I have found out very little about Fellner & Ziegler beyond the following. The company was founded by Johann Christian Fellner (1851-1902) with a plant in Frankfurt am Main specialising in domestic and commercial heating systems, and later in industrial dryers. In 1893, it formed a joint venture with Amme, Giesecke and Polysius (with F&Z as the major participant) to set up a factory in Hamburg to produce cement kilns, and produced rotary kilns from 1898. This plant was taken over by Polysius in 1904, and F&Z continued making cement equipment at Frankfurt.
Although independent before WWII, they have been subsidiaries of various larger companies post-war.
They supplied more than fifty rotary kilns to Britain in the first decade of the 20th century, mainly because they supplied APCM with their large first installations, but several other companies also obtained kilns from them. For APCM at least, they produced kilns to Hurry and Seaman specifications.