19.03.2010 | Editor: Marcel Dröttboom
As a result of the installation of new sludge dryers at the Ringsend Waste Water Treatment Plant, Dublin, Irland the two vibratory screens used to size the 4 mm diameter dried waste sludge pellets needed to be modified or replaced in order to satisfy the requirements of Atex Directive 94/9/EC.
Because of the continuous presence of a Class ST1 combustible dust at a temperature of 70 °C, the interior of each screen had been classified as a Zone 20 space. It proved to be impracticable to modify the existing screens satisfactorily. Therefore, two new machines specially designed to fit into the space occupied by the earlier machines and fully dust-proof have been supplied by Mogensen Raw Materials Handling. The feed inlet and product outlet positions of the two machines supplied match those of the original screens. In this way it was possible to install the new machines without modifying the existing structure of the plant. The feed inlet and product outlets are all flanged and fitted with high-pressure, flexible connectors. The Sizers, in which all product-contact components are manufactured from Grade 304 (Euronorm 1.4301) stainless steel, have been certified to Atex 94/9/EC Zone 20 and are designed to withstand an internal pressure of 0.4 bar should a dust explosion occur. Each machine is powered by two Invicta rotary electric vibrators rated at 1150 W. Each machine can handle a feed of 20 t/h of material at 70 °C with a minimum bulk density of 350 kg/m³, and separate it into oversize, saleable product and fines. The oversize and fines are re-circulated back into the pellet presses.
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