Dairy company DMK in Bad Bibra, Germany, processes one million liters of milk into cheese and whey concentrate every day. Atlas Copco oil-free, water-cooled ZR compressors supply the air for this process, while 75 percent of the energy used to generate the air is captured and reused a second time via an ingenious heat recovery system.
ZR compressor at dairy company
With 28 sites in seven German regions, DMK covers the entire northwestern area of the country from the Danish to the Czech borders and from the Baltic to the Rhine. The company processes 6.6 billion kilos of milk annually, making it the largest milk processing company in the German market. With extensive investments in its production facilities, services and logistics, DMK plays a strategic role in the region’s economy.
Oil-free air for the cheese cake
Quality and safety are paramount in milk processing, and DMK is certified in accordance with International Food Standard IFS6. In order to meet these high standards, the DMK dairy in Bad Bibra uses three Atlas Copco compressors – one ZR 55 VSD and two new ZR 45s – to supply 100 percent certified Class 0 oil-free compressed air to the cheese production lines. Since the compressed air comes into direct contact with the cheese, it is absolutely critical that any oil is completely eliminated during processing.
“In the past, we used oil-injected compressors,” explains Johannes Bechtle, Technical Manager at DMK. “We filtered the oil from the compressed air using activated carbon and other filters.” Ultimately, this method was not reliable enough for the dairy facility, and it was also costly because the filters needed to be changed extremely frequently.
Significant savings thanks to Variable Speed Drive
Today, DMK relies on a ZR 55 compressor with variable speed drive (VSD) and two ZR 45 compressors with load/unload regulators to supply air to its production lines. These water-cooled compressors use absolutely no oil in accordance with latest edition DIN ISO 8573-1 Class 0. Instead of the laborious process of filtering the oil out of the compressed air, oil-free air is produced from the outset. Furthermore, this method removes any other potential pollutants by using a combination of DD and PD filters in the compressors.
The highly efficient ZR 55 compressor’s VSD technology regulates its speed to meet peaks in the demand. One of the two ZR 45 compressors is switched on during peak demand periods; these fixed speed compressors are alternated at regular intervals. This configuration has resulted in significant energy savings for DMK.
Since the installation of the new machines in February 2013, energy consumption has been reduced from 12,000 kilowatt hours to 10,000 kilowatt hours per week, and the improved regulation also has meant that the no-load hours have decreased by 1,000 kilowatt hours per week. Energy efficiency has also been facilitated by the central controller, the Atlas Copco ES 6 energy-saving system, which monitors and controls the compressors in the air network and maintains a stable and narrow compressed air-pressure band between 7.5 and 8 bar.
Heat recovery system re-uses 75% of compressor heat
The ES 6 helps to absorb major fluctuations to save energy. For example, the second largest compressed air consumer in the dairy is the prepress vat, which is used to blow the cheese out of the molds. During operation, the compressed air requirement dramatically increases to 792 m³/h, but when it is down and being cleaned, the compressed air requirement is significantly reduced to 216 m³/h.
The ZR compressors are water cooled, and due to an ingenious heat recovery system, 75 percent of the energy that is used to generate compressed air can now be reclaimed and used during cheese production. When it leaves the compressor, the cooler water is nearly 80°C and can preheat the water for the wash system, which requires a water temperature of 90°C to operate, via two heat exchangers. This process saves a great deal of energy. As a result, of the 10,000 kilowatt hours per week, 7,500 kilowatt hours are reclaimed via heat recovery.