GB2084479A

GB2084479A - Separating solids from liquids

Info

Publication number: GB2084479A
Application number: GB8030696A
Authority: GB
Original assignee: Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Motor Co Ltd; Ford Motor Co
Priority date: 1980-09-23
Filing date: 1980-09-23
Publication date: 1982-04-15

Abstract

Aluminium swarf is separated from oil-based coolant by passing the contaminated coolant into a settling tank (2), through a rotary drum filter (3) and then through a plurality of cyclone units (12) connected in parallel. The first filtration stage removes particles greater than 50 mu , the second stage removes particles greater than 20 mu . Both stages can operate continuously. <IMAGE>

Description

SPECIFICATION Apparatus and process for separating solid particles from liquid media This invention relates to apparatus and processes for separating solid particles from liquid media, especially for separating aluminium swarf from oil-based coolant liquids.

In a machine tool shop, cutting tools are cooled by an oil-based liquid coolant which is sprayed on to the cutting tool. The contaminated coolant is collected from the machines and conducted to a central location at which the swarf is separated from the coolant.

It is desirable to separate the swarf from the coolant in a one-stage process, and a number of alternative processes have been proposed for this purpose. For example, the contaminated coolant may be passed through a filter bed or filter cloth.

In another process, the contaminated coolant is passed through a filter screen which is continuously scraped in order to remove solid material therefrom. In a further process, the contaminated coolant is filtered in a cyclone, in which the liquid coolant is caused to flow in a vortex so that the solid particles are concentrated in a boundary region of the vortex and can be diverted therefrom into a waste receptacle.

The separation of aluminium swarf from liquid coolants presents special problems in view of the low density of aluminium and the characteristic shape of aluminium swarf particles.

Although filter beds and filter cloths can be used successfully for the removal of aluminium swarf from coolants, the technique suffers from the disadvantage that the bed or cloth rapidly becomes clogged with solid matter and must be removed for cleaning periodically. Scraped filter screens can be used to remove large particles of aluminium swarf from coolant, but cannot be used to remove small particles e.g. of 20 to 50 micron average diameter. On the other hand, cylcone filtration is effective in removing particles in the 20--50 micron diameter range, but is unsuitable for the removal of large particles because the large particles interfere with the formation of a vortex in the cyclone.

According to the present invention, there is provided an apparatus for separating solid particles from a liquid medium in which the particles are suspended comprising a filter screen for removing separating relatively large particles from the medium and a cyclone filter arranged to receive filtered liquid from the filter screen and operable to remove relatively small particles from the filtered liquid.

The invention also provides a process for separating solid particles from a liquid medium which comprises passing the liquid medium in which the particles are suspended through a filter screen and thereby removing relatively large particles from the liquid, and passing the filtered liquid in a cyclone to separate relatively small particles from the liquid.

By passing the contaminated liquid first through a filter screen and then through a cyclone filter, a much more effective separation of the particles from the liquid can be achieved than by using either of the two filtration stages individually.

Preferably the filter screen is in the form of a self-cleaning filter, for example a back-flushed drum filter, so that the first stage in the process can be operated continuously without the need for replacement of the filter for cleaning. Typically, in the first stage of the process, particles having average diameters of 50 microns or more will be removed from the coolant. If desired, the coolant may be allowed to stand in a settling tank prior to the first filtration so that the largest particles are separated from the coolant by gravity.

After having been passed through the filter screen, the coolant is subjected to cyclone filtration, in which the liquid is caused to flow in a vortex. Preferably the stream of liquid from the filter screen is divided into a plurality of parallel streams and each stream is filtered in a respective cyclone unit. This arrangement reduces the operating cost of the process because the energy required to generate a vortex increases nonlinearly with the size of the vortex. Consequently, less energy is used in the operation of a series of small cyclones than in the operation of a single large cyclone.

In order that the invention may be better understood, a preferred embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings in which:~ Figure 1 is a schematic plane of apparatus for separating solids from a liquid medium and Figure 2 is a sketch of a cyclone unit used in the apparatus of Figure 1.

Referring to the drawings coolant containing aluminium swarf from a plurality of machine tools (not shown) is conducted along coolant return lines 1, 1 and is delivered into one end of a settling tank 2 on the bottom of which the largest particles of aluminium swarf collect. A rotary drum filter 3 is mounted at the other end of the settling tank 2.

The drum filter 3 includes a cylindrical screen 4 for retaining particles greater than 50 microns average particle size, a drive motor 5, which rotates the screen 4 about its longitudinal axis and, internal back-flushing jets which direct cleaned coolant outwardly onto the interior surface of the screen 4. The liquid level is higher on the outside of the drum 3 than on the inside so that the liquid flows through the screen under hydrostatic pressure and into a semi-clean tank 2a. A scraper conveyor 7 removes solid material from the bottom of the settling tank 2.

A pump 6 directs liquid which has passed through the screen 4 along a conduit 10 which divides the stream of coolant into a plurality of parallel streams each of which communicates with a respective cyclone filter unit 12.

As best seen in Figure 2, each cyclone filter unit 12 comprises a conical vortex tube 13 into which contaminated coolant is pumped by means of a pump (not shown) through an inlet 14. A tubular baffle 15 adjacent the inlet 14 directs the incoming liquid tangentially on to the inner surface 1 6 of the vortex tube 1 3 thus generating a vortex.

The radially outer layer of the vortex progresses down the vortex tube 13, as indicated by the arrows A towards a discharge orifice 17. An upward counter flow stream is automatically established in the radially inner layer of the vortex, as indicated by the arrows B. The counter flow stream B passes through the hollow centre of the bottle 15 and discharges from the cyclone through an outlet 18 above the inlet 14. The swirling action of the vortex concentrates the particles of solid material in the liquid in the outer layers of the vortex, so that the liquid discharged from the orifice 17 contains the solid material, whereas that discharged from the outlet 18 is relatively free from solids. In this way particles in the range 20-50 microns diameter can be separated from the coolant.

The discharge orifices 1 7 of the cyclone units 12 all discharge into a sludge tank 19, from which material is removed by a scraper conveyor 20.

The liquid coolant from the outlets 1 8 of the cyclone units 12 is directed into a common conduit 21, which discharges into a reservoir 22.

The clean coolant is then fed from the reservoir to the machine tools by pumps 23, 24 along a feed line 25.

Claims

1. Apparatus for separating solid particles from a liquid medium in which the particles are suspended comprising a filter screen for removing separating relatively large particles from the medium and a cyclone filter arranged to receive filtered liquid from the filter screen and operable to remove relatively small particles from the filtered liquid.

2. Apparatus according to Claim 1 wherein the filter screen comprises a rotary drum filter.

3. Apparatus according to Claim 1 or Claim 2 wherein the filter screen retains particles of average sizes greater than 50 microns.

4. Apparatus according to Claims 1, 2 or 3 comprising a plurality of cyclone filter units connected in parallel each arranged to receive filtered liquid from the filter screen.

5. Apparatus according to any one of Claims 1 to 4 further comprising a settling tank from which liquid medium carrying the solid particles may be passed to the filter screen.

6. Apparatus for separating solid particles from a liquid medium substantially as hereinbefore described and as illustrated in the drawings.

7. A process for separating solid particles from a liquid medium which comprises passing the liquid medium in which the particles are suspended through a filter screen and thereby removing relatively large particles from the liquid, and passing the filtered liquid in a cyclone to separate relatively small particles from the liquid.

8. A process according to Claim 7 wherein particles are allowed to settle from the liquid before the liquid is passed through the filter screen.

9. A process according to Claim 7 or Claim 8 wherein the solid particles comprise aluminium swarf, and the liquid comprises a coolant for machine tools.

10. A process for separating solid particles from a liquid medium substantially as hereinbefore described, and as illustrated with reference to the drawings.