High sulfidity cook for paper pulp using black liquor sulfonization of steamed chips

Claim 1

Apparatus for continuously digesting cellulosic fibrous material to produce paper pulp, comprising: (a) steaming means for steaming the material; (b) liquid slurrying means for producing a liquid slurry containing the steamed material; (c) a high pressure feeder having a low pressure inlet, low pressure outlet, high pressure inlet, and high pressure outlet; (d) a continuous digester comprising a slurry inlet at the bottom thereof to a central upflow conduit, said upflow conduit having a solids/liquid separator adjacent the top of said digester, and a separated-out liquid conduit extending downwardly within said digester exteriorly of the upflow conduit to the bottom of said digester for removing separated out liquid from said digester and feeding it to said high pressure inlet to said high pressure feeder; (e) black liquor withdrawal means for withdrawing black liquor from said continuous digester; (f) a first flash tank containing a steam outlet and a concentrated liquor outlet, and an inlet connected to said digester; (g) connecting means for interconnecting said concentrated liquor outlet from said flash tank to said slurrying means; (h) black liquor recovery or disposal means; and (i) means for connecting said low pressure outlet of said high pressure feeder to said recovery or disposal means.