Tweaking feed and a focus on aeration have seen the Mount Isa Mines copper smelter metallurgy and operations teams cut unplanned downtime related to the waste heat boiler.

The ISASMELT waste heat boiler was behind three major copper smelter outages in 2019 and 2020, costing the business significantly.

Mount Isa Mines metallurgy copper smelter superintendent Marc Moutin said that in addition to boiler outages, the presence of boiler build-up was constraining the operating feed rate by about 50 tonnes per hour in the months leading up to a shutdown event.

“These sticky accretions were produced due to the lack of oxygen in the top of the furnace, driven primarily by the finer fractions of coal becoming entrained in the off-gas and having a greater affinity with oxygen,” he said. 

“To combat these issues we implemented a number of actions, including using modified feed materials and additional aeration; and these actions have definitely paid off.”

Process feed materials (concentrate, fluxes, coal) are fed into the ISASMELT via a feed chute on the roof of the furnace.

The material drops into a molten bath at the bottom of the furnace where the metallurgical reactions primarily occur.

Off-gases generated in the reaction zone travel up the furnace and exit via an off-gas off-take which leads to the waste heat boiler where heat is extracted from the gas stream.

Some of the actions undertaken by the metallurgy and operations teams included:

• Sourcing a coarser coal, to reduce the risk of  the fine particle content becoming entrained in the off-gas;
• Tracking metrics to increase the ability to act upon negative trends;
• Undertaking manual gas sampling to dictate whether the addition of extra oxygen was required; and
• Implementing a lance port post-combustion system with the aim of facilitating oxygen injection.  

“As a result of these actions there has been no unplanned downtime associated with the waste heat boiler in 2021,” Mr Moutin said.

“Furthermore, the boiler differential pressure, which is a proxy for build-up formation, has successfully ramped down in the past months.”

Mount Isa Mines technical services manager, Martin Bakker applauded both the metallurgy and operations teams for their efforts, with the actions taken clearly making a significant impact on operational performance. 

“With any reoccurring issue, such as what we were experiencing with the waste heat boiler, it’s important to not only fix the breakdown, but look for ways to improve the process and prevent the issue from happening in the first place,” he said.

“At the copper smelter we foster a culture of continuous improvement and encourage our people to think outside the box, while striving for optimal performance.”