SE2050951A1 - Diverter for a feed out arrangement for a digester and feed out arrangement comprising such a diverter - Google Patents

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 OUTARRANGEMENT COMPRISING SUCH A DIVERTER TECHNICAL FIELD The present invention relates to a diverter for a feed-out arrangement for a digester, whereinthe diverter comprises a body having an upper end and a lower end, the lower end having alarger radial extension than the upper end. The invention also relates to a feed-outarrangement for a digester provided with such a diverter. The digester is generally a treatmentvessel 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 aregenerally subjected to treatment in a treatment vessel such as an impregnation vessel and/or acontinuous digester. Often, the cellulosic materials are introduced through an opening at thetop of the vessel and proceeds downwards during treatment before being discharged at abottom end of the impregnation vessel or digester. The discharge opening is generally locatedin the center of the bottom end, and a feed-out arrangement is arranged above the dischargeopening in order to discharge the material in a suitable way.

There are several problems associated with the discharge of material, primarily that thecellulosic material is compacted during its stay in the impregnation vessel or digester and thatchannels are created in the material, which makes the core pulp flow quicker through thevessel 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 thedischarge opening to divert the cellulosic material towards the side walls of the vessel ordigester, together with a rotating scraper arrangement for improving the mixing of thecellulosic material and dilution liquor, and for preventing the formation of channels at thedischarge opening.

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

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

SUMMARY OF THE INVENTION The object of the present invention is to eliminate or at least to minimize the problemsmentioned above. This is achieved through a diverter and a feed-out arrangement comprisingsuch a diverter according to the appended independent claims. Particularly advantageousfeatures of the invention are set out in the dependent claims.

The present invention has a number of benefits and advantages due to its configuration andoperation. The diverter comprises a body having an upper end and a lower end, the lower endhaving a larger radial extension than the upper end, and also comprising at least one bladeextending at least partly in a radial direction, said blade being arranged at the lower end of thebody. Thereby, an efficient spreading out of the cellulosic material in a radial direction isachieved, preventing the compacting of material at the discharge opening and creating animproved mixing of material before discharge. Preferably, the diverter comprises at least twoblades, more preferably at least three blades, in order to improve the distribution or spreadingof the material. A purpose of said at least one blade is thus to prevent that a “dead” orstationary zone is created at a lower, radially outer end of the body of the diverter, whichcould 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. adigester or an impregnation vessel, which has an outlet located in the center of the lower endof the vessel. To prevent canalization, i.e. that pulp flows in canals in the center of the vesselrather than being spread out over the whole cross-section of the vessel, the diverter haspreferably 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 thebottom 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 orless than twenty percent (20 %) of the cross-sectional area of the lower end of the digester orimpregnation vessel, to facilitate and promote efficient use of the lower end space of thevessel in question, such that the pulp can leave the vessel via the centrally located outlet. Ifthe cross-sectional area of the diverter would be excessively large, e.g. larger than twentypercent (20 %) of the cross-sectional area of the lower end of the vessel, the diverter wouldeffectively form a new floor in the vessel, which would counteract the purpose of theinvention. Here, the cross-sectional area is the circular area of lower end of the vessel inquestion as measured at a level above the onset of any cupped gable end. Thus, when viewedfrom above, the cross-sectional area of the diverter is simply equal to or less than twentypercent of the cross-sectional area of the digester.

According to one aspect of the invention, the at least one blade extends beyond acircumference of the lower end of the body. This also improves the spreading or distributionof 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 openingextending through the lower end. Thereby, small quantities of cellulosic material can also beallowed to proceed through the diverter body and be guided to the discharge opening. This isadvantageous since it creates an improved flow of material outwards in the radial directionand generally downwards towards the discharge opening, which improves the discharge fromthe impregnation vessel or digester.

According to yet another aspect of the invention, the at least one blade extends at a bladeangle relative to the radial direction, said blade angle being 45-l35°, preferably 70-l20°, morepreferably l00-l20°. Thereby, the distribution and spreading of material can be achieved inan 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 diverterspreads 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 inan even more efficient way. Due to the upper part of the diverter body having a smallercircumference than the lower part of the diverter body, a cone-like shape is created that alsoserves to generate a radial spreading of material as the material proceeds downwards in theimpregnation vessel or digester.

According to another aspect of the invention, the blade or blades is/are arranged on a separatepart. Thereby, a conventional diverter and feed-out arrangement can be modified by thearrangement of the separate part together with a conventional diverter so that the radialspreading or distribution of cellulosic material is achieved without further structuralmodifications 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 ablade edge extends away from the body. This also serves to improve the efficiency of thespreading, since the cellulosic material will be transported on either side of the blade edge andbe spread out by the blade as the diverter rotates.

According to the invention there is also provided a feed-out arrangement comprising adiverter 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 assemblymounted on a circumference of the shaft and the at least one scraper arm extending atleast partly in a radial direction.

By the diverter cooperating with the inventive feed-out arrangement, significantimprovements to the prior art can be achieved, especially in the decreasing of compaction inthe cellulosic material and the channeling that prevents treatment liquor from penetrating thematerial to perform the treatment in the impregnation vessel or digester. The distribution orspreading of the cellulosic material according to the present invention also serves to decreasethe 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 thediverter is arranged so that the at least one blade is lower than the outer end of the scraperarm. Thereby, any compaction of material will take place at a lower point than the outer endof 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 separatepart, said separate part being mounted on the shaft undemeath the diverter. This isadvantageous in allowing repair and replacement of the diverter and the separate partindependent of each other and also in the versatility in the feed out arrangement, wheredimensions of the diverter and of the separate part can be selected to provide an optimalspreading and/or distribution of material for any given impregnation vessel or digesterdepending on its size.

Many additional benefits and advantages of the invention will become readily apparent to theperson 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 inventionin a perspective view, planar view and top view, respectively; Fig. 3 discloses an alternative embodiment of the diverter having the blades arrangedon a separate part; andFig. 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 mayalso be applicable in impregnation vessels or other treatment vessels used for treatment oflignocellulosic materials. A feed-out arrangement comprising a diverter according to the priorart is disclosed having a revolving shaft l driven by a motor M, onto which shaft l a diverter3 having an essentially cone-like shape is mounted. The arrangement further comprises abottom scraper having at least two scraper arms 2a, 2b, onto which are also attached scraperblades 4. The bottom of the digester is a cupped gable end, and the scraper arms 2a, 2b arearranged to sweep over the inside of the gable end and push the treated, e.g. cooked, cellulosicmaterial, in the following referred to as pulp, towards a central outlet 20 disposed in a lowerend of the digester. Typically, the scraper arms 2a, 2b are angled at a scraper angle ot inrelation to a horizontal plane, the scraper angle ot being in the range of 5°-30° so that thescraper 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 washzone, where a cleaner wash liquid is introduced into the bottom of the digester through severalwash dilution nozzles, here shown as vertical nozzles VN and horizontal nozzles HN. Avertical counter-current flow, as indicated with black flow arrows, of this wash liquid isestablished up to a wash screen WS. As a complement to this axial displacement wash, a 4 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 screenWS is a slotted screen plate or preferably a stave/bar screen that withdraws used or spentwash liquid and collects it in a wash extraction chamber WEC, which in turn is emptied into awash 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, butthe retention time could also be lowered to about 5 minutes during production increases orincreased during production decreases to about 45 minutes. The power requirements fordriving this kind of feed-out arrangement with diverter and bottom scraper have been shownto 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 presentinvention, having a body 33 with an upper end 31 and a lower end 32. The lower end 32 has alarger radial extension than the upper end 31, wherein a radial direction is defined as adirection outwards from an axis A extending through the body 33 from the upper end 31 tothe lower end 32 (see Fig. 2b), i.e. a direction along a radial axis B (see Fig. 2c). In thisembodiment, at least a part of the body 33 is shaped like a cone but other shapes are alsopossible within the scope of the invention. At the lower end 32, at least one blade 5 extends atleast partly in the radial direction. In this preferred embodiment, the diverter 3 comprises fiveblades 5 that are mounted on the body 3 and rest against the lower end 32, which is shapedlike a plate. In other embodiments, the blade or blades 5 can extend along the body 33towards the lower end 32 or can be arranged at the lower end 32 without resting against asurface of the lower end 32. It is advantageous that the diverter 3 comprises at least twoblades 5, preferably at least three blades 5, but a single blade 5 would also be able to achievethe technical effect of spreading the pulp from the diverter. The single blade 5 can in such anembodiment 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, inorder to improve the radial movement of the pulp outwards from the lower end 32 of thediverter 3. The blades 5 are also preferably arranged at a blade angle ß in relation to the radialdirection along the radial axis B in order to optimize the spreading and/or distribution of thepulp in the radial direction while at the same time minimizing the torque on the diverter 3from the pulp. The blade angle ß is 45-135°, preferably 70-120°, more preferably 100-120°.In the preferred embodiment, the blade angle ß is about 120°.

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

The body 33 can also comprise at least one opening extending through the lower end 32. Inthe 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 lowerend 32.

An alternative embodiment is shown in Fig. 3, where a diverter 3” having an upper end 31”and a lower end 32” is mounted together with a separate part 6, on which a plurality of blades5 are arranged. In this embodiment, a prior art diverter can be adapted through the addition ofthe separate part 6 to achieve the advantages of the present invention without requiringreplacement of the diverter 3” as such. Preferably, the separate part 6 is mounted on the sameshaft as the diverter 3” in a manner similar to the mounting of the diverter in the prior artarrangement 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 endonto which a diverter 3 according to the invention is mounted. Also provided is a scraperassembly 200 having at least one scraper arrn 2a, 2b. The scraper assembly 200 is mounted ona circumference of the shaft 1 and the scraper arrn 2a, 2b extends at least partly in a radialdirection. As can be seen by comparing the feed-out arrangement 10 of the present inventionwith the prior art disclosed by Fig. 1, the main difference lies in the diverter 3 according to theinvention. In many other respects, the feed-out arrangement 10 is similar to the prior art, andthose components of the arrangement 10 and the digester which are similar to the arrangementshown in Fig. 1 are denoted by the same reference numerals and will not be described in moredetail herein.

The at least one scraper arrn 2a, 2b has an outer end 21 and the diverter 3 is arranged on therevolving shaft 1 in such a way that the at least one blade 5 is lower, i.e. closer to the motor Mand the discharge opening 20, than the outer end 21 of the scraper arrn 2a, 2b. Thereby, theradial spread of the pulp will take place undemeath the outer end 21 of the scraper arms 2a,2b, thereby reducing the torque on the scraper arms 2a, 2b which gives a significantadvantage in reducing the power needed to operate the feed out arrangement 10 and also toreduce the wear and tear of the scraper and thereby reducing the need for repair, replacementof 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 butmay be varied within the scope of the appended claims. It is especially to be noted thatfeatures from the various embodiments described herein may freely be combined, unless it isexplicitly stated that such a combination would be unsuitable.

Claims (2)

1. l. 10. Diverter for a feed-out arrangement for a digester or an impregnation vessel having acentral outlet located in a lower end thereof, wherein the diverter comprises a bodyhaving an upper end and a lower end, the lower end having a larger radial extensionthan the upper end, and also comprising at least one blade extending at least partly in aradial direction, said blade being arranged at the lower end of the body. Diverter according to claim l, comprising at least two, preferably at least three blades. Diverter according to claim l or 2, wherein the at least one blade extends beyond acircumference of the lower end of the body. Diverter according to any of claims l-3, wherein the body comprises at least oneopening extending through the lower end. Diverter according to any previous claim, wherein the at least one blade extends at ablade angle relative to the radial direction, said blade angle being 45-l35°, preferably70-l20°, more preferably l00-l20°. Diverter according to any previous claim, wherein the blade or blades is/are mountedon the body, preferably extending along a surface of the body. Diverter according to any of claims l-5, wherein the blade or blades are arranged on aseparate part. Diverter according to any previous claim, wherein the at least one blade is arranged sothat a blade edge extends away from the body. Diverter according to any previous claim, wherein the diverter has a cross-sectional areawhich is less than twenty percent of the cross-sectional area of the diverter. 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, wherein the diverter comprises a bodvhaving an upper end and a lower end, the lower end having a larger radial extensionthan the upper end, and also comprising at least one blade extending at least partlv in aradial direction, said blade being arranged at the lower end of the bodv a scraper assembly comprising at least one scraper arrn, the scraper assembly mountedon a circumference of the shaft and the at least one scraper arm extending at least partlyin a radial direction, wherein the at least one scraper arm has an outer end and whereinthe diverter is arranged so that the at least one blade is lower than the outer end of the SCI'8.| 261' aITII. 1

2. Feed-out arrangernent according to clairn 10 er-l-l, Wherein the at least one blade isarranged on a separate part, said separate part being rnounted on the shaft underneaththe diverter.