Optics: measuring and testing – For size of particles
Patent
1989-09-20
1991-04-30
Rosenberger, Richard A.
Optics: measuring and testing
For size of particles
356336, 2502222, 73DIG1, G01N 1502
Patent
active
050112856
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a method for performing an automatic analysis to determine a particle size distribution and deviation from the desired shape and color. The method includes the collection of particle samples and the generation of a particle curtain in a monolayer form, lighting of the latter and taking pictures that are then analyzed. The invention also relates to an apparatus, a particle feeding system, for carrying out the method. This includes means for generating a particle curtain in a monolayer form.
(2) State of the Prior Art
During production of particulate material, or in processes where such material is added in at least one process stage, it is important to be able to control the process, so that the desired size distribution of the particle shaped material is obtained. However, the shape of the particles can also be important for the quality of the product, and therefore it is desirable to know the deviation of the particles from the desired shape and color, so that the process can be controlled with regard to this criteria also.
It has long been desired in the fertilizer industry to have reliable information about the end product size distribution and particle shape, as optimal values for these parameters is of importance both from a purely economical point of view and when using the product, e.g. when spreading the produced prills or granules. Furthermore, a process will be most economical if it gives a product with a narrow sieve span, without having to sieve away large fractions that have to be run in return.
Several analysis apparatus and measuring techniques are already available, and are used to solve the aforesaid problem, however, their applicability is usually limited to very special processes. Thus a particle analysis apparatus is known from U.S. Pat. No. 4,497,576, where a silhouette projection method is used. The apparatus also includes use of parallel laser beams directed through a sample of particles, and means for recording the light which has passed through. This recording is then analyzed to reveal the particle size distribution in the aforesaid sample. A series of conditions which have to be satisfied for the measurements to be representative is listed in the patent, but it doesn't clearly appear how these conditions should be realized. The particles to be analyzed are transported on a conveyor belt and fall from it in front of a light source and down onto the next conveyor belt for return to the process. One condition which is stated is that the particles falling from the conveyor belt must form a monolayer of particles and that they should fall at the same speed. But how such a monolayer is to be practically obtained is not stated, and the aforecited means appears to be badly suited for the application.
Furthermore, from DE number 27 41321, an apparatus for determining the particle size distribution in a falling particle stream by recording and analysis of video pictures is known. The particles flow out of an extended slot in a silo and thereby form a curtain of particles passing a video recorder equipped with a heat picture camera. In addition to the size distribution, the means registers whether the particles deviate strongly form a spherical shape, as the particles' heat content is recorded. The patent neither states how to take representative samples, nor whether special measures are necessary for analyzed particle curtain to be representative. It is stated that fine dust does not substantially disturb the result of the analysis. The apparatus is primarily used for analysis of the size distribution of various additives for asphalt.
Although the aforecited patents give information which clarifies the problem of particle analysis to a certain extent, they do not give practical solutions to the problems of controlling fertilizer granulation/prilling through particle analysis, and that was what the inventor primarily had to find a solution to.
SUMMARY OF THE INVENTION
The object of the present invent
REFERENCES:
patent: 4288162 (1981-09-01), Sakamoto et al.
patent: 4295200 (1981-10-01), Johnson
patent: 4497576 (1985-02-01), Caussignac et al.
Asbjornsen Odd A.
Jorgensen Terje
Strand Oddbjorn E.
Norsk Hydro a.s.
Pham Hoa Q.
Rosenberger Richard A.
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