Two-layer control system of the spray booth is presented. Special attention is paid to the upper layer which optimizes operating point of the direct control layer to minimize the fuel consumption. The minimization is done on-line using measurements of the process variables and off-line identified models. In this way the actual distance to the limits of the process variables can be determined and the constraints can be shifted accordingly to determine a new set-point for the direct control layer. This algorithm assures safe performance of the system and minimizes the fuel consumption. (C) 2010 Elsevier Ltd. All rights reserved.