Worldwide consumption of PET bottles is booming. Mineral water, soft drinks and iced tea are sold all over the world in PET bottles. In fact, some 89 billion litres of mineral water are bottled in PET bottles every year. In the US, consumption is equivalent to 1,500 bottles per second, and in Germany alone, some 800 million PET bottles are in circulation at any one time. But what actually happens with the empty PET bottles?
Self-producer of heat and power
Vogtland PET GmbH in Neuensalz near Plauen is a German company that re-processes PET drink bottles. To provide the heat needed for this process and cover peak power demands, Vogtland PET has opted for a containerized CHP module based on a Series 400 natural gas engine from MTU Onsite Energy.
"Rather than producing heat electrically in the usual way, we have our CHP module which boasts 90% efficiency and allows us to avoid expensive peaks in electrical power consumption, which brings us a significant cost saving," explained general manager Uwe Röhn. It is not the first time that the company's management has chosen to endorse MTU Onsite Energy - it deployed its first genset back in 1990, and this was supplied by MDE Dezentrale Energiesysteme GmbH, which was taken over in 2006 by MTU Friedrichshafen GmbH."The very positive impression I got then of MTU Onsite Energy's cooperativeness and reliability prompted me to decide in their favor again," explained Röhn.
From bottle to regranulate
Since 2007, Vogtland PET has been converting PET bottles into what is known as regranulate in three production stages. The PET bottles are pressed into bales for the first stage of production. These are then broken down and the bottles sorted automatically according to color, with removal of metal, labels and other foreign matter. The bottles are then crushed, and separated into a polyethylene terephthalate or PET fraction and a polyolefin fraction, which are subsequently cleaned. "The utility water we need for washing is brought to the required temperature using waste heat harnessed from the engine in the CHP module," explained Röhn. After cleaning and drying, the PET flakes pass through an extruder, where they are melted and formed into strands which are briefly cooled in a water bath and then crushed, after which they take on a crystalline form. In the next stage, this material is decontaminated in what is known as solid-phase poly-condensation. The pure PET granulate that results can then be forwarded to the next processing plant in the chain where it is manufactured once again into bottles.