Project: Gold Mine - Ghana
Location: Ghana
Overview
The case study is a large gold project located in Ghana, West Africa. The comminution circuit comprises two primary gyratory crushing circuits, one producing a coarse product with the second unit feeding a secondary and tertiary crushing circuit to produce the fine ore feed. The two crusher products are fed into a SAG-Ball- with Recycle pebble crusher (SABC) milling circuit producing final product grind from two cyclone clusters.
The feed ore characteristics to the circuit are relatively consistent and the circuit runs at high overall utilisation. The client has a continuous focus on improvement and the objective of the project was to challenge the team to push the boundaries and explore options to improve throughout without sacrificing final product grind.
The Challenge
The circuit was unstable, making mill power draw difficult to maintain. As a result, the cyclone feed density (product size) was erratic, and mills underutilised. Annual production was below target.
The MillROC Solution
Recommendations were implemented to achieve improved stability through a continual improvement process with MillROC as its basis. This involved installation of MillROC and a MillSlicer.
MillROC provided a single source of knowledge for identifying constraints, analysing data and quantifying the impact of changes.
An improved process control strategy was implemented, stabilising cyclone pressure/ flow and ball mill power.
As a result of the improved stability, a modified ball retainer was able to be installed in the ball mill, further improving the average ball mill power draw.
In lieu of an expert system, training of operations to implement a modified SAG milling control approach which focuses on density, load stability and mill power utilisation. This resulted in better power split management between the SAG and ball mill and higher mill utilisation.
Ongoing optimisation of SAG mill relining strategy.
Outcome
7% increase in plant throughput with throughput variability (CoV) reduced from 23% to 4.2 % at equivalent total circuit power draw. This exceeded the original production target by 5%.
Grind P80 was 4% finer on average.
7.4% increase in grinding efficiency.
Reduced loading on cyclone feed pumps and cluster wear – overall annual circuit run-time increased by 1.1%.
Increase of USD 67 mil in annual revenue.