PSWS provide top class production for RMC Costessey

RMC Materials' Costessey Quarry is the company's third largest site in Norfolk and, in addition to aggregate processing, boasts a ready mixed concrete and mortar plant, as well as a full recycling facility. The quarry also supplies a nearby asphalt plant.
Now part of CEMEX, the global building materials company, RMC Materials operates over 700 quarries, plants and units in Great Britain. The Costessey site plays an important role in the local construction materials market particularly in respect of supplying ongoing development in the city of Norwich.

Over the past few years the site has been reduced in size as land was allocated to housing development; the original static plant relied on lagoons for silt disposal and as the site diminished, a decision was made to install a new plant with the technology to manage water efficiently without the need for lagoons.

Powerscreen Washing Systems of Coventry successfully tendered for a washing and screening plant that would produce high quality products whilst maintaining an efficient water management system.
Supplied and installed by PSWS the plant deals with the problems of lagoons and their elimination through installation of a plate press providing a closed loop system for the whole operation.

The plant is fed by wheeled loader into a 20 Tonne Commander 1400 feed hopper complete with remote controlled tipping grid; located close to the stockpile the material is fed onto an inclined transfer conveyor which delivers onto the primary screen, a Powerscreen 12 x 5 static rinser. Featuring six spray bars on the top and bottom decks the rinser is fitted with polyurethane screen modules. The vibrating top deck of the screen rejects all oversize material and delivers this to an adjacent ground stockpile via a T4026 radial conveyor.

Any midsize material passes from the rinser and is discharged into a Powerscreen Powerscrub. Capable of producing up to 120 tonnes/h of contaminant-free sand and gravel, the Powerscrub 120R unit comprises an inclined trough fitted with two counter-rotating axles with high-tensile exchangeable blades and an elevated spray-bar system. The unit mixes incoming feed while milling and washing the material at the same time. Any lumps of earth or clay are broken down during this process and carried away in the wash water, while any lighter particles are floated off through specially designed outflow exits. Two spray bars are mounted at the discharge end of the unit to provide a final rinse.

Midsize material is then fed onto a static transfer conveyor, which in turn provides material to the final screen; identical to the primary screen, except that it is fitted with a partial rinsing system, it splits the material into three final single-size products whilst recirculating foul water back to the Fines Master. These materials - 10mm, 20mm and 40mm - are then delivered to their respective ground stockpiles by three T4026 radial stockpiling conveyors.

The material from the bottom deck feeds a Powerscreen Fines Master 120 where it is classified and dewatered, working for maximum sand grade flexibility, the Fines Master 120 produces a combined total of around 120 tonnes/h of fine and coarse sand. Comprising a twin bucket wheel with 28 buckets, a centrifugal slurry pump, twin hydrocyclones, a collection tank and a high-frequency 12ft x 5ft dewatering screen mounted on a single carrier chassis, the machine delivers two grades of sand to stockpile via T4026 radial stockpile conveyors.

As water management was an essential part of the project PSWS in conjunction with their partner Tecnoidea supplied a Multi-Plate filter press complete with 36 plates. Based on its impressive technical specification, quality of build and technical support, PSWS always work in tandem with Tecnoidea Impianti to offer a fully automatic silt management system that is 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, automatic flocculent mixing and dosing plant; 6m diameter dynamic thickener tank with pneumatic discharge valve; silt buffer tank with two stirrers; 43m3 lime silo with automatic mixing and dosing tank, fresh water tank; and all the support framework, structure, walkways and access platforms.

Once in the thickener the silt settles to the bottom of the cone and is automatically discharged into a silt buffer tank where the lime is added.
The quantity of lime is controlled using a rotary valve which then feeds the lime onto a rotary screw which in turn feeds the lime into a mixing tank. At this point water is added to the lime to create a solution which is automatically distributed into the silt buffer tank as required. The lime solution reacts with any clay material in the silt to facilitate the water drainage in the 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.
As in any application, PSWS selects the correct size of press and takes into account such factors as the silt content, clay content and settlement rate of the raw material. The flocculent mixing and dosing system maintains 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.

Commenting on the success of the project, Mark Wood, RMC�s Operations Manager, said: "from initial quotation to the fitting of the last nut and bolt, PSWS have performed extremely well. Aspects such as build quality and the health and safety regime have been exceptional and any problems that have arisen have been dealt with efficiently and effectively". The plant is now in the final stages of handover.

Further Information:
Powerscreen Washing Systems Ltd, 1, Rye Hill Office Park, Birmingham Road, Allesley, Coventry CV5 9AB  Tel: 024 7640 5100 Fax: 024 7640 5020 Email: wash@psws.co.uk  Web: www.psws.co.uk