Method and apparatus to distribute the inflow of liquors in a Batch Digester
Method and apparatus for introducing liquors into a batch digester to produce enhanced or plug-flow of the liquors through the bed of cellulosic material. Wash out liquor can be introduced into the digester during the discharging in a manner to add wash out liquor into the digester and to prevent formation of a vortex of material during discharge.
This present invention relates to improved methods and apparatus for delignifying and discharging the delignified cellulosic materials from a Batch Digester during and at the end of a pulping or cooking step.
In conventional batch pulping operations, the wood material (softwoods, eucalyptus, or hardwoods) or the lignocellulosic crop material (e.g., bagasse, bamboo, kenaf, reeds, and so forth) is reacted with cooking liquor for a given time at a specified temperature. The cooking liquor may be any of kraft, soda, alkaline, sulfite, polysulfide, or modifications thereof, such as with anthraquinone. At the desired terminating point of the delignification reaction, the cooked material still resides at high pressure and high temperature inside the digester.
Conventional Batch Reactors (digesters) used for producing fibrous cellulose from fiber bearing sources, such as wood, have traditionally been filled with the wood chips and cooking chemicals required to liberate the cellulosic fiber. Recently, new processes have emerged that reuse stored liquors (spent liquor) from the previous batch cooks to save energy and to take advantage of the residual chemicals in the spent liquor. Some of these new types of digesters require that 1) the reuse of spent liquor is pumped into the bottom of the digester with the excess liquor exiting out the top of the digester (hence they are referred to as Displacement Batch Digesters) and 2) the contents of the digester after delignification must be pumped from the bottom of the digester with gravity as the only pressure available inside the digester during most of the discharging operation feeding the discharge pump.
In order for all the contents of the digester to have the same chemical activity and to produce consistent quality pulp, the liquor that is pumped into the bottom of the digester must flow upward in a plug flow (i.e. no channeling) fashion. The fluid dynamics of this type of arrangement favors the rising liquors to follow the path of least resistance which is to flow against the smooth outer digester walls instead of flowing uniformly through the chip bed. Therefore, the rising fluid tends not to form a plug flow profile and the contents of the digester are not exposed to the same chemicals and temperatures.
Conventional Batch reactors (digesters) used for producing fibrous cellulose from fiber bearing sources, such as wood, have traditionally been emptied by opening the hot pressurized vessel to an atmospheric tank. This process is referred to as a “blow” and the atmospheric tank is referred to as a “blow tank”. Recently, new processes using batch digesters have been developed to remove the hot liquor from the pressurized digester before the “blow” thereby cooling the contents which precludes the violent flashing that occurs from high temperature liquor flashing into a blow tank from a pressurized vessel. The processes have been commercialized by various companies and are marketed under trade names such as RDH, Superbatch, CBC and DDS. Since the cooled digester does not have pressure and thermal energy to flash (blow), the contents (the product pulp fiber) must be pumped out of the digester in what is sometimes referred to as a discharge operation.
The discharging of the cooled digester contents is very difficult because the material in the digester, the product cellulose fiber, does not flow smoothly due to the pulp's inherent thixotropic properties. This also occurs because the fibers in the pulp may clump together and the black liquor in the pulp can easily separate from the mixture leaving behind fibers stuck inside the digester.
The commercial systems use nozzle jets at the bottom of the digester to spray fluid into the pulp mass in order to direct and maintain the flow of pulp with liquor out of the digester. The spray nozzles may be placed so as to create a circular flow of liquor in the digester. The flow out of the digester must exit through a “drain” opening at the bottom of the digester by gravity alone in an operation very similar to draining of a sink or tub of water. Unfortunately, a vortex forms due to the earth's rotation which interferes with the flow into the drain opening (outlet flange). The vortex in a large vessel such as a digester becomes substantial and the air funnel in the middle of the vortex can block 50% or more of the drain opening which greatly interferes with the draining process.
U.S. Pat. Nos. 4,814,042; 6,719,878; 5,800,674; H1,681; 4,764,251; 4,849,052; 6,306,252; 6,346,166; 6,346,167; 6,350,348; 6,391,628; 6,451,172 and 6,514,380 disclose various aspects of the delignification (cooking) process for providing wood pulp including the removal of the delignified pulp from the digester.
BRIEF SUMMARY OF THE INVENTIONThe present invention pertains to methods and modifications to a Displacement Batch Digester to facilitate in-flow of pulping liquors through the material being pulped or cooked and the removal of cooked (delignified) pulp from any type of batch digester. The methods involve introducing liquid or liquor adjacent the bottom of the digester to accomplish a plug-flow regime in the digester during the cooking or pulping phase and also to introduce liquor during the discharge phase.
The apparatus of the invention involves modification to the digester to facilitate introduction of the wash out liquor (liquid) into the digester to assist in the discharging of the pulp. An overhead shower can be used to aid in emptying the cooked material. Mechanical devices can also be placed in the lower digester area to aid in removing the cooked pulp.
Therefore, in one aspect the present invention is a method of discharging delignified cellulosic material from a cooled Batch Digester at the end of a cook cycle, after removal or cooling of the hot liquor in the digester, comprising the steps of; introducing a shower of clean out liquor into the digester at a location above the material, the shower distributing the liquor substantially evenly across a cross-sectional area of the digester, and withdrawing the pulp from the digester while maintaining a flow of liquor sufficient to maintain consistency of the pulp until said digester is empty.
In another aspect the present invention is a batch digester of the type having a generally cylindrical section and a bottom generally conical section the conical section having an outlet located proximate the apex of the conical section, the improvement comprising; installing a distribution channel for liquid inside the digester at a location proximate a transition from the cylindrical section to the conical section, the distribution channel installed adjacent an inner surface of the digester and having means to direct a plurality of streams toward a vertical center line of the digester.
In yet another aspect the present invention is a batch digester of the type having a generally cylindrical section and a bottom generally conical section the conical section having an outlet located proximate the apex of the conical section, the improvement comprising; a plurality of distribution channels on the inner surface of the conical section the distribution channels extending from proximate where the conical section meets the cylindrical section to proximate the outlet, the distribution channels containing means to direct a plurality streams of liquor toward a vertical center-line of the digester.
In still another aspect the present invention is a method for enhancing plug-flow of pulping liquors introduced into a batch digester for delignifying cellulosic materials comprising the steps of: introducing a plurality of streams of the pulping liquor proximate a bottom location of the digester, the streams oriented to flow in a direction generally parallel to a vertical axis (up or downward flow) of the digester; and continuing flow of the liquor until the cellulosic material is delignified to a desired delignification.
In still another aspect the present invention is a method for enhancing plug-flow of pulping liquors introduced into a batch digester for delignifying cellulosic materials comprising the steps of: introducing a plurality of streams of the pulping liquor proximate a bottom location of the digester, the streams oriented to flow in a direction generally parallel to a vertical axis (up or downward flow) of the digester; and continuing flow of the liquor until the cellulosic material is removed from the digester.
In still a further aspect the present invention is a method of enhancing plug flow of pulping liquor introduced into a bottom of a batch digester for counter-current flow through a charge of cellulosic material to be delignified comprising the steps of: placing a flow directing device in the digester at a location proximate a bottom portion of a vertical portion of the digester, the flow directing device causing the pulping liquor to flow in a direction generally vertical to a center line of the digester; and containing flow of the liquor until the cellulosic material is delignified to a desired delignification.
BRIEF DESCRIPTION OF THE DRAWING
Referring to
According to the present invention three modifications can be made to a Displacement Batch Digester to mitigate the problems discussed above. The first is a liquor distribution channel placed at or above the bottom tangent (knuckle) line of the digester. The second is the use of liquor distribution channels placed on the bottom of the digester cone to distribute liquor and to help mitigate the formation of a large vortex during discharge or to inject liquors to entice plug flow. The third is to add a top shower head to keep the pulp on the top of the discharging mass diluted and to break up the flocs (which has been tested).
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Referring to
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Obstructions attached to the bottom conical section of the digester will dissipate the circular fluid energy and mitigate the creation of a large interfering vortex. Such devices can be in the form of anti-vortex vanes 60 shown schematically in
Having thus described my invention what is desired to be secured by Letters Patent of the United States is set forth in the appended claims which should be read without limitation.
Claims
1. A method of discharging delignified cellulosic material from a batch digester at the end of a cook cycle after removal of hot liquor from the digester comprising the steps of:
- introducing a shower of clean out liquor into said digester at a location above said material, said shower distributing said liquor substantially evenly across a cross-sectional area of said digester, and
- withdrawing said pulp from said digester while maintaining a flow of liquor sufficient to maintain consistency of said pulp until said digester is empty.
2. A method according to claim 1 including the step of placing means in said digester proximate a clean-out port of said digester to minimize or eliminate vortex flow of said delignified alkaline material as it discharges from said digester.
3. A method according to claim 2 including the step of installing anti-vortex vanes in said digester.
4. A method according to claim 2 including the step of installing anti-vortex vanes in said digester, said anti-vortex vanes including means to introduce liquor into said digester at any time during one of the charging, delignification, or discharging phase of the cooking cycle.
5. In a batch digester of the type having a generally cylindrical section and a bottom generally conical section said conical section having an outlet located proximate said apex of said conical section, the improvement comprising a shower device placed in an upper location of said cylindrical section of said digester said device adapted to distribute wash out liquor evenly across cellulosic material within said digester.
6. In a batch digester of the type having a generally cylindrical section and a bottom generally conical section said conical section having an outlet located proximate said apex of said conical section, the improvement comprising installing a distribution channel for liquid inside said digester at a location proximate a transition from said cylindrical section to said conical section said distribution channel installed adjacent an inner surface of said digester and having means to direct a plurality of streams upwardly and generally parallel to a vertical center line of said digester to enhance plug-flow of pulping liquors introduced into said digester during a liquor charging phase of a cooking cycle.
7. A batch digester according to claim 6 including means in said distribution channel to direct a plurality of streams in a downward direction to assist in discharging pulp during a discharge phase of a cooking cycle by one of diluting and/or directing pulp flow.
8. In a batch digester of the type having a generally cylindrical section and a bottom generally conical section said conical section having an outlet located proximate said apex of said conical section, the improvement comprising at least two distribution channels on the inner surface of said conical section said distribution channels containing means to direct streams of liquors generally upwardly and generally parallel to vertical center-line of said digester to enhance plug-flow of pulping liquors introduced into said digester.
9. A method for enhancing plug-flow of pulping liquors introduced into a batch digester for delignifying cellulosic materials comprising the steps of:
- introducing a plurality of streams of said pulping liquor proximate a bottom location of said digester, said streams oriented to flow in a direction generally parallel to a vertical axis of said digester; and
- continuing flow of said liquor until said cellulosic material is delignified to a desired consistency.
10. A method according to claim 9 including the step of varying the intensity of individual streams with the intensity being greater at the center line of said digester.
11. A method for enhancing plug flow of pulping liquor introduced into a bottom of a batch digester for counter-current flow through a charge of cellulosic material to be delignified comprising the steps of:
- placing a flow directing device in said digester at a location proximate s a bottom portion of a vertical portion of said digester, said flow directing device causing said pulping liquor to flow in a direction generally vertical to a center line of said digester; and
- continuing flow of said liquor until said cellulosic material is delignified to a desired consistency.
Type: Application
Filed: Jan 19, 2005
Publication Date: Jul 20, 2006
Inventor: Craig Bianchini (Allentown, PA)
Application Number: 11/039,663
International Classification: D21C 7/06 (20060101); D21C 7/08 (20060101);