Recovery system for oxygen bleaching of pulp
AssigneeKamyr, Inc.
InventorOliver A. Laakso
Life of this patent
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Abstract
A method is provided for recovery of white liquor and sodium hydroxide following the oxygen bleaching of pulp. A green liquor recovery system concentrates the spent black liquor, including spent liquor from the oxygen bleaching and spent black liquor, and then burns the spent liquor to form a smelt. This smelt is then dissolved in water to form the green liquor. The green liquor is divided into a first portion which is fed to a sodium hydroxide recovery system for recycling to the oxygen bleaching reactor and a second portion which is fed to a white liquor recovery system for recycling to the digester. A lime cycle is also provided to convert the resulting calcium carbonate (lime mud) to calcium oxide for recycling into the sodium hydroxide and white liquor recovery systems.
Claims3
A method of digesting and then oxygen bleaching cellulosic fiber material in successive zones and subsequently regenerating white liquor for digesting and sufficient NaOH for oxygen bleaching so that no make-up source of NaOH for oxygen bleaching is necessary, said method comprising the steps of
- (a) feeding spent liquor, including spent liquor from the oxygen bleaching zone and spent black liquor, to a green liquor recovery system,
- (b) concentrating said spent liquor,
- (c) burning said spent liquor to produce a smelt,
- (d) dissolving said smelt to produce green liquor containing a solution of sodium carbonate, sodium sulfide, and dregs,
- (e) feeding a first portion of said green liquor to a white liquor recovery system and subsequently treating said green liquor to recover white liquor therefrom,
- (f) recycling said recovered white liquor to said digesting zone,
- (g) feeding a second portion of said green liquor to an NaOH recovery system, and subsequently (i) treating said green liquor in a crystalizer to form sodium carbonate crystals, (ii) separating said crystals in a centrifuge, (iii) dissolving said separated crystals in a tank to produce a sodium carbonate solution, (iv) slaking said sodium carbonate solution with calcium oxide in a slaker to produce a sufficient quantity of NaOH solution suitable for treatment of cellulosic fiber material in said oxygen bleaching zone so that essentially no additional NaOH solution from a make-up source is necessary to continuously effect oxygen bleaching, and (v) separating the resulting NaOH solution in an NaOH clarifier, and
- (h) recycling said NaOH solution to said oxygen bleaching zone.
Dependencies are inferred from the claim text.