Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
  • D21D5/26—De-aeration of paper stock
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
  • D21B1/00—Fibrous raw materials or their mechanical treatment
  • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
  • D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
  • D21B1/30—Defibrating by other means
  • D21B1/34—Kneading or mixing; Pulpers
  • D21B1/342—Mixing apparatus

Definitions

• the present invention relates to a method and arrangement for treating pulp.
• the method and arrangement according to the invention are especially suitable for use in production of chemical pulp in situations where gas must be removed from the pulp and where the pulp must be diluted.
• the invention is, of course, also suitable for use in other corresponding applications in both chemical and mechanical wood processing industry.
• chemical wood processing can be considered to start from the digester, in which the wood material fed into the digester as chips is treated so that subsequent to the digester the pulp is mainly in fibrous state or it can at least be easily disintegrated into fibrous state.
• the so-called brown stock discharged from the digester is washed and taken into delignification stage, in which oxygen is usually used as the delignification chemical.
• the delignification stage ends with washing, which can be accomplished by means of wire or drum presses, pressurized drum presses or suction drum presses.
• DrumDisplacerTM-washer that in the recent years has become relatively popular, is by its working principle a pressurized drum washer, but a typical feature of it is that a number of washing stages have been arranged therein.
• the washers discharge the pulp in medium consistency, i.e. at a consistency of about 10 %.
• the presses can, however, discharge the pulp in a consistency of about 20 %.
• the brown stock, or, more generally, pulp has to be diluted prior to its introduction into a washing apparatus.
• the brown stock or pulp should be as gas-free as possible as the presence of gas in the pulp has a negative effect both in the washing/filtering operation and in the treatment of the filtrates later on. For instance, filtrates having a high gas content tend to start foaming when they are pumped further, just to name one problem caused by excess gas in the filtrates.
• delignification process is followed in the process by the pulp screening, the aim of which is to separate the material unwanted for further process and especially for the final product from the pulp.
• Screening is, however, an operation requiring the consistency of the pulp to be diluted to about 1 - 3 %, depending on some degree on the apparatus to be used.
• an intermediate tank is arranged in the process subsequent to the washing apparatus for pumping the necessary amount of dilution liquid.
• the pulp from the washing apparatus is discharged into the intermediate tank through the top thereof, whereby the pulp is discharged directly adjacent the dilution mixer located at the bottom of the tank and is quickly mixed with the dilution liquid introduced preferably through the mixer so that pulp in relatively even consistency can be pumped from the tank into the subsequent process stage, the screening apparatus.
• the fibre cover will over time cause the fibres remaining on the surface of the pulp to be spoiled by the influence of air.
• the tank is also used as a buffer tank, the surface of which is sometimes drained very low, this spoiled fibre material is mixed with the rest of the diluted pulp during the low surface condition, whereby the spoiled fibre material can be passed on as far as to the final product and cause a momentary deterioration of its quality.
• the consistency of the diluted pulp increases momentarily, because the consistency of the fibre cover floating in the tank is much higher than the consistency of the rest of the pulp in the tank. Subsequent to this it only depends on the dilution regulation system of the tank whether the change of consistency is seen in the whole process or whether the regulation system reacts correctly and fast enough to even out the consistency to a desired level.
• the size of the intermediate tank can be seen as a fourth problem, completely separate from the previous problems, the size varying from some tens of cubic meters to hundreds of cubic meters.
• the size of the tank is determined on the other hand mostly by the buffering needs of the process, i.e. the need to store pulp in case of fluctuations in the production of the digester side of the process.
• the consistency of the stored pulp is also important, because doubling the consistency would reduce the required size of the tank by half.
• tripling the consistency would reduce the required size to a third of the original. With such big differences between the high and low consistency tanks it is possible to achieve savings in both costs and space by changing to a higher consistency.
• the method for treating pulp according to the invention in which method pulp is moved from a first, higher consistency to a treatment in a second, lower consistency, is characterized in that a) gas is separated from the pulp in a consistency higher than said second consistency, b) pulp is pumped in the low consistency treatment, and c) pulp is diluted to said second consistency prior to the treatment in said consistency.
• the arrangement for treating pulp according to the invention comprising at least a first pulp treatment apparatus, from which pulp is discharged in a first consistency, a second pulp treatment apparatus, from which pulp is discharged at a first consistency, a second pulp treatment apparatus requiring a second consistency, lower than the discharge consistency of the first pulp discharge apparatus, and a pump for transferring pulp into the second pulp treatment apparatus, is characterized in that both an apparatus for degassing the pulp at a consistency higher than said second consistency and an apparatus for diluting the pulp into the consistency required by the second pulp treatment apparatus is arranged between the first and second pulp treatment apparatuses.
• figure 1 illustrates a prior art process arrangement
• figure 2 illustrates a process arrangement according to a preferred embodiment of the invention
• figure 3 illustrates a process arrangement according to another preferred embodiment of the invention
• figure 4 illustrates a process arrangement according to a third preferred embodiment of the invention
• figure 5 illustrates a process arrangement according to a fourth preferred embodiment of the invention.
• a prior art process arrangement starts with a washing apparatus 5, which can, as described above, be a pressurized drum washer, suction drum washer, a wire press or a roll press, to name a few examples.
• a washing apparatus 5 which can, as described above, be a pressurized drum washer, suction drum washer, a wire press or a roll press, to name a few examples.
• an intermediate tank 10 which can also be called a buffer tank or a storage tank.
• the tank is preferably provided with a mixer 12 as described in FI patent 90732 for mixing the dilution liquid into the pulp introduced into the tank 10.
• the pulp can be introduced into the tank 10 from the washer apparatus 5 through a conduit most often located on the cover 14 of the tank.
• the diluted pulp is discharged from the tank, from the bottom thereof, by means of a pump 16, the pump being, for example, a gas separating so-called AirSepTM pump.
• the pressure of the pulp is increased by means of the pump 16 for the subsequent screening stage 50 of the process.
• the prior art process arrangement does not work in an optimal way. It has, firstly, been noted that especially after the oxygen stage, oxygen delignification, there are relatively much gaseous substances present in the pulp, the substances passing through the washer 5 into the intermediate tank 10. In the atmospheric conditions of the intermediate tank 10 the gases on their part cause the relatively fast forming of a dense fibre raft on the surface of the pulp, the fibre raft preventing almost totally the separation of gas from the diluted pulp, whereby the gases are trapped in the diluted pulp and are transferred further into the process with the pulp.
• the fibre raft is slowly spoiled by the influence of air and other gases.
• the tank 10 is used also as a buffer tank, the surface of which is sometimes drained very low, the spoiled fibre material is mixed with the rest of the diluted pulp during the low surface condition, whereby the spoiled fibre material can be passed on as far as to the final product and cause a momentary deterioration of its quality.
• the consistency of the diluted pulp increases momentarily, because the consistency of the fibre cover floating on the surface of the tank 10 is much higher than the consistency of the rest of the pulp in the tank 10.
• the size of the intermediate tank 10 can be seen as a fourth problem, the size varying from some tens of cubic meters to hundreds of cubic meters.
• the size of the tank 10 is mostly determined by the buffering needs of the process, i.e. the need to store pulp in case of fluctuations in the production of the digester side of the process, a large tank 10 can be seen as a problem because of both, its space requirements and its production costs.
• FIGS 2 - 4 show process arrangements according to some preferred embodiments of the invention, the arrangements starting from the washing apparatus 5 as in prior art. Subsequent to that, however, the process arrangement has been changed so as to allow storing the pulp in the intermediate tank in higher consistency.
• the process arrangement is shown to end in the screening stage 50, which in practice thereby preferably remains unchanged, like the washing apparatus, despite the changes in the process part therebetween.
• FIG. 2 shows a process arrangement according to a preferred embodiment of the invention, in which pulp is discharged into the intermediate tank 20 from the washing apparatus 5 as in prior art, in the discharge consistency of the washing apparatus, the consistency being of course higher than the consistency of the screening stage 50.
• the pulp is not diluted in the intermediate tank, at least not to the consistency needed by the screening stage, but the consistency of the pulp is kept preferably equal with the discharge consistency of the washing apparatus.
• pulp when the discharge consistency is very high (most usually over 14 %), pulp must diluted in the tank 20, but even in this case to only the medium consistency range of about 10 - 12 %.
• a bottom scraper 22 has been arranged in connection with the bottom of the tank, by means of which pulp is discharged from the tank 20 to the drop leg 24. If dilution is needed, it can preferably be done by means of said bottom scraper 22.
• a so-called MC pumpTM 26 having gas separation capable of pumping medium consistency pulp various alternative examples of which have been disclosed in, for example patents US 4,921 ,400, US 5,058,615, US 5,019,136, US 5,167,678, US 4,971 ,519, US 4,877,424, US 4,877,368, US 4,981 ,413, US 5,152,663, US 5,538,597, US 5,114,310, US 5,078,573, US 5,116,198, US 5,151 ,010, US 5,842,833, US 6,120,252, US 6,551 ,054 of Sulzer Pumps Finland, which are hereby included as reference in this disclosure, has been arranged in the bottom end of the drop leg 24.
• a typical feature of said MCTM pump is that a rotor producing powerful turbulence in the pulp has been arranged at least partially inside the inlet tract of the pump. In most cases the rotor is integral with the impeller of said pump.
• the MCTM pump 26 is used for both discharging pulp from the drop leg and separating gas. Pulp is fed into the mixer 28 by means of a pump 26, the mixer being used for diluting the pulp into the consistency of the subsequent process stage, in this example the screening stage 50.
• this process according to the invention utilises both storing the pulp in the intermediate tank and discharging pulp from the tank in a consistency higher than that of prior art, mostly in MCTM consistency, which will prevent the detrimental effects of the fibre raft formed in connection with diluting. Simultaneously with the increase of the storage consistency it has been possible to decrease the size of the tank.
• Figure 3 shows a process arrangement according to another preferred embodiment of the invention. It can be used in applications in which no large buffer tank is needed, but the process is relatively stable, so that in order to ensure an even flow of pulp is sufficient to discharge pulp from the washing apparatus 5 directly into the drop leg 30, the lower end of which is connected to a so-called MCTM pump of the type mentioned above, subsequent to which there is a dilution mixer 28 and a screening stage 50.
• MCTM pump of the type mentioned above
• the first basic type can be seen as a solution most resembling the embodiment of figure 2, i.e. a situation in which the above-mentioned MCTM pump is connected to the bottom of the drop leg so, that it can discharge the drop leg directly without any auxiliary means.
• an essentially vertical rotor 32 has been arranged inside the drop leg 30 for helping the pulp flow in the drop leg 30 downwards until the inlet of the MCTM pump.
• the rotor 32 can be a rotor forming only efficient turbulence or it can additionally be provided with gas separation in a way known from prior art.
• the " drop leg 30 with its rotor 32 is. similar to that of the other basic type, but the pump is no longer an MCTM pump, but it's a simpler centrifugal pump that is not provided with a rotor forming efficient turbulence in its inlet.
• a rotor provided in the drop leg either with gas separation or without it, can ensure that pulp will fiow to the lower end of the drop leg and from there through the inlet to the impeller of the centrifugal pump.
• FIG 4 shows a process arrangement according to a third preferred embodiment of the invention. It is applicable to situations, in which pulp flow from the washing apparatus is essentially even and no considerable buffer capacity is needed in the fibre line at this point.
• US patent 5,851 ,350 which is hereby incorporated as reference in its entirety, discloses the pumping arrangement in more detail, a typical feature of the arrangement being that the discharge screw of the washing apparatus 5, most washing apparatuses being provided with one, feeds pulp essentially directly to the inlet channel 42 of the pump 26.
• the pump 26 does not have to be provided with a turbulence-forming rotor, even if it were preferred, especially in connection with higher consistencies.
• the dilution mixing can also be carried out either using a static mixer or a mixer rotating on its own in the flow.
• a conventional centrifugal pump, or an MCTM pump can also be used as a mixer, with the liquid required for dilution being introduced into the inlet channel or inlet duct or into a specifically designed inlet duct for the dilution liquid. It is naturally possible to use centrifugal pumps designed for this purpose, too, in which the impeller is designed with mixing in mind.
• the same apparatus can, optionally, be used for both degassing the pulp or stock, and for diluting the pulp one may imagine that the degassing of pulp does not take place exactly in the discharge consistency of the upstream storage tower, the treatment apparatus or the like but in a somewhat lower consistency. However, in any case, in accordance with the invention the degassing is done at a consistency higher than the feed consistency of the treatment apparatus later in the process.
• FIG. 5 yet another embodiment of the invention has been shown.
• the presence of gas is harmful to the operation of various kinds of pulp washing and dewatering equipment.
• the washing and/or dewatering or filtering equipment requires often dilution of pulp to a consistency well below 10 percent.
• Fig. 5 illustrates a process arrangement where pulp, or brown stock is introduced in at least medium consistency to a storage tower, or a blow tank (into which brown stock from a digester is blown) or some other vessel 20, from where the pulp is introduced into a pump 26 capable of pumping pulp of at least medium consistency.
• the pump 26 is capable of separating gas from the pulp while pumping the pulp.
• the pump 26 transfers the pulp to a washing, filtering or dewatering unit 55.
• a common feature to the unit 55 whether it is a vacuum drum washer, a pressurized drum washer, a wash press, or a wire press, just to name a few options without any intention to limit the scope of the applicable washing/filtering devices, is the need of receiving the pulp at a lower consistency.
• Fig. 5 suggests the use of a dilution mixer 28 between the pump 26 and the washing/filtering unit 55 just as the earlier embodiments, too.
• the pump 26 could also be used for diluting the pulp whereby a separate mixer for diluting the pulp would not be required.
• MCTM pump in addition to the above-mentioned so-called MCTM pump is being proposed to be used in pumping pulp and separating gas therefrom, it is also possible to use other suitable apparatuses for this purpose, the apparatuses being capable of both separating gas from the pulp and pumping the pulp in the desired consistency.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

Priority Applications (5)

Applications Claiming Priority (4)

Publications (1)

Family

ID=28043346

Family Applications (1)

Country Status (8)

Cited By (3)

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Citations (8)

Family Cites Families (1)

• 2003
  • 2003-08-18 FI FI20031164A patent/FI20031164A/sv not_active IP Right Cessation
• 2004
  • 2004-07-05 CA CA002531642A patent/CA2531642A1/en not_active Abandoned
  • 2004-07-05 US US10/564,265 patent/US20070158041A1/en not_active Abandoned
  • 2004-07-05 WO PCT/CH2004/000421 patent/WO2005005716A1/en active Application Filing
  • 2004-07-05 BR BRPI0412428-6A patent/BRPI0412428A/pt not_active IP Right Cessation
  • 2004-07-05 EP EP04738062A patent/EP1641977A1/en not_active Withdrawn
  • 2004-07-05 RU RU2006103785/12A patent/RU2352700C2/ru not_active IP Right Cessation
  • 2004-07-05 JP JP2006517931A patent/JP2008519167A/ja not_active Abandoned

Patent Citations (8)

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