US3780445A

US3780445A - Cleansing device for powder processing apparatuses

Info

Publication number: US3780445A
Application number: US00241031A
Authority: US
Inventors: O Hansen
Original assignee: Niro Atomizer AS
Current assignee: GEA Process Engineering AS
Priority date: 1971-04-15
Filing date: 1972-04-04
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25
Also published as: GB1381322A; DK124901C; DK124901B; IT954643B; DE2217496A1

Abstract

A cleansing device for cleaning perforated supporting plates in powder processing apparatuses, in which a flow of gas passes a perforated supporting plate more than one time or passes a number of perforated supporting plates for fluidizing a layer of powder on the plate or plates, comprising an arm parallel to the underside of the plate to be cleaned, said arm being provided with a number of gas nozzles connected with means for producing jets of gas shooting upwards against the underside, said arm being displaceable in a plane parallel to the underside of the plate in question.

Description

Unlted States Patent 11 1 1 1 3,780,445 Hansen Dec. 25, 1973 [54] CLEANSING DEVICE FOR POWDER 3,l |9,605 1/1964 Berz 34/57 D X PROCESSING APPARATUSES 3,140,864 7/1964 Lellep... 432/58 2,761,769 9/1956 Elder 34/57 D X Inventor: Ove Emll Hansen, Vaerlose, 2,412,057 12/1946 Nichols 432/58 D nma k e FOREIGN PATENTS OR APPLICATIONS [73] Assigme: Aktleselskabet Ammizer 64 95s 11/1949 Netherlands 34/57 1) Gladsaxevej, Sorborg, Germany [22] Filed: Apr. 4, 1972 Primary Examiner-William F. ODea Assistant ExaminerWilliam C. Anderson [21] Appl' 24l031 AttorneyRichard C. Sughrue et al.

[30] Foreign Application Priority Data [57] ABSTRACT Apr. 15, 1971 Denmark 1798/71 A cleansing device for cleaning perforated pp g 521 US. Cl. 34/57 1), 252/010. 17 Plates PWder Processmg apparatusfs whch a flow of gas passes a perforated supportmg plate more [51] Int. Cl. F26!) 17/10 than one time or asses a number of erforatedlsu 58 Field of Search 34/57 R, 57 A, 57 D; P P P portmg plates for flu1d1z1ng a layer of powder on the 432/58, 302/56, 259/8, DIG. l7

plate or plates, compnsmg an arm parallel to the un- 56] References Cited derside of the plate to be cleaned, said arm being prov1ded w1th a number of gas nozzles connected w1th UNITED STATES PATENTS means for producing jets of gas shooting upwards 3,423,843 1/1969 Laguilharre 34/57 D against the underside, aid arm being displaceable in a L465 1 H1968 shil'al 3457 D X plane parallel to the underside of the plate in question 3,298,792 1/1967 Di Drusco 34/57 A X 3,305,940 2/1967 lsler 432/58 X 7 Claims, 5 Drawing Figures PATENTEI] DEC? 5 3 3,780,4 1 5 SHEEI 5 OF 5 CLEANSING DEVICE FOR POWDER PROCESSING APPARATUSES The present invention relates to a cleansing device for powder processing apparatuses in which one or several perforated supporting plates for powder are provided, as well as means for producing a flow of gas through the perforations of the supporting plate or plates for fluidizing a layer of powder present on the plate or plates and where the device is arranged in such a way that the path of one and the same volume of gas passes more than once through a supporting plate.

Once the gas has passed through the layer of powder, it will entrain a certain amount of fine particles or dust which were present in the powder and when the gas has to pass through a supporting plate more than once, it will, by the time a second or subsequent passage is completed, be carrying along with it so much dust that a considerable danger of the apertures provided in the supporting plates being rapidly blocked up arises.

Such a multiple passing takes place in apparatuses fitted with several supporting plates that are passed through successively by the same gas volume as well as in apparatuses that are equipped with only a single supporting plate in which the volume of gas employed is recirculated.

It certainly is possible in the latter case to carry out a cleaning of the gas without encountering great difficulties but, on the one hand, this calls for rather expensive equipment and, on the other hand, it entails a heat loss in cases where the operation is effected while utilizing a gas that has a certain elevated temperature. In the first-mentioned case, however, especially if the plates are mounted on top of each other inside one and the same chamber, it will generally and to all intents and purposes be impossible to clean the gas present between the plates.

The blocking up of the perforations provided in the plates results relatively quickly in a significant reduction in the efficiency of the apparatus, for which reason a frequent stopping and cleaning of the apparatus becomes necessary.

It is the object of the present invention to obviate these difficulties which, in the device according to the invention, is done in that, on the underside of a supporting plate which is intersected by the path of the gas flow at a point which, taken in the direction of the gas flow, is situated past a point where the path has already intersected a supporting plate, an arm located parallel to the underside is mounted fitted with a plurality of gas nozzles which are directed against the underside and connected with means for producing jets of gas from the nozzles shooting upwards against the underside, which arm is displaceable in a plane parallel to the underside and connected with means for moving it in this plane. 1

Due to the jets of gas thus produced, the underside of the plate is swept absolutely clean of powder deposits so that a continuous cleaning of the plate occurs while the apparatus is in operation.

As is known, with devices of the type dealt with here it is important that the speed of the gas passing through the perforations is kept reasonably constant at a specific value. In theory, the gas jets will bring about an increase in the total speed of the gas flow at the time when they pass a number of holes, in practice, however, it has been found that this does not result in any deleterious effect since the volume of gas that is needed for the cleansing function can amount to a very small fraction of the total gas volume, added to which is the circumstance that the deposited dust particles do not lodge themselves in the apertures proper for so long as it is only a question of a beginning deposition, because this is produced on the underside of the plate around the apertures so that there is no call for a blowing through operation but only a blowing away of the deposited dust particles.

The nozzles may thus with advantage be directed obliquely against the underside and it will therefore be possible to dimension the perforations and nozzles as well as the means for producing the flows of gas in such a way that the gas flows originating from a nozzle in the immediate proximity of the underside of the supporting plate have a speed exeeding the speed of the fluidizing gas flow through the perforations by several times.

When the device is constructed with a supporting plate of circular shape it is advantageous, according to the invention, for the arms to be mounted underneath the plate and pivotably around an axis which is at right angles to the plate through its centre. If, however, the supporting plate is of an elongated, rectangular shape, then it is most advantageous for the arms to be mounted perpendicularly on the longitudinal extension of the plate and displaceable perpendicularly in relation to itself in a reciprocating direction across the entire length of the plate.

In both instances it is of advantage for the arm to be connected to means whereby it becomes possible to move it at such a speed that the underside of the supporting plate is swept by cleaning gas several times per minute.

Below, the invention is described in greater detail with reference to the accompanying drawings, in which HO. 1 shows an embodiment of an apparatus with a cleansing device according to the invention seen in side elevation and, partly, in axial section,

FIG. 2 shows a detail of the item shown in FIG. 1 but on a larger scale,

FIG. 3 shows a diagrammatical illustration of a modified embodiment of the device according to FIG. 1, and

FIGS. 4 and 5 show a modified embodiment of the cleansing device according to the invention seen in a plan view and in an end elevation.

FlG.1 shows, seen diagrammatically in side elevation and, partly, in axial section, a processing apparatus for processing powder with a gas in a fluidized layer of powder. The gas may, for example, be air for producing a secondary drying of the powder or any other type of gas as, for instance, nitrogen, all depending upon the type of powder in question and the processing it is to undergo in the fluidized layer.

The apparatus comprises a sealed chamber having an upper, cylindrical portion 1 and a lower, conical portion 2, as well as a ceiling 3 which seals the chamber at the top.

Located lowermost in chamber portion 1, a perforated plate 4 is mounted on which the fluidized layer of powder which is supplied through a feeder pipe 5 is formed with the aid of gas flowing through from below which is fed via a gas intake 6 in the conical portion 2.

To a carrier 7 secured to the top of chamber portion 1 and connected to ceiling 3, a spiral guiding wall 8 is fastened which extends down to the perforated plate 4 in the form of a vertical, spiral wall whereby, from within and to the outside, a spiral path is formed for the fluidized powder so that it is able to move from the inside, from powder inlet 5 and to the outside, to a powder outlet pipe 9, whose mouth is situated a distance above the perforated plate 4 and which, thereby, determines a certain layer thickness of the fluidized layer.

An outlet pipe stub 11 for processing gas is fitted in ceiling 3.

As is shown diagrammatically in the Figure, the discharge gas 12 is forced through a cyclone l3 and a heater 14 back into the gas intake 6.

A part of the powder entrained by the discharge gas is separated in cyclone 13, however, a considerable amount of dust will be left behind in the gas which is reintroduced through intake 6, which may involve a risk of powder depositing on the underside of perforated plate 4 and, thereby, a complete or partial blocking up of the holes in it thus considerably reducing the effectiveness of the apparatus.

In order to prevent this from happening, a cleansing device according to the invention is incorporated which consists of a pipe 15 that is mounted below the perforated plate a short distance from it and is equipped with a plurality of nozzles 16 that are directed obliquely upwards against the underside plate 4. Pipe 15 is secured to a hollow shaft 17 which is pivotably and coaxially journalled in the conical portion 2 in a bearing 18 and which is driven by means of a driving motor that may, for example, be an oil motor.

Pipe 15 with shaft 17 and bearing 18 are shown more clearly in FIG. 2 in that the bearing surrounds a space 20 airtightly surrounding shaft 17, which space communicates with a gas inlet 21 while shaft 17, outside this space, has a plurality of apertures 21 by means of which communication is established between space 20 and the inside of hollow shaft 17 and, thereby, likewise communication between inlet 21 and nozzles 16.

Through inlet 21, gas is led under pressure so that a plurality of gas jets are directed through nozzles 16 obliquely upwards against the underside of plate 4, while pipe 15 rotates and thereby sweeps the entire plate 4. Powder deposits that are beginning to form are thereby blown away from the underside of plate 4 and the risk of the holes in it becoming blocked up is eliminated.

As a rule, the gas which is supplied via inlet 21 should be of the same type as the gas that is supplied via intake 6 so as to form the fluidized layer.

Moreover, the gas should be fed under considerable pressure so that a sufficiently high outflow speed via the jets may be achieved, however, on account of the relatively small area taken up by the nozzles as compared to the area occupied by the apertures of the perforated plate, only a small volume of gas is required in comparison with the one that brings about the fluidization and this circumstance, in connection with the nozzles being directed obliquely against the underside of the plate, results in the volume of gas being discharged via nozzles 16 while having, to all intents and purposes, no influence on the fluidization process.

FIG. 3 shows diagrammatically an embodiment in which no recirculation of the processing gas is utilized, which gas in consequence will generally be air.

However, in this embodiment, two

perforated plates

25 and 26 are provided and the powder is first conveyed down onto plate 25 and, from there, to plate 26 located underneath while the processing gas flows in the opposite direction and thus first passes through plate 26 and, subsequently, through plate 25.

Since the gas, prior to arriving on plate 25, has passed the fluidized layer of powder present on plate 26, it will entrain a considerable amount of fine powder and, consequently, present the same risk of blocking up the holes in plate 25 as in the case where recirculation of the processing gas is employed.

For this reason, also in this apparatus, a cleansing device according to the invention has been incorporated constructed exactly as described in connection with FIGS. 1 and 2 and mounted underneath the topmost plate 25.'So far as plate 26 is concerned, no cleansing device has been provided as the air underneath this plate has not passed any layer of powder yet.

In connection with the construction shown in FIG. 3, a number of dimensions advantageous in practice will be stated below.

The cleaning arms are provided with nozzles or holes whose diameter is 1 mm and which number 40-100 per meter. A cleaning air pressure, that is to say a pressure drop of 1.5-3 atmospheres is applied above the nozzle. If, for instance, the number of holes is 50 per meter of arm, a cleaning air volume of 0.5 to 3 kg/h per hole is obtained, i.e., 25-150 kg/h per meter of arm.

The number of revolutions of the arm may be between 4-100 revolutions per hour.

An area of 7 m is covered with a total arm length of 3 m.

The cleaning air thus totals 1 1-65 kg/h m If the rate of fluidization is 0.2 m/sec. at C and the air density is calculated to be approximately I kg/m", the fluidization air volume amounts to l X 0.2 X 3,600 X l 720 kg/h m and the volume of cleaning air thus is of the order of magnitude of 1.5-9 percent of the fluidization air volume.

In the embodiments described in the foregoing, the device is circular in cross-section and the perforated plate is circular, for which reason the cleansing arm, in keeping herewith, is rotatingly mounted. However, apparatuses that are rectangular in cross-section also exist which are fitted with rectangular, perforated plates on which the fluidized powder moves from one end of the plate to the other. When the cleansing arm according to the invention is to be employed in such an apparatus then it is necessary for it to be able to move in one of the edge directions of the plate, as a rule, in the longitudinal direction of the plate, an embodiment of this is shown in FIGS. 4 and 5.

The device illustrated in FIGS. 4 and 5 has a perforated plate 30 mounted in a portion 31 of the device that has a rectangular cross-section. Portion 31 is composed of two

sections

32 and 33 which are interconnected by means of angle irons 34 that are secured to the sections so as to form flanges on them and, by their being assembled, perforated plate 30 is fixed between angle irons 34.

In this case, too, the cleansing arm consists of a pipe 35 provided with nozzles or holes 36, through which the cleaning gas is able to escape upwards against the underside of the perforated plate 30. This pipe is fitted with a shaft pin 37 in each end on which a wheel 38 is journalled and this wheel may run on rails 39 which are secured to the inside of section 32.

The supply of cleaning gas to pipe 35 is effected via a flexible hose 40, as appears from FIG. 4.

Since the entire underside of perforated plate 30 has to be swept by the cleaning gas, pipe 35 is made to run forward and backward with wheels 38 on rails 39 by means of a telescopic rod which, in the embodiment shown, consists of three pieces of

tubing

41, 42 and 43, as well as a rod 44, all of which are telescopically connected. Tubing 41 is sealed at its outermost end and has an inlet pipe stub 45 for pressure fluid. Tubing 41 thus acts as a cylinder and rod 44 as a piston, while tubings 42 and 43 act as telescopic extension pieces of the cylinder. In this way it is possible for pipe 35, which is connected to rod 44, to be moved forward and backward underneath perforated plate 30, e.g., 4-100 times per hour.

The processing gas is introduced into the device via an intake pipe stub 46 and removed at the top via and outlet pipe stub (not shown).

The device is intended to use recirculated processing gas in a manner similar to the one shown in FIG. 1.

In a device constructed in correspondance to the one shown in FIGS. 3 and 4, there may, besides the perforated plate 30 shown, be fitted one or several additional plates in such a way that the powder is able to move across successive plates.

In accordance with the features described in connection with FIG. 3, a cleansing device for the lowermost plates can be dis-pensed with in the case where the processing gas happens to be air.

The need for cleaning may vary considerably all depending on the type of materials undergoing treatment since the formation of deposits depends, on the one hand, on the properties of the material and, on the other hand, on the quantity of dust particles entrained by the fluidization gas. In such cases where only a minor cleansing effect is required, it will be advantageous according to the invention for the cleansing device to be constructed with means for intermittently supplying the cleaning gas so that the cleaning operation may be effected during certain periods and discontinued in others. By way of example, the cleaning periods may have a duration of minutes and the intervening periods in which no cleaning takes place may likewise have a duration of 10 minutes, they may, however, be of varying length depending on the circumstances.

The volumes of air per hour as stated in the foregoing refer, in this case only, to the condition during those periods when cleaning air is supplied and must, therefore, not be calculated as average values for those periods and the intervening periods when no cleaning air arrives.

What is claimed is:

1. In a cleansing device for powder processing apparatuses including at least one perforated supporting plate, and means for producing a flow of gas through the perforations of the supporting plate for fluidizing a layer of powder present on the plate, the device being arranged such that the same volume of gas passes more than once through the supporting plate, the improvements characterized in that on the underside of the supporting plate which is intersected by the path of the gas flow at a point which, taken in the direction of the gas flow, is situated past a point where the path has already intersected the supporting plate, an arm is mounted parallel to the underside and has a plurality of gas nozzles directed against the underside, means connected to the arm for producing jets of gas from the nozzles shooting upwards against the underside, and means connected to the arm for moving it in a plane parallel to the underside.

2. A cleansing device as claimed in claim 1, wherein the means for producing the fluidizing flow of gas and the means for producing the flow of gas through the nozzles are dimensioned such that the latter gas flow volume per unit of time is between 2 and 8% of the former gas flow volume per unit of time.

3. A cleansing device as claimed in claim 1, wherein the nozzles are directed obliquely against the underside.

4. A cleansing device as claimed in claim 1, wherein the supporting plate is circular in shape and the arm is pivotably mounted underneath the plate for rotation around an axis intersecting the center of the plate at a right angle.

5. A cleansing device as claimed in claim 1, wherein the supporting plate is elongated and rectangular, and the arm is mounted perpendicular to the longitudinal extension of the plate and is displaceable perpendicular to itself in a reciprocating direction across the entire length of the plate.

6. A cleansing device as claimed in claim 4, wherein the means for moving the arm operates at such a speed that the underside of the supporting plate is swept several times per minute.

7. A cleansing device as claimed in 1, further comprising means for intermittently supplying cleaning gas.