TIPS ON BUYING A FREEZE DRYER
What do I need to know about the electrical
source ?
Freeze Dryers, large or small, should have a
dedicated source of electricity, free of voltage line drops.
If your facility is located in an office building or "campus"
type complex, line voltage fluctuations can be significant.
These so called "line drops" are not critical for
office or small amperage lab equipment, but they can have
an appreciable effect on compressors, pumps and other components
needed for a freeze dryer to operate properly. A drop of 10%
or less in line voltage can mean greatly reduced performance
and a larger number of expensive service calls.
For example, a voltage drop of only 8-10% can
reduce compressor life by as much as 30%.
Check the line voltage for a twenty-four hour
period in the location where the freeze dryer is to be installed.
Because the Freeze Dryer will be running continuously for
this period or longer, you should know what output voltages
are present for the period of time the Freeze Dryer will be
running. If the low voltage periods are longer than one hour,
consider purchase of a "boost" type transformer
to maintain proper line voltage.
It is always preferable to install a dedicated
source of power to the Freeze Dryer due to the "unrecoverable"
nature of the drying process, which can be interrupted by
other equipment installed on the same line.
What About Other Utilities such as Water
?
This will depend on the size of the Freeze Dryer
you are considering for purchase. Generally, the size of a
Freeze Dryer is based on useable shelf area and condenser
capacity. For example, a Freeze Dryer that is equipped with
four useable product shelves measuring 24" x 36"
would be classified as a 24 square foot unit, as each shelf
would have a capacity area of 6 square feet. The top shelf,
often referred to as the "upper radiant" is not
considered in capacity determinations, as it cannot be used
for product, and is installed only to insure the same temperature
conditions for the useable top shelf as for those below it.
Ice collection condensers for a Freeze Dryer
are generally expressed in free water capacity measured in
liters or kilograms. It is important to roughly determine
the amount of water which will be sublimated from the product
during the Freeze Drying process. You can roughly estimate
this amount by determining 90-95% of product weight intended
as a typical batch. For example, if the product weight is
50 kilograms wet, you will need a condenser capacity of 45
kg or liters to process the batch. It is always advisable
to insure that the condenser is at least 10% greater than
the water load from the product. If you are looking for the
fastest cycle compatible with the frozen condition, you may
wish to increase the capacity by 30% or 40% of the load, as
the larger condenser will generally provide more surface area
to increase mass transfer rates.
A well designed Freeze Dryer will generally
be designed with one and one-half square feet of cooling surface
in the condenser for each square foot of shelf area in the
drying chamber.
Freeze Dryers above 15-20 sq. ft capacity will
generally be equipped with multi- stage refrigeration compressors
which are water cooled. The amount of cooling water needed
will depend on the cooling water temperature. For example,
if the cooling water temperature is 83-87 F (summer conditions
for cooling towers), the freezing portion of the lyophilization
process can be significant, around 18 to 20 gallons per minute
for a 24 sq. ft Freeze Dryer, which can elevate both water
and monthly sewer rental costs beyond your utility budget.
Consider a cooling system for the water supply,
which can reduce these kinds of costs (often by 70 %), and
may pay for itself in one or two years of operation.
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