Sand drying at Needingworth Quarry

When Hanson UK identified a need to reduce the moisture content in their medium concrete sand and fine de-gritted sand at Needingworth Quarry, in Cambridgeshire, quarry manager Frank Johnson and area unit manager Hilton Law, turned to Len McGarry, managing director of Moisture Reduction Systems Ltd (MRS), for a solution.

With the moisture content of the washed sand output from site’s tower cyclones averaging around 13% – too high for many customers, Hanson were having to use a front-end loader to move each day’s production (up to 2,000 tonnes) to a separate stockpile where the sand could be left to drain naturally.

However, when drawdown pumping tests using MRS’s purpose-built simulator apparatus indicated that the moisture content could be reduced to around 5% after only a few hours continuous pumping, Hanson agreed to the installation of an MRS four take-off moisture-reduction manifold system.

The system supplied comprises a 7.5kW, large air-handling, three-phase electric pump (to provide the required vacuum) coupled through the four take-off manifold to interconnecting underground vacuum/water pipes. These, in turn, are connected to filter-wrapped perforated drainage pipework that rests upon impervious heavy-duty Visqueen sheeting to exclude any contamination or groundwater recharge.

The entire system was installed within two days and culminated with the laying down of a drainage blanket of 3–6mm rounded filter gravel on top of the drainage pipework. This precautionary measure helps eliminate the migration of fines from the overlying sand stockpile and reduces the possibility of the drainage pipework becoming choked, thus ensuring the longevity of the system.

Once pumping commenced, the benefits of the system became apparent almost immediately. The MRS system dries the sand to 4% moisture content after only 4h of dewatering, while the excess water removed by the system is clear and free of fines, suitable for immediate recirculation back to the washing process.

Significantly, Hanson no longer have to double-handle the sand or wait for the effects of gravity drainage to take place. This has greatly reduced front-end loader operating hours and movements at the site, leading to improved site safety, higher production rates and faster turnaround times. Customer satisfaction has also increased, as the sand is now supplied with a consistently low moisture content.