How do we make a freeze drying cooling
system with a GWP of 1?
29 Nov 2021
In the past, industrial refrigerants were improved to avoid ozone depletion, but they still have a high potential to contribute to global warming.
Given that the availability of currently used refrigerants for pharmaceutical freeze-drying applications is already running low — and may well have disappeared from the market in 2030 — GEA Pharma & Healthcare has been looking for alternative low-temperature cooling solutions that use natural refrigerants in commercial-scale freeze-drying applications.
Industrial freeze drying
From its earliest applications in the stabilization of blood plasma, freeze drying has been in use in the life science industries for more than 50 years. During this period, the freeze dryer — or lyophilizer — has evolved from a simple device for vacuum drying at low temperature to an extremely sophisticated integrated system. Current options combine a number of processes to ensure that a product is consistently delivered to technical and biological specifications while also considering economic, safety and environmental issues.
Freeze drying is a dehydration process that’s typically used to preserve a perishable material or make the material more convenient for transport or storage. Freeze drying works by freezing the material and then reducing the surrounding pressure to allow the frozen water in the material to sublimate directly from the solid phase to the gas phase. The use of refrigerants is fundamental to the entire procedure.
GEA offers a variety of options for the implementation of a freeze dryer refrigeration system, either mechanical or cryogenic, which can be specifically adapted to individual process and product requirements. The two main considerations when selecting a suitable solution for freeze-drying processes are refrigeration temperature and cooling capacity.
As conventional synthetic refrigerants are becoming less common and increasingly restrictive laws prohibit the use of chemicals with a high global warming potential (GWP) — according to the Montreal and Kyoto Protocols — investing in a compressor cascade (multi-stage thermodynamic cycle) that uses natural refrigerants will become increasingly pragmatic. Accordingly, all GEA refrigeration units for freeze-drying applications have been designed to operate with natural refrigerants to meet a wide range of process and product needs.
One of the few usable compounds is ethane (C2H6). Owing to its very low boiling point (–88.5 °C), ethane is compatible with cascade cooling systems. In an indirect silicone oil-cooled ice condenser, for example, temperatures of less than –80 °C can be achieved. However, there is a downside; some natural refrigerants, including ethane, are explosive and need to be handled with additional care to comply with the ATEX Directive. However, companies such as GEA have the experience and expertise to make these systems as safe as possible. To ensure the protection of both product and operator, GEA incorporates a containment facility around every cascade working with explosive refrigerants — including all the required safety measures to ensure that such a system is ready for use in a standard pharmaceutical environment.
GEA has now developed an innovative air cycle system for freeze dryers that also incorporates carbon dioxide (CO2) cooling. The LYOAIR® system, which has been shown to demonstrate high levels of throughput and reliability, can be operated without special ATEX equipment and installed in a non-ATEX equipped room.
Why is a GWP of 1 so important?
GEA CO2 booster systems can reach temperatures down to –50 °C and are suitable for a wide range of product freezing applications. The LYOAIR® cooling system uses natural refrigerants and has a GWP of 1. Why is that important? The GWP scale was developed to allow comparisons of the global warming impacts of different gases. Specifically, it’s a measure of how much energy the emissions of 1 ton of a gas will absorb during a given period of time compared with the emissions of 1 ton of CO2. The larger the GWP, the more that a given gas warms the Earth. So, lower is always better and 1 is as good as it gets.
In summary, the GEA LYOAIR® employs natural refrigerants that comply with the 2015 fluorinated greenhouse gases regulation and benefits from the integration of highly efficient and economic third-party compressors. The combination of an air cycle system with a CO2 booster offers a lower energy consumption for freeze dryers compared with a regular air cycle system. Notable benefits also include the elimination of explosive or toxic natural gases, less vibration, quieter functionality and no GWP. It’s also easy to maintain and significantly less expensive to run that liquid nitrogen alternatives.
