Working Principle and Performance Characteristics of High-Temperature Boiler Induced Draft Fans

Working Principle and Performance Characteristics of High-Temperature Boiler Induced Draft FansIn single-stage high-temperature boiler induced draft fans, gas enters the impeller axially. As it passes through the impeller, the flow direction changes to radial, then enters the diffuser. Within the diffuser, the gas alters its flow direction, the duct cross-sectional area increases, and the gas flow slows down, thereby converting kinetic energy into pressure energy. The pressure increase primarily occurs on the propeller, after which the diffusion process continues. In multi-stage high-temperature boiler induced draft fans, a counterflow device directs air into the next impeller to generate higher pressure. The operating principle of high-temperature boiler induced draft fans is fundamentally similar to that of turbo compressors. However, due to the low gas flow rate and small pressure changes, changes in gas specific volume are generally not considered. The gas is treated as an incompressible fluid. High-temperature boiler induced draft fans can be manufactured for right-handed or left-handed operation. From the motor side: - Propeller rotates clockwise. This is termed a right-handed fan. - Propeller rotates counterclockwise. This is termed a left-handed fan. High-temperature boiler induced draft fans are essentially variable-flow, constant-pressure devices. At constant speed, the theoretical pressure-flow curve of a centrifugal fan is linear; the actual characteristic curve bends due to internal losses. The pressure generated by high-temperature boiler induced draft fans is significantly affected by variations in inlet air temperature and density. For a given air intake volume—i.e., the pressure caused by inlet air temperature—relative to a specified pressure-flow characteristic curve, there exists a power-flow characteristic curve. When the blower operates at a constant speed, the power requirement increases as the inlet air temperature decreases relative to the specified flow rate.