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Aggregate Processing at Penrhyn

Supplied and installed by Powerscreen Washing Systems of Coventry the plant deals with the problems of lagoons and their elimination through installation of filter press providing a closed loop system for the whole operation.

PSWS have supplied AMPL with a system that is specifically designed to operate at a general output of 180tph, the system being generally governed by the silt treatment plant, although the type of material has an effect on this as well.

The plant is fed by wheeled loader into a 30 tonne Powerscreen Commander 1400 hopper fitted with variable speed control, which loads onto an 80’00” static inclined conveyor, including a galvanised walkway full length, and around head drum. This conveyor is fitted with a belt weigher which is operated from the control room where it can be adjusted providing accurate production levels. The material then feeds onto a 16 x 5 two-deck rinser with vibrating top deck fitted with polyurethane screen mats; from this oversize material is passed direct onto a radial stockpile conveyor providing 30mm material. The material from the bottom deck feeds a Powerscreen Fines Master 120 where it is classified and dewatered and then fed onto two separate radial stockpile conveyors providing two grades of sand for building and concrete. Any midsize material passes from the rinser to a Powerscrub 120 logwasher which incorporates a by-pass facility (if there is not much clay in the feed), material then feeds onto a 100’00” static transfer conveyor, fitted with full-length galvanised walkway, (specifically this length to provide more room for the plant layout) which in turn provides material to a 16 x 5 part rinser complete with two radial stockpile conveyors providing 10mm and 20mm material.

The system is designed for recirculation of all fines from the logwasher and part rinser to be pumped back to the sand plant. All water and silt from the Powerscreen Fines Master is pumped via the bottom feed across the site to the adjacent press.

PSWS specifically sourced a Tecnoidea Multi-Plate Filter Press Model 1300 x 1300 complete with 33 plates; having explored all the available options throughout Europe, they eventually choose Tecnoidea for its impressive technical specification, quality of build and technical support. The silt management system was specifically designed and sized to minimise operator input and maintain low running costs. As well as the press, the system includes the foul water pump (ABRA type 60VS1 with automatic cooling system); automatic flocculent mixing and dosing plant with a control system that minimises use of flocculent; automatic anti-clog system; 4m diameter deep cone silt thickener tank with pneumatic discharge valve; silt buffer tank; fresh water tank; and all the support framework, structure, walkways and access platforms.

The complete system is fully automated and only requires an operator to add flocculent powder occasionally and remove the pressed silt cake using a loading shovel. As the sludge is fed into the thickening tank from the Powerscreen plant the density is monitored every 50 seconds. This allows the system to automatically adjust the feed rate of the flocculent solution thereby guaranteeing clean water for re-washing and minimising the amount of flocculent required. Once in the thickener the silt settles to the bottom of the cone and is automatically discharged into the sludge tank when the density is 25% solids. This is constantly monitored so that a consistent feed is pumped to the plate press. When the press has filled and drained the water, it opens and the silt cake drops down into a concrete bay below; the press then cleans itself ready for another cycle. PSWS in choosing the correct size of press for this application had to consider such factors as the silt content of the raw material, settlement rate and throughput had also to be considered. The flocculent mixing and dosing system has a continuous supply of clean water and automatically mixes a batch of flocculent solution when the level drops. An operator only has to add the powder to a storage bin.

After AMSL had completed the concrete civils the whole plant was erected and commissioned on the 14th July. Paul Chambury, AMSL’s Operations Director says of the installation: “It’s doing everything we wanted it to do-and it’s to a high specification. We are very please with it. We had strong co-operation between AMPL and Powerscreen Washing Systems all the way through the project.”