Flexibility
Calculating the exact cycle specifications for product cool-down rate, freezing, and temperature profiles to be delivered
by the refrigeration and heating system depend heavily on the particular characteristics of the product. These profiles may
differ radically depending on the product formulation. The more flexible the design of the refrigeration system, the more
versatile the unit will be. Additional flexibility and control will better position the owner for processing new formulations
with new requirements. Cryogenic refrigeration using LN2/GN2 enables manufacturers to operate across a broad range of processing parameters, both at cool-down and at constant cooling
to temperatures lower than –80 °C. Using a cryogenic system, the lowest temperature on the shelves is limited by the thermo-physical
properties of the HTF, not the refrigerant. Direct expansion of cryogens in the condenser or a nonfreezing cryogenic heat
exchanger with a high performance HTF can provide temperatures below –100 °C in the condenser.
Footprint
A cryogenic refrigeration system requires fewer and less complex components. Typically, a cryogenic refrigeration skid only
requires approximately one-half to one-third the space of a comparable mechanical compressor-based skid.
Environmental Impact
Nitrogen is an inert molecule that is nontoxic and nonflammable, with no ozone-depleting or global warming potential. It comes
from, and returns to the atmosphere after giving off its refrigeration. Most HFC-based refrigerants are either toxic, flammable,
or both. LN2/GN2 refrigeration of the lyophilization operation reduces space requirements and noise, and is environmentally friendly.
CONCLUSION
The growth of LN2/GN2 freeze drying is particularly driven by the need for 1) increased reliability for high-value products, 2) enhanced flexibility,
3) increasing number of formulations containing biologics and 4) dosages with high-fill depth and high volume. The users of
lyophilization technology and related equipment are just starting to realize many of its benefits. Many decision makers, still
unaware of the benefits associated with LN2/GN2 systems, are also surprised at the lower cost of ownership of a well-designed LN2/GN2 system offering high LN2 efficiency at a low capital expenditure. These features are also worth considering for manufacturers aiming to increase the
efficiency, operating flexibility, and profitability of lyophilization systems while controlling costs.
Balazs Hunek, PhD, is a senior manager of technology, 630.320.4242, balazs_hunek@praxair.com
Alan Cheng, PhD, is a senior development associate, R&D, and John Capettini is a manager of global applications market development, all at Praxair, Inc.
REFERENCES
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5. Telstar. GN2-Tech. Product brief;2005.
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7. Based on Praxair analysis of actual customer experience.
8. Usifroid. Liquid nitrogen applied to freeze drying: performance, reliability, flexibility. 2006. Available from: http://
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