This quarry on the Black Sea Coast, which had seen considerable growth in its market since it was opened in 2008, was not operating anywhere near its optimal throughput. We were asked to review the site to identify the problems affecting throughput and hence profitability.

Starting with the deposit, the limestone was very dirty and contained many voids and small caves contaminated with clay. Even during the summer, the rock retained quite a high moisture content, presenting problems in processing.

The plant was simple, comprising a 40mm grizzly screen feeding directly into a primary jaw crusher, followed by two locally manufactured horizontal shaft impactors that in turn fed the final screens.

The very small grizzly opening resulted in carry-over of fine and sticky material into the primary crusher, causing frequent blockages. Contaminated fines entered the final product, so the fines had to be washed in a sand screw and bucket wheel de-waterer. Screen capacity was compromised by inadequate feed arrangements, and poor feed distribution resulted in uneven output from the two secondary crushers. Overall set-up and maintenance were found to be unsatisfactory.

As a result, the plant was working at around half the designed capacity, and recommendations were made to improve this to 90% process efficiency. Modifications to the scalping system to promote higher quality product, balancing the two secondary crushers, improving feed distribution to the screens and adjusting the fines washing system, contributed to lower dust production and increased production without change to the operating hours.

Implementing our four main recommendations resulted in a €275,000 improvement to the annual operating profit.