Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-10-23
1988-12-13
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356338, G01N 1506, G01N 1507
Patent
active
047913053
DESCRIPTION:
BRIEF SUMMARY
Method for measuring the properties of a composition consisting of a liquid and solid particles and apparatus used in the method.
The present invention relates to a method as defined in the preamble of claim 1 for measuring the properties of a composition consisting of a liquid and solid particles and to an apparatus used in the method.
In particular, but not exclusively, the invention relates to a measuring method of the properties, especially the dry matter content of cellulose pulp. The most important measurement at the wet end of a paper-making machine is the measurement of dry matter content and quantity of the pulp. The material quantities can be readily measured from a finished product but the wet end optimal control requires a method and apparatus capable of measuring reliably the dry matter content of mass suspension.
Presently available are mechanical (FI 33814 and SE 343683) and optical (FI application 824185) methods and mechanisms, based on the measurement of the shearing force of a composition or the light scattered from a pulp. All these mechanisms are characterized by being non-linear and by the fact that they must be adjusted on the basis of laboratory samples. Another drawback in mechanical measuring methods are the measuring inaccuracies caused by the flow rate of a composition. A drawback in the optical composition measuring methods is that the properties of a composition, such as whiteness, chemicals, additives and variations in particle size distribution, lead to inaccuracies in the measurement. The above disturbance factors affect the outcome whenever any of them obtain a new value. In other words, the presently available mechanisms are capable of producing a signal suitable for a control operation and dependent on the dry-matter content when the dry-matter content is the only variable that changes. Variations in flow rate, composition whiteness, chemicals and additives are disturbing factors and lead to inaccuracy and adjustment requirements in the present measuring methods.
An object of this invention is to introduce a method for measuring the properties of a composition consisting of a liquid and solid particles in a manner that the method is capable of measuring the properties, espeacially the dry-matter content of a composition directly from the composition without allowing the other properties of a composition to affect the measuring results.
In order to achieve this object, a method of the invention is essentially characterized in that that is smaller than the smallest dimension of the particles in a composition to be measured, individual particle arriving in and passing by any given zone exposed to radiation and are proportional to the thus appearing properties of a particle.
The theoretical basis of the above-described method, particularly when a composition to be measured is cellulose pulp, can be derived as follows:
Fibres in a mass suspension build a three-dimensional network on rather low consistencies. The network accumulates in so-called flocs when consistency exceeds the value of one percent. It is natural that the pulp should be as free of flocs as possible when it comes onto the wire of a paper-making machine. There are studies available indicating that such flocs are produced on consistencies over one percent in a few milliseconds when the mass is not turbulent. In other words, cellulose pulp or mass must be in continuous motion. FIG. 1 is a schematical view of cellulose pulp with cellulose fibres in random order. Thus, cellulose mass or pulp consists of disorderly bundles of fibres, in which the fibre lengths are usually in the order of 100 . . . 1000 microns, sometimes more than that. The mass further contains short flour, whose length is less than 100 microns, as well as additives (clay etc.) with particle size less than 10 microns. In theory, it is conceivable that, as shown in FIG. 2, the fibres are evenly distributed over the entire mass volume. The pattern shown in FIG. 2 can be argued by pointing out that the fibres are Poisson-distributed with a certain pa
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patent: 3998552 (1976-12-01), Stewart et al.
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patent: 4441816 (1984-04-01), Hencken et al.
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patent: 4714347 (1987-12-01), Cole
Nelms David C.
Oen William L.
Valmey Oy
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