Clean and clear1 January 2003
One of the largest hydraulic pivoted rack cleaning systems in the world is operational at the Bad Abbach hydroelectric station in Germany. Martina Grandauer reports
NEARLY 16M from the rack base to the rack platform and a rake width of 7.5m describes in brief the trash rack system in operation at the 3.5MW Bad Abbach hydroelectric station on the river Danube in Germany. With a rack system of this size, an efficient rack cleaning system is an important element in the successful operation of the plant.
During the planning stages of the station, which was commissioned in July 2000, it was intended to equip the hydroelectric station with a conventional steel rope cleaning system with its own lateral trash cleaning system. However, due to the size of the rack system, Germany-based company E. muhr GmbH proposed the use of a hydraulic rack cleaning system with integrated trash disposal.
The requirements of the task were particularly demanding for the designers of E. Muhr GmbH in view of not only the size (which had never before been implemented) of a rack cleaning system of this type but also in view of the disposal of the trash and the extremely cramped conditions - there was less than 2.6m space available behind the rack for erection of the rack cleaning system.
The hydraulic trash rack cleaner EMRA-KBD is simultaneously a trash rack cleaner and trash transportation system. The cleared trash is collected by the rake gripper and, following the pivoting motion of the trash rack cleaner, deposited directly into the container.
Regardless of the level on which the container is positioned, the hydraulic trash rack cleaner is capable of depositing the trash. There is no obstruction to loading of the container by the disposal vehicle. After depositing the trash the rake is swivelled away and the trash rack cleaner pivots back by 90° into its base position.
At Bad Abbach, the EMRA-KBD cleans the 7.55m wide rack and deposits the trash in a container. During the cleaning process the 7.5m wide rake pivots from its base position by means of the lift and swivel arm and the hydraulic cylinder and is simultaneously lowered. At the same time the rake descends several meters in front of the rack towards the base of the rack. At the base of the rack the rake moves in an arc towards the rack.
The rake now moves upward along the 75° inclined rack. Simultaneously the rake is pressed against the rack by the swivel cylinder. The pressure on the rack can be individually adjusted on the hydraulic unit.
After a cleaning stroke of almost 13m the rake reaches the surface of the water. By closing above the surface of the water the rake gripper collects the trash. The rake then swings away from the rack and is lifted to approximately 1m above the top of the container.
The trash rack cleaner now pivots by 90° (the plant has a pivot range of 270°) to reach over the container. The distance from the centre point of the container to the swivel point of the cleaner is 7.6m. Since the 7.5m wide rake gripper is about 1m wider than the container it consists of two sections. At first the trash rack cleaner pivots until one half of the rake is positioned centrally above the container where it opens and deposits the trash into the container. The cleaner then pivots further until the other half of the rake is positioned centrally to deposit its trash.
In the base position the rack arm can be fully swivelled aside and the rake lowers to just above the water so that, despite the vast rack depth, the slender extension arm rises up by less than 5m.
The trash rack cleaner is rotated by a hydraulic transmission brake motor which meshes with the outer teeth of the massive live ring.
The hydraulic system is equipped with various operational and overload protection devices which operate accurately and with longterm reliability. The tubing is made of stainless steel, and the entire design conforms to ZTVW-Wasserbaunormen (German standard for waterprocessing plants).
All movements of the EMRA-KBD can be controlled manually by means of a portable controller.
| Rack cleaning system|
Platform height 15.580mm
Rack width 7.550mm
Rack incline 75degrees
Clearing length 13.000mm
Clearing width=rake width 7.450mm
Hydraulic pump output 22kW, 60 I/min, 200bar