World Grain - July 2005 - 40

grainoperations
sitions are just as important as the conveying equipment selection.
Fundamentally, the number of
impact points and direction changes
should be minimized, and the product
velocity kept low. Sharp edges should
be avoided. With fragile product, it
is relatively common to install "laddered" spouts containing baffles which
retard the flow of the product to keep
its speed down. Caution is advised in
designing the laddered spouts to prevent product hangup and the resulting
contamination opportunity. It may be
appropriate to space the baffles slightly clear of the bottom of the spout to
prevent hangup.
MINIMIZING CONTAMINATION
Because most facilities are not
dedicated to a single product, there is
a possibility for other grains to become
mixed into the product. This may happen due to a leak but is more commonly
caused by small amounts of grain hung
up in transitions or left in equipment
that doesn't entirely clean out.
When discussing contamination, it
is very important to define how much
is acceptable. While zero sounds
like a good target, zero tolerance is
unachievable for practical purposes.
Tolerances in the range of 0.1% are
commonly acceptable for the major
grains. While 0.1% sounds small, it is
useful to put this in perspective with
reference to rail car size. For a shipment of 195,000 pounds (3,300 bushels), 0.1% equates to 195 pounds (3.3
bushels) of contaminants. Therefore,
0.1% is quite a large number and even
smaller percentages (0.05%, 0.02%)
may be achievable.
The problem at very small allowable
contamination percentages is obtaining
and testing a representative sample.
LARGE AMOUNTS
Large contamination amounts can
occur due to misuse or malfunction of
the facility.
An obvious source of substantial
contamination is storing one product
42

in the same bin as a different product
or opening the incorrect bin when
blending. Care should obviously be
taken to avoid these errors. Modern
electronic control systems can be used
to help protect against this happening,
but users still must correctly tell the
system what grain is being received

To prevent physical grain
damage from an operational
standpoint, it is important
to minimize the handling of
the product and operate the
equipment with consideration
for product quality.

and keeping the contents of the bins
up to date.
The second common source of significant contamination is grain leaking
from or to an undesired location. Possible causes include:
* A misadjusted, poorly designed, or
worn out bin gate.
* A diverter valve which is poorly
designed, incorrectly set, or worn out.
* A distributor which is incorrectly
positioned or out of adjustment, and
therefore leaking some grain into an
adjacent spout.
All of these items can cause significant contamination as they can take
place on a continuous or frequent basis.
If significant contamination is occurring
in a facility, it is necessary to thoroughly
investigate the possible sources. A small
leak can be difficult to find but may still
cause significant contamination.
SMALL AMOUNTS
Small amounts of contamination can
be caused by equipment which doesn't
clean out entirely, although this is usually insignificant for most grains with
normal contamination limits.
Drag conveyors and belt conveyors

typically have very little product left
in them after use. Bucket elevators
naturally have more because there is
always some product left in the boot.
However, the product in the boot of a
bucket elevator tends to stay there and
very little will mix with the next product being moved. In all but the most
stringent systems, contamination in
the leg is usually not significant.
If equipment is not run long enough
after moving one product before
switching to another one, it is possible that significant contamination
may occur. In an automated system,
it is essential that the appropriate
safeguards and time delays be configured for the plant to allow complete
cleanout without wasting time. Similarly, with a manual system, the user must
be diligent to ensure the equipment has
cleaned out before changing to another
path. With large facilities and long drag
conveyors, it can easily take over a minute for the grain to reach its destination.
Some equipment, such as screw conveyors and grain pumps, do not clean
out as well as drags, belts, and legs.
Grain pumps are not recommended
for use in any multi-product system
because they have poor cleanout characteristics due to their fundamental
design concept.
One operational source of contamination may be overfilling bins, which
can cause product to back up the
distributor spout and overflow inside
the distributor into the bins adjacent
the desired spout. The severity of this
problem depends on the duration for
WG
which it occurs.
Kevin B. Mason is senior project manager
and division engineer for Agricore United,
Winnipeg, Manitoba, Canada. He may be
contacted at: kmason@agricoreunited.com
or 1.204.944.2251. This article is modified
from his presentation at the 2005 GEAPS
Exchange. For the full presentation, visit
www.geaps.com.
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inquiries to worldgrain@sosland.com. For reprints of
WG articles, e-mail reprints@sosland.com.

July 2005 / World Grain / www.World-Grain.com

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World Grain - July 2005

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