EP2295631B1

EP2295631B1 - Pressure diffuser internal guide

Info

Publication number: EP2295631B1
Application number: EP20100171422
Authority: EP
Inventors: John Weston; Grant Bechard
Original assignee: Andritz Technology and Asset Management GmbH
Current assignee: Andritz Technology and Asset Management GmbH
Priority date: 2009-08-03
Filing date: 2010-07-30
Publication date: 2012-10-24
Anticipated expiration: 2030-07-30
Also published as: EP2295631A1; JP2011038235A; BRPI1002956A2; JP5757700B2

Description

RELATED APPLICATION

This application claims priority to U.S. Provisional App. No. 61/230,766, filed on August 3, 2009 , the entirety of which is incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to pressure diffusers for use in a pulp and/or paper-making process.
Pressure diffusers are known in the industry (such as, for example, pressure diffusers described in U.S. Patent Nos. 5,020,178 ; 5,444,884 ; and 5,567,279 ). In a pressure diffuser, a slide (or catcher) is located between the pulp screen and the wash collection space in the center of the diffuser. In the space between the pulp screen and the wash collection, a mass of medium consistency pulp tends to gather.
Figure 1 illustrates a partial cross-sectional view of a conventional pressure diffuser 100, including the slide 108. The conventional pressure diffuser includes a shaft 104 attached to hydraulic cylinder(s) (not shown). The hydraulic cylinder(s) cause the shaft to travel in a periodic and/or predefined manner. Typically 3 to 6 support arms 106 (also known as spider arms) attach the shaft 104 to slide 108. Slide 108, in turn, is attached to screen 124 via outer edge surface 122. As the hydraulic cylinders move, the glide travels laterally as indicated by arrows 126.
Also illustrated is wash chamber 102, which supplies wash liquid (e.g., water) through wall 116. This wash liquid washes the slurry of refined cellulosic material 120 and pushes it against screen 124, as liquid enters space 132 between screen 124 and outer wall 128. The screen 124 is traditionally moved via the hydraulic cylinder(s) to induce a countercurrent wash to prevent or inhibit clogging of the pores in the screen.
Traditionally, a 15.24-cm (6-inch) thick slide mechanism is used to move the mass of pulp, referred to as the pulp bed, vertically through the length of the diffuser about every 6 seconds. The thickness of slide 108 is illustrated by distance 110. Because the distance 110 is so large, the distance 118 between inner edge surface 114 of glide 108 and wall 116 is small. The sealing ring 112 in sealing ring mechanism 130 prevents wash liquid from exiting at any portion except through screen 124.
As illustrated, slide 108 is in the "down" position and can be raised such that the lower portion of inner edge surface 114 is closer to sealing ring 112. Because the slide 108 is 15.24 cm (6 inches) thick, it is believed that the bed of pulp may only be about 15.24 cm (6 inches) thick. (The remaining space is believed to be largely wash water.) This movement of pulp allows for continuous flow of pulp through the diffuser while also allowing the movement of wash filtrate through the pulp into the filtrate collection chamber (through space 132).
In prior art applications, this 15.24 cm (6 inches) bed was believed to be necessary to achieve adequate and/or thorough washing of the fibers. It was generally believed that a smaller bed of fibers would not permit adequate throughput (e.g., tonnage processed), not allow adequate washing of the fibers in the diffuser, or both.
In addition, the prior art generally cannot be operated at a higher frequency. Each stroke requires a full "catch" of fibers. Increasing the speed of the slide would not increase throughput because the catcher would not fill with each stroke. An increase in stroke frequency would plug the machine and have very poor washing efficiency. The thickness of the bed below 15.24 cm (6 inches) is feared to produce inconsistencies in the bed throughout the length of the bed. These inconsistencies can cause operating concerns such as plugging the machine and poor washing efficiencies. These poor operating conditions, if realized would greatly reduce the ability of the mill to produce acceptable pulp and are to be avoided at all times. As the need to produce a greater volume of acceptable pulp for existing equipment has increased, solutions to prevent plugging of the equipment and provide sufficient washing capacity are sought.
Accordingly, there is an advantage to retrofit a pressure diffuser with a smaller slide in accordance with an aspect of the present invention. This smaller slide permits increased volumetric flow of fibers through the pressure diffuser without a decrease in the efficacy of washing.
There is also an advantage to retrofit existing equipment with a smaller slide, such that relatively smaller beds of fibers may exist within the diffuser.
There is also an advantage to fill a catcher with fibers on each stroke, such that stroke frequency may be increased and throughput may be increased.

BRIEF DESCRIPTION OF THE INVENTION

In an aspect, the present invention generally relates to increasing the production capacity of an existing pressure diffuser. This modification allows an increased flow of pulp through the vessel (i.e., increased throughput) without causing wash filtrate flow problems. The present invention generally relates to a previously unknown thickness.
In particular, the slide thickness is reduced from 15.24 cm (6 inches) to a smaller thickness. This heretofore unknown reduction in thickness causes a thinner pulp bed to be produced. This thinner pulp bed continues to be a medium consistency pulp material. And because of the thinner bed, the new slide allows movement of the pulp through the diffuser much faster, e.g., up to four times as fast.
By increasing the speed of the pulp bed through the diffuser and reducing the time to move the pulp through the diffuser, an increased flow of pulp through the diffuser can be accomplished (for example, if the cycle time is currently 6 seconds, as the cycle time is reduced to 3 seconds, the pulp production is increased without losing washing ability). Additionally, the thinner pulp bed enables more wash water (also known as wash filtrate) to move through the bed with the same pressure drop. This increased flowrate allows for an increase in production rate, e.g., about double the previous production rate.
In another aspect, the present invention relates to bed formation. Inconsistencies in the bed thickness can cause operational problems of the pressure diffuser. The thinner pulp bed allows the inconsistencies in the pulp bed (e.g., inconsistencies in the thickness of the bed can cause wash liquid to move across the thinner spots more easily and reduce the cleaning of the bed) to self correct or self heal by having more wash liquid, which carries some fibers, go through the thinner areas filling the thinner areas with fiber and thereby making the bed more uniform in thickness. As the bed becomes more uniform in thickness, there is more uniform displacement of the liquid in the cellulosic material giving a better washing efficiency.
In an aspect, there is a pressure diffuser for washing pulp comprising: a wash chamber that supplies a wash liquid through a wall, wherein the wash chamber is positioned within the center of the pressure diffuser, such that the wash liquid travels radially out towards an outer wall of the pressure diffuser; a screen between the outer wall of the pressure diffuser and the wash chamber defining a wash space in which pulp is washed, such that the wash liquid is supplied from the wash chamber and travels through the wash space and through the screen for removal from the pressure diffuser, such that the pulp is retained in the wash space by the screen; a hydraulic cylinder attached to a slide that is attached to the screen such that the screen can be moved in a direction substantially parallel to the outer wall of the pressure diffuser during operation of the pressure diffuser, wherein the slide has a thickness of 5.08 cm (2 inches) to 13.97 cm (5.5 inches) as measured in a radial direction between the wall of the wash chamber and the outer wall of the pressure diffuser. More preferably, the slide has a thickness of 6.35 cm (2.5 inches) to 12.7 cm (5 inches). This higher value of 6.35 cm (2.5 inches) allows for an even more consistently formed bed and the lower value of 12.7 cm (5 inches) produces an even better throughput of wash water with substantially the same pressure drop.
In another aspect, there is a method of retrofitting a pressure diffuser, the method comprising the steps of: removing from the pressure diffuser an existing slide that is coupled to a wash screen, wherein the slide has a thickness of 15.24 cm (6 inches); and replacing the existing slide with a smaller slide having a thickness of between 5.08 cm (2 inches) and 13.97 cm (5.5 inches), more preferably of between 6.35 cm (2.5 inches) and 12.7 cm (5 inches).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a partial cross-sectional view of a conventional pressure diffuser.
FIGURE 2 is a partial cross-sectional view of an embodiment of a pressure diffuser with a smaller slide in accordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 2 illustrates a partial cross-sectional view of a pressure diffuser 200 including the slide 208. The pressure diffuser includes a shaft 204 attached to hydraulic cylinder(s) (not shown). The hydraulic cylinder(s) cause the shaft to travel in a periodic and/or predefined manner. Due to the decreased size of the slide width, the period of travel may be relatively smaller compared to conventional slides.
Typically 3 to 6 support arms 206 attach the shaft 204 to slide 208. Slide 208, in turn, is attached to screen 224 via outer edge surface 222. As the hydraulic cylinders move, the glide travels laterally as indicated by arrows 226.
The term "attach" refers to any mechanism or technique known to those skilled in the art for securing, such as, for example, welding, bolting, etc. Furthermore, the materials used may be any suitable material known to those skilled in the art of pulping and/or papermaking, such as, for example, steel alloys.
Also illustrated is wash chamber 202, which supplies wash liquid (e.g., water) through wall 216. This wash liquid washes the slurry of refined cellulosic material 220 and pushes it against screen 224, as liquid enters space 232 between screen 224 and outer wall 228. The screen 224 is moved via the hydraulic cylinder(s) to induce a countercurrent wash to prevent or inhibit clogging of the pores in the screen.
Unlike the prior art (which uses a 15.24 cm (6 inches) thick slide), the present invention uses a 5.08 cm (2 inches) to 13.97 cm (5.5 inches) and, more preferably, a 6.35 cm (2.5 inches) to 12.7 cm (5 inches) slide to move the mass of pulp vertically through the length of the diffuser. This smaller slide enables a faster frequency of strokes - e.g., every 2 to 3 seconds versus every 6 seconds. The thickness of slide 208 is illustrated by distance 210. The sealing ring 212 in sealing ring mechanism 230 prevents wash liquid from exiting at any portion except through screen 224. The travel of the slide 208 and screen 224 can be about 1/2 meter.
As illustrated, slide 208 is in the "down" position and can be raised such that the lower portion of inner edge surface is closer to sealing ring 212. Because the slide 208 is about 5.08 cm (2 inches) to 13.97 cm (5.5 inches) thick, it is believed that the bed of pulp may only be about 5.08 cm (2 inches) to 13.97 cm (5.5 inches) thick. The remaining space is believed to be largely wash water. The thinner bed of pulp facilitates an increase in the volumetric flowrate of pulp through the apparatus, e.g., because the smaller thickness of fibers require less time for washing.
In certain embodiments, existing pressure diffusers may be modified with smaller slides (also known as spider arms). In this aspect, this retrofit may be applied to any number of existing configurations. For example existing pressure diffusers may have wash liquid supplied from the outside and removed from the inside or may have wash liquid supplied from the inside and liquid removed from the outside (e.g., as illustrated in Figures 1 & 2). Furthermore, the pressure diffuser may supply pulp from a refiner or digester at the bottom of the pressure diffuser or at the top of the pressure diffuser. That is, any number of vessels may be retrofitted within certain embodiments of the present invention. For example, certain embodiments may be applicable to pressure diffusers having screens of 7 to 10 meters tall and/or screens having surface areas of 30m² to 120m².
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

Claims

A pressure diffuser for washing pulp comprising:
a wash chamber that supplies a wash liquid through a wall, wherein the wash chamber is positioned within the center of the pressure diffuser, such that the wash liquid travels radially out towards an outer wall of the pressure diffuser, or wherein the wash chamber is positioned at the outer side of the pressure diffuser such that the wash liquid travels radially in towards an inner wall of the pressure diffuser, respectively;

a screen between the outer wall of the pressure diffuser or the inner wall of the pressure diffuser, respectively, and the wash chamber defining a wash space in which pulp is washed, such that the wash liquid is supplied from the wash chamber and travels through the wash space and through the screen for removal from the pressure diffuser, such that the pulp is retained in the wash space by the screen;

a hydraulic cylinder attached to a slide that is attached to the screen such that the screen can be moved in a direction substantially parallel to the outer wall or the inner wall, respectively, of the pressure diffuser during operation of the pressure diffuser, wherein the slide has a thickness of 5.08 cm (2 inches) to 13.97 cm (5.5 inches) as measured in a radial direction between the wall of the wash chamber and the outer wall or inner wall, respectively, of the pressure diffuser.
A pressure diffuser according to claim 1, wherein the slide has a thickness of 6.35 cm (2.5 inches) to 12.7 cm (5 inches).
A method of retrofitting a pressure diffuser, the method comprising the steps of:
removing from the pressure diffuser an existing slide that is coupled to a wash screen, wherein the slide has a thickness of 15.24 cm (6 inches); and

replacing the existing slide with a smaller slide having a thickness of between 5.08 cm (2 inches) and 13.97 cm (5.5 inches), preferably 6.35 cm (2.5 inches) to 12.7 cm (5 inches).