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
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
  • D21C9/005—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives organic compounds
• • 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
  • D21C9/18—De-watering; Elimination of cooking or pulp-treating liquors from the pulp

Definitions

• the present invention deals with a chemical addition to a pulp washing system which causes less liquid to remain with the pulp when it is formed into a mat, effectively increasing the pulp consistency. This increase in mat consistency during pulp washing allows for a washing operation to run cleaner and at a higher production rate.
• Pulp is commonly washed by subjecting it to a series of dilution/thickening phases, in which the stock consistency (% fiber) is diluted to approximately 0.5 - 5% and is thickened to approximately 10 - 30%.
• showers are also used to displace part of the dirty liquid fraction held by the pulp during the thickening phases.
• filtrate from the cleaner phase is used to shower and/or redilute a dirtier phase in the process.
• the most commonly used pulp washer is a vacuum drum system with 3 to 4 stages in series. There are a wide variety of systems in use, however, some of which do not use both dilution/thickening and displacement between phases, but rather only one or the other.
• the liquor commonly referred to as black liquor in the often used Kraft pulping process, tends to be very foamy due to its makeup (containing lignin and soaps or pitch) and the general nature of the process itself. Because of this, defoamers are a necessary additive in the washing process in order to efficiently thicken the stock (increase its consistency) in the various stages of washing, as a foamy stock tends to hold liquid rather than separate from it.
• the present invention refers to a method of enhancing the process of pulp washing, to remove from the pulp contaminants contained in the liquid fraction, by decreasing the tendency of the liquid to remain with the pulp (increase the pulp's consistency). This is particularly important in grades that will be bleached.
• a surfactant or surfactant mixture to the pulp thickening operation, e.g., to the washing process (preferably at about 0.5 - 2,000 parts per million parts of pulp) in addition to the defoamer which is already present, the liquid holding capacity of the pulp can be reduced. This increase in mat consistency during pulp washing can allow a washing operation to run cleaner and/or faster.
• Surfactants of the following general formula are the subject of the present invention: R-X(CH2CH2O) n YZ wherein R is alkyl or alkylaryl, X is or O, and n is from about 1 - 30; Y is hydrogen, sulfate, sulfonate, phosphate or carboxylate; and Z is a water soluble cation, wherein Z is not present when Y is hydrogen.
• the water soluble cation is preferably Na+, K+, NH4+, Ca2+, Mg2+ or H+.
• the surfactants of the present invention may be either nonionic or anionic.
• pulp thickening operation may occur under vacuum pressure or gravity, while the pulp may be produced from wood chips using mechanical or chemical means.
• the pulp may be deinked secondary fiber.
• R is preferably from about C4 - C22 alkyl or C2 - C12 alkylaryl.
• the ethylene oxide unit may optionally be ethylene oxide with propylene oxide in blocks within the chain or capping the chain, or a short C1 - C4 alkyl group.
• the surfactants may be added to the washing process through the stock washing showers and/or directly to the stock/liquor mixture either within the washer or anywhere prior to the stock reaching the washer.
• Many of these surfactants tend to be inherently foamy materials as is the stock itself, therefore a defoaming agent may need to be present in the system in order to obtain benefits from these materials.
• the treatments of the present invention may be added anywhere prior to the pulp thickening process, e.g., to the chips, in the digester or screens.
• the treatments may also be added after initial washing stages in order to benefit subsequent thickening operations (decker, bleach plant washers, market pulp machines, deink plants).
• Brown stock collected from a Southern Kraft softwood mill was diluted to 0.7% consistency stock with black liquor.
• the black liquor had been previously diluted to contain roughly 4% dissolved solids.
• Liquor used to shower the brown stock was diluted to contain roughly 1% dissolved solids. These solids levels correspond to a typical second stage of brown stock washing in a three stage vacuum drum setup.
• the diluted stock and shower liquor were heated to 160°F.
• the diluted stock 300 ml
• the shower liquid 25 ml was then applied and the system subjected to vacuum for an additional 10 seconds.
• the consistency of the mat was then measured. When treatments were added they were added to the stock and shower liquid prior to incubation.
• the defoamer (a) used in this study containing a combination of oil and ethylene bis stearamide, or EBS (typical components in brown stock washing defoamers), was added at 100 ppm (total weight basis).
• the surfactant used in this example was Rhodapex N-70 (available from Rhone Poulenc) which is an alcohol ethosulfate, added at 100 ppm actives. The results are contained in Table I.
• This laboratory device unlike a typical brown stock washer, is designed to minimize the generation of foam. This explains why the untreated sample actually has a higher consistency than that treated with the defoamer. The defoamer apparently inhibits liquid removal versus that of a non-foamy system. Unfortunately, brown stock washers cannot be operated without defoamers as the turbulent process tends to generate foam.
• Example 2 a similar type of study as described in Example 1 was conducted over a series of days. The results for the individual days are listed as variations in stock and liquor age, temperature, and starting consistency can affect the results. The simulations were all conducted as described in Example 1. In each case, Defoamer A was added to the stock (at 100 ppm). The treatment was added to the stock and displacement shower liquid (at 100 ppm actives). The resultant mat consistencies are listed along with the percent increase or decrease in mat consistency that was observed with the treatment addition, in Table II (anionic materials) and Table III (nonionic materials).
• the present invention is effective in increasing mat consistency in the presence of different types of defoamer.
• a mill trial was conducted using Formula I, discussed in Example 3, added to the system at 0.75 lbs/ton (lbs Formula I per ton of dry pulp produced).
• the mill was in a northern location using softwood pulped with the Kraft process.
• a typical three stage counter current, vacuum drum washer was used to wash the stock prior to bleaching.
• the brown stock defoamer used in the process was based on hydrocarbon oil and silica.
• a washing aid (made up of an anionic dispersant, nonylphenol ethoxylate, and an ethoxy/propoxy/ethoxy block surfactant) was also fed to the system (1.4 lbs per ton) where the second stage mat was diluted just before the pulp entered the third stage of washing during the pretrial period. This wash aid was replaced by Formula I for the trial period.
• Table V contains the results for third stage mat consistency, the carryover (lbs per ton) of contaminant solids in the liquor leaving with the third stage mat, and the vacuum that the third stage drum was pulling.
• TABLE V Results from Northern Mill Trial Trial Mat Consistency (%) Carryover (#/T) Vacuum (in Hg) Pretrial period 11.4 43.7 ------ 10.8 53.7 17.8 10.7 109.4 16.8 11.9 24.3 17.4 10.4 30.0 16.0 10.8 46.5 ------ 10.3 53.4 14.0 Trial period 11.6 16.1 16.8 11.7 19.1 13.8 12.0 21.0 15.5 11.7 17.9 15.0 11.2 43.5 16.0 11.8 22.1 14.2 Pretrial avg. std dev. 10.9 51.6 16.4 0.6 27.8 1.5 Trial avg. std dev. 11.7 23.3 15.2 0.3 10.1 1.1
• the increase in consistency of the mat also caused a decrease in the vacuum of the drum washer. With a greater amount of liquid removed from the mat, air could be pulled through thee mat, decreasing the measured vacuum.
• This example shows that the present invention not only works in pulp produced from the Kraft pulping process, but also pulp produced in the sulfite process.
• the treatments of the present invention may be used in combination with various detackification products (i.e., various water soluble surface active polymers such as those noted in U.S. Patent 4,744,865) which are commonly used in the pulp mill in order to, e.g., control pitch outbreaks.
• various detackification products i.e., various water soluble surface active polymers such as those noted in U.S. Patent 4,744,865
• water soluble surface active polymers such as those noted in U.S. Patent 4,744,865

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Paper (AREA)

Applications Claiming Priority (2)

Publications (1)

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Cited By (3)

Citations (5)

• 1995
  • 1995-09-29 EP EP95306920A patent/EP0709521A1/en not_active Withdrawn
  • 1995-10-03 CA CA 2159748 patent/CA2159748A1/en not_active Abandoned
  • 1995-10-20 NO NO954193A patent/NO954193L/no not_active Application Discontinuation
  • 1995-10-26 FI FI955110A patent/FI955110A/fi unknown
  • 1995-10-26 BR BR9504574A patent/BR9504574A/pt not_active Application Discontinuation

Patent Citations (5)

Non-Patent Citations (3)

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