Discharge from pulping vessels without the aid of mechanical agitation

Abstract

A continuous digester discharges pulp without mechanically engaging the pulp, by using one or more discharge transitions with one dimensional convergence and side relief. The transitions may be mounted within a pre-existing digester shell (after removal of the discharge rotor), and supported by a number of braces and/or a skirt shaped like a truncated cone. The operation of a digester, or other continuous vessel, may be controlled by automatically sensing the level of comminuted cellulosic fibrous material in the vessel and automatically controlling the introduction of dilution liquid into the vessel to discharge the material from the vessel in response to the sensing.

What is claimed is: 
     
       1. A method of utilizing a continuous digester for cooking comminuted cellulosic fibrous material with cooking liquor to produce pulp, the digester having an outlet having a mechanical discharge device located within a shell of the digester to facilitate discharge of pulp therefrom, said method comprising the steps of: (a) removing the mechanical discharge device from the outlet of the digester, out of the digester shell; then   (b) installing within the outlet, within the digester shell, a discharge transition having one dimensional convergence and side relief so that the pulp must pass through the discharge transition to pass from the interior of the digester to the outlet; and then   (c) operating the digester to effect cooking of the material with cooking liquor within the vessel interior and discharge of the pulp produced out the outlet through the discharge transition without bringing any moving mechanical elements into contact with the material or pulp within the vessel to facilitate discharge thereof.   
     
     
       2. A method as recited in claim 1 wherein the digester includes a bottom hemispherical head; and wherein step (b) is practiced, at least in part, by supporting the discharge transition on a conical support skirt engaging the head. 
     
     
       3. A method as recited in claim 1 wherein step (b) is practiced to provide nozzles for the introduction of dilution liquid into the material as it flows in the discharge transition; and wherein step (c) is practiced to introduce dilution liquid through the nozzles into the material as it flows in the discharge transition. 
     
     
       4. A method as recited in claim 3 wherein the digester includes a bottom hemispherical head; and wherein step (b) is practiced, at least in part, by supporting the discharge transition on a conical support skirt engaging the head. 
     
     
       5. A method as recited in claim 4 wherein step (c) is practiced to introduce dilution liquid through the nozzles into the pulp below the head as the pulp flows in the discharge transition. 
     
     
       6. A method as recited in claim 1 wherein step (c) is practiced to cause the material to flow through a device having one-dimensional convergence and side relief. 
     
     
       7. A method as recited in claim 6 wherein the device with one-dimensional convergence and side relief comprises at least two sloping sides; and wherein step (b) is practiced by inserting braces between the digester and the sloping sides. 
     
     
       8. A method as recited in claim 7 wherein the digester includes a bottom hemispherical head; and wherein step (b) is practiced, at least in part, by supporting the discharge transition on a conical support skirt engaging the head. 
     
     
       9. A method of controlling the operation of a vessel containing comminuted cellulosic fibrous material having an inlet, an outlet with single convergence and side relief, and dilution liquid introduction into one or more locations in the outlet, comprising the steps of substantially continuously: (a) automatically introducing a liquid slurry of the material into the inlet of the vessel to form a level of material in the vessel;   (b) automatically detecting the level of the material in the vessel;   (c) automatically controlling the flow of dilution liquid to the one nor more locations in the outlet in response to variations in the material level detected in step (b); and   (d) automatically discharging the material slurry from the outlet of the vessel.   
     
     
       10. A method as recited in claim 9 wherein step (c) is practiced by closed loop control of at least one automatic valve. 
     
     
       11. A continuous digester for digesting comminuted cellulosic fibrous material to produce cellulose pulp, comprising: a substantially cylindrical upright vessel having a top and a bottom, a first circular cross section at the top thereof, and a second circular cross section at the bottom thereof that is greater than the first cross section, said vessel being at least forty feet high;   a pulp outlet from the bottom of said vessel, said pulp outlet having a third cross-section that is less than one-fifth the cross-sectional area of said second cross section;   a screen for extracting liquid from material and causing the extracted liquid to pass outside of said vessel, said screen mounted above said pulp outlet; and   discharge means between said screen and said pulp outlet for causing pulp to flow without hangup and without bringing any moving mechanical element into contact therewith from below said screen to said pulp outlet, said vessel interior below said screen being devoid of moving mechanical elements which come into contact with pulp, comprising a discharge transition with one dimensional convergence and side relief including: a first, uppermost, portion having a generally right rectangular parallelepiped configuration including opposite side faces having generally triangular shapes, and providing one dimensional convergence and side relief; a second portion tapering from a generally rectangular parallelepiped configuration at an upper part thereof to a generally circular configuration at a lower part thereof and having opposite side faces having generally triangular shapes which align with said first portion generally triangular shapes to define substantially diamond shaped wail portions; a third portion substantially the same as said first portion, only smaller, and connected to said second portion lower part; and a fourth, lowermost, portion substantially the same as said second portion only smaller, and connected to said third portion in the same manner as said second portion is connected to said first portion, and connected to said pulp outlet; and   wherein said discharge means further comprises means for introducing dilution liquid into said vessel into contact with the pulp below said screen.   
     
     
       12. A digester as recited in claim 11 wherein said means for introducing dilution liquid comprises means for introducing dilution liquid into pulp while in said transition with one dimensional convergence and side relief. 
     
     
       13. A digester as recited in claim 11 further comprising a preexisting digester shell surrounding said transition, and supporting means disposed between said shell and transition for supporting said transition. 
     
     
       14. A digester as recited in claim 13 wherein said supporting means comprises a plurality of braces extending between said digester shell and said transition. 
     
     
       15. A digester as recited in claim 13 wherein said digester has a hemispherical head; and wherein said supporting means include a substantially truncated continuous or discontinuous conical skirt engaging said head and said discharge transition. 
     
     
       16. A digester as recited in claim 15 wherein said dilution liquid introducing means includes a dilution plenum disposed between said second and third portions of said discharge transition for introducing dilution liquid generally at the interface therebetween. 
     
     
       17. A digester as recited in claim 16 wherein said skirt engages said transition adjacent the bottom of said dilution plenum. 
     
     
       18. A digester as recited in claim 15 wherein said dilution liquid introducing means comprises at least one dilution liquid nozzle for introducing dilution liquid into said transition below said head. 
     
     
       19. A digester as recited in claim 12 wherein the amount of liquid introduced by said dilution liquid introducing means are controlled by a level controller controlling an automatic valve and receiving input from a level detector. 
     
     
       20. A digester as recited in claim 11 wherein said dilution liquid introducing means includes a dilution plenum disposed between said second and third portions of said discharge transition for introducing dilution liquid generally at the interface therebetween.