MXPA96001710A - Method and apparatus for recovering fiber of effluent currents - Google Patents

Abstract

The present invention relates to a method for recovering papermaking fibers and water from the effluent of the paper mill in a secondary fiber paper mill, the effluent contains fibers for the production of paper and opposing materials, characterized the method because it comprises: (a) collecting the effluents from the mill in a collection tank, (b) driving the mill effluents from the collection tank into a stream of liquid effluents to an extraction unit, (c) extracting the long fibers of the effluent stream in the extraction unit, (d) driving the long fibers in a stream of fibers from the extraction unit through a cleaning step and a de-inking step to return the fiber for the manufacture of paper to the mill, to make paper, (e) remove individually the combustible components and the suspended solids and the inks, and the inorganic solids and the water in the effluent stream, (f) only drive the fuel components to a waste recovery heater, (g) drive only the suspended solids and inks to a clarifier for further processing, (h) conduct only the inorganic solids to a waste disposal site, and (i) only return water from the removal step to the collection tank.

Description

METHOD AND APPARATUS FOR RECOVERING FIBER OF EFFLUENT CURRENTS - 1 - FIELD OF INVENTION The present invention relates to a method and apparatus for recovering fiber useful for the manufacture of paper from streams of mill effluents containing fiber and substantial amounts of impurities.

ANTECEDENTS OF THE. INVENTION In a mill for the manufacture of recycled fiber paper, paper, such as tissue paper, is made from recycled fiber pulps, such as recycled office paper, from newspapers and magazines, obtained from paper collection municipal to the edge of the sidewalk and collection of paper waste business, for example. The papermaking fibers are extracted from scrap paper sources and supplied to a conventional papermaking machine. Since the source of the fibers for papermaking is waste paper, other materials not useful for papermaking are usually present. These impurities, and the water in which these raw materials are transported, must be efficiently processed and managed and disposed of in an environmentally responsible manner.

The use of recycled fiber pulps continues to increase in the pulp and paper manufacture. The economic feasibility of using such recycled pulps depends on the useful fiber fraction, which can be extracted from the total pulp. The size of this useful fiber fraction, known as yield, depends to a large extent on the type of waste paper that makes up the pulp. As mentioned, recycled pulps contain substantial amounts of materials that are not useful for the manufacture of paper, called impurities or foreign bodies, for example, very short vegetable fibers, staples, paper clips, inks, clays and the like. Although the theoretical yield of a pulp can be accurately determined, up to now a perfect recovery of the theoretical yield has not been obtained due to the technological deficiencies in the recovery processes currently in use, or other difficulties. Conventional processes, as a result of such deficiencies, reject useful fiber that is later lost as waste. The actual performance of such conventional processes can be increased by recovering this fiber.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a method and apparatus for recovering useful fiber from effluents or wastewater which contain substantial amounts of impurities. In general, the present invention provides a method and apparatus that resolves deficiencies in the art and recovers fiber useful for the manufacture of paper from effluents with a higher yield than that obtained by conventional fiber recovery methods. More particularly, the present invention provides a primary or primary process, which uses well defined unit operations, for recovery of long fibers for the production of usable paper, from effluents of a mill. Unlike other methods, the method according to the present invention does not add additional water to the stream of effluents for processing, which results in a lower utilization of water and less water which must be subsequently cleaned, which, in advantageously, it allows savings in both resources and costs. The concentrations of solids in the waste water streams are usually very low, often in the range from 0.1% to 0.5% consistency. Impurities or foreign bodies in the effluent streams consist of a variety of materials, including: suspended solids such as kaolin clay, very short cellulose fibers, lignins, starches and tannins; large cuts of wood, plastic sheets and fiber bundles; staples, paper clips, sand and glass fragments; frits or coating flakes, sticks and styrene foam, and similar materials; grains or fine particles of coating and inks. The process according to the invention includes steps to process impurities according to the size and type, so as to optimize the recovery of useful fiber. In addition, separation techniques simplify the handling of impurities, which are separated into three categories, suspended solids and ink, coating frits and inorganic solids. The method also separates the impurities so that it recovers water for reuse in the fiber deinking process. A main process for the recovery of fibers for the manufacture of paper from a stream of effluents, according to the invention, comprises the steps of separating useful material from the waste material which minimizes the losses of useful fiber. The method of the invention includes the steps of: (a) collecting effluents or wastewater containing fiber in a collection tank or basin; (b) directing the effluents from the collection tank through a bar grid to separate the solid trimming materials from the effluents containing the fiber; (c) sieving the fiber-containing material through a sieve or coarse-barrier sieve (sieve with large holes) to remove the solid materials from the received effluents; (d) extracting the long fibers from the effluent containing fiber in a curved wire scrubber, a rotating drum or disk filters; (e) cleaning the long fibers extracted in a high consistency centrifugal cleaner to remove solids having a specific gravity greater than the gravity of the long fibers; (f) diluting and further cleaning the material received from the high consistency centrifugal cleaner into a low consistency active centrifugal cleaner to separate small or fine solids having a greater specific gravity than short fibers; (g) sieving the material received from the active centrifugal cleaner through a fine barrier sieve (sieve with small holes); and (h) destintar by flotation the material received from the fine barrier screen. An apparatus according to the present invention performs the steps of the method. A further aspect of the invention is the inclusion of secondary processes for the recovery of useful fiber from reject material in the main process. Secondary process or recycling operations that operate in parallel with the primary process capture long rejected fibers in the primary process and return the captured long fibers to the primary process for recovery, thereby increasing the net fiber yield of the overall method . The secondary process operations according to the invention also separate impurities for simplified handling and disposal. Secondary process operations separate impurities into three categories suitable for different handling operations, suspended solids and inks, coating frits and inorganic solids. Suspended solids can be cleaned or rinsed to produce water for recycling and the solid material suitable for producing industrial granular absorbers and other useful products. The coating frits can be used as fuel in a waste recovery burner. Inorganic solids, such as staples, sand and fragments or pieces of glass, are often disposed of in public landfills or garbage dumps. The lower amount of materials discarded to public landfills reduces the pressure on the environment and the costs of handling and disposal of solid waste.

BRIEF DESCRIPTION OF THE DRAWINGS OF THE DRAWINGS The present invention may be further understood with reference to the following description together with the accompanying drawing. The drawing is a schematic representation of the method and apparatus of the invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES According to a preferred embodiment of the invention, the drawing shows a primary or primary process for the recovery of long fibers from a stream of effluents or wastewater, indicated by the steps appearing in the upper row of the figure. The term "long fibers" refers to cellulose fibers having sufficient length to be retained in Fourdrinier wires of a papermaking machine. Usually, long fibers have a length greater than 1 mm (0.04 inches). The main process is supplemented with secondary processes that increase the performance of the main process, indicated by the stages that appear in the lower row. The main process is designed to recover approximately 80% of the long fibers useful for papermaking, while approximately 95% of impurities or foreign bodies are rejected. The secondary process is designed to recover approximately 80% of the long fibers that are rejected in the primary process. Approximately 90% of impurities entering the secondary process are rejected for disposal or sent for clarification of effluents with suspended solids. The effluent mill often consists of several streams of the various processes, in the processes of deinking and papermaking. The various streams are directed to a tank or collection basin 10, or pit, by gravity flow. All waste streams from potential fiber recovery sources, particularly floor drains, can be collected, and no source is left open for discharge to an industrial drain or to an effluent treatment facility that produces sludge for disposal. By collecting the streams in a collection vat 10, the effect of fluctuations in the flow velocity of the various streams is reduced. The collection tank 10 also adapts abnormal surges or transients caused by discharges of diluted pulp or spill containers. The materials recovered from the secondary recovery processes are also collected in the collection tank 10 for reprocessing in the main process. It has been found to be advantageous to provide a collection tank 10 large enough so that the effluent has a residence time of 10 to 15 minutes at the observed nominal flow rate. The main process takes the slurry or suspension of the effluents from the collection tank 10 and separates the long usable fibers from the impurities, and return the usable fibers to the papermaking process. Each stage of the main process separates a particular type or size of impurities from the slurry, and passes the received material, that is, the long fibers and the impurities not separated to an additional stage. The reject material is additionally concentrated and classified into secondary process operations, as described below.

In the main process, the effluents are discharged from the collection tank 10 to a channel 12 through a grid of bars 14 to screen out large segments of impurities or foreign bodies, for example plastic and wood chips. According to a preferred embodiment of the invention, the bar grid 14 can be constituted by a device interposed in the flow channel 12 having separate bars 6.4 cm (2.5 inches), separated 2.5 or 5.1 cm (1 or 2 inches) to form a thick vertical barrier. A rake device with teeth placed between the rods pulls the trapped material upwards to keep the face of the bar grating 14 clean. This material is discharged through a gutter 13 and finally discarded in a waste recovery burner. One device that is suitable is the Infilco Degremont Climber Sifter. Effluents or sewage that have passed through bar grid 14 are pumped through pipe 16 to a coarser barrier screen 18 which removes smaller impurities, such as coating chips, sticks, particles of foam. styrene and coarse sand as well as fragments or pieces of glass. The coarse barrier sieve preferably comprises a sieve basket having openings in the range of 1.3 to 1.6 mm (0.050 to 0.062 inches). The device includes a rotating element that generates pressure pulses to prevent the fibers from plugging the sieve. On -device found is Centriscreen "originally manufactured by Bird Machine Co. A pulp container, or tub, and pump 15 can be provided to collect the effluents from the bar grid 14 and pump them to the barrier screen coarse 18. The illustrated embodiment of the invention shows positions in which the diluted pulp container and the pump units 15 can be installed advantageously.The effluents passing through the coarse barrier screen 18 are subjected to pressure through a tube 20 to the extraction unit 22, which separates the suspended solids such as kaolin clay, very short fibers of cellulose, lignins, starches and tannins from the effluents Preferably, the extraction unit 22 is constituted of a curved wire screen formed of a plurality of parallel wedge wires, formed in an arc of 120 degrees and spaced approximately 100 to 300 microm (0.004 to 0.012 inches) to form a collection surface for the fibers. The flow of the effluents is directed tangentially against the top of the sieve. The suspended solids transported by the water pass through the slots and are directed through the tube 44 for clarification of the effluents. The fiber is retained on the surface formed by the ties. Such a device separates approximately 85 to 90% of the water and the suspended solids from the effluents. It has been found that the Micrasieve sieve of C-E Bauer, is suitable for use as the extractor. Other devices suitable for use include rotary drum scrubbers and disc filters. The accepted consistency of the diluted pulp is usually between 2% and 4%. The long fibers collected by the extraction unit 22 are pumped through the pipe 24 to a centrifugal cleaning device 26 to remove impurities with relatively high specific gravity, such as staples, sand, gravel and glass, from the fiber. In a preferred embodiment of the invention, the high consistency centrifugal cleaner, for example, the Liquid Cyclone from Black Clawson Co., is suitable as the centrifugal cleaning device. The fiber cleaned by the centrifugal cleaning device 26 is then pressurized through the pipe 28 to an active centrifugal cleaner of low consistency 30, to remove the small staple and similar material that was not removed in the high consistency centrifugal cleaner. A suitable device for the active centrifugal cleaner 22 is the RB 90 device, manufactured by Ahlstrom, which has a cone diameter of 7.6 to 10 centimeters (3 to 4 inches). It has also been found that the Centri-Cleaner device of CE Bauer is suitable, preferably the active centrifugal cleaner can be constituted by a group of cleaners in series In the illustrated embodiment, the rejected material of the active centrifugal cleaner 30 is sends through the pipe 50 to a secondary active centrifugal cleaner 31. The secondary active centrifugal cleaner 31 is similar to the active centrifugal cleaner 30, and removes very fine, high density particles such as glass fragments from the material. providing additional active centrifugal cleaner steps in order to minimize fiber losses by further reprocessing of the reject material The received material is supplied from the secondary active centrifugal cleaner 31 through the pipe 48 to the main process, which is immediately upstream of the active centrifugal cleaner 30, for its reprocessing. The rejected material is discarded through a gutter 62 for disposal to a public landfill. The material accepted from the front centrifugal cleaner 30 is pressurized through the pipe 32 by a fine barrier screen 34, which removes very small impurities, for example, small granules and sticks, from the fiber. According to a preferred embodiment, the fine barrier sieve 34 includes a sieve basket provided with slit-shaped openings, in the range of 0.10 to 0.15 nm (0.004 to 0.006 inches). The long papermaking fibers pass through the slab plate. A rotating element sweeps the surface of the sieve with pressure pulses to prevent the fibers from clogging the surface of the sieve. The fine barrier sieve 34 operates more efficiently with a wastewater or effluent with a consistency of about 1.3%. A fine barrier sieve 34 of the type contemplated herein is the LaMort Fiberprep SPM Series pressure screen. The material received from the fine barrier screen 34 is subjected to pressure through the pipe 36 and directed to the flotation deinking module 38. The deinking module 38 removes fine ink particles and fiber coating materials. In the flotation deinking module "38, an air diffuser induces and mixes air within the fiber slurry.The fine impurities, which have a size ranging from about 50 to 150 microns, are subsequently removed from the surface of the fiber. slurry as a foam The flotation deinking module 38 operates more efficiently with effluents with a consistency of approximately 0.7% to 1.3% It has been found that the CF Flotation Cell Series device, originally manufactured by Escher Wyss, is a module De-inking operation completes the main fiber recovery process The material recovered from the de-inking module is returned through line 40 to the main fiber preparation process of the plant for use in papermaking The fiber recovered by the method according to the invention is usually clean enough to be introduced current down in the process of fiber preparation. The operations of reduction to paste, elimination of residues and coarse cleaning are not usually necessary. The secondary process operations recover rejected usable fiber in the main process and recycle the fibers to the collection tank 10 or the extraction unit 22 for recovery in the main process. The various components in the secondary process are generally smaller in size and / or smaller in capacity compared to the corresponding units in the main process due to the lower amount of flow in the secondary process. The reject material from the secondary process is separated mainly in organic and inorganic fractions, concentrated and discarded for disposal or sent to clear effluents or wastewater. The reject material of the coarse barrier screen 18 which, as mentioned, consists of relatively large impurities, is pumped through the pipe 42 to a centrifugal cleaner of high secondary consistency 72, which preferably is a similar unit. to the high consistency centrifugal cleaner 26. The secondary high consistency centrifugal cleaner 72 removes the gravel-like material from the reject material of the coarse barrier lattice 18. The rejected gravel is removed by gravity through a gutter 70 to an endless screw 64 for the removal of gravel, which separates gravel solids from water. In addition, the gravel removed by the high consistency centrifugal cleaner 26 is discharged through a gutter 46 to the gravel removing screw 64. The gravel screw 64 separates the gravel from the water, and the gravel is removed through a gutter 66 for disposal, preferably to a public landfill. The water from the auger 64 for gravel removal is returned to the collection tank 10 through the pipe 68 for gravity unloading. It has been found that the Sand Separator device, manufactured by Con Silium Bulk-Babcok, is an auger for the removal of suitable gravel. The material received from the secondary high consistency centrifugal cleaner 72 is pressurized through a pipe 74 to a secondary coarse barrier screen 76, a unit similar to the coarse barrier screen 18 of the main process. The material received from the secondary coarse barrier screen 76 is recycled through line 78 to the collection tank 10 for reprocessing in the main process. The rejected material is pressurized through line 80 to a secondary coarse barrier screen 82 for further separation. The tertiary thick barrier screen 82 preferably comprises a horizontal cylinder having perforations in the range of 2.0 to 3.0 mm (0.080 to 0.120 inches) in diameter. The concentration of impurities of relatively large size in this reject material requires larger orifice sizes. Sieve 88 is kept clean by a rotating element together with a low pressure water sprinkler. The Reject Sorter device, originally manufactured by Bird Escher yss is a unit suitable for use as the tertiary coarse barrier screen 82. The received material is returned through line 86 to collection tank 10 by gravity flow. The rejected material from this stage, which usually has a consistency of 30% to 50%, is sent for disposal through the gutter 84, preferably to a waste recovery burner that is in place. The waste material from the fine barrier screen 34 is pumped through the pipe 52 to a secondary fine barrier screen 56, which is similar in design and operation to the fine barrier screen 34 in the main process. The materials received are pressurized through the pipe 54 to the extraction unit 22. The rejected material is discharged through the pipe 58 for the clearance of effluents. The rinsed water is suitable for recycling to the mill fiber preparation area. The concentrated solids removed by clearing the waste water can become denser, granulated and dried for use as industrial absorbers or agricultural vehicles. The foregoing has described the principles, modalities and preferred modes of operation of the present invention; however, the invention should not be considered as limited to the particular embodiments described. Instead, the modalities described above should be considered only as illustrative rather than limiting, and it should be appreciated that variations, changes and equivalents can be made by other persons, without departing from the scope of the present invention, as defined by the following claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (15)

1. A method for recovering fibers useful for papermaking, and lightening or cleaning from effluent water or waste water from a paper mill, the method is characterized in that it comprises: (a) collecting the effluents from the mill in a vat or collection sink; (b) driving the effluents from the mill from the collection tank into a stream of liquid effluents; (c) extracting the long fibers from the effluent stream and driving the long fibers into a stream of useful fibers through a cleaning step and a de-inking step to return the useful papermaking fibers to the papermaking mill; (d) removing the combustible components from the effluent stream and conducting the fuel components to a waste recovery burner; and (e) clarify the water in the effluent stream, and return the stream of clarified water to the collection tank.

2. The method according to claim 1, characterized in that the step of cleaning includes directing the effluent through a centrifugal cleaner of high consistency.

3. The method according to claim 1, characterized in that it also includes removing particles with high specific gravity from the effluent stream.

4. The method according to claim 3, characterized in that the removal of particles with high specific gravity is carried out by means of a centrifugal cleaner of high consistency that separates the coarse solids from the fibers.

5. The method according to claim 4, characterized in that it also comprises the steps of directing the reject material of the centrifugal cleaner of high consistency to a gravel or impurities separator, separating the gravel from the water in the reject material and directing the water towards the collection tank.

6. The method according to claim 1, characterized in that the combustible components are in a consistency between 30% and 50% when they are extracted from the effluents.

7. The method according to claim 1, characterized in that it additionally comprises the step of directing the effluents from the cleaning stage through a fine barrier sieve or screen (sieve with small holes) before the de-inking stage.

8. The method according to claim 1, characterized in that the step of extracting long fibers is carried out by means of a Dutch washing machine or sedimentation tank.

9. The method according to claim 8, characterized in that the step of extracting long fibers separates suspended solids of the type including clay, very short fibers and lignins from the long fibers.

10. The method according to claim 1, characterized in that the step of removing ink from the material received from the fine barrier screen is carried out by the operation of deinking by flotation.

11. An apparatus for recovering effluent fiber from a mill, characterized in that it comprises: (a) a collection tank or basin for collecting effluents or wastewater; (b) a grid of bars to separate large solid materials from effluents in the collection tank; (c) a coarse screen sieve or sieve (with large holes) downstream of the bar grating to remove additional solid materials from effluents; (d) an extraction unit for extracting material containing long fibers of effluents which passes through the coarse barrier sieve; (e) a high consistency centrifugal cleaner for removing solids having a specific gravity greater than that of long fibers in the material containing long fibers; (f) an active centrifugal cleaner of low consistency to remove additional solids from the material containing long fibers, from the high consistency centrifugal cleaner; (g) a fine barrier screen to separate additional solids from the long fiber containing material; and (h) a module for removing or removing ink, in order to remove ink from the long fiber containing material produced by the fine barrier screen.

12. The apparatus according to claim 11, characterized in that it additionally comprises a secondary active centrifugal cleaner for additionally concentrating the rejected material by the active centrifugal cleaner, and returning the material received to the process, upstream of the active centrifugal cleaner.

13. The apparatus according to claim 11, characterized in that it additionally comprises a gravel or impurity separator connected to receive the rejected material of the high consistency centrifugal cleaner to separate the gravel from the water in the reject material.

14. The apparatus according to claim 11, characterized in that it additionally comprises a centrifugal cleaner of high secondary consistency connected to the rejection material received from the coarse barrier screen, the centrifugal cleaner separates the long fiber-containing material from the rejection material.

15. The apparatus according to claim 14, characterized in that the centrifugal cleaner is connected to provide the reject material to the gravel eliminator.