Enhancing the arch-fired low-NOx performance with a throat overfire air for lowering NOx and hopper overheating

Abstract

Upon the background of China's dual-carbon energy and environment strategies and the requirements of green and sustainable development in the new era, how to gradually reduce coal consumption while at the same time enhance the efficient and clean use of coal and reduce pollutant emissions is attracting more and more attention. For a 600-MWe arch-fired furnace facing persistent challenges of high NO x output and an overheating risk in hopper as firing anthracite, a cascade-arched low-NO x and high-efficiency configuration (CLHC) was taken as an alternative to the existing multiple-injection and multiple-staging combustion technique (i.e., the MIMSCT, denoted as the reference furnace or technique in this study). In particular, along the furnace height the CLHC's overfire air (OFA) position in the burnout zone has an important influence on the low-NO x performance due to the shrunk furnace-arch space and a short upper furnace. Aiming at evaluating the OFA-location effect and confirming the CLHC in resolving the above problems, industrial-scale experiments and modeling were performed in the reference furnace and thereafter, the low-NO x characteristics with the CLHC was simulated considering three different OFA locations of the upper-furnace OFA, throat OFA, and arch OFA. In the OFA-location elevated order, the blending position of OFA and the main upward gas first lowered and then elevated, while the OFA penetration, overall combustion performance, and major low-NO x accomplishment indexes related to NO x yield and burnout loss initially improved but then deteriorated. As a result, the medium throat OFA presented the optimal low-NO x merit among the three setups, with the unburnt combustible of 5.3% in fly ash alongside NO x yield of 660 mg/m3 (O2 = 6%), respectively. By comparison to the reference technique, the CLHC gained a 30% NO x reduction ratio without affecting burnout and greatly relieved the hopper overheating issue via reducing sharply its temperatures by 400 K, thereby confirming the CLHC's viability. This study provided guidance on the safe furnace operations and reduction of pollutant emissions, benefiting the efficient and environmentally friendly usage of low-quality coals in industrial-scale furnaces.