Agriculture Reference
In-Depth Information
14.2.3 D
RYERS
There are several types of grain dryers: fixed-bed dryer, fluidized-bed dryer, and cir-
culated-grain dryer. The circulated-grain dryer is popular in Japan, because the mois-
ture content of grain right after harvesting is usually high (20-30% w.b.), and such type
of high-moisture-content grain needs to be dried as soon as possible after harvesting.
Moisture content of grain is always measured during drying by using an electrical resis-
tance grain moisture meter set in the dryer. Heated air temperature (40-50°C, as usual)
is automatically controlled to setting temperatures, which are usually low when there is
high moisture content and high when there is low moisture content. When the moisture
content of grain decreases to a setting moisture content (14.5% w.b. of rough rice), the
dryer automatically stops drying the rough rice. Moisture content and heated air tem-
perature can always be monitored at the central control board.
14.2.4 S
TORAGE
IN
S
ILOS
After drying, rough rice is cleaned by using a fine cleaning system, which is composed of
a wind separator, a gravity separator, and an indented cylinder separator (Kawamura et
al., 2006). The fine cleaning system enables separation and removal of immature kernels,
empty kernels, damaged kernels, and hulled kernels and thus improves rough rice quality
and minimizes quality deterioration of rough rice during storage.
After cleaning, rough rice is stored in a silo. During silo storage, aeration through
the silo is automatically carried out when the temperature of fresh outside air is below
-5°C in winter. The aeration is continued until the cooling front moves through all of
the rough rice in the silo. After about 100 h aeration time, all of the grain tempera-
tures throughout the silo decrease below the freezing point. The grain temperature in
the center of the silo remains below the freezing point despite the increase in outside
temperature in summer because of low thermal conductivity (about 0.09 W/(m*K);
Seno et al., 1976) and high specific heat (about 1.7 J/(K*g); Morita and Singh, 1979)
of rough rice. An automatic ventilation system is essential to prevent moisture con-
densation in upper vacant space inside the silo (Kawamura et al., 2004a). This stor-
age system, in which the temperature of grain during storage is below the freezing
point, is called a super-low-temperature storage system (Kawamura et al., 2004b).
14.2.5 H
ULLING
S
YSTEMS
After storage, rough rice is unloaded from the silo and the hull is removed. A hull-
ing system consists of a roll type huller and a paddy separator. There are two rubber
rollers rotating in opposite directions and at different revolving speeds in the huller.
Rough rice goes through between the rollers, and the hull is removed from rough rice
by pressure force and shearing force by the rollers. Pressure force and space distance
between the two rollers are automatically controlled. The hulling rate of a roll type
huller is about 90% (90% brown rice and 10% rough rice) as usual. Therefore, a
paddy separator is necessary after hulling.
The paddy separator consists of several layers of inclined trays with indented
surfaces at an angle. The trays oscillate in upward and forward directions, and the
