GB689497A - Improvements in or relating to spray drying - Google Patents

Abstract

<PICT:0689497/III/1> Spray-drying is effected by spraying the liquid into a downwardly-flowing stream of hot gases at a temperature not higher than 750 DEG F, and introducing into the resulting mixture, at a level below the spraying-device, hot combustion gases having a temperature higher than 1000 DEG F. The gas stream of lower temperature is obtained by diluting a portion of the hot combustion gases with cooler gases. Drying chamber 1 is provided with a spraying-device 6 comprising a liquid inlet pipe 6a, a vaned wheel 8 driven by an electric motor 7, mounted in cylinder 5 and surrounded by a duct 10 which contains directing-vanes 11. Furnace 14, which comprises a brick-lined cylinder provided at the base with gas-burners 19 and an air-inlet 20, is connected to chamber 1 at two different levels by ducts 21 and 13. Duct 21 is below the level of spray wheel 8, while duct 13 communicates with gas-flue 12, which opens into duct 10. An inlet 25 for supplying secondary air or a portion of the exhaust gases, into the furnace, is provided above duct 21. All the pipes leading into or out of the furnace are provided with dampers. Hydrocarbon gas or other fuel is burned in burners 19 with air introduced through inlet 20. A portion of the resulting hot gases, preferably at a temperature of about 1500 DEG F, is introduced into the drying-chamber through duct 21. The remainder of the hot gases is cooled to 750 DEG F or below by diluting gas introduced through inlet 25, and the mixture is introduced into the top of the drying-chamber via duct 13, where it forms a rotating gas blanket into which the liquid to be dried is sprayed by wheel 8. The gases containing the dried material are exhausted from the base of the drying-chamber at a temperature of about 230 DEG F, by means of a fan connected to a pipe 15 via cyclone separators (not shown).