GB1562073A - Hydrocyclone separator - Google Patents

Description

(54) HYDROCYCLONE SEPARATOR (71) We, AB CELLECO, a Swedish Corporate Body, of Fack, 100 52 Stockholm, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a hydrocyclone separator for the separation of a mixture into a first fraction of relatively low density, and a second fraction of relatively high density.

Hydrocyclone separators have many uses.

A major one is in the cellulose industry for the purification of cellulose fibre suspensions. Generally, a hydrocyclone separator system includes several stages coupled in series, with every stage comprising several hydrocyclone separators connected in parallel and having common inlet and outlet chambers. Such a hydrocyclone separator system separates the original, highly diluted cellulose suspension into diluted, purified fibres, called the "light fraction", and thickened impurities, called the "heavy fraction".

As modern process technology has advanced, cellulose suspension temperatures have increased, causing viscosities to decrease. With decreasing viscosities, and a given number of stages, the separating power of a hydrocyclone separator system decreases and more cellulose fibres are discarded with the heavy fraction. It is, of course, desirable to get as few cellulose fibres in the heavy fraction as possible. At the same time, from an environmental point of view, it is aimed at keeping the volume flow of the heavy fraction on a low level, which means that the concentration of impurities in this fraction will be high. The problem is to provide a hydrocyclone separator which separates efficiently into a light fraction and a heavy second fraction which can be discharged from the hydrocyclone separator in a minimal volume flow with a high concentration.

Many attempts have been made, some on a commercial scale, to solve the problems of fibre loss and clogging of the discharge outlet of the relatively heavy fraction. Most of the attempts entail supplying water under pressure to the individual hydrocyclone separators to dilute the heavy fraction and to wash out the valuable fibres. Generally, water is supplied tangentially near the heavy fraction outlet end of the hydrocyclone separator, or through a channel terminating inside the hydrocyclone separator at the heavy fraction outlet end. Discharge chambers, formed like cylinders or cones and provided with a tangential inlet for diluting water have been connected directly to the heavy fraction outlet of the hydrocyclone separator, as well. At best these attempts have solved the plugging problems and reduced the fibre loss to some extent.

Attempts have been made to provide the conical part of a hydrocyclone separator with axially directed guide bars designed to give the heavy fraction, flowing helically along the wall of the conical part, a component of movement directed radially inwards, in order to transfer to some extent light components from the heavy fraction to the light fraction.

The desired result has not been obtained by using the arrangements mentioned.

It might seem obvious to make the discharge outlet of the heavy fraction larger than it has been generally hitherto. This, however, is not possible, since such a design would result in too large a flow of the heavy fraction. Furthermore, the axially directed guide bars occupy part of the separation space in the conical part of the separation chamber. With consideration to the wear to which the guide bars are subjected, they have to be designed with a greater radial thickness than that theoretically necessary. Elimination of this drawback, i.e. the reduction of the separation space, would need a reduction in the cone angle, which in turn means a larger heavy fraction discharge outlet or the conical part of the separation chamber would have to be very long.

The present invention aims at a solution to the above problem and accordingly provides a hydrocyclone separator for separating a mixture into a light fraction of relatively low density and a heavy fraction of relatively high density, comprising a separation chamber including a circular cylindrical part provided with a tangential inlet for the mixture and a central outlet for the light fraction, and a frustoconical part forming a discharge outlet for the heavy fraction, means mounted in the separation chamber for giving the heavy fraction flowing helically along the inner wall of the frusto-conical part a component of movement directed radially inwards, and flow deflecting means arranged on the inner wall of the frusto-conical part in the vicinity of the discharge outlet for giving the heavy fraction of the mixture flowing towards the discharge outlet a component of movement directed axially inwardly towards the cylindrical part of the separation chamber.

This construction allows the cone angle of the conical part of the hydrocyclone separator to be reduced to provide space for one or more guide bars without restricting the separation space, since the discharge outlet opening for the heavy fraction can be rather large without making the heavy fraction flow too large.

In a preferred embodiment of the invention the flow deflecting means is also arranged to give the heavy fraction flowing towards the discharge outlet a component of movement directed radially inwards.

Compared with common hydrocyclone separators used for cellulose fibre suspensions, with a separator in accordance with the invention the loss of cellulose fibre in the discharged heavy fraction may be reduced by more than half without increasing the content of impurities in the purified cellulose suspension. i.e. the light fraction. As a reduced amount of cellulose fibres are discharged with the heavy fraction, this fraction flows more easily through the discharge outlet. Furthermore, as mentioned, the discharge outlet may have a larger opening.

Thus the risks of clogging can be practically eliminated.

One embodiment of the invention will now be described more in detail, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a hydrocyclone separator embodying the invention, in longitudinal section; Figure 2 is a section taken along line II-II in Figure 1; and Figure 3 is a section taken along line III-III in Figure 1.

The hydrocyclone separator shown in the drawing has a circular cylindrical part 1, a conical part 2, a tangential inlet 3 for the mixture to be separated, a central discharge outlet 4 for the light fraction, and a discharge outlet 5 from the conical part for the heavy fraction. In the conical part 2 there are four guide bars 6, extending in axial planes, and evenly distributed around the circumference of the conical part. The guide bars are shaped in cross-section (see Figure 2) as symmetrical ridges. The height of the ridges increases in the direction towards the discharge outlet 5.

Between the guide bars 6 and the discharge outlet 5 there is provided guide means in the form of a strip 7 extending in a screw path, running 1 t turns around the inner wall of the conical part 2. The screw strip is designed to give the heavy fraction, flowing towards the discharge outlet 5 an axial component of movement against the flow, i.e. in the direction towards the central discharge outlet 4 for the light fraction. If the hydrocyclone separator is regarded from the feed inlet end, the flow moves clockwise, whereas the screw path of the flow deflecting strip 7 is arranged to run counter-clockwise.

The plane of the strip is inclined with respect to the horizontal plane, inwardly towards the discharge outlet 5, whereby the heavy fraction, flowing towards the discharge outlet 5, is also given a component of movement, directed radially inwards.

The flow deflecting strip 7 is designed in such a way, that the discharge area is relatively large so that a free passage is left for the heavy fraction.

The hydrocyclone disclosed operates as follows. The mixture to be separated into one light fraction and one heavy fraction is fed through the inlet 3 and flows along a helical path towards the conical part 2 of the hydrocyclone separator. The heavier constituents tend to move close to the wall of the separator, whereas the Igihter constituents tend to move in the direction towards the axis of the separator. Some light constituents, however, will remain in the flow close to the wall. When the flow reaches the screw strip 7 a major part of it, the light fraction, will change its direction of axial movement and will flow, with its direction of rotation unaltered, towards the discharge outlet 4, while a minor part of it, the heavy fraction, is discharged through the discharge outlet 5. The guide bars 6 deflect the flow inwards towards the symmetry axis of the hydrocyclone separator, light constituents being brought into contact with the light fraction, flowing towards the discharge outlet 4. The flow deflecting strip 7 prevents a too large part of the flow being discharged through the discharge outlet 5. In the embodiment shown, where the strip 7 is inclined in relation to the horizontal plane, favourable flow conditions are obtained in the vicinity of the strip 7, which contributes to an improved separation result.

WHAT WE CLAIM IS: 1. A hydrocyclone separator for separating a mixture into a light fraction of relatively low density and a heavy fraction of relatively high density, comprising a separation chamber including a circular cylindrical part provided with a tangential inlet for the mixture and a central outlet for the light fraction, and a frusto-conical part forming discharge outlet for the heavy fraction means mounted in the separation chamber for giving the heavy fraction flowing helically along the inner wall of the frusto-conical part a component of movement directed radially inwards, and flow deflecting means arranged on the inner wall of the frusto-conical part in the vicinity of the discharge outlet for giving the heavy fraction of the mixture flowing towards the discharge outlet a component of movement directed axially inwardly towards the cylindrical part of the separation chamber, 2. A hydrocyclone separator according to claim 1, wherein the flow deflecting means is also arranged to give the heavy fraction flowing towards the discharge outlet a component of movement directed radially inwards.

3. A hydrocyclone according to claim 1 or 2, wherein the flow deflecting means extends in a helical path around the inner wall of the frusto-conical part.

4. A hydrocyclone separator substantially as herein described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. which contributes to an improved separation result. WHAT WE CLAIM IS:

1. A hydrocyclone separator for separating a mixture into a light fraction of relatively low density and a heavy fraction of relatively high density, comprising a separation chamber including a circular cylindrical part provided with a tangential inlet for the mixture and a central outlet for the light fraction, and a frusto-conical part forming discharge outlet for the heavy fraction means mounted in the separation chamber for giving the heavy fraction flowing helically along the inner wall of the frusto-conical part a component of movement directed radially inwards, and flow deflecting means arranged on the inner wall of the frusto-conical part in the vicinity of the discharge outlet for giving the heavy fraction of the mixture flowing towards the discharge outlet a component of movement directed axially inwardly towards the cylindrical part of the separation chamber,

2. A hydrocyclone separator according to claim 1, wherein the flow deflecting means is also arranged to give the heavy fraction flowing towards the discharge outlet a component of movement directed radially inwards.

3. A hydrocyclone according to claim 1 or 2, wherein the flow deflecting means extends in a helical path around the inner wall of the frusto-conical part.

4. A hydrocyclone separator substantially as herein described with reference to the accompanying drawing.