Experimental and numerical study on air flow uniformity in the isobaric windbox of a 600Â MW supercritical CFB boiler

Airflow velocity profile of the primary air in the isobaric windbox of the first 600 MW supercritical CFB boiler worldwide under cold state and various boiler loads was experimentally measured and numerically simulated to investigate uniformity of the primary air. Experimental measurements were conducted in the furnace under different boiler loads (100%, 85% and 70% BMCR for the right windbox; 100% BMCR for the left windbox) by a hot wire anemometer. Meanwhile, the effect of key structural parameters (including the pressure-stabilization section height W1, inlet area ratio AR, inclined angle θ and windbox depth) on the airflow uniformity of the isobaric windbox were analyzed based on two-dimension simulations of a series of isobaric windboxes with 43 different configurations, using the CFD software package FLUENT. The measured results showed that while the airflow velocity was basically uniform along the width direction of the windbox, it exhibited an obvious non-uniform profile along the depth direction. The airflow velocity was relatively higher in the front wall and obvious lower in the back wall. As the boiler loads increased, the airflow uniformity became worse because of intensified flow turbulence. Moreover, due to the jet flow at the entrance of the isobaric windbox, the airflow velocity in the initial a few simplified tubes was always lower than that of other parts regardless of the windbox depth. In addition, the airflow profile of the isobaric windbox within 12 m was significantly different from those beyond 15 m. The structural parameters of the isobaric windbox had obvious influence on the airflow uniformity, and this influence decreased with the increase of windbox dimension. The backflow phenomenon resulting from the interaction between W1 and AR was observed in some simulation cases. Finally, the optimal windbox structural parameters for primary air uniformity were determined by an optimization study of the isobaric windbox structural parameters.