FIELD OF THE INVENTION
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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.
BACKGROUND OF THE INVENTION
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It is customary to wash pulp following chemical and/or mechanical pulping of wood chips in order to remove excess contaminants within the liquid fraction. These contaminants occur both naturally from the wood (lignin and pitch) or are by-products from the pulping operation. The wash liquor is later evaporated so that the organics can be burned for energy or sold (crude tall oil, lignin), and the pulping chemicals can be reclaimed.
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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%. Generally, showers are also used to displace part of the dirty liquid fraction held by the pulp during the thickening phases. As a way of saving on fresh water (as well as later evaporation costs), the water runs counter-current to the flow of pulp. In this way, 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.
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It is desirable to achieve maximum consistency (minimizing the liquid, where the contaminants exist, remaining in the pulp mat) during the various stages of washing as this can either result in increased production and/or less contaminants remaining from stage to stage and in the final washed stock. The advantage of increased production is obvious, especially in systems which are limited by their washing capacity. Reducing the carryover of contaminants out of the process is also advantageous as it can reduce subsequent bleaching costs, reduce toxic chemicals in bleach plant effluents, and increase the amount of reclaimed cooking chemicals.
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Reducing the amount of contaminants that leave with the brown stock is particularly important in bleachable grades; the bleaching process follows brown stock washing. The effluent from bleaching is commonly discharged from the mill, and this effluent contains chlorinated organics, which may be toxic. Substances currently of concern include dioxins, furans, absorbable organic halogens, and color. Increased organics removal in brown stock washing has been shown to decrease the environmental impact of bleaching. Furthermore, reducing the level of contaminants sent to the bleach plant or within the bleach plant (by improved washing) may reduce the bleach chemical demand.
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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.
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Certain surfactants have been discovered, that when added in addition to a defoamer, can increase the consistency of stock leaving the washing process beyond that of the defoamer alone. These surfactants are the subject of the present invention.
SUMMARY OF THE INVENTION
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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. By adding 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)
nYZ
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⁺. Thus, the surfactants of the present invention may be either nonionic or anionic.
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Note that the 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.
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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.
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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.
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It is also expected that the present invention would find utility in any other operation in the pulp/paper industry where pulp is thickened. In these instances, a defoamer would only be necessary where the stock/liquid was inherently foamy.
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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).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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The invention will be further understood by reference to the following examples.
Example 1
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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. Using a laboratory device, the diluted stock (300 ml) was vacuum filtered on a polyester mesh at 1.3 inches Hg for 10 seconds. The shower liquid (25 ml) was then applied and the system subjected to vacuum for an additional 10 seconds.
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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.
TABLE I | Brown Stock Mat Consistency in Simulated Second Stage of Washing |
| Treatment | Mat Consistency |
| Untreated | 16.3% |
| Defoamer A | 15.3% |
| Rhodapex N-70 | 15.3% |
| Defoamer A and Rhodapex N-70 | 16.5% |
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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.
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The addition of the surfactant in combination with the defoamer, in the above example, surprisingly counteracted the negative effect of the defoamer alone treated system.
Example 2
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In the following example, 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).
TABLE II | Brown Stock Mat Consistency in Simulated Second Stage of Washing (Effect of Anionic Materials) |
| Test Day | Material | % Mat Consistency Defoamer Alone | % Mat Consistency Defoamer + Material | % Increase (I) or Decrease (D) |
| a | Rhodapex N70 | 13.9 | 14.6 | 5 I |
| b | Rhodapex N70 | 15.3 | 16.5 | 8 I |
| e | Rhodapex N70 | 13.6 | 15.3 | 12 I |
| g | Rhodapex N70 | 14.2 | 16.0 | 13 I |
| e | Alipal EP115 | 13.6 | 15.0 | 10 I |
| e | Alipal CO436 | 13.6 | 15.2 | 12 I |
| f | Gafac RE410 | 13.6 | 14.7 | 8 I |
| f | Gafac RB400 | 13.6 | 14.9 | 10 I |
| f | PolyTergent CS1 | 13.6 | 15.3 | 12 I |
| g | PolyTergent CS1 | 14.2 | 15.2 | 7 I |
| e | Igepon T33 | 13.6 | 15.4 | 13 I |
| f | Igepon T33 | 13.6 | 16.4 | 21 I |
| g | Igepon T33 | 14.2 | 16.3 | 15 I |
| a | Tamol SN | 13.9 | 14.2 | 2 I |
Material Description:
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- Rhodapex N70
- = alcohol ethosulfate (2 EO)
- Alipal EP115
- = nonyl phenol ethosulfate (20 EO)
- Alipal CO436
- = nonyl phenol ethosulfate (4 EO)
- Gafac RE410
- = alcohol based phosphate ester
- Gafac RB400
- = nonyl phenol based phosphate ester
- PolyTergent CS1
- = carboxylated alkoxylated alcohol
- Igepon T33
- = fatty sulfonate amide
- Tamol SN
- = naphthalene sulfonate
(Materials available under the above tradenames from Rhone Poulenc, Rohm & Haas, and Olin Chemicals)
As is demonstrated in Table II, all of the anionic materials, with the exception of naphthalene sulfonate, significantly increased the consistency of the brown stock mat.
TABLE III | Brown Stock Mat Consistency in Simulated Second Stage of Washing (Effect of Nonionic Materials) |
| Test Day | Material | % Mat Consistency Defoamer Alone | % Mat Consistency Defoamer + Material | % Increase (I) or Decrease (D) |
| d | Surfonic L24-7 | 13.8 | 14.9 | 8 I |
| e | Surfonic L24-7 | 13.6 | 15.7 | 15 I |
| g | Surfonic L24-7 | 14.2 | 15.5 | 9 I |
| e | Surfonic L24-12 | 13.6 | 15.2 | 12 I |
| f | Surfonic LF17 | 13.6 | 14.6 | 7 I |
| e | Antarox LAEP16 | 13.6 | 15.0 | 10 I |
| f | Antarox LAEP59 | 13.6 | 15.6 | 15 I |
| f | Antarox LAEP73 | 13.6 | 15.2 | 12 I |
| g | Antarox LAEP73 | 14.2 | 15.0 | 6 I |
| e | Surfonic JL80X | 13.6 | 15.5 | 14 I |
| f | Surfonic JL80X | 13.6 | 15.4 | 13 I |
| d | Tergitol Minfoam 1X | 13.8 | 14.4 | 4 I |
| e | Tergitol Minfoam 1X | 13.6 | 15.4 | 12 I |
| g | Tergitol Minfoam 1X | 14.2 | 15.4 | 8 I |
| e | Tergitol Minfoam 2X | 13.6 | 15.3 | 12 I |
| f | Tergitol XD | 13.6 | 14.6 | 7 I |
| e | Surfonic N95 | 13.6 | 15.3 | 12 I |
| d | Pluronic F108 | 13.8 | 13.5 | 2 D |
| g | Pluronic F108 | 14.2 | 14.6 | 3 I |
| a | PVP K90 | 13.9 | 13.7 | 1 D |
| b | PVP K90 | 15.3 | 14.8 | 3 D |
Material Description:
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- Surfonic L24-7
- = Alcohol Ethoxylate (7 EO)
- Surfonic L24-12
- = Alcohol Ethoxylate (12 EO)
- Surfonic LF17
- = Alcohol Ethoxylate capped in Propylene oxide
- Antarox LAEP16
- = Alcohol Ethoxylate capped in Propylene oxide
- Antarox LAEP59
- = Alcohol Ethoxylate with some Propylene oxide
- Antarox LAEP73
- = Alcohol Ethoxylate with some Propylene oxide
- Surfonic JL80X
- = Alcohol Ethoxy-Propoxy-Ethoxylate Blocks
- Terg. Minfoam 1X
- = Alcohol Ethylene Oxide/Propylene Oxide Random
- Terg. Minfoam 2X
- = Alcohol Ethylene Oxide/Propylene Oxide Random
- Tergitol XD
- = Alcohol Ethylene Oxide/Propylene Oxide Random
- Surfonic N95
- = Nonyl Phenol Ethoxylate
- Pluronic F108
- = Ethoxy-Propoxy-Ethoxy Block Surfactant
- PVP K90
- = Polyvinyl pyrrolidone
(Materials available under the above tradenames from Texaco, Rhone Poulenc, Union Carbide, and BASF.)
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As can be observed from Table III, all of the nonionic materials tested tended to increase the consistency of the brown stock mat, with the exception of polyvinyl pyrrolidone and the block surfactant of ethylene oxide and propylene oxide.
Example 3
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In this example, as with the previous examples, a second stage of brown stock washing was simulated. A formulation containing a combination of alcohol ethoxylate and alcohol ethosulfate was utilized (called Formula I) along with three types of defoamer. Defoamer A was based on oil and EBS (used in previous examples), Defoamer B was based on silicone and surfactant, and Defoamer C was based on ethoxylated/propoxylated glycerin. The results are listed in Table IV.
TABLE IV | Brown Stock Mat Consistency in Simulated Second Stage of Washing Effect of Surfactant Formula with Different Defoamers |
| Defoamer (100 ppm) | Consistency (%) with Formula I Dosage |
| | 0 ppm | 100 ppm | 200 ppm |
| A | 15.7 | 16.3 | 16.2 |
| B | 16.0 | 16.5 | 16.8 |
| C | 15.7 | 16.7 | 16.8 |
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As the above data indicates, the present invention is effective in increasing mat consistency in the presence of different types of defoamer.
Example 4
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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.
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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 |
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The results show that with the use of Formula I there was a significant increase in mat consistency, decrease in contaminant solids carry-over with the mat, and a decrease in the vacuum being pulled on the mat. The decrease in contaminant solids carryover, caused by the increase in mat consistency through the washing process, is significant as it offers two potential advantages. One advantage is that the pulp with greater cleanliness will require less bleaching chemicals over a long period of time and will provide increased recovery of pulping by-products. A mill will also be able to either increase its production or decrease the wash water necessary to produce pulp of the same degree of cleanliness as before.
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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.
Example 5
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A second trial was conducted using Formula I, described in Example 3. This trial was conducted at a southern location utilizing softwood pulped using the Kraft process. This pulp mill used a belt washer (sometimes referred to as a "chemi-washer"). In this type of system, pulp is not rediluted in between stages of washing, but is rather carried along on an open mesh belt under vacuum, where a series of showers spray the mat of pulp to clean it. As with the vacuum drum washer described in Example 4, the liquor used to shower the pulp is moved in a counter current flow pattern to the pulp, so that the cleaner liquid is showering the cleaner pulp and the dirtier liquor is showering the dirtier pulp (shower liquor being cleaner than the pulp it is showering).
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This mill was using two different defoamers, one based On oil/EBS, the other on silicone oil. Formula I was fed to the third shower out of six. The pulp exiting the washer was diluted prior to sampling it; therefore consistency measurements of the mat were not possible. However, the vacuum could be measured at seven locations along the washer. Therefore, vacuum was used to evaluate mat consistency.
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As there are many parameters that can be altered on a machine such as this to change the vacuum, the vacuum was monitored for a short time before and after changes were made to the Formula I addition rate. Within each of these time periods, major parameters such as production rate remained relatively constant.
TABLE VI | Results from Southern Mill Trial (Pre-trial to First Dosage Rate of Formula I) |
| | Day | Time | Vacuum at Positions Across Washer |
| | | | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Pretrial | I | 10:33 | 12 | 21 | 26 | 21 | 22 | 20 | 10 |
| | 10:40 | 12 | 20 | 25 | 19 | 21 | 20 | 10 |
| | 10:54 | 12 | 20 | 28 | 23 | 23 | 18 | 13 |
| | 11:15 | 13 | 22 | 31 | 20 | 21 | 18 | 6 |
| Trial (0.5 lbs/T) Formula I | I | 11:28 | 8 | 17 | 20 | 13 | 16 | 16 | 4 |
| | 11:42 | 9 | 18 | 25 | 12 | 15 | 12 | 5 |
| | 11:53 | 5 | 15 | 17 | 12 | 17 | 15 | 6 |
| | 12:06 | 7 | 18 | 17 | 12 | 15 | 11 | 6 |
| Pretrial average | | | 12 | 21 | 28 | 21 | 22 | 19 | 10 |
| Trial average | | | 7 | 17 | 20 | 12 | 16 | 14 | 5 |
TABLE VII | Results from Southern Mill Trial (First Dosage Compared to Second Dosage Rate of Formula I) |
| | Day | Time | Vacuum at Positions Across Washer |
| | | | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Trial A (0.5 lbs/T) | II | 5:28 | 16 | 23 | 26 | 24 | 24 | 27 | 15 |
| | 6:28 | 14 | 19 | 19 | 18 | 19 | 25 | 12 |
| | 7:29 | 13 | 19 | 20 | 21 | 20 | 27 | 13 |
| | 7:40 | 14 | 23 | 20 | 20 | 21 | 27 | 13 |
| | 8:30 | 16 | 24 | 26 | 18 | 20 | 26 | 9 |
| | 9:40 | 11 | 20 | 19 | 14 | 18 | 21 | 6 |
| Trial B (0.7 lbs/T) | II | 10:05 | 14 | 24 | 19 | 12 | 15 | 19 | 6 |
| | 10:13 | 14 | 22 | 17 | 9 | 13 | 18 | 3 |
| | 10:29 | 13 | 23 | 19 | 9 | 16 | 15 | 8 |
| | 10:47 | 11 | 22 | 20 | 10 | 16 | 14 | 8 |
| | 11:00 | 10 | 21 | 19 | 12 | 16 | 16 | 9 |
| | 11:14 | 10 | 21 | 18 | 11 | 16 | 14 | 8 |
| Trial A average | | | 14 | 21 | 22 | 19 | 20 | 26 | 11 |
| Trial B average | | | 12 | 22 | 19 | 11 | 15 | 16 | 7 |
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The reduction in vacuum observed on this belt washer indicated that a greater amount of air was being pulled through the mat due to an increase in the fiber consistency of the mat (reduction in the liquor held there).
Example 6
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Unbleached Kraft pulp was diluted to 0.7% consistency using deionized water and heated to 160°F. The stock was thickened using the laboratory device described in Example 1 with the exception that no displacement liquid was applied. The results are contained in Table VIII.
TABLE VIII | Defoamer A (ppm) | Consistency (%) with Formula I Dosage |
| | 0 ppm | 100 ppm |
| 0 | 11.8 | 15.7 |
| 100 | 11.4 | 14.4 |
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The above example demonstrates that the present invention is effective in increasing the consistency of a stock which is relatively clean of contaminants. It also shows that the addition of a defoamer is not necessary when the stock is not inherently foamy.
Example 7
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In this example, hardwood, produced from the sulfite pulping process, was sampled from the vat of an extraction stage bleach plant washer (the vat contains both the stock and extraction stage liquor just prior to being thickened on the drum). The extraction stage consisted of caustic extraction with some peroxide and oxygen. This stock was thickened in the laboratory and showered with deionized water in the same manner as in Example 1. The stock was treated with Formula I from Example 3; no defoamer was added to the test. The dissolved solids contained in the resulting mat were also measured so that the lbs. solids per ton of oven dry fiber which would be carried on to the next process could be calculated (termed carryover). The results are contained in Table IX.
TABLE IX | Results Simulating Bleach Plant Washer |
| Formula I Dosage (ppm) | Mat Consistency (%) | Carryover (lbs/ton) |
| 0 | 10.2 | 31.6 |
| 100 | 12.5 | 25.2 |
| 200 | 13.5 | 21.8 |
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These results demonstrate that Formula I was able to increase the mat consistency in bleach plant washers. Because of the increase in mat consistency, there was also less carryover of contaminants caused by Formula I.
Example 8
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In this example, pulp and liquor were sampled from two washers (two different mills) using pulp produced from the sulfite process. The studies were performed in the same manner as previous examples and Defoamer A (from Example 3) was also added. The results are found in Table X.
TABLE X | Results Using Sulfite Pulp |
| Formula I Dosage (ppm) | Stock from Mill 1 Mat Consistency (%) | Stock from Mill 2 Mat Consistency (%) |
| 0 | 10.9 | 10.2 |
| 100 | 11.2 | 11.1 |
| 200 | 11.4 | 14.4 |
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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.
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Note also that 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.
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While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.