by Kathie McGregor

How to overcome increasing slag viscosity and furnace instability

As high-quality ores are depleted, more metal smelters are having to smelt less desirable materials — those containing higher levels of impurities and refractory components.

You’ll know that these complex ores often require a higher temperature to smelt. Unfortunately, this causes a number of difficulties in furnace stability and productivity. The primary issue is excessive wall accretion formation, due to high rates of heat transfer through the furnace wall panels.

Clearly, maintaining furnace reliability, productivity and safety is a key concern for all smelters. So a new approach to modelling for furnace control may be necessary.

Furnace instability and the impacts on your organisation

As a result of having to smelt more complex ores and concentrates, there is a trend towards more viscous slags, less throughput or higher temperature operations. This in turn can mean:

• less refractory life
• more process interruptions
• less stable and efficient operations
• inefficient phase separation
• excessive energy costs.

Without a data-driven approach to electric furnace ore smelting, furnace instability can grow to restrict campaign life, cause unplanned downtime, and have an overall negative impact on productivity and profitability.

How do you maintain stability in your smelter when smelting complex ores?

In an environment where you need to be able to smelt base metal concentrates, melt iron scrap, and recover valuable components from slag, you need the right tools. These tools should to be able to control electric furnace operations, predict problems and optimise operations — such as feed selection.

Ultimately, you need to be able to improve furnace control and life.

A new and innovative way to optimise the control of your furnace is to develop an Electric Furnace Heat Transfer Process Model.

The model can integrate with your existing operational control systems and will help to balance the cooling of the furnace wall panels and assist with the formation of a slag freeze lining, while maintaining furnace volume and productivity.

Develop and optimise your operations with Heat Transfer Modelling

CSIRO has developed such a model for slag resistance AC electric furnaces.

The model uses heat and mass balance and electric field calculation — together with furnace operating conditions — to calculate temperature profiles, freeze lining thickness, smelting rates, heat losses and electric power density.

The Heat Transfer Model is designed to:

• predict temperatures at various locations in an electric furnace — e.g. slag, matte, freeze lining
• predict thickness of slag freeze lining
• predict smelting rate and heat loss
• aid in problem analysis, control and optimisation
• operate with sufficient accuracy and speed for on-line implementation
• ensure portability and flexibility to use on different electric furnaces.

The CSIRO model has been developed for large six-in-line furnaces and three electrode circular electric furnaces — but it can be modified to suit other electric furnace operations, e.g. three-in-line furnaces. It is customised based on the geometry, structure and operating practice of the furnace.

Want to revolutionise furnace efficiency and campaign life in your business?

Heat Transfer Modelling tackles the problems of reduced refractory life, process interruptions, operations efficiency, phase separations and energy costs. This is done through:

• controlling the slag furnace lining
• optimising the furnace temperature profile
• reducing excessive power consumption.

The CSIRO Pyrometallurgical team are world leaders in developing new approaches to the smelting process. Contact the Minerals Process Optimisation business unit on +61 3 9545 8912 or email me, Kathie.Mcgregor@csiro.au, to talk about how you can build on your data and optimise your operations with Heat Transfer Modelling.

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