US20060113048A1 - Method for washing pulp in a bleaching line and a bleaching line - Google Patents

Method for washing pulp in a bleaching line and a bleaching line Download PDF

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Publication number
US20060113048A1
US20060113048A1 US10/541,435 US54143505A US2006113048A1 US 20060113048 A1 US20060113048 A1 US 20060113048A1 US 54143505 A US54143505 A US 54143505A US 2006113048 A1 US2006113048 A1 US 2006113048A1
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Prior art keywords
main conduit
bleaching
wash
filtrate
pulp
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Abandoned
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US10/541,435
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English (en)
Inventor
Lennart Gustavsson
Vidar Snekkenes
Jonas Saetherasen
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Flsmidth Dorr Oliver Eimco Management Hungary Kft Luxembourg Branch
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Kvaerner Pulping AB
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Application filed by Kvaerner Pulping AB filed Critical Kvaerner Pulping AB
Assigned to KVAERNER PULPING AB reassignment KVAERNER PULPING AB ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GUSTAVSSON, LENNART, SAETHERASEN, JONAS, SNEKKENES, VIDAR
Publication of US20060113048A1 publication Critical patent/US20060113048A1/en
Assigned to GL&V MANAGEMENT HUNGARY KFT, LUXEMBOURG BRANCH reassignment GL&V MANAGEMENT HUNGARY KFT, LUXEMBOURG BRANCH ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KVAERNER PULPING AB
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    • 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
    • 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
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
    • 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
    • D21C9/10—Bleaching ; Apparatus therefor

Definitions

  • the present invention relates to a method of bleaching cellulose pulp and a bleach line for the method.
  • the bleaching department is ever more closed and most often the process water is lead in counter-current to the direction of flow of the cellulose pulp in the process steps of the bleaching line. Accordingly, the fresh water or the clean process water is used in the wash of the last step and the wash filtrate obtained there from is led as wash liquor to the wash of the preceding step and further up through the bleaching line.
  • the number or filtrate tanks also results in a risk of an increased outlet of odorous gases as all filtrate tanks require ventilation in order to level out changes in the volume in the filtrate tanks. Often, special degassing systems are required to handle and destruct such odorous gases.
  • One object of the invention is to reduce the need of, and in some cases completely eliminate, such expensive filtrate tanks, control systems and valves in the wash liquor systems, whereby the investment costs for the bleaching line may be strongly reduced.
  • the reduced number of necessary filtrate tanks also results in the possibility of a more compact and more optimal design of the bleaching line, without consideration of such filtrate tanks that conventionally numbers to at least the same number as the number of bleaching steps, with a more efficient layout of the bleaching steps of the bleaching line.
  • Yet another object is to increase the runnability/accessability of the system as several control valves may be removed, that otherwise are always potential risks for plugging/stoppage of the liquor distribution system.
  • Yet another object is to improve the runnability as the risk of mixing-in of air in the filtrate system is considerably reduced when the number of filtrate tanks can be considerably reduced.
  • accumulation of floating pulp is avoided, which floating pulp usually accumulates after a certain running time, by surface flotation in filtrate tanks. Principally in alkaline steps, such accumulated floating pulp may rise to a level of a few metres above the surface in the filtrate tanks and it must be continuously taken care of or recycled to the bleaching line in order not to risk plugging of the filtrate systems.
  • bleaching plant can be rendered more environmentally friendly as occasional overloads in certain positions, so called over-runs, need not result in outlet of gas or liquor.
  • Yet another object is to minimise the water consumption.
  • the system itself may compensate for occasional changes in wash liquor requirements in the various bleaching steps and secure that a required wash liquor quantity is always guaranteed the bleaching steps.
  • Yet another object is to decrease the length of the tube system, which reduces the costs of installation and the complexity of the system, whereby in the latter case the lucidity is also increased for the operators.
  • a cost reduction of between 1 and 2 millions USD can be obtained for a 4-step bleaching line D 0 -EOP-D 1 -D 2 with intermediate wash steps, if the invention is fully applied.
  • FIG. 1 shows a conventional prior art bleaching sequence D 0 -EOP-D 1 -D 2 in which the filtrate is led in counter-current, via filtrate tanks;
  • FIG. 2 shows the same bleaching sequence D 0 -EOP-D 1 -D 2 in which the filtrate is lead between the steps in accordance with the invention, according to an embodiment using a high pressure mode
  • FIG. 3 shows a part of the bleaching sequence as also shown in FIG. 2 , but according to another embodiment of the invention where a low pressure mode is used, and,
  • FIG. 4 shows a section of a further embodiment according to any of the bleaching sequences according to FIG. 2 or FIG. 3 , wherein minor modifications have been performed.
  • FIG. 1 shows a conventional bleaching sequence D 0 -EOP-D 1 -D 2 in which the filtrate from the washing between the steps is led in counter-current between the bleaching steps, via filtrate tanks FT 1 -FT 4 .
  • wash apparatuses of wash press type are schematically shown, having two contra-rotating wash drums where wash liquor is supplied to the web of pulp on both drums, but subsequently the figure only shows the supply of wash liquor to one drum of the wash press.
  • the bleaching takes place in reactors at a pulp consistency of 10-14% and that after treatment in the reactor, the pulp is diluted to about 5-10%, typically about 8%, before it is fed to the wash press. After the wash press, the pulp has a consistency of 20-35%, typically 30%.
  • the washed pulp is fed down into a chute in which the pulp is diluted by a liquor that is pumped from a filtrate tank FT 1 , from which chute it is pumped by a pump and a subsequent mixer M 1 to a subsequent bleaching step, here a first chlorine dioxide step D 0 shown as an up-flow tower (the pulp flows upwards in the tower).
  • the chemicals for the bleaching step, ClO 2 and acidifier H 2 SO 4 are mixed-in by the mixer M 1 before the pulp is led to the D 0 bleaching tower.
  • the pulp After the bleaching in the D 0 bleaching tower, the pulp is led to a chute in which the pulp is diluted by filtrate from the first filtrate tank FT 1 . From the chute, the pulp is pumped to a subsequent wash W 2 in which the pulp is washed by wash liquor from a third filtrate tank FT 3 .
  • the pulp washed in the wash W 2 is led to a chute in which the pulp is diluted by filtrate from a second filtrate tank FT 2 , and from the chute the pulp is pumped by a pump and a subsequent mixer M 2 to a subsequent alkaline extraction step, here an EOP step shown as an up-flow tower.
  • the chemicals for the extraction step, NaOH and peroxide H 2 O 2 , and oxygen gas if needed, are mixed in by the mixer M 2 before the pulp is led to the EOP tower.
  • the pulp After the treatment in the extraction tower EOP, the pulp is led to a chute in which the pulp is diluted by filtrate from the second filtrate tank FT 2 , where after the pulp is pumped to a subsequent wash W 3 . In the wash W 3 , the pulp is washed by clean filtrate FF 2 .
  • the washed pulp is fed down to a chute in which the pulp is diluted by filtrate from a third filtrate tank FT 3 , where after the pulp is pumped by a pump and a subsequent mixer to a subsequent bleaching step, here a second chlorine dioxide step D 1 , shown as an up-flow tower.
  • the chemicals for the D 1 bleaching step, ClO 2 and pH-adjuster are mixed in by the mixer before the pulp is led to the D 1 bleaching tower.
  • the adjusting of pH can take place by addition of e.g. NaOH in the preceding chute.
  • the pulp After the treatment in the D 1 bleaching tower, the pulp is led to a chute in which the pulp is diluted by filtrate from the third filtrate tank FT 3 , where after the pulp is pumped to a subsequent wash W 4 . In the wash W 4 , the pulp is washed by filtrate from a fourth filtrate tank FT 4 .
  • the washed pulp is fed down to a chute in which the pulp is diluted by filtrate from a fourth filtrate tank FT 4 , where after the pulp is pumped by a pump and a subsequent mixer to a subsequent bleaching step, here a third chlorine dioxide step D 2 , shown as an up-flow tower.
  • the chemicals for the D 2 bleaching step, ClO 2 and pH-adjuster are mixed in by the mixer before the pulp is led to the D 2 bleaching tower.
  • the adjusting of pH can take place by addition of e.g. NaOH in the preceding chute.
  • the pulp After the treatment in the D 2 bleaching tower, the pulp is led to a chute in which the pulp is diluted by filtrate from the fourth filtrate tank FT 4 , where after the pulp is pumped to a subsequent wash W 5 . In the wash W 5 , the pulp is washed by clean filtrate FF 3 .
  • the pulp bleached by the shown bleaching sequence, D 0 -EOP-D 1 -D 2 is subsequently led to a storage tower (not shown) and typically has a brightness above ISO 80 and is often a fuilly bleached pulp of ISO 90.
  • a subsequent treatment can be used to modify the properties of the pulp in respect of drainage properties etc.
  • the main principle of the filtrate distribution of the shown bleaching sequence is that there are filtrate tanks between the treatment steps, which filtrate tanks receive the filtrate from the wash in question.
  • the filtrate tank FT 4 of the last wash W 5 collects the filtrate and then the filtrate is led in counter-current to the flow of pulp through the bleaching line, via pumps, and is used as dilution or wash liquor in preceding positions.
  • filtrate from the wash apparatuses W 4 , W 3 , W 2 is collected in the filtrate tanks FT 3 , FT 2 and FT 1 , respectively, and then the filtrate is led via pumps, from the respective tank in counter-current to the flow of pulp through the bleaching line.
  • a certain share of the filtrate is also bled off, as is shown in the feed from the filtrate tanks FT 1 and FT 2 , in order to avoid accumulation of increasing contents of undesired substances, which bleeding-off is compensated by supply of cleaner filtrates FF 1 and FF 2 .
  • the bleeding-off of filtrate is the principle outlet from the bleaching line.
  • alkaline filtrate is separated from acidic. Accordingly, the alkaline filtrate from the EOP step is collected in the filtrate tank FT 2 , and no acidic filtrate is used in the wash W 3 , but instead clean filtrate FF 2 is used.
  • such alkaline filtrate can be fed on, upstream, to the oxygen delignification, where it is used as wash liquor in the wash after the oxygen delignification.
  • the wash liquor is led strictly counter-current to the flow of pulp, i.e. from FT 4 to FT 3 , and finally to FT 1 from where the acidic filtrate is bled off from the bleaching department since it can not be handled in the recovery system, mainly due to high contents of chloride that destroy the soda recovery boiler.
  • FIG. 2 shows an embodiment of the invention, in which the same bleaching sequence is performed as described/shown in relation to FIG. 1 , but in which the filtrate distribution system instead of the large number of filtrate tanks, has been replaced by a joint main conduit 1 for all acidic bleaching steps, in accordance with the invention.
  • bleaching of the cellulose pulp takes place in a bleaching line with at least two bleaching steps in the bleaching line and at some point including a first and a second bleaching step D 1 , D 2 in succession, as seen in the flow direction of the cellulose pulp, which bleaching steps have wash apparatuses W 4 and W 5 for the pulp arranged after the first and the second bleaching step, respectively.
  • FIG. 1 A bleaching line with at least two bleaching steps in the bleaching line and at some point including a first and a second bleaching step D 1 , D 2 in succession, as seen in the flow direction of the cellulose pulp, which bleaching steps have wash apparatuses W 4 and W 5 for the pulp arranged after the first and the second bleaching step, respectively.
  • wash liquor and dilution liquor is led in principle in counter-current to the flow of pulp via the main conduit 1 and through the bleaching steps of the bleaching line, which flow of pulp (bold arrows are flow lines) passes through the sequence W 1 -D 0 -W 2 -EOP-W 3 -D 1 -W 4 -D 2 -W 5 .
  • the wash liquor is supplied to the main conduit 1 that is arranged in parallel to the bleaching line, by a pump P 20 from a filtrate tank FT 2 .
  • the pump P 20 maintains a pressure of about 5-6 bar at a first branch portion A 1 within the main conduit 1 .
  • Al wash liquor and dilution liquor (depending on what kind of wash equipment is being used dilution liquor may possibly be dispensed with.
  • both liquors have to be supplied, which would not be the case if e.g.
  • wash liquor and dilution liquor is taken via L 3 to the wash W 4 of the first bleaching step D 1 , from a third branch position A 3 in the main conduit 1 , and the filtrate from this wash W 4 is led via L 4 to a fourth branch position A 4 of the main conduit.
  • the branch positions A 1 -A 4 connect to the main conduit with the first branch position A 1 arranged first, as seen in the direction of flow in the main conduit 1 , and the second to fourth branch positions A 2 -A 4 in succession thereafter, such that an open communication is established in the main conduit between the branch positions A 1 -A 4 .
  • the main pump P 20 pressurises the main liquor within the conduit and establishes a basic flow in the main conduit in a direction reverse to the formed flow of cellulose pulp in the bleaching line. Thanks to the pressurisation within the main conduit 1 there is no need to use an additional pump to supply wash liquor via each respective branch line supplying each respective wash press, see for example L 1 that supplies W 5 positioned finally in the bleach line.
  • the flow that is taken from the wash apparatus W 5 in return through line L 2 back to the main conduit 1 is somewhat larger than the amount that is supplied through L 1 .
  • FIG. 3 there is shown a further embodiment according to the invention, wherein a low pressure main conduit 1 is being used (merely a portion of the bleach line is shown since the process is the same as shown in FIG. 2 . Accordingly it is evident that the same principles as shown for the upstream portion of the main conduit shown in FIG. 3 also applies for the downstream portion). In such an embodiment a pressure of about 1-2 bar is maintained within the main conduit 1 . As can been seen in FIG. 3 there is therefore a need to use pumps P 21 , P 22 , to pressurise the wash liquid that has to be supplied to the wash apparatus through its respective line L 1 A, L 3 A, etc.
  • each standpipe SP 9 , SP 7 directly subsequent to a bleach tower is supplied via its line L 3 C, L 4 C without the need for a pump.
  • a pump P 21 ′, P 22 ′ is needed to pressurise the filtrate back into the main conduit 1 .
  • a modification for achieving the desired pressure in the main conduit i.e.
  • this embodiment is similar to the function as described in relation to FIG. 2 .
  • the invention may very well be used merely for two bleach steps, e.g. D 1 and D 2 as shown in FIG. 3 .
  • FIG. 4 there is schematically shown a part of a bleach line as in FIG. 3 , wherein it is presented that filtrate tanks FT 3 may be used within a bleach line according to the invention. Moreover it is also shown that a pressure buffer tank FT 4 may be used in order to balance the pressure within the main conduit 1 . It is evident that a number of filtrate tanks may be used and that they may be of comparatively limited size, e.g. less than 1 m 3 , possibly about 500 litre. As is disclosed the pump P 21 ′ may normally not be dispensed with, since the tank FT 3 is preferably positioned at a relatively low level and is preferably not a pressure vessel. It is also shown that in many cases a furher pump P 21 ′′ is used to supply the filtrate from the wash W 5 to the tank FT 3 .
  • main conduit 1 ′ may suitably be used for bleaching steps of different alkalnity (above or below pH7).
  • one main conduit,(e.g. as in FIG. 2 ) is used for a number of acidic steps and another main conduit is used for a number of alkaline steps (the latter not shown).
  • At least one additional bleaching step D 0 may be provided before the first and second bleaching steps D 1 and D 2 , respectively, as seen in the flow direction of the cellulose pulp, after which additional bleaching step D 0 there is a wash apparatus W 2 for the pulp. Then wash liquor and dilution liquor is taken to the subsequent wash W 2 of the additional bleaching step, from a fifth branch position A 5 in the main conduit 1 . At least a part of the wash filtrate from the subsequent wash W 2 of the additional bleaching step is led to a sixth branch position A 6 into the main conduit.
  • the branch positions connect to the main conduit with the fifth branch position A 5 arranged after the fourth branch position A 4 , as seen in the direction of flow in the main conduit 1 , and the sixth branch position A 6 in succession thereafter, an open communication being established in the main conduit between the branch positions A 1 -A 6 .
  • An alkaline extraction step, EOP or alternatively an EO step without peroxide charge, in a per se conventional manner, is arranged after the additional bleaching step D 0 and before the first bleaching step D 1 , as seen in the direction of flow of the cellulose pulp through the bleaching line, and a wash apparatus W 3 is arranged after the extraction step EOP.
  • the wash filtrate from the subsequent wash W 3 of the extraction step can be collected in a filtrate tank FT 1 and is suitably used as dilution liquor before the extraction step and a part of the wash filtrate can if needed be drawn off from the bleaching line, to sewage 11 , or be led forward to an oxygen delignification step.
  • the cellulose pulp is washed in a wash apparatus W 1 before the additional bleaching step D 0 , (as seen in the direction of flow of the cellulose pulp through the bleaching line) and dilution liquor is taken via L 7 to this wash apparatus W 1 from a seventh branch position A 7 in the main conduit.
  • the wash liquor to this wash W 1 is taken from a separate line L 0 as fresh wash liquor.
  • At least chlorine dioxide, or some other bleaching chemical that is compatible throughout the bleaching steps is used as active bleaching agent in the bleaching steps D 0 , D 1 and D 2 , which chlorine dioxide is added to the pulp before the respective bleaching step in a blending apparatus M 1 , M 3 and M 4 , respectively.
  • the outlet 10 is controlled by a flow controlling control valve FC, which control valve can establish a certain basic flow and/or a desired bleed-off level of filtrate, during normal operation.
  • the pump P 20 is suitable controlled by a pressure is regulator PC, enabling feed-back control of the main pump device P 20 in order to secure the desired predetermined pressure and/or flow throughout the entire main conduit 1 .
  • the flow controlling valve can establish a desired flow to the outlet 10 as long as the pressure in the main conduit can be maintained.
  • the flow controlling valve FC may be a fixed or variable throttle valve with a high pressure drop over the valve.
  • a bleaching line for the bleaching of cellulose pulp, having at least two bleaching steps comprising a first and a second bleaching step D 1 and D 2 , respectively, as seen in the flow direction of the cellulose pulp, which bleaching steps have wash apparatuses W 4 and W 5 for the pulp arranged after the first and the second bleaching step, respectively, and in which wash liquor and where appropriate dilution liquor is led in principle in counter-current to the pulp flow through the wash apparatuses in the bleach line.
  • the bleaching line preferably also includes at least one additional bleaching step D 0 , which is arranged before the first and second bleaching steps D 1 and D 2 , as seen in the direction of flow of the cellulose pulp.
  • a wash apparatus W 2 for the pulp is arranged. At least one liquor of wash liquor and dilution liquor is taken to the subsequent wash W 2 of the additional bleaching step, from a fifth branch position A 5 in the main conduit 1 and at least a part of the wash filtrate from the subsequent wash of the additional bleaching step is led to a sixth branch position A 6 in the main conduit 1 .
  • the branch positions A 5 -A 6 connect to the main conduit 1 with the fifth branch position A 5 arranged after the fourth branch position A 4 , as seen in the direction of flow in the main conduit, and the sixth branch position A 6 in succession thereafter, an open communication being established in the main conduit between the branch positions A 1 -A 6 .
  • An extraction step may be arranged in the shown bleaching line, preferably of EOP or EO type, which is arranged after the additional bleaching step D 0 and before the first bleaching step D 1 , as seen in the direction of flow of the cellulose pulp through the bleaching line, and a wash apparatus W 3 is arranged after the extraction step.
  • the wash filtrate from the subsequent wash W 3 of the extraction step is led to a filtrate tank FT 1 , via a conduit, and filtrate from the filtrate tank is, at least partly, led as dilution liquor after the wash step W 2 subsequent to the additional bleaching step D 0 , via pump P 30 and conduits, and a part of this wash filtrate is when needed drawn off from the process, preferably via an outlet from the filtrate tank FT 1 .
  • a part of the liquor in the filtrate tank may also be used as dilution liquor in the chute after the EOP reactor.
  • cellulose pulp is suitably washed in a wash apparatus W 1 before the additional bleaching step D 0 , as seen in the direction of flow of the cellulose pulp through the bleaching line, and to this wash apparatus W 1 at least one liquor of wash liquor and dilution liquor is led from a seventh branch position A 7 in the main conduit 1 to the wash apparatus W 1 , via a pump device P 24 and associated tubing.
  • the pulp in the storage tower ST is acidic, both wash and dilution liquor in and after the wash W 1 , respectively, can be taken from the main conduit. But if the pulp in the storage tower is alkaline, a cleaner alkaline filtrate or a clean filtrate is used as wash liquor in the wash apparatus W 1 , where the use of a clean filtrate is shown in FIG. 2 .
  • bleaching steps D 0 , D 1 , D 2 of the bleaching line e.g. chlorine dioxide is charged as active bleaching agent or some other bleaching chemical that is compatible throughout the bleaching steps, such as a chelating agent, a pH adjuster or some additional bleaching chemical, which chlorine dioxide or bleaching chemical is added to the pulp before the respective bleaching step in a blending apparatus M 1 , M 3 and M 4 , respectively.
  • active bleaching agent e.g. chlorine dioxide is charged as active bleaching agent or some other bleaching chemical that is compatible throughout the bleaching steps, such as a chelating agent, a pH adjuster or some additional bleaching chemical, which chlorine dioxide or bleaching chemical is added to the pulp before the respective bleaching step in a blending apparatus M 1 , M 3 and M 4 , respectively.
  • an outlet 10 is provided, from which wash liquor and filtrate can be drawn off from the main conduit.
  • the outlet 10 is controlled as is described above, by a pressure and/or flow controlling control valve PC and/or FC.
  • the invention can be varied in a number of ways, within the scope of the claims.
  • the bleaching steps that in their subsequent wash apparatuses have a joint main conduit that receives wash filtrate and dilution and/or wash liquor may, for example, all be of alkaline type or the bleaching chemicals in question may be compatible/blendable.
  • a main conduit may be used for the alkaline filtrate from two or more alkaline steps and another main conduit may be used for the acidic filtrate from two or more acidic steps.
  • the pumps P 21 -P 24 are placed in the feed conduits from the main conduit
  • powerful pumps may be provided in the return conduits that connect to the branch points A 2 , A 4 and A 6 , respectively, is which in such case, together with the main pump P 20 , pressurise the entire main conduit.
  • a pressure in the main conduit established at 4 bar pumps in the feed conduits for dilution and/or wash liquor can normally be eliminated.
  • the supply of dilution liquor after wash normally requires a very low pressure of about 1 bar, why a throttle is required for such dilution liquor supply.
  • the dilution liquor is supplied to an atmospheric dilution screw in which fluffed-up pulp of high consistency, about 30%, is blended with dilution liquor to a consistency suitable for subsequent pumping. Therefore, there is a low pressure need on the liquor supply.
  • a basic pressure of about 1 bar may be established in the main conduit, which is enough to feed dilution water, but in which a supplying pump is provided in the feed conduit for the wash liquor.
  • wash liquor is added in a converging wash slot in a wash press at a higher pressure and normally, a wash liquor pressure of at least 2-4 bar is required in this position.
  • a check valve may be provided between the branch positions for filtrate recycling to the main conduit and feeding of dilution and/or wash liquor to the wash apparatus in question, especially if the branch positions of construction reasons are close to each other. It is preferred that an open communication is established between all branch points in the main conduit, as seen in the direction from the first end of the main conduit, with the filtrate tank FT 2 , to the second end of the main conduit, with the outlet 10 , but this does not eliminate that valves may be positioned within the main conduit 1 .
  • wash presses may of course be used.
  • ordinary filters or simple presses (without washing) may of course be used, in which the filtrate from the filter or the simple press is led to the main conduit and optional dilution liquor before the filter or the press is taken from the main conduit.
  • wash presses such as a filter or a simple press without wash, may be connected to a joint main conduit.
  • the at least two bleach steps being connected to the main conduit 1 may have one or more non-connected bleach steps, belong in to the same bleach line, in intermediate position/s between them.
  • auxiliary equipment e.g. filtrate tank/s, valves
  • auxiliary equipment e.g. filtrate tank/s, valves
  • the extension of the main conduit may vary, e.g. following a straight line and/or being curved and/or having several bends (e.g. 90°), etc. to fit different needs at different cites, depending on the position of items in the bleach line.
  • pressurisation at different locations may be achieved by other means than a pump, e.g. instead of pump P 20 a tower or the positioning of the main conduit high up may be used to apply the desired pressure (static pressure).

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US10/541,435 2003-01-31 2003-12-09 Method for washing pulp in a bleaching line and a bleaching line Abandoned US20060113048A1 (en)

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SE03002763 2003-01-31
SE0300276A SE521780C2 (sv) 2003-01-31 2003-01-31 Förfarande för blekning av cellulosamassa samt bleklinje härför
PCT/SE2003/001915 WO2004067834A1 (en) 2003-01-31 2003-12-09 Method for washing pulp in a bleaching line and a bleaching line

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US10/542,265 Abandoned US20060090866A1 (en) 2003-01-31 2003-12-09 Method for washing pulp in a bleaching line
US10/756,234 Active 2024-09-16 US7077931B2 (en) 2003-01-31 2004-01-13 Method and bleaching line with a main conduit for wash liquor

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SE0300276L (sv) 2003-12-09
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AU2003283939A1 (en) 2004-08-23
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