FR2850520A1 - Micro-wave heating device for the high temperature treatment of solid particles or mud for expansion, rendering inert, vitrification and calcination applications - Google Patents

Abstract

Device for the micro-wave heating of a material, introduced as particles or as a paste, comprises a fixed external envelope (30) and delimiting a closed internal cavity (31) communicating with at least: (a) an inlet (35) for the material; (b) an orifice (32) for the introduction of a micro-wave field; (c) a system (36) for churning the material; (d) a system (41) for rotating the churning device; (e) an outlet (45) for the heated material; (f) a device for discharging the products from the churning device to evacuate it via the outlet; and (g) a system for capturing the micro-waves dimensioned on the different openings of the envelope to confine the micro-waves in the envelope during the different operating phases of the furnace. An Independent claim is included for the fabrication of granules using this micro-wave heating device.

Description

The present invention relates to a device and a method for

heating and the

  manufacturing of granules with an excellent compromise between cost - lightness - mechanical resistance.

  The uses of these products, in particular based on clay, are numerous and widely used in the construction field.

  Although not limited thereto, the invention applies more particularly to the production of expanded clay granules.

  Currently, the manufacture of expanded granules, most often in the form of beads, is implemented in production lines comprising rotary radiant ovens. The use of such ovens however poses numerous problems, for example described in the document WO 01/34533 previously filed by the applicant.

  Application WO 01/34533 describes the principle of a method for manufacturing 20 expanded clay granules. This document does not describe the device which is the subject of the present invention, nor the optimized means for implementing such a device.

  Document WO 02/79113 is also known, which describes an apparatus for the thermal treatment of expandable material coupling rotary thermal ovens and microwave ovens, the action of which aims at achieving the maximum expansion of the treated material. By the use of specific means, the device and the method according to the invention make it possible, in an alternative manner, to heat treatment by the sole action of microwave radiation.

  Thus, the present invention relates to a device for microwave heating of a material introduced in the form of particles or paste, the device comprising a fixed external envelope and delimiting an internal cavity closed in communication with at least: admission of the material, -an orifice for introducing a microwave field -means for stirring the material, -means for rotating the stirring means, -means for removing products from the heated material , means for discharging the products out of the stirring means to evacuate them by said evacuation means, means for capturing microwaves sized on the different openings of the envelope to confine the microwaves in said envelope during the various operating phases of said oven.

  The capture means arranged on the inlet and outlet means can be constituted by tubes whose diameter and length can be calculated at least in part as a function of the wavelength of the radiation used.

  The rotation means can consist of a support axis on which the stirring means are fixed, and means external to the casing can drive said axis and the axis can include a microwave seal.

  The device may further comprise a support allowing an inclination of 200 to 60 'of the axis of the stirring means relative to the vertical.

  The unloading means may include means cooperating and linked with the stirring means to allow the evacuation of the products.

  The stirring means can comprise a ferrule and a removable tray constituting a bottom, and the unloading means can comprise means for moving along the support axis of said stirring means in the cavity, and stopper candles of said ferrule placed so as to allow the separation of the ferrule and the plate during said displacement.

  The stirring means can comprise a ferrule, a plate and a spiral disposed on the internal wall of said ferrule, and the unloading means can comprise means for reversing the direction of rotation of said spiral.

  The stirring means can comprise a ferrule and a plate, and the evacuation means can comprise orifices with controlled opening in said plate.

  The ferrule may be made up of at least one material that is transparent or microwave-reflective.

  The tray may include a material transparent to microwaves and a metal support.

  The invention also relates to a method for manufacturing granules comprising the following steps: a) shaping by granulation of a pasty material, b) heating the aggregates formed during step a) by microwave radiation up to at a temperature between 400 and 2000 ° C., c) cooling the granules from step b), d) recovering said granules, and in which said step a) is carried out continuously and in that step b) heating is carried out in at least one heating device according to the invention.

  At least two heating devices can be arranged in parallel to implement step b), each of said ovens being successively supplied with aggregates from step a) discontinuously.

  The method may include a drying step before and / or after step a) of shaping.

  The drying step can be carried out using and recovering the heat energy produced by said cooling of the expanded granules during step c).

  The device and / or method according to the invention can be applied for the production of expanded clay granules.

  They can also be applied for the treatment of granular or pasty products based on clays, argillaceous sludges for washing quarry aggregates, industrial residual sludges, any divided or muddy solid product, interested in a high temperature transformation into view of expansion, inerting, vitrification, calcination.

  The invention has numerous advantages over heating devices of the prior art, and methods including, for example, the use of rotary ovens: - increased flexibility of the installation operating according to the principles of the present method, making it possible to absorb significant variations in the production of the final product or in the flow rate of initial material, - flexibility in the formulation of the initial material that can be treated by the device according to the invention as well as in the properties (expansion rate, size of the 10 granules, mechanical strength, etc.) of the material finally obtained at the outlet of said device, - the lightness of the infrastructure required to implement the invention, authorizing the installation of units according to the invention or operating according to the present process directly on the production site of the initial material, for example on an operating quarry, - flexibility and modu larity of such units, which can in particular be stopped then restarted without substantial expenditure of energy or thermal inertia, due to their compactness and the use of microwaves, - the absence of risk of fouling and seizure of the various mechanical parts in rotation and bonding of the hot material to the walls of the device, which leads to lengthen the time of use of such units and simplifies their operation, - a significant reduction in the energy cost of operation of the installation including the present device, the energy being directly transmitted to the material to be treated without an intermediate heat vector, - a strong reduction in pollutants emitted by the process due to the absence of fumes from a heating fuel, - a more rigorous control of the material transformation stages, making it possible to obtain a final product with high added value meeting specific requirements very precise cifications, generally impossible to obtain by a conventional process in a rotary kiln, - the possibility of manufacturing in small quantities said products with high added value, and this over a very short period.

  The present invention will be better understood and its advantages will appear more clearly on reading the description of the exemplary embodiments, which are in no way limitative, illustrated by the appended figures below, among which: - Figures 1A and 1B show a diagram of an installation for treating a pasty initial material according to the present method and including the use of the device according to the invention, FIGS. 1C and ID show diagrams of embodiments respectively of the drying and cooling devices which are particularly suitable for the implementation of a method according to the invention, - Figure 2 illustrates an embodiment of a microwave oven device according to the invention.

  In FIG. 1A the first phases of the process are described. Reference 1 relates to a hopper for receiving the basic materials. At the bottom of the hopper, there are motorized emitting means 2 which regulate and control the flow of material transported by the conveyor 3 to the mixing installation 4. The mixing carried out by several mixing means makes it possible to homogenize the material and to prepare the material for the production of pellets which takes place in the mixer-granulator 5. This device comprises an inlet 6 for additive products stored in a silo 7 and supplied by metering means 5, for example a screw Archimedes. The material formed into pellets is sent to a drying installation 9, optionally itself comprising means for forming into balls, pellets, granules, etc. (not shown in FIG. 1A). According to a preferred embodiment, the drying energy is supplied for all or part by a hot gas mainly coming from the downstream of the process by a conduit 10. The dried granules 10 fall into a hopper 11 forming a buffer storage before pneumatic (or other) transport 12, to the later stages of the manufacturing process.

  The basic materials used in the process can be: - clay sludge from washing quarry aggregates, - sludge resulting from waste treatment: industrial water, drilling, purification plant or residues from treatment of incineration of crushed recycled glass, - polluted soil, natural minerals such as kaolins ... The material at the entrance to hopper 1 must have a quality and a water content suitable for its further processing.

  The solid additives that can be used and stored in silo 7 can be additives specific to the nature of the base materials to achieve and optimize the following functions: - forming and drying of the beads, - coloring, - anti-sticking of the beads, - expansion maximum under the effect of microwaves, - mechanical properties of the expanded ball: resistance to rupture, to abrasion, - microwave heating accelerator, - modulation of density, permeability. Liquid additives can also be used and incorporated into the base material, for example in the mixer 4 and / or in the granulator 5. The material capable of being treated in accordance with the present invention can for example be a clay mud obtained an aggregate quarry, the density of which is 1.8 g / i and the water content of approximately 20% by mass, the clay present being predominantly, that is to say at least 50% by mass, preferably at least 10% by mass, in the form of Kaolinite, Ilite or Chlorite.

  Without limitation, the composition of the clay in its various constituents can typically come in the following proportions, by mass: - SiO2 50 to 70% - A1203 10 to 20% -C 0 to 5% - Fe2O3 1 to 10% CaO / CaCO3 5 to 40% -MgO, K20, ... 5 to 10% The temperature corresponds to a maximum expansion for such compositions is then between 11000C and 1400'C and generally close to 1250'C. The density of the finished product is generally between approximately 0.1 and approximately 0.9 g / i and its compressive strength between approximately 6 and approximately 15 MPa.

  Figure 1B describes the final stages of the process. The hopper 14 receives the dried granules by the pneumatic conveying line 13. It feeds a weighing hopper 15 equipped with a control valve 16. The granules are distributed to the various microwave ovens 18a, 18b, 18c, 18d by distribution means 17 comprising conduits 19a, 19b, 19c, 19d supplying the ovens. The granules, subjected to a suitable microwave radiation, for a determined period, are expanded and are directed to a cooling device 20 by injection of air, preferably countercurrent. The device 20 makes it possible to recover at the outlet of the installation a substantially continuous flow of expanded granules. An exemplary embodiment of such a device 20 is described below, in relation to FIG. 1c. The flow capacity is obtained by the succession of heating stages in the ovens arranged in parallel. In the nonlimiting example illustrated by FIG. 1A, it is described to have four ovens according to the invention in parallel. The present method can be implemented by at least two ovens but the number of ovens arranged in parallel according to the invention is not limited and can be determined inter alia according to the nominal capacity of an oven relative to the 20 overall capacity sought of the installation. The total flow of the installation can for example vary between 100 kg / h and 10 tonnes / h.

  The device 20 has a function of recovering the heat energy produced by the microwave ovens 18a, b, c, d, by means of a fan 21 which sends the hot gases to the drying installation 9 via a pipe 22. An exemplary embodiment of an installation 9 adapted for the reception of said gases is described in the remainder of this description, in relation to FIG. Id. The flow of hot gases is controlled by the control of the fan 21 and of the valve means. 23, also comprising auxiliary heating means 24, for example electric, making it possible to regulate the drying temperature.

  After cooling, the expanded beads are transported to storage means by a conveyor 25.

  The expanded granules generally have a density between 0.1 and 0.9 tonnes / m3 and a size or diameter between 0.1 and 50 mm. Depending on the desired application, the present process also makes it possible to have aggregates of calibrated size or diameter, for example between 0.1 and 1 mm, between 1 and 20 mm or between 50 mm.

  FIG. 1C illustrates a nonlimiting example of an embodiment of a cooling installation 20 particularly suited to the implementation of the present method.

  The expanded granules are introduced alternately by unloading the microwave ovens and through a pipe 101 into the device 20. The device 20 comprises an enclosure 100 delimiting at the outlet of the pipe 101 a so-called buffer zone 102 which advantageously makes it possible to dampen variations in installation flow. The dimensions of this zone 20 are for example calculated in such a way that the level of granules, in operation, fluctuates between a lower limit and an upper limit comprised in said zone 102. Zone 102 is delimited in its lower part by a neck of narrowing 103 which leads to a cavity 104 completely filled with granules and in which said granules are cooled by a heat transfer fluid, for example air.

  By heat transfer fluid, it is understood within the meaning of the present description any fluid known for exchanging heat (by heating or cooling) with the medium into which it is introduced. According to an advantageous embodiment, and as shown in FIG. 1C, a first means for introducing fluid 106 is disposed near the lower end of the enclosure 100 in a space 111 for introducing and distributing the fluid, delimited for example and as shown in FIG. 1C by a conical grid 107. According to an advantageous embodiment of the device, a second means 10 for introducing fluid is disposed at the level of the neck 103, in the free space of granules 108 under the neck 103.

  In operation, the granules periodically discharged from the microwave ovens are discharged into the cavity 102 in a discontinuous manner, and form, after crossing the neck 103, a moving bed descending of granules in the cavity 104. This bed is traversed by the heat transfer fluid introduced by the medium 106 and the granules are thus cooled to the set temperature. This temperature could, for example, be adjusted by the quantity and the temperature of the injected fluid or by controlling the speed of progression of said bed, which itself, for example, is controlled by means of drawing off 110 of the cooled granules placed at the bottom of the installation. After crossing the bed, the hot fluid is evacuated from the enclosure by an outlet pipe 109.

  According to a possible embodiment, a variable part of the heat transfer fluid, for example between 10 and 30 mol%, can be introduced by means 105. This distribution has certain advantages: - better control of the outlet temperature of the fluid coolant, - the cooling of the material constituting the neck 103 by radiative exchange with the cold fluid introduced by the means 105, said material being able to be subjected to very high thermal stresses, in the absence of such a cooling system.

  FIG. ID illustrates a nonlimiting example of an embodiment of a drying installation particularly suited to the implementation of the method according to the invention. The pellets enter the drying installation 9 through a pipe 201 delimited by a cylindrical envelope 202, and are distributed inside said enclosure 10 in a homogeneous manner by any internal suitable for this function, for example by a distribution plate 203. The casing 202 comprises an internal chimney 204, the internal cavity of which allows the drying fluid to be evacuated. The chimney 204 is pierced in its lower part with orifices 208 allowing the circulation of the fluid in the installation.

  Said fluid, for example hot air from device 20, enters installation 9 by means of introduction means 205. These introduction means are arranged in such a way that at the end of said introduction, the distribution of said fluid is circularly uniform around the cylindrical cavity delimited by the envelope 202. It is possible for this purpose to envisage multiplying the points of introduction of the fluid around the cylindrical envelope 202, or more advantageously and as described in FIG. 1D, using interns 20 delimiting, on the periphery of the envelope, an internal crown 206 for distributing the fluid.

  These internals have openings 207, arranged substantially at the orifices 208. These orifices can be constituted by holes, grooves, grids, etc. For example, Johnson grid interns can be used.

  During the operation of the installation, the pellets introduced by the means 201 are distributed homogeneously by the means 203 in the space delimited on the one hand by the cylindrical envelope 202 in the upper part of the installation or by the internal crown 206 in the lower part of the installation and on the other hand by the chimney 204. Said pellets thus form a descending moving bed 211 whose speed of progression is, for example, controlled by a withdrawal means 209 disposed at the bottom of the installation. The fluid introduced by the means 205 is distributed homogeneously in the internal crown 206. The fluid, via the openings 207 and 208, then passes through the mobile bed of pellets 211 distributed at this location in a thin layer, dries them and is finally discharged through the chimney 204 and the opening 210. The at least partially dried pellets finally leave the installation 9 under the action of the withdrawal means 209.

  This embodiment has many advantages: - the installation only comprises fixed internal walls, and therefore poses no mechanical problem of fouling or sticking, unlike conventional drying systems comprising rolling belt systems, - the crossing by the hot fluid of a thin layer of a mobile bed of uniformly distributed pellets on the one hand ensures high drying efficiency and limits the pressure losses due to said crossing, which leads to making the use optional a fan or an air extractor at the outlet of the installation.

  FIG. 2 schematically describes an embodiment of a microwave oven according to the invention for heating solids in the form of beads at high temperature, that is to say between 400 ° C. and 2000 ° C., in particular between 800 and 1300 ′ vs. The characteristics of this oven advantageously make it possible to combine the following functions: - mixing of the granules (or balls) to obtain a homogeneous cooking product, - loading and emptying without a door system so as to minimize or even eliminate any leakage of micro -waves, - high temperature rotary internal cavity in a microwave enclosure, - direct heating without heat transfer fluid, therefore better efficiency, - microwave heating which allows heating from the inside to the outside of the product, this type of heating being more homogeneous and making it possible to improve the characteristics of the product, - precise regulation allowing the obtaining of products of specifications more difficult to reach by a conventional process, - very reduced cycle time compared to the conventional process (3 to 20 times faster), very reduced gas emissions since they only come from the combustion (if applicable) of the heated material.

  - low thermal inertia and immediate availability of microwave energy, - flexibility in obtaining the properties of the final product.

  The oven comprises an enclosure constituted by an external envelope 30 and an internal cavity 31.

  The casing 30, generally metallic (preferably made of stainless steel), is hermetically closed, apart from the inlet holes for the initial material and the outlet for the final product and the arrival of a waveguide 33. A chimney 50 can also pass through the envelope 30 to evacuate the gases generated by the heating of the material. The microwave field has a frequency between 300 and 6000 MHz. The waveguide system 33 brings the microwaves generated by a magnetron to the orifice 32.

  The dimensions of the enclosure are between 500 mm and 2500 mm for its width (for example of cylindrical section), and 500 mm to 2500 mm for its height.

  The enclosure can be thermally insulated by a refractory coating 34, consisting for example of silico-aluminous bricks which can line the interior of the envelope 30.

  The material is introduced in the form of granules, or sludge, through line 35, of diameter between 10 mm and 130 mm and of a width chosen as a function of said diameter, the dimensions being chosen as a function of the length of the microwave radiation. so as to avoid leaks outside the enclosure, according to a technique well known to those skilled in the art.

  The material falls into the drum 36 consisting of a ferrule 37, for example made of concrete, and a plate 38, also made of concrete with a metal support 39.

  This plate 38 can receive air or gas circulation orifices, passing through its support axis 40 with a diameter between 10 and 100 mm. The shaft is thus cooled and the gas injected can promote oxidation reactions, for example from monoxide to carbon dioxide.

  The ferrule has a diameter between 500 mm and 2450 mm. The thicknesses of the plate and the ferrule are between 5 and 200 nm.

  Once the filling of the drum is complete, it is rotated by means of a motor 41 to allow the mixing of the material introduced. The linear speed at the periphery of the shell can be between 5 and 100 cm / s.

  A seal 42 makes it possible to avoid microwave leaks around the rotary shaft.

  Heating then begins with the activation of the microwave generator.

  When the heating step is finished, a jack 43 triggers the descent of the entire drum 36 along the axis of rotation, the rotation of the cavity then being stopped.

  When the ferrule 37 comes into abutment on jack stands 44, the plate becomes detached from the ferrule by continuing its movement, and lets the granules escape through the opening formed between the ferrule and the plate. The products are channeled towards the evacuation duct 45.

  This duct is, as well as the intake duct 35 for the products, consisting of one or 15 of several cylinders with a diameter between 10 and 130 mm making it possible to avoid microwave leaks. It is the same for the opening of the chimney 50.

  The whole of the enclosure is fixed on a support 46 allowing an inclination of the axis of rotation of the drum contained in the enclosure between 20 and 600 with the vertical.

  The drum can include other means for discharging the finished product, for example a spiral arranged on the internal wall of the shell, the reversal of the direction of rotation making it possible to pass from a brewing mode to an unloading mode.

  Also, the tray may include orifices with controlled opening.

  This type of oven is particularly suitable for the temperature setting of granular or non-clay-based products, clayey mud for washing quarry aggregates, industrial waste sludge, and in general any solid product (granules or under 5 in the form of so-called "fine" or muddy particles, interested in a high temperature transformation with a view, for example, to expansion, inerting, vitrification, calcination.

  The materials treated can be of mineral or organic origin.

Claims (16)

  1. Device for the microwave heating of a material introduced in the form of particles or paste, said device comprising an external envelope (30) fixed and delimiting an internal cavity (31) closed in communication with at least: - means (35) for admitting said material, - an orifice (32) for introducing a microwave field - means for stirring (36) said material, - means for rotating (41) said materials stirring means (36), -means for discharging (45) products from the heated material, -means for discharging said products from the stirring means (36) to evacuate them by said means of evacuation, -from means for capturing microwaves sized on the different openings of the envelope (30) to confine the microwaves in said envelope during the various operating phases of said oven.   2. Device according to claim 1 wherein said capture means disposed on the intake means (35) and discharge (45) are constituted by tubes whose diameter 20 and length are calculated at least in part according of the wavelength of the radiation used.   3. Device according to claim 1 or 2 in which the rotation means consist of a support axis (40) on which are fixed the stirring means (36), in which external means (41) to the envelope drive said axis (40) and in which the axis (40) comprises a microwave seal (42).   4. Device according to one of the preceding claims further comprising a support (46) allowing an inclination of 200 to 60 'of the axis of the stirring means (36) relative to the vertical.   5. Device according to one of the preceding claims in which the unloading means comprise means cooperating and linked with the stirring means to allow the evacuation of the products.   6. Device according to claim 5 in which the stirring means (36) comprise a ferrule (37) and a removable plate (38) constituting a bottom, and in which the unloading means comprise displacement means (43) the along the support axis (40) of said stirring means (36) in the cavity (31), and of the stop rods of said ferrule (37) placed so as to allow the separation of the ferrule (37) and the plate (38) during said displacement.   7. Device according to claim 5 in which the stirring means comprise a ferrule, a plate and a spiral disposed on the internal wall of said ferrule and in which the unloading means comprise means for reversing the direction of rotation of said spiral .   8. Device according to claim 5, in which the stirring means comprise a ferrule and a plate, and in which the discharge means comprise orifices with controlled opening in said plate.   9. Device according to one of claims 6 to 8 wherein said ferrule is constituted by at least one transparent or microwave-reflective material. 10. Device according to one of claims 6 to 9 wherein said tray comprises a material transparent to microwaves and a metal support.   11. Method for manufacturing granules comprising the following steps: a) shaping by granulation of a pasty material, b) heating the aggregates formed during step a) by microwave radiation to a temperature comprised between 400 and 2000'C, c) cooling the granules from step b), d) recovering said granules, and in which said step a) is carried out continuously and in that step b) of heating is carried out in at least one heating device according to one of claims 1 to 10.   12. The method of claim 11 wherein at least two heating devices are arranged in parallel to implement step b), each of said ovens being successively supplied with aggregates from step a) discontinuously.   13. The method of claim 11 or 12 further comprising a drying step before and / or after step a) of shaping.   14. Method according to one of claims 11 to 13, wherein said drying step is carried out using and recovering the heat energy produced by said cooling of the expanded granules during step c).   15. Application of the device according to one of claims 1 to 10 or of the method according to one of claims 11 to 14 for the production of expanded clay granules.   16. Application of the device according to one of claims 1 to 10 or of the method according to one of claims 11 to 14 for the treatment of granular or pasty products based on clays, argillaceous muds for washing quarry aggregates, industrial waste sludge, any divided or muddy solid product, interested in a high temperature transformation with a view to expansion, inerting, vitrification, calcination.