GB2034609A - Hydrocyclone separators - Google Patents

Abstract

A hydrocyclone separator has a separation chamber 1 with cylindrical and frusto-conical parts 2, 8, tangential inlet 3 and opposed axial outlets 4, 9, and an outer mantle 10 defining a closed chamber 12 around the conical part 8. In operation, abrasive particles are allowed to wear a hole 13 through the wall 750 that material enters chamber 12 in which it is confined, after which operation is continued for a substantial time without any reduction in performance. Baffles (14), Figure 2 (not shown) in chamber 12 prevent material rotating in this chamber. <IMAGE>

Description

SPECIFICATION Hydrocyclone Separators This invention relates to the separation of mixtures which include abrasive particles, into two fractions by means of a hydrocyclone separator.

Hydrocyclone separators have many uses, for example in the cellulose industry where they are used for the purification of cellulose fibre supsensions. In this case the impurities to be separated consist substantially of sand, bark particles and incompletely digested fibres. These impurities, especially the sand particles, act abrasively on the wall of the hydrocyclone, in particlar in the lower part of the separation chamber, where the particles can wear grooves which lie in planes perpendicular to the axis of the hydrocyclone. Such grooves can eventually wear right through the wall of the hydrocyclone separator.In the pulp and paper industry the process temperatures have increased in modern plants, partly due to new processes having been introduced, and partly due to the processes already in use being carried out in a more "closed" form, which means that process water is recirculated to a higher extent than previously. In this way considerable savings have been obtained as regards fibres, chemicals and energy. The environmental problems have also diminished.

The higher process temperatures have, however, created problems concerning the hydrocyclone separators in the plants insofar as there is an increased leakage risk. In view of the hundreds of hydrocyclone separators that are usually present in plants in the pulp and paper industry, this is a serious problem, both from a security and an economical point of view. Uncontrolled leakage of a liquid at a temperature of 80 to 90"C can cause injury to operating personnel by burning. In practice any such leakage means that the operation must be interrupted and the damaged parts of the apparatus replaced by new equipment. Such an unplanned break in operation is extremely costly to the industry.

The problem concerning abrasion in hydrocyclone separators has been known for a long time. It has been suggested that hydrocyclone separators be provided with a double mantle in the conical lower part of the separation chamber, a replaceable conical part being arranged within an outer mantle in such a way that a closed chamber is defined between the outer mantle and the conical part. In this connection reference is made, for example, to British Patent Specification No. 769 906, according to which the conical part, which can be manufactured in one piece from a highly wear resistant material, is replaced after a certain time of operation, i.e. before it has become completely worn through.

According to the present invention there is provided a method of operating a hydrocyclone separator in the separation of a mixture including abrasive particles into two fractions, the separator having a separation chamber including a circular cylindrical first part with a tangential inlet and an axial outlet, and a frusto-conical second part coaxial with and connected by its larger end to the first part, the second part defining a second outlet at its smaller end, and means confining a closed chamber extending around the second part, the method comprising the steps of feeding mixture to be separated through the inlet, allowing the abrasive particles to wear a hole through the wall of the second part to com municatethe separation chamber with the closed chamber, and continuing to supply mixture to the inlet for a substantial period time after said hole has been formed.

The method of the invention is surprisingly simple and admits a long period of operation before the conical part of the separation chamber has to be replaced without any loss in the separation efficiency.

It has been found that it is possible to continue, without deterioration in the separator performance, the operation of a double-mantled hydrocyclone separator for a considerable period of time after the moment when abrasive particles have cut through the conical part of the separation chamber. The closed chamber, confined by the outer mantle, ensures that the material within the conical part is not discharged from the hydrocyclone separator.

The closed chamber fills with material and forms a "hydraulic mantle", which allows continued operation without deterioration of the separation ability.

In one preferred embodiment of the invention, the material entering the closed chamber is prevented from rotating in the chamber by axially oriented baffles provided in the closed chamber and preferably extending radially from the outer mantle to the wall of the conical part.

The invention is described more in detail below, reference being made to the accompanying drawings, in which: Figure 1 is longitudinal sectional view through a hydrocyclone separator for use in performing the method of the invention; and Figure 2 is a cross-section taken along line ll-ll in Figure 1.

The hydrocyclone separator comprises a separation chamber, including a circular cylindrical part 2, having a tangential inlet 3 and a central, axial outlet 4 provided in a plane cover 5 which projects radially beyond the wall 6 of the circular cylindrical part, and a frusto-conical part 7 having a wall 8 and definining a second axial outlet 9. The separation chamber 1 is surrounded by an outer mantle 10 extending from and tightly surrounding outlet 9 to the cap 5 to which it is secured by bolts 11. Between the wall 8 of the conical part 7 and the outer mantle 10 a closed chamber 12 is formed. In the conical part 7 there is shown an annular slot 13 worn through the wall 8 by hard particles. Between the outer mantle 10 and the outer side of the conical part 7 axially oriented baffles 14 extend, as shown in Figure 2.

In operation, material to be separated is fed through inlet 3 to be separated in the separation chamber 1 into two fractions, of which one fraction, the so-called "accept" is discharged through central outlet 4, whilst the other, so-called "reject", is discharged through the outlet 9. The mixture is presumed to contain hard, abrasive particles, which act abrasively on the inner wall of the conical part 7 in such a way that, a slot 13 is worn through the wall 8 of the conical part. The mixture enters the chamber 12 through the slot 13 and fills it, whereby pressure equalization between separation chamber 1 and chamber 10 is established. The separation operation may continue for a considerable period of time until the inner wall of the conical part 7 is worn away to such an extent that the performance suffers. The mixture is prevented from rotating in the closed chamber 10 by the axial baffles 14 which also supportthe wall 8 of the conical part which is of particular advantage if the wall 8 is cut through in more than one plane.

Claims (8)

1. A method of operating a hydrocyclone separator in the separation of a mixture including abrasive particles into two fractions, the separator having a separation chamber including a circular cylindrical first part with a tangential inlet and an axial outlet, and a frusto-conical second part coaxial with and connected by its larger end to the first part, the second part defining a second outlet at its smaller end, and means confining a closed chamber extending around the second part, the method comprising the steps of feeding mixture to be separated through the inlet, allowing the abrasive particles to wear a hole through the wall of the second part to communicate the separation chamber with the closed chamber, and continuing to supply mixture to the inlet for a substantial period of time after said hole has been formed.

2. A method according to claim 1, wherein material entering the closed chamber from the separation chamber is prevented from rotating in the closed chamber by one or more baffles in the closed chambers.

3. A method according to claim 1, wherein the baffle is located in an axial plane and extends radially from the wall of the second part to an outer mantle confining the closed chamber.

4. A hydrocyclone separator comprising a separation chamber including a circular cylindrical part with a tangential inlet and an axial outlet, and a frusto-conical part coaxial with the cylindrical part and having its larger end connected thereto, the smaller end of the frusto-conical part defining a second axial outlet, and an outer mantle surrounding the separation chamber and defining therewith a closed chamber extending around at least the frustoconical part of the separation chamber, the mantle being sealed to the separation chamber to prevent escape of material therebetween from the closed chamber, and the frusto-conical part of the separation chamber being readily separable from the cylindrical part thereof and the mantle for replacement.

5. A hydrocyclone separator according to claim 4, wherein at least one baffle is provided in the closed chamber to prevent material rotating therein.

6. A hydrocyclone separator according to claim 5, wherein at least one baffle lies in an axial plane and extends radially from the separation chamber to the mantle.

7. A method according to claim 1 and substantially as herein described.

8. A hydrocyclone separator substantially as herein described with reference to the accompanying drawings.