There is an article 'Newton, Chambers: Thomas Smith and the Steam Powered Coke Drawer' by Paul Jackson in the latest (Issue 75) of Archive, published by Black Dwarf. It includes details of Coke Ovens at Thorncliife Works, Rockingham, Smithy Wood and Grange Collieries. In particular it refers to the Rockingham Koppers by-product ovens, which started in 1910. I don't know if Koppers was a German company - but this may be a clue.