“…els become available testing of controllers can be done on simple test models derived from first principles or identified by using input-output data from the GTM or a real furnace. Identification of input-output data ( (Haber et al, 1981), (Ljung, 1987), (Wertz and Demeuse, 1987), (Wertz et al, 1992)) will lead to better models for a particular furnace in a certain operating range but it can only be applied in that range and for that furnace. Here a simple model is proposed that may be useful for:…”