Washing the Fines in Sand, Gravel and Crushed Rock Production

Aggregates Processing

Washing the Fines in Sand, Gravel and Crushed Rock Production

Additional Fines Product together with improved Water Utilisation
A Swedish quarry wanted to improve the quality of its products as well as its economics. Therefore they got their sand and gravel washing plant extended which now utilizes fines in the washed sands and aggregates. The turnkey plant has been specifically designed for both the company’s specific requirements and the climate in Sweden.
(ed. WoMaMarcel - 24/9/2015)
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The Washing Process

The raw feed is delivered to the M2500 E4X via a S20 integrated hopper with a capacity of 20 tons. The material travels up the feed conveyor with a fitted belt weigher which enables Björklunds Grus to quickly and easily monitor the flow of material through the plant while also having real-time access to operating capacity information. The belt weigher is an enhancement package under CDE Plantplus which enables existing customers to add enhancements to their plant after purchase.

The material enters the Prograde screen which is fitted with18 non-bolted Isenmann modular polyurethane panels. The +16 mm material is removed on the top deck and stockpiled using the first of the M2500’s four conveyors. The bottom deck of the ProGrade is a split screen where the first part of the screen has smaller apertures where the 0-2mm material can pass through and further down the screen deck, the apertures are larger to allow the 2-8 or 2-5 mm material to pass through. The remaining 8/16 mm is removed on the bottom deck.

The Evoscreen dewatering screen on the integrated Evowash sand washing plant is a split dewatering screen to allow two sand sizes to be dewatered at once and the 2-8 or 2-5 mm material is transferred via jet pump to one side of this Evoscreen. Design engineers at CDE introduced an innovative concept to meet with Bröderna Björklunds Grus’ requirement for mixing their 0-2 mm and 2-8 or 2-5 mm sands when required.

Olofström sand and gravel washing plant — the other side.

This is a dual sand conveyor with a diverter system that allows the conveyors to be moved hydraulically to match the screening mats in the dewatering screen. The chassis of the machine has been redesigned to have two supporting legs at each side rather than one central leg which stabilises the plant in order to perform the conveyor adjustment. This unique feature has since been introduced as a permanent design enhancement as a result of the success of this Swedish project.
After dewatering on the Evoscreen, the 2-8 mm material is stockpiled via the third M2500 conveyor. Meanwhile a sand pump transfers the 0-2 mm material to the next stage of processing The CFCU (counter flow classification unit) uses upward flow classification to separate particles by density and eliminates the oversize sand particles from the final sand product. The CFCU operates successfully in this project due to the inclusion of a Glycol system, a first for CDE.

Glycol was used in place of air to ensure maximum uptime in the coldest conditions. The Glycol system is required for the extreme temperatures experienced in Sweden in winter. The Glycol acts as antifreeze and ensures that the pinch valves, which are used to discharge the fine material from the CFCU tank, can open and close successfully despite the cold temperatures.

The 0-2 mm material is sent to the second half of the Evowash dewatering screen for stockpiling via the fourth conveyor on the M2500. The CFCU overflow contains 0-0.250 mm material, which still contains valuable product and therefore is transferred to the next stage of processing, the Evowash 71. Here the material enters the Evowash sump, is pumped to the hydrocyclones and a fine 0.063 – 0.250 µm sand is dewatered and stockpiled on a fifth conveyor.
The fine material removed in the CFCU through the two 500 mm hydrocyclones is sent to the Aquacycle A600 thickener, along with the 0.063 µm material from the Evowash hydrocyclones. The thickener recovers up to 90 % of the water used in the plant and complies with ever-increasing environmental requirements from planning authorities.

Mr Bjorklund commented, “Our company prides itself on using the best technology in its operations and avoiding anything that may be harmful to the environment. The Aquacycle ensures we have a clean, safe and efficient site at all times as a result of reduced waste water management requirements.” Eoin Heron, Senior Sales Manager for CDE in Europe also commented on the benefits of the Aquacycle for the company, “The Aquacycle significantly reduced the sludge basin requirement, saving Bjorklunds significant excavation costs while ensuring minimal environmental impact. This lead to many advantages, especially with planning requirements.”

The company invested in CDE preventative maintenance inspections which Mr Heron explains are proven to have a positive impact on plant production levels. “The CDE performance guarantees ensure that the customer has visibility of expenditure through a fixed cost agreement and our regular PMI inspections guarantee maximum efficiency and productivity. Investment in a CDE PMI package means our expert technicians will visit a customer’s site on an agreed number of times every year which can be easily continued as a regular contract. These specialised engineers provide support and guidance to our customers and a detailed understanding of how the plant is performing to help them to maintain plant performance at the optimum level and achieve high quality end products.”

The plant has been operating successfully since September 2013 and Mr Bjorklund is confident that he has made the right decision in choosing a CDE solution. “The sand plant means that we can maximise our customer base and offer our products for specialised applications such as golf sands and play-ground sands. The plant is extremely flexible. We can control the mixtures to achieve the optimum screening curves for customers. This is very important, especially for the concrete and dry mix industry which needs an optimum screen curve to keep costs down and maintain constant product quality. As discussed at the outset of the project, the plant as a whole can also be relocated to another quarry with ease which will allow our company to keep producing sand and gravel for a long time to come.”

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