Heating – With heating gas conveying – agitating – scattering or...
Patent
1996-10-10
1998-07-07
Capossela, Ronald C.
Heating
With heating gas conveying, agitating, scattering or...
432106, F27B 1500
Patent
active
057758905
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a plant for heat treatment of lumpy material such as limestone, other carbonate minerals, cement raw materials, or the like, which plant comprises a preheating zone, preferably in the form of a shaft preheater, with at least one material inlet, at least one material outlet, at least one inlet for preheating gas, and at least one outlet for used preheating gas, in which preheating zone the material is preheated by means of hot preheating gas from which it is subsequently separated, a burning zone, e.g. in the form of a rotary kiln, with material inlet and outlet, for burning the preheated material, connecting means which connect the material outlet of the preheating zone to the material inlet of the burning zone, and a separating device fitted in connection with the connecting means for separating the finest particles from the preheated material.
When operating a plant of the aforementioned kind, the material leaving the preheating zone may contain a certain amount of fine material being produced either by decrepitation of the material during the preheating, or resulting from the material being exposed to wear or dust from the burning zone which is drawn along up to the preheating zone, subsequently settling there.
There are primarily two reasons why it is desirable to minimize the amount of this fine material before the preheated material is fed to the kiln. One reason is that the fine material may have a disturbing effect on the kiln operation because of dust generation and coatings in the kiln and/or in exhaust gas ducts connected thereto. The second reason is that the amount of substances which are undesirable in the finished product, and which have the strongest tendency to stick to the finest material fractions during the manufacturing process, can be reduced in this way.
As a case in point, it can be mentioned that the permissible sulphur content in lime which is utilized in the steel-making industry is normally specified to be 0.03 to 0.05%. It follows that the sulphur content in the lime product depends on the amount of sulphur being fed to the kiln plant via the raw materials and the fuel. The sulphur content in raw materials may range from approximately 0 to 0.5%, while the sulphur content in fuel types such as oil and coal may be as high as 5%. In the majority of cases it will, therefore, be necessary to remove sulphur from the manufacturing process in order to meet the requirements which apply in terms of sulphur content in the finished product. This can be done by removing the finest material fractions, since, in relative terms, these fractions absorb the highest amount of sulphur because of their greater surface area.
A known method for removing the finest material consists of simple mechanical screening where the finest material is screened off by means of a sorting grate installed in the duct for feeding of material to the kiln. The disadvantage of using such a sorting grate is, however, that clogging of the grate will occur within a relatively short period of time, which entails that the grate loses its function. This occurs particularly in cases where the preheated feed material to the kiln is fine. Another disadvantage is the attendant risk of deformation of the grate due to the temperature between 650.degree. and 900.degree. C. which prevails in this area.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a plant for heat treatment of lumpy material by means of which the aforementioned disadvantages are remedied.
This is achieved according to the invention by a plant of the kind mentioned in the introduction, and being characterized in that the separating device is provided as a part of the connecting means and consisting of a duct, with gas introducing means being provided at the lower end of the duct and with means for discharge of gas/material suspension being provided at the upper end of the duct, and in that the plant comprises means for generating a gas stream through the duct from below a
REFERENCES:
patent: 5193997 (1993-03-01), Aoyama et al.
patent: 5283959 (1994-02-01), Nagayoshi et al.
patent: 5289920 (1994-03-01), Godderidge et al.
patent: 5292247 (1994-03-01), Bauer
patent: 5580241 (1996-12-01), Koeberle
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Capossela Ronald C.
F. L. Smidth & Co. A/S
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