DRY CEMENT PRODUCTION INSTALLATION WITH PRECALCINATION KILN

Abstract

The invention relates to an installation for the manufacture of cement by dry process according to the main patent and comprising a cyclone heat exchanger 1-5, 1'-4', a pre-calcination kiln 12, a cyclone 14 connected to the outlet of said kiln, a clinker kiln and a clinker cooler and in which the conduit 17 connecting the clinker kiln to the last stage 5 of the exchanger has an enlarged portion constituting a reactor 20, the outlet of the materials of said cyclone 14 is connected to the lower part of said reactor and the outlet of the materials of the penultimate stage 4 + 4' of the exchanger is connected to the pre-calcination kiln 12 and to the upper part of the reactor.To increase the decarbonation rate of the materials entering the clinkerization kiln 16, said reactor 20 is equipped, at its lower part, with means 48 for the introduction of an auxiliary fuel placed, preferably, above the inlet of the materials coming from the cyclone 14 associated with the precalcination kiln 12.

Description

The present invention relates to an installation for the manufacture of cement by dry process according to the main patent, comprising a cyclone heat exchanger which has several stages, a pre-calcining kiln where the raw materials are treated and suspended in a gas stream, a cyclone connected to the outlet of said kiln and where the materials are separated from the fumes, a clinkerizing kiln and a clinker cooler, and in which the conduit connecting the clinkerizing kiln to the last stage of the heat exchanger has an enlarged portion constituting a reactor, the outlet of the materials from the cyclone associated with the pre-calcining kiln is connected to the lower part of said reactor, the outlet of the materials from the penultimate stage of the exchanger is connected to the pre-calcining kiln and to the upper part of said reactor, and the outlet of the materials from the last stage of the exchanger is connected to the inlet of the clinkerizing kiln. This arrangement makes it possible to improve the calcination of raw materials and to increase thermal efficiency, in particular by allowing complete combustion of the fuel injected into the pre-calcination furnace when it is characterized by a high fixed carbon / volatile matter ratio. The present invention aims to increase the tau of decarbonation of materials introduced into the clinkerization kiln, which in particular allows for a reduction in the length of the kiln and, consequently, the cost of the installation. The installation of the present invention is characterized in that said reactor includes means for introducing supplementary fuel into its lower part, preferably above the inlet of materials from the cyclone associated with the precalcination furnace. The air required for the combustion of this supplementary fuel may be supplied to the reactor either by a branch of the duct supplying air from the clinker cooler to the precalcination furnace, or by passing through the furnace. The calories provided by this combustion are used to complete the decarbonation of the material fraction originating from the penultimate stage of the heat exchanger. The relative position of the fuel injection point and the entry of this material fraction into the reactor will be chosen to achieve optimal decarbonation while avoiding the formation of hot spots. The features of the invention will become apparent from the following description and refers to the accompanying drawing, which is a diagram of an installation carried out in accordance with the invention. This installation consists of a cyclone heat exchanger, a pre-calcination kiln 12 to which a cyclone 14 is associated, a clinkerization kiln 16 and a clinker cooler, not shown. The exchanger has five stages, each stage, with the exception of the last, comprising two cyclones. Cyclones 1, 2, 4 and 5 form a first group associated with the clinker kiln 16 and cyclones 1', 2', 3' and 4' constitute a second group associated with the pre-calcination kiln 12. The numbering of the cyclones and stages corresponds to the direction of flow of the materials introduced at R and A' in the pipes connecting cyclones 1, 2 and 1', 2' respectively. The inlet of cyclone 5 is connected to the smoke hood 15 of the furnace 16 by a conduit 17 having an enlarged portion constituting a reactor 20 and an upper portion in the form of a gooseneck, and the outlet of the gases of each of the cyclones 2 to 5 is connected to the inlet of the cyclone placed above by conduits 22, 24, 26 and 28 so that the fumes of the furnace 16 pass successively through cyclones 5, 4, 3, 2 and 1 and are finally released into the atmosphere. The inlet of cyclone 14 is connected to the outlet of the pre-calcination furnace 12 and the outlet of the gases of each of the cyclones 2' to 4' and 14 is connected to the inlet of the cyclone placed above by pipes 22' 24', 26' and 28', so that the fumes of the furnace 12 pass successively into the cyclones 14, 4', ', 2' and 1' and are finally released into the atmosphere. Conduits SD, 32, and 34 for the evacuation of preheated materials are connected to the tips of cyclones 1 and 2 and open into conduits 26, 24, and 22, respectively. Materials exiting cyclone 4 are introduced, by means of conduit 36, either into the upper part of reactor 20 or into the portion of conduit 17 located directly above the reactor. A conduit 42 connected to the tip of cyclone 5 opens into furnace 16. Conduits 0', 32', and 34' for the evacuation of preheated materials are connected to the tips of cyclones 1' and ' and open into conduits 26', 24', and 22', respectively. Materials exiting cyclone 4' are conveyed to furnace 12 via conduit 36'. Materials collected at the tip of cyclone 14 are introduced via conduit 50, either directly into the lower part of reactor 20 or into the section of conduit 17 located between the smoke hood 15 and reactor 20. The precalcination kiln 12 is of a known type; it may consist of a vertically oriented chamber of revolution, the upper part of which is cylindrical and the lower part frustoconical. At its base, it has an air inlet volute 13 connected to the clinker cooler by a conduit 44, and at its upper end, an outlet connected to the inlet of the cyclone 14. A feeding device 46 allows solid fuel to be injected into the lower part of the kiln 12, at one or more points. The reactor 20 is designed, in general, as oven 12 and includes, in its lower part, a fuel supply device 48 and an air inlet connected to the pipe 44 by a pipe 52. The raw materials introduced at point A, in the form of flour, into conduit 28, pass successively through cyclones 1, 2, 3, and 4, and are then introduced into reactor 20. The raw materials introduced at point A' into conduit 28' pass successively through cyclones 1', 2', 3', and 4', and are then introduced into furnace 12 where they are partially calcined. The necessary heat for this reaction is supplied by the combustion of a fuel that is difficult to burn, for example, one with a low volatile content, introduced into the furnace by means of device 46.6. At the outlet of furnace 12, the solid materials are separated from the fumes in cyclone 14 to be introduced into reactor 20 where they are suspended in the fumes coming from furnace 16. These materials still contain fuel particles which burn in reactor 20 with the fuel injected by device 48.Combustion air is supplied via line 525; alternatively, some or all of the oxygen required for combustion can be supplied through furnace 16. This combustion is favored by the high temperature of the flue gases from furnace 16 and the high decarbonation rate of the materials from furnace 12. The heat released by this combustion is used partly to complete the calcination of the pre-calcined materials in furnace 12 and partly to calcine the materials from cyclone 4. The calcined materials carried by the flue gases escaping from the top of reactor 20 are separated in cyclone 5 before being introduced into furnace 16. The distribution of fuel between furnace 12, furnace 16 and reactor 20 can be chosen so that all of the raw materials are practically totally calcined before entering furnace 16. The installation described above, which is designed for the use of difficult-to-burn fuel, can be adapted to operate with higher-quality fuels. To do this, it will suffice to provide bypasses, represented by dashed lines on the drawing, allowing the raw materials exiting cyclone 14 to be directed to furnace 16 and the materials exiting cyclone 4 to be introduced at a lower level into reactor 20. Although the invention has been described in application to an installation comprising two columns of cyclones, it is quite evident that it also applies to the installations described in the main patent where the exchanger comprises only one column of cyclones and the gas outlet of the cyclone associated with the pre-calcining furnace is connected to the exchanger downstream, considering the direction of gas flow, of the last cyclone.

Claims

CLAIMS 1. Installation for the manufacture of cement by the dry process, according to claim I of the main patent, characterized in what said reactor (20) comprises in its lower part means (48) for introducing a fuel extra.

2. Installation according to claim 1, characterized in that that said means (48) for introducing a fuel are placed above the material entrance from the cyclone (14) associated with the precalcination furnace (12). Installation according to claim 1 or 2, characterized in that in said exchanger, each stage, with the exception of the last, has two cyclones, in that one of the cyclones (1 to 4 > of each stage is crossed by the fumes of the clinkering furnace (16) and the other (1' to 4') by the fumes from the precalcination furnace (12), the top floor does not comprising only one cyclone through which the fumes pass of the clinkering furnace, and in that, in the front last stage, the exit of the materials from the cyclone (4) crossed by the fumes from the clinkering furnace is connected to the upper part of said reactor (20) and the outlet of the materials from the cyclone (4') through which the fumes from the furnace precalcination is connected to said furnace (12).

4. Installation according to claim 1 or y characterized in that in said exchanger each stage comprises a single cyclone tos the cyclones being placed in series and traversed by the fumes from the clinkering furnace, and in that the gas outlet of the associated cyclone the precalcination furnace is connected to the exchanger, downstream, considering the direction of gas circulation, of the last cyclone.