 Desiccant
and Hot Air Dryers
Foremost Machine Builders
designs and manufactures hot air and dehumidifying
or desiccant dryers for drying hydroscopic and non-hyroscopic
plastic resins. To create a high quality product from a particulate
material you have to make sure that the moisture content of the
material is reduced to an acceptable level as quickly and as efficiently
as possible. While our hot air dryers can handle both hydroscopic
and non-hydroscopic materials, our patented twin tower desiccant
dyers were specifically designed for drying hydroscopic materials
such as plastic resins.
Many plastic pellets
are hygroscopic in that they absorb moisture both on the surface
and inside the granulate pellet. While there are many theories as
to what is the most effective way to reduce the moisture content
of a plastic pellet, the most successful drying technology has been
the desiccant based drying system. For the last fifty years, desiccant
dryers have been a stalwart in the plastics industry proving time
and again that they are the most reliable, economical and effective
plastic resin dryers on the market.
Choosing the correct dryer for your process can be difficult given
that there are as many types of dryers as there are materials to
dry. As always, your buying decision will have to balance initial
price against operating cost, flexibility, reliability, and any
extra features.
 Hot
Air Dryers
Hot air dryers use warmed air as their drying medium and are typically
chosen for particulate materials that are non-hydroscopic, i.e.,
have moisture only on the surface, or for surface drying hydroscopic
regrind material such as polypropelene and polyurethane. Heat lowers
the relative humidity of the surrounding air improving its drying
ability. The moist air is expelled into the atmosphere while fresh
ambient air is drawn in to continue the process. These dryers are
not known for removing absorbed water from hygroscopic materials.
But if your processing plant is located in a climate with relatively
low humidity, with the right hopper size, a hot air dryer can be
the solution you are looking for. Typically, hot air dryers, which
only supply hot air and have no dehumidification system, may also
be used on non-hygroscopic materials as a preheater. In drier areas
of the world that have relatively low humidity, a processor can
use these units on hygroscopic materials with decisive results.
With only one blower and a heater, the initial cost will be much
easier to handle and your maintenance and service costs will be
minimal.
 Desiccant
Dryers
Before you buy a desiccant dryer you should know what your options
are and be clear about what you expect from the dryer you choose.
When selecting a dehumidifying or desiccant dryer, you have four
basic configurations to choose from: machine-mounted, beside-the-press,
and the newer portable or off-the-press systems. Central
drying systems - a larger version of beside-the-press designs -
are the fourth option. Within each of the basic configurations,
you also have a choice between the traditional twin-tower dual
desiccant units, multiple-bed units and the more unconventional
types, i.e., desiccant impregnated cartridges.
Traditional twin tower desiccant dryers work the following way:
warm dry air is sent through a hopper containing plastic resin and
removes the moisture from the resin. The moisture laden air is sent
through a dessicant bed where the moisture is absorbed from the
air stream by the desiccant. This air is then reheated and sent
back to the hopper of resin to remove additional moisture in a closed
loop. The quality of the dry air is monitored by a dew-point sensor
set as required for the desired degree of drying. When the moisture-absorbing
capacity of the desiccant reaches its limit, the airflow is automatically
switched to a second desiccant chamber to maintain the drying process.
Meanwhile the first desiccant chamber is regenerated by heating
it to remove moisture and then cooling it so it can resume absorbing
water. As an alternative to electric heaters, gas fired process
heaters are frequently used for more efficient use of energy. As
a trusted drying technology, twin tower desiccant dryers function
well and typically last a very long time.
For more information about our blenders, please contact us at sales@foremostmachine.com.
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