The Gropper group of companies, based in Bissingen in Swabia, Germany, processed approximately 290 million kilograms of milk (of which 50 million was biomilk) in 2015 in order to create a variety of milk products. The majority of these were sold under the brand names of large retail chains in Germany, and some in other European nations. Gropper employs around 700 people, buys milk from 870 suppliers and in the last fiscal year they achieved a turnover of approximately 400 million euros.
The company is continually expanding and in the last few years they began to manufacture smoothies and not-from-concentrate fruit juices. This has been a success: their annual production of these goods has already reached 80 million kilograms. To pave the way for further growth, Gropper opened a completely new plant in Stockach in autumn 2015. This plant will focus solely on the production of not-from-concentrate juices, which require refrigerated transport and storage. This ensures that the naturally fresh flavour is well preserved.
Those responsible for planning this system and associated peripheral equipment at Gropper were able to draw on existing experience: four PET blow-moulding machines and bottling lines are already in use in Bissingen. Therefore Gropper had no doubt that multi-stage piston compressors would be the most economic way to generate this pressure level.
When compared directly, a W-series machine from Belliss & Morcom – a Gardner Denver Group company – proved to be the best value. Therefore, a type WH 29 3N oil-free piston compressor with a 325 kW shaftless motor and a maximum volume flow of 1,800 m3/h (at 40 bar) was purchased.
One of the features of the W-series piston compressors is the special drive concept, which does not have a belt drive or gear and clutch. This direct drive shaftless motor makes for an exceptionally high degree of efficiency, long service life, and extremely low space requirement.
The W-series piston machines are double-acting: two suction and compression cycles are performed per revolution. They are also easy to control, even with the basic version, because they can be operated half load (50 % of full load) by means of unloading suction valves without reducing efficiency. As they are are optimally balanced and can be supplied on antivibration mounts there is no need for a special foundation. And the precision guidance of the piston and piston rod according to the crosshead principle makes for an extremely long compressor service life.
The optimum integration of the compressor in the temperature-controlled processes is crucial for the efficiency of compressed air generation. The system in- Stockach ensures optimum conditions for this, as the entire plant was planned and built from scratch. Berthold Burgmeier: “The compression of the air produces waste heat, which we use for other processes.” Therefore, along with the piston machine, Gardner Denver supplied a heat exchanger. The volume flow can be adjusted via a control valve so that the discharge temperature is kept as high as possible, i. e., at approximately 50 °C.
The key component for heat recovery is a water tank with a capacity of 10 m3, which can be used as a source of hot water or, as an energy reservoir via the heat exchanger. Both the cooling circuit and the heat recovery are also controlled via central PLC of the compressed air station.