Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1996-09-20
1998-01-13
Marcantoni, Paul
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106743, 106762, 432 37, 432103, 110190, 73 232, 73 2331, 2057855, 2057865, F27B 700
Patent
active
057074445
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling the temperature in a kiln for manufacturing cement clinker.
It is common knowledge that cement is manufactured by a number of raw materials, particularly lime (CaCO.sub.3), clay, sand, pyrite ash, fly ash and other materials being mixed and interground into a raw meal in which the content of the oxides CaO, SiO.sub.2, Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3 must be specifically adapted within relatively narrow boundaries. The raw meal is subsequently preheated and calcined, during which process H.sub.2 O and CO.sub.2 are driven off. A range of reactions will then occur between the oxides, first and foremost the following reactions:
2 CaO+SiO.sub.2 .fwdarw.(CaO).sub.2 (SiO.sub.2) (belite) (CaO).sub.2 (SiO.sub.2)+CaO.fwdarw.(CaO).sub.3 (SiO.sub.2) (alite)
These reactions between solid substances take place in a molten mass, with the aluminium and iron oxides which are necessary for forming the molten mass.
For every burning process the overall objective is always to ensure that the sufficient amount of alite is formed and that, simultaneously, the volume of free, not yet consumed CaO is reduced to an acceptably low level. Traditionally the burning process takes place in a rotary kiln and the final reaction occurs in the burning zone of the rotary kiln, with the reaction process being controlled by a regulation of the temperature by adjusting the firing rate and the flame setting. The temperature during the burning process approaches the 1400.degree.-1450.degree. C. range for the common types of clinker.
Accordingly, it will be necessary to perform a measurement providing continuous indication of the temperature in the kiln, hence indicating also the composition and quality of the clinker, but so far it has not been possible to measure the interesting temperature directly.
Thermocouples (Pt-PtRh) are impossible to install in a manner ensuring that they are not destroyed within a short period of time as a result of the contact with the hard clinker.
Radiation pyrometers can be used, but only if there is good visibility in the burning zone, which is rarely the case since a certain dust load will inevitably be generated during the burning process.
An indirect signal, which is extensively used to indicate the temperature, is a measurement of the force which is used to rotate the kiln. The reason why this signal can be used is that the higher the temperature of the clinker, the greater the amount of molten mass being formed, hence causing more of the charge to be drawn higher upwards along the side of the rotary kiln during rotation. As a result, the moment of force (force x arm) will be increased, hence increasing also the power required to rotate the kiln. However, the moment of force is a relative signal which is affected by a multitude of factors: arbitrary skewness in the crust formation, the adhesive properties of the raw materials along the entire length of kiln etc. Consequently, it is impossible to indicate exactly what the moment should be to ensure sufficient burning.
Another method for measuring the temperature in the burning zone involves measurement of the NO.sub.x -emission from the kiln. The NO.sub.x formation in the burning zone relates specifically to the temperature level in the flame, and it is influenced, at constant production and unaltered burner setting, only by the surplus air required for the burning process, and, since the overall aim is to keep the surplus air constant, the NO.sub.x emission is a direct measure of the burning temperature. As it is, kilns have been operating for many years on the basis of NO.sub.x -measurements, being controlled both manually and automatically, e.g. by means of Fuzzy logic.
However, it is a recognized fact that the emission of NO.sub.x is detrimental to the environment, and, therefore, many efforts are mainly concentrated on reducing the emission of NO.sub.x, including the emission of the rotary kiln, of a cement kiln plant.
These measures severely reduce the possibilities
REFERENCES:
patent: 3578299 (1971-05-01), Hurlburt
patent: 4111554 (1978-09-01), Colin et al.
patent: 4738147 (1988-04-01), Tomlin
patent: 5596154 (1997-01-01), Baughman
F. L. Smidth & Co. A/S
Marcantoni Paul
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