Method and apparatus for digesting cellulose material without screening digesting liquid withdrawn through the digester top

Claim 1

Apparatus for continuous digestion of cellulose material chips comprising a cylindrical vertically disposed impregnation vessel having a first given diameter, an inlet at the top thereof, and an outlet at the bottom thereof, means for introducing cellulose material chips and digesting liquid at relatively low temperature into said impregnation vessel inlet, a cylindrical vertically disposed liquid-filled digesting vessel having a second given diameter, greater than said first given diameter, a top, and having a digesting zone and other treatment zones therein, the area of said impregnation vessel outlet being approximately 1/4-166 as great as the area of said digesting vessel, said impregnation vessel extending through the top of said digesting vessel, concentric therewith, a predetermined distance so that said impregnation vessel outlet is disposed a significant distance below the top of said digesting vessel, a chips column formed in said digesting vessel below the outlet from said impregnation vessel by chips entering said digesting vessel from said impregnation vessel outlet, a liquid outlet formed in the top of said digesting vessel, a substantial distance above said impregnation vessel outlet and above said chips column, means for introducing digesting liquid at relatively high temperature into said cellulose material chips column at a point a distance J below said impregnation vessel outlet great enough so that even distribution of liquid through said chips column results and so that short-circuiting of liquid to said liquid outlet formed in the top of said digesting vessel is prevented, said distance J being equal to or greater than 1/2 said second given diameter, the quantity of liquid introduced into said digesting vessel and the first and second diameters being so dimensioned that the velocity of liquid flowing through said chips column to said digesting vessel outlet is substantially less than the velocity of liquid that entrains a significant amount of cellulose material, so that substantially no cellulose particles pass upwardly from said chips column to said liquid outlet, means for withdrawing treated cellulose material from the bottom of said digesting vessel at a given rate so that the chips column is maintained at substantially the same level while individual particles thereof move downwardly through said vessel, and means for removing any particles entrained in liquid passing from said chips column to said digesting vessel top outlet from said liquid, said means comprising a pair of vertically arranged screens, one atop the other, disposed on generally vertical side walls of said digesting vessel above said chips column and below said liquid outlet, and means for alternately applying suction to one of said screens and not the other to withdraw liquid from said digesting zone while particles are screened out.

Claim 6

A method for continuously digesting cellulose material in a vertical digester having an impregnation zone defined by an impregnation vessel having a first diameter, and a digesting zone and subsequent treatment zones defined by a digesting vessel having a second diameter substantially larger than said first diameter, said impregnation vessel extending downwardly into said digesting vessel a significant distance, and an outlet being disposed in the top of said digesting vessel above the outlet of said impregnation vessel into said digesting vessel, and the area of said impregnation vessel outlet being approximately 1/4-1/3 as great as the area of said digesting vessel, said method comprising the steps of introducing cellulose material and digesting liquid at relatively low temperature into said impregnation vessel at the top thereof, said material and liquid passing downwardly through said impregnation vessel toward said digesting vessel. introducing chips-liquid mixture from said impregnation vessel into said digesting vessel through said impregnation vessel outlet so that the chips form a chips column in said digesting vessel, the highest point of which is at said impregnation vessel outlet, introducing digesting liquid at a relatively high temperature into contact with chips at a point a distance J below said impregnation vessel outlet great enough so that even distribution of liquid through said chips column results and so that short-circuiting of liquid to said liquid outlet formed in the top of said digesting vessel is prevented, said distance J being equal to or greater than 1/2 said second given diameter, withdrawing liquid flowing through said chips column from said digesting vessel through said liquid outlet disposed at the top of said digesting vessel without straining at said liquid outlet, the quantity of liquid introduced into said digesting vessel and the first and second diameters being so dimensioned that the velocity of liquid flowing through said chips column to said digesting vessel outlet is substantially less than the velocity of liquid that entrains a significant amount of cellulose material in its flow so that substantially no cellulose particles pass upwardly from said chips column to said liquid outlet, withdrawing treated cellulose material from the bottom of said digesting vessel at a given rate so that the chips column is maintained at substantially the same level while individual particles thereof move downwardly through said vessel, and removing any particles that are entrained in liquid above said chips column flowing from said chips column to said digesting vessel top outlet from said liquid by alternatively applying suction to one of two screens disposed on generally vertical digesting vessel walls between the chips column top and said liquid outlet while not applying it to the other screen.

Claim 7

A method for continuously digesting cellulose material in a vertical digester having an impregnation zone defined by an impregnation vessel having a first diameter, and a digesting zone and subsequent treatment zones defined by a digesting vessel having a second diameter substantially larger than said first diameter, said impregnation vessel extending downwardly into said digesting vessel a significant distance, and an outlet being disposed in the top of said digesting vessel above the outlet of said impregnation vessel into said digesting vessel, and the area of said impregnation vessel outlet being approximately 1/4-1/3 as great as the area of said digesting vessel, said method comprising the steps of introducing cellulose material and digesting liquid at relatively low temperature into said impregnation vessel at the top thereof, said material and liquid passing downwardly through said impregnation vessel toward said digesting vessel. introducing chips-liquid mixture from said impregnation vessel into said digesting vessel through said impregnation vessel outlet so that the chips form a chips column in said digesting vessel, the highest point of which is at said impregnation vessel outlet, introducing digesting liquid at a relatively high temperature into contact with chips at a point a distance J below said impregnation vessel outlet great enough so that even distribution of liquid through said chips column results and so that short-circuiting of liquid to said liquid outlet formed in the top of said digesting vessel is prevented, said distance J being equal to or greater than 1/2 said second given diameter, withdrawing liquid flowing through said chips column from said digesting vessel through said liquid outlet disposed at the top of said digesting vessel without straining at said liquid outlet, the quantity of liquid introduced into said digesting vessel and the first and second diameters being so dimensioned that the velocity of liquid flowing through said chips column to said digesting vessel outlet is substantially less than the velocity of liquid that entrains a significant amount of cellulose material in its flow so that substantially no cellulose particles pass upwardly from said chips column to said liquid outlet, withdrawing treated cellulose material from the bottom of said digesting vessel at a given rate so that the chips column is maintained at substantially the same level while individual particles thereof move downwardly through said vessel, and removing any particles that are entrained in liquid above said chips column flowing from said chips column to said digesting vessel top outlet from said liquid by alternatively applying suction to one of two screens disposed on generally vertical digesting vessel walls between the chips column top and said liquid outlet while not applying it to the other screen.