Biomedical Engineering Reference
In-Depth Information
storage of fuel in power or process plants that is not necessarily underground.
Silos could be fairly large in diameter (4
10 m), and are very tall, which is
good for storing grain-type biomass. For example, Figure 12.5 shows a tower
silo for cattle feed. Bins are for smaller capacity temporary storage.
12.3.2.3 Hopper Design
Hoppers or chutes facilitate withdrawal of biomass or other solids from tem-
porary storage such as a silo. Major issues in their design include: (1) mode
of solids flow, (2) slope angle of discharge, and (3) size of discharge end.
There are several modes of solids flow in a hopper: funnel flow, mass
flow, etc. Funnel flow would have an annular zone of stationary solids and a
moving core of solids at the center. In this case, the solids flow primarily
through the core of the hopper. Solids in the periphery either remain station-
ary ( Figure 12.6C , left) or move very slowly ( Figure 12.6C , right). Fine par-
ticles tend to move through the core while coarser particles stay preferen-
tially in the annulus. The particles from the top surface can flow into the
funnel, thus violating the design norm of “first in first out.” When that does
not happen, a stationary annulus is formed and the discharge stops, causing a
rat hole to form through the hopper that becomes void and stops the flow.
Remaining solids in the hopper stay in the annulus ( Figure 12.6A , right),
which prevents the hopper from emptying completely. The only positive
thing about a funnel-flow hopper is that it requires a lower height.
FIGURE 12.5 Typical grain silo used for storing cattle feed. Source: Photograph by the
author.
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