A combined heat and power station in Pfaffenhofen, near Munich, in Germany is using a fully automatic grab crane to supply fuel to the furnace. The fuel is wood chippings from sawmills and other small pieces of wood from forestry and agriculture.
The 28MW station supplies heating to Pfaffenhofen and electrical energy to the mains system. To generate this amount of energy, the furnace must be supplied with around 30m3 of wood chippings an hour, 24 hours a day.
After delivery, the material is transported by automatic crane to the storage area and from there to the sliding trays as required. The 65m long and 14m wide storage area is divided into five zones with 12 grab positions in each. These X and Y coordinates are permanently stored in the control of the automatic crane, a Siemens SPC S7. The filling heights of the storage area and the amount of fuel on the sliding trays are constantly registered by three Leuze laser scanners.
The double girder overhead travelling crane, supplied by R Stahl Fördertechnik, has a span of 24m and travels at up to 80m/min on a 65m runway, also supplied by Stahl. The heart of the crane is a special double rail crab equipped with an AS 5025 wire rope hoist with two rope lead-offs. In every lifting cycle the crane is taken near to its 5t SWL. The grab has a deadweight of 2.2t and the weight of the wood chippings varies between 200kg/m3 and 400kg/m3. The crane has long and cross travel drives equipped with frequency converters and is controlled from a control centre. For non-standard procedures, a radio remote control is provided with which all crane functions can be operated manually.
A WCS2 contact-free positional measurement system was installed both on the crane runway and on the crane bridge. It continuously transmits the position coordinates of crane and crab to the Siemens SPC via an interface module with Profibus interface. The data are transmitted to the control via the SLB4 conductor line bus. This type of data transmission eliminates cables which are susceptible to faults. In addition, an SMC1 Multicontroller monitors the hoist and registers all operating data.
The crane has been functioning smoothly in three-shift operation since June 2001 in cycles of up to 50m3 of wood chippings an hour.
