FOR thousands of years farmers have understood the basic benefits of nitrogen, (although non-specifically), through crop rotation and use of fertilizers. As an inert gas, nitrogen acts as a perfect carrier or blanketing agent in all kinds of chemical processes.
Production of Liquid Nitrogen (LN2) as a by-product of oxygen production has lead gas companies developing a wide variety of applications over the past 100 years or so. The food industry is one such industry that has benefited in the use of nitrogen in both its gaseous and liquid form \\$quot;“ certainly over the past 30 years.
Our industry is familiar with some of those applications in which we market the benefits of liquid nitrogen freezing and chilling over mechanical processes. However, in regions such as North America and Western Europe, these applications are relatively mature but in other regions around the world \\$quot;“ particularly in Asia/Far East and also in South America \\$quot;“ such uses are still developing strongly.
In many cases the use of Liquid Nitrogen (LN2) freezing, or Cryogenic freezing as it is known, is a preferred alternative to the use of Mechanical Freezing devices such as traditional refrigeration units (spiral freezers, bed freezers etc.). Cryogenic freezing has traditionally been attractive due to its low capital costs as units tended to be far smaller, and cheaper to produce. Companies have been able to gain large refrigeration capacity at little or even zero capital cost, simply by renting cryogenic storage tanks and freezing/chilling equipment from gas companies and buying Liquid Nitrogen (LN2) to suit demand.
Major players in the food industry have used Liquid Nitrogen (LN2) for freezing meats, fish, poultry, dairy and bakery products and many others such as pasta, prepared meals (microwave meals), fruit and vegetables. In some cases the very rapid freezing with Liquid Nitrogen (LN2) has very marketable benefits. Such as the prevention of crystal formation on food stuffs which causes cell damage to the product. Liquid Nitrogen (LN2) prevents oxygen from reaching the food\\$quot;s surface this denies bacteria the oxygen they need to grow and multiply. Where mechanical freezers can cause dehydration of products cryogenic freezers can avoid any dehydration, which in turn provides producers with a better yield.
The gases food market sector has been developed by the likes of Praxair, BOC, Air Products, Air liquide, Linde Gas, SIAD and others, all produce an extensive range of cryogenic freezers capable of handling most food products. The majority of equipment is made from stainless steel primarily to cope with the low temperatures (Liquid Nitrogen is - 196Â°C) and meet with international hygiene regulations. The spiral freezer type offers the largest capacity, a mesh belt, on which the food is placed, spirals vertically within the freezer box allowing a large capacity for a relatively small floor space.
Another popular design is the Tunnel freezer. These are either straight tunnels with single or multiple deck conveyor belts, sometimes three, situated above one another. Also popular has been the dip freezer, which initially immerses the product in liquid nitrogen to achieve rapid crust freezing before it is carried away in standard tunnel arrangements to attain the required frozen temperatures (-180C).
More recent developments include fluidized bed freezers and impingement freezers that achieve high heat transfer rates by subjecting the product to high velocity gas movement. All of these types of freezer, apart from the immersion freezer, are versatile enough to run on both Liquid Carbon Dioxide (LCO2) and liquid nitrogen (LN2) \\$quot;“ the advantage nitrogen has over carbon dioxide is it much higher cold content.
Perhaps the most interesting recent development in the field is in what has become known as Cryo-Mechanical Freezing. This process combines the benefits of the rapid \\$quot;˜crust freezing\\$quot; dehydration loss minimization ability of Liquid Nitrogen (LN2) or liquid carbon dioxide (LCO2) with the low running cost of Mechanical Freezing to finish the freezing of the food product.
Development from freezing to chilling foods
Apart from the frozen foods sector there is a vast and rapidly expanding market for Liquid Nitrogen (LN2) in the \\$quot;˜chilling\\$quot; of foods. For fresh fruit and many convenience foods that do not withstand or even require freezing food chilling equipment is required. For fresh fruit in particular on site chilling solutions are required to prevent field heat deterioration. Several ground and diced food products are also cryogenically chilled in blenders using Liquid Nitrogen (LN2).
The two main methods of freezing food, cryogenically with Liquid Nitrogen (LN2) and Mechanical Freezing, broadly speaking, represent the options available to food manufactures. So in today\\$quot;s rapidly changing environment with fixed costs for energy production rising for all industrial users, are we about to see a fundamental shift in the market of food product freezing and chilling.
gasworld spoke to the industry experts to gauge opinion.
Mr. Karel Vanacke of Cryogenic
Equipment and Services (C.E.S), based in Belgium:
KV: \\$quot;I think for the moment the gas companies are surely trying to get prices up because of the increases in energy costs, but this is not a new phenomenon\\$quot;\\$quot;¦..\\$quot;I think indeed there are two things to remember, one is that customers are very sensitive to the gas price as the smallest change can increase cost considerably. Secondly that this does not necessarily happen at the same rate in the mechanical freezing market\\$quot;¦.. The LN2 market is very sensitive to price instability, an increase of cost of up to 20 per cent will scare off a lot of customers, that\\$quot;s a fact.\\$quot;
Stateside Mr. Bryan Smith (BS) of Cryoquip Inc, based in California, was more circumspect when asked if higher energy costs was driving customers out of the LN2 market:
BS: \\$quot;Not to my knowledge. You either pay for the gas or the power. The few remaining cryogenic freezers are probably locked into the process unable to justify the capital expenditure to go me chanical or the process is unique enough to justify cryogenic freezing.\\$quot;
If then we are indeed seeing the demise of cryogenic freezing on a large scale basis is mechanical freezing making a comeback?
BS: \\$quot;The mechanical freezing industry made its \\$quot;comeback\\$quot; years ago. Once the FDA changed the rules allowing water extracted by the freezing process to be added back, it killed the cryogenic freezing industry [in the US], and gave the mechanical freezing boys a new market. With this new incentive they developed a whole new range of highly effective highly efficient machines that displaced practically all of the large cryogenic freezing installations. In turn that released enormous quantities of good quality nearly new machines into the market.\\$quot;
It would seem then that regulations have created somewhat differing market outlooks for Europe and the US. So what of future forecasts for the Liquid Nitrogen (LN2) food freezing market?
KV: \\$quot;I think that changes will not be dramatic and fast, they will be slight and they will be slow. One possibility is that the more centralized and concentrated the production of food becomes, with bigger and bigger plants servicing the large multi-national producers we may see the balance switch from cryogenic to mechanical freezing methods. The incentive being the increased speed which mechanical freezing offers.\\$quot;
The US viewpoint is somewhat different:
BS: \\$quot;The future for liquid nitrogen (LN2) in the food industry is that it will do well to hold its own. Growth will be hard to come by, and unless a surplus of LN2 is generated by the gas companies it is hard to see how it will compete with the new generation of mechanical freezers\\$quot;¦.. \\$quot;We are virtually out of the freezer manufacturing business, there are so many good freezers available second hand or through \\$quot;˜refurbishers\\$quot; that the new \\$quot;˜standard freezer\\$quot; market is dead. We have diversified into other products.\\$quot;
Diversification is something that has become a fact of life in the European market as well:
KV: \\$quot;˜We are seeing diversification. We are now also selling to the bio -pharmaceutical industry, and now also the steel industry. That has been a big change for us. For the Steel industry particularly we are seeing a rise in demand for sub zero quenching applications\\$quot;.
So will we see Liquid Nitrogen (LN2) use in cryogenic freezing go the same way as the US market? Without the same regulatory pressures Mr Vanacke sees a balance to be struck:
KV: \\$quot;In the future we may see greater use of both methods together, what is known as \\$quot;˜Cryomechanic\\$quot; freezing. Whereby immersion type freezers are placed in front of a larger the mechanical freezer. The immersion freezer acts as a booster, reducing temperature, before items move through to the mechanical freezer. A small immersion freezer, only two to three metres long can increase output from the conjoined
mechanical freezer by as much as 20 \\$quot;“ 30 %.\\$quot;