AU703599B2

AU703599B2 - Method for removing pitch from mixed tropical hardwood pulp

Info

Publication number: AU703599B2
Application number: AU50714/96A
Authority: AU
Inventors: Bruce Crossley
Original assignee: Beloit Technologies Inc
Current assignee: Beloit Technologies Inc
Priority date: 1995-04-17
Filing date: 1996-04-17
Publication date: 1999-03-25
Anticipated expiration: 2016-04-17
Also published as: CN1143131A; KR960037956A; AU5071496A; JP2787669B2; JPH09105090A

Description

1

TITLE

METHOD FOR REMOVING PITCH FROM MIXED TROPICAL HARDWOOD PULP FIELD OF THE INVENTION The present invention relates to apparatus and methods for cleaning papermaking pulp in general, and to apparatus and methods employing hydrocyclones in particular.

BACKGROUND OF THE INVENTION Papermaking pulp manufactured from wood or recycled materials is 10 often contaminated with particles that diminish the quality of the paper made from the fibers. The contaminants are generally divided into high-density contaminants and low-density contaminants. High-density contaminants include sand, ink specks, shives, and bark specks. Hydrocyclones, such as those disclosed in U.S. Patent 5,240,115 to Crossley, et al., have proven to be highly effective for removing high density contaminants from paper stock.

Paper stock may also be contaminated with low-density contaminants, particularly when the stock is manufactured from recycled paper or cardboard. Low density contaminants include waxes, hot melts, polystyrenes, and polyethylenes. These and other low-density materials, as well as plastics, are particularly troublesome in paper. They not only contaminate the final product, but can stick to the rolls, felts and blankets of the papermaking machine, thereby requiring more frequent blanket and felt replacement. Furthermore, the buildup of sticky materials on the papermaking machine itself may lead to more frequent paper breaks.

Paper generally remains at an elevated temperature as it is wound onto a reel at the end of a papermaking machine. The presence of -2low-density materials with low melting temperatures produces stickies where adjacent layers of the paper become adhered together. Stickies in the formed paper roll can result in paper breaks when the roll is rewound.

Further, the stickies reduce the quality of the paper by introducing surface tears into the paper web. To reduce the incidence of these problems, hydrocyclones have been developed for removing lightweight contaminants from papermaking pulp. One particularly advantageous type is the UNIFLOW cleaner available from the Jones Division of Beloit Corporation, Dalton, Massachusetts.

In the manufacturing of paper, cellulose fibers from a variety of sources are utilized as a starting material. Starting materials include softwoods, hardwoods, bamboo, hemp, and even sugar cane wastes. Each oo: type of material has its unique characteristics. As the art and science of 000.

0 papermaking have continued to develop, both new and old techniques have been employed for purifying diverse pulps to manufacture better, lower cost paper of these diverse materials.

Papermaking feed stocks that have proven particularly troublesome are those manufactured from mixed tropical hardwoods from Malaysia and other tropical regions. Pulps manufactured from these woods are 0 o 20 contaminated with pitch particles, small shives, and some fiber vessels S0: containing pitch. Previous trial work on these mixed tropical hardwoods revealed that dispersion of the pitch reduced its visual impact in samples.

Such dispersion, however, was quite expensive as the equipment needed to effect dispersion is power intensive. Conventionally, the removal of pitch from wood fibers has been attacked through the use of high density separators. In the case of mixed tropical hardwoods, this has proven less than totally effective.

What is needed is a method for improving the quality of pulp produced from mixed tropical hardwoods.

-3- SUMMARY OF THE INVENTION The method of this invention operates on pulp made from mixed tropical hardwoods. It is preferable that the method employs two types of separation means such as hydrocyclones. The first type is optimized for the removal of high-density materials. The second type is optimized for the removal of high-density materials. The preferred hydrocyclones for the removal of high-density materials will preferably be

POSIFLOW

T M cleaners available from Beloit Jones Division, Beloit Corporation, Dalton, Massachusetts. The low-density hydrocyclones will preferably be the UNIFLOW cleaners which are also available from the Beloit Jones Division of Beloit Corporation. The preferred method of cleaning pitch and resin from the mixed tropical hardwood pulp involves processing pulp in a stock having a consistency of 0.7 to 0.8 percent through two primary high-density hydrocyclones connected in series. The reject flow from the high-density hydrocyclones is processed by two secondary hydrocyclones.

15 The reject flow from the secondary hydrocyclones is in turn treated by two series connected tertiary hydrocyclones. The output of the primary high-density hydrocyclones is sent to two low-density hydrocyclones connected in series. The output is substantially free of pitch and resins. The output of the secondary hydrocyclones is diluted to 0.6 percent consistency 20 and sent to the primary hydrocyclones, while the output of the tertiary hydrocyclones is diluted to between 0.5 and 0.6 percent and sent to the input 9.

of the secondary hydrocyclones. The output of the tertiary high-density cleaners and the two low-density cleaners are sent to a clarifier so the water may be cleaned and reused.

It is a feature of the present invention to provide a method for removing pitch and resin from pulp made from mixed tropical hardwoods.

It is another feature of the present invention to provide a method of purifying the pulp of mixed tropical hardwoods to extend the life of the blankets and felts used on a papermaking machine utilizing such pulp.

-4- It is another feature of the present invention to improve the quality and appearance of paper manufactured from mixed tropical hardwoods.

Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flow diagram of the method of this invention.

FIG. 2 is cross-sectional view of a high-density hydrocyclone cleaner utilized in the method of FIG. 1.

o 10 FIG. 3 is a cross-sectional view of a low-density hydrocyclone cleaner employed in the method of FIG. 1.

DESCRIPTION OF THE PREFERRED

EMBODIMENT

Referring more particularly to FIGS. 1-3, wherein like numbers refer to similar parts, a first type of hydrocyclone 20 is shown in FIG. 2. The S 15 hydrocyclone 20 is of the type designed to remove a high-density contaminant from a flow of papermaking stock. A hydrocyclone device 22, shown in FIG. 3, is designed to remove low-density particulate contaminants from a flow of paper making stock.

The high-density cleaner 20 and the low-density cleaner 22 function on similar principles. In the high-density separator 20, water containing papermaking fibers and undesirable contaminants is injected into an infeed 24 at the top 26 of a tapered cylindrical chamber 28. The tangential injection of the jet of water causes it to spiral about the walls 30 of the chamber 28 creating a centrifugal acceleration towards the walls 30. The centrifugal acceleration causes a separation of the feed stock by density. In the high density separator 20, the hydrocyclone has been optimized for the removal of high-density materials from the feed 21. The accepts 31 are removed from an outflow 32 and rejects 34 are removed from the bottom 36 of the cyclone The preferred high-density separator is a POSIFLOWTM cleaner which is available from Beloit Jones Division of Beloit Corporation, Dalton, Massachusetts.

The hydrocyclone 22, shown in FIG. 3, has been optimized for the removal of low-density materials and similarly has an infeed 40 which injects feed 21 tangentially into a chamber 42 with walls 44. Low-density materials are removed by a tube 46 which extends upwardly into the bottom 48 of the chamber 42 and removes the central portion of the swirlina column of water formed within the chamber 42. Lightweight rejects 50 are channeled through the tube 46 and removed through a drain 52. The accepts 33 are i. collected at an outlet 54 from a collection chamber 56. The preferred S'low-density hydrocyclone 22 is of the type known as a UNIFLOW cleaner, available from Jones Division of the Beloit Corporation, Dalton, Massachusetts. Hydrocyclone devices such as those shown in FIGS. 2 and 3 are employed separately to remove various contaminants from paper pulp.

Further, they are ganged together and used sequentially in the processing of recycled paper where the paper wastes contain light components such as plastic and hot glue as well as heavy components such as ink particles and ***dirt.

*e 20 However, known approaches for dealing with pulp made from mixed e tropical hardwoods involve removing high-density materials or dispersing of the pitch to reduce its visual impact. Pitch is normally a high-density material and those skilled in the art of designing systems to clean pulp would normally remove pitch through a high-density cleaning system. Thus, prior experience and the experience of those skilled in the art would approach removing pitch from a fiber stock through the use of high-density separators, since pitch is normally a high-density material. In fact, most of the visible pitch is removed from pulp made from mixed tropical hardwoods by passing the pulp through a high-density separator such as the one shown in FIG. 2.

MMM

-6- Research has revealed, however, that mixed tropical hardwoods contain pitches of a wide range of densities, extending from densities greater than one to densities less than one. Further, the low-density pitch particles tend to be light in color and thus are not readily detected in a visual analysis of a pulp. In fact, the way in which this fraction of light color of lightweight resins can most readily be detected is through separation in a low-density separator such as the one shown in FIG. 3, which prior experience would indicate would not be effective in removing pitch and thus would not be an avenue normally pursued.

It has been found after bleaching and processing that these *lightweight amber or light colored pitch specks are responsible for dark *specks as well as an overall darker color to the paper manufactured. The precise mechanism whereby the lighter colored, lower density materials, which are difficult to detect visually in the pulp, affect the quality of the paper is not clear. It is felt that these small pitch or resin particles can agglomerate as they move through the papermaking process. As th;s agglomeration takes place, the particles become more visible and possibly pick up small dirt particles or go through a chromophoric reaction making them dark in color, thereby resulting in dark specks in the final product. It is also possible that a pH shock in the process will affect the nature of the resin such that it becomes invisible in the acid loop.

Removal of the lightweight pitch component also provides benefits in improving performance of the papermaking machine. The pitch materials which build up on blankets and felts require more frequent changing of the blankets and felts and more frequent cleanings of drum surfaces. Further, the lightweight components can cause stickies. Stickies are undesirable, particularly when the hot paper is wound onto the reel, as fusible components may cause adjacent sheets to stick together.

-7- The discovery of the nature and characteristics of the less visible, lower density pitch results in the solution, which is processing the pulp made from mixed tropical hardwoods with both high-density and low-density hydrocyclone cleaners. It is to be understood that high density refers to materials with densities greater than the pulp, which has a density of about one; and low density refers to materials with densities less than the pulp or less than about one.

The contaminants present in mixed tropical hardwood pulps are primarily pitch and resins with specific gravities ranging from 0.93 to 1.1. The processing of the mixed tropical hardwood pulp through the high-density and *low-density cleaners can be performed either before or after bleaching. It is preferable to perform it before bleaching as the removal of the contaminants reduces the amount of chemicals necessary for the bleaching of the pulp.

Cleaning of mixed tropical hardwood pulps may be effected with either 15 the high-density hydrocyclones followed by the low-density hydrocyclones or the low-density followed by the high-density. The low-density cleaners such as the UNIFLOW cleaner 22, due to the very low mass reject rate, thickens the accepted pulp and will to some extent remove entrained air from the pulp.

Where the pulp, following cleaning, is thickened using a gravity decker 20 or other similar device, both of these attributes, thickening and deaerating, of the UNIFLOW low-density cleaners can be taken advantage of if the UNIFLOW cleaners are placed in the system just prior to the thickener.

Because some pulp is lost with the heavy materials in the rejects 34 from the high-density hydrocyclones 28, it is desirable to use a secondary and tertiary set of high-density cleaners to minimize the amount of fiber which is lost in the cleaning process. On the other hand, the rejects from the low-density cleaners 22 contain very little fiber, with the consistency varying between 0.01 and 0.02 percent. The fibers present are fines which have little -8or no value in the papermaking process. The use of secondary low-density cleaners will compromise the overall system efficiency. Thus, secondary low-density cleaners should not be used unless necessary to use a clarifier of lesser capacity.

The preferred process for removing pitch from pulp made from mixed tropical hardwoods is shown schematically in FIG. 1. Feed stock having a consistency of 0.7 to 0.8 percent is supplied from an infeed source 58 to the infeed 24 of the first primary hydrocyclone 60. The accepts 31 leave the outflow 32 of the first primary high-density separator 60 and are passed to the input 24 of the second primary high-density separator 62.

9:00 The accepts 31 of the second primary high-density separator 62 flow to the inlet 40 of the first low-density separator 64. The accepts of the first low-density separator 64 flow to the second low-density separator 64. The accepts 39 from the second low-density separator 64 supply the outfeed 68 15 of the cleaning method illustrated in FIG. 1. The output can then be sent to a thickener 70 such as the gravity decker shown in FIG. 1.

:::The rejects streams 50 from both the first and second low-density separators 64, are disposed of normally through clarification in a clarifier 72 such as the dissolved air flotation clarifier shown in FIG. 1. After clarification, 20 the water can be reused in the papermaking process.

The reject flow 34 which is the output of the primary high-density hydrocyclones 60, 62, is diluted by the addition of water to about 0.6 percent consistency and fed to two series paths of secondary high-density hydrocyclones 76. The reject streams 34 of the secondary hydrocyclones 76 are diluted with water 74 to a consistency of 0.5 to 0.6 percent and fed to tertiary high-density cleaners 80. The reject stream 34 from the tertiary cleaners 80 is supplied to the clarifier 72 for clarification and reuse. The output of the secondary high-density cleaners 76 is supplied to the input 24 -9of the primary cleaners 60, 62 along with the stock supplied at the infeed 58.

The output of the tertiary cleaners 80 is fed to the input 24 of the secondary cleaners 76.

Trial runs employing two high-density hydrocyclones of the

POSIFLOW

T M type obtainable from Beloit Jones Division and two of the UNIFLOW low-density hydrocyclones, also obtainable from Beloit Jones Division, resulted in a one point brightness gain as well as a shift in color from yellow towards blue in the paper manufactured from one test lot of pulp from mixed tropical hardwoods.

It should be understood that the process illustrated in FIG. 1 is o capable of removing not only visible dirt such as measured by the Tappie dirt o.

count, but removes amber colored particles which are not included in dirt counts and yet which are suspected of causing quality problems as they pass through the papermaking process. Furthermore, the process may be 15 practiced on brownstock but preferably will be used with bleach stock in order to reduce the amount of bleach chemicals necessary.

Low-density cleaners may discharge pulp for treatment to high-density cleaners, although it is preferable if the low-density cleaners follow the :°°°ohigh-density cleaners. In some circumstances, it may be desirable to utilize .ooo°i S 20 high-density cleaners of the POSIFLOW T M Ultra type which are supplied by the Jones Division of the Beloit Corporation and are disclosed in U.S. Patent 5,240,115 to Crossley, et al. which is incorporated herein by reference.

The steps of removing high-density components and low-density components can be performed simultaneously in a single properly designed hydrocyclone of varying types well known to those skilled in the art.

The term "mixed tropical hardwoods" is a term used by those skilled in the art, and herein, to designate a feedstock material used in the 10 papermaking industry, and generally refers to the result of cutting tropical forest land without selection for species and will thus, in general, incorporate fibers from numerous tropical hardwood species. While the method disclosed herein is useful in general on pulps from mixed tropical hardwoods, the processes were developed during tests on mixed tropical hardwoods from Malaysia.

It should also be understood that the specific gravity of the mixed tropical hardwood fibers is approximately one but in some cases it may be slightly greater than one or slightly less than one and that the hydrocyclones for removing high density particulates and the hydrocyclones used for i removing low-density contaminants may be adjusted by means known to o those skilled in the art to remove particles of greater than and less than the specific gravity of the fibers. Thus, although high density generally refers to *specific gravities greater than one and low-density generally refers to specific gravities less than one, in practice, the separation between high and low density must be referenced to the specific gravity of the fibers which is desired to pass unimpeded through the hydrocyclones discussed herein.

~It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but 20 embraces such modified forms thereof as come within the scope of the following claims.

following claims.

11 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A method for improving the quality of paper manufactured from mixed tropical hardwoods comprising the steps of: diluting a pulp made from mixed tropical hardwood to a consistency of about 0.7 to about 0.8 percent; feeding the diluted pulp through a first means for removing high density contaminants; removing high-density contaminants, including pitch and resin having a specific gravity greater than about 1 up to about 1.1, from the stream of pulp in said first means for removing high-density contaminants, and outputting said pulp; i conducting the output of said first means for removing high-density contaminants to a means for removing low-density contaminants, 15 including pitch and resin having a specific gravity from about 0.93 to less than about 1; and removing low-density contaminants in said means for removing lowdensity contaminants.

20 2. The method of claim 1 wherein the step of feeding through said first means for removing high density contaminants includes feeding the diluted pulp through a first hydrocyclone and a second hydrocyclone in series.

3. The method of Claim I wherein step of removing low density contaminants comprises passing the diluted pulp through at least two hydrocyclones connected in series.

BGC:JH:#20373 17 December 1998

Claims

4. A method for improving the quality of paper manufactured from mixed tropical hardwoods comprising removing pitch and resin from a stock of mixed tropical hardwood fibers suspended in water with at least one hydrocyclone wherein pitch and resins with specific gravities ranging from about 0.93 to about 1.1 are separated from the fibers. A method for removing pitch and resin from stock having pulp made from mixed tropical hardwoods comprising the steps of: feeding the stock made from mixed tropical hardwoods to a first hydrocyclone; subjecting the stock to centrifugal accelerations within the first hydrocyclone and separating out materials contained in the stock which have a density of greater than the pulp; collecting the lower density fraction of the diluted pulp and feeding it to 15 a second hydrocyclone substantially similar to the first hydrocyclone; feeding the output of the second hydrocyclone to a third hydrocyclone, and removing a fraction from the diluted pulp which is less dense Sthan the pulp; and SC. 20 feeding the output of the third hvdrocyclone to a fourth hydrocyclone substantially similar to the third hydrocyclone, thus producing a stock wherein all components greater than or less than the density of the pulp are removed.
6. A method for improving the quality of paper manufactured from mixed tropical hardwoods comprising the steps of: diluting a pulp made from mixed tropical hardwood to a consistency of about 0.7 to about 0.8 percent; BGC:JH:#20373 17 December 1998 feeding the diluted pulp through a means for removing low-density contaminants; removing low-density contaminants, including pitch and resin having a specific gravity from about 0.93 to less than about 1 from the stream of pulp in said means for removing low-density contaminants; conducting the output of the means for removing low-density contaminants to a means for removing high-density contaminants; and removing high-density contaminants, including pitch and resin having a specific gravity greater than 1 up to 1.1, in said means for o:*o*o removing high density contaminants.
7. A method for removing pitch and resin from pulp made from mixed 15 tropical hardwoods substantially as described in the preferred embodiment with reference to Figures 1 to 3 of the accompanying drawings. 9DATED: 17 December 1998 9 20 CARTER SMITH BEADLE Patent Attorneys for the Applicant: BELOIT TECHNOLOGIES, INC. 17 December 1998 ABSTRACT To improve the quality of pulp made from mixed tropical hardwoods the pulp is supplied to first hydrocyclones optimized for the removal of high-density materials and subsequently to hydrocyclones optimized for the removal of low-density materials. The hydrocyclones for the removal of high-density materials will preferably be POSIFLOW M cleaners, the low-density hydrocyclones will preferably be UNIFLOW cleaners both available from Beloit Jones Division of Beloit Corporation. The preferred method of cleaning pitch and resin from the mixed tropical hardwood pulp involves using two primary high-density hydrocyclones connected in series. The reject flow from the high-density hydrocyclones is processed by two S.:6 secondary hydrocyclones, the reject flow of which is in turn treated by two series-connected tertiary hydrocyclones. The output of the primary I high-density hydrocyclones is sent to two low-density hydrocyclones o connected in series. o o00 0*6 o