CFD-guided optimization of airflow distribution to mitigate overheating in a CFB boiler under-bed ignition system

During ignition, non-uniform airflow within the windbox of a circulating fluidized bed (CFB) boiler can cause severe operational failures, including flame flashback, localized overheating, and thermal damage to the air nozzles. To diagnose and resolve this issue, a comprehensive three-dimensional computational fluid dynamics (CFD) model was developed, incorporating the realizable k - ε turbulence model, as well as combustion and radiation transport. A numerical analysis of the original configuration was conducted, which confirmed that uneven flow can result in significant temperature spikes near the air nozzles. A modified primary air (PA) distribution system design was subsequently proposed, introducing a dual-path air supply mechanism to route PA through the burner’s pre-combustion chamber. This modification significantly improved flow uniformity, eliminating localized hot spots and reducing the peak temperature adjacent to the air nozzles by over 45% (comparing Case 3 and 8). This study proposes a rigorously validated method to enhance ignition reliability and component durability in CFB boilers.