This is a Thomas converter. It’s used in steel plants to increase the quality of steel and produce the so-called Thomas steel after the British discoverers Percy Gilchrist and Sidney Gilchrist Thomas. Those interested in more details, I’d also recommend reading the corresponding article in the German Wikipedia, because it is IMHO better than the English one.
The converter in the above image is one of the smaller ones (the kids are about 1.70m tall) used in a small steel plant. It was hanging in the plant and when the steel was ready, the converter swung over a train to spill out the liquid steel for further processing.
More of my images can be seen on my own blog.