Atlantic Install Transfer Station at Tarmac Crown Farm

Overview

This large sand quarry needed to transport dredged sand from the submerged dig face to the washplant.

Atlantic Pumps designed, built and installed a Sand Transfer Station that pumps 800m3/hr of slurrified sand some 300m. The system includes an oversize screen and stacker, and auto-flush system to prevent blockages whenever the process stops

This 135-hectare Cheshire sand quarry opened in 1989 and still contains many years of reserves. Previously worked areas are restored to nature, forming the Crown Farm Nature Reserve, funded largely by Tarmac and run by the Cheshire Wildlife Trust.

The graded, washed sand is sold predominately to local industry; concrete and asphalt plants, and a large construction material manufacturer who makes roofing tiles, mortars and screeds.

Having completed the dry-extraction at the quarry, the final works are dredging sand in what will become a lake extension to the nature reserve (subject to a pending planning decision).

Challenge

The existing sand washplant was now a significant distance from the current workings, and as the sand was now being dredged, the former system of haul trucks no longer met the needs.

As a company, Tarmac are known for drive to reduce carbon emissions, increase sustainability, and minimise noise and dust emissions during their quarry activities. They sought an innovative, effective, environmentally sound method of bulk sand transfer, that would reduce the site’s carbon footprint and could be deployed without delay.

Solution

Conveyors are great for shorter distances and where a stationary, fixed system is suited. On this site, the increased distanced from the extraction point to the washplant, and the nature of dredging made pumping the preferred method.

However, if you’ve ever been involved in trying to pump large amounts of sand through a long pipe, you’re probably aware that this can be a recipe for disasterous blockages.

Can sand be pumped?

Pumping sand-laden slurry is something that Atlantic Pumps have long specialised in. “Keeping abrasive fluids moving” is something Atlantic Pumps is known for, making them the obvious people to turn to.

The two challenges of pumping sand:

1. Sand is abrasive, causing rapid wear of equipment.
2. Sand is heavier than water, making it prone to settling.
3. The angular shape of sand can cause it to form a solid-like blockage, which is very difficult to clear from pipes.

Over the years, Atlantic Pumps have developed numerous ways of pumping solids-bearing slurry and offers a variety of pump technologies to achieve the optimum life-cycle efficiency for each particular application. Although this situation – moving as much sand as possible, as opposed to pumping sand-laden slurry – is a little rarer, our abrasive pump experience served us well.

The problem with pumping sand-laden slurry, particularly over long distances, is that it settles out as soon as the flow rate drops below its settling velocity. Due to the weight, size, and shape of sand grains, when they fall out of suspension, they often ‘lock together’, causing a blockage that is notoriously difficult and expensive to clear. This is compounded if the pump continues to exert pressure, further compressing the sand; typically into the most difficult-to-reach part of the system!

Supply consistency and fluctuations – avoiding the dreaded sand blockage.

It was to be expected that the feed supply from the dredger would fluctuate, as the suction head moves around to new areas. This posed problems for both the 300m long pipeline flow and the washplant efficiency itself.

Also, washplants have to be shut down periodically for maintenance and like any equipment, could break down or stop automatically if triggered by a safety sensor. As pointed out earlier, it is important that the sand slurry in the feed pipe doesn’t back up as , or the flow will reduce below its critical settling velocity.

The Sand Transfer Station – Keeping Sand Moving

The solution we developed was a “Sand Transfer Station”. Acting as a buffer between the dredger and the washplant, it also screens out the oversized (6mm+) sandstone, reducing the energy burden on the downstream system.

Fluidization is a known way to move dry material power, by using compressed air to cause dry sand to behave like a liquid. The Atlantic Sand Transfer Station operates on a similar principle, but uses recycled process water instead of compressed air, which is less prone to problems in large systems such as this.

The station also uses vibration motors to keep the sand in suspension and aid the seperation of oversize. Filtering out oversized material at an early stage reduces the wear and energy burden on downstream process equipment.

The final loop of the system takes used process water from the washplant and returns it to the lagoon, making this a closed loop recycling system that conserves the water in the ecosystem.

Auto-draining System Stops Blockages

A key benefit of this installation is that the whole system is protected from blockage if a fault stops the processing plant.

Should, for instance, the washplant stop for any reason, then the dredger arm wil raises, drawing clearer water through to flush the system. After a sufficient delay to clear the sand through the pipes, the dredger pump will switches off, followed by the sand transfer station.

A washplant bypass can also be activated, using automatic valves to divert sand slurry back to the source lagoon.

Connecting the various stations was a challenge, as the new dredger’s electrical controls were much more advanced than the legacy washplant. Atlantic Pumps’ mechatronics engineer worked with the site electrician to figure out the best way to link the different programming languages.

To avoid the extra cost of a whole new control panel, we also developed a hybrid interface, enabling the three existing systems to network together.

Results

The big advantage of using stationary bulk handling equipment like pumps or conveyors, rather than tanker lorries or dumper trucks, is the ability to power it efficiently with electricity from the grid. With the UK’s national grid now at its lowest ever carbon intensity (162 grams/kWh as of early 2024), it is finanacially and ecologically better tha diesel engines or diesel-powered generators.

The challenge of pumping 200 tonnes of dry matter (25% TDS) and keeping it suspended for the pipeline length was an exciting challenge for Atlantic Pumps’ engineering team and we are pleased to report that the solution is working extremely well for the client.

The Benefits of Pumping vs Trucking

This alternative method of sand transfer brings many advantages over the use of heavy mobile plants:

• Health and Safety improvements from less heavy plants crossing the site.
• Reduced noise, lessening the need for abatement
• The fully electrified process means they can use grid energy (subject to planning permission for a new sub-station). This is more efficient than diesel power and will drastically reduce the CO2 footprint as the National Grid transitions to fully renewable energy.
• Automation gives a smooth process flow, regardless of shift patterns or staff shortages.

Many quarries dewater the dig-face to enable extraction, but sites like this can cut out a whole process (or two), retaining the lake for future re-wilding and reducing costs by combining the dredging and sand transfer processes.

To discuss similar projects for your particular situation, please reach out to Atlantic Pumps Project Lead Deryck Harmer on 080081965108