignification, and the effluent from the oxygen delignification stage can be returned to the process.
A Kraft pulping process in which pulping chemicals are used to treat cellulosic fibrous feed material to form pulp, in a process loop in which the fibrous feed material is heated with a white liquor in a digestion stage to produce fibrous pulp and a black liquor, and in which the black liquor is treated in a recovery cycle which includes the steps of concentrating the black liquor, burning the concentrated black liquor in a recovery boiler to yield a smelt, treating the smelt to form a said white liquor and returning the white liquor to the digestion stage;
A method for purifying chemicals used in a Kraft pulping process, comprising the steps of:
A Kraft pulping apparatus in which pulping chemicals are used to treat cellulosic fibrous feed material to form pulp, in a process loop, the apparatus comprising means for heating cellulosic fibrous feed material with a white liquor in a digestion stage to product fibrous pulp and a black liquor, and means for treating the black liquor in a recovery cycle to concentrate the black liquor, burn the concentrated black liquor in a recovery boiler to yield a smelt, and form from said smelt a said white liquor to be returned to said digesting means;
An apparatus as claimed in 17, wherein said means for collecting pulping chemicals from the process loop comprises means for collecting white liquor prior to delivery of said white liquor to the digestion stage, and means for pre-treating the white liquor to remove sulfide.
For use in combination with a Kraft pulping apparatus in which pulping chemicals are used to treat cellulosic fibrous feed material to form pulp, in a process loop, the apparatus comprising means for heating cellulosic fibrous feed material with a white liquor in a digestion stage to product fibrous pulp and a black liquor, and means for treating the black liquor in a recovery cycle to concentrate the black liquor, burn the concentrated black liquor in a recovery boiler to yield a smelt, and form from said smelt a said white liquor to be returned to said digesting means, apparatus for recovering useful pulp and chemicals,
Dependencies are inferred from the claim text.