Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1997-05-09
1998-09-01
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106753, 106757, 106765, 432 14, C04B 742
Patent
active
058006109
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing cement clinker by which method the raw meal is subjected to preparatory processing, e.g. by comminution, homogenization and/or drying, whereafter the raw meal is preheated and calcined and, eventually, nodulized and burned, and where nodulization takes place in a stationary burning reactor.
A stationary burning reactor is defined as a reactor with stationary walls as opposed to a rotary kiln. The most prevalent types of stationary reactors are fluid bed or spouted bed reactors.
Nodulization and clinkerization take place when the preheated and possibly calcined cement raw meal, subject to simultaneous input of heat and a consequential formation of a melting phase, is transformed from a particle-formed material with a fineness which is typically less than 15% in excess of 0.090 mm into a grained or ball-shaped material with a fineness of more than 80% in excess of 0.5 mm.
In the general cement clinker manufacturing process, the formed melting phase is an oxide fusion which is formed at a temperature of approximately 1300.degree. C. and with a composition which is roughly as follows: 55% CaO, 6% SiO.sub.2, 23% Al.sub.2 O.sub.3 and 17% Fe.sub.2 O.sub.3, and where the oxide fusion will normally constitute 15-25% of the total clinker mass.
In the vast majority of existing manufacturing plants, clinkerization takes place in a rotary kiln. Given that the costs of construction and the expenditure relating to the maintenance of the rotary kiln are very high because of the moving parts, numerous attempts have been made to eliminate the need for the rotary kiln in the cement manufacturing process.
2. Description of the Prior Art
It is known practice, e.g. from the published German patent application No. 42 19 697, to manufacture cement clinker according to a method where the burning of the calcined material is effected in two stages and where the first stage consists of a fluid bed or spouted bed. In this first stage the raw meal is heated to a presintering temperature, at which a melting phase is formed, and clinkerization is initiated once the melting phase is present. The mate-rial is subsequently directed to the second stage where the clinker is eventually burned at a temperature of minimum 1300.degree. C.
However, practical implementation of this method is difficult due to the fact that the melting phase formed occurs within a range of a few degrees, hence making it extremely difficult to maintain the process conditions necessary to ensure constant presence of a predetermined, small amount of melting phase. This may, in particular, pose problems since the amount of fused material depends to a major degree on the composition of the raw meal, and not just on the temperature.
In the U.S. patent application Ser. No. 2.465.420 a process is described for calcination and nodulization of calcareous sludge using a salt fusion of alkali metals. Such a salt fusion is not always suitable for the manufacture of cement since an excessively high content of alkali metals in the finished cement may give rise to the formation of expanding reaction products, which will lead to cracks in the finished concrete.
In Danish patent application No. 1579/85 is described a method for treatment of a used absorbent from a dry exhaust gas desulphurization process. Since, according to the method described in this application, presence of a certain amount of chlorides is a precondition, it would not be advantageous to use this method for manufacturing cement clinker since chlorides may cause operational problems in the form of cakings in preheater and calciner.
It is prior art to add to the raw meal for manufacturing cement up to about 5% gypsum together with fluorine in order to lower the temperature at which C.sub.3 S is formed, and hence also the burning temperature, but up to this point in time the nodulization and burning of these cements have been carried out in rotary kilns.
SUMMARY OF THE INVENTION
By means of this invent
REFERENCES:
patent: 3857714 (1974-12-01), Mehta
patent: 4040853 (1977-08-01), Binder et al.
patent: 4997363 (1991-03-01), Hundebol
patent: 5049198 (1991-09-01), Ribas
patent: 5356472 (1994-10-01), Odler
patent: 5556459 (1996-09-01), Cohen et al.
patent: 5626667 (1997-05-01), Bohle
Date!.
ALSOP et al, "Cement Plant Operations Handbook", Tradeships. Publ. Ltd, pp.
F.L. Smidth & Co. A/S
Green Anthony
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