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
  • D21B1/14—Disintegrating in mills
  • D21B1/18—Disintegrating in mills in magazine-type machines
  • D21B1/22—Disintegrating in mills in magazine-type machines with screw feed

Definitions

• This invention relates to a method for improving the performance of compression type feeders for bulk materials such as wood chips.
• the pulp and paper industry utilizes compression devices (plug screw feeders) which are based on the principle of a screw rotating inside a cylindrical or conical cage, where the volume available at the inlet of the screw is greater than the volume available at the discharge.
• the cage can be equipped with holes, usually conically drilled, or slots or bars arranged in such a fashion as to provide drainage of liquor squeezed from material being compressed.
• the cage is usually equipped with anti-rotation devices such as bars, pins or slots to prevent the compressed material from turning with the screw.
• United States Patent 2,943,012 entitled “Method and Apparatus for Fiberizing” discloses a plug screw feeder assembly in which wood chips are compressed to remove excess water and the wood chips are further compressed into a plug. Mechanical force is applied at an angle to said plug for the mechanical tearing off of layers from the plug. Pressure is built up in the press barrel by restricting the discharge at the opening by an adjustable choke device and by progressively increasing the diameter of the shaft while maintaining the barrel diameter uniform.
• pressafiner Another device called a pressafiner and a similar device called a French Oil Press have similar applications and usually have theoretical compression ratios of 6:1 or higher.
• United States Patent 2,975,096 entitled “Impregnation of Wood Chips” discloses a plug screw feeder in which fluid is pressed from the wood chips in the first part of the plug screw feeder, impregnating liquor is added to the high consistency wood chips in the next part of the plug screw feeder.
• the apparatus also discloses the use of conical formations on the rotating shaft. The exterior of the conical formations is in close proximity to the inside of the chamber and the compressed material provides plug seals at the restricted points in the chamber. While Figure 1 of the patent discloses screw feeders, the screw feeders are not designed to force feed the wood chips into the chamber of the plug screw feeder.
• CTMP chemical thermal mechanical pulp
• the various uses of plug screw feeders involve a number of mechanisms for creating pressure between the chamber and the shaft bearing flights.
• the inner diameter of the chamber may be cylindrical, conical, or may contain restricted areas. All of these features together with variations in the diameter of the shaft or diameters of the flutes on the shaft can produce changes in the pressure exerted on the wood chips or other material being treated in the plug screw feeder.
• the chamber of the plug screw feeder may be comprised of bars, screens or be solid depending upon whether the plug screw feeder is being used to drive off excess water or being used to refine wood chips or both remove excess fluid and refine.
• the pressure and throughput is controlled by the voids if any in the chamber, the restrictions in the chamber, the shaping of the shaft or flutes and the torque applied to the screw feeder. The applicant has found that in many applications improved efficiency and throughput of a plug screw feeder can be achieved by feeding wood chips or other materials under pressure into the plug screw feeder.
• the theoretical compression ratio of a plug screw feeder is the volume of the first enclosed pocket or flight spacing in the inlet zone, divided by the volume of the last enclosed pocket or flight spacing in the discharge zone.
• Reasons for the actual compression ratio not being equal to the theoretical are thought to be as follows: 1) Inadequate filling of the inlet zone.
• Wood chips being a non-homogeneous substance have a bulk packing density approximately 1/2 that of solid wood.
• the bulk density of chips is approximately 12 lbs/ft.
• Production tests show that a typical plug screw feeder will have 60% of its theoretical capacity when a packing density of 12 lbs/ft is used in the calculation.
• the compression device for bulk material such as wood chips of this invention overcomes the limitations of inadequate and/or unpredictable inlet filling associated with such compression devices now in use.
• the varied force feed screw to the inlet of the compression device works like a "supercharger" by forcing material into the inlet section of the compression device, thus providing an increased and uniform packing density in the inlet.
• the fully packed inlet also prevents back flow of chips from the compression cone. The full compression of the screw is then available to work on the material thus increasing the effective compression ratio.
• One embodiment of the invention relates to a compression device for bulk material such as wood chips, comprising an inlet, a screw operating within a cylindrical or conical cage and an outlet wherein the volume of space available at the inlet of the compression device is greater than the volume of space available at the outlet, and the improvement wherein means is provided to feed bulk materials under pressure into the inlet of the compression device.
• the means for feeding the bulk material under pressure into the inlet of the invention is variable and the feeding may be at variable pressures.
• variable speed force feed screw is used to control the inlet pressure.
• Another embodiment of the invention relates to a method of compressing bulk material such as wood chips comprising feeding the materials to be compressed under pressure into the inlet of the compression device, operating a screw within a cylindrical or conical cage, having a greater volume at the inlet than at the outlet.
• the means for feeding the compressible material is variable to provide variable feed pressures to the compression device.
• a variable speed control feed screw is used to control the inlet pressure of the compressible material to the compressor.
• the force feed screw has a variable speed drive.
• Figure 1 is a schematic drawing of a plug screw feeder.
• the plug screw feeder 1 is comprised of a power source 2, power drive shaft 3, transmission 4, screw drive shaft 5 and screw 6 which are all interconnected.
• the screw 6 is enclosed within compression cone or cylinder 7.
• Compression cone or cylinder 7 includes screen plates 8 through which liquid is drained during compression and thickening of the bulk material.
• the plug screw feeder 1 has an inlet housing 9 and an outlet housing 10.
• the inlet housing 9 is comprised of a force feed screw 11 inside force feed cylinder 12. Force feed cylinder 12 rests below surge bin 13. Force feed screw 11 is attached by drive shaft 14 to variable feed screw power source 15.
• the outlet housing 10 includes discharge chamber 16, discharge outlet 17 and fluid or blowback damper 18.
• the plug screw 6 is comprised of a series of flights or pockets commencing at 19 proximate the inlet housing 9 and decreasing in volume until the flight or pocket 20 of least volume proximate the outlet housing 10.
• a series of antirotation pins 21 are mounted in the wall of compression cone or cylinder 7.
• the power source 2 is activated and the plug screw 1 begins rotating and compressing the compressible material in compression cone or cylinder 7.
• the variable feed screw power source is turned on and forces feed screw 11 continues to force the compressible material into the largest volume flight pocket 19.

Landscapes

• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)
• Screw Conveyors (AREA)
• Refuse Collection And Transfer (AREA)
• Circuit Arrangement For Electric Light Sources In General (AREA)
• Disintegrating Or Milling (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=4140627

Family Applications (1)

Country Status (9)

Cited By (2)

Families Citing this family (6)

Family Cites Families (2)

• 1989
  • 1989-09-19 CA CA000612010A patent/CA1309962C/en not_active Expired - Lifetime
• 1990
  • 1990-09-17 WO PCT/CA1990/000298 patent/WO1991004371A1/en active IP Right Grant
  • 1990-09-17 EP EP19900913446 patent/EP0493422B1/de not_active Expired - Lifetime
  • 1990-09-17 ES ES90913446T patent/ES2047340T3/es not_active Expired - Lifetime
  • 1990-09-17 AU AU63315/90A patent/AU642160B2/en not_active Ceased
  • 1990-09-17 DE DE69005311T patent/DE69005311T2/de not_active Expired - Fee Related
  • 1990-09-17 JP JP2512338A patent/JPH05500086A/ja active Pending
• 1992
  • 1992-03-10 NO NO920935A patent/NO180546C/no not_active IP Right Cessation
  • 1992-03-18 FI FI921162A patent/FI97732C/fi active

Non-Patent Citations (1)

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