Woodhall Spa Sand & Gravel Ltd’s new processing plant under construction Replant at Woodhall Spa New processing plant and new owners for Lincolnshire operator or the last 70 years Woodhall Spa WSSG work the sand and gravel deposits on Sand & Gravel Ltd (WSSG) have the flood plain of the Old River Bain between operated as an independent family- the villages of Kirkby-on-Bain and Tattershall Frun aggregates business, based in Thorpe, producing a full range of aggregate the heart of rural Lincolnshire. The company products in line with the new European were founded at their current site near Standards. The company also market their own Woodhall Spa in 1934 by the Jones and decorative gravel under the brand name Coulson families from Yorkshire and London, Golden Spa, a product that has proved respectively, and since then have built up a particularly popular with builders’ merchants reputation in Lincolnshire and the East and the general public because of its warm Midlands for the quality of their products and golden-yellow colour. service. The indigenous flint sand and gravel deposit Last month, however, WSSG were acquired in the Woodhall Spa area is glacial in origin and by Aggregate Industries, but although the variable in depth and thickness. The sand to company will now be operating as part of a gravel ratio at the current extraction site is much wider portfolio, WSSG will continue to around 30:70 although this can vary serve their well established customer base considerably, necessitating tight processing under their current name. controls to keep finished products within The company’s decision to invest in a new specification. plant followed the granting of planning With the water table lying just below the permission to extract sand and gravel from a topsoil, dewatering ahead of extraction allows further 80 acres of land adjacent to their the sand and gravel to be worked in a semi- existing operations. dry state. Material is delivered to the new QM May 2004 www.qmj.co.uk 9 WSSG’s new Liebherr 944B long-reach excavator has reduced the frequency of field conveyor movements processing plant by a recently installed 900m installed by Morley-based Finedoor, this unit long field conveyor system. Commissioned in has a 4.7m wide feed opening with an inclined June 2003 and with the ability to deliver up to static grid and features a hydraulically operated 200 tonnes/h, this has removed the need for flow-control door at its base that discharges articulated haulers and provides a quieter, the raw material on to a 900mm wide by 5.9m more environmentally friendly transport long 11kW electronically controlled variable- solution. Moreover, in order to reduce the speed belt feeder. Ramped access to the rear number of feed hopper/field conveyor of the hopper allows separate or simultaneous movements as extraction progresses, WSSG feeding by mobile plant. have recently invested in a new Liebherr 944B The belt feeder discharges on to a 650mm long-reach excavator. wide by 47.5m long inclined main conveyor, On arrival at the new processing plant the again supplied and installed by Finedoor. field conveyor discharges on to the inclined Driven by a 15kW motor and shaft-mounted section of a 5m high overhead conveyor that gearbox, and operating at a speed of 1.5m/s, delivers the material directly into the plant’s this delivers the raw feed to a Finedoor twin- 40-tonne capacity feed hopper. Supplied and deck primary rinsing screen measuring 5m in The 40-tonne capacity feed hopper and 47.5m long main feed conveyor, both supplied by Finedoor 10 www.qmj.co.uk QM May 2004 length x 1.5m in width and mounted on a The new Linatex coarse-sand raised platform with an all-round walkway for separator tower with its three ease of maintenance. Directly driven by an discharge chutes 11kW motor and cardan shaft, the screen is fitted with SCS modular polyurethane mats with 40mm apertures on the top deck and 6mm apertures on the bottom deck. Any oversize rejected by the top deck is stockpiled on site for subsequent crushing. Once crushed, the material is fed back into the process flow via the main feed hopper. Coarse sand contained in the underflow from the bottom deck of the primary screen is recovered by a new Linatex sand plant arrangement. The slurry is fed initially to a 1,676mm diameter Linatex S-type classifier. From here a 75kW Linatex Mk III 200/150mm centrifugal pump is used to pump the denser underflow to a tower-mounted Linatex HK200 sand separator/dewaterer via 200mm diameter suction pipework and trestle-mounted delivery pipework. The separator tower includes three sets of Linatex-lined discharge chutes and is of and delivers a maximum throughput of 120 sufficient height to provide a coarse-sand tonnes/h. The unit incorporates a contraflow stockpile capacity of 3,750 tonnes. The system which allows water and sand to be overflow from the sand separator is delivered removed from both the feed end and the to the site’s extensive effluent-treatment discharge end of the barrel. This, say Wileman, lagoons via 250mm diameter return pipework has the effect of creating a cleaner dewatered and an effluent buffer tank, with facilities product prior to final grading — a claim fully provided for partial recirculation of the slurry endorsed by WSSG who confirm that the by means of butterfly valves. cleanliness of the products now being The –40mm +6mm fraction from the produced would not have been possible with primary rinsing screen discharges directly into their original scrubber barrel. Dirty process a high-specification scrubber barrel supplied by water from the scrubber is also fed back to Wileman Engineers Ltd of Ashby-de-la-Zouch, the S-type classifier for coarse-sand recovery. Leicestershire. Measuring 3m in length x 2m in The clean –40mm +6mm material is diameter and equipped with Linatex rubber discharged from the scrubber barrel on to a liners, a Renold gearbox/drive unit, FAG short inclined conveyor which delivers it bearings and Michelin tyres, the barrel has a directly to a second Finedoor twin-deck maximum water requirement of 400 gals/min rinsing screen featuring a similar drive The mid-range fraction from the Finedoor twin-deck primary rinsing screen is fed into a 3m long x 2m diameter Wileman scrubber barrel QM May 2004 www.qmj.co.uk 11 The second Finedoor twin-deck rinsing screen arrangement to the primary screen. This unit, to keep the products within specification. The however, is fitted with SCS modular company say Rugby-based SCS (Screening polyurethane mats with 24mm apertures on Consultancy and Supplies Ltd) have been very the top deck and 6.5mm apertures on the first helpful in this respect, supplying customized section of the bottom deck and 13mm decks in short lead times and developing a apertures on the remainder. A discharge chute screen mat ‘rotation’ system using a and two short stockpile conveyors deliver the combination of old and new mats to achieve final gravel products (40mm, 20mm and 10mm optimum results. Moreover, the use of modular single sizes) to their respective piles. Process deck units means that downtime is kept to a water from this screen is also piped back to minimum when mats are being moved or the S-type classifier for sand recovery. replaced. According to WSSG, the irregular The overflow (containing fine sand) from the composition of the local gravel deposit, which S-type classifier mentioned earlier is fed into contains a relatively high proportion of the first of two new 2,440mm diameter elongate particles, means that continual fine- Linatex feed-regulating sumps. From here an tuning of the modular screen mats is needed 11kW Linatex Mk III 150/125mm centrifugal pump is used to pump the sump’s underflow to a new Linatex sieve bend unit where any lightweight contaminants are removed. This in turn discharges into the second feed-regulating sump from where the underflow is pumped by an existing pump and 150mm diameter delivery pipework to the site’s original fine- sand tower and Linatex separator/dewaterer. The overflow from both feed-regulating sumps is fed to the site’s effluent tank together with the overflow from the separator, although the latter can be partially recirculated to both sumps, for liquid make-up purposes, by means of butterfly valves. Acknowledgement The editor wishes to thank Woodhall Spa Sand & Gravel Ltd for permission to visit the site and, in particular, Peter Gray, quarry manager, and Allen Smith, works manager, for their help in preparing this article. Part of the new Linatex sand plant arrangement 12 www.qmj.co.uk QM May 2004.