World Grain - December 2008 - 71

FEEDOPERATIONS

used, and there can be no panacea for all
circumstances. There needs to be a regular inspection of what suits the circumstances at the time, and there might be
occasions when it becomes economically
viable to change dies before they are
completely worn out on the basis that raw
materials have changed and power costs
need to be taken into consideration.
Refurbishing dies and skimming them
down are not recommended, but many
millers do this and offer sound economic
arguments for adopting the practice.
The increased internal diameter of the
die that results from refurbishing and
skimming it down, the extra wear and
stress it puts on the rolls and the stresses
it puts on the press bearings and housings can, at worst, lead to unforeseen expense and, at best, reduced product quality. However, some modern-day presses
are being engineered in recognition of
the practice being more widely adopted.
Casings, housings and bearings are all
being strengthened to accommodate the
increased die diameter and the increased
demand placed on the mechanics of the
pellet press. No doubt, this topic will be
debated at length along with choice of
die specification.
COOLING AND STORAGE
After pelleting comes cooling, and
all millers are aware of the developments in cooling technology, from the
initial inception of vertical coolers to
the use of horizontal coolers and rotary

coolers, and, finally, to the modern-day
counter-flow box coolers being almost
universally adopted in today's mills. The
current coolers are efficient, adaptable,
easy to install, and allow for rapid product changeover. More attention is being
paid to the internal workings to reduce
power consumption, and emissions to

When deciding on the die
specification to be used, one
needs to take into account the
grist spectrum from the blending and mixing system.

the atmosphere are also being monitored
with closed-circuit applications being
experimented with in some quarters.
You will certainly see further developments in cooler technology over months
and years to come.
Cooling times are associated with
the temperature of pellets leaving the
press and, perhaps more significantly,
the moisture of pellets, since it is just as
much the pellet moisture that needs to
be controlled as the temperature.
To avoid mold growth, you need to
reduce both of these parameters, which
cannot be done in the few seconds it
takes to pass through a cooler. Correct
air flow during storage is just as important and often neglected. Negative pressure applied to bulk storage for finished

products can show significant benefits.
As millers who have used them will testify, the use of tote bags demonstrates
that the amount of moisture given up
by pellets after cooling is quite remarkable. Placing pellets in a tote bag with
a closed top for 24 hours will show just
how much water is evacuated from pellets in the 12 hours or so immediately
after processing.
Seeing this makes one appreciate how
important adequate storage bin ventilation really is. Alternatively, when pelleted feed is kept on a vehicle overnight,
you may be surprised the following day
how much moisture and mold has accumulated on the underside of the vehicle
cover sheet, again demonstrating the
point that pelleted feed needs considerable time to cool, and no matter how
much you try to rush nature, it will take
its own sweet time.
Effective cooling is required, but
good storage conditions and proper
bin ventilation after the event is just as
WG
important.
Jonathan Bradshaw is a consultant to the
agribusiness and food processing industries,
specializing in project management and bespoke
training programs through his company, J.B.
Bradshaw Ltd. He has extensive experience in
flour and feed milling in Africa, the Americas,
Europe and the Caribbean. He may be contacted
at: jonathan.bradshaw2@btopenworld.com.
We want to hear from you - Send comments and
inquiries to worldgrain@sosland.com. For reprints of
WG articles, e-mail reprints@sosland.com.

Extruder OEE
Flexible shaping
of different products

l J l ,_ .

AMANDUS KAHL GmbH & Co. KG, Dieselstrasse 5-9, D-21465 Reinbek / Hamburg, Phone: +49 40 727 71 0, Fax: +49 40 727 71 100
info@amandus-kahl-group.de, www.akahl.de

For more information, see Page 82.

December 2008 / World Grain / www.World-Grain.com

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World Grain - December 2008

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