BF Watson says "The hole is where the electrode entered the furnace." (Thanks!) The brick lining the interior of the hole defintely appears to be from a furnace of some sort.

This patent description defines it as:

A lengthwise graphitization furnace for the conversion of a string of amorphous carbon bodies to graphite has an open semi-cylindrical shell of corrugated steel modules lined with cast refractory. The combination of the corrugated shell and cast refractory liner contributes to faster heat transfer by both convection and radiation, and to greater mechanical and thermal stability. The furnace is designed in modules allowing for easy replacement of worn components.