Figure 1. Design of the dryer
Detailed Process Description
The drying chamber, 1.37m wide, 2m tall and 2.9m long, contains two
movable tray carts having 26 trays each. It is made of galvanized iron sheets
framed together by angular steel bars. The trays (of dimensions 0.98m x
0.97m) are made of polyethylene plastic mesh reinforced with aluminum bars.
The total area of the drying trays can accommodate 200 kg of mango slices.
The chamber also has an air distribution nsystem, which ensures distribution
of air into the entire height of the chamber. The air distribution system is
composed of an axial fan (with a 0.35m dia. rotor) and a distributor duct. The
distributor duct has a converging shape from top to bottom, and has thirteen
concentric rings of varying diameter, arranged one above the other, at specific
spacing. This system can deliver an air volume of up to 0.37 m3/sec.
Biomass furnace - Heat exchanger
The rice husk-fuelled furnace is composed of five parts: the combustion
chamber, heat exchanger system, fuel hopper, air inlet duct, and the chimney.
The combustion chamber is made of bricks enclosed in galvanized sheet
metal while the heat exchanger system is made of 27 boiler tubes arranged in
a rectangular array. All other parts of the furnace are made of galvanized iron
sheet. A butterfly valve controlled by a variable speed electric motor (0.5 hp)
controls the feed rate of rice husk; the fuel hopper is inclined at 45º (angle of
repose of rice husk) to allow free flow of rice husk into the combustion
chamber. An auxiliary blower (0.5 hp) was installed in the combustion
chamber to supply the primary air required for complete combustion. The
primary air supply to the furnace can be controlled by adjusting the opening of
the blower air inlet.
The main blower installed between the furnace and the drying chamber draws
the ambient air through the furnace-heat exchanger unit, and supplies hot air
to the drying chamber. An S-shaped duct is installed at the air inlet to the heat
exchanger. The mouth of the duct is located away from the combustion
chamber to avoid suction of ashes that may otherwise contaminate the
product to be dried. The fuel hopper has a capacity of three sacks of rice hull
per loading which lasts for about 3 to 4 hours of dryer operation.
Investment and Operating Cost
The total cost of fabricating this dryer is about US$1,800.
Example of Real Life Application
For drying agricultural products
Research UPLB Philippines
University of the Philippines Los Banos