Classifications

• • 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
  • D21B1/32—Defibrating by other means of waste paper
  • D21B1/325—Defibrating by other means of waste paper de-inking devices
  • D21B1/327—Defibrating by other means of waste paper de-inking devices using flotation devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
  • B03B13/00—Control arrangements specially adapted for wet-separating apparatus or for dressing plant, using physical effects
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/14—Flotation machines
  • B03D1/1406—Flotation machines with special arrangement of a plurality of flotation cells, e.g. positioning a flotation cell inside another
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/14—Flotation machines
  • B03D1/1443—Feed or discharge mechanisms for flotation tanks
  • B03D1/1475—Flotation tanks having means for discharging the pulp, e.g. as a bleed stream
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/14—Flotation machines
  • B03D1/24—Pneumatic
  • B03D1/247—Mixing gas and slurry in a device separate from the flotation tank, i.e. reactor-separator type
• • 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
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/02—Working-up waste paper
  • D21C5/025—De-inking
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/66—Pulp catching, de-watering, or recovering; Re-use of pulp-water
  • D21F1/70—Pulp catching, de-watering, or recovering; Re-use of pulp-water by flotation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/14—Flotation machines
  • B03D1/1412—Flotation machines with baffles, e.g. at the wall for redirecting settling solids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
  • B03D1/00—Flotation
  • B03D1/14—Flotation machines
  • B03D1/1443—Feed or discharge mechanisms for flotation tanks
  • B03D1/1462—Discharge mechanisms for the froth
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/64—Paper recycling

Definitions

• the present invention relates to a flotation apparatus according to the preamble of claim 1 and a deinking method for removal of ink and colour pigment particles.
• wastepaper used in pulping processes increase both in absolute volume and proportion in dif ⁇ ferent product grades.
• This development sets tighter requirements on the quality and processing techniques of wastepaper.
• Particularly deinking comprising the removal of printing ink, colors and other impurities by means of flotation has been the object of intensive research in order to achieve a more selective way of chemical removal of impurities.
• Prior-art embodiments which most commonly are based on rotor-agitated applications adapted from mineralogical equipment to deinking use, have not been optimized for accurate control of air feed, but rather aim to assure sufficient supply of air. Therefore, the use of excess air has resulted in a disadvantageous fiber suspension- air ratio as well as nonselective deinking and high rejects.
• patent publication AT 342 528 according to which air is introduced by means of an air injection pipe to the center of the flotation cell, at its narrowest point.
• patent publications DE 3144 386.0 and DE 3120 202.0 disclose a method of introducing air by air injection pipes either at the restriction point, or alternatively, before or after it, and ways of installing the air feed and restriction arrangements on a circula ⁇ tion pipe passed from one cell to another.
• the furnish flow in the cell is forced by virtue of the geometry of the cell to circulate in a horizontal plane around in the cell.
• furnish agitation and the air feed pipe are adapted in a cell in which the furnish runs about a vertical shaft.
• a mechanical froth removal method described in patent publication DE 3120 202 C2 fails to remove the froth in its fresh state, because the froth will be mixed back into the furnish thus undergoing a collapse before the furnish flow can reach the froth discharge roller.
• the present invention provides a method in which the travel of air bubbles is continued upward until separating from the furnish flow, that is, as high as possible in the separa ⁇ tion space, and in which the fresh froth emerging on the surface is immediately skimmed away, thus achieving improved selectivity.
• liquid level control in the cell will be easier as the cell can be run at constant liquid level irrespective of furnish flow rate.
• An alter ⁇ native embodiment possible herein is to utilize the extra space available in the separation space by making the height of the froth scraping means adjustable according the liquid level.
• Prior-art embodiments are limited in that their goals have not been in the control of bubble size and air flow rate, but instead, only in sufficient supply of air. This results in unsatisfactory contact between the air and the fiber suspension at the point of air feed, where the excess air increases the probability of interbubble col- lisions and produces air bubbles of unfavourable size.
• the rejects have been removed as an overflow or carried along with the furnish flow onto the froth discharge roller without the use of a separation space of the furnish flow from the froth in which the material flows are arranged counter- directional. Resultingly, the froth will collapse and become mixed back into the furnish thus increasing the amount of rejects and making the surface level control of the cell difficult.
• the goal of the present invention is advantageously achieved by means of a symmetrical pipe tapered at its mid-section, where the narrowest point is provided with an air feed opening capable of producing bubbles of opti ⁇ mum size.
• the bubble size is determined by the diameter of the opening.
• the capacity of the air feed device according to the invention can be increased by drilling a greater number of air feed openings in it using multiples of the design dimensions (pipe diameter, length of taper and expansion sections, pipe diameter at the air feed point) .
• flotation chemicals can be optimized by divid ⁇ ing their feed channels with respect to the inflows and recirculation flows analogously with the distribution of the air feed flows.
• the froth discharge roller is made self-adjustable according to the liquid level in the cell.
• An alternative method is to control the cell liquid level by adjusting the flow rates. This possibility of using both control methods gives a wider latitude in the management of the separation variables and process control.
• the rate of bubble contacts may be further increased by applying the invention to the internal circulation of the flotation cell. Then, improved selectivity and froth control can be achieved by increasing the liquid level in the cell with a simultaneous increase in the froth separ ⁇ ation space.
• Figure 1 is a longitudinal section of an air feed device according to the invention.
• Figure 2 shows preferred embodiments of the air feed opening of the air feed device illustrated in Fig. 1; and Figure 3 is a diagrammatic illustration of the flotation process scheme utilizing an embodiment according to the invention;
• an air feed device according to the invention is shown therein.
• the function of the device is to feed air into a furnish prepared in a pulper from wastepaper and chemicals solution, whereby the purpose of air flotation is to deink the furnish in a flotation washing cell.
• air is fed orthogonally to the furnish flow at the narrowest point 3 of a tapered pipe.
• the air feed opening 4 is advantageously a round hole with a diameter of approx. 0.3 - 1.0 mm.
• the upper limit for the air feed hole is set by the minimum length of fiber which for wastepaper fiber may be less than 1 mm.
• Bubble size is determined by the diameter of the air feed hole 4. Actually, the bubble size distribu- tion is almost insensitive to variations in the air flow rate and pressure.
• the air feed may in principle be run using no external pressure as the negative head at the tapered point makes the device self-priming with respect to air feed. In practice, however, the air feed rate is usually controlled by the pressure of compressed air supplied to the air feed line.
• the tapering angles of the tapering section 3 and flaring section 10 are preferably made identical.
• the ratios of the pipe diameter to the length of the conical sections to the width (diameter) of the narrowest point are most advantageously selected as 5:10:1.
• the capacity dimen ⁇ sions may be increased in multiples of, e.g., two, three or four by providing a larger number of air feed holes 4 (at 180°, 120° or 90° angles) in the manner shown in Fig. 2.
• the velocity imparted by the conical flaring section 10 to the furnish is sufficient to prevent interbubble col ⁇ lisions, and on the other hand, to achieve efficient mixing of the furnish.
• the contact between the air and the furnish being deinked can be further improved and the air flow rate may be controlled to desired level according to the operating conditions.
• FIG. 3 a diagrammatic illustration of the flotation equipment operating scheme is shown therein.
• the equipment comprises at least one cell 1, 11. As the cells can freely communicate with each other, their liquid levels will be equalized. The furnish flow is laminar.
• the furnish will be transferred from one cell to another via a "transfer" channel 5.
• Counterflow recirculation of furnish from one cell to another is also arranged by pumping from the transfer channel. Proper selection of feed angle and point for the entry of the recirculation flow makes the furnish rotate in a desired direction in the cell.
• Air is fed via nozzles into the circulation flow divided by the distribution piping.
• the recirculation flow is pumped counterdirectionally 9 from one cell to another.
• Ink micelles are removed immediately after their forma ⁇ tion by mechanical means with the help of, e.g., dis ⁇ charge rollers 8 from above the liquid level in the cells.
• the apparatus is capable of providing counterdirectional flows between that of ink particles adhering to the air bubbles and the furnish flow, whereby selective separation of froth from furnish results .
• Air is fed by means of the air feed device 4 according to the invention, into either the inflow to the cell or the recirculation flow 9. With the help of the directed inflow to the cell, the furnish-air suspension is forced to circulate in a desired manner in the floatation space 1 of cell. Next, the furnish flow passes via a discharge space 7.
• Selectivity of the appa ⁇ ratus is achieved by means of combining the froth separa- tion space 6 and rapid removal of fresh froth 8 with the vertical rise of bubbles orthogonally to the furnish flow.
• the furnish is trans ⁇ ferred by pumping or gravity flow into the recirculation flow 9, or alternatively, via a transfer channel 5 forward to, e.g., the next cell 11.
• the air feed 4 may be arranged to exit into the inflow channel and/or the recirculation flow 9, which is divided by the distribu ⁇ tion piping and pumped counterdirectionally.
• the froth is removed fresh by means of, e.g., froth discharge rollers 8.
• the cells communicate freely with each other via the transfer channel 5 of the discharge space 7.
• the recir ⁇ culation flows are finally pumped out from the discharge spaces.
• the above-described flotation apparatus and the operating method associated therewith offer improved contact between the air and fiber suspension as well as improved separation in the bubble flotation space, both of these factors facilitating operation with elevated consistency thus further improving the throughput capacity of the deinking system.
• the method according to the invention permits operation with elevated consistences twice as high as conventional. If the filler content becomes high, the interfiber distances will approach a critical limit below which ink particles cannot be separated selectively even in the flotation space. Given this constraint, the estimated operating consistency achievable by virtue of a factory-scale apparatus according to the invention is in the range 1.0 - 1.6 %, most advantageously 1.2 - 1.4 %.
• the method and apparatus according to the invention have been able to cut the deinking time from 12 min to 5 min to reach the same end brightness of the furnish as compared to deinking in a conventional rotor-agitated cell equipped with air feed. Simultaneously, the reject fraction was cut by 80 - 90 %.
• the reject fraction will increase drastically if the operating consistency is ele ⁇ vated in conventional embodiments. Practical limits of consistency therein will remain at 0.9 - 1.1 %. In labor ⁇ atory-scale cells, the practical consistency range of a rotor-agitated simulation apparatus is at 0.5 - 0.8 %.
• a laboratory-scale apparatus according to the invention can be run using consistencies in the range 1.0 - 1.2 % with a simultaneous reduction of the reject fraction by 80 - 90 %. Accordingly a plant-scale appa ⁇ ratus according to the invention offers a significant improvement in yield at a comparable consistency. Provided that the consistency can be elevated to a calculated value of 1.2 - 1.4 %, the yield improvement offered by the apparatus according to the invention is even appreciably higher.
• Air flow rate is controllable. Air 4 is fed orthogon ⁇ ally to the furnish flow at the narrowest point of the tapered pipe. - The volume of generated froth can be adjusted by con ⁇ trolling the air supply pressure and flow rate. Correct bubble size can be selected optimally by the dimensioning of the air feed openings.
• the contact surface between the air bubbles and sus- pended fibers is larger than in conventional embodi ⁇ ments . When fed to the narrowest point 3 of the tapered pipe, the air bubble contact surface with respect to the furnish flow is maximized. When generated at the point of pipe restriction, the air bubbles are prevented from colliding with each other due to the accelerated movement of the furnish.
• the expansion 10 after the air feed point imparts the air-furnish suspension such a high acceleration that prevents immediate merging of air bubbles into large bubbles.
• the imparted acceleration mixes the furnish as it enters the cell, whereby the probability of contact with bubbles is enhanced.
• Optimized design of the separation space 6, cell geometry and location of the feed, recirculation and discharge flows provides an orthogonal flow of the air bubbles into the furnish flow. The improved selectivity and yield thus obtained may further by enhanced by the use of the separation space.
• the froth separated in ehe separation space 6 is advantageously removed fresh 8, immediately after the bubbles emerge on the surface. Mechanical froth discharge directly connected to the separation space improves selectivity and yield.
• Counterflow recirculation 9 from one cell to another combined with the use of the distribution piping and controlled air feed arrangement by fraction, achieves a result resembling counterflow washing in terms of end product cleanliness and permits circulation con ⁇ trol of the furnish in a desired manner in the cell.
• Control of recirculation 9 and discharge openings of the transfer channels 5 of the discharge space 7 individually by cell prevents the movement of separated ink particles from cell to another thus improving the deinking efficiency of each cell and the cleanliness of the end product.
• All the operating method principles of the present flotation apparatus can be applied to existing equip ⁇ ment to improve their yield and capacity and to achieve a cleaner product with reduced consumption of chemicals.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Biotechnology (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8541921

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (3)

• 1994
  • 1994-12-02 FI FI945713A patent/FI105212B/sv active
• 1995
  • 1995-12-01 WO PCT/FI1995/000663 patent/WO1996016743A1/en active Application Filing
  • 1995-12-01 AU AU39859/95A patent/AU3985995A/en not_active Abandoned

Patent Citations (3)

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