Various designs of drying chambers are seen on the market. The most common
one is the cylindrical chamber with a cone of 40-60º, where
gravity forces the powder to leaves chamber. The drying chambers with a
flat bottom require a scraper or suction device to remove the powder
fraction from the chamber. Also horizontal box type drying
chambers are seen, and they, too, operate with a forced powder removal
system (i.e. scraper or screw). Illustrations of the different types of drying
chambers are seen below. (Fig. 39)
Generally, it can be concluded that chambers with a cone for gravity
discharge of the powder give the best flexibility for adapting various drying
processes like integrated fluid beds or belts to the plant and therefore offer
the greatest possibilities for drying different products.
DRYING CHAMBER DESIGN TENDENCIES
The tendency today is to design the drying chamber, so that nothing inside
the chamber will obstruct air flow, which can result in powder deposits.
In the tall-form drying chamber, the emphasis has been on designing a plant
with a laminar air flow and a special air outlet system, where the diameter of
the cone is larger than the diameter of the cylindrical part thus forming a
ring duct termed a "bustle". This minimizes the cyclone fraction by the low
velocity of the exhaust air. The tall-form drying chamber is especially suited
for baby-food products or protein products dried from a low solids content in
the feed.
The development of Cleaning In Place bag filters has made it
possible to design drying chambers with built-in bag filters.
The
drying chamber should always be equipped with inspection doors, light sources,
over-pressure vents, and other safety equipment such as fire extinguishing
equipment in the form of water or steam nozzles.
Drying chambers are
usually insulated, either with removable air-filled sandwich panels, see Fig.
40, or with 80-100 mm mineral wool covered with a stainless steel plate or a
galvanized plate covered with PVC. The advantage of the removable panels is
that inspection for cracks in the chamber wall is a possibility, and wet
insulation material, in which bacteria can develop or result in cold spots on
the chamber wall whereupon deposits are formed, is avoided.
