Mathematical procedure for predicting tube metal temperature in the radiant superheaters of a tangentially and front fired utility boilers

Abstract

The superheaters can be indicated as one of the most critical components of the utility boilers experiencing highest temperatures. The local overheating of the heat exchangers material is a significant operational issue. The current and future market conditions implicate new unfavourable regimes of boiler operating conditions bringing the need for prediction capability of tube wall temperature in either design or retrofit process. There is a need to obtain a realistic metal temperature distribution based on uneven heat flux absorbed and complex steam flow. The current paper demonstrates a computational methodology of predicting tube metal temperature of radiant superheaters platens. It couples a full scale 3-D boiler simulations based on CFD technique on the combustion side with an in-house 1-D heated pipe flow model of the steam side. The methodology was applied to two different boilers with different firing strategy (front fired and tangentially fired) to demonstrate the model flexibility. The model is capable of identifying the exact location of specific platen in which the metal maximum temperature occurs. A validation study was conducted by utilising the available measurements. The computations are in qualitative and quantitative agreement with measurement. The modelling approach can be easily extended to boilers utilising all types of fuels as well as heat recovery steam generators.