A full evaluation of the operation of this large limestone quarry revealed unbalanced production and opportunities for cost saving.
The site supplies two distinct markets, the roadstone and concrete aggregate market, and a highly developed product range of armour rock for river defence and harbour construction. In the quarry, material is selected for delivery into the primary crusher for aggregate production, or to a very large trommel for armour stone production, with fines from the trommel being returned to the aggregate section via belt conveyor. The primary is a gyratory crusher feeding to a very large surge pile with nine recovery points feeding three conveyors. These in turn fed onto a feed conveyor for the secondary gyratory crusher, which was identified as the primary bottleneck in the production process. The product from the secondary was then fed to a cone and two VSI’s that also took recirculating feed from the final bins.
An inescapable visual feature of the site is a huge stockpile of dust that has clearly been growing for many years. Aggflow analysis gave a clear indication that the excessive dust problem was a function of VSI crusher capacity on the site. Pit balance problems were resolved by changing the secondary for a horizontal shaft impactor that would produce a more through-graded product, and allow one VSI to be closed down permanently, or both from time to time. This helped to balance dust production. Further improvement resulted from recent restrictions on new reserve consents in NE France, leading to an opportunity to sell 0-4mm into this new market.
A review of the profit by product indicated that four products were being sold at less than cost. The proposal was to cease these sales or negotiate a price increase to recover the negative contribution margin to break-even or better.
Evaluation of drilling and blasting practice showed money-saving possibilities, firstly from reducing the base charge, and secondly, when the contract for drilling and blasting was renewed, by including clauses on drill hole accuracy to control oversize, and fuel consumption. Further savings were expected from bringing secondary breakage in-house rather than using a contractor.
We evaluated a project for the location of a fuelling station within the quarry, rather than persist with the longstanding practice of taking all of the load and haul fleet to the fuelling point in the main plant area.
Sales were loaded from the final product bins through one line and stocking was handled by a second line. By combining stock and sales load-out functions, a saving of one full-time employee on each of the three shifts was achieved.
The audited benefit from the above was a 0.50€/t improvement to site profitability.