Key points
If you are a food processing specialist, you may not be gripped by the question of what refrigerant your chilling or freezing plant uses. But for those who work with the technology, it is an important – not to say urgent – question.
According to Graeme Maidment, professor at London South Bank University’s Centre for Air Conditioning and Refrigeration Research, the biggest challenge faced by the industry is the quest for the refrigerant of the future.
The phase-out of one of the most widespread refrigerants, R22, has been progressing for some time, and it will finally be taken off the EU approved list for new installations by the end of 2014. R22 is effectively the last of the hydrochlorofluorocarbon (HCFC) family of gases to still be in industrial use. So what do suppliers have lined up as a replacement?
“Attention has shifted to HFCs (hydrofluorocarbons) such as R404A, but they’re under threat, too,” says Maidment. “These, too, are refrigerants with high global warming potential (GWP), and their use is likely to be restricted by the new wave of fluorinated greenhouse gas (F-gas) regulations, including a phase-down and a cap. This second phase is coming, and it will be much stricter. The drop-in replacements to R22 simply won't be available in certain applications.”
The up-and-coming alternative is the hydrofluoro-olefin (HFO) group of gases. “These new-generation refrigerants are on their way, with a low GWP,” he says. “But we also know relatively little about them.”
Also competing for consideration are the ‘natural’ refrigerant gases such as ammonia and carbon dioxide. “They have fantastic properties, but they have their issues,” Maidment concludes.
At Refrigeration Developments and Testing (RD&T), director Judith Evans agrees that, with its low GWP and relatively high efficiency, ammonia will often be the refrigerant gas of choice for larger or integrated plants, even though its toxicity is always going to be a concern.
According to Evans, it is not only users of ammonia who should worry about the possibility of a spill. When it comes to the use of R22, she says, surveys last year and this indicate that industrial users are not phasing it out or seeking alternatives. “That’s fine if it doesn’t leak," she says. “But if it does, the company will not be permitted to top it up with more R22.”
Frigoscandia supplier JBT Food Tech takes a similar view: that there is no perfect drop-in replacement for R22. It says it has not used R22 for the past decade and a half, instead typically supplying ammonia-based systems. “People have tended to shy away from it because of the tighter regulation, and the fact that, if you do have a leak, it means you’re evacuating whole areas,” admits regional sales manager Barry Jackson. But tighter regulations and safeguards mean incidents are much rarer today, and ammonia remains an efficient refrigerant offering even higher rates of heat transfer than R22.
Frigoscandia has tended to supply installations at the larger, integrated end of the scale, but a recent introduction has been a range of more compact, “competitively priced” spiral freezers targeting mid-range capacities more cost-effectively. The new freezers hit the 1.8–2.2t/h range for par-fried chicken nuggets, for example, or the 2–2.4t/h range for croissants, says JBT.
Power used for freezing (Return to top)
With energy bills rising inexorably, for a business freezing product, power used for freezing is likely to be largest single component in the firm’s utility bills, Jackson argues.
Are manufacturers really concerned about this? “It all depends on their size,” he says. “A big business freezing peas, for instance, could be turning out 15t of product an hour through 15MW of refrigeration. That equates to around 1.5MW of electricity usage per hour. On that scale, any reduction is significant.” And with more categories tending towards consolidation around larger plants, the benefits of any saving on chilling and freezing costs are becoming clearer, he believes.
Partly for cost reasons, partly for reasons of flexibility, JBT says it has seen a migration of its Low Volume System (LVS) refrigeration technology from the largest plants to smaller systems. “This dry suction method means we only recirculate the gas, not liquid-and-gas, which makes it more efficient and easier to expand,” says Jackson. “The traditional route of the surge drum limits that potential.”
As he explains, retrofitting an LVS means that a manufacturer can opt either to increase efficiency on the same volumes or reduce temperatures to cope with a larger throughput.
Evans at RD&T sees some different priorities at work. “For cold stores, energy costs may be a concern, but for many food production facilities, it’s more about getting the product out of the door at the right temperature,” she says.
“With meat, for instance, the cost in terms of weight loss in not chilling product quickly enough might be up to 24 times what a company could recover through energy savings,” says Evans. “Yes, the cost of energy has gone up but though it's not fashionable to say so – it’s still relatively cheap.”
Freezing capacity (Return to top)
Freezing capacity is likely to be the pinch-point for any frozen food manufacturer looking to expand production beyond what was ever predicted for the plant. Two or three years ago, RD&T worked with Apetito to analyse the options for adapting operation of its three spiral freezers in order to cope with increased output.
“They wanted to put different-sized products through the various freezers,” says Evans. “Production had increased so much that, in the end, they had no choice but to buy new kit. This is quite a common problem for manufacturers.”
At GEA Refrigeration UK, sales and product development director Robert Unsworth takes up this theme. “Today, many investors focus on flexibility. Is it possible to vary the load of my freezer without wasting energy? Can I change product shape without disadvantages while freezing? How can I minimise energy consumption while maintaining product quality? These are questions that drive R&D,” he reports.
GEA has launched its High Velocity Freezer, an impingement system said to offer improved nozzles and overall efficiency. “The faster products are frozen, the smaller the ice crystals,” Unsworth explains. “In fast freezing, ice between cells has virtually no chance of sucking moisture from inside the cells.” This benefits final texture and flavour since, when the product thaws, most of the water lost is from the ice between cells.
In fact, manufacturers looking for either of these advantages – faster freezing or flexibility – or both, will often consider cryogenic freezing.
Cryogenic freezing (Return to top)
At Air Products, European food cryogenic and water manager Ann Callens adds: “Mechanical freezing systems are relatively inflexible. They’re set up for a given capacity, and once you’re at the maximum, it’s hard to move beyond it. With one of our tunnels, on the other hand, if you’ve set up a line for 100kg of product an hour, it’s likely that you can push that to, say, 300kg. It’s to do with the speed of the belt, the amount of nitrogen you inject. The programme can be adapted.”
Of course, the acknowledged drawback with cryogenic systems is the high operational cost of the nitrogen. Responding to these concerns, Air Products offers monitoring, to ensure efficiency is not compromised, and has an optimisation programme to maximise heat transfer.
As Callens explains, as well as offering standalone flexibility, cryogenic systems can help mechanical systems to adapt, too. “For instance, if a company has a large spiral freezer, where increased output means that product is coming out at -12°C, say, rather than -18°C, it may decide to add a tunnel at the infeed to the existing system, providing an initial boost to the temperature,” she says.
At Grimsby Institute's Food Refrigeration and Process Engineering Research Centre (FRPERC), senior research fellow Christian James points to a further advantage of cryogenics in seasonal produce categories. “If you switch off mechanical refrigeration and mothball it for months at a time, getting it up and running again isn’t so easy,” he says. “They like constant running.” This is not the case with cryogenic chilling and freezing.
Meanwhile, FRPERC is among those looking at chilling and freezing technologies which are still a long way from being mainstream. Supercooling brings and maintains product below its freezing point, but without the formation of ice crystals. “It gives you a few more degrees and a longer storage life,” says James. “But we’re currently researching the right conditions for stable storage.”
Not to be confused with supercooling, superchilling is probably more accurately described as ‘partial freezing’, he says. It has been used in the fish industry for some time. “But, depending on the category, there’s a question mark over how much damage it does to product. And a lot more work needs to be done on target temperatures and how they should be achieved,” he recommends.
Supercooling and superchilling are just two of the technologies jostling for recognition in the world of food industry refrigeration. As issues such as food waste grow in importance, any capacity for maintaining quality while extending shelf-life will be studied very carefully.