Cryogenic blast freezing to -90°C in minutes increases throughput

The biotech and biopharma industries utilise freezers to rapidly freeze and store thermally sensitive products such as vaccines and biopharmaceuticals as well as biological materials such as blood plasma. However, conventional compressor-based systems can take hours to reach an ultralow target temperature, which slows production throughput.

For these industries, the availability of cryogenic, liquid nitrogen (LN₂) blast freezers that lower the temperature to -90°C in minutes can significantly increase production throughput, compared to conventional compressor-based systems. The product can then be transferred to long-term storage or the next process step. The quicker the product is frozen to the desired temperature, the faster the production.

When San Diego Blood Bank sought to improve its process, it turned to upright LN₂-cooled plasma flash freezers and documented the successful results compared to a modern traditional freezer. The LN₂ freezer offers increased load capacity (456%) and throughput (317%) in freezer-to-freezer comparisons at maximum load, as well as demonstrating a return on investment (ROI) of 28.5 months, according to a study by San Diego Blood Bank’s Development & Research Services.

Conventional freezers circulate refrigerants to cool products, but LN₂ blast freezers begin with a dramatically lower temperature coolant, so can achieve considerably lower temperatures much faster. They are designed to eliminate the need for compressors and refrigerants, and so offer energy efficiency as well as low maintenance. To further facilitate throughput in space-constrained production areas, some units are designed to do ‘double duty’ by rapidly thawing product when required.

“Liquid nitrogen units cool faster because LN₂ has a boiling point of -196°C, enabling freezers that utilise it to cool to temperatures as low as -196°C,” said Kim Boyce, President of Reflect Scientific, a Utah-based manufacturer of cryogenic cooling technologies. “Most refrigerants have boiling points higher than -100°C, making it difficult for the compressor-based freezers using them to operate at temperatures below that. The key difference is starting off with a much cooler carrier gas.

“Many blast freezers also use metal plates to freeze product, severely limiting their use to thin, flat objects,” added Boyce. “Others inject LN₂ directly into the payload bay, risking harmful exposure to the product. A more versatile, efficient approach allows blast freezing anything that can fit inside with LN₂-cooled air.”

Reflect Scientific’s Cryometrix B-90 blast freezer utilises safely contained liquid nitrogen at -196°C to freeze products with cooled air. The system is designed so there is no contact between the LN₂ and the operator or product, which helps to ensure safety and product quality. Since the system is designed with eight fans adjacent to a heat exchanger, it can cool product inside from +20 to -90°C in less than 10 minutes. The temperature is adjustable from +40 to -90°C, with temperature uniformity of ±3°C throughout. The product also provides state-of-the-art temperature and data logging, which can be easily accessed through a touch screen or downloaded to a computer.

Unlike compressor-based units that exhaust heat into the room, the blast freezers do not require additional HVAC systems to cool the ambient temperature to operate. Indeed, the San Diego Blood Bank found significant production and maintenance advantages utilising a Cryometrix LN₂-cooled plasma flash freezer instead of traditional options.

The study authors noted that conventional plasma freezing methods have typically included blast freezers with heavy-duty compressors, walk-in freezers and use of dry ice. Freezers may have remote mounted or smaller onboard compressors and utilise single- or two-stage refrigeration systems. The mechanical systems, with many moving parts, increase maintenance costs. As the systems age, the units experience failures requiring service and requalification.

“The LN₂ freezer is a novel approach that is expected to increase freezer load capacity/throughput, reduce cost of operation including maintenance/repair costs, and be more environmentally friendly,” the study authors wrote.

The study stated that the modern traditional mechanical freezer tested had a maximum load capacity of 36 units of blood plasma, with a 90-minute cycle time and 24 units/hour throughput. In contrast, the LN2-cooled flash freezer demonstrated a maximum load capacity of 200 units, with a 120-minute cycle time and 100 units/hour throughput. In fact, second-generation blast freezers have double the capacity of the original freezers, allowing a maximum load capacity of 400 units.

Additionally, there were operational benefits from this approach. According to the study, the LN₂ freezer “reduces costs by eliminating traditional refrigeration related mechanical systems … replaces most of the electrical power usage with LN₂ cooling … and eliminates use of refrigerants that are harmful to the environment”.

Another aspect of Cryometrix LN₂ blast freezers is the option to add a rapid thawing capability up to 40°C in the same machine, which can streamline production and make the most of constrained operating space. With this option, the end user does not need two separate machines but can perform both rapid freezing and thawing procedures with one unit as required.

After the study, the blood bank ultimately increased its throughput by about eight-fold by switching to a rapid cooling blast freezer. The blood bank could have replaced 10 large mechanical blast freezers, along with a large rooftop compressor, with just two Cryometrix B-90 blast freezers, Boyce said.

*Del Williams is a technical writer based in Torrance, California.

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