Depending on what size unit you want probably not much. As an operator of a vintage first generation pyropower (now Foster wheeler)CFB built in 1989 twin boilers, a lot has changed since then. Some now have intrex loop seal heat exchangers, and others have plates in stead of hot cyclones and loop seals. As far as spec-ing similar size boilers they would by about the same size physically with some different auxiliary equipment. Both are very reliable and are great units both companies are well respected in the industry. not much help here.
Doug