Continuing my discussion of flow types and the factors that affect flow
type selection for a given application, in this issue I will look at
cross, impingement and fountain flows and factors affecting dryer
selection.
Numerous different types of dryers use gases (most commonly air) as the
carrier. Mostly, they are categorized into a type of dryer (spray,
flash or fluid bed, for example), mode of heating (direct or indirect),
or mode of drying (batch or continuous). But, within these categories,
there is a less commonly referred to dynamic: the flow. Flow refers to
the direction of the gas relative to the direction of the feed travel.
Continuing my discussion of the variables that can be altered to
achieve a specification or control dryer operation, I'll look at
control parameters than can control operation. The customary method of
controlling a dryer is by modulating the inlet temperature (source of
energy) or feed rate against fluctuations in the exhaust temperature.
The success of most drying processes is defined by the final moisture
content of the product. Some dryer installations perform more than
simply drying - applications where the color, particle or material
configuration, or integrity, size, etc., also influence the
performance. But, for most, the final moisture is key.
In last month's column,
I began to look at ways to reduce energy costs by minimizing the system
losses. Suggested methods include optimizing process performance, using
a heat recuperation system or employing a direct heating approach,
among others.
These same concepts hold true for other processes -- to the dryer's benefit.
At the time of this writing, available reports state that thermal dehydration, or drying, accounts
for as much as 6% of the world consumption of energy. In the United
States, we are literally spoilt with the relatively low cost of energy.
Even the oil crisis of the early '70s did little to dampen the rampant
and frequently inefficient use of energy for dehydrating systems.
by Darren A.Traub | January 11, 2000 | Comments (0)
Another way to harness the heat in your dryer is to recover some of the
dry product energy. Cooling the dry product with atmospheric air will
increase that air's temperature. This gain can be used effectively as
the inlet air to a prior zone or to preheat the feed product. Here are additional ways to improve your dryer's performance and potentially increase its output.
by Darren A.Traub | November 1, 1999 | Comments (0)
Most dryers currently in service, being used as designed or
specified, offer the potential to increase output and productivity with
a minimal investment. The performance of others, which may not be
operating as designed due to a number of conditions, also can be
improved using the same techniques. Here are some simple concepts that
can be implemented to improve your dryer's performance and potentially
increase its output.
by Darren A.Traub | October 1, 1999 | Comments (0)
This
series looks at 30 questions that should be asked -- and answered --
when
preparing the specification of a thermal drying plant. In part 4, look
at the chemical characteristics of both the product and the moisture to
be driven off.
