DK153104B - SPRAY DRYING APPLIANCE OF A FLUID - Google Patents

Description

DK 153104 B

The invention relates to an apparatus of the kind specified in the preamble of the claim for spray drying of a liquid. Such appliances are known in many different embodiments and especially intended for the preparation of dry milk, so-called milk powder.

In appliances of this type, intentional powder particles are often formed with some moisture, which is important for a subsequent drying process. However, powder particles with a certain moisture content tend to adhere to the wall of the lower conical shaft portion and form coatings thereon. This has been attempted to avoid this by imparting a rotary movement in the shaft to the drying gas by supplying the drying gas in a tangential direction. This drying gas is then blown into the conical shaft.

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the central part of the portion, however, which requires a central position located in the lower part of the shaft, the flow obstructing body which causes disturbances in the flow.

The invention aims at avoiding dusting of powder particles in the tapered lower part of the shaft in a more convenient and efficient manner, which is achieved by the characterizing part of the patent claim. Namely, by combining these features, the drying process is accomplished in a central region of the spray-drying shaft, while the flushing gas flows around this central drying region on a helical flow path, thereby preventing the powder particles from adhering to the wall of the shaft.

Conveniently, the openings for supplying flushing gas are designed and have such a direction that the flushing gas from the openings flows along the conical wall of the shaft wall.

When treating a thermoplastic material, the air should have a cooling effect, while in other cases the air should have a drying effect. As a rule, the spray dryer according to the invention is therefore provided with means for conditioning this air.

In the following, the invention is explained in more detail with reference to the drawing, in which fig. 1 is a vertical section through an embodiment of an atomizer dryer according to the invention; and FIG. 2 and 3 show two different embodiments of a detail of FIG. First

The FIG. 1, a liquid cylindrical column or shaft 1 having a downwardly conical narrowing lower shaft portion 2 having a lower outlet opening 3 through which liquid, partially or completely dried powder can be removed from the apparatus, is shown. The shaft 1 has at the top a top wall 4 with a centrally located inlet 5 known per se with a means for atomizing the liquid.

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that must be dried. The apparatus further has an inlet 5 concentric surrounding ring 6 of downwardly directed inflow openings for supply of dry gas. The drying gas therefore flows concentrically around the inlet 5. In the wall of the conical lower shaft part 2 there are a number of tangentially directed openings 7 which are connected to a pipe 8 for supply of flushing gas, e.g. air supplied by a blower 9. Immediately at the top wall 4, in the cylindrical wall portion of the shaft, there is an outlet opening 10 for removing the waste gas. This aperture 10 communicates with a cyclone separator 11 with a fan 12 for the separation of still fine solids present in the waste gas.

The flow path of the gas in the upper portion of the shaft 1 and its lower tapered portion 2 is indicated by arrows showing that the drying gas passes downwardly into the chamber in the form of a substantially cylindrical drape, thereby drying the atomized liquid droplets from the inlet 5. When the gas has reached at a certain level in the tapered portion 2 of the shaft, the gas flows radially outward to all sides and then into an arc upwards, after which the gas passes out through the outlet opening 10. The flushing gas is introduced into the shaft at a flow rate of more than 10 m / sec. and approximately half the height of the tapered shaft portion 2. This gas flows turbulently upwardly on a helical flow path immediately within the wall of the shaft and also passes out through the opening 10. The added rinsing gas prevents the powder particles from contacting the inside of the conical shaft portion 2 wall so that the powder will not be able to adhere to the the wall and make embossings on this one. In this way, the material outlet opening 3 is kept open so that the apparatus can operate continuously for a long time.

FIG. 2 and 3 show the tangentially directed apertures 7 for supplying the flushing gas in another embodiment. In FIG. 1, the supply pipe 8 opens into a ring channel 13 surrounding the conical lower part 2 of the shaft, with which the openings 7 are connected. In FIG. 2, the entire downwardly tapered lower shaft portion 2 has a cylindrical middle wall portion 14 enclosed in an annular housing 15. The apertures 7 are located in the cylindrical wall portion so that the inner channel 15

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the openings are easily connected to the interior of the tapered lower shaft.

FIG. 3 shows a modified version with interruptions in the wall of the tapered shaft part 2 * to form tangential apertures 7..

In all three embodiments, the openings 7 are located in one and the same level. However, these openings 7 for supplying rinsing air may also be located at different heights in the wall of the lower shaft portion 2 *. In any case, the openings 7 should be located in an area of the wall located at least one-fifth of the overall height of the shaft portion 2 corresponding to the upper end of the tapered shaft portion, the shaft portion having its largest diameter.

The nature of the rinsing air, i.e. its temperature and moisture content should be so adapted to the properties of the powder particles that, when treating particles of a thermoplastic material, a cooling effect or a drying effect is obtained if the powder particles are moist. The sky air supply openings 7 do not necessarily have to be exactly tangentially aligned as it flows in through these passing rinse air along the inside of the conical shaft wall to obtain the intended "air sweep effect" along the wall.

Claims (1)

GB 153104B Patent claim: Apparatus for spray drying a liquid, e.g. milk, and formed as a substantially cylindrical shaft (1) having at least one waste gas upper outlet (10), a downwardly conical narrowing lower shaft portion (2) having a plurality of tangentially directed openings (7) and a lower outlet opening (3) ) for powder particles formed during the drying of the liquid; a top wall (4) with a central inlet (5) for the liquid and a liquid inlet (5) concentric surrounding ring (6) of downwardly directed inlet openings for drying air, and with a fan (9) for providing a gas flow passing through the shaft, characterized in that the tangentially directed openings (7) in the wall of the tapered lower shaft part (2) are connected to the pressure side of the blower (9) for introducing a flushing gas stream which flows under pressure on a helical path along the inside of the shaft and together with the drying air passing out through the outflow opening (s) (10) in the vicinity of the top wall (4).