Method and plant for manufacturing mineralized portland cement c

Details Method and plant for manufacturing mineralized portland cement c Method and plant for manufacturing mineralized portland cement c

1996-11-01

1997-12-16

Marcheschi, Michael

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

106748, 106765, 106768, 106745, 106771, 432 11, 432106, 432 14, 432266, C04B 704, C04B 742

Patent

active

056980272

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of international application number PCT/DK95/00075, filed Feb. 21, 1995.


BACKGROUND OF THE INVENTION

The present invention relates to a method and a plant for preparing mineralized Portland cement clinker in a dry or semidry process kiln system where the rawmix feedstock is being subjected to preheating, calcination, burning, and, finally, cooling.
The major oxide components of Portland cement clinker (CaO, SiO.sub.2, Al.sub.2 O.sub.3 and Fe.sub.2 O.sub.3) normally account for 96-97% of the chemical analysis. The relative levels of these four oxides control the proportions of the four principal clinker minerals, C.sub.3 S, C.sub.2 S, C.sub.3 A and C.sub.4 AF, and these proportions have a fundamental influence on cement properties. However, the minor components which account for the remaining 3-4% can have a very significant influence on the clinker-making process and the properties of the cement.
In the pure four component system C.sub.3 S does not form below 1250.degree. C. The presence of minor components can lower this temperature, thus facilitating C.sub.3 S formation. The term mineralizer is used for components which encourage the formation of C.sub.3 S and facilitate the sintering reactions in the rotary kiln.
A method for manufacturing mineralized clinker is known from the British patent No. 1 498 057. According to this method fluorine and sulphur are added during the rawmix preparation, usually in the form of flourite (CaF.sub.2) and gypsum (CaSO.sub.4 .multidot.2H.sub.2 O), the major goal being to achieve a clinker with a fluorine content of about 0.25 wt % and a SO.sub.3 content of about 2.5 wt %. The method of said patent focuses on utilization in a rotary kiln of the wet process type, which was extensively used at the time of publication in 1975, but regarded today as being uneconomic due to the substantial amounts of energy needed for drying, and it has proven to be extremely difficult to transfer the method to the newer, more energy efficient dry or semidry process kiln systems incorporating a preheater and a calciner.
So, despite the very substantial improvements in the cement quality which can be achieved (see e.g. Moir, Phil Trans Roy Soc Lond., 1983, A310, 127-138) by this method according to the British patent No. 1 498 057, it is noteworthy that the field of application of this method has been very limited. This is probably ascribable to the operational difficulties associated with the implementation of the method, both in terms of controlling of clinker production and with respect to the occurrence of blockages in cyclones and riser ducts.
Therefore, it is the objective of the present invention to provide a method and a plant for manufacturing mineralized cement clinker, where the plant is constructed so that preheating and at least part of the calcination process takes place outside the kiln, in such a way problems associated with the known technique are avoided.
A first operational difficulty is to determine how to control the input of mineralizer and how, at the same time, to ensure the necessary degree of homogeneity in the rawmix feedstock. From the British patent No. 1 498 057 it appears that the mineralizer is mixed with the rawmix feedstock before it is burned (page 5, line 89-page 6, line 43).
Addition of the mineralizer in this way will, admittedly, result in a high degree of homogeneity, but it will not be possible to make a swift regulation of the mineralizer input relative to the raw materials so that the kiln operation and the properties of the finished cement clinker can be controlled in this manner, since the mineralizer constitutes a fixed percentage of the total quantity of raw materials.
Particularly in connection with the production of mineralized clinker with a high content of sulphate, it is of importance to control temperature variations in the burning zone. This is due to the tendency of the sulphate to decompose into SO.sub.2 in the burning zone and to condense in the cooler regions of the kiln. When the burning zone temperature is

REFERENCES:
patent: 4042408 (1977-08-01), Murray et al.
patent: 4135941 (1979-01-01), Skalny et al.

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