Measuring and testing – Particle size
Reexamination Certificate
1998-10-16
2001-09-11
Raevis, Robert (Department: 2856)
Measuring and testing
Particle size
Reexamination Certificate
active
06286376
ABSTRACT:
This invention relates to improvements in or relating to the sampling of a mixture to be analysed for particle size distribution, and to sampling apparatus therefor, which may include particle size distribution analysers and associated samplers.
BACKGROUND OF THE INVENTION
There are many times in industry when it is a requirement to measure the particle size characteristics of materials (often to check that a manufacturing process is operating correctly, or that materials that are to be input to a process are suitable). Processed slurries are an example of a kind of material that needs to be analysed in, for example, the mining and ore-extraction industry. In, for example, platinum refining it is common to have a slurry of ground and sieved ore and to want to ensure that the grinding and sieving operation is working properly. This will be taken as an example of a field where the invention has application, but should not be seen as being restrictive: the invention has applicability to many other fields.
A slurry is often far too concentrated to be passed through existing particle size distribution analysers (e.g. laser light scattering equipment). Slurries can be more than 50% solids whereas typical measurement conditions should be 1% or less solids. Up until now dilution of the slurry has been achieved by mixing a sample of slurry in a tank and then taking a sample volume of the diluted mixture. This process is slow: time needs to be allowed for the concentrated sample to be thoroughly mixed with the diluent (e.g. water). It is difficult to suspend large particles and when in suspension such particles have a tendency to differentially sediment. Furthermore, taking a small volume of a large volume of diluent with sample mixed in it has the possibility of large sampling errors: different sized particles mix in different ways, and simply taking out a bucket of mixture from a large tank of diluent plus sample can skew (or otherwise distort) measured particle size distribution significantly. Furthermore, after taking the sample from the diluted substance sample there is the problem of what to do with the remaining (vast majority) of the diluent plus sample. If the slurry/sample is toxic it may not be possible simply to pour it into a drain or river.
SUMMARY OF THE INVENTION
According to a first aspect of the invention we provide a particle size distribution analysis sample dilution apparatus comprising progressive sample delivery means adapted for delivering, in use, substantially the whole of the sample gradually to an analyser, coupling means adapted for coupling the apparatus to a particle size analyser for observing the size of particles in diluting liquid passed through the analyser, and diluting means adapted for continuously diluting the sample with the liquid prior to delivery of said liquid with its sample content.
By delivering substantially the whole of a sample to an analyser we void distortions of the measured particle size distribution which may be ntroduced in systems where a diluted mixture is itself sampled.
By progressively delivering the diluted sample to the analyser over time we enable a low concentration of particulates to be seen at the analyser.
The apparatus is adapted to run with liquid, usually water, flowing continuously through the progressive sample delivery means and/or the dilution means.
Preferably at least parts of the apparatus are self-cleaning in between testing samples. This is typically achieved by the continuous flow of water in the apparatus.
The progressive sample delivery means preferably delivers a sample to the dilution means spread out over a period that is in the range ½ minute to 10 minutes; or 1 minute to 5 minutes; and most preferably 2 minutes to 3 minutes. In one example it takes about 2½ minutes to deliver a full sample to the dilution means. The apparatus may be adapted to perform tests on successive samples at an interval of 10 minutes or less, and possibly at about 5 minutes intervals.
The dilution means may comprise a primary dilution unit adapted to receive the sample from the progressive sample delivery means and a secondary dilution unit adapted to receive primary diluted sample and also having a clean diluent input.
Preferably the secondary dilution unit comprises mixing means adapted to mix primary diluted samples with a much greater volume of clean diluent. The ratio of volume of primary diluted liquid to clean diluent mixed in the secondary dilution means may be in the range 1:50 to 1:2, and is preferably in the range 1:20 to 1:5, and is most preferably in the range 1:12 to 1:8. In one example, it is about 1 to 10.
The volume flow rate of diluted sample reaching the analyser may be at least 5 liters per minute, and possibly at least 10 litres per minute.
In one embodiment it is about 20 liters per minute, but it could be higher.
By having such a high volume flow rate we can dilute a sample by, say, 500 to 2000 times and still pass the whole sample through an analyser in a short time (e.g. about 5 minutes or under).
Preferably the primary dilution unit comprises a funnel.
Preferably the progressive sample delivery means comprises an inclined surface upon which a sample is deposited in use. The progressive sample delivery means may also comprise a diluent supply directed onto the inclined surface to progressively feed the sample, for example a sprayer adapted to spray diluent. Flow control means may be provided to control the supply of diluent to the progressive sample delivery means. The flow control means may be manually adjustable and/or under computer control).
The primary dilution unit and/or the progressive sample delivery means may comprise cleaning means adapted to clean it/them between the delivery of successive samples. An additional supply of diluent may be provided for these purposes and may be under computer control. Of course, the same supply of diluent may be used as opposed to the provision of an additional supply.
The primary dilution unit may have a liquid level sensor adapted to monitor the level of liquid within the primary dilution unit. The arrangement may be such that if the level of liquid falls below predetermined level additional diluent may be delivered to the primary dilution means. This may be used to prevent air from entering the apparatus.
There may be a diluent reservoir which supplies the primary dilution means and/or the secondary dilution means with clear diluent. We may prefer a head pressure/reservoir supply because it can give us a reserve should there be an interruption to the supply of diluent to the apparatus. A diluent supply line to the reservoir may have a sensor adapted to detect a failure or problem with a supply. The sensor could be a pressure sensor or a flow sensor or a temperature sensor (or any suitable sensor). An alarm may be activated should there be an interruption in the supply of diluent.
The apparatus may have no movable control valves which come into contact with sample or diluted sample. All of the controls may be in the supply lines for clean diluent. This helps to avoid problems associated with abrasive particles wearing components or blocking valves.
Similarly, there may be no pumps in contact with particles: all pumps may be provided clean diluent lines. No moving parts may be in contact with the sample.
Alternatively, or additionally particles may contact at least one pump which is provided to flush at least part of the apparatus of particles. However, such a pump may contact substantially only fine particles and so not be at risk of being damaged. Moreover, having only, this one pump in contact with particles reduces the number of pumps which are prone to wear, and we can arrange for the “flush pump” to be readily serviceable.
According to a second aspect of the invention we provide a particle size distribution analysis system incorporating apparatus in accordance with the first aspect of the invention, a particle size analyser, and a controller (e.g. a computer) arranged to control the apparatus.
The system may be adapted to react to the pr
Davidson Gregory Paul
Fielding Stephen John
Jennings Robert James Henry
Malvern Instruments Limited
Michael & Best & Friedrich LLP
Raevis Robert
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