GB2121153A

GB2121153A - Process and apparatus for drying powdery materials

Info

Publication number: GB2121153A
Application number: GB08313500A
Authority: GB
Inventors: Janetti Claudio Bianchi
Original assignee: ITALIANA ESSICCATOI
Current assignee: ITALIANA ESSICCATOI
Priority date: 1982-06-03
Filing date: 1983-05-16
Publication date: 1983-12-14
Also published as: CH654904A5; GB8313500D0; DK157259C; DK157259B; IT1151577B; ES522466A0; FR2528159A1; DE3318313A1; DK250183D0; DK250183A; ES8404044A1; DE3318313C2; IT8221689A0; FR2528159B1

Abstract

Drying air which crosses supporting screen (E) for the material is given a whirling movement up to entrain dust particles with a helical ascending spiral trend, along the walls of drying chamber B overlying said screen, thereby lengthening the contact time of the material granules with the air. After the dried material has reached the top of chamber (B), it re-descends along the axis of said chamber (B) and may be removed and selected by suction and collecting means (24-28), the position of which is adjustable in height. <IMAGE>

Description

SPECIFICATION Process and apparatus for drying powdery materials This invention relates to a process for drying powdery materials and the related equipment embodying said procedure.

Continuous type dryers for powdery materials in fluid beds have long been known; said dryers, by exploiting the velocity of the drying air and the reduction in weight of the single dust particles as a result of moisture loss during treatment, continuously transport the dried material to the exterior, to be successively collected.

The efficiency of this procedure is however quite low and does not permit selection of the dried material by different particle sizes.

The purpose of this invention is to provide a drying procedure for powdery materials included in fluid bed and to provide an apparatus apt to permit both efficient drying and collection of the product according to particle fineness, as well as recovery and disposal of the agglomerated heavier parts.

Unlike dryers in which the air passes through the fluid bed supporting screen for the material in a vertical direction or low ascensonal turbulence direction, in the process according to this invention a vortical motion is imparted to the air stream which transports the material with ascending helical motion, into the peripheral zone of the drying chamber, located above the screen.

In this manner, the material remains in contact with the air for a longer time, to achieve an optimum degree of drying and, in falling back toward the axis of said housing in a counter current flow, the material can be collected and aspirated by suitable means to be successively discharged to the exterior.

In alternative embodiments, the drying chamber may have either substantially the same diameter as the underlying chamber where the helical flow of the blown air is formed, or be characterized by a housing of greater diameter to further improve performance as will be explained hereinafter. A suitable mobility of the collecting means in the vertical sense affords the possibility to select the material according to different particles sizes, while, to complete the plant.

auxiliary mixing means for the fluidized bed and for grinding and/or collecting the material agglomerates are provided, to improve the efficiency of the process.

The invention will now be described in conjunction with the annexed drawings which illustrate, by way of example only, the equipment for drying dust laden materials. In the drawings: Figure 1 is a schematic cross sectional view of drying equipment according to the invention.

Figure 2 is a variant of the embodiment of the drying chamber illustrated in Figure 1.

Figure 3 and 4 are respectively cross sectional and plan views of the screen of the apparatus shown in Figures 1 and 2.

In Figure 1, letter A identifies the apparatus which consists of a cylindrical shell or housing 2, divided into two pneumatic chambers being separated by a supporting screen E for the material to be dried, which is loaded through a hopper 4.

Lower chamber C is provided with a conical bottom or diaphragm 6, and a fan 8 delivers an air stream into said chamber C through a nozzle 9, directed tangentially with respect to the inside wall of the chamber.

Above screen E, a horizontal arm 10 rotates on a shaft 12 driven by a gear 14. The arm 10 is provided with means such as skimmer blades 16 apt to remove the discharge to the exterior, through devices 18, the heavier particles and the refuse which remain on the fluidized bed surface, and other means, such as rollers or scrapers 20, to crush agglomerated materials deposited on the surface of the screen.

Suction pipe 22 is located on the axis of drying chamber B; a telescoping sleeve 24, apt to travel vertically by means of a toothed rack 26 actuated through a pinion gear driven from the exterior by a motor 27, in associated with said sleeve.

Sleeve 24 is provided with a truncated cone shaped cap 28 associated, in turn, with a deviating diaphragm or baffle 30, the opening of which is suitably spaced from that of cap 28 by adjustable means 32, through which the possiblity is afforded to vary the distance between the edges of said elements.

Suction pipe 22 is connected with cyclone 52 and the outlet of the latter is connected in turn with bag filter 54 to collect and separate the powdery material entrained in the air stream originating from said cyclone, and not retained by the latter. Said apparatus 52 and 54 can be utilized either simultaneously or singly, and this in relation to requirements of the material being treated.

In Figures 3 and 4, screen E, of the known type consists of a set of concentric lamellae a, b, all identically formed with a plane tract 40 and arranged in such a manner that the upwardly folded edge of each overlaps with opposite edge 44 folded downward. In this way, the moist bed of material is supported by the screen and the air blown into chamber C passes through the fissures formed by the edges of the pairs of lamellae and cooperates to cause the air stream to assume the desired rotary motion. The central part 50 of the screen (see also Fig. 1) is blind and therefore impermeable to the air flow for a circular surface of diameter coinciding substantially with that of baffle or diaphragm 30, so as to impart the required ascending motion to the air in chamber B according to a spiral trajectory within the peripheral zone of the chamber itself.

Based on the above, it is clear that the objects of the invention, intended to achieve a high efficiency of the drying plant. are obtained in full, as the principle of imparting to the air a vortical spiral motion causes an increase in the path travelled by the particles entrained in the air stream with consequent increase of the active drying time.

An advantageous variant which provides a still further increase in the drying time, hence overall efficiency, is shown in Figure 2.

According to this variant, which differs from the plant shown in Figure 1 where the diameter of chamber B is equal to that of chamber C (consequently to screen E), the diameter of chamber B in its top part, is even double with respect to the preceeding one, as it is connected to the level of the plane of the screen by an inverted truncated cone shaped fitting 3 apt to provide a reverse cyclonic flow for the drying air.

The air issuing from the layer of powdery material, in expanding, slows down its ascending rotary motion increasing still further the contact time of the material entrained, whilst the principle of collecting, the dry particles in the central zone of housing B remains unaltered.

The invention thus received may be modified and varied, for example as regards both overall sizing of the plant and in regard to its parts as a function of the type of dust to be treated, as well as the material used for construction, but without departing from the scope of the invention.

Claims

1. Process for drying and possibly selecting powdery materials, by means of an air current under pressure, blown through a fluid bed of said powdery material, characterized by imparting to the fluid air stream carrying the material to be dried an ascending helical motion and successively reversing the flow at least once in a centripetal direction by 1800 to form two streams in countercurrent, and in removing the dried material substantially at the axis of the helical flow formed by the air.

2. Process according to claim 1, characterized in that a rotary ascending motion is parted to the drying air and in that the rotating air flow, at a suitable speed, is directed through the material to be dried to remove from the material being dried, the particle sizes required, and in separating, successively the dried material from the removing air stream.

3. Process according to claims 1 and 2, characterized in that the air issuing from the layer of powdery material is caused to expand so as to slow down the rotary ascending motion of the dried material carried in the air stream.

4. Apparatus for carrying out the process according to any one of claims 1 to 3, in which a pressurized air generator conveys an air stream through a supporting screen (E) for the material to be dried, characterized by means (6, 9) apt to impart a helical ascending motion to the powdery material carried in the air under pressure; by deviating means (28, 30) conveniently spaced from said prime means to deviate by 1800 and centripetally the flow of the powdery material and by means (24, 28) placed substantially on the helical flow axis of the air to take up and remove the desired material from said stream and convey it to a collecting tank.

5. Apparatus according to claim 4 characterized by a housing (2), subdivided in two overlapping pneumatic chambers (B, C) separated from each other by supporting screen (E) for the material to be dried and in the bottom chamber (C) of which outlets at least one nozzle (9) for the air under pressure, said nozzle being suitably inclined with respect to the axis of said container to blow an ascending helical air stream through the material to be dried supported on said screen, and which entrains with it at least a part of said material; at least two deflecting baffles (6, 30) coaxial with the axis of the said container and spaced from each other in a manner such that the lower one (6) is located on the bottom of said container and the top one (30) suitably spaced above the supporting screen and associated with a duct (22-24) for removing and conveying of the dried material provided with adjustable means (26, 27) to vary its position within top chamber B, the inlet opening 28 of which is suitably spaced from the bottom element formed by the last deviating baffle diaphragm (3) and the outlet of which communicates with the collecting tank for the dried material.

6. Apparatus according to claims 4 and 5 characterized in that inlet aperture (24) of the take up duct for the dried material is provided with a truncated cone shaped cap (28) coaxial with the cylindrical housing, while supporting screen (E) for the dried material being treated is provided, in alignment with the aperture of said cap, with a corresponding zone (50) which is impermeable to the passage of air, at the positoin of a conical diaphragm (30), the axis of which coincides with that of the cylindrical container while its opening is aligned and spaced suitably from the opening of take up cap (28) for the dried material.

7. Apparatus according to claim 6, characterized in that conical diaphragm (30) is retained by the end of take up cap (28) for the dried material through adjustable elements (32) which make it possible to vary the distance between the edges of said conical diaphragm and take up cap.

8. Apparatus according to any one of claims 4 to 7, characterized by mixing devices above screen (E) comprising an arm (10), rotatable horizontally by means of a vertical axle (12) driven by a motor gear reducer assembly (14), to which arm are connected skimmer blades (16) adjusted at a convenient distance from screen (E) to remove from the surface of the fluid bed any agglomerates or reject materials, and scraper means (20) to crush said conglomerated material being dried.

9. Apparatus according to any one of claims 4 to 8 characterized in that the material, dried and aspirated through duct (22) is further selected in 'series by a cyclone (52) and/orfurtherfiltered by a bag filter (54).

1 0. Apparatus according to any one of claims 4 to 9, characterized in that chamber (B) above screen (E) consists of a top cylindrical part (2a) of diameter greater than that of chamber (C), to which it is connected through an inverted truncated cone fitting (3).

11. Process for drying and possibly selecting powdery materials, substantially as hereinbefore described with reference to the accompanying drawings.

12. Apparatus for drying and possibly selecting powdery materials, substantially as hereinbefore described with reference to the accompanying drawings.