WEIMA America Inc.

Size reduction of substitute combustibles (RDF)

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Courtesy of WEIMA America Inc.

The new pilot installation of SITA Wiebe GmbH, Bielefeld/Germany, processes highly calorific commercial and industrial waste to become quality-assured substitute combustibles for cement industry and/or power plants. Basic items of this ultra-modern processing installation are two one-shaft size reduction machines of type WLK 30 Super-Jumbo of WEIMA Maschinenbau GmbH, Ilsfeld. The total output of the installation in two-shift operation is approx. 60,000 t/a. 

Controlled feed 
The energy content of the processed waste fractions lies in a narrow field of 22-25 MJ/kg which is obtained by a controlled composition of the input. The input is grossly pre-classified by means of a gripping crane and the recoverable components are fed into a preliminary size reducer where the complete material is reduced to a size smaller than 200 mm. Afterwards, the abrasive mineral constituents (sand, dust, and the like) are separated in a star screen. In the downstream air separation the light material (highly calorific films and paper) are sucked off and fed to the two one-shaft size reduction machines via a star wheel valve. After separation of the metallic constituents by means of an integrated FE separator, the heavy material separated in air separation is conveyed into containers and then transported to an industrial combined heating and power station.  
Universal size reducer WLK Super-Jumbo 
Subsequent size reduction of materials is carried out by means of one-shaft size reducers type WLK 30 Super-Jumbo with a rotor width of 3,000 mm to a blowable grain size of approx. 20-30 mm and an average grain thickness of up to 2 mm.
The WLK series is characterised by a strong and sturdy drive and a high and practically proven solidity of the machine body. The machines are driven by a hydraulic double drive with 110 kW drive rating each on every side of the rotor. The speed range is between n= 80 and n=100. As a consequence there is a considerable reduction of the noise level in comparison with high-speed size reduction machines (n>400).
The hydraulic drive permits a flexible regulation of speed and of torque and - in comparison with electromotive drives - a smoother buffering of rough and jerking impacts in the course of the size reduction process. This optionally also permits a feeding of the machines with not preliminarily size-reduced material fractions of a known composition and without disturbing substances that can directly be reduced to the final grain size. 

Fast material feed permits high throughputs 
Material feeding to the rotor is performed by a drawer in the machine room with horizontal bearing. The drawer pushes the material in a load-controlled manner against the rotor. The newly developed limit switch controlled turbo-hydraulic system considerably increases the cycle frequency of the drawer in comparison with conventional controls and thus considerably increases the throughput achieved.

In case of an overload the machines switch to a reversed operation causing the drawer to relieve as well. The drawer is exactly guided by means of segmented and exchangeable bottom guideways and equipped with a brass layer safeguarding and guaranteeing a smooth and easy guiding. Moreover, the drawer is laterally equipped with re-adjustable stripper rails that avoid and prevent an undesired draw-in between drawer and machine housing. 
This is what is important: Quality of output and a high availability 
The rotors - the diameter of which is 600 mm - are manufactured from the solid block and they possess a particular profiling as well as a patented knife seat. This technology permits an exact cutting and a fast material removal. In this manner, a thermal load of the size-reduced material and a joining by casting and sticking of individual particles is avoided and prevented. This is very important since weight and size of the particles is decisive for the blowability and the complete combustion in the kilns of cement industry.
The cutting tools mounted on the rotor circumference are concavely ground hollow knives having an edge length of 60 mm. The knives are made of a special knife steel and can be used in for ways. Three rows of knives with a total of 135 knives are mounted on the rotor circumference resulting in a short holding time of the material and thus a large throughput.
An exact adjustment of the cutting gap is achieved by means of the flexible bed knife rail. In connection with the knives used here (with particularly constructed knife tips) this so-called Super-Cut also permits and guarantees the processing of materials that are hardly to reduce in size (such as films) at a high cutting quality and a low dust portion. The bed knife rails consists of 5 segments. In case of a possible damage this means that you do not have to exchange the complete knife bed rail but only the individual damaged segment. Segmentation also facilitates the complete exchange necessitated by wear and tear.
The machines are equipped with a hydraulically pivoted screen cage which permits a fast screen change of a screen that has also been designed in segments. The screen hole diameter of the roundish screen openings is 30 mm. 70 to 80 percent of the grain size of the material withdrawn is between 20 mm and 30 mm. Exchanging the screen and thus changing the final grain size results in a fast and flexible responding to particular requirements individual customers may have. The fast access to the rotor furthermore results in short setting times in case of cleaning and maintenance and thus guarantees lower periods of standstill and a high availability of the machines.

SITA Wiebe GmbH is an old-established Bielefeld disposal management company of the SITA group of companies and - among others - disposes waste of more than 5,000 industrial and commercial customers.
Dipl.-Ing. Jürn Düsterloh, 'Prokura' holder/Managing engineer and constructive designer of the installation: 'Until the expiry of the transitional period from TASi (technical regulations concerning estate waste) in the year 2005 according to which the disposal of untreated waste with organic constituents will no longer be possible, it is the strategic target of SITA Wiebe to gain and achieve sufficient experience in treating and processing of quality-assured substitute combustibles (RAL quality sign) such that we are able to warrant and guarantee a disposal security for our customers at economic terms and conditions. With WEIMA Maschinenbau GmbH we have found a partner who supplies us with size reduction machines for our tasks and targets offering best possible and reliable engineering. Our decision in favour of WEIMA Maschinenbau GmbH is confirmed by the facts that promised throughput and operational capacity are exceeded and that comprehensive service has always been rendered during commissioning and afterwards.' 

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