Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C13/00—Disintegrating by mills having rotary beater elements ; Hammer mills
  • B02C13/20—Disintegrating by mills having rotary beater elements ; Hammer mills with two or more co-operating rotors
  • B02C13/205—Disintegrating by mills having rotary beater elements ; Hammer mills with two or more co-operating rotors arranged concentrically
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C13/00—Disintegrating by mills having rotary beater elements ; Hammer mills
  • B02C13/22—Disintegrating by mills having rotary beater elements ; Hammer mills with intermeshing pins ; Pin Disk Mills
  • B02C13/24—Disintegrating by mills having rotary beater elements ; Hammer mills with intermeshing pins ; Pin Disk Mills arranged around a vertical axis
• • 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
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D1/00—Methods of beating or refining; Beaters of the Hollander type
  • D21D1/20—Methods of refining
  • D21D1/34—Other mills or refiners
  • D21D1/36—Other mills or refiners with vertical shaft

Definitions

• the present invention relates to a method and apparatus according to the preambles of the independent claims presented below for processing pulp stock, particularly silted broke in a pulp or paper mill.
• Broke is generated in many steps in a paper manufacturing process, and the broke contains fibres and possible fillers, adhesives, coating materials, etc.
• the broke contains both useful raw material and waste, which must be removed from the recycled raw material.
• the task of the broke processing system is to return the valuable raw material components of the broke into the process.
• the first processing step is pulping of the broke.
• pulpers at several locations under the paper machine and the coating machine. In break situations the production of the machine can be directed to these pulpers.
• pulpers There are further pulpers adjacent to the glazing calanders and the slitter winders.
• edge trimmings of the slitter winders can be directed to any of the above mentioned pulpers or to a separate edge trimmings pulper. Most often there is a separate pulper for pulping broke rolls.
• the system generally also contains a two-stage screening before the pulp deposition and defibration, because the mill broke contains plastics and other impurities.
• Pulping means to mix broke in web form with water, so that there is created a pulp stock which can be pumped and where the fibres are at least partly apart from each other.
• Broke equalisation is carried out in the pulper.
• a dry cellulose or paper sheet the fibres are closely bonded to each other.
• the pulp In order to break the bonds between the fi- bres the pulp must be soaked in water. Then the fibres also will swell when water penetrates the pores of the fibres. External forces are also required in order to separate the fibres. They are generated by strongly agitating the pulp stock. This is provided by a rotor located in the pulper. It operates like the impeller of a pump; the pulp flies outwards from the periphery and at the same time a strong suction is created in the centre of the rotor.
• the dispersion property of broke paper depends on the paper quality.
• the dispersion is reduced by paper adhesives, surface treatment and coating.
• the most easily dis- persed paper qualities are newsprint and other uncoated wood-containing paper qualities. Calandering makes it more difficult to disperse the above mentioned paper qualities.
• Paper qualities which are particularly difficult to disperse are for instance wet strength papers and coated paper qualities as well as kraft liner and kraft paper.
• a production line making coated paper qualities has usually separate broke storage towers for uncoated and coated broke. This is because it is desired to portion out the coated broke in a controlled way back to the paper machine, for instance due to ash control of the base paper.
• a modern screening and defibration line for broke typically comprises - a protective screen, generally a pressure screen provided with a perforated drum,
• pressurised screen which is a pressure screen provided with a slit drum or a perforated drum, and
• broke reject screen which is either an oscillating strainer or a pressure screen.
• the purpose of the protective screen is to remove large solid impurities from the broke, for instance pieces of tape, pieces of threading rope, shives.
• the pressurised screen returns to the defibration such fibre clusters which were not dispersed.
• broke reject screen The purpose of the broke reject screen is to separate from the pulp such refuse and other solid particles, which must be removed, and to return approved pulp to the screening circulation and back to the process. If the papers in question contain fillers and corresponding non-organic components, the mineral containing fraction is supplied further to a separate recovery plant (filler recovery).
• the object of the invention is to eliminate the above mentioned problems and to provide a method in a pulp or paper mill for processing pulp stock containing fibres and/or any other components in order to disperse agglomerates contained in the pulp stock.
• This processing can also substantially improve the optical properties of the produced paper, in other words increase both the lightness and the opacity.
• pulp stocks containing extractives in an adhering form (agglomerate form) and to disperse the agglomerates contained in these pulp stocks, in order to transform the extractives into a non-adhering form.
• pulp stock covers any stock made of a wood-based pulp.
• the pulp can be mechanical pulp, semi-chemical pulp or chemical so called virgin stock, or it can be any broke flow present in the paper making, or a mixture of said components.
• broke processing covers in this invention also the deinking of printed paper, where the ink is removed from the fibrous pulp.
• An apparatus according to the invention comprises
• the material flow to be processed (the pulp stock) is supplied into the feeding opening which opens out to the rotor naves and the material flow is caused to flow via the blades of the rotors arranged within each other, to the outermost rotor ring, and to be discharged from there as a discharge flow from the apparatus.
• silted broke fraction can be coated broke from the pulpers, a flow containing filler and directed to the filler recovery plant, reject from the filler recovery plant, or reject discharged from the screening and defibration plant.
• the method is also particularly well applicable for the reduction of extractives ad- hering to different virgin pulps.
• the solid contents of the pulp stock can vary in a wide range, suitably from 3 to 60 %.
• the suspension obtained as the discharge flow from the double action impact mill is recirculated either wholly or partly, one or more times, to the double action impact mill.
• Another suitable embodiment utilises two double action impact mills connected in series.
• An apparatus is provided with a housing of its own.
• the number of rings of the apparatus is at least two.
• the energy consumption of the apparatus increases when the number of the rings increases, and therefore an optimal number of the rings is probably 2 to 5.
• Figure 1 A shows in a vertical cross section the double action impact mill used in the method according to the invention
• Figure IB shows an alternative solution to that of figure 1A
• Figure 2 shows an apparatus of the type in figure 1, in a horizontal cross section
• Figure 3 shows an equipment for processing broke with a method according to the invention
• FIG. 4 shows another equipment, where the apparatus according to the invention is used for processing broke
• Figure 5 shows a third equipment, where the apparatus according to the invention is used for processing broke
• Figure 6 shows a fourth equipment, where the apparatus according to the invention is used for processing broke
• Figure 7 shows a fifth equipment, where the apparatus according to the invention is used for processing broke
• Figure 8 shows schematically the broke processing system in a paper mill producing coated paper
• Figures 9a to 9d, 10a to lOd and 11a to l id show microscope photographs of a sample taken from the reject of a filler recovery plant.
• Figure 12 shows the effect of the method according to the invention on the particle size distribution of the reject from a filler recovery plant.
• Figure 1 A shows in a vertical cross section the double action impact mill 20 used in the method according to the invention, whereby the mill comprises a housing 10, within which there is disposed a rotor 11 provided with blades la, lb, ..., 3a, 3b, ..., and so on (the individual blades are better seen in figure 2). Within the housing there is also disposed another rotor 12, which is coaxial with the first rotor 11. The second rotor 12 is also provided with blades 2a, 2b, ..., 4a, 4b, ..., and so on. The blades la, lb, ..., 2a, 2b, ... 3a, 3b, ...
• the rotors 11 and 12 are disposed in coaxial rings 1, 2, 3, ... so that the rings 1, 3, 5 of the first rotor 11 and the rings 2, 4 of the second rotor 12 are arranged in an intermeshed fashion. Then the rotors 11 and 12 with their blades can freely rotate in opposite directions.
• an opening 14 which opens out to the naves of the rotors 11 and 12, whereby this opening acts as the feeding opening of the pulp stock.
• This feeding arrangement is possible as the axes of the rotors are disposed within each other, as in the solution of the patent application FI 946048.
• an opening 15 which opens out to the outermost blade ring, whereby this opening acts as the discharge opening.
• Figure 2 showing an apparatus of the type in figure 1A in a horizontal cross section (however, modified so that each rotor 11, 12 has one ring more than in the apparatus of figure 1), presents the direction of rotation of the rotors. Each rotor can of course also rotate in the opposite direction.
• FIG. IB shows a solution in which the apparatus used in the method according to the invention is not provided with a fixedly mounted housing of its own.
• the apparatus comprising the rotor pair 11, 12 is disposed in a container 30 having an opening 14a arranged in connection with the feed opening 14, and having a discharge opening 15a for the processed material flow.
• the horizontal distance L between the rings 1, 2, 3, ... is about 3 mm and equal between all rings.
• the apparatus can be constructed, or the apparatus can be adjusted, so that the distance L between the adjacent rings increases or decreases towards the outermost ring 7 (not shown in the figure).
• the apparatus can be constructed so that the distance S between the blades of the outermost rings is smaller or larger than the distance between the blades of the inner rings.
• the above mentioned measure can present a possibility to ensure that also coarser material can be supplied to the apparatus (for instance reject pulps containing large agglomerates), but despite that provide a final product which is sufficiently well dispersed.
• An essential advantage is that the number of blades on the rotor rings and the distances between the rings (tightness) are selected according to the requirements. The distance between the rings, as well as the distance between the blades in the rings, can be arranged so that they decrease towards the outer ring. Then the dispersed agglomerates will pass into ever tighter spaces before the obtained suspen- sion is discharged from the apparatus.
• the blades which have a rectangular profile in cross section, are turned so that the impact surfaces of the blades are directed radially.
• the blades of one or more rings can also be turned so that the direction of their impact surfaces are different from the radial direction.
• the blade profile in the cross section can also be replaced by a triangular cross section, whereby the impact surfaces of the blades are not parallel, but they form a certain angle between them.
• FIG. 3 shows the apparatus used in the invention, where the double action impact mill 20 is connected to a recovery container 16 with a volume of 300 litres in the tests.
• the recovery container 16 contains a mixer driven by a motor M.
• the reference numeral 17 is the feed piping and 18 is the discharge piping.
• the discharge pump is marked by the reference numeral 19.
• Figure 4 shows another apparatus, which contains only the double action impact mill 20 and the feed piping 17 and discharge piping 18.
• Figure 5 shows a third embodiment of the invention where the material flow accumulated in the recovery container 16 is partly returned to the double action impact mill 20 with the aid of the recirculation piping 21. Of the material supplied to the container 16 this arrangement suitable returns 1/4 ... 1/2 to the double action impact mill 20. The rest is returned to the process via the overflow pipe 18.
• Figure 6 shows an apparatus solution which in other respects is similar to that of figure 5, except that two double action impact mills 20 and 20' are connected in series. Instead of returning the material flowing in the overflow pipe 18 to the process it is directed to the second double action impact mill 20', from which the material is discharged via the pipe 18'.
• Figure 7 shows an apparatus solution which in other respects is similar to that of figure 6, except that there is no material recirculation to the first double action impact mill 20.
• a factory test was made where samples were taken from the broke stock processing line of a paper mill producing coated paper, and these samples were supplied to a double action impact mill for processing. The test was made under operating conditions, so that small side flows were supplied to the double action impact mill from the sampling points.
• the figure 8 shows the marked sampling points 1 to 4 in a very schematically presented broke process in a paper mill.
• No. 1 at the flow input to the filler recovery plant from the broke processing and screening section before the dispergator (the point is before the Supraton dispergator, or before the double action impact mill, respectively);
• Samples were taken at each test point both before the double action impact mill and after it. At the sampling point no. 1 a sample was taken also after the Supraton dispergator. This sample acted as a reference for the double action impact mill, because the Supraton dispergator and the double action impact mill were connected in parallel.
• test run variables were:
• SR numbers drainage resistance, Schopper-Riegler
• particle size distribution Sedigraf
• test point 1 40 % test point 2: 4,3 % test point 3: 7,2 % test point 4: 17 %
• Figures 9a to 9d show microscope photographs (enlargement 90x) of a sample taken at the test point 4, which was unprocessed (9a), once processed in the double action impact mill (9b), twice processed in the double action impact mill (9c), and processed three times in the double action impact mill (9d).
• the unprocessed sample (9a) contained large filler agglomerates, and that every cycle through the double action impact mill caused a substantial reduction of the particle size.
• Figures 10a to lOd show another similar test result, however, taken at another factory, where the sample corresponded to the above mentioned test point 4.
• the en- largement is 90x.
• Figure 10a represents an unprocessed sample
• figure 10b represents a sample which is processed once in the double action impact mill
• figure 10c represents a sample which is processed twice in the double action impact mill
• figure lOd represents a sample which is processed three times in the double action impact mill.
• these figures show the effect of the double action impact mill in dispersing the pigment agglomerates.
• the double action impact mill was con- nected before the tank before the cyclone cleaner equipment of the filler recovery plant.
• the figures 11a to l id show microscope photographs (90x) of the samples taken at the test point 4: before (11a) the double action impact mill was connected to the process, 1.5 hours later (1 lb), 3 hours later (l ie), and 4.5 hours later (1 Id).
• Figure 12 shows the effect of the method on the particle size distribution of the reject from a filler recovery plant.
• the x axis of the figure represents the particle size and the Y axis represents the undercut, i.e. the proportion of material having a particle size which is below the particle size marked on the X axis.
• the light columns represent material which is not processed in the double action impact mill.
• the dark columns represent material which is processed once in the double action impact mill.
• Material with a particle size smaller than 15 ⁇ m is in practice accept, useful for the process.
• the accept ratio of untreated material is only about 27 %, while the accept ratio of material processed once increased to about 91 %.
• the rotational speed of its outermost ring is 40 to 80 m/second.
• a factory test was also performed, where the pulp after the broke tower was processed only in the manner according to the invention, in a double action impact mill, after which the pulp was run in the paper machine.
• the paper's technical properties were at least as good as in normal operating conditions.
• the retention was improved and the filler consumption decreased, because the pigment originating from the coating replaced fresh filler.
• the invention provides essential advantages.
• the apparatus according to the invention is connected to a broke processing equipment it would make it possible to substantially reduce the size of the cyclone cleaning equipment, which at present comprises 6 stages.
• the broke processed with an apparatus according to the invention i.e. the feed to the cyclone cleaning plant, would require only a 2-stage cyclone cleaning.
• the amount of adhering extractives of any pulp stock containing extractives can be reduced by processing the pulp stock with the method according to the invention.
• the pulp stock can be coated broke, as in the test described above, another reject flow, or a fresh pulp (mechanical, semi-chemical, or chemical), which is processed in connection with the pulp making (for instance before the drying of the cellulose) or in connection with the paper making, before said pulp is supplied to the paper machine. It is also possible to supply talc or some other dispersing agent together with said pulp stock into the double action impact mill, so that the dispersing agent will "capture" the dispersed particles and prevents the creation of inconvenient agglomerates.
• Particu- larly mechanical pulps such as thermomechanical pulp

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• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)
• Crushing And Grinding (AREA)

Applications Claiming Priority (7)

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• 1999
  • 1999-04-13 WO PCT/FI1999/000306 patent/WO1999054045A1/en not_active Application Discontinuation
  • 1999-04-13 CA CA002328205A patent/CA2328205A1/en not_active Abandoned
  • 1999-04-13 AU AU34231/99A patent/AU3423199A/en not_active Abandoned
  • 1999-04-13 EP EP99915779A patent/EP1087840A1/de not_active Withdrawn

Non-Patent Citations (1)

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