Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Patent
1996-09-20
1998-06-16
Husar, John M.
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
241 27, 241 33, 241 38, B02C 1912
Patent
active
057657645
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method for controlling the grinding of mineral raw materials, which is primarily based on a current determination of the specific surface area of the fines, and an appliance for performing said method as well as fines obtainable by such grinding.
A constant quality of fines, e.g. of cement fines, can be obtained at minimum production costs if several measured variables are watched and, correspondingly, the grinding process is controlled in an exact manner. Preferably raw material components are fed to a mill in a constant composition and by a constant mass flow. This also applies to the furnace temperature and to the temperatures of the ingredients. Tolerances are within narrow intervals. Some producers obtain products of good quality by empirically controlling the furnace and the mill on the basis of simply measurable physical quantities as e.g. at the mill on the basis of a residue percentage on a 90 .mu.m sieve and on the basis of measuring the mill sound by an electric ear.
As a precautionary measure, cement is often ground to a higher fineness than required. However, this is an expensive measure since finish grinding requires about 38% of the total power demand of a cement plant, and this precaution can be omitted by continuously surveying the fineness of the cement fines (W. Duda, Cement Data Book, 1985 Bauverlag GmbH, Wiesbaden, Berlin, Vol. 2, pp. 76-92).
It has been proved by investigations that by refined methods higher quality products can be obtained. A surveillance of the fineness of the fines has to be a part of the control system of an automated grinding plant.
For this purpose at Holderbank, Switzerland, a Blaine permeability-meter, operating continuously and coupled to the grinding process, has been devised to determine the specific surface areas of cement (Wieland, W., Automatic Fineness Control, IEEE Cement Industry Technical Conference, May 1969, Toronto, Canada). A measurement can be carried out every 4 minutes. In an open circuit grinding plant a feed weigher is controlled by measurement results, whereas in a closed circuit grinding plant the speed of a selector drive in a separator for the separation of fine and coarse particles is controlled by the Blaine permeability-meter and the feeding of the raw material at the mill inlet is controlled by an electric ear signal and by the mass flow of the fines leaving the mill. In industrial operation the Blaine permeability-meter is exposed to clogging since fresh cement fines are more adhesive than stored cement used for measurements in a laboratory (W. Wieland, Automatic Fineness Control, IEEE Cement Industry Technical Conference, May 1966, Denver, Colo., USA).
Further there has been known a highly sophisticated mesurement system "Turbo Powsizer" of Sankyo Dengyo, Tokyo for on-line fineness control of cement fines (Powder Handling & Processing, 4 (1), 9-22 (1992)). Cement fines are automatically sampled from a production separator and after weighing, weight being memorized, the fines are fed to a turboclassifier. The turboclassifier is set to a speed that matches the desired dimension limit of the fines particles. The coarse material from the turboclassifier is weighed again and the ratio of coarse material mass to sample mass is converted into the Blaine specific surface area of the fines leaving the production separator. The speed of the production separator is controlled so that the prescribed Blaine specific surface area is obtained from the measuring system. By the turboclassifier, of course, also fine cement particles agglomerated to clumps of right dimension are separated out.
U. Haese cites various particle size distribution analyzers for the determination of the distribution of the fines particle size (U. Haese, Powder Processing Machinery and Equipment in Japan, Powder Handling & Processing, 4 (1), 9-22 (1992)): light scattering analyzers, Fraunhofer diffraction analyzers, analyzers based on light extinction by a homogeneous fines suspension during a liquid phase sedimentation,
REFERENCES:
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EPEE Cement Industry Technical Conference, May 1966, Denver, Colorado, pp. 106, W. Wieland "Automatic Fineness Control".
Journal of the American Ceramic Society, vol. 72, No. 11, Nov. 1989, New York, pp. 2126-2130, S. Bhattacharja et al. Internal Structure of Porous Silica: A Model System for Characterization by Nuclear Magnetic Resonance.
Journal OF Applied Physics, vol. 59, No. 8, 15 April 1986, New York, pp. 2788-2797, E. J. Schmidt et al. Quantifying Solid-Fluid Interfacial Phenomena In Porous Rocks with Proton Nuclear Magnetic Resonance.
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