Biomass Handling - Biomass Gasification, Pyrolysis and Torrefaction - page 433

12.4.3.8 Belt Feeder
Belt feeders are very effective for feeding nonfree-flowing biomass that is
cohesive, fibrous, friable, coarse, elastic, sticky, or bulky. However, they are
not recommended for fine or granular solids. Typically, a moving belt is
located directly under the outlet chute of the fuel hopper. The belt is sup-
ported on rollers that can be mounted on load cells to directly measure the
fuel feed rate. Such feeders are referred to as belt-weigh feeders.
The width and speed of the belt depend on the density and size of the
feed material. A narrow belt with a high design speed may be the most eco-
nomical, but it is limited by other considerations such as dust generation and
hopper width. Most manufacturers provide data on available belt widths, per-
missible speed, feed density, and recommended spacing of idlers supporting
the belt. Such data can be used for the design of the belt feeder and the feed
system.

12.4.4 Fuel Feed into the Reactor
Biomass feed into the reactor of biomass conversion unit needs special con-
siderations that are discussed in the following sections. For bubbling fluid-
ized beds, we have the choice of two types of feed systems: (1) overbed and
(2) underbed ( Figure. 12.20 ).

Feed hoppers

Gravity chute

Variable speed
feeders

Insulated
extension

Air lock value

Fluidized bed

Conveying air

FIGURE 12.20 Position of over- and underbed feeders in a bubbling fluidized bed.