Automation and operational safety
With the carbon at 700°C, great care has to be taken to ensure safe interactions between the kiln and the upstream and downstream processes, particularly in the event of any process malfunction. This means the kiln needs a safety shutdown system which operates independently of any external systems or power. A momentary loss of control by the DCS (Distributed Control System) or a power outage could have catastrophic results. The drum which carries the carbon runs at temperatures of between 850°C and 1000°C. Stopping the kiln drum from rotating, even for a short period of time, will cause the drum to sag under its own weight.
Loussikian explains, “Even the smallest changes in tolerances will have dramatic effects on the kiln’s ability to operate correctly; it may not operate at all. With no easy way to rectify damage, it is likely the kiln would be offline for up to 6 months, whilst a new one is constructed and installed. Our design takes care of this problem with a special shutdown operation that is driven by a battery backup system in case of power failure. It keeps the kiln rotating until all the carbon is safely out of the kiln and the drum has cooled down sufficiently to safely stop.”
Once the kiln had been assembled and tied in with the mechanical and electrical components of the upstream and downstream processes, testing and cold commissioning started. Although the kiln will be controlled by the site’s Yokogawa DCS, the kiln’s operation and control needed to be tested and proven independent of the DCS. Metso and Electrical Board Manufacturers designed a complete system that was only required to control the kiln’s operation during testing and commissioning. David Merrick, Electrical Board Manufacturers’ automation and control engineer, explains in more detail “Once testing was complete, control of the kiln was transferred to the Yokogawa DCS. To ensure that control is exactly the same, our programming and our control interface hardware were integrated into the DCS. This was a complex process, but the cooperation I enjoyed from KCGM and Yokogawa, made the process really simple. ”
Cooperation and team work a key success factor
Replacing roasting with UFG impacted every process downstream, including the interaction between the newly designed kiln and scrubber. Unique engineering solutions had to be developed and applied throughout the commissioning process to ensure optimal performance of these two critical elements in the process.
According to Paul Antcliff, KCGM’s Project Engineer, a lot of cooperation was required between the various parties. “Everybody was committed to the success of the scrubber, and when problems arose everybody would be part of finding a solution.” he said.
“Many customized designs were developed, and Metso played a very active role by sharing their insights and ideas to identify improvements and find solutions. This included a strong participation in our HAZOPS (Hazards and Operability Study).”
In the final step, Mining Combustion Services commissioned the gas burners. Precise settings are critical for the effective and economical operation of the kiln, and all possible conditions need to be considered and tested. One example is air flow, which is an important factor in efficient gas burner operation. The unique design of KCGM’s scrubber affected airflow from the kiln, and so input from many parties was required to achieve optimum results.
Michael Allen, Mining Combustion Services elaborates “The scrubber has the capability of taking gases from one, two or three kilns. I don’t think that this has ever been done before.”
“KCGM’s effort and investment into the scrubber design is truly admirable. They spared no expense in getting it to work 100%. Every single chemical element from the process is eliminated. Even any volatiles not caught in the scrubber are incinerated. It is a fantastic tribute to the importance that KCGM place on the wellbeing of the community.”
An outstanding result
With the roasters no longer in operation, atmospheric emissions have been eliminated from the Gidji Processing Plant. Everybody wins – with emission reductions the environment and community wins and the process can run 24/7, without the need to halt operations due to prevailing wind conditions.
According to Max Wijasuriya, Metso’s Vice President Capital Equipment, the collaboration and knowledge sharing between the Metso and KCGM teams was a key success factor in delivering such a positive outcome.
“Working closely with our customers is what we do – we leverage our knowledge, people and solutions to help make the big difference” he said.
To mark the opening of the new UFG Mill at Gidji, KCGM held a celebratory event attended by members of the local community and industry. This is a win-win for the community and KCGM, demonstrating how closely their success is intertwined.
*Metso Outotec was formed July 1, 2020 when Metso and Outotec merged into one company. This case study has been written prior to the merger under the old company name.