Energy efficient iron-ore reduction technologies employed

Mpumalanga-based steel and vanadium giant Evraz Highveld Steel & Vanadium is in the process of implementing new iron-ore reduction technologies that will reduce energy consumption of the company’s furnaces by up to 50%.

Evraz COO Franz Holy says the company is using about 1 800 kWh/t of liquid iron, compared with a conventional scrap-based arc furnace, which uses up to 800 kWh/t of liquid iron.

South Africa’s second-largest steel producer also consumes 1 t of coal for every 1 t of liquid iron, which is three times higher than processing iron-ore by using a blast furnace that consumes between 300 kg/t and 400 kg/t.

Holy explains that Evraz does not use conventional reduction technologies because of the type of iron-ore it processes, which is a magnetite ore with a ferrous content of about 54%. It is also rich in titanium oxide and vanadium oxide, which comprise 13% and 6% of the ore respectively.

“If this iron-ore is processed in a conventional blast furnace, the titanium-carbides would block the furnace” says Holy.

This subsequently resulted in the steel producer’s initial devel- opment of a new reduction tech- nology when the company, formerly known as Minerals Engineering, was first established in 1957.

“It was a strategic set-up aimed at using this type of ore and developing a process by which steel is produced, like a normal steel company, but also to generate vanadium-rich slag as a by-product,” says Holy.

Minerals Engineering devel- oped a technology, based on a rotary kiln, which involved the ore being prereduced. Final reduction is conducted in an electric arc furnace, in which titanium is extracted and liquid iron is produced.

Holy tells Mining Weekly that the process was ideal when it was initially designed more than 50 years ago, as South Africa was known for its low-cost coal and electricity.

“However, the whole framework of steelmaking has changed, owing to the increasing costs of electricity and coal. Therefore, we are considering new reduction technology that makes the prereduction in the rotary kiln much more effective, substantially decreasing the electricity requirement of the arc furnace,” he says.

Prefeasibility and Project Progress 
In collaboration with engineering consultancy Hatch, Evraz conducted a prefeasibility study in 2011, which indicated that it would benefit the company to improve the prereduction process in the kilns, thereby ultimately improving efficiency.

This is achieved by implementing preheating mechanisms such as placing a preheating aggregate before the kiln and using the hot off-gases to preheat the material. “You promote metallisation in the kiln and, therefore, reduce the power required by the furnace,” explains Holy.

“Another option is to build new kilns that are longer and more modern in terms of design and automation to increase efficiency by better using heat in a counter current flow.”

Holy says the company wants to increase the metallisation in its kilns from 30% to 64%, using a more advanced preheating mechanism which will ultimately reduce the energy consumption of furnaces by up to 50%.

“This is not really a ‘new’ technology; it’s just something which is more advanced than what we are doing now,” admits Holy.

He adds that there are not many steel plants with a similar reduction process, especially in South Africa, but highlights steel and vanadium slag producer New Zealand Steel as a leading developer of energy-efficient iron-ore reduction technologies for this type of ore.

New Zealand Steel has been using these preheating mechanisms for 20 years, an achievement Evraz is aiming for.

“We are not breaking ground or placing ourselves at risk by using new technology – this technology has already been proven. We aim to combine what is available on the market and find the most efficient way to implement that combination,” he says.

Having shortlisted various reduction technologies, Evraz has started a detailed prefeasibility study, which will run until November.

The outcome of this study will influence how the steel producer will forge ahead with the iron-ore reduction project. It will reveal the most suitable kiln and whether using the kilns offline or linking them to the furnace will be more energy efficient.

Evraz plans to start constructing, implementing and commissioning the new reduction technology in the first half of next year. This process will take about two years to complete, reveals Holy.

In conjunction with the implementation of new reduction technologies, Evraz is planning the commissioning of a cogeneration plant for 2015.

“We decided that, if we were going to change the process [at Evraz] by building a new preheating furnace, or a longer kiln, we will also automatically implement a system whereby we take the hot off-gases and convert them to electrical power [using steam generation],” says Holy.

This will help the company mitigate the increasing price of electricity and South Africa’s strained power supply.

“At the present prices [of coal and electricity] and considering the fact that our off-gases are available for free, the company will generate power at cost, which makes cogeneration very attractive,” he adds.

The plans for cogeneration comprise two phases. The first and more advanced phase uses a carbon monoxide- (CO-) rich off-gas, similar to blast furnace gases used by the company, to generate power.

An environmental impact assessment (EIA) for Phase 1 of the cogeneration plant, which will produce about 30 MW of power, is currently under way. Holy says the company expects to receive the outcome of the assessment early next year, after which it will proceed with construction.

Phase 2 of the company’s cogeneration plant, however, is linked to the outcome of the iron-ore reduction technologies’ prefeasibility study, as it will depend on the hot off-gases emitted once the new reduction technologies have been implemented and the number of kilns Evraz will convert to the new system.

Depending on the final process design and the capacity of kilns converted, Holy estimates the cogeneration plant will generate between 75 MW and 150 MW of power but expects a 12-month gap between the commissioning of the two phases.

Once both phases of the cogeneration plant are under way, Evraz will continue to seek cost-effective and energy-efficient initiatives, with the aim of providing stability during tough economic times, he concludes.