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Ammonia brings home the bacon

MEAT is still one of the most popular items on the menu in Europe. For instance, each citizen of the European Union eats about 90kg of meat a year, on average.
Ammonia brings home the bacon
Refrigeration, of course, plays a vital role in meeting the strict regulations concerning freshness, quality and hygiene that are demanded in meat processing, and ammonia refrigeration systems are proving to be as popular as the meat it cools.

Since 2005, Danish Crown has operated the world's most modern pig abattoir near the little Danish town of Horsens. As well as being one of the most modern, it is also one of the largest in the world, with a production area of 75,000m2. Each day an average 10,000 pigs arrive here for slaughter.

For the new plant, Johnson Controls Denmark planned and installed a two-stage ammonia refrigeration system in co-operation with Güntner.

To provide air conditioning for the staff rooms, an indirect refrigeration circuit containing glycol is connected to the system via a plate heat exchanger.

The refrigeration system itself is charged with 48 tons of ammonia and cools the various processing and storage areas through direct evaporation.
Via a network of pipes that is some 15km long, a total of 175 valve stations distribute the ammonia to around 150 air coolers, which distribute the chilled air.

The various temperature requirements around the plant are met using twelve screw compressors made by Sabroe, with a total capacity of approximately 14MW. Four of the compressors generate a temperature of -3°C, three cool to -10°C, and the final five to -25°C. The air supplied to various other parts of the plant such as the offices, the kitchen and the canteen is being conditioned as well.

Because air channels could not be used for hygiene reasons, the system uses a large number of compact, soundproofed air conditioning units mounted on the roof to deliver the processed air precisely where it is needed.

A total of 142 heat exchangers made by Güntner are used to cool the air, or heat it in case dehumidification is needed. These units are made of stainless steel and aluminium components and measure up to 2.5 x 4m in size. Their dimensioning ensures that the evaporation temperatures are never unnecessarily low, and that all of the requirements are met while minimising energy consumption.

Savings are also achieved through heat recovery, which is used to recover as much as 5MW altogether from the oil coolers, from overheating the refrigerant and from the condensation heat.
A 1.8MW heat pump uses this heat energy to heat the process water for the abattoir.

Organic solution
The organic meat producer Mühlviertler Alm Biofleisch GmbH has also opted for an ammonia-based solution at its production facility in Unterweißenbach, Austria. All of the meat processed into sausage, ham and bacon here comes from organic farms.

To ensure that the company can systematically adhere to its 'green' approach to meat production, engineering consultants KWN Engineering devised a water chiller charged with the refrigerant R723, an azeotropic blend of 60% ammonia and 40% dimethyl ether.

Charged with 55kg of this blend, the refrigeration system built by Frigopol and installed by Hauser provides cooling for the processing and storage rooms as well as air conditioning for the staff rooms, with a refrigerating capacity of about 111kW.

Cooling is provided by absorbing the heat using a 38% mixture of water and propylene glycol, which is then taken away to the evaporator. There, the heat is transferred to the R723, which evaporates at -11°C in the refrigerant circuit.

Depending on the required cooling capacity, the gaseous refrigerant is then compressed using one or both of the open type reciprocating compressors.
The heat is finally removed by the air-cooled condenser, which liquifies the R723 at a temperature of between 20 and 40°C, depending on the outside temperature. It then flows back into the evaporator, where refrigeration oil that was carried by the R723 from the compressor into the refrigerant circuit is deposited.

Due to the dimethyl ether, the refrigerant is able to mix well with the oil and can carry it reliably through the suction line back to the compressor, where it lubricates the moving parts. For this reason, the use of R723 allowed Frigopol to do without a separate oil return system and keep the design of the refrigeration system simple. Apart from this, the comparatively low final compression temperature of the R723 - which is due to its alcoholic component - made it possible to use an air-cooled condenser instead of a water-cooled condenser for heat removal.

Frigopol fitted the condenser with four fans to reduce the noise level of the system, which is mounted outdoors. The system also contains a 24kW desuperheater to transfer the waste heat to the process water.

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