Water is both friend and foe to aggregate producers. Too much of it in the pit, and mining slows or stops — but without it, products aren't washed and sand recovery is difficult. Yet, once used for processing, water must be clarified, stored or both, which can be expensive. So, it's not surprising that there are as many products for removing water from various locations and materials as there are for delivering it to where it's needed. Starting with groundwater removal and moving on into the plant, here is a look at both new and time-tested dewatering products.

In the Pit…

ITT Flygt's new 2600 submersible dewatering pump series was officially launched in April at the Intermat show in Paris. Replacing the successful Bibo range, the new line comprises six models. The series features a new high-chrome cast-iron impeller design that is adjusted with a single trimming screw. Other innovations, according to Flygt, that offer reduced component wear and maintenance include the spin-out system, which drastically reduces seal wear; the dura-spin hydraulic system, which minimizes impeller wear; and a one-piece plug-in seal that provides double the security and is easy to replace. Output ranges from 1.2 to 27 horsepower. The 2600 series will be available in North America this autumn.

Last year, Flygt upgraded its line of small and lightweight Ready submersible construction pumps to include the model 8S, specifically designed for transferring water mixed with solids. The 8S can handle particle sizes up to 1.5 inch, with capacity ranging from 63 to 111 gallons per minute with a head of 35 to 46 feet. Ready pumps are built with composite materials to reduce weight and stainless steel for strength, durability and high impact resistance. A new plug-in connection allows users to change damaged cables within a few seconds, and a new, two-position discharge outlet enables users to select a horizontal or vertical outlet position, which reduces the risk of a blocked hose. Accessories include a level regulator that turns the pump on and off, depending on water level; a low-suction collar for the Ready 4 and 8 models, enabling water to be pumped down to a very low level; and plain or threaded discharge connections.

Godwin Pumps says its HL series extreme high-head pumps are gaining popularity due to their single-stage, dry-priming design and ability to perform in extreme high-pressure discharge or high-discharge lift applications. The three models in this line include the 100- × 80-millimeter (4- × 3-inch) HL110M, the 150- × 100-millimeter (6- × 4-inch) HL130M, and the 200- × 150-millimeter (8- × 6-inch) HL160M. The pumps can handle solids from 20 to 35 millimeters and dynamic heads up to 185 meters (615 feet) at flow rates of 115 cubic meters per hour (500 gallons per minute), 295 cubic meters per hour (1,300 gallons per minute) and 126 cubic meters per hour (2,000 gallons per minute), respectively. All HL pumps include Godwin's Dri-Prime air-ejector priming system for fully automatic priming up to 8.5 meters (28 feet) of static suction lift.

In a recent installation at a quarry in Iowa, Schildberg Construction replaced a standard dewatering pump with a Godwin HL model after experiencing almost weekly seal ruptures with the original unit. The original could handle only about 90 feet of head instead of the 135 feet needed to lift water out of the pit. A Schildberg manager said that, in addition to easily handling the high lift, the new 6- × 4-inch. HL unit offers other benefits over a standard pump; for instance, the diesel-powered HL is equipped with a float switch that automatically turns the pump on and off as required, thus saving fuel. The high-suction power of the pump allows placement at an elevated point in the pit, safe from flooding. And the self-priming feature eliminates the need to have a worker on site to manually haul priming water to the pump during sudden nighttime rainstorms — an expensive and potentially dangerous task.

… And in the Plant

Dewatering screens, often placed downstream from screw washers, cyclones or classifiers, are one of the most common dewatering devices. They produce a drier sand that may bring higher prices and be used immediately without further stockpiling. Screen designs vary from the simple to the complex, as do the methods they employ to extract water from sand fractions.

Sizetec manufactures a number of dewatering screens for various mineral applications including curved and V-deck versions of its Intensive dewatering screen machines. The V-deck model is recommended for dewatering of concrete and silica sand and is available in many standard screen sizes from 2 × 7 feet to 8 × 14 feet. It uses a high-frequency linear-stroke vibrating motion to draw water from fines ranging in size from 4-mesh to 150-mesh. The machine's modular polyurethane panels have reinforced steel supports to withstand up to a foot of bed depth, according to Sizetec. For reliability, the screen is fitted with vibrators rather than a shaft and bearings. Deck angle can be easily changed to adjust retention time. The screens are able to provide end products that contain less than half the moisture level of other types of equipment such as sand screws, Sizetec says.

Derrick's Vacu-Deck dewatering screen incorporates a low-horsepower blower that develops a slight vacuum and draws air through the bed of solids on the last screen section. The screening machine can be configured in two ways: to recover and dewater the maximum amount of the feed solids, or to be fed with a thickened slurry produced by a sand separator or equivalent. Alternatively, for efficient wet sizing followed by dewatering of the oversize, the screen can be fed with a more dilute water-solids mixture. Particle sizing is accomplished on the upper-screen sections followed by dewatering of the oversize on the vacuum section.

The LPT-Velco dewatering screen, a mature product that has been around since 1980, now is available from McLanahan Corp. In 2001, McLanahan acquired the rights to Linatex process products, and subsequently formed a new division earlier this year to market McLanahan's classifying tanks, screws, log washers and Velco screens and other Linatex Process Technology products. The Velco screens feature a combination of standard wear resistant linings; optional deck dividers and dams, designed to remove 80% to 85% of moisture in aggregate products. Performance flexibility is enhanced by modular screen panels that can be easily changed or replaced, and by an adjustable discharge weir plate. Reinforced side plates and heavy rectangular tube support frames, along with Huck-bolt construction, provide greater reliability. A variety of surface coatings is available to suit job site conditions.

For an high degree of product dryness, rotary or fluid bed dryers can be installed. Ventilex USA, which makes Fluid Bed Dryers, says it has increased the maximum air temperature in its units from 840° F to 1,112° F. This results in more evaporation per square foot and thus less electrical energy use per ton of dried product. Drying air in Ventilex FBDs is heated by natural gas in standard configuration, but light fuel oil or LPG-fired versions are available. Construction features offered on the FBDs include round hatches to avoid cracking, special mounting of the footplate to allow free movement at all times, elimination of sharp angles and corners, and an overall design that takes into account the expansion and contraction of metal during heating and cooling cycles. An optional evaporative cooling feature, in which the last 1% of moisture in the product is removed in the cooling section rather than the dryer, can save owners energy costs, the company says.

CFS density separator is a hydraulic classification device consisting of an upper, parallel-walled section of a square or rectangular cross section and a lower section consisting of one or more pyramidal discharge units. A rising pre-determined flow of water is introduced through a series of horizontal pipes located at the junction of the upper and lower sections. Evenly spaced spray nozzles provide uniform water distribution.

Slurry continuously introduced into the upper unit through feed wells expands into a teetered state by the rising water current. The particles are classified with coarser material reporting to the bottom of the teetered mass while the finer material is distributed in the upper portion. Pulp level is maintained by continuous overflow. Interstitial water velocity and pulp specific gravity increases with depth from the overflow weir to the bottom of the upper section.

For producers who choose not to purchase dewatering equipment for their damp products, Aggregates Equipment Inc. says that bivi-TEC screens can handle and classify high-moisture materials. The unique screening action developed by the bivi-TEC's single-drive, dual-vibratory design is claimed to eliminate clogging and blinding, while generated forces up to 5 Gs on the screen mats for high separation efficiency.

Cyclones are widely used for dewatering products. The Krebs sand stacking cyclone combines a Krebs cyclone with a CycloStack attachment and overflow pipe and siphon-control assembly. The CycloStack is designed for use in solids dewatering applications and can be attached to the bottom of a standard Krebs cyclone to minimize the moisture content in the hydrocyclone underflow. The attachment, according to Krebs, provides a low-cost method to automatically control the dewatering and discharge concentration of the hydrocyclone underflow, allowing direct discharge of the underflow onto a conveyor belt or into a pile. This occurs even with fluctuating feed conditions.

The CycloStack units comprise a urethane flap that opens when solids are present and allows the solids to discharge while retaining water in the hydrocyclone. The CycloStack closes if there are no solids present, and improves hydrocyclone efficiency by constantly adjusting the apex diameter to virtually eliminate plugging and consequently allow attention-free operation.

On the portable plant side, Powerscreen's Finesmaster 200 sand recovery plant is designed to produce one or two grades simultaneously at up to 200 tons per hour. It does this while discharging virtually no saleable product to the pond system, thus increasing production and reducing pond maintenance. Smaller 120- and 60-ton-per-hour models also are available. Powerscreen says Finesmasters recover 96% to 98% of all material above 200-mesh and 100% above 100-mesh. The Finesmaster 200 incorporates twin bucket wheels with variable speed control up to 3.3 rpm, a centrifugal slurry pump, a collection tank and two rubber-lined hydrocyclones with fixed-spigot discharge to a split (coarse and fine product) dewatering screen. Each 8.5-foot-diameter wheel has 14 buckets with a capacity of 0.14 cubic yards each.

Reader Service

To learn more about these products and companies, complete the reader service card on page 39 and mail it to Rock Products or visit www.freeproductinfo.net/RP

Name	RSN
CFS	179
Derrick	180
Flygt	181
Godwin Pumps	182
Krebs	183
McLanahan	184
Powerscreen	185
Sizetec	186