What are the power reduction options for boiler induced draft fans?

Due to the high medium temperature of boiler induced draft fans, determining motor power differs from standard centrifugal fans. Constrained by transformer capacity limitations, customers cannot select motors based on standard configurations. Motors with power ratings below the rated capacity must be chosen. To ensure fan operating parameters meet application requirements, how much can the adaptive power of boiler induced draft fans be reduced?

First, it is crucial to understand that under unchanged operating conditions, this reduction is not achievable. Lowering power inevitably results in reduced airflow or pressure. However, in the following two scenarios, power reduction has been demonstrated to be feasible—though fundamentally achieved by modifying operating parameters:

1. The required air pressure for the boiler induced draft fan is based on standard conditions. For example, if the customer requires a standard air pressure of 7 kPa and the operating condition air pressure is also 7 kPa, the difference arises. That is, when the gas temperature passing through the fan is 20°C and the air pressure is 7 kPa, an increase in medium temperature reduces the required power. In this case, the required motor power can be reduced.

2. If the above condition does not apply, the boiler induced draft fan requires air pressure at operating conditions. However, if a variable frequency drive (VFD) controls the fan motor, motor power can also be reduced due to the boiler induced draft fan's design parameters. This approach features a higher mechanical reserve coefficient. Nevertheless, the start-up time will increase, with the specific duration of the extended period depending on the duct length and the time required for the gas temperature passing through the fan to rise.

At constant speed, the required fan power for a boiler induced draft fan gradually decreases as the medium temperature rises. Therefore, employing variable frequency starting and control for the fan effectively reduces starting current, alleviates the motor's starting load, and prevents triggering the motor's overload protection function. A smaller motor power rating can be selected for the boiler induced draft fan.