Numerical investigation of low NOx combustion strategies in tangentially-fired coal boilers

• Published in: Fuel (Guildford) Vol. 142; pp. 215 - 221
• Main Authors: Zhang, Xiaohui, Zhou, Jue, Sun, Shaozeng, Sun, Rui, Qin, Ming
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.02.2015
• Subjects: Air staging; Combustion simulation; Horizontal bias combustion (HBC); NOx emission; Tangentially-fired pulverised-coal boiler; Air staging; Tangentially-fired pulverised-coal boiler; NOx emission; Combustion simulation; Horizontal bias combustion (HBC)
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2014.11.026

•The prediction shows a good agreement with the measurement on-site.•HBC can reduce the NOx in the primary combustion zone when there is no air staging.•The predicted results have shown that OFA has a remarkable reduction of NOx emission.•Air staging dominates the integral contribution when combined with HBC burner.•The lower stoichiometry and unburned char in PCZ contribute to the final NOx reduction. A numerical model is developed to investigate the effects of horizontal bias combustion (HBC) and air staging combustion (over-fire air, OFA) technologies on the performance of a 200MWe tangentially-fired pulverized-coal boiler. The devolatilization rate and volatiles amount are determined by a kinetic devolatilization model, which predicts the coal devolatilization prior to the volatile matter and char combustion. The characteristics of the devolatilization, combustion, heat transfer and NOx emission are studied and compared to achieve a comprehensive understanding of the low NOx combustion. The prediction shows a good agreement with the on-site measurement results, which confirms that the model is capable of predicting the characteristics of the investigated boiler. The predicted results have shown that the OFA has a remarkable effect on the reduction of NOx emission. The HBC makes a significant NOx reduction in the primary combustion zone (PCZ) when there is no air staging. In terms of the NOx reduction, the air staging plays a dominant role in comparison with HBC burners. The application of OFA tends to lead to slagging in the PCZ, which can be avoided using HBC due to the higher stoichiometry close to the furnace wall. The details of this study improve the understanding of combustion and NOx emissions in tangentially-fired pulverized-coal boilers with low NOx combustion technologies, especially for boilers adopting HBC burners and OFA.