At 6 AM the first gripper crane gets underway at Holzkontor Preussen GmbH in Berlin's Spandau neighbourhood. The plan for the day? The same as every day - shred at least 500 tonnes of used wood, clean out the metal and load it for transport, to feed a large wood-fired power and heating plant.
"We're the main supplier for the plant, with an annual volume of 150,000 tonnes of fuel," says operations manager Uwe Kulitzscher of the company's responsibility. "Buffer capacity is limited, both here and at the power plant, so we need to continuously prepare and deliver fuel." Normally a stationary system would be used to handle this enormous throughput, but a breakdown about six months ago prompted the company to start using two mobile machines. "It was clear to us from the beginning that our requirements represented an extreme case for the mobile machines. We work used wood of all kinds, from simple pallets to heavy construction timbers with massive iron clamps. Despite our best efforts at presorting, massive contraries still get into the shredders and we have to deal with it," says Kulitzscher of the tough conditions the Crambos must cope with until the stationary unit is up and running again.
The three criteria
"The interplay of throughput, consumption and wear was the deciding factor in selecting the machines," says Kulitzscher. "We tested a number of machines, and it was often obvious after just an hour that they weren't up to the task." The Komptech shredders ultimately won the daily waste wood marathon. They work in a two-stage process. A Crambo 5200 direct with large screen basket does the pre-shredding. A magnet on its discharge conveyor removes most of the metallic contraries. A Crambo 6200 direct then fine-shreds the material to the 0 to 200 mm grain desired by the customer. Another magnet separator further reduces the metal content. Gripper cranes feed the shredders, a demanding task despite their polyp grippers. "We can consistently turn out 40 tonnes of finished product per hour, and maintain that rate over the long term," says Kulitzscher, praising the Crambo shredding system. It only shuts down for refuelling.
Efficiency has a special place in the overall fuel preparation concept. The processing plant and the power plant are situated so that fuel supply can be by ship. They're only 20 km apart by road; the water route is longer, but shipping is significantly more environment-friendly than it would be to deliver by truck. Uwe Kulitzscher appreciates the location advantage. "I can load 500 tonnes of fuel on a ship. To deliver that amount by road I would need to send 50 trucks through town. That means higher transportation costs, and more exhaust and noise pollution. In cold winters the canals can freeze over, and that creates a real logistics challenge for all concerned."
Efficient - quiet - clean
For true sustainability, low-emission transportation also needs to include low energy consumption in the fuel production. That is precisely where the Crambo shines: Its mechanical drive system uses energy extremely efficiently. Even at high loading, its diesel consumption remains under 40 litres per hour. Energy costs are a very important factor, but so are noise and pollutant emissions. Here again these shredders are at the head of the class; the latest exhaust scrubbing and special sound-insulated engine compartment makes them anything but "loud and smelly."
Uwe Kulitzscher also has plans for later, when the stationary system comes back online. Then the mobile machines will be set free once again, to shred waste wood or possibly other biomass materials at customer sites.