Influence of over-fired air location on gas-particle flow characteristics within a coal-fired industrial boiler under radial air staging

To achieve low-NOx emission in the coal-fired industrial boiler, the radial air staging method is proposed. The location of the over-fired air (OFA) is an essential parameter as it affects the combustion stability, NOx generation, burnout, and slagging trend. These are related to the gas-particle flow such as the recirculation region, gas mixture, and gas-particle mixture. Therefore, in this paper, taking a coal-fired industrial boiler with radial air staging method as an object, in a cold-modeling furnace, the gas-particle flow characteristics under various OFA locations (L-D of 1.29, 1.43, 1.72, and 2.00) are studied. When OFA is radially arranged, the OFA jet diffuses towards the furnace center. As the L-D increases, the size of the central recirculation region increases, thereby improving combustion stability. When the L-D is 2.00, the mixing of the OFA jet and PCC jet obviously is delayed. Moreover, an increase in L-D leads to more returned particles in the furnace center, promoting the reduction reaction of NOx. In addition, as the L-D increases from 1.29 to 1.72, the gas-particle mixing uniformity is enhanced, which is beneficial to the uniform temperature distribution. Comprehensively, the L-D of 1.43-1.72 is recommended when radial air staging is adopted in coal-fired industrial boilers.