Difficult to separate from low-gravity materials?
Since the beginning of 2007, with his company Soil-Tec Mineralstoffe GmbH & Co. KG, Sven Wendt has been operating a mobile building rubble processing plant in Dusseldorf-Heerdt (Fig. 1). The focus of Soil-Tec’s activities is both the cost-efficient processing of excavated earth (mainly contaminant class II) and the processing of all building materials of mineral origin to a certified secondary resource. The material delivered is heavily contaminated with impurities – often lightweight materials such as wood or polystyrene – well, with everything that “floats and flies”. In his machine park, Wendt relies on mobile equipment as he not only operates on his own company site, but can travel to other sites when required. When he has some free capacity, he also has the possibility of temporarily hiring out equipment.
A small mobile impact crusher from the start-up phase was replaced after just around 1.5 years with a track-mobile Lokotrack LT1110 from Metso Minerals with approx. 50 % higher capacity, larger rotor diameter and much larger feed inlet. With more stable speeds (especially for reinforced concrete) as well as shorter machine running times, Wendt profits from greater operational reliability, giving him more time (and space) to take on other work. Previously, Soil-Tec had invested in a mobile heavy-duty screen – as a replacement for its small, stationary screen.
Prior to commissioning, Apex-Lieben made available to Soil-Tec a container-mobile lightweight materials separator known as the “Wash-Bear” for test purposes (Fig. 2). The Wash-Bear is not a pneumatic classifier operating with air and therefore difficult to adjust to achieve precise separation. Classifiers generally only operate with a narrow grain size range and require complex pre- and after-sorting. In addition, with pneumatic classifiers, efficient exhaust air cleaning is necessary. With the stream of air, large volumes of sand, adhesive particles, stones are unavoidably discharged. This inevitably increases the volume of waste to be landfilled, increasing transport costs and landfill charges. An extension to the landfill volume is not planned in the Soil-Tec business model.
The Wash-Bear is similar to a sand screw and operates according to the principle of dense-media separation. The medium-size product from the upstream heavy-duty screen is fed to the Wash-Bear – the machine is capable of processing a particle size range from 10–170 mm in one pass. The low-gravity materials with a specific density < 1 kg/dm³ float and are discharged by means of a top-mounted brush strip (Fig. 3). The high-gravity particles sink to the bottom of the trough, to be discharged from there with a conveyor screw. The bottom of the trough is subject to almost no wear on a permanent basis as here a protective bed of material is formed. Depending on the material handled, a conveyor screw made of highly wear-resistant material achieves an absolute throughput rate of 200 000 to 300 000 t. The costs for the proportional water and energy consumption (here 15 kW for up to 100 m³/h throughput rate) can be classed as extremely low. The otherwise usual labour costs for the manual sorting of the material are therefore eliminated. Operation of the Wash-Bear does not produce any waste water that needs to be clarified. The suspended matter dissolved in the water settles during the idle phase and is conveyed out of the washer. The Wash-Bear conveys and dewaters the material in one cycle. Compared to a plant with belt operation, no cleaning of a conveyor belt soiled with sediment sludge is necessary. After dismantling of the brush strip, the container-mobile Wash-Bear can be transported with a hook-lift lorry and is ready for action within 1–2 hours.
APEX-LIEBEN GmbH, Geilenkirchen (D),
Tel.: +49 2451 4095-884, www.apex-lieben.de
