Liquid CO2 and low temperature applications

By Sam A. Rushing, President, Advanced Cryogenics, Ltd.
Special to The Digest

By far, cryogenic freezing of food products is the hallmark of low temperature applications for the commodity. My personal experience with respect to low temperature applications for the commodity have been the lion’s share of the merchant work, in the past with the former AmeriGas, CO2 Division, by far. The same applies today when I work with independent gas companies outside of North America, such as in Africa and the Middle East, when developing and instructing such companies in the art of CO2 usage in food processing, cryogenic freezing and temperature reduction. Cryogenic freezing (usage) of the product is often represents the lion’s share of new developments which these companies put into action. Since near 40% of North America’s merchant usage, on average, is found in food processing, it is impressive to find applications primarily in temperature reduction, and cryogenic freezing. Such usage of course includes cryogenically freezing food products as IQF (individually quick frozen) products, which employ various machines, including batch freezers, which are for smaller operations or test kitchens. Often such batch freezers receive product in trays, on racks, which are pushed into the freezer, using an established residence time for the freezing of select food products. Then, from the batch freezer, in terms of varying sizes of freezers there are a range of configurations, including spiral freezers, single pass, and multi-pass freezers. Some years ago, and today, various gas companies contracted out the construction of freezers with their label or brand name affiliated, using specific valves and stated ‘proprietary’ features to make such freezers unique for the suppler of the equipment – and of course, marketing the associated liquid carbon dioxide product. The goal, of course, is to sell CO2 under contract to the customer; and the machines are a means to an end. Even though is it not legal to ‘tie’ the hardware such as freezers and storage to the supply of liquid, there is a certain inherent ‘obligation’ which can be used, or is inferred, gaining loyalty to the supply of liquid to the customer which is leasing such equipment. This has been the sticking point which companies such as Epco overcame, as they offered highly competitive prices for CO2 to food processing customers, who were leasing from the majors. In any event, the freezers, storage vessels, and other hardware are for sale as new and used pieces, on the open market, and any processor or gas supplier can purchase such assets for their requirements. The used market is particularly popular in this industry.

Over the years, the very large consumers of CO2 such as Tyson Foods, have battled with the price of the commodity, and leveraged nitrogen (LIN) and mechanical refrigeration, primarily, as a means of either selecting the most efficient, or lowest priced means of achieving their temperature reduction goals; or seeking CO2 price stabilization. In the end, the lowest price sources, with the best distribution, and best – located plants tend to win the contracts.

The science of cryogenics is indeed, fascinating. With respect to the mechanism behind freezing, since moisture, as largely water is frozen within the cellular structures of the product, the low temperature and rapid rate of freezing results in less cellular wall damage within the food product; perhaps fewer sharp ice crystals penetrating the cell wall, which inhibits product ‘weeping’. Therefore, less moisture loss, and less weight lost to the food product being sold. Therefore, in the end, the more profit is gained, with a fresher looking, more appealing, and slightly heavier food product; all appeal to the customer. In the end, less moisture loss going to the market. These benefits leave mechanical and glycol refrigeration behind, due to the inherent nature of cryogenic freezing, as just summarized.

With respect to the history of cryogenic freezing via carbon dioxide and other cryogens, such as LIN, this probably dates to an earlier time with the major gas companies, such as Air Products. When air separation plants were producing oxygen for the military in World War II, sometimes there was an excess of nitrogen. Logically, the search for markets with growth opportunities were sought, and developments for CO2 along this timeframe, as well as a decade or two forward, were the early beginnings of CO2 applications in the food industry. There was a need for more applications than (primarily) beverage carbonation, welding, and cylinder gas usage, which are still the backbone in developing markets. Over the years, during my work in the industry, from the merchant to the consulting work, I have noticed significant growth emerging within specific areas of the food industry, such as rapid expansion of CO2 usage in the poultry processing operations; when poultry became a significantly cheaper form of protein than beef, thus, the rapid growth of CO2 demand in this sector.

Another area which is interesting as a CO2 liquid, is the application as a super critical solvent, and ‘green’ chemical synthesis. Under high pressure, the solvent has excellent properties for decaffeinating coffee and tea, extraction of essential oils from spices, and other organic matter, which is in turn used for various food and scented products. When CO2 liquid is applied in a range of industrial uses, such as extrusion for dry ice blasting; these cold products, as a liquid or dry ice represent a ‘green’ alternative to other agents which achieve such an end. This includes LCO2 v. hydrocarbons in supercritical extraction; and replacement of a ‘green’ alternative v. other agents in blast cleaning (i.e. solvents, etc.). Some of these properties also include the obvious, as a non-flammable alternative, and relatively non – toxic, and inert. Kin to this, would be dry cleaning usage for CO2 with specific machines, v. the use of perc, which has been linked to cancer – this is not a cryogenic app per se, but interesting in any event.

With respect to the CO2 applications in food processing, as a cryogen, when piping in liquid to a freezer, for example, there is always the component of CO2 gas, which must be exhausted. The same applies to other configurations, such as producing snow for the food processing application. It is critical to have adequate ventilation in the workplace when using CO2 in freezers, dry ice machines, etc.; thus, proper exhaust is a must in these applications. Of course, the lack thereof is both uncomfortable and dangerous. Over the years, I have been in plants with varying degrees of inadequate ventilation – sometimes overwhelming, and sometimes mildly uncomfortable, the effects of low oxygen and high CO2 levels, range from headache to fatalities.

Major consumers of CO2 in food processing facilities, which consume hundreds of tons per day, often locate near CO2 sources, to remain competitive, such as poultry processors in Mississippi, near the abundant natural sources originating from Denbury Resources’ wells. Also, an interesting large processor in Iowa, is very close to a CO2 source from ethanol, located in Nevada, IA. Such arrangements make for the best – case scenarios, that being supplying adequate large sums of CO2 for processing, very near, or close to the source. The major hurdle with respect to being competitive in the sale of bulk liquid CO2 as a cryogen, is the cost of transportation; this is the age – old challenge in the industry.

As to low temperature reduction applications for bulk liquid CO2, there is a significant market beyond that of the food industry. Applications such as rubber de-flashing, and temperature reduction usage in the manufacture of industrial rubber belts and allied products, often generate heat, and CO2 has been a favorite in some markets for temperature reduction. Since CO2 can accomplish several tasks as a liquid, there is of course the primary benefit as a refrigerant, whether this is food – related or industrial – based. When thinking of low temperature applications for carbon dioxide, dry ice is equally important.

The refrigeration value of dry ice is of course the primary reason for using the product in most meat and food chilling applications, such as injecting CO2 snow into bins, boxes, grinders, and blenders, to chill or cool down products either being ground or blended – thus generating heat – as well as application for simply cooling products, and maintaining lower temperatures during shipments, such as the use of CO2 snow, or dry ice in boxed meat and poultry products shipped via over the road trucks. An interesting niche market for CO2 snow has been the use in specific rail cars, for the chilling of frozen French fries and other food products – this was once a significant market in the US Northwest. The further benefit, which I always mention, beyond a reduction of temperature, of course, is creating an anaerobic environment, as the CO2 sublimates from a solid to a gas, unique to CO2 products, there is an added benefit of inhibiting aerobic bacterial presence and growth. This added value is often not mentioned but is an integral part of the improved ‘bloom’ found in meat product frozen and chilled with CO2; as well as extending the shelf life of food products which are being sold. When considering MAP applications for gas flushing, there are similar objectives sought – where the liquid is vaporized to a gas to achieve this application.

As to trends and developments within the low temperature realm of carbon dioxide applications, some gas companies have proposed cryo-mechanical freezing systems, such as crust freezing via the cryogen, then the rest of the product is frozen mechanically; where the thought is to lock in moisture, then continue the freezing process mechanically. This, among other techniques such as once using sub-coolers along the liquid line into the process, represent claims to drop the liquid temperature, or use a lesser amount of CO2 to yield the result.

For the gas companies, I recommend taking a fresh look at all possible application options for current plants where they supply CO2, as well as facilities which are using other means of freezing and refrigeration. Upon doing so, one can be surprisingly pleased to find new or greater opportunities for sale of the product.

About the author: Sam A. Rushing is president of Advanced Cryogenics, Ltd., a major CO2 and cryogenic gas consulting firm, operating globally, with over 30 years of experience. When you have a need for consulting work, please call or write. Tel: 305 852 2597 Web: www.carbondioxideconsultants.com Email: rushing@terranova.net