Page 56 - HUB-4 Magazine Issue 82

Quarrying News
Main collection sump tank
The main collection sump tank is one of the critical components of the plant. Its primary function is to collect the water used in the washing process and provide a central point for the collection of fluidised fine material.
Water from the wash plant flows into the sump tank, and from here pumped to the cyclone stage for sand cleaning and separation.
Underground Water Storage
Uniquely for Keohane’s the reservoir for the recycled water used in the wash plant is located beneath the plinth to safe footprint on the overall layout. The water recycling system employed reduces the amount of freshwater required for the operation. In addition, this subterranean tank helps to maintain the proper balance of water in the system and prevents overflow during heavy rain or excessive water use.
Pumps and maintenance
Two types of pumps are used for handling sand and water – coarse sand pumps and fine sand pumps.
Typically, the pumps used in a wash plant are natural red rubber-lined to provide resistance against abrasive wear and tear caused by the sand particles. Terex has lined all the pipework to protect against wear and tear from the abrasive nature of the sand particles. The lining is a wear resistant rubber that can withstand the harsh conditions of the wash plant environment.
Regular maintenance of pumps is crucial to ensure their smooth operation and prevent breakdowns that can cause production downtime. During maintenance, the pumps are rolled out of their positions, dismantled, and inspected for any signs of wear and tear. Worn parts are replaced, and the pumps are reassembled, aligned, and reinstalled back into position.
Cyclones and underflow blending
The sand and water slurry is pumped to two rubber lined cyclones. The larger 660 Cyclone receives the higher volume coarse fraction, while the 500 Cyclone receives the lower volume 0-2mm fraction. Inside the cyclones, silts and clays are separated from the sand and discharged out the top of the cyclone, while the in-spec sand is discharged via the spigot into the underflow collection box.
Easy access lids allow for visual inspection of the umbrella flow out the bottom of the cyclone. A simple blending box within the main underflow box provides a second opportunity to blend fine sand into the coarse sand.
Sand dewatering screen
The sand is then discharged onto a 14x6 high frequency dewatering screen, which uses polyurethane media and dividers to keep the material apart the entire length of the screen. By the time the sand reaches the end, the moisture content has been reduced to below 14 per cent. The dewatering screen's underflow is returned to the central collection sump for maximum recovery of fines.
TWS designed a custom lined chute for Keohane’s site to use one standard radial conveyor for the fine fraction, and a radial conveyor for the higher volume 0-5mm sand. This chute provides the third and final opportunity for the Keohane to blend some of the fine sand into the coarse sand.
All dirty water reporting out the top of the cyclones is collected and discharged into the ground collection sump, and pumped from there via a high capacity, wear resistant vertical shaft pump to the water treatment stage.
Scrubbing
When there is a high concentration of silts and clays in feed material, the aggregates can bind together, making it difficult to remove the clay through washing alone. The material analysis completed during the initial proposal stage determined that scrubbing of the material was required.
Scrubbing involves a process of stone-on-stone attrition, which breaks down conglomerates and frees the aggregates. TWS washers are designed to handle a feed rate of 60 to 200 tonnes per hour and produce a clean and marketable aggregate. The AS150 version is modular and can be easily transported and assembled. It comes equipped with a part- rinsing sizing screen, a high-volume trash screen, and a central collection sump, and offers easy access to all serviceable areas.
In this specific application, most of the conglomerates are found in the mid fines portion. The stock is diverted to the AS150 via the Aggresand extended conveyor. The challenge is to then liberate valuable aggregates and light material, such as organics or trash, from difficult-to-break-down fines and insoluble clay.
The Aggrescrub range features twin rotating bladed shafts with two dedicated motor gearboxes that introduce energy to the feedstock, causing the particles to collide and scrape against each other. This stone-on-stone attrition liberates conglomerates, which are transported across the water and expelled out of the rear weirs, and onto the trash screen where they are dewatered. The water then travels to the integrated sump tank.
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www.hub-4.com September/October - Issue 82