Optics: measuring and testing – For size of particles
Patent
1987-01-09
1988-12-27
Willis, Davis L.
Optics: measuring and testing
For size of particles
250564, 356427, G01N 1502
Patent
active
047937068
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to both the is a process and equipment for the determination of grain size distribution of particles in suspension.
The known or prior art and equipment processes for the determination of grain size distribution are characterized by the fact that the measurement is carried out by drawing samples independent of the technological process under laboratory conditions. The time required for measurement and evaluation is fairly long therefore this kind of solution is not suitable for continuous measurement and process control. The equipment called "Analysette 20" of the Fritsch-make represents the basis of a process for the determination of grain size distribution wherein the settling rate/velocity of particles is determined by photoextinction density measurement and further on the grain size distribution as a function of the path of settling. By this instrument the samples taken from the technological process are similarly treated under laboratory conditions. The principal part of the unit is a cell filled with suspension sample which is, after some predetermined time, scanned by a photoextinction measuring head moved continuously in an opposite direction to the settling. As a result of movement of the measuring head the extinction of the smaller particles can be determined after a shorter path of settling and the measurement can be performed within 15-20 minutes i.e. far before total settling would be completed. Disadvantage of the solution lies in the condition that measurement cannot earlier be terminated and evaluated before measuring a moving head reaches the surface of liquor, at the same time the accuracy of measurement improves in direct proportion to the height of the column of liquid which means that higher accuracy is associated with longer measuring time. Minimum measuring time with this kind of measurement of result resulting in acceptable results would take about 15 minutes. This time is too long to apply the solution for direct control of the technological processes.
A further disadvantage of the known device lies in the condition that the measuring range of grain size distribution is comparatively small because measuring time can only be reduced by the reduction of useful height of the cell thus limiting the upper limit of measuring range and the interfering effect on the photoextinction measurement of the reflection of liquor surface in the cell limits the lower limit of measuring range. Particles exhibiting a settling path less than 1 cm can no longer be measured by this device, it only provides acceptable measuring results in the particle range of 1-200 .mu.m.
SUMMARY OF THE INVENTION
For a number of technological processes, e.g. classification, sizing, grinding, crystallization, settling and agglomeration, a solution for the measurement of grain size distribution is needed. The results of which should be useful directly for the contemporary regulation and control of the process. The invention is based on the recognition that for the determination of the photoextinction grain size distribution, the optical density is repeatedly measured at several points in the container holding the suspension, and the grain size distribution is determined from the data obtained by the use of a digital data processing unit. This way, partly the measuring range can be extended, partly the measuring time can be reduced thus the measuring results may directly be used for the control of some technological processes.
Accordingly the invention represents a process for the determination of grain size distribution of particles in suspension in the course of which the suspension is allowed to settle in a settling tank while the optical density of the suspension in the settling tank is measured and from this the grain size distribution is determined.
According to the invention, the suspension is homogenized by circulating it in the settling tank, then circulating is stopped and optical density is repeatedly measured at at least three points of different height. Rep
REFERENCES:
patent: 2379158 (1945-06-01), Kalischer
patent: 3739180 (1973-06-01), Carlson
patent: 3879129 (1975-04-01), Inoue
patent: 4159639 (1979-04-01), Simms et al.
patent: 4282745 (1981-08-01), Burr
Bulkai Denes
Csillag Zsolt
Farkas Ferenc
Fodor Maria
Kovacs Ferenc
Koren Matthew W.
Magyar Aluminiumipari Troszi
Willis Davis L.
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