MXPA96002684A - Procedure and installation to treat pulverulenta unamateria based on calcium sulfate, new hidraul agglutinant - Google Patents

Abstract

The present invention relates to a process for treating a pulverulent raw material based on natural calcium sulfate or synthesis to prepare a hydraulic binder comprising a stable mixture of alpha anhydrite and basamite, in which the weight ratio of alpha anhydrite is greater than 35%, characterized in that the following two successive treatment stages are combined: a) the pulverulent material is heated to a temperature practically comprised between 220 ° C and 360 ° C in the presence of steam under appropriate conditions to form a majority , calcium sulphate of alpha variety, b) the matter heated in this way is subjected to a thermal tempering which consists of cooling it of at least 150 ° C in a time less than 15 minutes by means of a cold and dry gas injected under pressure on the heart of it. Hydraulic binder based on calcium sulphate, characterized in that it comprises a stable mixture of alpha anhydrite and basaite, in which the weight ratio of anhydrite alpha is greater than 3

Description

PROCEDURE AND INSTALLATION TO TREAT A PULVERULENT MATERIAL BASED ON CALCIUM SULFATE, NEW HYDRAULIC AGGLUTINANT DES IPTION The present invention relates to a process for treating a pulverulent material based on natural calcium sulphate (gypsum) or synthesis JLQ ísulfoyeso, phosphogypsum and other byproducts of the same type), to prepare a new hydraulic binder. It is extended to an installation that allows the procedure to be put into operation, as well as to the hydraulic binders that can be manufactured by means of the process. i5 Various types of process have been proposed to treat calcium sulfate to prepare gypsum. In particular, it is known to prepare improved plasters (sometimes referred to as "alpha plasters") which, once hardened, have markedly more mechanical characteristics 2 higher than those of ordinary plasters. The phenomena that develop during the course of the treatments are poorly known and are generally attributed to the improvement of mechanical behaviors, to the presence of the crystallographic variety at products that were obtained, without knowing exactly the proportion of this variety in these products, nor the conditions that allow to obtain it in a stable and reproducible way. Traditionally, these improved plasters are manufactured from gypsum, subjecting them to a baking phase by autoclaving, and then to a hot drying phase by a dry and hot air stream. The cooking is carried out in a saturated vapor atmosphere at a pressure of the order of 5 to 10 bar for a time of the order of 10 hours. To try to reduce the shortcomings of this traditional procedure to manufacture improved gypsum, extremely expensive construction, uncertain reproducibility), other procedures have been proposed, in fact, they try to reproduce the essential conditions of the traditional procedure (wet cooking) , followed by hot air drying), using different means and technologies (patents FR 2,389,855, FR 2,445,940, FR 2,272,721, US 2,269,580, US 3,145,980). The object of the present invention is to provide a new treatment process that leads to a new perfectly characterized hydraulic binder, which benefits, once hardened, from remarkable behavior, in particular fire behavior and mechanical resistance, especially in total submergence. Another objective of the invention is that of providing an installation that allows to implement this procedure, under economic conditions. The process object of the invention, for treating a pulverulent raw material based on calcium sulphate to prepare a new hydraulic binder, is characterized in that it combines the following two successive stages: (a) - The pulverulent material is heated to a practically temperature comprised between 220 ° C and 360 ° C in the presence of water vapor under appropriate conditions to form majoritapamente, calcium sulphate of variety to fa; ib) - Matter heated in this way is subjected to a thermal tempering which consists in cooling it to at least 150 ° C in a time of less than 15 minutes by means of a cold and dry gas injected under pressure in the heart of this. "Cold and dry gas" means a gas whose temperature is below about 50 ° C (preferably the ambient temperature of the order of 20 ° C to ° C or a temperature lower than this) and whose percentage of water vapor content is less than about 5% i mass of vapor in relation to the total mass of gas) preferably less than 1%. The process of the invention was conceived from the following observation: when a calcium sulfate is treated in a customary manner, to obtain "improved gypsum", the product obtained is in fact a mixture that effectively contains alpha anhydrite, but in which this variety remains very minor and mixed with other anhydrous forms (anhydrite gamma) or L Q hydrated (semihydrated, bihydrated, etc ...). The studies of the inventor showed that this comes essentially from two factors: a cooking that leads to alpha anhydrite but also to other forms, and in all an evolution of the product after cooking, with partial transformation of this, especially through hydration. The essential idea led to the procedure of the invention and was that of making a stable final product containing a weight ratio of anhydrite to the fa much higher than that containing the known improved plasters, and to do this, setting the structure of the compound that was obtained just at the end of the cooking, by thermal tempering. In this way, the further transformation of the anhydrite to the fa that was formed is severely limited with cooking.

According to a preferred mode of implementation of the procedure, just at the end of the cooking operation, the heated material is sent in the form of rain, from a higher level to a lower level where it is carried by vibration, to walk on a bed; the tempering operation is carried out, on the one hand, by sending a first flow of cold and dry air over the curtain of matter falling in the form of rain, between the upper level and the lower level, and on the other hand, by injecting air flows cold and dry at the heart of the bed of matter in the course of being routed to the lower level. The new hydraulic binder obtained by the aforementioned process is a stable mixture of anhydrite to the fa of calcium sulfate and oasanite. wherein the weight ratio of anhydrite to fa is greater than 35%, and in particular comprised between 40% and 65%; that mixture does not contain or contains very little gamma anhydrite. The composition of this mixture and its high proportion of alpha anhydrite, conditions some remarkable characteristics of the products obtained by the setting of the binder, in particular: fire behavior: inflammation classified in the category OM according to the NF P 92-507 standard; - resistance to compression: between 250 and 300 bar; - resistance to bending: between 55 and 70 bars. An explanation of these behaviors is related in part to the soluble character of the 0 anhydrite at the fa and the highest specific surfaces obtained with this variety (approximately 6 m2 / g), which lead, at the time of the binder's work, to a rapid and homogeneous precipitation. It should be noted that the products obtained L S incorporating: classic argas to the binder of conformation with the invention, have remarkable mechanical resistances in submerged situation in water, much higher than the analogous products obtained with the known improved plasters. The essential inventive principle of the invention, therefore, is that of increasing the anhydrite ratio Mf: the product; The essential environment that is used is to limit, by means of temperate, the evolution of the product after cooking. For To further increase this proportion of anhydrite to the fa, the inventor dedicated himself to optimizing the cooking operation, in order to obtain the most important quantity possible of this variety just after cooking. The following commissioning conditions seem to provide the best results: the moisture content of the raw material is previously controlled and, if this is the case, this rate is adjusted to a value practically comprised between 12% and 25%; then, the cooking operation is put into operation bringing the powdery material to walk in a stirred bed in a confined gaseous atmosphere containing at least a part of the water vapor released by the matter, and heating the set under its own conditions to raise the temperature of the gases above the bed of matter, at a value between 400 ° C and 500 ° C, and in bringing the average temperature to the heart of the material to a value higher than 250 ° C and lower than 300 ° C. The heating is carried out in particular by means of infrared radiators arranged above the material bed; the emission power of these radiators is regulated in correlation with the speed of the routing of the bed of matter, to obtain the appropriate values of the temperature of the gases above the bed and of the temperature at the heart of the material. - 3 - These conditions of implementation were defined pragmatically at the end of long hesitations and tests. A possible explanation of the best results obtained thanks to these operating conditions, is the following: the temperature of 250 ° C / 300 ° C at the heart of the bed of matter, is ideal to produce the anhydrite to the fa in the absence of other varieties; the extracted water vapor escapes above the bed of matter in a warmer atmosphere whose temperature is higher than its critical point (365 ° C): it reaches very quickly the supercritical state, which avoids (or limits) a rehydration and a evolution on the surface of the material in such a way that, at the end of the cooking, the proportion of anhydrite to the fa is very high (without it being possible to give precise proportions, since some shots before tempering evolve immediately). The proportion of basaite observed in the final binder comes essentially from a certain transformation of the anhydrite aifa that occurs at the beginning of tempering; this phenomenon could be revealed, studying the temperature profile during the course of the treatment: in fact a slight temperature rise of the material is observed at the mere beginning of the tempering i 15 ° C to 20 ° C) which can only be explained by the exothermic transformation reaction of annidpta to fa in basaite; but this transformation is blocked very quickly by the tempering that stabilizes the alpha anhydrite. In addition, it appears that tempering completely blocks an evolution of alpha anhydrite towards gamma anhydrite (insoluble or sparingly soluble) which is found only in the traces state in the final product (contrary to known binders comprising a large proportion). of this variety). The invention extends to an installation that allows the putting into surplus of the procedure that is defined in the foregoing. This installation comprises, in combination, a cooking tunnel having one end behind and one end forward, means for feeding raw material from the rear end of the cooking tunnel, longitudinal gutters juxtaposed in the cooking tunnel and which may contain the material, combs of heat conductive material inserted in the gutters and adapted to divide the mass of material contained therein, adjustable means of vibration of the gutters adapted to produce a routing of the material from the rear end towards the front end, means of heating, in particular radiators, of adjustable power located above the gutters in the cooking tunnel, a cooling device having a rear end and a front end and which is situated at a lower level in relation to the tunnel cooking, a container of elongated shape that extends into the cooling device to contain material, adjustable means of vibration of that container adapted to produce a routing of the material from the rear end towards the front end, means, gravity passage of matter from the front end of the cooking tunnel to the rear end of the device of cooling, means for injecting dry and cold compressed air at the level of the aforementioned passage means, means for injecting dry and cold compressed air into the cooling device, and means for evacuating matter to the front end of the cooling device . Other features, objectives and advantages of the invention will be apparent from the description below referring to the accompanying drawings, in which: Figure 1 is a schematic perspective view of an embodiment of a processing treatment facility; with the invention; Figure 2 is a side view; Figure 3 is a cross section through a plane AA '; Figure 4 is a cross section of a cooking tunnel by a plane BB '; Figure 5 is a longitudinal section of a level of the cooking tunnel according to dashed line CC; Figure 6 is a detailed perspective view of the means of passage of a level of the cooking tunnel to the lower level; Figure 7 is a detailed view of the means that allow the passage of matter by gravity of the cooking tunnel to the cooling device, and means of injection of compressed air, cold and dry; Figure 8 is a partial longitudinal section showing in particular the cooling device and its compressed air injection ramps. The treatment plant, represented by way of example in the figures, makes it possible to prepare an improved hydraulic binder of a pulverulent raw material based on calcium sulphate. This installation essentially comprises, on the one hand, an upper cooking tunnel 1 consisting of several levels la, Ib, ... le, arranged one after the other, with a vertical downward movement between two successive levels, and on the other hand part, a lower cooling device 2.

Each level of tune! of cooking is constituted by insulating walls, resistant to heat, such as 3, which close the tunnel on the side: the top, the bottom and the front between two levels (figures 3, 4, 5). These walls are supported by a tubular frame 4. Longitudinal gutters 5 are arranged in the tunnel to contain the pulverulent material and guide it from the rear end of the cooking tunnel (corresponding to its upper part) and its front end (which corresponds to its lower part). These juxtaposed gutters are carried by elastic supports 6 such as spring systems 7 and attached to adjustable vibration means that allow to transmit to the ranalones a vibration of adjustable amplitude and frequency. In the example, a vibrator 8 of the type of adjustable amplitude and frequency is associated with a lattice 9 which is fixed laterally on the frame 4 by means of the elastic blocks 10 of the "sil on t block" type. The vibrator vibrates the assembly of the lattice 9, the support 6, the gutters and ensures a routing of the pulverulent material by vibration. Between two levels, the gutters 5 are extended by vertical or very inclined portions 11 which perform - .3 - the role of means of passage by gravity of matter from one level of gutters to the lower level; matter falls in the form of rain from one level to the other. Of course, any other vibration system can be provided, in particular a plurality of vibrators distributed along the cooking tunnel to directly vibrate the supports of the gutters 6 (in the absence of the lattice 9). The gutters contain combs such as 12 of a heat conducting material, in order to locally divide the mass of material and ensure a supply of heat to the core thereof by conduction. Those combs distributed along the gutters are supported by sleepers 13 fastened on the sides of the side gutters. The upper level of the gutters may not contain these combs. In addition, the cooking tunnel comprises infrared radiators such as 14, each of which is arranged transversely above the gutters so as to radiate the entire width of the gutters. These radiators, placed close to one another, are provided with an electrical supply connected to means for regulating the emitted power, associated with temperature probes of the conventional type (not shown), arranged in the cooking tunnel. The lower level of the gutters does not include radiators. The number of radiators and their power are designed in such a way as to raise and maintain the temperature of the gases in the tunnel at a value between 400 ° C and 500 ° C and to bring the average temperature at the heart of the matter, at a value between 250 ° C and 300 ° C. The precise setting of the temperatures can be obtained by regulating the emission power of the radiators in correlation with the speed of the routing of the material. Above the rear end of the cooking tunnel, a nozzle 15 for feeding raw material is provided, which preheats with means that allow the hot gases to be taken in the tunnel in the vicinity of this rear end and to transfer those gases to the matter contained in the feed nozzle. In the example, these means are very simply constituted by a duct 16 which opens into the nozzle 15 and takes hot gases at the upper level of the tunnel by means of three nozzles distributed along this upper level. On the other hand, the cooling device 2 is arranged below the cooking tunnel l just described. This device comprises a container 17, of elongated shape, which is supported by the sleepers 13 by means of the interposition of elastic means such as spring systems 19. These sleepers 18 are integral with the frame 4. These means are arranged in such a way that the container is slightly inclined from its rear end 17a toward its forward end 17b. A vibrator 20 of the same type as the vibrator 8, allows the container to be vibrated with an adjustable amplitude and frequency. The rear end of the container 17, extends beyond the gutters of the level of the cooking tunnel so that the pulverulent matter falls above a ramp 26, from the gutters in the container. At this level the device is provided with means 21 for injection of cold and dry compressed air, the curtain of material falling in the form of rain in the container was born. It should be noted that this curtain of material produces a sufficient stopper to block the heating air of the cooking tunnel and prevent the passage of this in the cooling device; on the contrary, the hot air has a tendency to rise again in the cooking tunnel from its front end towards its rear end by a natural pulling effect, favored by the ascending geometry of the cooking tunnel from the front to the rear, by the peratu-ra mas ba at the lower levels, and by the gas intake at the upper level. In this way, in the cooking tunnel, the gases circulate counter-direction in relation to the pulverulent matter, which increases the solid / gas exchanges. The thermal tempering to which the pulverulent material is subjected at the moment of its passage in the cooling device is ended by injecting cold and dry air flows into the bed of matter in movement in the container 17. For this purpose, the ramps 22 of injection of compressed air are arranged in the container so as to descend to the heart of the bed of matter, as shown in figure 8. These ramps are inclined in the direction of the displacement of matter and contribute to put the matter in motion: agitation on the place leading to a kind of suspension of the particles in the cold air stream, routed from set back to front. These ramps are fed by a network of ducts 23 connected to a common compressed air supply. The aforementioned injection means allow to obtain good air / solid heat exchanges and an excellent hardening efficiency. In practice, the flow of cold and dry compressed air will be adjusted to obtain a cooling of the material, from a value between 250 ° C to 300 ° C at the exit of the cooking tunnel to a value lower than 100 ° C at the exit of the cooling tunnel; the duration of the cooling is between 6 and 10 minutes approximately. Evacuation means, such as the nozzle 24 provided with a helical extraction screw 25, allow the material to be collected after the treatment. The installation described allows a new hydraulic binder to be manufactured from calcium sulphate, giving preference, in the cooking tunnel, to the formation of calcium sulphate alpha anhydrite (the gamma form is practically absent) and limiting, thanks to the thermal tempering carried out in the cooling device, the evolution of the product that comes from cooking. In the implementation example below, the raw material is a phosphogypsum that comes from Morocco, crushed to provide a powder with a granulometry of less than 0.5 mm. This powder has a humidity rate of 20%. The power of the radiators 14 of the cooking tunnel and the vibratory regime of the vibrator 8 are regulated so that the powder remains approximately 12 minutes in the cooking tunnel, that the average temperature of the gases is 480 ° C - 13 - approximately and the average temperature at the heart of the material is 250 ° C. This heat treatment ensures a dehydration of the raw material and, in the heated gaseous atmosphere containing a part of the released water vapor, a transformation of a high proportion of that calcium sulfate alpha anhydrite material. The compressed air injected, on the one hand on the curtain of dust falling from the cooking tunnel in the cooling device, and on the other hand on the ramps 22, has a humidity rate of less than 1% and a temperature of 25 ° C. . The air flow is adjusted so that the powder at the exit of the cooking tunnel is cooled to room temperature in the cooling device in ten minutes. An analysis of the temperature profiles shows a rise in temperature of the order of 20 ° C (at the beginning of the cooling tunnel) that is due to certain exothermic rehydration of the product; however, this is blocked very quickly by tempering and at the outlet of the cooling device, the product has the following composition: - calcium sulfate anhydrite (soluble anhydrite) 50% by weight; - basaite: 50% by weight; - anhydrite range of calcium sulfate (anhydrite more soluble): trace only.

This composition is evidenced by the following analyzes: thermal analysis by weight, defractométpcos analysis, X-ray analysis, infrared spectrometry. The specific surface of the product is measured by nitrogen adsorption (method B.E.T.) and the value found is 5.96 m- / g (to be compared with that of cement in the order of 1 m2 / g). The same analyzes are made on an improved plaster sample that comes from Germany and that is manufactured from thermal plant desulphurization products.

The results obtained for those improved plasters are the following: - anhydrite at the fa of calcium sulphate: 8%; - basaite 37"-, - anhydrite gamma of calcium sulphate: 55% The measured surface area is: 3.64 m ^ / g The high specific surface area of the binder according to the invention and its high proportion of soluble alpha anhydrite They give to the products manufactured by the setting of these binders (in the absence or in the presence of fillers), remarkable mechanical qualities of fire behavior, in this way the product obtained by the setting of the binder according to the invention described above (without load), it was subjected to flammability tests according to the NF P 92-507 standard (test tubes of 0.30 m / 0.40 m subjected to radiation from a constant heat source) .The determination of the four indices that are foreseen in this standard (index of inflammation, development index, maximum flame length index, combustibility index) allowed to classify the product in the highest category MO of the six categories In addition, tests of resistance according to the norm gave the following results: - resistance to compression: 280 bars; - Flexural strength: 65 bar. In addition, qualifying tests in a submerged situation, showed that the product has good qualities of resistance in this situation.

Claims (3)

1. NOVELTY OF THE INVENTION Having described the invention, we consider it as a novelty and, therefore, we claim as our property, what is contained in the following clauses. 1. Process for treating a pulverulent raw material based on natural calcium sulfate or synthesis to prepare a hydraulic binder comprising a stable mixture of alpha anhydrite and basaite, in which the weight ratio of alpha anhydrite is greater than 35 %, characterized in that the following two successive treatment steps are combined: (a) - The pulverulent material is heated to a temperature practically comprised between 220 ° C and 360 ° C in the presence of water vapor under appropriate conditions to form mayoptially, Calcium sulfate of variety al fa; (b) - The matter heated in this way is subjected to a thermal tempering which consists in cooling it to at least 150 ° C in a time less than 15 minutes by means of a cold and dry gas injected or pressure in the heart of this.
2. 2. Processing method according to clause 1, characterized in that the tempering operation (b) is put into operation in order to bring the material to a temperature below 100 ° C in a tempering comprised between 6 and 12 minutes.
3. 3. Process of treatment according to any of clauses 1 or 2, characterized in that the tempering operation (b) is carried out by means of cold and dry compressed air, injected in several places in the moving matter; The air flow is adjusted to obtain the appropriate cooling speed. 4.- Treatment procedure according to the clause 3, characterized in that at the end of operation (a), the heated material is sent in the form of rain from a higher level to a lower level where it is carried by means of vibration to walk in bed; the tempering operation is carried out, on the one hand, by sending a first flow of cold and dry air over the curtain of matter falling in the form of rain, between the upper level and the lower level, and on the other hand, by injecting air flows cold and dry at the heart of the bed of matter during the course of the lower level. 5.- Treatment procedure according to any of clauses 1 to 4, characterized in that the humidity rate of the raw material is previously controlled and, if it is the case, it is adjusted to a value practically comprised between 12% and 25%; the cooking operation (a) is put into operation bringing the pulverulent material to walk in a stirred bed in a confined gas atmosphere containing at least a part of the water vapor released by the matter, and heating the set under the proper conditions to raise the temperature of the 5 gases above the bed of matter, at a value between 400 ° C and 500 ° C, and in bringing the average temperature at the heart of the material, to a value higher than 250 ° C and lower than 300 ° C. 6. Treatment procedure according to clause O 5, characterized in that the heating of operation (a) is carried out by means of infrared radiators arranged above the bed of matter; the power of these radiators is regulated in correlation with the routing speed of the material bed, in order to obtain the appropriate values, on the one hand, of the temperature of the gases above the bed, and on the other hand, of the temperature in the heart of matter. 7. Process of treatment according to any of clauses 5 or 6, characterized in that, in the course of the cooking operation (a), the material is brought to be routed by means of vibration in juxtaposed gutters, in which combs of heat conductive material are inserted to divide the bed of material and ensure a supply of heat to the core thereof by conduction. 3. - Treatment procedure according to clause 7, characterized in that, in the course of the cooking operation (a), the material that walks in the gutters, it is taken several times so that it falls in the form of rain from one level of the gutters to a level of lower gutters, and a part of the street gases is recovered in the upper part, to serve as preheating of the raw material. 9.- Installation for treating a raw material that is presented in a pulverulent form, such as natural calcium sulfate or synthesis to implement the procedure in accordance with any of clauses 1 to 8, to prepare a hydraulic binder, characterized in that it comprises, in combination, a cooking tunnel 5 having one end behind and one end forward, means for feeding raw material from the trailing end of the cooking tunnel, longitudinal gutters juxtaposed in the cooking tunnel and which can contain the material, combs of material 20 heat conductor inserted in the gutters and adapted to divide the mass of matter contained therein, adjustable means of vibration of the gutters adapted to produce a routing of the material, from the rear end to the front end, 25 adjustable power heating means located above the gutters in the cooking tunnel, a cooling device having a rear end and a front end and which is located at a lower level in relation to the cooking tunnel, a container of elongated shape that extends in the cooling device to contain the material, adjustable means of vibration of that container adapted to produce a routing of the material from the rear end to the front end, means of passage by gravity of the material of the back end of the cooking tunnel to the rear end of the cooling device, means for injecting dry and cold compressed air at the level of the aforementioned passage means, means for injecting dry and cold compressed air into the cooling device, and means for evacuation of matter to the front end of the cooling device. 10. Installation according to clause 9, characterized in that the cooking tunnel comprises several levels of gutters and means of passage by gravity of the material of a level of gutters to the level of lower gutters. 11. - Installation according to any of clauses 9 or 10, characterized in that the gutters are carried by supports mounted on elastic means and joined to the vibration-setting means of the type of adjustable amplitude and frequency of vibration. 12.- Installation according to any of clauses 9, 10 or 11, characterized in that the heating means of the cooking tunnel comprise infrared radiators that have an electrical supply connected to means for regulating the emitted power, associated with temperature probes arranged in the cooking tunnel. 13. Installation according to any of clauses 9, 11 or 12, characterized in that it comprises, near the rear end of the cooking tunnel, gas intake means associated with means for transferring those gases towards the material that is contained in the feeding means for preheating. 14. Installation according to any of clauses 9 to 13, characterized in that the means for injecting compressed air into the cooling device, comprise air injection ramps arranged in the above-mentioned container. 15. Hydraulic binder based on calcium sulfate, characterized in that it comprises a stable mixture of anhydrite to fa and of basaite, in which the weight ratio of anhydrite to fa is greater than 35%. 16. - Hydraulic binder according to clause 15, characterized in that the weight ratio of alpha anhydrite is between 40% and 65%. 17.- Hydraulic binder according to clause 16, which leads after setting, to the following characteristics of the products that were obtained: fire behavior: flammability classified in the category OM according to the norm NF P 92-507; - resistance to compression: between 250 and 300 bar; - resistance to bending: between 55 and 70 bars.