GB2121325A

GB2121325A - Cleaning centrifuge

Info

Publication number: GB2121325A
Application number: GB08315463A
Authority: GB
Inventors: Benjamin Whishaw Hawkins
Original assignee: FSP
Current assignee: FSP
Priority date: 1982-06-07
Filing date: 1983-06-06
Publication date: 1983-12-21
Also published as: GB8315463D0

Abstract

Built-up solids may be cleaned from inside a centrifuge for separating solids out of a liquid by the use of high pressure fluid jet cleaning, e.g. at a pressure of about 20,000 kPa. The centrifuge may have a two-part rotatable portion 3, 4, the fluid jets cleaning the upper part 3 and spent cleaning fluid passing out through a gap 14 between the parts 3, 4. If the cleaning fluid is the same as the liquid from which solids are to be separated out, then the inside of the centrifuge is not contaminated by the cleaning fluid, and spent cleaning fluid may be passed to the entry 2, 12, 13 into the centrifuge for the liquid after at least some of the dislodged solids have settled out. <IMAGE>

Description

SPECIFICATION Cleaning centrifuges The present invention relates to centrifuges and the cleaning of them. Centrifuges are used (inter alia) for separating solids out of liquids. In this process the solids tend to build up on the inside of the centrifuge and it is necessary to clean them away from time to time.

In the prior art centrifuges have been built with apparatus for cleaning away solids while the centrifuge is in situ. The apparatus operates by some sort of mechanical scraping such as rotating vanes. The centrifuge has to have a differential gear box and a dual electric drive, or some similar system, to operate the cleaning apparatus, and the apparatus as a whole has to be robust.

Consequently, it is expensive.

We have realised that a simpler and cheaper centrifuge cleaning system can be provided by adopting high pressure fluid jet cleaning instead of the mechanical scraping used hitherto. "High pressure" in this context means at least 200 Ib per square inch (about 1400 kPa). A liquid at about 3000 Ib per square inch (about 20,000 kPa) is preferred.

An embodiment of the invention, given by way of example, will now be described with reference to the accompanying drawing, which is a schematic sectional view from the side of a centrifuge embodying the present invention.

The figure shows a centrifuge suitable for the cleaning by centrifugal filtration of liquids such as oil to remove solid particles of sizes down to the order of a micron. It operates in a conventional manner while centrifuging the liquid. Its rotational speed could for example be about 3000 rpm.

The liquid to be cleaned enters a chamber 2 via a pipe 1. The level in chamber 2 is maintained by instrumentation or a weir system. A rotating bowl assembly 3, 4 is turned by an electric motor, or similar 5. The lower part 4 of the rotating bowl assembly extends below the liquid surface level in chamber 2. Liquid enters the part 4 through ports 12 and central pipe 1 3. The rotation and conical shape of part 4 induces liquid to flow up it. The liquid at this stage contains solids. At the top of cone 4 the liquid moves across, by centrifugal force, to bowl 3. There are vanes in cone 4 and in bowl 3 which accelerate the liquid and keep it travelling at the full circumferential speed of the bowl and cone. Liquids and solids build up in the bowl 3 until their level reaches the outlet ports 6.

Solids are thrown to the circumference of the bowl and only clean liquid exits out of the ports 6.

Clean liquid subsequently collects in a chamber 7 and exits by pipe 8.

From time to time the solids accumulated at the circumferentially outermost part of the bowl 3 must be removed. The removal may be done after a set time, or in response to the amount of solid as determined ultrasonically, or in accordance with some other deciding principle. When the solids are to be removed the bowl is slowed, either by removing drive along or with additional braking, to a speed so low that gravity overcomes the centrifugal effect and the bowl contents tend to travel downwards. Then the inside of the bowl 3 is cleaned by high pressure jets of fluid from nozzles 9. Preferably the bowl 3 continues to rotate slowly (e.g. at about 500 rpm) so that the nozzles 9 sweep around the circumference of the bowl. The fluid is supplied to the nozzles 9 through pipes 1 0.

The cleaning fluid, and the solid material dislodged by it, travel down the side of the bowl 3 and through a gap 14 to pass outside the cone 4. It falls onto a sloping plate 11 which forms the top of the chamber 2. The plate 11 has an upturned lip where the cone 4 passed through it so that the cleaning fluid and solids do not enter the chamber 2. The cleaning fluid and solids collect in the space outside the chamber 2. The solids are then removed by a suitable means, conveniently a slowly rotating system such as an Archimedean screw which lifts out solids which have settled to the bottom of the space.

Drive is transmitted to the cone 4 from the bowl 3 by a series of spokes 1 5 which link them.

The nozzle(s) 9 which direct a fluid jet up the side of the bowl 3 is disposed below the path of the spokes 1 5 so that they do not foul one another when the centrifuge rotates.

It may be especially convenient to use cleaned liquid from the centrifuge as the cleaning fluid. In this case there is no contamination of the inside of the centrifuge by the cleaning fluid, and the spent fluid collected in the space outside the chamber 2 can be returned to the chamber 2 (e.g. by flowing through a port in the side wall of the chamber 2).

The cleaning system is simple, and therefore cheap, whilst being effective to remove the accumulated solids.

1. A method of operating a centrifuge for separating solids out of a liquid in which solid deposits built-up on the rotatable inner surface of the centrifuge are removed from time to time by high pressure fluid jet cleaning with the centrifuge in situ.

2. A method according to claim 1 in which a cleaning fluid jet at a pressure of about 20,000 kPa is used during the high pressure fluid jet cleaning.

3. A method according to claim 1 or claim 2 in which the cleaning fluid used in the high pressure fluid jet cleaning is the same liquid as the centrifuge is being used to separate solids from.

4. A method according to claim 3 in which the cleaning fluid flows to an inlet to the centrifuge after it has been used in high pressure jet cleaning and after at least some of the solids cleaned from the centrifuge have been allowed to settle out.

5. A method according to any one of the preceding claims in which the centrifuge is rotated during the high pressure jet cleaning at a speed substantially below its normal operational speed of rotation.

6. A centrifuge for separating solids out of a liquid, the centrifuge having high pressure fluid jet

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cleaning centrifuges The present invention relates to centrifuges and the cleaning of them. Centrifuges are used (inter alia) for separating solids out of liquids. In this process the solids tend to build up on the inside of the centrifuge and it is necessary to clean them away from time to time. In the prior art centrifuges have been built with apparatus for cleaning away solids while the centrifuge is in situ. The apparatus operates by some sort of mechanical scraping such as rotating vanes. The centrifuge has to have a differential gear box and a dual electric drive, or some similar system, to operate the cleaning apparatus, and the apparatus as a whole has to be robust. Consequently, it is expensive. We have realised that a simpler and cheaper centrifuge cleaning system can be provided by adopting high pressure fluid jet cleaning instead of the mechanical scraping used hitherto. "High pressure" in this context means at least 200 Ib per square inch (about 1400 kPa). A liquid at about 3000 Ib per square inch (about 20,000 kPa) is preferred. An embodiment of the invention, given by way of example, will now be described with reference to the accompanying drawing, which is a schematic sectional view from the side of a centrifuge embodying the present invention. The figure shows a centrifuge suitable for the cleaning by centrifugal filtration of liquids such as oil to remove solid particles of sizes down to the order of a micron. It operates in a conventional manner while centrifuging the liquid. Its rotational speed could for example be about 3000 rpm. The liquid to be cleaned enters a chamber 2 via a pipe 1. The level in chamber 2 is maintained by instrumentation or a weir system. A rotating bowl assembly 3, 4 is turned by an electric motor, or similar 5. The lower part 4 of the rotating bowl assembly extends below the liquid surface level in chamber 2. Liquid enters the part 4 through ports 12 and central pipe 1 3. The rotation and conical shape of part 4 induces liquid to flow up it. The liquid at this stage contains solids. At the top of cone 4 the liquid moves across, by centrifugal force, to bowl 3. There are vanes in cone 4 and in bowl 3 which accelerate the liquid and keep it travelling at the full circumferential speed of the bowl and cone. Liquids and solids build up in the bowl 3 until their level reaches the outlet ports 6. Solids are thrown to the circumference of the bowl and only clean liquid exits out of the ports 6. Clean liquid subsequently collects in a chamber 7 and exits by pipe 8. From time to time the solids accumulated at the circumferentially outermost part of the bowl 3 must be removed. The removal may be done after a set time, or in response to the amount of solid as determined ultrasonically, or in accordance with some other deciding principle. When the solids are to be removed the bowl is slowed, either by removing drive along or with additional braking, to a speed so low that gravity overcomes the centrifugal effect and the bowl contents tend to travel downwards. Then the inside of the bowl 3 is cleaned by high pressure jets of fluid from nozzles 9. Preferably the bowl 3 continues to rotate slowly (e.g. at about 500 rpm) so that the nozzles 9 sweep around the circumference of the bowl. The fluid is supplied to the nozzles 9 through pipes 1 0. The cleaning fluid, and the solid material dislodged by it, travel down the side of the bowl 3 and through a gap 14 to pass outside the cone 4. It falls onto a sloping plate 11 which forms the top of the chamber 2. The plate 11 has an upturned lip where the cone 4 passed through it so that the cleaning fluid and solids do not enter the chamber 2. The cleaning fluid and solids collect in the space outside the chamber 2. The solids are then removed by a suitable means, conveniently a slowly rotating system such as an Archimedean screw which lifts out solids which have settled to the bottom of the space. Drive is transmitted to the cone 4 from the bowl 3 by a series of spokes 1 5 which link them. The nozzle(s) 9 which direct a fluid jet up the side of the bowl 3 is disposed below the path of the spokes 1 5 so that they do not foul one another when the centrifuge rotates. It may be especially convenient to use cleaned liquid from the centrifuge as the cleaning fluid. In this case there is no contamination of the inside of the centrifuge by the cleaning fluid, and the spent fluid collected in the space outside the chamber 2 can be returned to the chamber 2 (e.g. by flowing through a port in the side wall of the chamber 2). The cleaning system is simple, and therefore cheap, whilst being effective to remove the accumulated solids. CLAIMS

6. A centrifuge for separating solids out of a liquid, the centrifuge having high pressure fluid jet cleaning means usable whilst the centrifuge is in situ for removing from time to time solid deposits which have built up on the rotatable inner surface of the centrifuge.

7. A centrifuge according to claim 6 having an upwardly diverging lower rotatable member often at its upper end and an upper rotatable member open at its lower end andsconverging towards both its upper and lower ends, the rotatable members having a common axis of rotation and overlapping each other with the upper end portion of the lower member being radially within the lower end portion of the upper member, the said end portions defining between them a gap, the high pressure jet cleaning means acting when in use to remove solid deposits from the inner surface of the upper rotatable member and the gap providing an exit for spent cleaning fluid and dislodged solid deposits to leave the upper rotatable member under the influence of gravity and pass outside the lower rotatable member.

8. A centrifuge according to claim 7 in which, during the operation of the centrifuge to separate solids out of a liquid, the liquid enters the lower rotatable member at its lower end, and, under the influence of the centrifugal effect, passes upwards within the lower rotatable member to its upper end, crosses the gap to the upper rotatable member, passes upwards to the radially outermost part of the upper rotatable member where it accumulates and passes out of the upper rotatable member at its upper end, the lower end of the lower rotatable portion being disposed within a reservoir for the liquid about to enter the lower rotatable portion and the reservoir having a sloping roof in its area beneath the said gap so that during the use of the high pressure jet cleaning means spent cleaning fluid passing through the gap is directed by the sloping roof to pass outside the reservoir.

9. A centrifuge according to claim 8 which has a volume for the accumulation of spent cleaning fluid, there being means to remove solids which have settled to the bottom of the volume and means to allow cleaning fluid to pass from the volume into the said reservoir.

10. A centrifuge according to any one of claims 7 to 9 in which the two rotatable members are joined together by one or more members crossing the said gap, the rotatable members being drivable in rotation by a common drive means.

11. A centrifuge for separating solids out of a liquid substantially as herein described with reference to and as illustrated in the accompanying drawing.