WO1990006394A1

WO1990006394A1 - Device for chip washing

Info

Publication number: WO1990006394A1
Application number: PCT/SE1989/000669
Authority: WO
Inventors: R. Baltsar Lundgren
Original assignee: Sunds Defibrator Industries Aktiebolag
Priority date: 1988-11-25
Filing date: 1989-11-20
Publication date: 1990-06-14
Also published as: JPH04501891A; FI912523A0; SE8804261D0; AU4522189A; EP0445143A1; CA2003768A1; NZ231500A; SE462566B

Abstract

A chips washing device comprising a cylindric tank (1) provided upwardly with inlet for chips and water directly in front of a chute (2), which extends in screw-shape downward at least half a turn along the inside of the tank (1). The chute (2) is defined outwardly by the tank wall and inwardly by an edge (4), the height of which decreases downward along the chute. At the end of the chute adjacent the tank wall a scrap outlet (5) is located. The tank bottom slopes downward to a central outlet (7).

Description

Device^' foi? chip washing

This invention relates to the washing of chips from wood material.

The manutacture pT pulp normally proceeds from wood material, which was chipped to small pieces, so-called chips. With these chips also follow along heavy impurit¬ ies (scrap) such as gravel,, metal pieces and the like. These impurities must be removed before the chips chem¬ ically or mechanically are disintegrated to pulp. This removal takes place in a so-called chip washer, which can be designed in different ways.

The washing of the 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 its weakness, because at a smaller size and weight of the impurities the separ¬ ation is uncertain, due to the fact that the particles to te separated are not caused to move to some 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 simultan¬ eously be affected by the centrifugal force. Chips and water, besides, are discharged continuously while at the same time the impurities are concentrated and thereby their separation is facilitated.

The invention implies that the first separation step and the pump tank in a conventional arrangement can be replaced by a device, which can be connected directly to the subsequent thickener.

The characterizing features of the invention become appar¬ ent from the attached claims. The invention is described in greater detail.in the foll¬ owing, with reference to the accompanying drawing, in which

Pig. 1 is a section through a device according to the invention, and Pig. 2 is a section II-II of the same device as shown in Pig. 1.

This embodiment of the invention comprises a cylindric tank 1, the size of which, of course, depends on the desir¬ ed capacity. The tank can have a diameter, for example, of 1,5-3 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. Por 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 downward along the chute. The chute bottom is inclined outward to the tank wall, which inclination increases along the chute. The chute can be steeper at the beginning. In its first part, preferably 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 open¬ ing altematingly. A water supply conduit 6 is.connected to the scrap outlet 5 in order to bring about a counterflow through the scrap outlet. The bottom of the tank 1 is ishaped conically so as to slope down to a central outlet 7 for washed chips. About the outlet 7 possibly one or several additional annular scrap traps 8 can be arranged. In connection to these traps openings can be located for manual emptying.

The chips to be washed are supplied together with water through the inlet 1 down into the chute 2 and follow the chute downward. Heavy objects and particles are collected by sedimentation on the chute bottom. The separation of scrap is increased by action of the centrifugal force and by the fact, that the chute bottom is inclined outward to 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 subsequent part of the chute sedimentation is desired.

At the same time as the impurities are directed to the bottom of the chute and outward to the tank wall, an overflow of chips and water from the surface over the edge 4 takes place. This edge should have a continuously decrease ing height so dimensioned thai? only 30-50% of the incoming flow of chips and water remain? at the end of the chute. The impurities collected o the chute bottom adjacent the tank wall are removed through the scrap outlet 5. The counterflow through the conduit 6 should be 0,1-0,2 m/s. The flow of chips and water free of scrap is taken out through the outlet 7 and 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 at extreme scrap loads which in exceptional cases can arise. Such loads may, for example, occur when the chips are taken with a bottom scraping device of a chip bucket from a chip plane. The invention, of course, is not restricted to the embodim¬ ent shown, but can be varied within the scope of the in¬ vention idea.

Claims

1. A device for washing chips, comprising a cylindric tank (1), which upwardly is provided with an inlet (3) for chips and water and at its bottom with an outlet (7) for washed chips, c h a r a c t e r i z e d i n that a chute (2) extends in screw-shape downward at least half a turn along the inside of the tank from the inlet (3), that the chute is defined outwardly by the tank wall and inwardly. by an edge (4), the height of which decreases downward along the chute, that a scrap outlet (5) is located at the end of the chute adjacent the tank wall, and that the tank bottom slopes down to the outlet (7), which is located centrally.

2. A device as defined in claim 1, c h a r a c t e r ¬ i z e d i n that the bottom of the chute (2) is in- clined outward to the tank wall.

3. A device as defined in claim 2, c h a r a c t e r ¬ i z e d i n that the inclination increases along the chute.

4. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the chute (2) is steeper at the beginning nearest the inlet (3).

5. A device as defined in any one of the preceding claims, c h a r a c e r i z e d i n that the first part of the chute (2), preferably the first quarter, at the bottom is provided with unevennesses or steps.

6. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that additional scrap traps (8) are arranged annularly about the central outlet (7).