FR2546508A1 - SECONDARY RAW MATERIALS FOR THE MANUFACTURE OF CEMENT - Google Patents

Abstract

THE SECONDARY RAW MATERIALS FOR THE MANUFACTURE OF CEMENT ARE CONSTITUTED BY RESIDUES FROM COMBUSTION ACCORDING TO THE PRINCIPLE OF THE FLUIDIZED BED, TAKEN IN THE FORM OF "BED ASH" BEHIND THE FLUIDIZED BED OR IN THE FORM OF FINE DUST BY OR BY A DUST DRIVE FILTERED. THESE RESIDUES ARE MIXED AND CRUSHED WITH THE CEMENT RAW MATERIALS BEFORE FIRE OR WITH THE CEMENT CLINKER ALREADY BAKED.

Description

Secondary raw materials

for the manufacture of cement.

  The invention relates to the use of secondary raw materials, for the manufacture of cement, which occur during the following combustion.

the principle of the fluidized bed.

  The raw materials which are used for the manufacture of cement must contain the following main constituents: lime, silica, alumina and iron oxide As natural raw materials, preferably used for this purpose marly limestone or marl having a content of calcium carbonate from about 60 to

  % In cases where there is no lime scale

  nous or of marl, one must exploit deposits of

  high value limestone and clay pits.

  The principle of fluidized bed fireplaces is particularly suitable for the combustion of low-value fuels and even industrial residues which would otherwise have to be landfilled at great expense and to the detriment of the environment, and which consist of for example by waste or sterile flotation,

  washing wastes, basin sludge from coal-

  thickened leers and deschlammes; according to this process, one can naturally also burn other fuels such as better quality coals, ballast coals, peat and oil shale Thanks to the combustion of such waste, one can certainly mitigate the problem of their discharge but we are not yet

  managed so far to economically exploit the

  fluidized bed combustion sidus So far, they have had to be landfilled again

  attempted to implement residues from special-

  of the combustion of flotation wastes for the manufacture of bricks, as an additive to mortar binders and for the manufacture of an addition material to light concrete Because of their physicochemical analogy with natural raw materials (clay, for example ),

  residues from the combustion of flotation waste pos-

  a peculiarity which cannot be found on the combustion residues of other materials and in particular coal and which we will therefore avoid talking about in what

  follows This is particularly for the residues of the combustion-

  tion of fossil fuels, according to the principle of the fluidized bed, that at present there is no

possibility of use.

  The residues that are produced during the

  fluidized bed bustion can completely differ

  each other with regard to their physical-

  chemical This depends on: the type of material to be burned; the combustion procedure; materials used for desulfurization and the degree of desulfurization;

  sampling locations in the installation

  tion (eg ashes behind a bed

  fluidized, ash behind a cyclone, ash

dres behind a filter).

  Residues from various sampling locations also show differences in

relates to their particle size.

  These residues are also not analogous to ash from installations using other combustion techniques such as a grate hearth, atomized fuel hearth; and furnace with melting chamber because, in this case, combustion takes place at significantly higher temperatures (above 10,000 C) While the residues of grating, pulverized fuel or melting chamber fireplaces have a content of glassy constituents which is most often greater than 90%, the residues of combustion in a fluidized bed are mainly present in the state

  which is opposed to their use in many

  many areas of the building materials industry.

  The object of the invention is therefore to solve the problem

  prevents residue from combustion in a fluidized bed as well as sparing deposits of high-value raw materials. To this end, it is proposed, according to the invention,

  to use, as secondary raw materials of the fa-

  cement brication, residues that occur during

  combustion according to the principle of the Advantageous fluidized bed

  These secondary raw materials have a content of

  weight, based on the mixture constituting the raw powder to-

  tale, between 1 and 60% and preferably between 5 and%, the secondary raw materials being able to be ground

  with the main raw materials According to their composition

  chemical sition, the residues which are produced in various places during combustion in a fluidized bed (bed ash, cyclone dust, filter dust) can be

  used in isolation two by two or three by three, in combination

  dry cloth In other words, the combustion residues can be taken up behind the fluidized bed, as "bed ash", or as fine dust behind a cyclone separator, or behind a filter, and be used as secondary raw materials either without being mixed with other residues from bed combustion

  fluidized, either after being dry mixed to make

  kill a single residue. Secondary raw materials can be used in various ways They can be

  brought in metered quantities to the preparation facilities

  usual and known, with natural raw materials

  them, and finally be ground with them to constitute the raw powder of, cement It is for this purpose of interest very

  particular to use residues with car-

  high bone, the latent energy of which is used during the cooking of the clinker In this case, the limestone component not used in the case of direct desulfurization with absorption means containing calcium can also be used according to the invention in as a necessary constituent of the

  raw cement powder According to the invention, the raw materials

  secondary materials preferably contain from 0.1 to 34% by weight, from 1.5 to 15% by weight, of excess lime

or Ca O free.

  According to the invention, the secondary raw materials

  can be added to an already cooked cement clinker,

  in proportions of between 5 and 30% by weight and, from

  ference, between 10 and 15% by weight and be ground with it

  ci Before their addition, the secondary raw materials can be divided into particle size fractions For this purpose, it is particularly advantageous to use the raw materials containing anhydrite, as well as Ca O and the carbonaterestant, with a smaller grain size

  at 90 micrometers for the most part, after sieving.

  Tests have indeed revealed this phenomenon over-

  taking the Ca SO 4 component (anhydrite II) enriched by-

  Particularly in this particle size range In this case, the anhydrite is also used for the subsequent regulation of the setting of the cement and can, in this way, replace in whole or in part the addition of a raw sulfating agent. If necessary, materials / secondary can also be ground separately and added

  in this form to the raw cement powder.

  The secondary raw materials advantageously contain 1 to 40% by weight, preferably 3 to 20% by

  weight, of Ca SO 4 in the form of anhydrite II.

  A decisive advantage that the

  vention consists in that, when adding to the raw cement powder residues produced by combustion in a fluidized bed, the properties of the finished cement comply with the specifications This economic factor is further reinforced by the fact that a landfill expensive is avoided

  and that high-value deposits are also spared.

Claims (11)

  1 Secondary raw materials for manufacturing   cement, characterized in that they are made up of   killed by combustion residues according to the principle of fluidized bed.   2 Secondary raw materials according to claim 1, characterized in that they are taken in the form of "bed ash" behind the fluidized bed and are used as raw materials without having been   mixed with other residues from fluidized bed combustion.   3 Secondary raw materials according to the claim   tion 1, characterized in that they are collected in the form of fine dust behind a cyclone separator and are used as raw materials without having been   mixed with other residues from fluidized bed combustion.   4 secondary raw materials according to claim 1, characterized in that they are removed behind a filter and are used as raw materials without having been mixed with other combustion residues in fluidized bed.   5 Secondary raw materials according to any one   as claims 1 to 4, characterized in that the   residues produced at the various sampling locations are, in whole or in part, dry mixed so as to constitute a unique residue.   6 Secondary raw materials according to any one   as claims 1 to 5, characterized in that they   contain between 1 and 40% by weight, preferably between 3   and 20% by weight, of Ca 504 in the form of anhydrite II.   7 Secondary raw materials according to any one   as claims 1 to 6, characterized in that they   contain between 0.1 and 34% by weight, preferably between   1.5 and 15% by weight of free Ca O.   8 Secondary raw materials according to any one   as claims 1 to 7, characterized in that the an-   hydrite as well as Ca O and the remaining carbonate are contained therein for the most part with a grain size less than 90 micrometers.   9 Secondary raw materials according to one   any one of claims 1 to 8, characterized in that   that they are ground with the main raw materials   cement in proportions of between 1 and 60% by weight, preferably between 5 and 40% by weight, so as to form a raw cement powder.   10 Raw materials according to any of the   Vendications 1 to 8, characterized in that after the raw powder has been cooked, they are ground, in a proportion of between 5 and 30% by weight, preferably between 10 and% by weight, with the cement clinker cooked, so at form the cement.   11 Raw materials according to any of the   vendications 1 to 5 and at least one of claims 9   and 10, characterized in that they are divided into frac-   particle size before their addition.