NZ231500A

NZ231500A - Helical chute washer for removing impurities from wood chips

Info

Publication number: NZ231500A
Application number: NZ231500A
Authority: NZ
Inventors: Baltsar Lundgren
Original assignee: Sunds Defibrator Ind Ab
Priority date: 1988-11-25
Filing date: 1989-11-23
Publication date: 1991-07-26
Also published as: JPH04501891A; AU4522189A; WO1990006394A1; SE8804261D0; CA2003768A1; EP0445143A1; FI912523A0; SE462566B

Description

231500 o Priority Date(s):. zs n-^ Complete Specification Filed: ..A Class- (5) D^CLWO~Zj wwvv* ^wi»* *«r*« ••••••••• i«««M ••••«• (ty* • • »n • • ••••••• *«i»p ••••••••• 2'6'JKLW" ^>ication Date: Journal, No: l5b>.Cr^ec?..

O Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION DEVICE FOR CHIP WASHING o jyWEf SUNDS DEFIBRATOR INDUSTRIES AKTIEBOLAG, A Swedish Body Corporate of, S-851 94 Sundsvall, SWEDEN hereby declare the invention, for which ^?We pray that a patent may be granted to mj^/us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) n -<•***» n 231500 - la - This invention relates to the washing of wood chip material.

The manufacture of pulp normally proceeds from wood material, which was chipped to small pieces, so-called chips. With these chips are carried heavy impurities (scrap) such as gravel, metal pieces and the like. The impurities must be removed before the chips are chemically or mechanically disintegrated to pulp. This removal takes place in a so-called chip washer, which can be designed in different ways.

The washing of chips usually is carried out in two steps. The first step comprises the removal of heavy impurities in a container, in which chips and water are stirred by a rotor provided with blades, whereby the impurities sink to the bottom. Thereafter sand and finer impurities are removed in a screw thickener.

Between these steps the chips are collected in a tank, from which they are pumped to the second step.

This conventional equipment has a disadvantage, because for impurities of small size and weight separation is uncertain, due to the fact that the particles to be separated do not move to a separation zone, but are stirred together with the chips.

The present invention offers a solution of the aforesaid problem. By using a tank equipped with a screw-shaped chute for chips and water the impurities can be separated along a relatively long sedimentation path and simultaneously be affected by centrifugal force. Chips and water are discharged continuously while at the same time the impurities are concentrated and thereby their separation is facilitated.

The invention provides that the first separation step and the pump tank in a conventional arrangement can be (followed by page 2) 2 231500 replaced by a device, which can be connected directly to the subsequent thickener.

The novel features of the invention become apparent from the attached claims.

The invention is described in greater detail.in the following, with reference to the accompanying drawings, in which Fig. 1 is a section through a device according to the invention, and Fig. 2 is a section 11-11 of the same device as shown in Fig. 1.

This embodiment of the invention comprises a cylindrical tank 1, the size of which depends on the desired capacity. The tank can have a diameter, for example, of l35-3 m. In its interior the tank is provided with a chute 2, which extends in the form of a screw slightly more than one turn about the tank wall. For achieving a satisfactory separation effect, the length of the chute 2 in the tank should be at least half a turn. Preferably the length should be at least one turn. An inlet 3 for chips and water is located upwardly in the tank 1 at the upper end of the chute 2. The chute is outwardly defined by the tank wall and inwardly by an edge 4, the height of which decreases downwardly along the chute. The chute bottom is inclined outwardly to the tank wall, which inclination increases along the chute. The chute can be steeper at the beginning. In its first part, pcfeferably in its first quarter, the chute can also be provided with unevennesses or steps in the bottom, while its subsequent part should be smooth.

At the end of the chute adjacent the tank wall, a scrap outlet 5 is located. Said scrap outlet preferably is designed for interval discharge, i.e. provided with two valves opening alternatingly. A water supply conduit 6 is connected to the scrap outlet 5 in order lu ■ c| counterflow through the scrap outlet. o r * p looi Z U i ifA * V I w I ?3!500 The bottom of the tank 1 is ishaped conically so as to slope down to a central outlet 7 for washed chips. About the o outlet 7 possibly one or several additional annular scrap traps 8 can be arranged. Adjacent these traps openings can be located for manual emptying.

The chips to be washed are supplied together with water through the inlet 3 down into the chute 2 and follow the chute dcwnwardly. Heavy objects and particles are collected by sedimentation on the chute bottom. The separation of scrap is enhanced by the centrifugal force generated aid by the fact that the chute bottom is inclined outwardly the tank wall. Unevennesses in the bottom of the first part of the chute and a steeper inclination promote the scrap removal in this part of the chute, while in the 15 subsequent part of the chute sedimentation occurs.

At the same time as the impurities are directed to the bottom of the chute and outwardly to the tank wall, an overflow of chips and water from the surface over the edge ^ takes place. This edge has a continuously aecreas- ing height so dimensioned that only 30-50% of the incoming flow of chips and water reaches the end of the chute. The impurities collected on the chute bottom adjacent the tank wall are removed through the scrap outlet 5. The count.erflow through the conduit 6 should be 0,1-0,2 m/s. 25 The flow of chips and water free of scrap is taken out —^ through the outlet 7 ana conveyed by means of a pump 9 _ to subsequent processing steps, which normally are thicken -ing steps.

The additional scrap traps 8, which can be arranged about the central outlet, are a safety feature for extreme scrap loads, which in exceptional cases can arise. Such loads may, for example, occur when the chips are taken wi-SPa""5ottoni ' scraping device of a chip bucket from a chip ; O 231500 The invention, of course, is not restricted to the embodim ent shown, but can be varied within the scope of the invention as defined in the appended claims. 6 o 231500 O a

Claims

WHAT WE CLAIM IS:

1. A device for washing wood chips, comprising a cylindrical tank which is provided at the top thereof with an inlet for chips and water and at its bottom with an outlet for washed chips, wherein a chute extends spirally downwardly for at least half a turn along the inside of the tank from the inlet, the chute being defined outwardly by a wall of the tank and inwardly by an edge, the height of which edge decreases downwardly along the chute, a scrap outlet being located at the end of the chute adjacent the tank wall, and the tank bottom sloping downwardly to the outlet, which is located centrally.

2. A device as defined in claim 1, wherein the bottom of the chute is radially downwardly inclined from the edge to the tank wall.

3. A device as defined in claim 2, wherein the radial inclination of the bottom of the chute increases along the chute.

4. A device as defined in any one of the preceding claims, wherein the chute is steeper at the beginning nearest the inlet.

5. A device as defined in any one of the preceding claims, wherein the bottom of the first part of the chute is provided with unevennesses or steps.

6. A device as defined in claim 5 wherein the bottom of substantially the first quarter of the chute is provided with unevennesses or steps.

7. A device as defined in any one of the preceding claims, wherein additional scrap outlets are arranged annularly about the central outlet.

8. A device for washing chips, as claimed in claim 1, substantially as herein described with reference to the drawings. SDNDS DEFIBRA'