A trip to warmer climes – furnace excavation in Bjølvefossen

Stein kollage blogg
I’ll admit, being a trainee really has quite a few perks. An open mind, a few connections and an eager interest can get you into some pretty awesome situations – and I’m talking literal awe-some, as in: I’m in AWE of this...

This blog post is written by Liv Carlhamn Rasmussen (2nd year trainee).

Sitting in a meeting about a completely unrelated topic I heard of a furnace excavation that was going to take place at Elkem Bjølvefossen, and was invited to join. It was no matter-of-course that I should participate – lacking any expertise on the subject and having no previous connection to the plant in Bjølvefossen – but I decided to speak to the trainee coordinator on the off chance, and to my delight he agreed to let the trainee program sponsor my trip.

I may sound childishly enthusiastic about it, but come on, check out this picture:

Who could watch a still-hot furnace being dismantled with dynamite, drilling machine, wheel loader and other heavy equipment, its contents sometimes spewing out like lava, and not think: hey, this is pretty damn cool.

But, you have to keep your wits about you when working in close proximity to explosives and smoldering materials. Elkem operates according to the premise that we should all leave work as healthy as when we arrived, and that entails rigorous security measures. A great deal of thought and preparation goes on behind the scenes of this sort of spectacular event, but it integrates smoothly into the apparatus and mind-set of HSE already in place at Elkem’s plants.

For those less familiar with the process, I’m talking about an 18 MW arc furnace producing ferrosilicon. The crucible – containing the raw material mix and the tips of the electrodes – is where the magic happens, with temperatures up to around 2000°C in the hot zones, enabling the extremely energy-intensive reduction of SiO2 to take place. The steel mantle alone could not withstand such temperatures, so it’s lined with refractory materials (alumina, carbon and silicon carbide).

Furnace linings get worn out with time, faster or slower depending on the conditions and how the furnace is run (or even more importantly: stopped). Generally they are replaced every 10-20 years or so during a planned stop, so as to prevent dangerous “burn-throughs” of the lining, but furnace 1 in Bjølvefossen was the oldest active furnace in Elkem, the furnace lining having survived 24 years (!) of tough conditions, and despite such a venerable age it was relatively well preserved, even when retiring.

I joined Professor Merete Tangstad from NTNU and Post-Doc Michal Ksiazek from SINTEF in the work of documenting the dig-out and collecting samples from the furnace. After a few intense days we ended up with some 15 GB worth of pictures and videos and probably close to half a ton of materials.

For the most part the materials coming out of a furnace look like a rather dull mix of grays and browns:

But upon closer inspection…:
Beauty from within

Alkalis, carbides, metals and various slag compositions form beautiful patterns and shapes, and some very interesting phenomena can arise from the chemical mixtures and high temperatures. There were some large blocks of slag that were rock-hard (though rock isn’t all that hard, relatively speaking, but you know what I mean); drilling, picking, scraping barely made a scratch – nothing short of dynamite could bring it down. But once out of the furnace, going from high temperatures to the cool air of barely-spring, these blocks started disintegrating, pulverizing before our very eyes!

Awe-some, no?

I look forward to seeing the analysis results of the samples, and contributing to the characterization work myself, using the XRD skills I’ve picked up so far at the R&D lab here in Kristiansand.

It was a treat to get to partake in the excavation, and besides Merete and Michal (who were wonderful and educative company during the long shifts) I would like to extend a thank you to Jan-K Lutro who received us in Bjølvefossen and whose friendly face it is always nice to see.

Way better than a trip to the south! (And much warmer…)