Method and device for the production and/or conditioning of powdered material

A method and a device for producing and/or conditioning powdered material. The aim of the invention is to provide a method and an associated device which are used for producing and/or conditioning powdered material in a spouted bed comprising inert particles and in which a dry, fine powder having a very small particle diameter is produced at a low cost and at adequately large quantities in a continuous operation. This aim is achieved by a method in which the material is treated in several stages in a spouted bed comprising inert particles. In the method, the powdered material that is preprocessed in a first spouted bed and is separated from the larger material particles in an integrated dust collector is fed to a superimposed second spouted bed as a material-gas flow along with the gas flow discharged from the first spouted bed in order to be further reduced in size and be conditioned. After separating the fine particles from the larger material particles in a dust collector that is integrated into the second stage, the fine particles are discharged from the two-stage spouted bed treatment along with the gas flow as a powdered material having very small particle diameters. The separated larger material particles are once again fed to the second spouted bed of the second jet chamber. The device includes a spouted bed apparatus in which a jet chamber encompassing an integrated dust collector as well as a second superimposed jet chamber encompassing another integrated dust collector are disposed.

BACKGROUND

The invention relates to a method for the production and/or conditioning of powdered material with the features mentioned in the preamble of claim1and the associated device having the features mentioned in the preamble of claim9.

It is known to produce powdered material in a fluidized bed, in which a gas flow is supplied to maintain said fluidized bed. Here, the following types of operating a fluidized bed are known, which can be produced with the granulated or powdered material.

In a spray dryer, such as known from the patent publication DD 285 724 A5, a liquid containing solid materials is sprayed into the hot material-laden gas flow. Particles develop in the gas flow by way of drying, showing a hollow helical shape or fractions thereof. The material particles that develop have a relatively large grain size and usually show poor re-dispersing properties. A spray dryer according to the prior art is a very large and thus expensive apparatus, requiring a lot of space and large amounts of energy. Such spray dryers are not suitable to produce very small solid particles. An additional thermal conditioning of the particles produced in the spray dryer is impossible.

2. Fluidized Bed Arrangements with Inert Beds

Fluidized bed arrangements with inert beds, such as known from the U.S. Pat. No. 6,187,238, have a gas-permeable fluidized bed bottom. A fluidized material bed is formed by the gas supplied from the bottom via the fluidized bed bottom in which appropriate inert bodies are provided as well. However, no very fine particles with appropriately 100 μm can be produced here either, because the impulse acting on the inert particles is determined only by the predominantly vertical up and down motion of the inert particles in the given area of the fluidized bed, thus only between the fluidizing point and the discharge point and therefore it is insufficient for the requirement to produce fine particles from vaporized/evaporating liquids. In addition to drying the solid matter entrained in the introduced liquids on the surfaces of the inert bodies no additional thermal conditioning is possible in a fluidized bed stage.

3. Spray Towers with Fluidized Beds

Spray towers are known for example from the patent publication DD 272 576 A3, which are operated with a fluidized bed at their lower end. Here, the fluidized beds can be operated with or without any inert bodies. Here, thermal or mechanical post-conditioning by way of a respective abrasion of the particles falling from the spray tower is possible. It is disadvantageous here that during the thermal post-conditioning various gas flows are being mixed. In this combination the production of fine particles is also limited for the above-mentioned reasons.

In an inert spouted bed stage the impulse potential to effect the inert particles is considerably greater than in a fluidized bed with equivalent inert bodies, because in the jet range the particle speed is considerably higher (e.g., 10 times higher) than the discharge speed of the particles and in spite thereof the particles are not removed due to the design typical for spouted bed arrangements. From the (patent publications DD 225 630 A1, DD 224 233 A1, DE 103 03 836 B4) spouted bed arrangements are known for the production of powdered material. Here, a gas flow is supplied from the bottom to the spouted bed arrangement at a high speed to create a vertically rotating spouted bed. A liquid containing solid matter is sprayed in, for example by one, two, or more spray nozzles from the bottom, the top, or the side of the jet chamber such that the liquid always wets the surfaces of the inert particles to the extent possible, i.e. that no overflow develops. The liquid containing solid matter, for example sediment, can also be added to the inert bed in motion via suitable conveyer devices, such as screws and/or slurry distributors, e.g., rotating wheels. Steel balls, ceramic balls, or Teflon particles having a suitable grain size, shape, surface condition, and density are used as inert particles provided in the spouted bed. The liquids are evaporated by the hot gas flow such that, on the one hand, dry material particles develop and material then develops on the inert particles, which adheres while drying. The material particles and the adhering dry solid matter is abraded by the inert particles moving in roller-shaped jets and are discharged from the jet chamber in the form of dust (e.g., <50 μm). The dust is usually removed as a product at one or more externally located, consecutively arranged different solid matter collectors of equal or different type (cyclones, filters.) Powdered products of increasingly smaller particle dimensions can be yielded, according to the capacity of the inert bed—spouted bed stage by the multiple consecutive arrangements of dust collectors downstream in reference to the spouted bed arrangement. It is disadvantageous that the desired small grain sizes are produced at minute amounts only. Additionally the consecutive arrangement of dust collectors is energy-consuming and thus expensive.

SUMMARY

The object of the invention is to provide a method and an associated device for producing and/or conditioning powdered material in a spouted bed with inert particles, in which a dry fine powder with very small particle diameters can be produced and/or conditioned cost-effectively and in appropriately large amounts in a continuous operation.

This object is attained according to the invention for the method by the characterizing features of claim1and for the device by the characterizing features of claim9.

The method according to the invention is characterized in at least a two-step conditioning of the material in a spouted bed having inert particles. Here, the powdered material, pre-treated in a first spouted bed and separated from the coarser material particles in an integrated dust separating device, is fed by the gas flow leaving the first spouted bed as a material gas flow to a second spouted bed located thereabove for an additional milling and conditioning. After separating the fine particles from the coarser material particles in a second stage of the integrated dust collection device the fine particles are discharged together with the gas flow from the spouted bed treatment having two- or more stages in the form of a powdered material with very small particle diameters. The separated coarser material particles are resupplied to the spouted bed of the second spouted bed chamber.

The device according to the invention comprises a spouted bed arrangement, in which a first spouted bed chamber is provided, having an integrated dust collection device and a second spouted bed chamber is located thereabove having another integrated dust collection device.

By the arrangement of heating and/or cooling devices and/or the supply of liquids or liquids containing solid matter the material to be produced can additionally be thermally treated and conditioned in a defined manner, such as polymerized, solidified, or coated.

The advantage of the method according to the invention and the device comprises that in a continuous process a homogenous, fine powdered product having a very small particle diameter is produced effectively. Additionally the material to be produced can be treated (conditioned) in the spouted bed in a thermally gentle fashion, if necessary, in order to thus yield a powder with properties of known and also novel product morphologies.

Another advantage is the fact that the production of the powdered material with very small particle diameters is performed in a single device, so that no additional external heat producers, mills, or sieves are necessary any more. Only a commercially available, powerful fan is necessary in the pressure and or suction operation, or a combination thereof, in order to overcome the initial loss in pressure of the spouted bed, in order to then allow a continued production in the operational state with the loss of spouted bed pressure known to be much lower.

Additional advantageous embodiments are described in the dependent claims; they are explained together with their effectiveness in the description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a spouted bed device1according to the invention, which preferably has a cross-section bilaterally symmetrical. It is also possible to embody the spouted bed device1with a round cross-section. The spouted bed device1comprises a first jet chamber6with an integrated dust collection device7and a second jet chamber8located thereabove having an integrated dust collection device9. Nozzles10for liquids or liquids containing solid matter, such as suspensions, solutions, melts, or slurries, are arranged in the jet chamber6and/or the jet chamber8. A separator, not shown, for a final collection of the target product with a uniform size is arranged downstream in reference to the spouted bed device1.

The dust separating devices7and/or9arranged above the jet chamber6and/or8represent a zigzag-sifter, for example. The dust separating devices7and9can also be formed by an expansion of the cross-section of the exterior walls of the spouted bed device1. The dust separating device9has a higher collection ratio than the dust separating device7so that only material having the desired particle size is removed from the spouted bed device1via the dust separating device9.

In their lower area the jet chambers6and8are provided with an almost centrally arranged opening2. The opening2opens into a channel16, pointing at both sides in the direction of the side walls3. The side walls3are here inclined outwardly in reference to the vertical and straight or provided with an interior curve. A wedge-shaped installation part5is arranged above the opening2of the jet chambers6and8. Here, the lower walls of the installation part5each form a side wall of the channel16. The installation part5located in the jet chambers6and8is embodied hollow, with a controllable heating device11, for example high-frequency heating elements, can be arranged in the installation part5embodied hollow for the thermal conditioning of the material. The side walls of the wedge-shaped installation part5show a straight or inwardly curved contour, with the angle A between the side walls and the base area of the installation part5ranging from approx. 45° to 60°.

Alternate embodiments of the installation part5are shown inFIG. 3.

InFIGS. 3aand3cthe exterior walls of the installation part5are embodied straight, with the exterior walls inFIG. 3cextending higher than inFIG. 3a.FIG. 3bshows the exterior walls with a contour curved inwardly. InFIG. 3dthe curved exterior walls are extended higher. InFIG. 3ethe curved exterior walls are not extended as high and the inclined exterior walls are tracking.

In the method according to the invention a gas or material gas flow12is fed to the jet chamber6and a material gas flow15almost centrally to the jet chamber8and deflected in the direction of the exterior side walls3of the spouted bed device1such a roller-shaped flow13develops, positioned in the axial direction of the jet chambers6and8and aligned upwards at the exterior side walls3. It has been found that in this flow alignment the abrasive effect of the inert bed, moving in form of a roller upward along the exterior inclined side walls3, is essentially greater than in a flow alignment from the outside towards the inside. The gas flow in the jet chambers6and8forms a spouted bed4, comprising material particles, inert bodies, and moist and dry material particles adhering to the inert bodies. By the upward flow13the material particles and the inert particles are rapidly thrown upward along the inclined exterior side wall3and along the interior inclined side walls of the installation part5according to the arrow direction14and returned to the gas flow, and thrown upward once more so that a roller form of the inert particle flow develops. By this roller a rapidly oscillating particle layer can form, if applicable. This particle circulation occurs very rapidly and stably.

The spouted bed4in the jet chamber6and/or the jet chamber8can be supplied with liquids or liquids containing solid matter, such as suspensions, solutions, melts, or slurries via the nozzles10.

Above the jet chamber6, material collection occurs by the dust separator7, in order to prevent the discharge of dust particles considerably too large from the first spouted bed4of the jet chamber6and in order to return them downwards to the first spouted bed4. The dust separator7is sized such that both the dust particles of the desired dimensions as well as dust particles of slightly lager dimensions are allowed to pass, but no particles being considerably larger. The dust particles being considerably too large fall back into the first spouted bed4of the jet chamber6and are here further milled and discharged upwards once more.

The material particles that have passed the dust separator7together with the gas flow are fed to the jet chamber8located thereabove in the form of a material-gas flow15. A spouted bed4is created once more in the jet chamber8, which is adjusted to the changed conditions, though. The spouted layer4is provided with inert bodies, which have e.g., smaller and/or lighter inert particles with rough surfaces and a similar bed mass. In the roller shaped spouted bed4of the jet chamber8the particles still too large are being milled and then pass, together with the dust particles already showing the target size, through the dust collection device9, located above the jet chamber8, which is sized to only allow particles of the target size to pass. Any dust particles still too large fall from the dust separating device9back to the jet chamber8and are further milled.

The precise temperature adjustment inside the device, if necessary also for the thermal conditioning of the materials, occurs gradually in the jet chambers6and8according to the invention, primarily by a conventional high-frequency heater11at a frequency range from 30 kHz to 300 MHz. The heating devices11are arranged in the installation parts5. The material and the inert bodies in a dense mass move gliding down the exterior side walls at a slow speed such that here particularly beneficial conditions for a good heat transfer are given, on the one hand, by heat conduction from the inductively heated metal surface of the installation parts5to the di-electrically heated, moist, coated inert particles, primarily however by way of induction from the high frequency heater11directly to the moist coated inert particles.

Particularly beneficial conditions for the use of the high frequency heater11are given when the moist product, moist dust, sprayed liquid, or injected slurry, has sufficient ohmic conductivity on the surface of the inert body in order to allow heating by ionic conduction in the electric field. The electric conductivity is sufficiently high if for example dissolved salts are included in an aqueous-moist solid matter. Due to the fact that the electric conductivity in such solid matter itself depends on the moisture content, moister sections are heated more intensely than the areas already dry, greatly benefiting the solution of the given problem. Therefore, these high frequency heaters11operate carefully when increasing the temperature or stabilizing, both with regard to the perhaps moist coated side walls of the installation parts5as well as primarily the intensely moved and mixed spouted bed when the inert bodies are made from a material suitable to transfer high frequency and are coated with solid material particles to be abraded being more or less moist. This way a rapid, effective, and precise heat transfer to the coated or uncoated inert bodies is ensured and thus to the product to be conditioned.

In order to adjust the temperature at low temperature ranges, instead of the high frequency heater, beginning at the second spouted bed8a cooling gas or a cooling liquid can be inserted directly through the installation part5embodied hollow.

Furthermore, for the same purpose a cooling gas can be fed to the second spouted bed stage8via a gas supply17.

LIST OF REFERENCE CHARACTERS USED