Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
  • B01D33/067—Construction of the filtering drums, e.g. mounting or sealing arrangements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
  • B01D33/073—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/44—Regenerating the filter material in the filter
  • B01D33/48—Regenerating the filter material in the filter by flushing, e.g. counter-current air-bumps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/58—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element
  • B01D33/60—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for washing
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
  • D21C9/06—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents in filters ; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces

Definitions

• the present invention relates to a method and apparatu ⁇ for cleaning a fiber pulp washer from sticky substances, i.e. stickies.
• chemicals are used which release organic compounds from wood material.
• the purpose of the washing process is to remove as much of this liquor solution produced as possible with a minimal amount of wash liquid so that the pulp is clean enough for further treatment, washing the pulp is one of the most important partial processes in a sulphate pulp mill.
• the wash aims at: separating liquor from pulp, recovering the liquor in order to regenerate cooking chemicals and to combust combustible substances dissolved in the liquor; and reducing the efflued load from the mill. Further, washing the pulp is necessary in view of the runnability of subsequent processes.
• Dirty pulp causes problems, for example in screening it foams. Also chemical costs (e.g. anti-stickies agents) in bleaching and paper manufacture will increase. The most important physical basic operations in washing pulp are dilution, thickening, displacement, diffusion, flotation and mechanical labor. Displacement wash is clearly the most efficient washing method. In connection with the method and apparatus of the present invention, cleaning a pulp washer, i.e. washing the filter surfaces of a pulp washer, is for clarity called a cleaning wash.
• stickies mean all different substances which tend to plugg the apertures in the filter surfaces of a pulp washer.
• stickies for example in addition to resins also silicates, oxalates, and other possible substances forming deposites which cause plugging of the apertures of the filter surface are covered by the term stickies.
• the invention is particularly well applicable in connection with a so-called DD washer (DRUM DISPLACER ® ) of A. Ahlstrom Corporation, and it may be used also in other pulp washers such as washing presses where applicable.
• a DD washer is a pulp washing apparatus employing displacement; in the apparatu ⁇ , wash liquid is forces through a pulp cake of a consistency of approx. 10 %.
• the pulp wash liquid continuously flows through the pulp cake collected onto the surface of a rotating drum by means of a pressure diffecence and displaces the dirty liquid (liquor) in the cake.
• the liquid (liquor) in the cake i ⁇ replaced by a cleaner liquid.
• the pulp washing process may be carried out in one and the same drum from one to four times depending on the number of stages of the washer.
• a DD washer operates on the countercurrent principle, i.e. filtrate from the last washing stage is used as wash liquid in the second last washing stage, etc.
• 3 - 4 pulp washing stages are needed for washing brown stock.
• Figure l illustrates schematically the operation principle of a two-stage DD washer representing prior art technology.
• a DD washer fiber pulp is washed by pulp wash liquid flowing through the pulp. The flow-through takes place via perforated plate sectors in the surface of a drum l (partial enlargement in Fig. l) .
• Pulp is washed in 1 - 4 stages, depending on the structure of the washer, according to the so-called countercurrent principle. Filtrate from a cleaner pulp washing stage (i.e. the subsequent washing stage) is used as the pulp wash liquid in each stage. Filtrate flowing into filtrate compartments is circulated countercurrent relative to the revolving direction of the drum.
• the wash liquid in the las washing stage is as clean process water 13 as possible.
• reference number 10 refers to a filter unit which cleans the filtrate used in the last wash liquid feed point for use in the second last wash liquid feed point.
• the operation principle of the washer has been described in detail for example in Finnish patent no. 74752 and corresponding U.S. patents no. 4,919,158 and 5,116,423.
• a DD washer mainly comprises a rotating drum 1, a stationary casing 20 surrounding the drum, and a distribution valve 25 (illustrated in Fig. 6) disposed either in one end or both ends of the drum.
• the rim l of the drum has been divided by intermediate walls in feed chambers, each of which comprises an inlet for the wash liquid used for washing pulp. Wash liquid is guided from wash liquid feed chambers to the pulp in pulp compartments 24 to displace the liquid therein.
• the bottom of the feed chambers is made of a liquid-pervious filtering surface, most commonly perforated plate.
• the surface of the rim l of the rotating drum of a DD washer illustrated in Fig. 1 i ⁇ provided with a filter surface 7 (e.g.
• perforated plate which has been divided into compartments with dividing ribs 2 which are 50 - 70 trim high and disposed at 200 - 300 mm spacing. These dividing ribs form with the perforated filter surface the so-called pulp compartments 24, and between the filter surface and the rim of the drum so-called filtrate compartment/compartments 17 (Fig. 2) .
• Filtrate obtained from the first washing stage B of a DD washer is usually extracted as one fraction and it is taken via line 12 to pulp dilution and/or chemical recovery.
• the thickness and porosity of the pulp cake are homogenous and the consistency i ⁇ approx. 10 - 12 %.
• filtrate from a cleaner stage is used to displace the dirtier wash liquid in the pulp cake in the previous stage and the filtrate is taken via pipe lines 5 to be used as the displacement liquid in the previous, dirtier stage; thus for example in Fig. l from washing stage C to washing stage B.
• the pressure of the wash liquid is usually of the order of approx. 0 - 100 kPa (l bar) because strength calculations are made for a liquid pressure of 100 kPa but in future constructions, for example a pressure of about 120 kPa is probably quite possible.
• the pressure of the washing filtrate may be slighly increased between the washing stages by circulation filtrate pumps 8.
• the pressure of the wash liquid and the filtrate pumps provide the pressure for the entire wash and filtrate circulation which prevent ⁇ air from being mixed into the pulp.
• the pulp passes from the last wa ⁇ hing zone to a discharge zone D.
• a suction pump of the filtrate duct is opened and filtrate remaining in the flow duct under the perforated plate is .removed by the pump.
• a pressure air pulse pressure air duct 9 is directed in the compartment under the perforated plate and the pulp cake is detached from the perforated plate.
• Reference number 10 refers to a filter unit employed in cleaning the filtrate used in the last wash liquid feed point for use in the second last wash liquid feed point.
• the cleaning wash of the perforated plate may be intensified from time to time for example by means of jets from a high-pressure washing duct, for example at wash cycles of 5 minutes. In this case the normal displacement wash process has been disconnected and the washer drum is rotating. Also this cleaning wash has an effect primarily on the filter surface.
• FIG. 2 illustrates a projection of the end of a prior art washing drum, illustrating depicting schematically securing of the perforated plate of a DD washer.
• the perforated plate 7 is supported towards the center of the drum by a supporting plate 14.
• the supporting plate again comprises a metal plate 16 forming the filtrate duct, and vertical supports 15 welded thereto.
• the bottom of the supporting plate 14 rises in the direction away from the distribution valve. The purpose of this is to make the flow of wash liquid through the pulp cake more even in the longitudinal direction of the drum.
• the perforated plate is supported by axial dividing ribs 2 which divide the rim 1 of the drum into sectors.
• the perforated plate is prevented from moving in the direction away from the center of the drum by support blocks 18, 19 welded in the end of the drum and in the dividing ribs 2.
• the supporting plate 14 and its vertical supports 15 are places as backing for the perforated plate 7.
• the perforated plate is placed against the supporting plate and the supporting blocks 18, 19 supporting the perforated plate are welded on.
• the perforated plates are not designed to be replaced. Therefore, when in practise it has been necessary to replace the perforated plate because of damages, the replacing has been a very difficult operation.
• the supporting blocks 18, 19 supporting the perforated plate must be detached, in other words the welding seams must be opened.
• the damaged perforated plate is transported away and a new plate is installed in its place.
• Working conditions during the replacement of the perforated plate are, however, very inconvenient.
• the space is wet and the temperature prevailing depends on when the washer has been disconnected from operation and how well it has cooled down (the running temperature is about 100°C) .
• the only spot where the perforated plate may be reached is the maintenance opening of the screw transporter 6 under the DD washer.
• the operations necessary for the replacement must be carried out on top of the screw.
• An object of the present invention has been to provide an alternative perforated plate construction which is better in view of the maintenance of the perforted plate.
• Replacing a perforated plate may be necessary not only for purely maintenance reasons but also for mechanical reasons, such as too intensive bulging of the perforated plate in connection with the pressure air pul ⁇ e applied when detaching the pulp cake. Also fatique and reasons caused by the cyclic fluctuations in the temperature differences as well as various combination of these sometimes cause the need to replace the perforated plate by a new one.
• Another object of the present invention has been to find a method of washing fiber pulps which are difficult to wash.
• a DD washer has not been intended for washing pulps containing silicates or plenty of other sticky substances. It is common belief that probably the stickies would quickly plugg the apertures in the perforated plate. Paper industry has poor experiences for example of cleaning plugged perforations of suction rolls.
• the aperture size used in the perforated plate of a DD washer is smaller and there are more apertures in the plate. Cleaning of a severely plugged perforated plate would be difficult and would take much time. A particularly difficult problem in bleaching is caused by oxalate deposits.
• fiber pulp may originate in addition to the conventional softwood trees (long-fibred pulp) and birch
• Fiber pulps manufactured from the raw material ⁇ available contain varying amounts of silicate ⁇ and different stickies, such a ⁇ resin etc.
• the invention aims at solving the problems present in the existing apparatu ⁇ and washing methods and providing improved methods and apparatus applicable in many variou ⁇ washer types and capable of reaching almost the optimal washing result typical of each washer and proces ⁇ type and fiber pulp raw material.
• Figure l illustrate ⁇ schematically the operation principle of a prior art 2-stage washer
• Figure 2 illustrates a projection of an end of a prior art washer drum, disclosing schematically securing of the perforated plate of a DD washer,- Figure 3 illustrates schematically a filter element according to the invention
• Figure 4a illustrates a preferred embodiment of an element according to the invention, based on the use of a wire
• Figure 4b illustrates a section along line A-A of the element of Figure 4a
• Figure 5 illustrates a tool for use in connection with the replacement of an element
• Figure 6 illustrates an opening in the end of a washer for use in the replacement of an element according to the invention
• Figure 7 illustrates an embodiment in which the thermal expansion of an element according to the invention has been taken into account
• Figure 8 illustrates a construction for carrying out the cleaning wash method of the invention.
• Figure 9 illustrates another construction for carrying out the cleaning wash method of the invention.
• the filtering surface is formed by an element which may be easily and quickly replaced if necessary.
• the cleaning wash stage i.e. the stage between the discharge of the pulp web and the feeding of new pulp
• the intensified cleaning wash method of the present invention provides a solution also to cleaning problems of the entire washing apparatus system, including filtrates pipe lines, pumps, wash liquid feed chambers, pulp feed zones etc.
• special attention has been paid to keeping the washer drum clean while the process is running, i.e. during operation, particularly when processing difficult fiber pulps rich in stickies.
• the intensified on-line cleaning wash method of the present invention provides a solution also to these problems.
• the operation of a DD wa ⁇ her may be ⁇ ignificantly improved by employing the method and appratus of the invention.
• Reliable operation and ease of maintenance of the washer and properties of the proces ⁇ ed pulp may be improved ⁇ ignificantly by applying the present invention.
• processing of fiber pulps is possible which previously have not been treated in a DD washer, or their treatment has been extremely difficult for example due high stickie ⁇ content ⁇ .
• Remarkable improvements are obtainable also in processing of conventional fiber pulps by applying the present invention.
• proces ⁇ ing mean ⁇ both wa ⁇ hing and bleaching proce ⁇ es.
• the plate 16 forming the filtrated duct may be made of metal or other suitable material such as a composite of metal, cheramic or plastic material, or the like. If there are material or other problems discussed above the element may be pulled out via the end of the washer and a new replacing element pushed in place. This new method allows a remarkably quicker and cheaper maintenance of the washer.
• This new element serving as a filter surface may be effected for example as based on the use of a wire. Also various slot or perforation elements may be utilized in the filter surface according to the invention.
• An element must be replaced if it has been damaged ⁇ o that too much fibers pass through the filter surface or if the surface in very demanding conditions with time is clogged permanently/to a harmful extent de ⁇ pite the u ⁇ e of efficient washing methods.
• a damage is detected from a too high fiber content of the thickening filtrate and clogging from a high pumping pressure of the wash liquid.
• Securing the element 21 to the surrounding structure may take place for example by mean ⁇ of a ⁇ pring 22 welded in the end of the element a ⁇ illu ⁇ trated in Figure 4b.
• the contact ⁇ urface of the element and the drum is large and fibers are collected with time into the slots between. Further the element may be damaged by a hard particle which results in minor deformations. Due to this, the element may be tightly caught and the use of great force may be necessary in replacing the element. Because of this, particular attention has been paid to the securing/replacing means of the element.
• a construction as illustrated in Figures 4a and 4b has been found to be good in connection with the element of the invention.
• An element 21 is replaced in the following stages: l. Pulp feed must be collected to a blow tank and the filtering surface mu ⁇ t be cleaned with a washing means. 2. The window (not illustrated in the Figures) in the side of the discharge block is opened and the damaged element 21 is detected visually.
• the element 21 is marked so that it may be clearly seen from the end of the drum.
• Fibers which have adhered to the surface of the drum are cleaned off for example by means of a water jet of a scraper.
• a new assembled element 21 is installed. 8.
• the closing piece 39 of the distribution valve and the window of the discharge block are closed. 9. Pulp feed may be commenced.
• the own maintenance group of the pulp mill may replace the elements and the time the work requires is so short that the pulp digestion process need not be interrupted.
• Working conditions in the replacement operation are essentially better than in replacing the prior art filter elements.
• Figure 4 illustrates the structure of a filter element 21 in which the cover of the filter compartment is manufactured of a bendable surface.
• a bendable surface like this may be effected for example by means of a wire.
• the wire element comprises a bag 26 made of the wire material one end of which has been clo ⁇ ed for example by ⁇ ewing.
• a ⁇ upporting plate 16 ⁇ erving a ⁇ the wire element body is disposed inside the wire bag 26 and it guides the wash liquid to a distribution valve 25 at the end of the drum, inside the wire bag 26 on top of the supporting plate there is a sparse perforated plate 27 preventing the wire from hanging due to the pressure of the pulp cake.
• the wire is secured in its place by means of a rib 28 placed at the end of a filtrate opening.
• the wire bag 26 surrounding the structure formed by the supporting plate 16 and the perforated plate 27 is made of ⁇ uch a ⁇ hrink material that it will withstand both the temperature of the wa ⁇ her and the influence of the chemical ⁇ u ⁇ ed in the wa ⁇ her.
• the wire is pres ⁇ ed with screws 29 between the perforated plate 27 and the rib 28.
• the surrounding structure prevents the screws 29 from being detached and damaging for example filtrate circulation pumps 8.
• the wire material may be for example PVDF, polyvinylidene fluoride, a plastics thread material which tolerates the operation temperature of 100°C of the washer and the chemicals used in the wa ⁇ h. PVDF is a fabric sleeve material and it shrinks aboun 10 % when heated to 100°C.
• the supporting plate of the element has been provided with vertical supports 15, which have been for example welded with laser, and support the perforated plate and the wire against the pressure of the pulp cake.
• the bottom of the supporting plate is treated by bending or pressing to form a bulge 30 which is used instead of the rise of the bottom in the prior art structure.
• the heigth of the bulge decreases evenly towards the filtrate opening. Thu ⁇ , by the filtrate opening only the vertical supports 15 and the spring ⁇ 22 keeping the element in place provide cross- sectional area preventing the flow.
• the flow area of the filtrate increase ⁇ and the flow is linear.
• the filter surface or the cover of the filtrate compartment which in the example presented here is a wire bag made of a wire, may be replace, if desired, by a stiff filtrate compartment cover such as slot plate or a perforated plate while the rest of the element structure remains mainly the same as above.
• a filter surface element effected by means of a wire may rapidly be replaced by an element effected by means of a slot plate or a perforated plate.
• the structure of a ⁇ lot plate and a perforated plate element greatly re ⁇ embles the structure of a wire element.
• the replaceable element comprises in this case a stiff surface having holes, ⁇ lot ⁇ or the like aperture ⁇ serves as the filtrate compartment cover.
• a stiff surface means here a surface made of a material which does not require a separate spar ⁇ e perforated plate disposed on top of the supporting plate to prevent the wire from hanging under the pres ⁇ ure of the pulp cake which is required when a bag made of wire is used as the cover of the filtrate compart ⁇ ment.
• normal prior art surface materials and plates used in conventional fiber pulp washer drums may be used as the stiff surface of the filtrate compartment of the element of the invention.
• a ⁇ upporting plate guiding wash liquid to a distribution valve located at the end of the drum serves as the body of the element.
• Vertical supports which carry the cover of the filtrate compartment against the pressure of the pulp cake have been for example welded to the supporting plate of the element.
• Prior art apparatus do not pay adequate attention to transition caused by thermal expansion.
• Thi ⁇ ha ⁇ been one of the factor ⁇ initiating damages.
• the structure according to the invention allow ⁇ also for thermal expansion and it may freely take place because the securing of the element permits the element to move the distance that is required by the thermal expansion. This allowance of the element ha ⁇ been illu ⁇ trated in Figure 7 with reference nuumber 31.
• the invention relates to an improved method during the application of which the pulp washing apparatus is disconnected from the process.
• This method pays special attention to the cleaning wash ⁇ tage, i.e. the stage between the discharge of the pulp web and the feed of new pulp, by improving al ⁇ o the con ⁇ truction of the machine element ⁇ required in thi ⁇ important proce ⁇ ⁇ tage.
• a DD wa ⁇ her may be provided with new washing apparatus most of the components of which, however, already exist.
• all the components of a fiber pulp washer may be cleaned which come in contact with the fiber pulp to be washed during normal displacement wash of fiber pulp.
• all pipe lines, pumps, perforated plates, filter surface ⁇ , pulp feed and tran ⁇ port duct ⁇ may be cleaned from material adhered thereto.
• the method of the invention is effected by a cleaning wa ⁇ h apparatu ⁇ in which the di ⁇ charge zone ha ⁇ been carefully i ⁇ olated from other zones by means of sealing elements, i.e. in practice from the pulp feed zone and the last washing zone.
• the cleaning wash apparatus comprises a cleaning wash liquid pipe line and the required vessels and pumps. If necessary, cleaning wash liquid may be brought to the system straight from outside via a separate feed and discharge pipe line.
• the cleaning wash method according to the invention may be effected for example by means of the following cleaning wash system illustrated in Figure 8.
• the discharge zone has been carefully isolated from other zones by means of sealing elements 3.
• a separate tank 32 with required pumps and cleaning liquid pipe lines 33, 5, 34, 35, 36 have been constructed in connection with the fiber pulp washer and connected via appropriate valves to the wash zones of a DD washer, from which wash liquid is guided during displacement wash to a previous wash zone. From this spot on, the same pipe lines and pumps are used as in a normal di ⁇ placement wa ⁇ h of fiber pulp.
• the pipe line of the first wash zone of a DD washer has been extended by means of an appropriate valve so that the wash pipe line 34 reaches also the fiber pulp feed box 37. Between the wash line and the fiber pulp feed box there is al ⁇ o an appropriate valve.
• Figure 8 doe ⁇ not illustrate these valves which are necessary to make the cleaning wash liquid flow in the pipe line in the way desired.
• the wash pipe line discharge duct 36 from the feed box 37 has been connected to the discharge duct 35 of the wash liquid of the starting end washing zones of a DD washer.
• This entity has then been connected to the tank 32 in which the contaminated cleaning wash liquid is cleaned and returned for recirculation.
• the cleaning is effected by disconnecting the washer from the normal proces ⁇ and by washing the surface of the drum according to an ordinary high-pressure washing program.
• cleaning liquid is circulated via tank 32 and pipe lines 33, 5, 34, 35, 36 through the washer which has been stopped.
• the cleaning wash liquid washe ⁇ al o ⁇ t all the member ⁇ , i.e.
• Cleaning wash liquid is fed, in addition to one pipe line or several pipe lines of the displacement wash proces ⁇ , al ⁇ o via the pulp feed line of the displacement wash process, if neces ⁇ ary, in order to ensure that the entire pulp treatment apparatus including the pulp feed line and the by-pass line of the pulp feed are cleaned.
• cleaning liquid is circulated through the same apparatus which is u ⁇ ed in normal displacement wash of fiber pulp, even the parts of the displacement wash system which until now have been difficult to clean, are cleaned.
• Areas of this kind which are excluded from prior art cleaning wa ⁇ h methods are for example all pipe lines of the washer, pumps, ducts, casings, and the pulp feed pipe line.
• the cleaning wash method of the present invention for cleaning a fiber pulp washer from stickies comprises at least the following stages.
• Cleaning wash liquid is circulated from the tank 32 or directly from a separate wash liquid pipe line via one pipe line or several pipe lines of a washing stage/stages of the displacement wash proce ⁇ s onto the surface of the washer drum on the same principle as in the displacement wash process, i.e. in the same direction as in the displacement wash C -> B.
• the entire wash liquid pipe line 5 pulp feed box 37 and pumps 8 used in the displacement wash are cleaned.
• the wash liquid used in the wash of the washer is returned to the circulation tank 32 for cleaning or is pumped/guided elsewhere for proces ⁇ ing. If nece ⁇ sary the washer drum is rotated after the first cleaning wash stage gradually onwards and the cleaning wash is continued by supplying cleaning wash liquid through the washer drum shell untill the whole drum shell is clean. If all the pipe lines of the displacement wash are utilized which is natural the cleaning wash of the entire washer apparatus may be carried out in two stages as described above. After the cleaning the washer, e.g. a DD washer is reconnected to the normal displacement wash process.
• cleaning wash liquid is supplied via the pulp feed pipe line of the displacement wash process in order to clean the entire washer apparatus.
• the entire cleaning wash ocess of the invention may be effected as a closed circul ⁇ Xon proces ⁇ . Thu ⁇ there i ⁇ no danger of the wa ⁇ h liquid from leaking to the fiber pulp dicharge zone D.
• the influence of the cleaning wa ⁇ h liquid is based primarily on its ability to dissolve stickies.
• the cleaning wash may be carried out at first with an acid wa ⁇ h liquid and after that with an alkaline wash liquid or only with an acid wash liquid.
• Figure 9 illustrates a simpler way than the basic idea of "entire apparatu ⁇ wa ⁇ h" de ⁇ cribed above for carrying out the cleaning wash.
• Thi ⁇ embodiment is a reduced ver ⁇ ion of the idea of the entire apparatus wash and in this embodiment cleaning wash liquid is supplied only to those washing zones from which filtrate produced during normal displacement wash is directed straight to further- treatment, for example combustion (pipe line 12, Fig. 1).
• the drum of the washer must be rotated onwards in stages several times until the whole filter surface of the drum ha ⁇ been cleaned.
• the structure of the cleaning wash apparatus required is remarkably simpler than the one required for the "entire apparatus wash” .
• Figure 9 does not illustrate all the valves required for ensuring the flow of cleaning wash liquid to the desired places in the washer; the location of the valves is obvious to a per ⁇ on of ordinary ⁇ kill in the art.
• the cleaning wash is preferably effected in connection with a normal high-pre ⁇ ure wa ⁇ h of a washer drum. At that time the surface of the drum is washed by a high-pressure wash apparatus known per se. When the first high-pressure washed drum ⁇ urface portion rotates to a reduced cleaning wa ⁇ h zone the ⁇ ame drum ⁇ urface portion is washed again by the reduced wash method.
• This reduced wash apparatus may be used for example when stickie ⁇ tend to be collected to a harmful extent onto the filter surface of a washer drum fa ⁇ ted than in other member ⁇ of the displacement wash apparatu ⁇ .
• the object of this cleaning wash is primarily to clean the drum surface.
• the perforated plate at the cleaning wash zone and the portion of the washer pipe line which is used both in the normal cleaning wash and in this method for circulating the cleaning wash liquid are cleaned at the same time.
• An object of the invention is also an improved method during application of which the pulp washing apparatu ⁇ operate ⁇ while a normal pulp wa ⁇ hing proce ⁇ is running.
• This method of cleaning a fiber pulp washer from stickies is practiced by an apparatu ⁇ compri ⁇ ing a ⁇ tationary casing; a rotatable drum, dispo ⁇ ed inside the casing and having a liquid-pervious surface, i.e. filter surface composed of one entity or elements, and having holes, slots or corresponding openings, filtrate compartments disposed in ⁇ ide the surface and having side and bottom surfaces and intermediate walls extending out ⁇ ide the filter surface; a perforated substantially cylindrical surface disposed surrounding the drum, chambers with side and cover surfaces being disposed outside the perforated surface.
• a liquid-pervious surface i.e. filter surface composed of one entity or elements, and having holes, slots or corresponding openings, filtrate compartments disposed in ⁇ ide the surface and having side and bottom surfaces and intermediate walls extending out ⁇ ide the filter surface
• a perforated substantially cylindrical surface disposed surrounding the drum, chambers with side and cover surfaces being disposed outside the perforated surface.
• This cleaning wash apparatus further comprises one high-pressure nozzle or several adjacent high-pressure nozzles movable in the axial direction of the wa ⁇ her drum and di ⁇ posed separately following the normal cleaning wash zone of the washer, i.e. after the space where the wash nozzles are located which are used in conncection with a normal cleaning wash in a fiber pulp di ⁇ placement wash stage, viz. in the wash following the detachment of pulp cake.
• High-pres ⁇ ure feed nozzles may alternatively be ⁇ tationary di ⁇ posed along the whole length of the washer drum in its axial direction.
• This stickies removal apparatus operating continuously has been isolated by appropriate ⁇ ealing element ⁇ from the feed zone of the pulp to be washed and from the discharge zone of washed pulp/normal wash zone.
• This cleaning wash apparatus designed for continuous operation of removal of stickies also comprises a cleaning wash liquid pipe line with required tanks and pumps. If required, cleaning wash liquid may be introduced directly from elsewhere via a ⁇ eparate feed and return pipe line. The wa ⁇ h liquid used in the cleaning wash of the washer is reciculated to a circulation tank for cleaning or it is transported for treatment somewhere else.
• high-pressure cleaning wa ⁇ h liquid is supplied continuously onto the filter surface of the drum on the area defined by the operation range of the high-pres ⁇ ure nozzle ⁇ .
• the wash liquid used in the cleaning wash of the washer i ⁇ returned to the circulation tank for cleaning and reuse or it i ⁇ pumped/guided to be processed somewhere else or the liquid i ⁇ guided via a ⁇ eparate discharge pipe line to be processed somewhere el ⁇ e.
• the principle of closed circulation may be applied advantageously.
• the method is well applicable in removing oxalate depo ⁇ ites from a bleaching plant where they exist abundantly and continuously.
• high- pre ⁇ ure cleaning wash liquid is supplied onto the filter surface of the drum to an area determined by the coverage of the high-pressure nozzles.
• the wash liquid used in the cleaning wash of the washer is returned to the circulation tank for cleaning and for reuse or it is pumped/guided to be processed somewhere else.
• a separate cleaning wash pipe line is employed the liquid i ⁇ guided via a separate discharge pipe line to be proces ⁇ ed somewhere else. If the operation conditions allow for example the following arrangement is advantagous for minimizing the amount of wash liquid used.
• the operation of the high- pressure nozzles is connected to a control logic which activates a part of the nozzles at a time. In this way the wa ⁇ h water amount needed may be reduced remarkably. Thi ⁇ arrangement, however, presupposes that the properties of the fiber pulp to be treated are such that continuous operation of the high-pressure nozzles is no necessary to keep the surface of the drum clean.
• a DD washer of this new type may be used in washing also pulp materials, for example fiber pulps rich in silicates or other stickie ⁇ , which DD washers or other corresponding washers having small perforation diameters have previously not been able to treat.
• the solutions provided by the invention, both the apparatu ⁇ and the cleaning wa ⁇ h method may be u ⁇ ed in connection with treatment methods of fiber pulp in which DD washers have not been applicable before. Such treatments are for example bleaching and treatment of fiber pulp in a closed circulation for example in connection with washing and/or bleaching stage ⁇ in a fiber line.
• inventive idea of the present invention may be employed in addition to DD washers also in washing presses where applicable.
• washing processes and apparatus of wood proces ⁇ ing indu ⁇ try have been developed by the present invention to permit washing and/or bleaching of fiber pulp ⁇ which differ from previou ⁇ pulps and particularly which are "difficult" and will become more common in future, in DD washer ⁇ or corresponding apparatu ⁇ without the ri ⁇ k of ⁇ tickie ⁇ affecting to a too harmfull extent the proce ⁇ ing of the fiber pulp ⁇ .
• DD wa ⁇ hers becomes wider the fiber pulp treatment line becomes much more versatile in view of the fiber pulp to be washed, and closing the circulation make ⁇ the ⁇ ystem more economical and environmentally friendly.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
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• 1996
  • 1996-01-31 FI FI960438A patent/FI960438A/sv unknown
  • 1996-09-11 EP EP96930185A patent/EP0853700A1/en not_active Withdrawn
  • 1996-09-11 WO PCT/FI1996/000482 patent/WO1997010380A1/en not_active Application Discontinuation

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