Delayed planning consent necessitated extraction of the majority of this quarry’s rock from newly consented reserve. The top rock in this area was badly contaminated with clay; in fact, the top two benches were like vertical fingers of limestone with clay in between, leading to frequent stoppages due to blockages of the scalping screen.
The solution proposed was to scalp at the face and deliver a higher quality limestone to the plant, increasing the feed rate to the primary. Material in excess of the primary crusher’s capacity could then be stockpiled, and fed to the plant by FEL later in the day. This freed up labour and plant to undertake much needed development work.
The scalping screen was identified as being too small. Replacement with a probability screen was proposed.
AggFlow analysis of the plant’s capability indicated the potential to remove a tertiary VSI that produced excessive dust and fines. This machine was heavily loaded only because the primary jaw and secondary HSI crushers were severely under-utilised: There was a belief that limestone created little or no wear, so primary and secondary settings were rarely checked, and indeed the secondary HSI was so worn as to be in danger of internal disintegration. We suggested a regular regime of checking settings and then adjusting or replacing machine wear parts to maintain the required grading curve. This enabled the site to remove the VSI from the crushing circuit and reduce the excess volume of dust being made.
Production was frequently interrupted by the need to stop the plant due to high bin levels. The rate of discharge from the bins was so slow — only three loads an hour in the case of dust — that sales and stocking out vehicles found it difficult to maintain continuity of production. To improve loading times, we recommended that the bottoms of the bins were replaced, removing the 600mmx600mm single openings with double doors to draw from about 85% of the bin’s cross-sectional area. Loading was made capable of remote operation from the nearby weighbridge. A dust suppression system was added to each bin to improve visibility when loading.
The benefit of these modifications was a 0.71€/t improvement to the site’s profitability.