Dowlow Success for Linatex!

Dowlow quarry lies in the heart of the Peak district; operated by Lafarge Aggregates and is their second most important site in the UK. Producing over 1.1/2 million tonnes per annum the site has some considerable history, originally dating back to 1899. The excavated material is carboniferous limestone, containing a high clay contamination requiring washing.

From Lafarge's past experience 25% waste was coming off production, which in the seventies was sold off as bulk fill, today the company are unable to sell this waste. To resolve the problems and to increase quality and production a 1500 metre deep bore hole was drilled which today provides water to a newly installed 1 million gallon holding tank, this has not only provided the company with the confidence to wash but also enabled  Lafarge to wash continuously.

The decision of Lafarge to install a completely new wash plant included a complete sand processing system from Linatex.

The material being processed is -125mm limestone, the task for Linatex being to treat and handle 110 tph of -5mm material of which about half is passing 75 micron. On initial sampling of the material Linatex achieved an analysis of only 31% passing 75 micron, which would provide a much coarser useful material. The solids are associated with 2000 gpm of water, which is the quantity that Lafarge require to wash the limestone feed.

The basic requirement of the plant was to wash and basically separate the silt from the useful sand enabling the manufacture of a coarse concrete sand. The product to be treated using a dewatering screen, the end product to be stockpiled by a conveyor.

The process requires the -5mm material and water to be flumed down to the centre of a Linatex 5500mm dia feed regulating sump, fitted with central feed box, anti-turbulence ring, supporting legs and overflow weir; overflow from this sump terminating at the effluent tank. From the base of this sump a Linatex 200/150mm Mk 111 centrifugal bore pump draws the slurry to feed a Linatex HK200 914mm diameter sand separator fitted with extended feed box and discharge regulator. This extended separator, ensures capture of the useful sand whilst removing the majority of the unwanted silts and clays from the overflow, this overflow then discharges into an effluent collecting sump.

The first part of the sand processing system is to pre-wash and remove the vast majority of the -75 micron (silt) material. The material discharging from the separator will still have approximately 12-15% silt, which needed to be reduced further to an acceptable level. At this stage in the process all the initial water has been removed with the unwanted silt, thus requiring a further input of 600 gpm of water.

The pre-washed -5mm material discharges from the above separator, together with with the additional 600 gpm of water which is then directed to the centre of a Linatex 3658 mm dia feed regulating sump, which is incorporated in a final washing and dewatering system to remove the remaining unwanted silt. The overflow from this sump terminating at the effluent tank. From the base of the sump, a Linatex 150/125mm Mk 111 centrifugal bore pump draws the slurry and delivers to a Linatex HK150 sand separator for final cleaning. The underflow from the separator discharges onto a Linatex VD12 velco dewatering screen, complete with urethane decks, side wear liners, suspension components, lined underpan and lined discharge chute, this removes the free moisture before discharging onto a conveyor for stockpiling. At this point in the process the moisture content of the product is approximately 12-15%, any throughs from the screen being directed back to the sump, ensuring no loss of useful material.

Additionally, from the separator overflow a quantity of liquid is recirculated back to the sump for make-up, the remaining flow terminating at the effluent tank.

All feed and return pipework was fully supported, the sand tower incorporating maintenance platforms, flooring, handrailing, tower ladders to full health and safety standards, all delivered, erected and commissioned by Linatex engineers.

Further Information:

Linatex Ltd
Wilkinson House,
Galway Road
Blackbushe Business Park
Yateley
Camberley
Hants
GU46 6GE
UK

T: 01252 743000
F: 01252 743030

http://www.linatex.com/