In this paper a neural network-based strategy is proposed for the estimatio
n of the NOx emissions in thermal powerplants, fed with both oil and methan
e fuel. A detailed analysis based on a three-dimensional simulated of the c
ombustion chamber has pointed out the local nature of the NOx generation pr
ocess, which takes place mainly in the burners' zones. This fact has been s
uitably exploited in developing a compound estimation procedure, which make
s use of the trained neural network together with a classical one-dimension
al model of the chamber. Two different learning procedures have been invest
igated, bath based on the external inputs to the burners and a suitable mea
n cell temperature, while using local and global NOx flow rates as learning
signals, respectively. The approach has been assessed with respect to both
simulated and experimental data.