Quarrying
One of the other important savings we’ve found is that on the old plant, the feed hopper was a significant distance from the raw material, so we positioned the feed hoppers much closer to the ship discharge point, so the loading shovel doesn’t have to travel so far. One loading shovel (a Komatsu W500) can feed the plant at 600 tph quite comfortably.” This reduces fuel consumption by 28% and increases throughput by a factor of 2.5. Eliminating the old mobile crushing equipment meanwhile gives further fuel savings of 75,000 litres.
ABOVE: Hanson sand washing plant and effluent treatment
consistent specific gravity to be discharged onto the dewatering sand screens. Haith’s Autofloc in-line measurement of the incoming solids, assessing the dosing level required to maintain the water quality set during commissioning.
Explaining the combination of the Linatex and Haith systems, Mike says: “Within the product there is always some fine material, which the sand plant doesn’t take out and it ends up going back into the water system. So the Haith thickener allows the fines to coagulate together and fall to the bottom to be then pumped back onto the Linatex screens and out into the sand. “Effectively it’s a closed circuit: we are recycling water all the time, which is a huge benefit. With the old plant we were producing silt or fines at the rate of approximately 250-500 tonne/month. So we would buy the product and then end up producing an unsaleable product that had to go to landfill: a lose/lose situation. By combining the Linatex plant and Haith thickener working in conjunction we are utilising the entire product that ends up back in the sand.”
Mike adds: “The other big advantage of this system is that we have a poly dosing system that is monitored consistently to give the optimum amount of flocculent to make the fines coagulate. There’s a tremendous saving in cost on that as well.”
The end result
End product is stockpiled in locations just a short travel distance for loading shovels supplying materials to Aggregate Industries. The footprints are as big as possible to eliminate double handling: the 10 and 20 mm piles are approximately 10,000 tonnes while the sharp washed sand is round about 20,000 tonnes. “The site previously had small stockpiles and we were continuously moving material,” says Mike. “Now we can load straight from stockpiles and this saves fuel and wear and tear on loading shovels. The cost saving in fuel has dropped from about 24 litres/hr down to approximately 19, purely because the shovel is running very short distances and it does not have to rush, which is a significant saving.”
Frindsbury is now a 1.2 million tonne a year plant, without having to work 24 hours a day. “We don’t have to produce as often as we did before to reach the sales target,” says Mike. “On the old plant, we worked essentially 24 hours a day to produce approximately 400,000 tonnes a year. So the new plant is extremely efficient.”
36 Solids & Bulk Handling • March 2010
www.solidsandbulk.co.uk
Hanson has full control over the new plant, which can be started or shut down (in sequence) by pressing a single button. The computer-based control system provides full diagnostics and Hanson can control all of the plant’s numerous parameters remotely and fine tune the system. Each of the plant’s stations has a control box with internet cables coming out of it to communicate with the control room, which means adjustments can be made without the need to rewire. All the plant’s cabling is underground. “We keep daily and running records of the water we use, belt wears on the main conveyor, the kW hours we are using as well as running totals of materials produced. This all goes into a reporting system, which gives the directors a clear view of performance of plant through key performance indicators (KPI).” In addition to numerous health and safety aspects, the design allows easy maintenance with walkways giving access to all areas of the whole structure, which is double-dip galvanised to marine standard. Because components have been kept predominantly to four sizes, spares inventory is minimised. The external lighting is accessible from inside the plant buildings so scaffolding towers are not required for maintenance. Internal lighting is also located at a low height to eliminate the need for ladders. Installation was carried out in two parts: building one half of the new installation while the old plant - essentially mobile kit mounted on stilts - continued operating until it was time to shut it down. The build commenced in May 2009, the old plant was pulled down in September 2009 and commissioning of the new plant commenced around mid-April 2009.
Mike concludes: “The new plant is far more efficient, requires fewer staff, maintenance is easier and safer, and the access issues we had in the plant have all been eliminated.”
For more information contact Centristic on tel: 01626 83 43 10; Linatex on tel: 01252 743000 Haith Industrial on tel: 01302 831911 and Skako Comessa on tel: 01937 838010
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