Prediction of the tube temperature and oxide scale formation of boiler superheater by a coupled combustion and hydrodynamic model

Excessive oxide scale formation due to tube overheating is one of the major causes of boiler tube failures. Boiler tube overheating is caused by both the highly uneven gas heat flux distribution in the furnace and steam flow distribution in boiler tubes. Currently few models could predict oxide scale formation since incorporating the gas and steam flows that have huge scale difference in the same model framework presents a great challenge to such models. Therefore, this paper proposed a coupled combustion and hydrodynamic model that integrates a three-dimensional CFD model describing the gas flow and combustion processes in the furnace with a one-dimensional hydrodynamic model describing the steam flow and heat transfer processes in boiler tubes. This model was applied to predict the oxide scale formation in the platen superheater of a coal-fired boiler. The results closely agreed with the measurement data and demonstrated that tube overheating and the resultant oxide scale formation form a mutually promoted cycle that further accelerates oxide scale formation. By optimizing steam flow distribution, however, the tube temperature deviation of tube panel can be reduced from 60 °C to below 10 °C, and the growth of oxide scale can be reduced by 55 %.