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Publication numberUS3646689 A
Publication typeGrant
Publication dateMar 7, 1972
Filing dateSep 11, 1970
Priority dateSep 17, 1969
Also published asDE1946997A1
Publication numberUS 3646689 A, US 3646689A, US-A-3646689, US3646689 A, US3646689A
InventorsHentzschel Wolfgang, Kuchenthal Gunther
Original AssigneeWerner & Pfleiderer
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Continually operating fluidized bed dryer for drying loose material
US 3646689 A
Abstract
A continuously operating fluidized bed dryer for loose material such as granulated material comprises a housing in which the fluidized bed is generated by feeding the material into the housing and fluidizing the same by a flow of pressurized air directed upon the material in the housing. Two or more meshing conveyor screws are rotatably mounted in the housing substantially occupying the space therein within which the fluidized bed is generated. The meshing turns or windings of the screws define a plurality of individual fluidizing chambers by which the material fed into the housing at the intake end thereof is conveyed to the discharge end of the housing.
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n Unite States Qatent 1151 3,646,689

I Kuchenthal et al. Mar. 7, 1972 [54] CONTINUALLY OPERATING 2,444,383 6/1948 FLUIDIZED BED DRYER-FOR DRYING 1;"

LOOSE MATERIAL 3,118,744 1/1964 [72] Inventors: Gunther Kuchenthal, Ludwigsburg-Pflug- 3,425,640 2/1969 felden; Wolfgang .Hentzschel, Stuttgart- 3,452,864 7/1969 7 Sud, th of rm y 3,549,000 12/1970 [73] Assignee: Werner 8: Pfleiderer, Stuttgard-Feuerbach, Germany Primary ExaminerFreder1ck L. Matteson Assistant Examiner-Robert A. Dua [22] led: Sept 1970 Attorney-Plane, Baxley, & Spiecens [21] Appl. No.: 71,547 Y [57] ABSTRACT 30] Foreign Applimfion Priority mm; A continuously operating fluidized bed dryer for loose material such as granulated material comprises a housing in which Sept. 17, 1969 Germany ..P 19 46 997.7 I the fluidized bed is generated by feeding the material into the housing andfluidizing the same by a flow of pressurized air [52] CL I directed upon the material in the housing. Two or more mesh 207/1 ing conveyor screws are rotatably mountedin the housing sub- [51] In. F26, 17/20 stantially occupying the space therein within which the 58] Field ofSearch...............:547l68 174 183 236 571) fluidized bed is generated- The meshingmmsmwindingwl 34/57 B 10, 182; 198/213; 362 29, 50;23 the screws define a plurality of individual fluidizing chambers 7 284; 209/11, 464 by which the material fed into the housing at the intake end thereof is conveyed to the discharge end of the housing. [56] References C ted 8 Claims 2 Drawing Figures UNITED STATES PATENTS CONTINUALLY OPERATING FLUIDIZED BED DRYER FOR DRYING LOOSE MATERIAL The invention relates to a continually operating fluidized bed dryer for drying loose material such as granulated or pulverized material, and more particularly to a fluidized bed dryer of this kind including conveying means in a housing within which the fluidized bed is generated.

BACKGROUND With known continually operating fluidized bed dryers of the general kind above referred to it is not possible, or at least not to a satisfactory extent, to maintain a selected definite dwell time for the material to be dried by the fluidized bed generated in the dryer. Dryers as now conventionally used provide only a limited forcible movement of the material and have thus a more or less broad range of the dwell time for the material to be dried. There are known, for instance, devices equipped with a single conveyor screw located at or near the bottom part of the fluidized bed in the dryer housing.

It has also been found that differently sized particles and variations in the number of particles of a specific size present within a given unit of the material as unavoidably occur in the material, result in the formation of layers or strata in the material which forms the fluidized bed. As a result, conveyance of the strata of material toward the discharge end of the housing occurs at different velocities. Tests have shown that uniform conveyance of stratified material cannot be reliably obtained by a single conveyor screw or similar simple conveyors mounted at or near the bottom of the fluidized bed as generated within the housing of the dryer. Such nonuniform conveyance of the material is due to the free spaces which are left between the conveying means such as the windings of a conveyor screw and outside the screw windings or other conveying means. These free spaces permit the particles to jump part of the conveying means since the movements of particles within the bed are completely at random.

Due to such uncontrollable or only poorly controllable length of the dwell time of the material to be dried, over-heating of sensitive material to be dried can and does occur. Moreover, the dwell time cannot be accurately selected in accordance with the drying requirements of a specific material. As a result, additional drying of the material after it has been discharged from the dryer is often still necessary.

THE INVENTION It is an object of the invention to provide a novel and improved fluidized bed dryer of the general kind above referred to in which the dwell time of the loose material to be dried can be accurately controlled. As a result, a dryer according to the invention has the advantage that the material when discharged from the dryer is fully dried without danger of deterioration of the material by overheating.

Another important object of the invention is to provide a novel and improved fluidized bed dryer of the general kind above referred to in which stratification of the material during the fluidizing operation is effectively avoided thereby assuring that the material is homogeneous when discharged.

SUMMARY OF THE INVENTION The aforepointed out objects, features and advantages, and other objects, features and advantages which will be pointed out hereinafier are obtained by providing in the housing of a fluidized bed dryer of the kind above referred to, conveying means comprising two or more meshing screw conveyors. These conveyor screws are disposed within the space in which the fluidized bed is generated. The meshing turns or windings of the conveyor screws form a plurality of lengthwise aligned fluidizing chambers. The screws have advantageously equal outer diameters and are driven at adjustable rotational speeds.

The dimensions of the screws are preferably so selected that they extend through substantially the entire fluidized bed, the dimensions of which, in turn, are defined by the dimensions and the shape of the housing. It is particularly advantageous to arrange the conveyor screws so that they satisfy the equation: H=(nl )-0+D/2, where H maximal height of the bed layer within the housing;

n= number of conveyor screws;

a= distance of the rotational axes of the screws;

D= the outer diameter of the screws.

In addition to the aforepointed out advantages, a fluidized bed dryer according to the invention offers other important advantages. As is well known, a thick fluidized bed is desirable. Good stabilizatidn of a fluidized bed requires a minimum volume of air in relation to the loss of pressure at the housing bottom through which the pressure air flow is supplied to the housing. If the fluidized bed is comparatively shallow, the pressurized air flow through the bottom of the housing is insufficiently utilized for the actual fluidizing or whirling action. Accordingly, a highly efficient operation of the dryer can be only obtained when the bed has a considerable height or thickness. In addition, better utilization of the airflow with a high or thick bed also results in an increased passage of material through the dryer for an equal dwell time of the material per unit of time.

The use of meshing screw conveyors arranged in accordance with the invention also makes unnecessary the use of specific devices for breaking up lumps, etc., which tend to interfere with the fluidizing action. As is evident, conveyor screws according to the invention will automatically disintegrate any lumps which may be present in the material as it is fed into the dryer.

According to another advantageous aspect of the invention the drive means for the screws are so arranged that the rotational velocity of the screws can be gradually varied. As it is evident, such gradual variations of the rotational speed of the screws permits accurate adjustment of the dwell time in accordance with the requirements of a specific operation.

The invention also provides that the windings of the conveyor screws are formed by helically wound strips such as metal strips. Such strips are wound about a rather thin core shaft suitably secured thereto. The use of screws of this kind reduces the total space occupied by the screws within the fluidized bed, thus correspondingly increasing the space available for the material to be dried without in any way interfering with the fluidizing action.

The fluidized bed according to the invention may be visualized as being formed by a row of individual fluidizing chambers, or as the sum total of several fluidizing actions carried out in the individual fluidizing chambers. Such chambers are formed by the windings of the meshing conveyor screws, as previously described. The rotation of the chambers causes conveyance of the material to be dried toward the discharge end of the housing at a speed controlled by the selected rotational speed of the screws. Tests have shown that when the winding pitch A=0.6D is used, good results are obtained. It has been further found that it is advantageous to arrange the meshing screws so that the flanks of the meshing windings are as close one to another as practical and that the apices of the screw winding extend as closely as possible to the core shaft of the respective other screw. In other words, it is advantageous to operate the screw with tight mutual engagement.

DETAILED DESCRIPTION OF THE DRAWING In the accompanying drawing, a preferred embodiment of the invention is shown by way of illustration and not by way of limitation. In the drawing:

FIG. 1 is an elevational diagrammatic view, partly in section, of a fluidized bed dryer according to the invention; and

FIG. 2 is a fragmentary section takenon line lI-II of FIG. 1.

In the figures, only those components of the dryer are shown as are essential for the understanding of the invention.

Referring now to the figures more in detail, the exemplified fluidized bed dryer comprises two conveyor screws 1. Various types of conventional conveyor screws may be used but it is particularly advantageous to provide screws which as shown have a comparatively thin core shaft 2 about which a strip 20 is spirally or helically wound. The strip may be visualized as being suitably secured to thecore shaft as by welding.

As it is clearly shown, the two screws are in tight mesh with each other and the windings thereof define a plurality of chambers 3 along the lengths of the screws. The individual aligned chambers assure that the entire fluidized bed generated in a housing 15 of the dryer is divided in a plurality of individual fluidizing actions. As is also evident, rotation of the screws will convey material within the housing from an intake or feed end B toward a discharge C.

While only two meshing screws are shown, it should be understood that it is within the concept of the invention to provide three or more superimposed meshing screws.

As it is shown in FIG. 2, the aforereferred to distance a between the rotational axes of the two screws is designated by 4. FIG. 2 also indicates the height or thickness H of the bed within the dryer.

The material to be dried is preferably fed into the dryer via a bucket wheel gate 5 and discharged via a bucket wheel gate 6. Other suitable agitating devices may, of course, be provided at the inlet end and the discharge end of the dryer housing.

Pressurized air is supplied to the dryer via a duct D. The air, after being preferably heated in a suitable conventional heater 7, flows into a distributing chamber 8 and from this chamber into the space of the dryer housing in which the fluidized bed is to be formed, via an apertured bottom wall 9. This bottom wall may be a sieve or it may be a sintered wall; it is only essential that it is sufliciently air pervious.

Both screws are driven by a motor 10, the output speed of which should be visualized as being gradually variable. Variable speed gears or other suitable speed-regulating means are well known and readily available for the purpose; they are not described in detail as they do not constitute part of the invention. As pointed out before, a gradual variation of the rotational speed of the screws permits precise adjustment of the dwell time of the material within the fluidized bed, as the speed of the screws controls the speed with which the material is conveyed and thus the dwell time.

A stilling or calming zone 11 for the pressurized air is provided within the housing above the screws and thus the bed proper. Fine particles as may be carried along by the spent air, that is, by the air flow above the screws are separated from the airflow, for instance by means of a conventional cyclone separator 12 which is connected, preferably tangentially, to chamber 11 by a duct lla. As it is shown and conventional for such separators, the purified air is discharged from the separator through a duct E while the collected particles (the socalled heavies in this case) leave the separator through a duct F. A bucket wheel-type gate 12a or other suitable agitators may be included in the discharge duct F for the heavies as they leave the separator.

Bottom wall 9 through which the airflow generating the fluidized bed within housing passes has, as previously stated, a multitude of apertures. It has been found to be particularly advantageous to arrange these apertures in the form of nozzles slanted toward the discharge end C of the housing. Such orientation of the nozzles imparts to particles of the material and particularly to coarse particles, a movement toward the discharge end; in other words, the slanted airflow through bottom 9 supplements the conveying force provided by screws 1. The generation of such auxiliary conveying force is of particular importance because space portions 13 directly adjacent to bottom 9 are not within the range of the direct conveying action of the screws, as it is clearly shown in F IG. 2. Hence, the conveying force applied to material in spaces 13 tends to be at a minimum.

Theoretically, it would be possible to eliminate the more or less dead spaces 13 by shaping bottom 9 substantially in confonnity with the peripheral outline of lower conveyor screw 1. As stated before, it is desirable to dimension and arrange the conveyor screws so that they extend substantially through the entire space in which the fluidized bed is maintained in housing 15 during operation. However, in actual practice a housing bottom-shaped, that is curved, in conformity with the peripheral outline of the respective conveyor would adversely 5 affect the stability of the fluidized bed to such an extent that the advantage obtained by eliminating spaces 13 is more than nullified.

As it is evident and within the concept of the invention, two or more dryers can be arranged side-by-side and a common stilling or calming zone 11 for all the dryers may be provided in the housing.

While the invention has been described in detail with respect to a certain now preferred example and embodiment of the invention, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. A continuously operating fluidized bed dryer for drying loose material comprising in combination:

a closed housing for generating therein a fluidized bed;

two or more meshing conveyor screws of equal diameter rotatably mounted in the housing in superimposed relationship, said screws having an intake and a discharge end and the meshing windings of said screws defining a plurality of individual fluidizing chambers along the lengths of the screws, said housing including an inlet adjacent to the intake end of the screws for feeding loose material to be dried to the intake end of the screws and an outlet adjacent to the discharge end of the screws for discharging dried material from the housing, said chambers conveying the material from the inlet of the housing to the outlet thereof and fluidizing the material while conveying the same; and a conduit communicating with the housing below said conveyor screws for feeding pressurized air into the housing to generate therein a layer of whirling loose material constituting a fluidizing bed,

said conveyor screws being disposed and dimensioned to extend through substantially the entire space occupied by said bed within the housing and to satisfy the equation:

khr-l )rH-D/Z wherein H is the maximal height of the fluidized bed;

n is the number of conveyor screws;

a is the distance between the rotational axes of the screws;

and

D is the outer diameter of the screws.

2. The dryer according to claim 1 and comprising a second conduit communicating with space within the housing above said conveyor screws for discharging spent air from the housing and particles of material escaping from said chambers and entrained in the air.

3. The dryer according to claim 2 wherein said housing includes above the conveyor screws an air-stilling space, said second conduit communicating with said air-stilling space.

4. The dryer according to claim 2 wherein said second conduit includes a cyclone separator for liberating the spend air from particles entrained therein.

5. The dryer according to claim 1 wherein said conduit communicates with the housing through apertures in the bottom wall of the housing.

6. The dryer according to claim 1 wherein a drive means with gradually variable speed is drivingly coupled to said conveyor screws.

7. The dryer according to claim 1 wherein each of said conveyor screws comprises a shaft having mounted thereon a helically wound strip, said strips defining the windings of the screws.

8. The dryer according to claim 7 wherein the windings of adjacent conveyor screws mesh tightly one with another and have outer diameters extending closely adjacent to the respective shafts.

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US3815255 *Sep 20, 1972Jun 11, 1974Yamato Sanko Mfg LtdFluidized bed dryer
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Classifications
U.S. Classification34/182, 209/11, 198/625, 222/413, 34/580, 34/236, 422/145, 222/238, 222/195, 209/464
International ClassificationF26B3/02, F26B3/092, F26B17/00, F26B17/20
Cooperative ClassificationF26B17/20, F26B3/0923
European ClassificationF26B17/20, F26B3/092B