GB819643A - Method and apparatus for spray-drying solutions, dispersions and emulsions - Google Patents

Abstract

819,643. Spray evaporators; drying milk. LUWA A.G. Dec. 2, 1955 [Dec. 11, 1954], No. 34597/55. Class 32. [Also in Group XXIX] In a method of spray drying wherein a solution, dispersion or emulsion, comprising a. volatile liquid and a non-volatile constituent, is sprayed into a drying chamber, the deposition of the non-volatile constituent on the spraying device is obviated by supplying, to those parts of the device on which such deposition is liable to occur, a mixture of a gas and the vapour of a volatile liquid which prevents evaporation of the volatile liquid from the substance being sprayed at those particular parts of the device. In drying milk, the " blocking gas " is a mixture of air and water-vapour. The spraying device shown has a disc 20 mounted on shaft 10 which rotates in bearing 11. The bearing is mounted in supports connected with tube 15 which is fixed in the wall 15a of the drying chamber. The oil used for lubricating the bearing is guided by splash-ring 27 into an oil sump formed in bearing support 13, from which it is discharged through a conduit (not shown). The liquid to be sprayed is conveyed through a conduit (not shown) to annular duct 24, from which it passes through two small tubes 24a to the disc 20. This disc has an upstanding rim which forms a shallow well, the top of which is partly closed by annular plate 23. The liquid discharged from tubes 24a spreads along the bottom of the well in the rotating disc, and is sprayed out into the drying chamber through radial openings 21 in the rim of the disc. Hot gas flows through the drying chamber in either the same direction or the opposite direction to the sprayed liquid. In a specific example, milk is dehydrated using air at 140 ‹ C. as drying gas. In order to avoid incrustation in the space 19 between the rotating disc and the fixed plate 18, it is arranged that air containing water-vapour, at a temperature of about 50‹ C., flows continuously through the space. This is achieved by supplying air and water-vapour through conduits 14 and 26, respectively, to mixing chamber 16, from which the mixed gas flows through openings 17 into the space 19. The blocking gas flows from space 19 under a flange at the end of tube 15 into the drying chamber, the rotation of the gas being prevented by vanes 18a on the side of plate 18 facing the disc. The end of tube 15 may be made to project somewhat beyond the rim of disc 20 so as to approach the nozzle openings 21 as closely as possible ; blocking gas flowing out of space 19 can thus be brought into the immediate vicinity of the nozzles without being diluted by drying gas. In another embodiment, three currents of blocking gas are passed to the rotating disc, one of them being supplied via a bore-channel in the shaft. A rotating disc provided with radial blades may be used for spraying the liquid. A fixed spraying nozzle may also be used.