Method of producing cement clinker and associated device

Details Method of producing cement clinker and associated device Method of producing cement clinker and associated device

1998-02-16

2001-07-24

Marcantoni, Paul (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S757000

Reexamination Certificate

active

06264738

ABSTRACT:

The invention relates to methods of producing cement clinker from basic and acid raw meal components by drying, grinding and heat treatment thereof in stages by means of preheating, calcination, sintering and cooling stages according to the wet and dry process, with heat being supplied from fuel of any type in both the calcination stage and the sintering stage with equipment of any type. Apparatus for carrying out the method is also described.
BACKGROUND OF THE INVENTION
Usually, in order to increase the reactivity of the raw meal, the sieve residues are reduced to the 80 &mgr;m and 200 &mgr;m sieve, but this leads to an increase in the energy consumption and the operating costs for grinding the raw meal.
It is known that, below a reactivity of the raw meal which is still kept relatively high, the sieve residues on the 80 &mgr;m sieve can be raised from approximately 10% up to 20% and on the 200 &mgr;m sieve from approximately 1% up to 5%. This corresponds to a grain size ratio of the 0.01-80 &mgr;m grain size to the 80.01-500 &mgr;m grain size of 9:1 to 4:1. Nevertheless, this is associated with high energy consumption and high operating costs for grinding the raw meal.
The object, therefore, is to set the grain class ratio of the raw meal, particularly of the basic raw meal component, that is to say to grind up the raw meal extremely coarsely, so that the reactivity of the raw meal under extreme coarse grinding is not hindered but favoured, and so that under the extremely changed grain class ratio of the raw meal a method of producing cement by grinding, drying, mixing and then roasting the raw meal is provided with which the necessary energy consumption, and likewise the operating and investment costs for the least possible grinding assemblies required from the point of view of apparatus, are reduced, particularly in the case of grinding raw meal, with a simultaneous increase in the throughput of the raw meal apparatus and the kilns as well as simultaneous reduction of the specific fuel requirement.
The object is achieved by a first example with a method of producing cement in which the basic raw meal component is ground to a grain class ratio of the 0.01-80 &mgr;m grain class to the 80.01-500 &mgr;m grain class of 1.5:1 to 1:9 so that before the formation of the clinker melt in the sintering zone apart from the conventional topochemically formed C
2
AS, C
3
A, C
12
A
7
and C
4
FA, the easy to melt CS and C
3
S
2
are largely produced instead of the difficult to melt C
2
S.
By this measure it is possible to raise the clinker melt content in the sintering stage and to lower the melting temperature, which accelerates the clinker formation and lowers the sintering temperature during the clinker formation. Naturally, in this case the energy consumption during grinding of raw meal is considerably reduced and the output of the grinding plant is increased. The cement properties are improved by the better mineral formation particularly of alite and belite. The discharge of dust from the kiln is reduced thereby, so that the heat loss from the kiln is reduced.
The phenomena which occur in this case are explained as follows:
The clinker formation may be considered as a function of the state of matter (liquid or solid) in the two stages of development. The first stage of development of the mineral formation consists of the topochemical reactions (solid state reactions) and lasts up to 1250° C. The second stage of development of the clinker formation begins at 1250° C. and is principally completed above a temperature of 1300° C. because of the melting process.
It is known from the prior art that in order to lower the fuel requirement during clinker burning and to raise the quality of the clinker it is advantageous to accelerate the rate of mineral formation not only through the melt but also through topochemical reactions. Usually the increased reactivity of the raw meal with unchanged LS II is achieved by relatively fine grinding, relatively low SM and TM and by the use of mineralisers.
The existing conceptions of an optimum fractional composition of the raw meal, i.e. that the content of the particles greater than 80 &mgr;m should not amount to more than 10-15%, are not fully substantiated.
As evidence it may be mentioned that due to the solid state reactions between the calcite and SiO
2
carrier particles smaller than 60-80 &mgr;m premature belite formation because of an increasing time and temperature interval between the alite formation and the belite formation leads to the crystal growth of the topochemically formed belite and of the residual free lime. As a result the dissolving of the recrystallised belite and of the recrystallised free lime in the melt is hindered, which causes a delay in the alite formation, i.e. requires an increase in the sintering temperature. It follows, therefore, that an acceleration of the topochemical reactions in general does not always lead to an increase in the rate of clinker formation. The clinker formation may even be hindered.
The question arises as to how the clinker formation may be optimised.
It is known that the rate of mineral formation through the melt is approximately 10,000-100,000 times higher than through the topochemical reactions. From this it may be concluded that a delay in the topochemical reactions can frequently be made up for at the stage of development of the reactions in the melt. This means that latent reserves for increasing the throughput of the kiln are also located in the sintering zone. It is obvious that at an increased throughput of the kiln, with the other conditions remaining the same, because of a reduction of the specific heat losses the lowest specific energy requirement for the clinker formation can be achieved. For this reason numerous attempts have been made to accelerate the clinker formation and to increase the proportion of clinker melt. However, with the conventional technology for cement production the possibilities described above are greatly restricted because of the necessary properties of the cement and the resulting necessary chemical compositions of the raw meal.
It is, moreover, very important that the rate of clinker formation through the melt is in practice not very dependent upon the size of the particles, particularly of calcite. This is confirmed elsewhere, for example in the crushed stone technology for producing the cement clinker and in metallurgical processes in which the reactions proceed completely in the melt, although the grain size fractions of the starting raw materials may be very coarse-grained (up to 50 mm).
Because of this it may be concluded, contrary to the known conceptions, that hindering of the clinker formation through the melt is not dependent upon the size of the calcite particles (limestone particles) but upon the diversion of the Ca
2+
ions which are located at the boundary between the melt and solid phases, i.e. at the boundary layer.
Until the boundary layer is saturated as regards the Ca
2+
ions the dissolution of the solid free lime phase in the melt is hindered.
The elimination of the negative retarding effect of the boundary layer which is saturated with Ca
2+
ions on the rate of clinker formation can only be achieved by an increase in the reaction surface between the solid and melt phases. For this it is necessary to increase the proportion of melt.
With an increased proportion of clinker melt a mechanical stress is very helpful, since in this case by comparison with the proportion of clinker melt which is reduced below the usual eutectic an effective abrasion of the saturated zone takes place. Thus the slowest reaction stage is accelerated through the melt. As a result the clinker formation is considerably accelerated, particularly in the case of raw meal containing the coarsely ground limestone.
In the question which results from this, “How can the proportion of melt be increased?”, it helps us to consider the phase diagram in the C-S-A and C-S-A-F systems.
The analysis of the 3 and 4 substance system shows that for the raw meal, the

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