Food processing

The term “food industry” is used here to cover all industries that process foods. As well as dairies and breweries, this includes slaughterhouses, large bakeries, coffee roasting operations and chocolate factories. Here the refrigeration capacity installed is mostly larger than in the applications described above, and may range up to several megawatts (MW).

Today the food processing industry largely uses ammonia and CO₂ as refrigerants for new systems. In many cases, however, existing systems still contain R 22. The use of R 22 in new systems has been banned in Germany since 1 January 2000. While CFCs were used until they were banned in the mid 1990s, they were only of minor importance even then [UNEP 2003;

UBA 1989; FKW 1998b]. Despite the ban on the sale of virgin R 22 scheduled for 2010, little

revealed that about half of all refrigeration systems in the food processing sector contain R 22.

Experts [KK 2009b] believe that these figures can be applied to Germany as well, and that an estimated 4,000 t of R 22 is present in such systems. Conversions, like some new systems, mostly use HFC mixtures as refrigerant [FKW 1998b; FKW 2001].

Although refrigeration in the food processing sector plays an important role in the field of industrial refrigeration, energy considerations have resulted in most major installations going over to using ammonia, or in recent years CO₂ as well. In 2001, HFC emissions arising from refrigeration in the food processing sector came to nearly 120 t [Schwarz 2003b].

Reduction options

In individual cases natural refrigerants such as CO₂ and ammonia can also be considered for conversion of CFC / HCFC systems [UNEP 2003; Gebhardt 2000; Gebhardt 2002b]. As a rule, however, this causes problems because of incompatible materials or high pressures [Witt 2009].

“For new systems, natural refrigerants have always been used for preference in industrial refrigeration for reasons of energy efficiency alone – ammonia is acknowledged to be the most economical refrigerant of all” [Witt 2009]. Thus ammonia is the usual refrigerant in the food industry as well. It is particularly suitable for industrial purposes above –35°C. In the industrial context it is also possible to use direct refrigeration systems with ammonia. In the refrigeration capacity range required here, ammonia systems are energy-efficient and inexpensive. Thanks to their energy efficiency, ammonia systems also contribute to reducing total greenhouse gas emissions.

Apart from pure ammonia, a mixture of ammonia and dimethyl ether (DME) has also been used in refrigeration systems in the food industry for some years now. This blend, known as R 723, has a very low global warming potential of 8. One example of its application in food processing is found at Südbayerische Fleischwaren GmbH. Two R 723 multi-compressor systems with a capacity of 150 kW each were installed at their factory in Obertraubling, near Regensburg [KK 2009a].

For some years now, CO₂ has again been used increasingly in new systems, either as refrigerant in the lower stage of cascade systems, or as secondary refrigerant. According to manufacturers, the use of CO₂ in transcritical refrigeration systems is currently not being pursued for industrial refrigeration, partly for energy efficiency reasons [Danfoss 2007].

However, UNEP [UNEP 2009] lists CO₂ as a refrigerant for transcritical industrial applications as well, so it remains to be seen how industrial systems with CO₂ as refrigerant develop.

In some cases CO₂ is used to reduce the quantity of ammonia present in these systems, which are often very large, thereby simplifying authorisation procedures [Axima 2003a; Danfoss 2010]. This trend has been observed for nearly ten years in the case of very large systems in particular, not only at European level, but also worldwide.

It is not the size of the system, but the temperature that is crucial for the use of CO₂ as a

systems have economic and other advantages. For example because the high volumetric refrigeration capacity of CO₂ makes it possible to build compact systems (system components). Its good availability combined with a low price also reduces costs. CO₂ refrigeration systems also have a positive impact on product quality: Where CO₂ cascade systems are used for shock freezing fish, the greater efficiency of the system makes it possible to freeze the fish faster and at lower temperatures. This improves its quality. This process also consumes less energy than when using other refrigerants [Danfoss 2007]. Possible refrigerants for the high-pressure side in CO₂ cascade systems - apart from HFCs (e.g. R 410A or R 507) - are especially ammonia and also, for thermodynamic reasons, halogen-free hydrocarbons.

CO₂ is very attractive as a secondary refrigerant in applications with low and medium temperatures (up to 0°C) [Danfoss 2007]. Systems with CO₂ as a secondary refrigerant have been implemented, as have two-stage CO₂/ammonia cascade systems in the deep-freeze range (down to about -50°C), e.g. for frosters (freezers for bakery products and other foods) [eurammon 2002, KK 2006b], freeze-drying [Selmer 2001; Gebhardt 1999] and breweries [KK 2006b].

Another means of providing refrigeration without using HFCs (or using smaller quantities) is to use ice slurry (as secondary refrigerant) in combination with a (halogen-free) primary refrigerant. Ice slurry can be used, for example, in the meat industry, breweries and fruit and vegetable processing. According to one supplier, the higher fluid temperature and the resulting higher evaporation temperature compared with direct evaporation or operating with brine make it possible to reduce operating costs thanks to lower energy consumption [Integral 2003]. However, this does not apply specifically to the use of ice slurry in combination with a halogen-free refrigerant.

The energy efficiency of systems with natural refrigerants is undisputed in industrial refrigeration. For example, practical experience in cost calculations for funding applications repeatedly show that, because of their greater efficiency, systems with natural refrigerants are up to 40% lower than the TEWI figures for conventional systems [KK 2009a].

Information about abatement costs based on CO2 equivalent dates from 2000 and earlier. This was based on the state of technology at the time. It does not take account of the very economical use of CO2 as a refrigerant. At 2.7 € per tonne of CO2 equivalent for total HFC substitution in new systems [Harnisch, Hendriks 2000] and 20-30 € per tonne of CO2

equivalent – combined with reduced HFC input and a significant reduction (of up to 3%) in annual HFC leakage rates – in the remaining HFC systems [March 1998], the calculated abatement costs are nevertheless low compared with the estimated costs of a straight reduction in emissions from HFC systems (62 € per tonne CO2 equivalent [Harnisch, Hendriks 2000]). Particularly because of the continued developments in the field of natural refrigerants over the last ten years, these cost estimates – despite all uncertainties – permit the conclusion that replacement of HFC is economically possible and should be preferred to technical emission reduction measures from an economic point of view as well.

The economic and energy-related assessment of CO2 systems, and especially CO2 cascades

are compared with ammonia systems, since HFC systems are not of any great significance in this field of application. On balance, CO₂/ammonia systems are considered to be cost-effective and energy-efficient [e.g. Gebhardt 2002a; Gebhardt 2002b; Roth, König 2002].

In addition to compressor refrigeration systems, to which the above remarks refer, the food industry sometimes uses absorption systems, which basically manage without HFCs. The reader is referred to Chapter 3.1.2.

Conclusions

Whereas a few years ago the standard refrigerants in the food industry were R 22 and ammonia, since the ban on R 22 this has only been true of ammonia and increasingly of CO2 as a low-temperature refrigerant. Ammonia systems are notable for their high cost-effectiveness and great energy efficiency. CO2/ammonia systems have also demonstrated their cost-effectiveness and are now state of the art.

HFCs are negligible as refrigerants in the food industry and are not necessary. This is due to their lower cost-effectiveness in this field of application.

When considering cost, the capital expenditure and operating costs must always be included. In individual cases, it may only emerge at this point that HFC-free systems are the better alternative in the long term.