WO2019190375A1

WO2019190375A1 - Diverter for a feed out arrangement for a digester and feed out arrangement comprising such a diverter

Info

Publication number: WO2019190375A1
Application number: PCT/SE2019/050230
Authority: WO
Inventors: Jonas SAETHERÅSEN; Roger JANSSON; Roland Bengtsson
Original assignee: Valmet Ab
Priority date: 2018-03-29
Filing date: 2019-03-14
Publication date: 2019-10-03
Also published as: SE1850365A1; SE2050951A1

Abstract

The present invention relates to a diverter for a feed-out arrangement for a pulp treatment vessel such as a digester or an impregnation vessel, wherein the diverter comprises a body having an upper end and a lower end, the lower end having a larger radial extension than the upper end, and also comprising at least one blade extending at least partly in a radial direction, said blade being arranged at the lower end of the body. The invention also comprises a feed-out arrangement comprising such a diverter.

Description

DIVERTER FOR A FEED OUT ARRANGEMENT FOR A DIGESTER AND FEED OUT ARRANGEMENT COMPRISING SUCH A DIVERTER

TECHNICAL FIELD

The present invention relates to a diverter for a feed-out arrangement for a digester, wherein the diverter comprises a body having an upper end and a lower end, the lower end having a larger radial extension than the upper end. The invention also relates to a feed-out arrangement for a digester provided with such a diverter. The digester is generally a treatment vessel for the treatment of cellulosic material in a continuous pulp treatment process.

BACKGROUND

During a continuous treatment process such as a pulping process, cellulosic materials are generally subjected to treatment in a treatment vessel such as an impregnation vessel and/or a continuous digester. Often, the cellulosic materials are introduced through an opening at the top of the vessel and proceeds downwards during treatment before being discharged at a bottom end of the impregnation vessel or digester. The discharge opening is generally located in the center of the bottom end, and a feed-out arrangement is arranged above the discharge opening in order to discharge the material in a suitable way.

There are several problems associated with the discharge of material, primarily that the cellulosic material is compacted during its stay in the impregnation vessel or digester and that channels are created in the material, which makes the core pulp flow quicker through the vessel than pulp passing down at the digester wall and being subjected to friction at the wall. This leads to deteriorated or uneven pulp quality.

The feed-out arrangement generally comprises a central diverter placed directly above the discharge opening to divert the cellulosic material towards the side walls of the vessel or digester, together with a rotating scraper arrangement for improving the mixing of the cellulosic material and dilution liquor, and for preventing the formation of channels at the discharge opening.

Due to the compacting of the cellulosic material, the feed-out arrangement is subjected to high pressure and the rotation of the scraper is interfered and hindered, potentially damaging both the scraper itself and the motor generating its rotation.

There is therefore a need for an improved diverter and feed-out arrangement for a treatment vessel such as an impregnation vessel or a continuous digester that can overcome these drawbacks.

SUMMARY OF THE INVENTION

The object of the present invention is to eliminate or at least to minimize the problems mentioned above. This is achieved through a diverter and a feed-out arrangement comprising such a diverter according to the appended independent claims. Particularly advantageous features of the invention are set out in the dependent claims. The present invention has a number of benefits and advantages due to its configuration and operation. The diverter comprises a body having an upper end and a lower end, the lower end having a larger radial extension than the upper end, and also comprising at least one blade extending at least partly in a radial direction, said blade being arranged at the lower end of the body. Thereby, an efficient spreading out of the cellulosic material in a radial direction is achieved, preventing the compacting of material at the discharge opening and creating an improved mixing of material before discharge. Preferably, the diverter comprises at least two blades, more preferably at least three blades, in order to improve the distribution or spreading of the material. A purpose of said at least one blade is thus to prevent that a“dead” or stationary zone is created at a lower, radially outer end of the body of the diverter, which could be the case without this at least one blade.

The diverter according to the present invention is adapted to be arranged in a vessel, e.g. a digester or an impregnation vessel, which has an outlet located in the center of the lower end of the vessel. To prevent canalization, i.e. that pulp flows in canals in the center of the vessel rather than being spread out over the whole cross-section of the vessel, the diverter has preferably a cross-sectional area, as seen from the above, which covers that the outlet. Thus, in other words, the cross-sectional area of the diverter is equal to or larger than the cross- sectional area of the centrally located outlet of the digester or impregnation vessel. The cross- sectional areas referred to herein are the circular areas a person would see when viewing the bottom area of the vessel from above (with other parts, such as scrapers and cap, removed).

According to one aspect of the invention, the cross-sectional area of the diverter is equal to or less than twenty percent (20 %) of the cross-sectional area of the lower end of the digester or impregnation vessel, to facilitate and promote efficient use of the lower end space of the vessel in question, such that the pulp can leave the vessel via the centrally located outlet. If the cross-sectional area of the diverter would be excessively large, e.g. larger than twenty percent (20 %) of the cross-sectional area of the lower end of the vessel, the diverter would effectively form a new floor in the vessel, which would counteract the purpose of the invention. Here, the cross-sectional area is the circular area of lower end of the vessel in question as measured at a level above the onset of any cupped gable end. Thus, when viewed from above, the cross-sectional area of the diverter is simply equal to or less than twenty percent of the cross-sectional area of the digester.

According to one aspect of the invention, the at least one blade extends beyond a circumference of the lower end of the body. This also improves the spreading or distribution of material and provides a mixing of the material beyond the circumference of the diverter.

According to another aspect of the invention, the body comprises at least one opening extending through the lower end. Thereby, small quantities of cellulosic material can also be allowed to proceed through the diverter body and be guided to the discharge opening. This is advantageous since it creates an improved flow of material outwards in the radial direction and generally downwards towards the discharge opening, which improves the discharge from the impregnation vessel or digester. According to yet another aspect of the invention, the at least one blade extends at a blade angle relative to the radial direction, said blade angle being 45-135°, preferably 70-120°, more preferably 100-120°. Thereby, the distribution and spreading of material can be achieved in an efficient way and with a low resulting load on the diverter. By adjusting the blade angle, the torque on the diverter can be adjusted and thereby also the force with which the diverter spreads the cellulosic material in the radial direction.

According to a further aspect of the invention, the blade or blades is/are mounted on the body, preferably extending along a surface of the body. Thereby, the cellulosic material is spread in an even more efficient way. Due to the upper part of the diverter body having a smaller circumference than the lower part of the diverter body, a cone-like shape is created that also serves to generate a radial spreading of material as the material proceeds downwards in the impregnation vessel or digester.

According to another aspect of the invention, the blade or blades is/are arranged on a separate part. Thereby, a conventional diverter and feed-out arrangement can be modified by the arrangement of the separate part together with a conventional diverter so that the radial spreading or distribution of cellulosic material is achieved without further structural modifications to a feed-out arrangement according to the prior art.

According to yet another aspect of the invention, the at least one blade is arranged so that a blade edge extends away from the body. This also serves to improve the efficiency of the spreading, since the cellulosic material will be transported on either side of the blade edge and be spread out by the blade as the diverter rotates.

According to the invention there is also provided a feed-out arrangement comprising a diverter as disclosed above. The feed out arrangement further comprise:

a revolving shaft driven by a motor, the shaft having an upper end,

a diverter mounted on the upper end of the shaft, and

a scraper assembly comprising at least one scraper arm, the scraper assembly mounted on a circumference of the shaft and the at least one scraper arm extending at least partly in a radial direction.

By the diverter cooperating with the inventive feed-out arrangement, significant improvements to the prior art can be achieved, especially in the decreasing of compaction in the cellulosic material and the channeling that prevents treatment liquor from penetrating the material to perform the treatment in the impregnation vessel or digester. The distribution or spreading of the cellulosic material according to the present invention also serves to decrease the torque on the scraper and thereby to prevent damages to the scraper and the motor and to decrease the power required for operating the feed out arrangement.

According to an aspect of the invention, the at least one scraper arm has an outer end and the diverter is arranged so that the at least one blade is lower than the outer end of the scraper arm. Thereby, any compaction of material will take place at a lower point than the outer end of the scraper arm, efficiently decreasing the torque on the scraper arm. According to another aspect of the invention, the at least one blade is arranged on a separate part, said separate part being mounted on the shaft underneath the diverter. This is advantageous in allowing repair and replacement of the diverter and the separate part independent of each other and also in the versatility in the feed out arrangement, where dimensions of the diverter and of the separate part can be selected to provide an optimal spreading and/or distribution of material for any given impregnation vessel or digester depending on its size.

Many additional benefits and advantages of the invention will become readily apparent to the person skilled in the art in view of the detailed description below.

DRAWINGS

The invention will now be described in more detail with reference to the appended drawings, wherein:

Fig. 1 discloses a feed out arrangement according to the prior art;

Figs. 2a, b, c disclose a diverter according to a preferred embodiment of the present invention in a perspective view, planar view and top view, respectively;

Fig. 3 discloses an alternative embodiment of the diverter having the blades arranged on a separate part; and

Fig. 4 discloses a feed out arrangement according to the invention.

DETAILED DESCRIPTION

Fig. 1 discloses a conventional design of a bottom portion of a continuous digester but may also be applicable in impregnation vessels or other treatment vessels used for treatment of lignocellulosic materials. A feed-out arrangement comprising a diverter according to the prior art is disclosed having a revolving shaft 1 driven by a motor M, onto which shaft 1 a diverter 3 having an essentially cone-like shape is mounted. The arrangement further comprises a bottom scraper having at least two scraper arms 2a, 2b, onto which are also attached scraper blades 4. The bottom of the digester is a cupped gable end, and the scraper arms 2a, 2b are arranged to sweep over the inside of the gable end and push the treated, e.g. cooked, cellulosic material, in the following referred to as pulp, towards a central outlet 20 disposed in a lower end of the digester. Typically, the scraper arms 2a, 2b are angled at a scraper angle a in relation to a horizontal plane, the scraper angle a being in the range of 5°-30° so that the scraper arms 2a, 2b are tilted slightly upwards in the digester.

As in most digesters, the bottom of the digester is also designed to implement a final wash zone, where a cleaner wash liquid is introduced into the bottom of the digester through several wash dilution nozzles, here shown as vertical nozzles VN and horizontal nozzles HN. A vertical counter-current flow, as indicated with black flow arrows, of this wash liquid is established up to a wash screen WS. As a complement to this axial displacement wash, a radial displacement wash is also established by adding wash liquid through a central pipe CP, whose outlet can be located slightly below or above the wash screen WS. The wash screen WS is a slotted screen plate or preferably a stave/bar screen that withdraws used or spent wash liquid and collects it in a wash extraction chamber WEC, which in turn is emptied into a wash header WH before being withdrawn from the digester.

Typically, the total retention time for the pulp in this wash zone is about 10-30 minutes, but the retention time could also be lowered to about 5 minutes during production increases or increased during production decreases to about 45 minutes. The power requirements for driving this kind of feed-out arrangement with diverter and bottom scraper have been shown to be quite large, since the scraper arms 2a, 2b need to extend to a wall of the digester, subjecting the arms to higher torque than with shorter arms.

Figs. 2a, 2b and 2c disclose a diverter 3 according to a preferred embodiment of the present invention, having a body 33 with an upper end 31 and a lower end 32. The lower end 32 has a larger radial extension than the upper end 31, wherein a radial direction is defined as a direction outwards from an axis A extending through the body 33 from the upper end 31 to the lower end 32 (see Fig. 2b), i.e. a direction along a radial axis B (see Fig. 2c). In this embodiment, at least a part of the body 33 is shaped like a cone but other shapes are also possible within the scope of the invention. At the lower end 32, at least one blade 5 extends at least partly in the radial direction. In this preferred embodiment, the diverter 3 comprises five blades 5 that are mounted on the body 3 and rest against the lower end 32, which is shaped like a plate. In other embodiments, the blade or blades 5 can extend along the body 33 towards the lower end 32 or can be arranged at the lower end 32 without resting against a surface of the lower end 32. It is advantageous that the diverter 3 comprises at least two blades 5, preferably at least three blades 5, but a single blade 5 would also be able to achieve the technical effect of spreading the pulp from the diverter. The single blade 5 can in such an embodiment be arranged in a spiral shape around the body 33.

The blades 5 preferably extend beyond a circumference of the lower end 32 of the body 33, in order to improve the radial movement of the pulp outwards from the lower end 32 of the diverter 3. The blades 5 are also preferably arranged at a blade angle b in relation to the radial direction along the radial axis B in order to optimize the spreading and/or distribution of the pulp in the radial direction while at the same time minimizing the torque on the diverter 3 from the pulp. The blade angle b is 45-135°, preferably 70-120°, more preferably 100-120°. In the preferred embodiment, the blade angle b is about 120°.

The blades 5 are mounted on the body 33 in this embodiment and extend along a surface of the body 33 in order to improve the radial spreading of the pulp and also to minimize the risk of damage to the blades 5 and the mounting of them. It is also advantageous that the blades 5 are arranged in such a way that a blade edge 51 extends away from the body 33, since thereby the blades 5 have their flat sides 52 to press against the pulp in order to improve the radial movement of the pulp.

The body 33 can also comprise at least one opening extending through the lower end 32. In the preferred embodiment, this would be in the form of openings through the plate shape at the lower end 32 between the blades 5 so that a quantity of pulp is able to penetrate the lower end 32.

An alternative embodiment is shown in Fig. 3, where a diverter 3’ having an upper end 3 and a lower end 32’ is mounted together with a separate part 6, on which a plurality of blades 5 are arranged. In this embodiment, a prior art diverter can be adapted through the addition of the separate part 6 to achieve the advantages of the present invention without requiring replacement of the diverter 3’ as such. Preferably, the separate part 6 is mounted on the same shaft as the diverter 3’ in a manner similar to the mounting of the diverter in the prior art arrangement shown in Fig. 1.

A feed-out arrangement 10 for a digester according to the present invention is shown by Fig. 4 and comprises a revolving shaft 1 driven by a motor M, the shaft 1 having an upper end onto which a diverter 3 according to the invention is mounted. Also provided is a scraper assembly 200 having at least one scraper arm 2a, 2b. The scraper assembly 200 is mounted on a circumference of the shaft 1 and the scraper arm 2a, 2b extends at least partly in a radial direction. As can be seen by comparing the feed-out arrangement 10 of the present invention with the prior art disclosed by Fig. 1, the main difference lies in the diverter 3 according to the invention. In many other respects, the feed-out arrangement 10 is similar to the prior art, and those components of the arrangement 10 and the digester which are similar to the arrangement shown in Fig. 1 are denoted by the same reference numerals and will not be described in more detail herein.

The at least one scraper arm 2a, 2b has an outer end 21 and the diverter 3 is arranged on the revolving shaft 1 in such a way that the at least one blade 5 is lower, i.e. closer to the motor M and the discharge opening 20, than the outer end 21 of the scraper arm 2a, 2b. Thereby, the radial spread of the pulp will take place underneath the outer end 21 of the scraper arms 2a, 2b, thereby reducing the torque on the scraper arms 2a, 2b which gives a significant advantage in reducing the power needed to operate the feed out arrangement 10 and also to reduce the wear and tear of the scraper and thereby reducing the need for repair, replacement of parts and the risk of interruption of operation of the feed out arrangement 10.

The present invention is not to be seen as limited by the embodiments described above but may be varied within the scope of the appended claims. It is especially to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Claims

1. Diverter for a feed-out arrangement for a digester or an impregnation vessel having a central outlet located in a lower end thereof, wherein the diverter comprises a body having an upper end and a lower end, the lower end having a larger radial extension than the upper end, and also comprising at least one blade extending at least partly in a radial direction, said blade being arranged at the lower end of the body.

2. Diverter according to claim 1, comprising at least two, preferably at least three blades.

3. Diverter according to claim 1 or 2, wherein the at least one blade extends beyond a circumference of the lower end of the body.

4. Diverter according to any of claims 1-3, wherein the body comprises at least one opening extending through the lower end.

5. Diverter according to any previous claim, wherein the at least one blade extends at a blade angle relative to the radial direction, said blade angle being 45-135°, preferably 70-120°, more preferably 100-120°.

6. Diverter according to any previous claim, wherein the blade or blades is/are mounted on the body, preferably extending along a surface of the body.

7. Diverter according to any of claims 1-5, wherein the blade or blades are arranged on a separate part.

8. Diverter according to any previous claim, wherein the at least one blade is arranged so that a blade edge extends away from the body.

9. Diverter according to any previous claim, wherein the diverter has a cross-sectional area which is less than twenty percent of the cross-sectional area of the diverter.

10. Feed-out arrangement for a digester, comprising:

a revolving shaft driven by a motor, the shaft having an upper end,

a diverter mounted on the upper end of the shaft,

a scraper assembly comprising at least one scraper arm, the scraper assembly mounted on a circumference of the shaft and the at least one scraper arm extending at least partly in a radial direction,

wherein the diverter is a diverter according to any of claims 1-9.

11. Feed-out arrangement according to claim 10, wherein the at least one scraper arm has an outer end and wherein the diverter is arranged so that the at least one blade is lower than the outer end of the scraper arm.

2. Feed-out arrangement according to claim 10 or 11, wherein the at least one blade is arranged on a separate part, said separate part being mounted on the shaft underneath the diverter.