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. Since 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 purchasing 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 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 types of costs (often by 70 %), and may pay for itself in one or two years of operation.
One fine body…