By using Fluent software

the resistance in hot secondary air duct of a 1 000 MW unit boiler manufactured in Dongfang Boiler Group was numerically studied.Several factors

such as the 90°elbow at the preheater outlet

the horizontal transition segment

the uneven velocity distribution around the front and back wall and the branches

were considered as the major reasons for the large resistance in the original hot secondary air duct.Against this problem

a series of detailed improvement measures were put forward

like applying streamline design for the hot secondary air duct

selecting appropriate elbow

adding guide plate and using fillet angle at local place.After the above measurement were taken

the uneven velocity distribution and reflow problems were solved

and the resistance in the hot secondary air duct was decreased.