GB2284165A - Dust Separator - Google Patents

Abstract

A separating device (1) is provided for separation of particles from a stream of air or other gas. The particles are separated from the gas stream in a cyclonic separator (3) whose lower end feeds into a cylindrical chamber (6) enclosing a falling cylindrical film of liquid into which the separated particles are fed so as to be entrapped. The entrapped particles are then fed away in the liquid for analysis. A second device includes two cyclones in tandem with the first acting as a pre-filter to separate out over large particles prior to the airstream going to the second cyclone for entrainment of the remaining particles in the liquid. <IMAGE>

Description

DUST SEPARATOR The present invention relates to apparatus for the analysis of particles carried in a gas, for example dust particles in air.

Various devices are available for analysis of the contents of air. For example in buildings it is sometimes desirable to monitor air quality, and to analyse airborne contaminants such as microorganisms, dust, gases and vapours. A particular problem arises when analysing particles such as microorganisms, since it is desirable to capture such particles and hold them in suspension for analysis by bio-illuminescent assay or such other method as is deemed appropriate.

With this objective in mind, the present invention provides an apparatus where such particles can be separated from the gas stream and then be entrained in a liquid, which liquid can then be fed to a further analysis apparatus such as a bio-illuminescent assay device.

Accordingly the present invention provides apparatus for use in analysing particles carried in a gas stream comprising a separator for separating the particles from the gas stream, and an entrainment device in communication with said separator for receipt of said separated particles and having an internal wall around which an entrainment liquid can be caused to travel to provide a moving hollow liquid film of circular section maintained in place centrifugally and arranged to entrain said separated particles, an inlet for the entrainment liquid which enables the liquid to be directed onto and round said internal wall to provide the film, and an outlet for discharge of the circulated liquid and entrained particles for analysis.

Preferably the separator is a cyclone and this cyclone will be designed to have a shape and operating parameters so that particles in the size range of interest (1.50 microns) can be separated.

The entrainment device will be arranged to provide a moving hollow liquid film of circular section. The simplest and most convenient such shape of film is a hollow cylinder. Other shapes where a circular section arises such as in hollow cones or spheres may also be used.

Generally the inlet for the entrainment liquid will enable liquid to be injected onto the surface of the internal wall so as to travel round the wall and gradually fall to a lower level where an outlet will be provided for discharge of the circulated liquid together with its entrained particles.

Preferably there will be a further inlet and outlet 4 within the entrainment device for a purging fluid. The purging fluid inlet should preferably be at a slightly higher level than the entrainment liquid inlet so that the purging fluid cleans off any liquid which may have been caused to flow above the level of the entrainment liquid inlet. The outlet for purging fluid can be at the same level as the outlet for the entrainment liquid or indeed purging fluid can go out through the same outlet to be branched off at a later point in the circuit.

A particular form of the invention involves an apparatus of the kind already described connected in tandem with a second similar apparatus. The first apparatus can be designed to separate out large particles and the second apparatus to entrain the remaining smaller particles for analysis.

An embodiment of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings: In which: Figure 1 is a diagram of a first apparatus according to the invention and Figure 2 shows a tandem form of apparatus.

Referring to Figure 1, a cyclone 1 has a slot inlet 2 for the air which is to be sampled, a conical flow chamber 3 around which the air by virtue of its incoming velocity flows in cyclonic fashion (lines in the diagram show the airflow) and travels downwards down the cone with an increasing angular velocity as the diameter of the cone becomes less. This causes particles to be forced to the outside of the cyclone chamber 3 while the air eventually emerges through a central passage 4 and thence to an outlet 5. This aspect of cyclonic separation is perfectly standard.

The lower part of the apparatus embodies the inventive feature. A cylindrical chamber 6 is in open communication with the lower end of the cyclone chamber 3 so that the separated particles can flow down into this chamber, and during that stage they will still maintain rotational momentum from the cyclonic action above.

Then, within the chamber, is an inlet 7 for an entrainment liquid and an outlet 8 at the lower end of the chamber for that liquid. The liquid is fed in under pressure so that it circulates round the internal wall surface of the chamber 6 and thereby provides a falling liquid film of circular section.

The particles falling from the cyclonic chamber 3 will therefore be entrained by the liquid and can then be carried away for analysis.

The chamber is cylindrical, but other shapes of circular section which would support a centrifugally maintained falling film could also be used.

A purging inlet 9 and outlet 10 are provided for a purging liquid which can be fed through the system after completion of an entrainment operation in order to clean out the system. It will be noted that the inlet 9 is higher on the chamber surface than the inlet 7 so as to take care of any liquid spill in an upwards direction from the high pressure entrainment liquid at its inlet.

Figure 2 shows a tandem apparatus and the left hand cyclone and entrainment chamber are the same as those of the Figure 1 apparatus and the reference numerals used are the same with the addition of 20 in each case. This has attached to it a second apparatus where the reference numerals used are again the same but in this case with the addition of 40.

In this device air comprising a range of particles of various sizes feeds into the second cyclone via the inlet 42. Cyclonic separation takes place in the cyclonic chamber 43 causing large particles to fall to the bottom while smaller particles remain entrained and are then fed through the central passageway 44 up and into the inlet 22 of the second cyclone apparatus.

In this second cyclone apparatus a second stage of separation takes place and the remaining particles are separated out to the entrainment chamber 26.

Size selectivity is achieved by positioning of the central passageway in each case. Thus, the closer the passageway entry is to the base of the cyclone the smaller the spectrum of particles which falls into the base trap. In cases where tuning of the system by positioning of this central tube is insufficient, adjustment of the overall dimensions of the two cyclones can also be made.

In this particular apparatus, it is only the smaller particles which are to be analysed and these are fed out at the lower end of the entrainment chamber 26 via the outlet 28 for analysis. A purging circuit takes purging liquid in through the inlet 29 of the first apparatus where the first apparatus entrainment chamber 26 can be purged and the liquid then is fed through to the lower chamber 46 of the second apparatus which allows the larger particles to be washed out.

It should be explained that separating out the larger particles is important since gross microbiological contamination by these larger particles has to be eliminated so that the sensitivity of the apparatus through overloading - is not impaired. Moreover using a pre-cyclone rather than a more conventional filter for these large particles enables the system to be cleaned or purged continuously at every cycle, and this is important for an apparatus which may need to operate unattended for long periods and over a large number of sampling cycles.

Claims (5)

CLAIMS:

1. Apparatus for use in analysing particles carried in a gas stream comprising a separator for separating the particles from the gas stream, and an entrainment device in communication with said separator for receipt of said separated particles and having an internal wall around which an entrainment liquid can be caused to travel to provide a moving hollow liquid film of circular section maintained in place centrifugally and arranged to entrain said separated particles, an inlet for the entrainment liquid which enables the liquid to be directed onto and round said internal wall to provide the film, and an outlet for discharge of the circulated liquid and entrained particles for analysis.

2. Apparatus according to claim 1 in which said separator is a cyclone.

3. Apparatus according to claim 1 in which said entrainment device further comprises an inlet for purging fluid located above said entrainment liquid inlet and an outlet for discharge of the purging liquid.

4. Apparatus according to any preceding claim connected in tandem with a second apparatus according to any preceding claim so that the first apparatus can separate out large particles and the second apparatus can entrain smaller particles for analysis.

5. Apparatus substantially as herein described with reference to the accompanying diagrammatic drawings.