GB2065279A

GB2065279A - Improvements in or relating to processes and installations for precalcinating powderous or granular substances

Info

Publication number: GB2065279A
Application number: GB8029773A
Authority: GB
Original assignee: LAFARGE CONSEILS ET ETUDES SA; Lafarge Conseils et Etudes
Current assignee: LAFARGE CONSEILS ET ETUDES SA; Lafarge Conseils et Etudes
Priority date: 1979-09-17
Filing date: 1980-09-15
Publication date: 1981-06-24
Also published as: FR2464742A1; GB2065279B; CA1133249A; FR2464742B1; DE3032803A1

Abstract

An installation for calcinating powderous or granular substances, such as cement making raw material, comprises a preheater (13) formed by at least one column of cyclones (I, II, III and IV) wherein a flow of the material to be treated is circulated. A rotary kiln (10) is fed with the material flow, and a cooler (not shown) is provided for cooling (by way of conduit 21) the product treated in the kiln. The installation further comprises a fumes outlet flue (14) coaxial with the kiln (10) constructed so as to constitute an extension of the kiln (10) and discharged directly into at least one junction cyclone (12) which is connected to the last stage of the (22). <IMAGE>

Description

SPECIFICATION Process and installation for precalcinating powderous or granular substances The present invention is related to a process and an installation for caiculating powderous or granular substances, such as raw material for making cement, which calcination is carried out prior to the burning (or firing) of said materials in a furnace or kiln.

Calcinating installations of this kind are already known, which comprise a preheater constituted by one or more columns, a rotary kiln and a cooler adapted to cool the product treated in said kiln.

Each column may be provided individually with a precalcinator adapted to calcinate entirely or partially the raw material introduced into the kiln.

In the known installations the gases issuing from the top of the rotary kiln are directed toward the lower portion of the preheater by means of a conduit which deviates the flow path of the fumes issuing from the kiln from a substantially horizontal trajectory to a substantially vertical trajectory, which deviation occurs within the fumes chamber.

Furthermore, it is known that when a fuel having a sulphur content higher than 1% is used in a rotary kiln of this type, considerable deposits will occur at the junction of the kiln and the exchanger.

These deposits result in progressively reducing the cross-sectional flow area of the gases issuing from the kiln, which entails a considerable decrease of the output of the installation.

These deposits are due partially to the abrupt change of the flow direction of the gases issuing from the kiln, which changement brings about areas of turbulence or so-called "dead area" prone to lead to decantation and depositing of solid particles.

Two French patent applications filed by the Applicant (nO 74-1 1 196 and nO 74-30 711) disclose methods aimed at eliminating such deposits.

It is an object of the present invention to transform the transition zone between the kiln and the preheater so as to confer on such zone an optimus aerohydrodynamic profile. With this object in view, the invention relates to an installation comprising a preheater constituted by at least one column of cyclones wherein flow of material to be treated is circulated, a rotary kiln fed with said flow of material and a cooler for cooling the product treated in said kiln, and further comprising a flue for evacuating the fumes issuing from the kiln, said flue being coaxial to said kiln and prolongating the same, while opening into at least one junction cyclone, which cyclone is connected to the last stage of the preheater by a gas outlet conduit.

In a preferred embodiment of the invention the said gas outlet conduit has an angled configuration. Thus the gases issuing from the kiln are directed through a flue coaxial to said kiln, and are directed without any modification of the flow direction toward one or two cyclones from which they issue to flow then toward the preheater. The modification of the flow direction of the gases issuing from the kiln is thus not achieved in a fumes chamber but in a cyclone and is consequently achieved under optimum aerohydrodynamic conditions. Any matter issuing from any of the stages of the preheater is injected into the flue connecting the kiln to the junction cyclone with a view to decreasing the temperature of the fumes issuing from the kiln and to limiting the risk of formation of deposits in said flue.

Depending on the flow rate for which the installation is designed, one or two junction cyclones may be provided.

The invention will be described hereinafter in a more detailed manner with reference to the appended drawings which are given by way of illustration but not of limitation.

Fig. 1 of the drawing is a schematical view of an installation according to the invention, wherein air issuing possibly from the cooler is injected into the lowermost end of the junction cyclone, while burners are provided within the latter.

Fig. 2 shows a detail of the installation according to Fig. 1.

Fig. 3 is a horizontal sectional view of a modification of the installation shown in Fig. 1, comprising two junction cyclones.

Fig. 4 schematically shows another modification of the installation according to the invention, wherein the matter passing through the junction cyclone is taken up by an air flow issuing possibly from the cooler, and is then directed toward the precalcinator.

In a first embodiment of the invention, as shown in Fig. 1 the calcinating installation comprises a conventional rotary kiln 10 wherein the raw material is treated, or fired at a temperature of about 1 5000C by means of a counter-current flame, this kiln being connected according to a feature of the present invention, through a cyclone 1 2 to the last cyclone IV of a four-stage column forming a preheater 13. The matter issuing from the penultimate cyclone III of said preheater 13 is directed toward a horizontal fumes outlet flue 14 connecting kiln 10 to junction cyclone 12 through a conduit 20.Said conduit 20 preferably is adpated to direct the matter in the form of a curtain or screen into the fumes issuing from the kiln, where said matter is taken up by said fumes and circulating in cyclone 1 2 with a view to removing suspended matter from the fumes, prior to being taken up again by gases issuing from a cooler (not shown) by way of a conduit 21 into a lower conduit 1 9 of junction cyclone 12, said matter then passing through an angled or cranked flue 22 toward the last cyclone stage IV of the preheater, whereafter said matter passes from said cyclone IV toward the kiln through conduit 23. Fuel is injected by burners 24 provided at the base of cyclone 12 so as to provide the energy required for total or partial decarbonation. The coolant carried by conduit 21 may be air.

Fig. 2 is a section view of a detail of the installation of Fig. 1, shown on a larger scale. As clearly shown in Fig. 2 the conduit 20 through which flows the matter issuing from the penultimate cyclone Ill which discharges into flue 14 through a flattened injection nozzle, while conduit 23 discharges into flue 14 by way of outlet 25, which flue constitutes an extension of the ferrule 26 of kiln 10.

According to an aspect of the present invention two junction cyclones such as cyclone 12, connected to flue 14 of kiln 10, may be provided.

Such modification is shown in Fig. 3 which is a horizontal sectional view taken along line Ill-Ill in Fig. 2.

As shown, two junction cyclones 1 2a and 1 2b associated to conduits 23a and 23b connected to the preheater are provided in this embodiment.

Fig. 4 shows another embodiment of the present invention wherein the fumes issuing from kiln 10 pass through flue 14 coaxial to said kiln and enter the junction cyclone 12 according to the invention. The matter issuing from cyclone IV of the preheater is introduced through a conduit 25 and flue 14 into said junction cyclone 12; said matter is then introduced at 19 into a cooling gas flow issuing possibly through 21 from the cooler, whereafter said matter enters a precalcinator 27 comprising burners 28 where it undergoes partial or total decarbonation prior to being separated from the gases in cyclone IV' and prior to being finally introduced through conduit 23' into the rotary kiln.

The gases issuing at 30 and 30' from cyclone IV and IV' are introduced into a cyclone Ill prior to flowing through pairs of cyclones Il and I. The two circuits carrying the gases issuing from the kiln as well as the cooling gas flow from conduit 21 may be balanced by means of an adjustable valve 32 provided in the conduit outlet 30 of cyclone IV.

The invention is not limited to the embodiments shown and described herein-above; numerous modifications and variants may be envisaged by those skilled in the art without departing therefore from the scope of the invention as defined in the appended claims.

Claims

1. An installation for calcinating powderous or granular matter, such as cement making raw material, comprising a preheater constituted by at least one column of cyclones wherein a flow of the material to be treated is circulated, a rotary kiln fed with said material flow, and a cooler for cooling the product treated in said kiln, said installation further comprising a fumes outlet flue coaxial to said kiln for evacuating fumes from said kiln, said flue being constructed so as to constitute an extension of said kiln and to open into at least one junction cyclone which is connected to the last stage of said preheater by a gas outlet conduit.

2. An installation according to claim 1 , wherein said gas outlet conduit has an angled configuration.

3. An illustration according to any one of claims 1 and 2, wherein said junction cyclone is fed at its lowermost end with air issuing from said cooler.

4. An installation according to claim 1, wherein burners are provided at the basis of said junction cyclone.

5. An installation according to claim 1, which comprises two junction cyclones connected to said fumes outlet flue.

6. An installation according to claim 1, wherein said preheater comprises two cyclone columns, wherein said junction cyclone is connected to the last cyclone of one of said cyclone columns, and wherein the last cyclone of the other cyclone column is associated to a precalcinatorfed with an air flow issuing from said cooler, into which the material issuing from said junction cyclone is introduced.

7. A process of calcinating powderous or granular material in an installation comprising a preheater, a rotary kiln and a cooler, wherein fumes issuing from said kiln are treated in a cyclone with a view to removing suspended matter from said fumes, whereafter said fumes are introduced into the last stage of a cooler.

8. An installation for calcinating powderous or granular matter, substantially as hereinbefore described with reference to Figures 1 and 2, 3 or 4 of the accompanying drawings.

9. A process for calcinating powderous or granular matter substantially as hereinbefore described with reference to Figures 1 and 2, 3 or 4 of the accompanying drawings.