The Aggre-Dry Washer — GreyStone Inc.’s sand dewatering unit — combines a fine material screw and dewatering screen to produce sand and gravel products with a moisture content as low as 8 to 13 percent, by weight, while using only 30 hp (22 kW) to wash and dewater up to 100 tons (90.7 t) per hour.
Here’s how the Aggre-Dry Washer washes and dewaters aggregate material: a standard GreyStone inclined single-spiral fine material washer (FMW) initially dewaters the material, doing the bulk of the work. At the same time, the rotation of the dewatering screw scrubs the material to help remove surface dirt. The action of the screw flights sends the sand up the inclined tub, and ensures that the dewatering screen located at the top of the flights will be evenly fed. The vibratory dewatering screen further removes moisture from the sand. This combined process produces a caked, dry sand product that neither an inclined dewatering screw nor a vibratory screen can separately achieve.
The GreyStone dewatering screen, curved around the spiral flights on the Aggre-Dry Washer, has several features. A 0.25-mm screen opening reduces the amount of material that can fall through the screen. The feed from the screw allows the material to build to a bed depth of 14 in. (36 cm) on the screen, squeezing additional moisture from the sand as the vibratory motors move it along the length of the screen cloth, further reducing moisture content.
The GreyStone unit re-introduces the throughs from the screen back into the screw’s washing process, where the screw portion of the unit again pushes it to the unit’s dewatering screen, increasing the amount of salable product.