Why during purging of utility boiler air flow maintain 30 to 40 percent?

During purging of a utility boiler, the air flow is maintained at 30 to 40 percent to ensure that there is enough air in the boiler to displace any potentially hazardous gases or vapors. Purging is a process that removes any hazardous gases or vapors that may be present in the boiler before the boiler is started up.

Maintaining an air flow of 30 to 40 percent during purging ensures that there is enough oxygen in the boiler to react with any hazardous gases or vapors that may be present, and convert them into harmless products. However, if the air flow is too high, it can cause excessive cooling of the boiler, which can result in condensation and corrosion of the metal surfaces inside the boiler.

On the other hand, if the air flow is too low, it may not provide enough oxygen to react with the hazardous gases or vapors, and may result in incomplete combustion or formation of explosive mixtures. Therefore, maintaining an air flow of 30 to 40 percent during purging is a safe and effective way to ensure that the boiler is free from hazardous gases or vapors before start-up.

During the purging of a utility boiler, maintaining an air flow rate of 30 to 40 percent is important for several reasons:

1. Safety: Purging is done to remove any combustible gases or liquids that may have accumulated in the boiler or piping system. If the air flow rate is too low, there may not be enough oxygen to dilute and safely vent these gases or liquids. Conversely, if the air flow rate is too high, it can create turbulence that may stir up any accumulated dust or debris, which can be a safety hazard.
2. Efficiency: Maintaining an optimal air flow rate during purging ensures that the fuel-air mixture is within the flammability limits. If the air flow rate is too low, there may not be enough oxygen to support combustion, leading to incomplete purging. On the other hand, if the air flow rate is too high, it can waste energy by requiring more fuel to be burned to maintain the desired temperature.
3. Time: Purging can be a time-consuming process, particularly if there is a large volume of gas or liquid to be removed. By maintaining a consistent air flow rate, the purging process can be completed more efficiently, saving time and reducing downtime for the boiler.

Overall, maintaining a 30 to 40 percent air flow rate during purging helps to ensure a safe, efficient, and effective process for removing combustible gases or liquids from a utility boiler.