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Wood Waste to Heating Energy

König + Neurath AG, one of the leading European office furniture manufacturers, in Karben near Frankfurt/Main process derived timber products such as chipboards and multiplex boards to produce office furniture for nearly any furnishing purpose. The resulting wood residues are not discarded but processed to become combustible by means of which the complete heating and process heat demand of the company is met (wood waste recycling).

Up-to-date production  
Central components of this up-to-date production facility are automated machining centers which produce the basic elements of the respective pieces of furniture starting from ready-made chipboards and/or multiplex boards. The wood residues resulting from this production are transported from the machining centers to Weima grinders via conveying belts.  

Treatment of wood residues - reliable and quiet   
The conveying belts of two machining centers each run into the hopper of a downstream WL 6S single-shaft size reduction grinder made by WEIMA Maschinenbau GmbH, Ilsfeld. The lateral insertion openings of the hopper are covered with a strip-type plastic curtain.  The remaining sides are completely closed. These measures result in a very low annoyance caused by noise and dust. Through the hopper the wood residues fall onto the bottom of the machine body. From there they are pushed against the turning rotor by a hydraulically actuated pushing device which is controlled depending on the load, and which is horizontally arranged in the machine body.

The rotors of the single shaft (shredding) machine of the WL series are made from solid steel.  The profiling of the V-rotor is unique and includes a patented knife seat design. The knife carriers are welded onto the circumference of the rotor. Into these carriers the cutting knives are screwed from behind. This guarantees a quick knife change.  The design and construction of the screw heads are configured to prevent damage during size reduction. The rotor width is 800 mm with a rotor diameter of 368 mm.

The 42 cutting knives are made of tool steel. Despite the highly abrasive material the knife service life for each knife edge is approximately half a year, meaning a total of approximately 2 years.

The pushing device is equipped rail guides to prevent undue wear on the machine housing. Optionally, the pushing device is equipped with a horizontal and/or a vertical toothed rails in order to feed bulky material. The hydraulic system of the pushing device is installed within the machine body such that it is protected from wood dust and damage. The hydraulic cylinder is suspended on a universal joint to avoid undesired transverse forces acting onto the piston.

The machines are driven by an electric motor which transmits the force via the hydraulic clutch, V-belt and gearbox to the rotor - with a driving power of 22 kW and a rotor speed of approx. 80 rpm. The machines are equipped with a hydrodynamic centrifugal clutch for a load-free start up. They are controlled optionally by conventional contactors or by a programmable controller.

The chips produced are carried off and discharged through the screen which encases the rotor. The objective is to produce a chip of approx. 15 mm. In order to achieve this objective a screen with a hole diameter of 12 mm in the first third and 15 mm in the remainding section is used.  Because of this design, longer chips and/or splinters that pass through the counter-knife are also reduced.

The chips are pneumatically conveyed through connection pieces attached laterally to the machine body or - optionally - carried off and discharged through a screw conveyor or a conveyor belt and transported with no pressure into central chip hoppers. The air used is afterwards separated from the dusts and chips which are also transferred to the chip bins. Through a mixer the chips and dusts are homogenized and - depending on the respective demand - all year long fed to the downstream heating boiler plants in order to produce primary energy. The complete energy demand of approx. 20 MW for the required process heat, the air-conditioning systems and the heating of the complete premises is covered by this. 

Size reduction of bulky wood residues   
With a single shaft size reduction machine of model series installed in the open and also connected to the chip hoppers, bulky wood residues such as larger chipboard residues and stored away production WL 18 Jumbo wastes. The size reduction machine possesses a rotor width of 1,800 mm with a feeding opening of 1,800 mm x 1,500 mm and a rotor diameter of 482 mm. The driving power is 75 kW. The machine can be started under full load. In this case the hopper contents will be reduced in size and afterwards the machine will automatically shut off. The uncovered metal parts such as nails, screws, clamps, etc. are transferred outward through a metal separating installation which is integrated in the suction system. The hopper volume is approx. 5.4 m³. The hopper can be designed in accordance with customer specifications. As an option, particularly bulky material can be fed to the rotor by force through a press down device from above.

Horst Zimmer, Building Services Systems Manager of König und Neurath:  "The disposal and treatment of our own production wastes to become valuable energy result in large saving potentials for us with regard to disposal and energy cost. The compact design of the WEIMA America's single -shaft shredders and the good interface connection to our machining centers along with the competent and individual consultation and the comprehensive service which was available any time during commissioning and thereafter were convincing arguments for our purchase decision."

Article by Lothar Vetter

WEIMA America, Inc.

3678 Centre Circle
Fort Mill, SC 29715
Phone: +1 803 802 7170
Fax: +1 803 802 7098
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