To hardly cause any clogging inside an exhaust duct due to collision of a powder against the inner wall of the exhaust duct and to prevent the powder from being stuck to the inside of the exhaust duct by placing air blowing slits for blowing air along the inner wall surface of a cylindrical exhaust duct connected to the lower section of a drying column, inside the exhaust duct so as to cause a swirling air stream within the exhaust duct, in a spray drier.
The spray drying process using this spray dryer comprises: allowing a powder in an internal fluidized bed 3 of a drying column 1 to flow over a weir placed at the inlet of a pipe 20 and then to flow into an external fluidized bed 12 through a rotary valve 21; supplying hot air from a blower 22 while passing air through a heater 23 and a pipe 24 to the external fluidized bed 12 at a point on the upstream side to dry the powder; also, supplying cold air from a blower 25 while passing air through a cooler 26 a pipe 27 to the external fluidized bed 12 at a point on the downstream side to cool the dried powder; supplying hot air from a blower 28 while passing air through a heater 29 to the inside of a hollow annular body 30 and blowing out hot air from nozzles each used for causing a swirling air stream in the intermediate section of the drying column 1 into the drying column 1 along its inner wall surface; and further, supplying hot or cold air that is obtained by passing air delivered from a blower 31 through a heater or cooler 32 to air blowing slits 34 arranged within an exhaust duct 4b in its longitudinal direction, through a pipe 33 to cause a swirling air stream within the exhaust duct 4b in the circumferencial direction.
UCHIYAMA MASASHI
UEDA HIROYUKI
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