Apparatus For Fluidizing Powders

Abstract

The apparatus comprises a vertical vessel provided with a rotating gas-feed unit for maintaining powders in a fluidized state. The rotating gas-feed unit is provided above the bottom of the vessel with at least one tube extension terminating in a nozzle. The gas-feed unit may contain a plurality of tube extensions with nozzles, the tube extensions having different lengths and being bent in such a way, that the longitudinal axis of the nozzles forms an angle of 0.degree. - 90.degree. with respect to a radial direction passing through the nozzle opening in the direction of nozzle rotation and an angle of 0.degree. - 45.degree. in the same plane in the direction towards the bottom of the vessel. The vessel can be provided by several gas-feed units to which mixer blades may be attached.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention

The subject of the invention is an apparatus for bringing powders into a state of fluidization. The invention is especially concerned with apparatus for introducing gases into fluidized beds of cohesive powders.

2. Prior Art

Fluidized bed processes have gained great importance in modern technologies. They are base on the ability of a gas stream to suspend solid particles in the gas stream. A great advantage of these processes is the great contact area between the gas and the surface of the solid particle.

The choice of the type of the equipment for introducing gases into fluidized beds depends on the type of particulate solid that is to be fluidized. When it is necessary to fluidize a powder which has a certain degree of cohesion, normal types of grids with gas inlets opening from below are unsatisfactory since channels or cavities form in the powder above the grid, the gas flowing through such channels or cavities without coming into contact with the treated material. Various studies have therefore been undertaken to overcome these difficulties.

For example, Gelperin et al., in the book Fundamentals of Fluidization, Chimia, Moscow 1967 describe a movable grid wherein the grid usually rotates. These grides are usually designed in the form of a plate provided with slots or openings forming gas inlets and are situated near the bottom of the vessel, or are in the form of a cone provided with openings and rotating around a vertical axis.

Although this type of equipment has brought certain improvements, it has not altogether overcome all the existing difficulties which particularly occur when fine powders with a high degree of cohesion are fluidized. The problem is in the inability of these types of equipment to break up the firm channels and domes that have formed in the powder. Another difficulty that appears in that the openings in the grids are very often clogged with adhered material so that the technological process is hindered or fails altogether.

SUMMARY OF THE INVENTION

The present invention has among its objects the provision of an apparatus for introducing gases into fluidized beds which does not have the above-mentioned disadvantages of the prior art, and especially an apparatus wherein there are not formed in the treated material cavities or channels through which gas can flow without coming into contact with the treated material.

The above-mentioned objects are filled by this invention. In accordance with the invention there is provided an apparatus for fluidizing powders which comprises a vertical vessel provided by at least one gas inlet and if need be also by a mixer, equipment for heat supply and heat removal, and an inlet and discharge opening for powder. The invention includes a gas-feed unit which is used either singly or in multiple. Each gas-feed unit, which is independently rotatably mounted in bearings in the bottom of the vessel and connected to a driving means is provided with at least one channel for gas flow independently connected to a source of gas and provided by at least one tube extension with a nozzle. The longitudinal axis of the nozzle in the direction of its rotation forms with the radial direction passing through the nozzle's opening the angle .beta. in the range 0 to .+-. 180.degree., conveniently 0 to + 90.degree., and the longitudinal axis of the nozzle in the direction of the bottom of the vessel forms with respect to the radial direction passing through the nozzle opening the angle .alpha. in the range 0 to .+-. 60.degree., conveniently 0 to + 45.degree., the distances between nozzle openings and the axis of rotation in every gas-feed unit in a given vessel being different. If required the vessel can be provided by at least two gas-feed units, at least one gas-feed unit can be provided by at least two channels for gas through-flow independently connected to sources of gas, and every channel for gas through-flow may be provided by, for example, three tube extensions with nozzles. A mixer can be attached to the gas-feed unit.

Powders having a considerable cohesion can be fluidized by the above described device. The described design enables gas to be introduced into the powder by a relatively small number of streams with high kinetic energy; this prevents the formation of structural domes in the cohesive powder. The walls of the domes which may start to form are disrupted by the revolving gas stream so that they break apart and the resulting falling powder is mixed by the penetrating gas stream.

The slope of the longitudinal axis of the nozzle in the direction of rotation and towards the bottom of the vessel causes the rotating movement of the nozzle to provide the gas streaming from the nozzle with additional kinetic energy and so the gas stream can penetrate into the powder over a greater radial distance from the axis of the gas-feed unit and thus can aerate and mix a greater volume of material. By the repeated movement of the gas streams ejected from the nozzles rotating at unequal distances from the axis there is created a certain pulsation of the gas layers which is transmitted to the fluidized material and this makes the formation of cavities in the powder quite impossible. When gas is introduced into the treated material by means of several gas-feed units, by several channels for gas through-flow in every gas-feed unit and when every channel for gas through-flow is provided with three nozzles, or even by only one nozzle, then the gas being introduced can be distributed almost evenly over the whole volume of treated material. This also renders possible an exact control of the whole fluidization process because the clogging of any nozzle is immediately indicated by a lowering of gas flow rate or pressure increase in the inlet piping. The clogged nozzle can then be easily cleaned even during operation by simply connecting it temporarily to a source of high pressure gas, by which the clogging is removed. By attaching blades to the head of the gas-feed unit, the treated material can be thoroughly mixed so that gas can be introduced and evenly dispersed throughout even exceptionally cohesive powders.

This invention can be utilized in may cases when classical methods of fluidization fail. It can be used for the fluidization of particulate solids containing a larger proportion of particles with particle sizes under 100 microns which have a considerable cohesion. Such processes are particularly efficient because such fine materials have an exceptionally large specific surface. It insures that no opening in the gas distributing device becomes clogged. A particulate solid can be fluidized by a limited amount of gas when the linear velocity of the gas is just over or even just under the incipient fluidization velocity. The mixing effect of the revolving gas streams and of mixer blades, when such blades are attached to the rotating nozzles, aids in keeping the material in movement.

The method and device according to this invention can, however, be utilized even in cases when the particulate solid can be fluidized by normal non-movable grids, since fixed grids for fluidized beds of a large cross-section can be more expensive than the device according to this invention to fit the same area.

A typical example of the utilization of the invention is for reactors for the direct synthesis of methyl- or phenyl-chlorosilanes from silicon and methylchloride or silicon and chlorobenzene. The reason is that it is very advantageous to conduct this synthesis with very small particles of silicon, most conveniently with particles in the size range under 60 microns, because then high conversions can be obtained and only a small amount of unreacted methylchloride or chlorobenzene has to be recirculated .

BRIEF DESCRIPTION OF THE DRAWINGS

The enclosed drawings show a preferred embodiment of a device for fluidizing powders according to this invention, wherein:

FIG. 1 is a view in vertical section through a rotary gas-feed unit independently fitted in bearings at the bottom of a vessel;

FIG. 2 is a view in plan of a non-symmetrical system of nozzles according to the invention;

FIG. 3 is a view in vertical section through a gas-feed unit to which a mixer is attached; and

FIG. 4 is a view in plan of the unit of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment of FIG. 1 a gas-feed unit 2 is mounted in the bottom 1 of a vertical vessel in such a way that the axis of the gas-feed unit is perpendicular to the bottom of the vessel. The gas-feed unit 2 is journalled in an upper bearing 3 and a lower bearing 3', and is provided with two parallel longitudinal passages 4, 4' for gas through-flow. At unequal distances from the bottom 1 of the vessel passages 4, 4' bend at right angles and are connected to sources of gas under pressure by means of packings 8, 8' and 8". In the head of the gas-feed unit 2, which extends above the bottom 1 of the vessel, the openings of the channels 4, 4' for gas through-flow are connected at right angles to tube extensions 5, 5' and these terminate in nozzles 6, 6'. Tube extensions 5, 5' are unequal in length and are inclined downwardly at the ends at an angle .alpha. of 30.degree. in a radial direction. The gas-feed unit 2 is sealed in the bottom 1 of the vessel by a packing 9. The gas-feed unit 2 is rotated by a prime mover such as an electric motor (not shown) which drives a pulley at the bottom of the unit 2 through a V-belt, also not shown.

FIG. 2 shows a non-symmetrical system of two nozzles 6, 6' at the end of tube extensions 5, 5' connected to the head of the gas-feed unit 2. The lengths of the tube extensions 5, 5' differ, and are deflected at the ends so that the nozzles 6, 6' at the ends of these tube extensions 5, 5' form an angle .beta. of 45' in the plan-view plane with the radial direction in the clockwise direction of rotation indicated by the curved arrow.

In FIGS. 3 and 4 there is shown a gas-feed unit 2 journalled in bearings 3, 3' in the bottom of the vessel. The gas-feed unit 2 is provided by only one channel 4 for gas through-flow through only one tube extension 5 and only one nozzle 6. Mixer blades 7, 7' extending almost to the bottom of the vessel 1 are fixed to the head of the rotating gas-feed unit 2. As indicated by the arrows in FIGS. 3 and 4, the gas-feed unit rotates clockwise; the mixer blades 7, 7' are inclined in such direction that they throw the powder upwardly.

Mixer blades such as those shown in FIGS. 3 and 4 can also be attached to the embodiments of gas-feed units shown in FIGS. 1 and 2.

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

Claims

What is claimed is:

1. Apparatus for fluidizing powders, comprising a vertical vessel, a rotatable gas-feed unit journalled in bearings in the bottom of the vessel, means for drivingly rotating the gas-feed unit, a passage in the gas-feed unit for gas through flow independently connected to a source of gas under pressure, the gas-feed unit being provided within the vessel with a tube extension having a nozzle, the longitudinal axis of the nozzle forming an angle of from 0 to + 120.degree. in the direction of rotation of the nozzle with respect to the radial direction passing through the nozzle opening.

2. Apparatus according to claim 1, wherein the gas-feed unit has a plurality of tube extensions having nozzles, the distances between each of said nozzles and the axis of rotation of the gas-feed unit being substantially different.

3. Apparatus according to claim 1, wherein the longitudinal axis of the nozzle is inclined downwardly toward the bottom of the vessel at a second angle with respect to the radial direction passing through the nozzle opening in the range 0 to + 60.degree..

4. Apparatus according to claim 1, wherein at least two gas-feed units are disposed in the vessel.

5. Apparatus according to claim 1, wherein the gas-feed unit is provided with at least two passages for gas through-flow, each passage being connected to an independent source of gas.

6. Apparatus according to claim 1, wherein the passage for gas through-flow is provided with a plurality of tube extensions with nozzles.

7. Apparatus according to claim 1, comprising a mixer blade attached to the gas-feed unit and rotatable therewith.