These are the lids on the top of the blast furnaces. This plant was built in the late 1800's.
These devices were used for carring raw materials all over the plant. They run on a track and to me seem very similar to a chair lift used on a ski slope.
Both coal and iron ore were brought to the plant via the rail system and steel was brought out. The plant was built on the river and close to the railroad. These two elements were essential for success. River water was used throughout the plant and especially employed to cool the newly created coke.
A tour of the plant takes around 3 hours, is a bit technical and very interesting.