Effect of staged-air box structure on combustion and NOx emissions from a 300 MWe downshot-fired utility boiler

Downshot-firing systems are widely used to burn coals with low volatile matter content, but often reported to have operational problems. This paper comprehensively investigates the effect of the staged-air box structure on the performance of a 300 MWe downshot-fired utility boiler.
First, testing and modelling are done on a 1:1-scaled model of the staged-air box to study the cold flow under one original and two new windbox structures, which sheds light on the proper use of a new staged-air box in the boiler. Then, simulations are performed for the utility boiler
to further investigate the influence of the new staged-air boxes on the boiler performance. Finally, the utility boiler is retrofitted by using one of the newly designed staged-air box. Performance tests are made for the boiler before and after the retrofit, showing the use of the new staged-air box greatly improves the boiler performance at full load, e.g., NOx reduction by 20.7% and thermal efficiency improvement from 88.76% to 90.48%.