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A new design was engineered to improve the lifetime of a boiler induced draught fan (ID) impeller in a large industrial plant. The lifetime of the fan was being shortened by a considerable amount of abrasive dust in the exhaust gases. In particular there was erosion damage to the highly stressed areas of the impeller blades, backplate and bolted-on hub assembly.
Mainstream Engineering Ltd (MEL) ASEL division, was engaged to investigate impeller design options for improved operating life. Theoretical wear life calculations on an improved design indicated at least a 50% increase in operating life.
Features of the MEL design included an aerodynamically designed impeller inlet, cutaway backplate, replaceable bolt-on blade and backplate wear plates, separate replaceable blade nose pieces and a welded hub assembly with wear liners. Wear liners made from abrasive resistant material (450 HBW) and the impeller was built to AS/NZS 1554.4: 2014.
Design: Heavy duty backward inclined plate bladed impeller
Impeller diameter: 1,567 mm
Speed: 1,050 rpm at design, 1500 rpm during grate cleaning
Impeller Tip Speed: 86.2 m/sec design, 123 m/sec during crate cleaning
Control: Variable speed drive (VSD)
Arrangement: Duct inlet
Materials: High strength steel + abrasion resistant wear liners
Design temperature: 230 C