Biomedical Engineering Reference
In-Depth Information
12.4.3 Feeder Types
The six main feeder types for biomass are: (1) gravity chute, (2) screw con-
veyor, (3) pneumatic injection, (4) rotary spreader, (5) moving-hole feeder,
and (6) belt feeder. These are broadly classified as traction, nontraction, and
other types as shown in
Figure 12.16
. In the traction type, there is linear
motion of the surface carrying the fuel, as with a belt feeder or a moving-
hole or drag-chain feeder. In the nontraction type, the motion is rotating and
oscillatory screw feeders and rotary feeders belong to this group. Oscillatory
feeders are of the vibratory or ram type. Other feeder types move the fuel by
gravity or air pressure.
12.4.3.1 Gravity Chute
A gravity chute is a simple device in which fuel particles are dropped into
the bed with the help of gravity. The pressure in the furnace needs to be at
least slightly lower than the atmospheric pressure; otherwise, hot gas will
blow back into the chute, creating operational hazards and possible choking
of the feeder due to coking near its mouth.
In spite of the excellent mixing capabilities of a fluidized bed, a fuel-rich
zone is often created near the outlet of a chute feeder that is subjected to
severe corrosion. Since the fuel is not well dispersed in gravity chute feed-
ing, much of the volatile matter is released near the feeder outlet, which
causes a reducing environment. To reduce this problem, the chute can be
extended into the furnace. However, the extension needs insulation and some
cooling air to avoid premature devolatilization of the feed passing through it.
Additionally, a pressure surge might blow fine fuel particles back into the
chute, while reducing conditions might encourage corrosion. An air jet can
help disperse the fine particles away from the fuel-rich zone.
Feeders
Traction type
Nontraction type
Other type
Pneumatic injection
Gravity
Moving hole
Belt
Drag chain
Vibratory
Rotary
Pushed chute
Vinratory bin
Walking floor
Star
Screw
Ta b l e
Rotary plough
arm
FIGURE 12.16
Types of feeders used in biomass plants.
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