WO1996034144A1

WO1996034144A1 - Feeding and discharge of comminuted fibrous material

Info

Publication number: WO1996034144A1
Application number: PCT/US1996/000907
Authority: WO
Inventors: J. Robert Prough; Jerry R. Johanson
Original assignee: Kamyr Inc
Current assignee: Kamyr Inc
Priority date: 1995-04-27
Filing date: 1996-01-18
Publication date: 1996-10-31
Anticipated expiration: 1997-10-27

Abstract

A discharge assembly (19) and method allow cellulosic material slurry even at a consistency of greater than 12 % to be fed to a pump mixer, or other mechanical device (33). A substantially vertical and cylindrical feed chute (20) is connected by a number of transitions (e.g. three substantially planar transitions) (27, 28, 29) to an open top trough (23). The transitions force the material toward a material outlet (30) which is at a portion of the chute and/or trough devoid of significant transitions so that the movement of material through the outlet and to the mechanical device is facilitated and promoted. The open top (21) of the chute may be fed by one or more single convergence outlet structures with side relief, or by other feed mechanisms.

Description

FEEDING AND DISCHARGE OF COMMINUTED FIBROUS MATERIAL

BACKGROUND AND SUMMARY OF THE rNVENTION

Modern pulp mills typically include various treatments of comminuted cellulose fibrous material in converting the cellulose material from its raw form to a form that can be either delivered to a paper machine or shipped as market pulp. The raw material may include any form of cellulose, such as comminuted hardwood or softwood chips, sawdust, recycled paper, bagasse, or any other conventional non-wood source of cellulosic fiber, for example, grasses or cornstalks. The treatment processes may include pulping processes, such as chemical pulping, e.g., the kraft (i.e. sulfate) process, the sulfite process, or the soda process; semi-chemical pulping; mechanical pulping; chemi-mechanical pulping, or any other form of pulping process that produces a comminuted cellulosic fibrous material. The cellulose material may also be treated in a washing or bleaching stage after being pulped.

Typically, different treatment stages are performed in different treatment vessels and the material must be transferred from one vessel to the next. This transfer is typically done under the force of gravity or by means of hydraulic pressure. This pressure is typically generated either by a pump or by introducing high pressure steam to the vessel. The pump may transfer material to a vessel or from a vessel. Pressure may also be generated in one vessel by means of a common conduit with a prior pressurized treatment vessel. One preferred method of transferring material is by pumping, or pumping combined with mixing. As seen in co-pending U.S. applications 08/401,503 filed March 10, 1995 and 08/366,581 filed December 30, 1994, material may be discharged from one vessel without the aid of an agitator or without the aid of vibration by employing a single-convergence outlet with side relief. Similar, though distinctly different, geometries may also be used as a means of feeding material to the inlet of a pump or mixer.

When designing a feed chute for feeding a pump with medium consistency pulp, there are three major aspects that must be considered. The first is that there is a limit to which a critical diameter may converge, such as by a DIAMONDBACK™ outlet, without promoting bridging of material across the convergence. The critical dimension can be determined by experimentation in a laboratory. For medium consistency pulp this limiting or critical diameter typically ranges between 38-48 inches, more specifically usually between 41 to 45 inches. With convergences below this diameter the pulp is more prone to bridge across the diameter. Therefore it is preferable to not reduce the vessel diameter below the critical diameter of 38 to 48 inches without adding dilution liquid. Secondly, medium consistenc}' pulp has the tendency to thicken or dewater when it encounters a converging transition. When a flow of medium consistency pulp encounters a tapered transition the flow of pulp is restricted but the flow of liquid within the pulp slurry is not restricted and continues to flow, for example, under the force of gravity. The free flow of Uquid from the restricted pulp mass can result in a local thickening of the pulp slurry, or any other dewaterable slurry. This thickening reduces the flowability of the slurry and causes pluggage and bridging. In conventional designs of convergent outlets of vessels this tendency to bridge is avoided by positioning a rotating agitator or outlet device within the convergence. In this way, the material is preventing from forming a stable bridge since any bridge that does form will be mechanically disrupted.

Similar to the critical diameter above, there exists a critical convergence angle - also determinable in the lab ~ below which a slurry will not tend to dewater and plug but flow without bridging. However, for a slurry of medium consistency pulp this convergence angle is so small, less than 15°, that it is impractical to build a transition long enough to accommodate it. The third aspect is that, typically, pumps and mixers used to discharge material from conventional chutes agitate a volume of pulp that projects from the inlet of the pump or mixer located in the chute. The volume agitated by the pump impeller is assumed to be conical in shape and project from the inlet of the pump. The conical shape reflects an assumed diminishing of the zone agitated by the impeller as the distance from the impeller increases. At some distance from the impeller the pulp is not agitated. In conventional designs pulp tends to stagnate in the areas of the chute beyond the influence of the agitation cone. The stagnant pulp then dewaters and forms unstable "bridges" around the circumference of the chute above the impeller. These unstable accumulations of higher consistency pulp then intermittently fall into the impeller causes temporary fluctuations in the load on the pump. This is experienced as intermittent surges in pump load and stock flow. The present invention minimizes the potential for these pump load and flow fluctuations while allowing higher consistency pulp, for example at consistencies up to and exceeding 15%, to be readily pumped.

According to one aspect of the present invention a feed and discharge assembly is provided comprising the following elements: A substantially vertical and cylindrical feed chute having a top and a bottom, material flowing through the chute toward the bottom. An open top trough disposed adjacent the bottom of the chute, and having first and second ends. A material outlet adjacent the second end of the trough. And, a plurality of converging side wall elements extending from the feed chute to the trough, providing funneling of material to the trough around substantially the entire periphery of the trough except for a portion adjacent the material outlet to relieve lateral compression of the material in the direction of the material outlet and thereby promote the movement of material being discharged through the outlet.

The assembly also preferably further comprises a mechanical device for acting on the material, connected to the outlet and adjacent the outlet. The mechanical device may comprise a fluidizing pump or mixer for pumping or mixing a comminuted cellulosic fibrous material slurry having a consistency of about 6-18%, or may comprise a wide variety of other structures such as pumps and mixers of all types, fluidizers, degassers, cleaners, latency removers, etc.

Typically the top of the chute is open, and the assembly further comprises a single convergence outlet structure with side relief disposed on top of the open chute top, and feeding material to it. Alternative feeding means can be provided, such as a single conical transition or chisel-shaped transition, or even mechanical feeding devices such as screw feeders.

In the preferred embodiment the plurality of converging side elements comprise first, second and third substantially planar transitions, the first and third transitions opposite each other, and the second transition therebetween, and the second transition adjacent the trough first end and opposite the trough second end and the material outlet. Typically each of the first, second, and third transitions makes an angle with respect to the substantially vertical and cylindrical feed chute of between about 15-45°, preferably about 25-35°, most preferably about 30° for the first and third transitions, and about 30-32° for the second transition. If desired, dilution liquid addition ports may be provided at the first end of the trough and in the chute just above the second transition.

According to another aspect of the present invention a method of feeding and discharging comminuted cellulosic material slurry having a consistency of greater than 12% (e.g. even 15% or more) is provided. The method comprises the following steps: (a) Causing the material to flow generally vertically downwardly in a first path having first and second opposite ends and first and second opposite sides, and a first cross-sectional area, (b) Funneling the material to a second path having a second cross-sectional area smaller than the cross-sectional area of the first path at the first end and the first and second sides, but not at the second end, so as to relieve lateral compression of the material at the second end so that the material flow toward the second end is promoted. And, (c) by using a mechanical device, withdrawing the slurry from the second end at the second path. The method may also comprise the further step of initially feeding slurry at a consistency of greater than 12% to the top of the first path from a single convergence outlet structure with side relief.

Step (c) may be practiced utilizing a fluidizing pump or fluidizing mixer connected to an outlet from the second path at the second end, and step (b) may be practiced by causing the material to funnel in the second path at an angle of between 15-45° at both sides and at the first end. There may also be the further step of introducing dilution liquid into the first and second paths adjacent the first end. --,-. ~.*_n** _AA PCT/US96/00907

WO 9634144

According to still another aspect of the present invention a feed and discharge assembly is provided comprising: An open top, open bottom, substantially vertical and cylindrical feed chute. A substantially semi-circular cross-section open top trough. First, 5 second, and third transitions extending from the open bottom of the feed chute to the trough open top, each of the transitions converging inwardly about 15-45° with respect to the substantially vertical and cylindrical feed chute, the first and third transitions opposite each other. A material outlet opposite the second transition and provided

10 in a portion of the feed chute and trough substantially devoid of converging transitions. And, a mechanical device connected to the material outlet for withdrawing material therethrough.

It is the primary object of the present invention to provide a method and assembly for the effective feeding of even 12% or greater

15 consistency, comminuted cellulosic fibrous material slurry, particularly to a mechanical device such as a pump or mixer, without bridging and other adverse consequences. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.

20

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a top perspective view of an exemplary prior art assembly for feeding medium consistency stock to a pump;

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FIGURE 2 is a bottom plan view of an exemplary assembly according to the present invention;

FIGURES 3-5 are side, second end, and first end views of the 30 assembly of FIGURE 2; FIGURES 6-8 are bottom plan, side, and second end, views respectively of a second embodiment of an assembly according to the present invention; and

FIGURES 9-11 are bottom plan, side and second end, views respectively of a third embodiment of an assembly according to the present invention.

DETAILED DESCRD7TION OF THE DRAWINGS

FIGURE 1 shows a typical feed chute 10 for feeding medium consistency wood pulp, i.e., pulp of 6-18% consistency, to the inlet 11 of a pump or mixer 12. The incoming comminuted fibrous material, or stock, flows from a previous treatment stage, e.g., washing, bleaching, etc., through the cylindrical tube or chute 10, under the force of gravity or hydraulic pressure, to the inlet 11 to the pump or mixer 12. One or more chemical reagents, e.g., caustic or peroxide, may be added to the stock via inlet(s) 13 before or in the pump or mixer 12, if desired. The stock is discharged from the device 12 to a subsequent treatment stage, for example to a retention vessel, to another bleaching stage or to storage, via discharge conduit 14.

The device 12 used in such an application may be an MC® pump or mixer, an Ahlmix™ mixer or an AMZ mixer, all sold by Ahlstrom Kamyr, Inc. of Glens Falls, New York. These devices 12 are typically driven by an electric motor 16 and may include a vacuum pump for degassing, or may have an internal degassing system incorporated into the impeller of the device.

Although, the system 15 shown in FIGURE 1 provides an effective means for transporting or mixing chemicals into pulp, and many such installations exist throughout the world, this typical system and others like it are usually in practical terms limited to transporting stock at consistencies below about 12%. If the consistency of the stock entering the feed chute 10 approaches or exceeds about 12%, the stock flow may be hampered by the formation of rigid "bridges" of stock across the width of the feed chute 10. These bridges may prevent the uniform flow of material through the chute 10 and can cause considerable downtime to clear the chute 10. In fact, dilution liquor is often added to the feed chute, by means of dilution nozzles (not shown), to ensure that the consistency is low enough to ensure uniform flow without plugging or bridging.

FIGURES 2-5 illustrate one embodiment of the invention that addresses this limitation due to consistency, i.e. is usable with stock having a consistency of 12% or more, e.g. 12-18% (although it is also usable with lower consistency stock too). FIGURES 2-5 show an assembly 19 including a substantially vertical and cylindrical feed chute 20 having an open top 21 and a bottom 22. Material (e.g. cellulose slurry at a consistency of about 6- 18%, preferably 12-18%) flows downwardly in chute 20 through the open top 21 toward the bottom 22. At the bottom 22 of the chute 20 is an open top trough 23, e.g. one that is semi-circular in cross-section as shown in FIGURES 4 and 5. The trough 23 is preferably completely open in the interior thereof (i.e. contains no feed screws or the like). The trough 23 has a first end 24, and an opposite second end 25. The open top of trough 23 is connected to the chute 20 by a plurality of converging side wall elements extending from chute 20 to trough 23. While in the preferred embodiment illustrated in FIGURES 2-5 three such elements are shown, another number may be provided. Preferably first 27, second 28, and third 29 substantially planar transitions are provided as the converging side wall elements.

As seen in FIGURES 4 and 5, the transitions 27, 29 each make an angle α with respect to the chute 20 (typically the angle α is with respect to the vertical) of from 15-45°, preferably 25-35°, and most preferably about 30°. The transition 28 makes an angle α with respect to the chute 20 (e.g. vertical) which is also from about 15-45°, preferably 25-35°, most preferably about 30-32°.

The transition 28 is opposite the second end 25 of the trough 23, and adjacent first end 24 thereof. The portion of chute 20 adjacent trough end 25 does not have a significant convergence, but rather is essentially a continuation of chute 20, and therefore relieves compression of the material thereat, in the direction of material outlet 30. FIGURES 2 and 4 in particular clearly show the continuation portion 31 of chute 20 which provides relief of lateral compression.

The material outlet 30 is connected to a mechanical device for acting on the material, e.g. the device 33 seen in FIGURE 3, adjacent outlet 30 and connected thereto. The device 33 preferably is a fluidizing pump or mixer (e.g. an MC® pump or mixer as sold by Ahlstrom Kamyr, Inc., Glens Falls, New York). However device 33 may also comprise other types of pumps or mixers, a fluidizer, a degasser, a cleaner, a latency remover, or like device. The actual connection of outlet 30 to device 33 may be as conventional, such as illustrated in FIGURE 1.

Opposite the outlet 30 one or more dilution liquid inlets may be provided, such as inlet 35 at the end 24 of trough 23, and inlet 36 just above the transition 28 in chute 20, if the interior dimensions of the components are such that dilution liquid is necessary or desirable. The construction of the invention, however, minimizes the need for dilution liquid for any given dimensions.

The open top 21 of chute 20 may be fed by any form of conventional feed arrangement, such as — shown schematically at 38 in FIGURE 3 ~ a simple conical transition or chisel-shaped transition; or by a discharge device from a vessel (such as a scraper), or a feed screw, or by any other mechanism that can be used to transfer material from a previous stage to the chute 20. In the preferred embodiment, however, a single-convergence outlet with side relief, or a double such arrangement, is utilized, as seen in FIGURES 6-11.

In operation of the assembly 19 of FIGURES 2-5, comminuted cellulosic material slurry having a consistency of about 6-18%, e.g. greater than 12%, flows generally vertically downwardly in a first path defined by chute 20. The material is then funneled (by transitions 27-29) at one end and two sides of the first path to a second path, defined by trough 23 and having a smaller cross- sectional area than the first path defined by chute 20. Because there is no transition at portion 31, lateral compression is relieved, and material flow toward the outlet 30 (and device 33) is promoted and facilitated. Then, by using device 33 (e.g. the centrifugal action of a pump impeller) the material slurry is withdrawn from outlet 30.

The embodiment shown in FIGURES 6-8 is the same as that of FIGURES 2-5 except that a single-convergence outlet (or conduit) structure 40 is connected to the open top 21 of the chute 20. The same structures in the FIGURES 2-5 and 6-8 embodiments are shown by the same reference numerals.

The structure 40 preferably is such as shown in U.S. patent 4,958,741 (the disclosure of which is hereby incorporated by reference herein), and such as sold by J.R. Johanson, Inc. of San Luis Obispo, California, and Ahlstrom Kamyr, Inc. of Glens Falls, New York, under the trademark DIAMONDBACK, and also as generally shown in said co-pending applications 08/401,503 and 08/366,581.

The embodiment of FIGURES 9-11 is the same as that of FIGURES 6-8 except that a "Double Diamondback" feed structure 42 is provided, comprising two stacked single-convergence outlets with side relief.

It will thus be seen that the invention comprises an advantageous method and assembly in which a pump, or similar mechanical device, is fed in such a way that much higher consistency pulp (material) than conventionally can be handled without bridging, and without need for dilution liquid, or with reduced need for dilution liquid.

While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment thereof it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent methods and assemblies.

Claims

WHAT IS CLAIMED IS:

1. A feed and discharge assembly comprising: a substantially vertical and cylindrical feed chute having a top and a bottom, material flowing through said chute toward said bottom; an open top trough disposed adjacent said bottom of said chute, and having first and second ends; a material outlet adjacent said second end of said trough; and a plurality of converging side wall elements extending from said feed chute to said trough, providing funneUng of material to said trough around substantially the entire periphery of said trough except for a portion adjacent said material outlet to relieve lateral compression of the material in the direction of said material outlet and thereby promote the movement of material being discharged through said outlet.

2. An assembly as recited in claim 1 further comprising a mechanical device for acting on the material, said mechanical device connected to said outlet and being adjacent said outlet.

3. An assembly as recited in claim 2 wherein said mechanical device comprises a fluidizing pump or mixer for pumping or mixing a comminuted cellulosic fibrous material slurry having a consistency of about 6-18%.

4. An assembly as recited in claim 2 wherein said top of said chute is open; and further comprising a single-convergence outlet structure with side relief disposed on top of said chute open top and feeding material thereto.

5. An assembly as recited in claim 2 wherein said top of said chute is open; and further comprising means for feeding material to said open top.

6. An assembly as recited in claim 5 wherein said feeding means comprises a single conical transition or chisel-shaped transition.

7. An assembly as recited in claim 2 wherein said plurality of converging side elements comprise first, second and third substantially planar transitions, said first and third transitions opposite each other, and said second transition therebetween, and said second transition adjacent said trough first end and opposite said trough second end and said material outlet.

8. An assembly as recited in claim 7 wherein said first and third transitions each make an angle with respect to said substantially vertical and cylindrical feed chute of between about 15- 45°.

9. An assembly as recited in claim 7 wherein said first, second, and third transitions each make an angle with respect to said substantially vertical and cylindrical feed chute of between about 25- 35°.

10. An assembly as recited in claim 7 further comprising dilution liquid addition ports provided at said first end of said trough and in said chute just above said second transition.

11. An assembly as recited in claim 1 wherein said plurality of converging side elements comprise first, second and third substantially planar transitions, said first and third transitions opposite each other, and said second transition therebetween, and said second transition adjacent said trough first end and opposite said trough second end and said material outlet.

12. An assembly as recited in claim 11 wherein said first, second, and third transitions each make an angle with respect to said substantially vertical and cylindrical feed chute of between about 25- 35°.

13. An assembly as recited in claim 3 wherein said plurality of converging side elements comprise first, second and third substantially planar transitions, said first and third transitions opposite each other, and said second transition therebetween, and said second transition adjacent said trough first end and opposite said trough second end and said material outlet.

14. An assembly as recited in claim 11 wherein said second transition makes an angle of about 15-45° with respect to the vertical.

15. A method of feeding and discharging comminuted' cellulosic material slurry having a consistency of greater than 12%, comprising the steps of: (a) causing the material to flow generally vertically downwardly in a first path having first and second opposite ends and first and second opposite sides, and a first cross-sectional area; 144 PCI7US96/00907

15

(b) funneling the material to a second path having a second cross-sectional area smaller than the cross-sectional area of the first path at the first end and the first and second sides, but not at the second end, so as to reUeve lateral compression of the material at the second end so that the material flow toward the second end is promoted; and (c) by using a mechanical device, withdrawing the slurry from the second end at the second path.

16. A method as recited in claim 15 comprising the further step of initially feeding slurry at a consistency of greater than 12% to the top of the first path from a single convergence outlet structure with side relief.

17. A method as recited in claim 15 wherein step (c) is practiced using a fluidizing pump or fluidizing mixer connected to an outlet from the second path at the second end.

18. A method as recited in claim 15 wherein step (b) is practiced by causing the material to funnel in the second path at an angle of between 15-45° at both sides and at the first end.

19. A method as recited in claim 15 comprising the further step of introducing dilution liquid into the first and second paths adjacent the first end.

20. A feed and discharge assembly comprising: an open top, open bottom, substantially vertical and cylindrical feed chute; a substantially semi-circular cross-section open top trough; first, second, and third transitions extending from said open bottom of said feed chute to said trough open top, each of said transitions converging inwardly about 15-45° with respect to said substantially vertical and cylindrical feed chute, said first and third transitions opposite each other; a material outlet opposite said second transition and provided in a portion of said feed chute and trough substantially devoid of converging transitions; and a mechanical device connected to said material outlet for withdrawing material therethrough.