Powerscreen Washing Plant Project In Spain

Processing natural fine sand from a lakebed

Every site is unique and each has its own challenges when setting up and running a washing plant, but having worked in many markets around the world, Powerscreen say they are able to meet these challenges through their in-depth industry knowledge, experience and understanding of a wide range of different material requirements and site specifications.

The company has a wealth of experience in the design and installation of washing plants for many applications, including sand, gravel, iron ore, magnesium ore, railway ballast, construction demolition waste, dredged marine sand, quarry overburden, scalpings, slag, crushed material, crushed fines, and silica sand.

Powerscreen say they are also able to advise on, and handle, many other areas of plant design and set-up, including aspects such as: local planning issues, transportation and logistics, site planning and preparation, local health and safety regulations, and climatic conditions.

The company has recently installed a large static washing plant facility in northern Spain, in conjunction with regional Powerscreen dealers Terex Espana. The plant, which is designed to process natural fine sand from a lakebed, includes a 40-tonne feed hopper, an M80 feed conveyor, a 20 x 6 twin-deck rinser, a Finesmaster 200, two T6532 sand conveyors, an overflow waste water sump and fresh water pumps.

It produces two end products (0–2mm and 0–4mm), which are sold as building sand and concrete sand respectively.

The plant itself arrived on site in December 2007 and was installed during January/February, with full commissioning taking place in March 2008. The facility is now fully operational and processing material at a rate of 180 tonnes/h.

The first step in the installation process involved site preparation. For this particular project Powerscreen recommended a concrete plinth as a foundation, both for stability and for ease of cleaning. This had to be at least 200mm deep with a hardcore fill beneath it.

Water inlet pipes, water return pipes, electric conduit pipes and other additional equipment were put in position before the concrete was poured, which took place some 7–10 days before plant installation commenced, to ensure that the plinth was fully cured.

An experienced installation team, supported by Powerscreen engineers, installed the washing plant, including the electrics, in just seven days. Commissioning of the plant was carried out over a five-day period during which end-product quality and production targets were reached.

The raw material is natural fine sand comprising approximately 90% –4mm material, with a silt content ranging from 8–12%. Owing to this very high percentage of fine material, particularly careful consideration had to be given to the size of screenbox and sand plant required.

Material is fed into a 40-tonne feed hopper by a 40-tonne dumptruck. This large-capacity hopper was essential, as the lakebed, which provides the source of the raw material, is some 1.5km distant.

An M80 conveyor, complete with walkway, transfers the material to a Powerscreen 20ft x 6ft (6m x 1.8m) twin-deck washing screen, selected because of its ability to process large volumes of sand and to deliver two grades of quality sand in a single unit. Approximately 300m3/h (1,100 gal/min) of fresh water is pumped to the plant using a 55kW electric water pump.

As the material passes along the screen it is blasted with high-pressure water to wash the material and create slurry. The small amount of +12mm and –12mm +4mm material present in the raw sand is discharged from the end of the screen into a bay. The split bottom deck of the 20 x 6 screen separates the sand into the 0–2mm and 0–4mm sand products. These are transferred to a Finesmaster 200, where the sand is recovered and the silt is flushed out with the waste water.

The Finesmaster 200 sand-classification system, said to be the largest of its kind, uses a three-step dewatering process to remove the maximum amount of water, while an integral high-frequency dewatering screen ensures the finished sand has a moisture content of 10–12%. On-board hydrocyclones recover the fine sand particles to ensure no saleable product is lost to the silt pond. Silt content in the finished products is around 2.7%. Waste water/silt from the Finesmaster 200 is discharged into a sump from where it is pumped to a water-management system.

The two sand sizes recovered and dewatered by the Finesmaster unit are discharged on to two powered T6532 radial conveyors to give maximum stockpile capacity.