SE537483C2

SE537483C2 - Method and apparatus for cleaning lignocellulosic material during impregnation

Info

Publication number: SE537483C2
Application number: SE1250289A
Authority: SE
Inventors: Anders Hawén; Dino Muhic
Original assignee: Valmet Oy
Priority date: 2012-03-23
Filing date: 2012-03-23
Publication date: 2015-05-19
Also published as: SE1250289A1; WO2013141776A1

Abstract

14 ABSTRACT An impregnation arrangement (1) includes an impregnator Chamber (10), aninlet (11) arranged at a bottom end of the Chamber conﬁgured forintroducing material to be impregnated into the Chamber, a conveyorarrangement (20) configured for moving the introduced material in adirection from the bottom end of the Chamber to a top end of the Chamber, atleast one outlet (12) arranged at the top end for extracting the impregnatedmaterial from the Chamber, and at least one inlet (13) configured forintroducing impregnation liquid into the Chamber. Further, the impregnatorarrangement includes an outlet (14) configured for extracting liquid from theChamber during operation, to provide a liquid ﬂow in the Chamber in acounter-current or opposite direction of the direction of the introduced material. (F ig.2)

Description

METHOD AND ARRANGEMENT FOR CLEANING TECHNICAL F IELD The present invention relates to treatment of lignocellulosic material ingeneral and in particular to improved Cleaning of lignocellulosic materials e.g. Wood chips before further treatment, e.g. a refining step.

BACKGROUN D The separation of ﬁbers from each other in a lignocellulosic material can beachieved in several Ways. The preparation of pulp typically comprises amultitude of process steps that serve to transform lignocellulosic materialsuch as Wood chips to a wet pulp, i.e. a fiber suspension, suitable formanufacture of various paper products or the like. Pulping processes may bemainly chemical, Wherein the lignin keeping the ﬁbers connected to eachother is at least partly removed by adding chemicals and applying processconditions dissolving the lignin, or mainly mechanical, Wherein the fibers areseparated from each other mechanically, e.g. by grinding or refining. Theprocesses are commonly referred to as chemical and mechanical pulpingprocesses, respectively. There are also dry processes Where separated fibers are utilized for making fiberboard products.

A typical mechanical pulping process can be summarized as Cleaning of theWood chips, preheating, impregnation, and subsequently refining. Thepreheating aims to Warm the chips and equalize the moisture content of thechips before refining. It is also possible to fine-tune the pulp properties Withthe temperature. Subsequently, the chips are conveyed to an impregnatorWhere they are impregnated With Water or sodium sulfite solution, or otherimpregnation liquid. Finally, the impregnated chips are introduced into thefinal reﬁning steps. The same basic processing is also utilized in themanufacture of fiberboard, up until the refining steps, Which differ due to the different end use of the ﬁbers. For fiberboard products it is of interest to 2 separate the fibers Without ﬁbrillation (i.e. Without any unraveling of thefiber Wall from the fiber surface) While for mechanical pulp intended forpapermaking, the fibrillation is needed in order to achieve adequate bondingproperties. The refining equipment for ﬁberboard is foremost a deﬁbrationequipment, accomplishing separation into individual fibers While the refining equipment for mechanical pulp achieves defibration and fibrillation both.

Present impregnators for mechanical pulping typically comprise addingimpregnation liquid at the bottom of a container before refining [1]. Duringthe impregnation, process contaminants and impurities such as pin-chipsand larger contaminants as Well as fine sand, dust and smaller particles arereleased into the impregnation ﬂuid, thereby reducing the efficiency of theimpregnation process. In addition, the contaminants that remain in thechips that are ejected from the impregnator process Will cause abrasive Wear of the process equipment.

Therefore, there is a need for an improved cleaning during an impregnationprocess, which removes the impurities to increase the purification process,Which Will improve the product as Well as reduce the abrasive Wear on theprocess equipment.

SUMMARY The present invention aims to obviate some of the above-mentioned problems With prior art impregnators.

A first aspect of the present disclosure presents an impregnationarrangement comprising an impregnator Chamber, a first inlet arranged at afirst end of the chamber conﬁgured for introducing material to beimpregnated, such as a lignocellulosic material e.g. Wood chips, into thechamber, a conveyor arrangement configured for moving the introducedmaterial in a direction from the first end to a second end of the chamber.Further, the arrangement includes an outlet arranged at the second end of the chamber for extracting the impregnated material from the chamber, and 3 a second inlet configured for introducing impregnation liquid into thechamber. Further, the arrangement includes a second outlet conﬁgured forextracting liquid from the Chamber during operation, to provide a liquid ﬂoWin the chamber-in an opposite direction of the direction of the introduced material.

A second aspect of the present disclosure presents a method of impregnatingmaterial, such as lignocellulosic material e.g. Wood chips, comprisingintroducing material to be impregnated at a first end of an impregnatorchamber, and conveying the introduced material in a direction from the firstend towards a second end of the chamber. Subsequently, the disclosurepresents introducing impregnation liquid/ chemicals into the chamber, andextracting the impregnated material from the chamber at the second end.Further, the method includes extracting liquid from the first end of thechamber during operation, to provide a liquid ﬂoW arranged in an opposite direction of said direction of said introduced chips in said chamber.

Advantages of the present invention include improved cleaning oflignocellulosic material e.g. Wood chips, and as a direct consequence thereof, reduced abrasive Wear of the process equipment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, together With further objects and advantages thereof, maybest be understood by referring to the following description taken together With the accompanying drawings, in Which: Fig. 1 is an illustration of a known impregnator arrangement; Fig. 2 is an illustration of an embodiment of an arrangement accordingto the present disclosure; Fig. 3 is a further embodiment of an arrangement according to the present disclosure; 4 Fig. 4 is a schematic ﬂow chart of an embodiment of a method according to the present disclosure.

DETAILED DESCRIPTION The present disclosure relates to fiber process equipment for lignocellulosicmaterial e.g. wood chips, in particular to improved Cleaning of the materialin or before impregnator arrangements in such equipment. The disclosureWill be presented with reference to wood chip processing, but is equallysuitable for other lignocellulosic materials e.g .suitable for fiberboard products.

An impregnator is utilized to equalize the moisture content of thelignocellulosic material e.g. wood chips or to reduce the extractives contentof the lignocellulosic material e.g. wood chips. A Widely used system is theso-called PREX-impregnator system. Chips from a chip washing system arepreheated at atmospheric pressure before the PREX plug screw feeding tothe impregnator. The water squeezed out from the chips has a high contentof dissolved and colloidal substances and therefore is led to the efﬂuent. Thepressed chips are fed to a vertical screw impregnator where the chips areimpregnated with water or sodium sulfite solution. A level controller adjuststhe ﬂow of the liquid to the impregnator. The amount of water impregnatedis about 0.5-1.0 m3 per ton of wood chips. The moisture content of the chipsincreases about 6 %-7 % units. The screws are available with two different compression ratios, 2:1 or 3:1 respectively.

Inside the impregnator, a conveyor e.g. two counter-rotating screws arearranged to elevate and mix the material, such as a lignocellulosic materiale.g. wood chips, with an impregnation ﬂuid, e.g. a mixture of chemicals andwater added at or near the chip inlet of the vessel. Each screw is typicallydriven by an AC-motor via a shaft mounted gear reducer and a v-belt drive.The screw shafts are replaceable shaft ends journaled by grease-lubricated bearings at the top and by bearing bushings at the lower end. An example of 5 an impregnator is the so-called IPAXXX, Which consists of a shell with aninlet with a back-ﬂow protection device at the lower end and outlet chute atthe upper end, and the aforementíoned twin feeding screws. Theimpregnated material, e.g. wood chips, is then transferred into a screw conveyor to a retention bin before being further processed in a reﬁner.

With reference to Fig. 1, a Simplified illustration of a prior art impregnator inwhich the present disclosure can be implemented will be described. Theimpregnator 1 includes an impregnator chamber 10 with a chip inlet 11arranged at a first end e.g. bottom end of the chamber 10, and a chip outlet13 arranged at a second end e.g. top end of the chamber 10. A conveyor unit20 e.g., screw conveyor is arranged in the chamber 10 to convey chips fromthe chip inlet 1 1 towards the chip outlet 13. Additionally, the impregnator 1includes an impregnation liquid inlet 12 for introducing impregnation liquidsinto the chamber. Consequently, the introduced impregnation liquid willform a more or less stagnant volume of liquid at the bottom of theimpregnation chamber. The addition of impregnation ﬂuids is controlled tomaintain the level of impregnation liquid inside the chamber at a certain level or Within a certain interval.

As illustrated above, the prior art impregnators for mechanical pulping arewith impregnator liquid typically added as a stagnant liquid volume at thebottom of the impregnator chamber. As for today, this is only animpregnation step before refining. By adding the teachings of this disclosure, this can be improved With a cleaning step as well.

The inventors have identified the benefits of providing a counter-currentliquid ﬂow opposite the transport direction of the lignocellulosic material e.g.Wood chips, in the impregnator chamber, and optionally to circulate theliquid via a filtering arrangement i.e. after passing the wood chips. Byintroducing a liquid ﬂow in a direction opposite of the conveyed material e.g.wood chips in the impregnator chamber, impurities e.g. sand and dust particles, Will be prevented from exiting the chamber together with the chips. 6 Instead, the impurities Will be Washed away from the Chips by the introducedﬂoW, and optionally the flowing liquid can be extracted from the Chamber,cleaned, and re-introduced into the Chamber. The general idea is to improvethe process such that the impregnator liquid is added at the upper part(directed Water stream) and overﬂow liquid is discharged through the bottomof the impregnator Chamber. The liquid is then, according to a furtherembodiment, re-circulated in a Closed loop through a ﬁltering device. Theﬁltering device Can, according to a particular embodiment, include a screenfor removal of pin-Chips and large contaminants. This Can be followed by a ﬁltration device to separate fine sand, dust and smaller impurities.

With reference to F ig. 2, a basic embodiment of the present disclosure Will bedescribed. The same reference numerals are used for the correspondingunits of Fig. 1. The impregnator arrangement 2 includes an impregnatorChamber 10, an inlet 11 for introducing material to be impregnated into theChamber arranged at a first end e.g. bottom end of the Chamber forintroducing material e.g. Chips into the Chamber, a Conveyor arrangement 20Conﬁgured for moving introduced material e.g. Chips in a direction from thefirst end e.g. bottom end to the second end e.g. top end of the Chamber.Further, the impregnator includes at least one outlet 13 arranged at the topend for extracting the impregnated material from the Chamber, and at leastone inlet 12 for introducing impregnation liquid into the Chamber. Inaddition, the arrangement includes a second outlet 14 located at the bottomend of the Chamber for extracting liquid from the Chamber during operation,to provide a liquid ﬂoW in an opposite direction of the direction of the Chipsmoving on upwards on the Conveyor 20. By providing an extraction outlet14, it is possible to induce a counter Current e.g. opposing ﬂoW of liquid inthe Chamber, Which aids in Cleaning the moving Chips from any impuritiesand transporting the impurities towards the bottom of the Chamber and outthrough the outlet 14. The rate of extraction and the rate of addition ofimpregnation liquid are controlled to maintain a predetermined level of impregnation liquid in the Chamber. 7 Although the present embodiment is described With relation to asubstantially vertically arranged impregnator arrangement, it can be equallyimplemented in an impregnator With some other orientation. In addition, theembodiments of the present disclosure can be easily adapted to provide animproved Cleaning process in other parts of the pulp manufacture process.The important consideration is to introduce an opposing liquid ﬂow into a Chamber in Which chips are transported.

Also With reference to Fig. 2, a further embodiment of an arrangementaccording to the present disclosure Will be presented. In order to furtherimprove the cleaning efficiency of the arrangement, increase the liquid ﬂowin the chamber, and reduce the amount of consumed impregnation liquids,it Would be beneficial to reuse or re-cycle the impregnation liquids. This isenabled by a cleaning unit 30 externally arranged between the outlet 14 anda second inlet 15 of the Chamber. The second inlet 15 can, according to oneembodiment be co-located With the inlet 13 for introducing impregnationliquid into the chamber. According to a preferred embodiment, the two inlets13, 15 are separate entities located at a respective bottom and top end of thechamber e.g. opposite ends. Thereby, impregnation ﬂuids as Well as anyimpurities can be extracted from the chamber 1 through the outlet 14, becleaned in the cleaning unit 30, and subsequently be reintroduced into thechamber 10 through the inlet 15. According to a further embodiment, a unitfor providing liquid in addition to the impregnation liquid can be provided to the inlet 15.

With reference to Fig. 3, a further embodiment of an impregnationarrangement 3 according to the present invention Will be described. Thesame reference numerals are used for same or similar components as for theprevious drawings. In this embodiment, the cleaning unit 30 comprises atleast one filtering arrangement or unit 31, 32, Which is configured forfiltering out any particles larger than a predetermined particle size from theliquid. According to a particular embodiment, the cleaning unit 30 includes a first screening or filtering unit 31 for filtering out particles larger than 0.2 8 mm, and a second ñltering unit 32 for filtering out particles in the intervalfrom 0.65 mm to 0.2 mm. However, any arrangement suitable for removingthe impurities Can be utilized, and can be configured for any size of particlesas well depending on the specific needs of the process. The filtered liquid isthen re-introduced into the Chamber through inlet 15. It is evident that anynumber of filter arrangements, and any method of filtering can be appliedand speciﬂcally tailored for particular sizes of impurities. Likewise, theCleaning arrangement could be provided with chemical or mechanicalCleaning functionality depending on the particular process parameters. Inaddition, functional units such as pumps can be included to further improve the efficiency of the process.

With reference to Fig. 4, an embodiment of a method of Cleaning andimpregnating material such as lignocellulosic material e.g. wood chipsaccording to the present disclosure Will be described. The method includesintroducing Sll material to be impregnated, such as wood chips, at a firstend of an impregnator Chamber, conveying S20 the introduced material in adirection from the first end towards a second end of the Chamber. Typically,the material is Conveyed from a bottom end towards a top end of theChamber. Subsequently, impregnation liquid/ Chemicals are introduced S12into the Chamber, and the impregnated material is extracted S13 from theChamber at the second end. In addition, liquid is extracted S14 from the firstend of the Chamber during operation, to provide a liquid flow in an oppositedirection of the direction of the introduced material in the Chamber. Thereby,the Counter-Current or opposing flow of liquid enables Cleaning anyimpurities from the introduced material and effectively prevents conveying the impurities further in the process.

According to a further embodiment, the method includes introducing S15 afurther liquid into the Chamber at the second end, and extracting liquid S14at the first end, and optionally Cleaning S30 the extracted liquid and re-introducing S40 at least the cleaned extracted liquid into the Chamber to provide a ﬂow of the liquid in the Chamber. lO The technique can be used for processing of Water - and chip Washing in thechip-Washing equipment. Although the present disclosure mainly describedchip Cleaning Within an impregnator arrangement, the same basic methodcan be applied for other parts of the chip processing line, and for other typesof lignocellulosic materials. ln particular, the disclosure can be easilyadapted to the already existing chip Cleaning equipment in a pulp processingplant. By introducing an opposing ﬂoW of liquid e.g. Water in a chip Cleaningtank, Which aids in removing impurities from the chips, and enablingextracting and Cleaning the Water before reintroducing it into the Chamber, the chips can be Cleaned more effíciently.

In summary, the main idea of the present disclosure is to Change the processsuch that the impregnation liquid and potentially any added liquid is addedat the upper part of the Chamber and overﬂow liquid is discharged at thebottom. The liquid is then Circulated in a closed loop through a screen (orequal) for removal of pin-Chips and larger Contaminants. This is followed bya filtration device (NimClearTM or equal) to separate fine sand, dust and smaller impurities.

The main benefit of the present disclosure is improved Cleaning of Chips priorto refining in order to minimize abrasive Wear in the process equipment.Improved refining is Closely connected to better pulp and paper quality. Theprocess optimization is tailored for each Customer in order to reach higherenergy savings and to be a sustainable competitor on the market. Further benefits could be more effective liquid uptake in impregnation.

REFERENCES [1] Mechanical pulpíng, Paperrnaking Science and Technology, Book 5, pages166-168,

Claims

1. An impregnation arrangement (2;3), comprising a verticallv arranged n impregnator Chamber (10), a ﬁrst inlet (11) arranged at a ﬁrst end of saidChamber Conﬁgured for introducing material to be impregnated into saidChamber, a Conveyor arrangement (20) Conﬁgured for moving introducedmaterial in a direction from said ﬁrst end of said Chamber to a second end ofsaid Chamber, at least one outlet (12) arranged at said second end forextracting impregnated material from said Chamber, and a second inlet (13)Conﬁgured for introducing impregnation liquid into the Chamber,characterized by said first end Corresponding to a bottom end of said Chamber, and saidsecond end corresponding to a top end of said Chamber. a second outlet (14) located at said bottom end of said Chamber ( 10) ap_<¿l_conñgured for extracting liquid from said ﬁr-strbottom end of saidChamber (10) during operation, to provide a liquid ﬂow in said Chamber (10)in an opposite direction of the direction of said introduced ehipsmaterial,äšßl a third inlet (15) Conﬁgured for introducing a liquid into the Chamber( 10) at said top end of said Chamber, and a Cleaning arrangement (30) connected between said third inlet (15)and said second outlet (14), Wherein said Cleaning arrangement (30)comprising at least one ﬁltering unit (31, 32) and is Configured for Cleaningsaid extracted liquid and providing the cleaned extracted liquid to said third inlet (15) to provide said liquid ﬂow in said Chamber ( 10). 512. The arrangement according to claim _1_3, characterized by said second inlet (1 å) and said third inlet (15) being arranged at separate locations. êvß. The arrangement according to claim 25, characterized by said second inlet (1 32) being located at said bottom end of said chamber, and said third inlet (15) being located at said top end of said chamber. 7-4. The arrangement according to claim _l_3, characterized by said secondinlet (1 _32) and said third inlet (15) being co-located. 9-5. The arrangement according to any of claims Låg, characterized by said cleaning unit (30) comprising a first ﬁltering unit (31) and a secondñltering unit (32). l0f6. The arrangement according to any of claims 1-59, characterized byby said arrangement (2;3) being conﬁgured for impregnating lignocellulosic material. I -l-lf7. The arrangement according to claim QH, characterized by said arrangement (2 ; 3) being conﬁgured for impregnating wood chips. _E_š_._ A method of impregnating lignocellulosic material, comprising introducing (S11) material to be impregnated at a ﬁrst end of a verticallv arranged n impregnator Chamber, conveying (S20) said introduced material in adirection from said bottom-Ägg end towards a second end of said Chamber,introducing (S12) impregnation liquid/ chemicals into said chamber, andextracting (S13) impregnated material from said chamber at said second end,characterized by said first end corresponding to a bottom end of saidchamber, and said second end corresponding to a top end of said chamber,aggLextracting liquid (S14) from said ﬁæst-bottom end of said chamber duringoperation, to provide a liquid ﬂow arranged in an opposite direction of said direction of said introduced material in said chamber, and Cleaning (S30) said extracted liquid and re-introducing (S40) at least the cleaned extracted liquid into said chamber to provide a ﬂow of said liquid in said chamber. 1-679. The method according to claim å-l-â, characterized by said method being adapted for impregnating wood chips.