Method and apparatus for washing pulp by means of intensified suction

Patent metadata

Field	Value
Publication number	US-9901853-B2
Application number	US-201214365860-A
Country	US
Kind code	B2
Filing date	Dec 14, 2012
Priority date	Dec 15, 2011
Publication date	Feb 27, 2018
Grant date	Feb 27, 2018

Abstract

A method and an apparatus for washing a solids-containing suspension by means of a suction drum washer comprising a drum provided with a filtration surface, a main vacuum source such as a drop leg and washing tubes connected to the frame of the suction drum washer. A washing liquid stream is introduced by a first washing tube is directed to contact the pulp layer on the surface of the drum in a point below 10 degrees after the surface of the suspension and a vacuum of at least 0.1 bar greater than the main vacuum source, i.e. intensified suction is applied by means of a separate vacuum source to filtering surface at the contacting point of the first liquid stream and the pulp layer or maximum of 10 degrees before the contacting point. The intensified suction may be utilized also for boosting end of filtration stage (II) and drying stage (IV). Filtrate from the drying stage (IV) can be used at the same washer as a washing liquid at the first or the second washing tube.

First claim

The invention claimed is:

1. A method of washing a pulp suspension comprising:
supplying a pulp suspension to a drum inside a basin of a washing unit, the washing unit includes a plurality of washing pipes that supply washing liquid spray, a suction leg that creates a vacuum on an inner surface of the drum, pipelines that provide washing liquid, and at least one vacuum source that produces an intensified suction to less than three sectors on the drum, the intensified suction creates a vacuum that is at least 0.1 bar higher than the vacuum created by the suction leg;
submerging the drum partly in the pulp suspension inside the basin, the drum including a filtering surface on an outer periphery of the drum on which pulp accumulates, filtrate compartments under the filtering surface, a distribution chamber inside the drum along a rotating axis of the drum having a valve inside the distribution chamber that directs intensified suction to sectors on the drum;
rotating the drum partly submerged in the pulp suspension with a vacuum directed to the drum produced by the suction leg and intensified suction directed to sectors of the drum produced by the at least one vacuum source;
accumulating a pulp layer on the filtering surface of the drum while the drum is submerged in the suspension, wherein an outer surface of the pulp layer is at atmospheric pressure and an inner surface of the pulp layer is adjacent the filtering surface;
washing the pulp layer by spraying washing liquid onto the pulp layer, a first washing liquid spray is located between a surface of the suspension and 10 degrees above the surface of the suspension, wherein the 10 degrees is measured from the surface of the suspension to the washing liquid spray in the direction of rotation of the drum;
drying the washed pulp layer;
discharging the dried pulp layer from the filtering surface of the drum; and
washing the filtering surface of the drum.

2. The method of claim 1 , wherein an entire or a partial first sector of the filtrate compartment receives intensified suction, the intensified suction begins at no less than 10 degrees below the surface of the suspension, and the sector terminates at the surface of the suspension.

3. The method of claim 1 , wherein an entire or a partial second sector of the filtrate compartment receives intensified suction, the sector begins at the surface of the suspension and terminates between about 10 to 20 degrees above the location of the first washing liquid spray.

4. The method of claim 1 , wherein an entire or partial third sector of the filtrate compartment receives intensified suction beginning after a last washing liquid spray, and terminating within a drying stage of the drum.

5. The method of claim 1 wherein the valve comprises intermediate walls that define valve channels within two intermediate walls, and wherein the valve channels direct the intensified suction to the sectors.

6. The method of claim 1 wherein the sectors include a first sector and a second sector, and further comprising a hand wheel to control intensified suction to the first and second sectors by being connected to a channel component comprising two intermediate walls and a casing for filtrate flow in the valve channel that is directed to a first and second sectors, and the hand wheel is adapted to rotate and control the relative size of the channel component, and positions of the intermediate walls are either controlled together or separately in a corresponding way.

7. The method of claim 1 , wherein the intensified suction is formed by the withdrawal of filtrate from the sectors via pipelines, and the filtrate withdrawn from the sectors is recirculated and used as washing liquid.

8. The method of claim 1 , wherein a first sector and a second sector receive intensified suction that is directed by a single suction channel.

9. The method of claim 1 wherein the steps of washing the pulp layer, drying the washed pulp layer, and discharging the dried pulp layer from the filtering surface of the drum are performed while an outer surface of the pulp layer is under atmospheric pressure.

10. A method for washing pulp in a suction washer having a basin, a rotating drum having an annular outer filtering surface, and a suction leg, the method comprising:
as the drum rotates the filtering surface through the pulp suspension, forming a pulp layer on the filtering surface by applying by suction to filtrate compartments internal to the drum and adjacent a portion of the filtering surface submerged in the suspension;
as the drum rotates the filtering surface above the pulp suspension and the filtering surface is within ten degrees in the direction of rotation of a surface of the pulp suspension, spraying a liquid onto the pulp layer and drawing the liquid through the pulp layer by applying suction into the filtrate compartments adjacent a portion of the filtering surface aligned with the spraying;
as the drum rotates the filtering surface beyond the spraying, drying the washed pulp layer on the filtering surface by applying suction to draw the liquid into the filtrate compartments adjacent a portion of the filtering surface beyond the spaying and above the surface of the pulp suspension;
as the drum rotates beyond the drying, removing the dried pulp layer from the filtering surface and suppressing the suction applied to the filtrate compartments adjacent a portion of the filtering surface aligned with the removal of the pulp layer;
applying the suction at a first pressure difference during at least the drying by flowing the liquid from the filtrate compartments down through a suction leg pipe and into a filtrate basin below the drum, and
applying the suction during at least a portion of the forming of the pulp layer and the spraying of the pulp layer by applying a second pressure difference to the pulp layer, wherein the second pressure difference is greater than the first pressure difference,
wherein the first and second pressure differences are each a pressure difference between a pressure applied to an outer surface of the pulp layer and a pressure applied to an inner surface of the pulp layer facing the filtering surface.

Assignees

• Andritz Oy

Inventors

• Harkonen Pasi
• Karjalainen Simo
• Lintunen Tuomo
• Savolainen Erkki

Classifications

• B01D33/09 Primary

  with surface cells independently connected to pressure distributors · CPC title

• D21D5/06

  Rotary screen-drums · CPC title

• B01D33/06

  with rotary cylindrical filtering surfaces, e.g. hollow drums (B01D33/044 takes precedence {; rotating drums for paper-making D21B}) · CPC title

• D21C9/06

  in filters {; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces} · CPC title

• B01D33/463

  nozzles · CPC title