1. What are the key differences between a conventional EAF and Consteel?
The main difference is the way the scrap is charged to the furnace. In a conventional EAF, the roof is swung to one side, and a bucket of scrap is lowered into the furnace. The bucket’s clam shell bottom is opened to drop all the scrap into the furnace in one go. The roof is then swung back over, and the electrodes are energised so they bore down into the scrap pile. Eventually a pool of liquid steel is created with a layer of slag above it known as flat bath, a very stable operating condition. 

In the Consteel EAF, the scrap is continuously charged through the side wall of the furnace, so the furnace can maintain the flat bath condition, with the arcs constantly submerged in a layer of slag.

2. What are the main advantages of the Consteel method?
Not having the roof swinging off means a shorter cycle time, so productivity is higher, as well as reducing heat loss and dust emissions. The constant immersion of the arcs allows higher average power input, and because they are not exposed to air, the steel has a lower nitrogen level. Without the bore down process, there is less damage to the refractory and the electrodes.  

3. The scrap is preheated. How does that work and why is that beneficial?
The hot process off gas, created from the oxygen blowing (which removes impurities) from the furnace flows through a tunnel where the scrap charging conveyor runs. Pre-heating the scrap in this way helps in the energy efficiency of the furnace.

4. Are there other environmental and safety advantages to the Consteel? 
Keeping the roof closed means lower dust emissions into the working area and the flat bath operation means less dust in the off gas.  All emissions to air are tightly controlled by our new fume treatment plant.

The stable nature of the flat bath operation also removes some of the higher risk activities of a conventional EAF, particularly the bucket charging of a large quantity of scrap in one go. As you would expect on a modern furnace, many of the jobs that might put an operator into higher risk areas are now done automatically, such as sample taking, sanding tap holes, and camera based visual inspection.

5. Can you tell us about the Electromagnetic Stirring System (EMS)?
Compared to a BOS steelmaking vessel, the EAF has a larger diameter and shorter depth, so it cannot replicate the violent stirring of the BOS vessel’s big oxygen lance that helps achieve a homogeneous steel. We are using stirring technology from ABB to generate an electromagnetic field within the bottom of the EAF and enhance the stirring that occurs naturally from convection.  

6. What temperature is the EAF kept at?
During normal operation there will always be at least 150 tonnes of liquid steel inside the shell at temperatures between 1,550°C and 1,640°C. The refractory brick lining means that the shell of the furnace will be kept at below 300’C.

7. What will be the typical mix of scrap vs iron?
This will vary depending upon the grade of steel we need to make, but on average we will be charging around 75% scrap and 25% fresh iron to the furnace.

8. What will be the annual output of the EAF?
The furnace can produce 320 tonnes every 43 minutes, so in principle if it operates for 7,200 hours it is capable of producing 3.2 million tonnes. In reality, it cannot always operate at full speed because we need to match to the speeds of our casters which vary with width.  We are planning for an annual output which matches well with the downstream throughputs, but there is scope for future development.

There are around 60 Consteel furnaces installed throughout the world.