Numerical Simulation And Experimental Investigation Of Air Flow Uniformity In The Windbox Of Large-Scale CFB Boiler

Airflow velocity profile of the primary air in the windbox of two 300MW subcritical CFB boiler under cold state and various boiler loads and various differences between the volume flow rates in the two side of the primary air tubes,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?,and under different inflow rate differeces??=0%,5%,10%,20%,30%?,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?and bottom section height W₂?on the airflow uniformity of the several kinds of windbox?isobaric windbox,rectangle windbox,and windbox with clapboard inside?were analyzed based on two-dimension simulations of a series of windboxes with 33 different configurations,using the CFD software package FLUENT.The measured results showed that while the airflow velocity was basically uniform along the depth direction of the windbox,it exhibited an obvious non-uniform profile along the width direction.The airflow velocity was relatively uniform in the middle section of the air distributor and obvious lower in the side walls.As the boiler loads and the inflow volume differences between the two sides increased,the airflow uniformity became worse because of intensified flow turbulence and the backflow.Moreover,due to the jet flow at the entrance of the windbox,the airflow velocity in the initial a few simplified tubes was always lower than that of other parts regardless of the windbox width.In addition,the rectangle windbox without clapboard inside shows an insensitivity on the variation of neither the boiler loads or the inflow volume difference of the two side.The structural parameters of the windbox had obvious influence on the airflow uniformity.Finally,the optimal windbox structural parameters for primary air uniformity were determined by an optimization study of the windbox structural parameters.