Predicting effects of air staging application on existing coal-fired power steam boiler

Abstract

The results of an extended research performed with the aim of investigating influence air staging application on processes occurred in boiler furnace have been presented in this paper. This subject was developed as a result of the need to obtain valid engineering methods for estimating the intensity of combustion and heat transfer processes under sub-stoichiometric conditions. The used calculation method, presented in previous publications, has been established by linking the differential mathematical model of processes in the furnace and conventional integral calculation procedures of all heating surfaces within the boiler. Such verified calculation method provided the algorithm for qualitative analysis of steam boiler operation regardless of the applied combustion scheme. In this research, by use of such approach, the operation of power boiler within TPP Kostolac has been assessed where combustion system was reconstructed during 2015. Calculation results in case of application of designed combustion system (UNR) and alternative air staging configuration (TC1) have been considered. In addition, the present air distribution scheme with the applied primary measures (R) has been analyzed. Comparison of such gained results listed in the same table ensures the trend of the change occurred by application of the air-staging system which needs to be more closely defined.Results of research showed that air staging throughout the furnace height slows down the combustion with the simultaneous intensification of the heat transfer process. Although this phenomenon led to the reduction in NOx concentration (195/470 mg/Nm3, dry, 6% O2), it decreased the power of considered boiler (725.5/774.0 MW) and increased boiler’s efficiency (86.49/85.52%). Furthermore, due to the temperatures of superheated (517.0/540.0 °C) and reheated (524.0/540.0 °C) steam being below the designed level, the safety of the boiler’s operation was significantly affected.The study also reveals that the boiler’s efficiency rate is, in any considered case with applied air staging system, higher due to the possibility to run the boiler with the lower value of excess air ratio (1.15/1.22). Additionally, results demonstrate that distribution of the amount of air, as well as air introduction location, can significantly influence parameters of superheated and reheated steam as well as the regulation area of the same.