Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With squeezing – compression – rubbing – kneading
Patent
1998-03-23
2000-12-12
Fiorilla, Christopher A.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With squeezing, compression, rubbing, kneading
162 60, D21C 500, D21C 902
Patent
active
061593389
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method of and apparatus for intensifying the washing of pulp with various washing apparatus. The method and apparatus are particularly well applicable in connection with the so-called Drum Displacer washers, DD washers, by A. AHLSTROM CORPORATION, and also in some wash presses. Because the method and apparatus of the invention are applicable in connection with other washing devices also, different apparatus used in washing are discussed here.
Several types of different washing apparatus and methods are know from the prior art. Diffusers, drum washers and belt washers clearly differ from each other. Pulp is supplied into washing diffusers at a consistency of approx. 10%. The feeding consistency for drum and belt washers is most usually 1-3%. Suction washers, wash presses and pressurized or super-atmospheric washers are examples of drum washers used today.
A conventional suction washer comprises a wire-covered drum revolving in a vat. The shell of the drum comprises under a perforated plate collecting compartments, and each compartment is connected with a tube of its own to a valve system on the shaft at the end of the drum. Filtrate from the valve is guided via a drop leg, or a centrifugal pump providing the required suction, for example to a filtrate tank. Due to the valve arrangement, the influence of the drop leg may be directed appropriately in the desired spots of the web formation.
Web formation in a suction washer takes place as follows: inside the drum revolving in the vat, sub-atmospheric pressure sucking pulp suspension from the vat onto the surface of the drum has been arranged by means of a drop leg or some other device generating suction. When the liquid passes through the drum the fibers in the pulp are collected onto the surface of the drum. The consistency of the suspension in the drum in approx. 0.5-2% and the consistency of the layer thickened onto the drum surface is approx. 10-12%. The web formation area, i.e. the portion of the drum periphery which is in the vat in the fiber suspension, is about 140 degrees. The maximum revolution velocity of the drum is 2-2.5 r/min; at higher revolutions speeds the filtrate collecting compartments and tubes do not have time to be emptied.
Washing is carried out as displacement wash by spraying wash liquid onto the surface of the drum which has risen up from the pulp vat. The sub-atmospheric pressure sucks the wash liquid through the pulp layer and displaces most of the liquid in the pulp. Thus, the displacement area is about 120 degrees. The typical specific square load of a suction washer is approx. 5 BDMT/m.sup.2 /d and the thickness of the pulp web is of the order of 25 mm. In a bleaching plant, the square load of a suction washer is about 8 BDMT/m.sup.2 /d and the web thickness about 30 mm.
A wash press comprises a drum covered with a wire or having a drilled perforated plate shell. Pulp is fed at a consistency of 3-4% and knots and corresponding impurities must have been removed from the pulp prior to the washer. There are compartments provided in the shell of the drum from which filtrate is discharged via a chamber at an end periphery. Also, the drum may be open so that filtrate is collected inside the drum and is discharged via an opening at an end.
The length of the web formation stage is about 90 degrees and that of the displacement stage about 150 degrees. The revolution velocity of the drum is about 2 r/min and the specific square load about 15-20 BDMT/m.sup.2 /d. The consistency of the washed web may rise even up to 35%.
The displacement, however, takes place at a consistency of about 10-15% while the thickness of the pulp web is about 30-50 mm.
An example of a superatmospheric pressure washer is a device disclosed in FI patent publications 71961 and 74752, which is composed mainly of a rotating drum and a stationary shell surrounding the drum. The drum is comprises a perforated cylinder the outer surface of which is provided with 50-60 mm high ribs at about 200 mm
REFERENCES:
patent: 3454970 (1969-07-01), Sutherland
patent: 4705600 (1987-11-01), Jacobsen
patent: 5116423 (1992-05-01), Kokkonen et al.
patent: 5741399 (1998-04-01), Antkowiak
Qvintus Harri
Tervola Pekka
Andritz-Ahlstrom Oy
Fiorilla Christopher A.
LandOfFree
Supply of washing liquid in a fractionating multi-stage washer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Supply of washing liquid in a fractionating multi-stage washer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Supply of washing liquid in a fractionating multi-stage washer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-212764