Maximised efficiency by washing crushed dust stockpiles

CDE Global hosted visitors from throughout Great Britain at an open day in County Tipperary to witness first hand the M2500 mobile washing plant in operation
(Fig. 1). The event was hosted at Gleeson Quarries near Laffansbridge, where a CDE washing plant is processing waste material from the dry crushing and screening process to produce washed sand and aggregates. Gleeson Quarries was established in 1987 to serve the growing market for quality construction materials in Tipperary and surrounding areas. The company supplies a full range of readymix concrete, concrete blocks, crushed limestone, granular fill, agricultural lime and washed sand and gravel.

 

The washing plant includes the M2500 mobile washing plant, AggMax attrition system and AquaCycle thickener to ensure more than 80 % of the water used in the washing process is recycled (Fig. 2), thus minimising the amount of space required on site to accommodate settling ponds. The M2500 integrates a feed system with a ProGrade P2-75 double deck rinsing screen and EvoWash 71 sand washing plant. The M2500 has a total capacity of 250 t/h and will produce 70 t/h of a single washed sand to the required specification. In this instance Gleeson Quarries required a concrete sand for use in their on site concrete batching plant. There are a number of other models available within the M2500 range allowing up to 120 t/h of single or dual sand production if required.

 

Material is first delivered to the feed hopper which removes the +100 mm material (Fig. 3). The integrated feed conveyor then delivers material to the ProGrade double deck screen via a 14 m conveyor with a 1000 mm belt. The belt width of the feed conveyor is the same width as on the belt feeder that is integrated within the feed hopper. This ensures efficient transfer of material between the hopper and conveyor, removing any choke points for sticky material. In addition to this the M2500 is fitted with polyurethane wear pads at all points where material is transferred from one stage of processing to another. This automatically reduces instances of material impacting onto steel, which reduces wear and has a direct positive impact on plant efficiency while reducing ongoing maintenance costs. From the feed conveyor material is then discharged to the ProGrade P2-75 double deck rinsing screen. Prior to this a wash box fitted to the head of the feed conveyor ensures sufficient water is added to allow effective screening. The top deck removes the +50 mm material which is stockpiled using one of the 9 m wing conveyors. These wing conveyors discharge at 4.7 m offering a stockpile capacity of 150 m3. The bottom deck of the ProGrade rinsing screen removes the 5 mm to 50 mm material while the minus 5 mm material is pumped to the integrated EvoWash sand washing plant where the concrete sand is produced.

 

Due to the levels of silts and clays in the feed material the aggregates require additional attrition in order to ensure the final products are as clean as possible, thus ensuring they command the highest commercial value. This is achieved through the introduction of the AggMax 150 system (Fig. 4). The AggMax integrates the RotoMax RX150 log washer with a proven capacity of 150 t/h and an EvoScreen dewatering screen on a single easily transportable chassis. The 5 mm to 50 mm material from the bottom deck of the ProGrade screen is fed to the AggMax via the 9 m wing conveyor integrated onto the M2500 washing plant (Fig. 5).


There are many features of the integrated RotoMax log washer that make it stand out from other systems on the market but the one that really seemed to capture the attention of all at the recent open day was the specification of the blades within the log washer. These are manufactured from chrome molybdenum which is the same material as is used on impactor crushers. Once the aggregates have passed through the RotoMax they are then discharged onto the EvoScreen dewatering screen that is integrated onto the single AggMax chassis. The dewatering screen is fitted with spray bars to give the aggregates a final rinse. Meanwhile any < 5 mm material that has been liberated from the aggregates during the scrubbing within the RotoMax is pumped with the waste water to the EvoWash sand washing plant ensuring maximum recovery of all commercial grade sand material. The 5 mm to 50 mm aggregates are then delivered to a 4 way split which classifies material into the desired grades, in this instance a 40-50 mm, 20-40 mm, 14-20 mm and 5-14 mm.

 

The washing plant at Gleeson Quarries also includes an AquaCycle thickener system to enable recycling of more than 80 % of the water used in the washing plant. The model employed in this instance is an A200 with a tank diameter of 6 m and a capacity of 200 m3/h. This is supplied complete with a FlocStation P25 polyelectrolyte dosing plant and an AquaStore water recycling and pumping system. Waste water from the EvoWash sand washing plant is sent to the AquaCycle thickener via a gravity feed. The waste water containing all of the minus 63 µm material enters the deaeration chamber on the thickener tank where the polyelectrolyte is added before the material is piped to the centre of the tank. This slows down the flow of material into the tank which ensures effective settling within the tank by allowing the polyelectrolyte to disperse efficiently. A set of rakes at the bottom of the tank ensure that the settled sludge is maintained at an even consistency while the clean water over­-flows the weir at the top of the tank and is sent to the AquaStore W372 pumping system for recirculation around the washing plant. An automatic sludge pumping mechanism is then employed to pump the sludge from the AquaCycle thickener to the on site settling ponds.

 

The washing plant at Gleeson Quarries has been in operation for 5 months and has processed approximately 100 000 t of material that was previously a waste product. This material was taking up valuable space on site at Gleeson Quarries before installation of the washing plant from CDE Global. In addition, the customer was missing out on a significant revenue opportunity that could be realised through the introduction of an effective washing plant. “At a time when operators are focused more than ever on maximising efficiencies within their sand and aggregate processing operations, our plant at Gleeson Quarries provides evidence that there are significant opportunities to be taken advantage of with the processing of waste stockpiles”, explains Terry Ashby, CDE General Manager in Great Britain. “We have numerous plants in operation throughout the world doing this very same job and it is always the case that considerable volumes of quality sand and aggregates can be recovered when the right system is employed.”


CDE Ireland Ltd., Cookstown (IRL),

Tel.: +44 28 8676 7900, www.cdeglobal.com

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