At least once every how many hours must the boiler be bottom blown after lit-off following EDTA cleaning?

The correct answer is based on the operational procedures for maintaining boiler water quality after an EDTA cleaning. Following the use of Ethylenediaminetetraacetic acid (EDTA), which is a chelating agent used to remove hardness and other impurities from boiler water, it is essential to manage the water chemistry effectively.

After performing such a cleaning, the boiler must undergo bottom blowing to remove sediment and contaminants that may have entered the system during cleaning or that may have precipitated due to changes in water chemistry. It is recommended that the boiler be bottom blown at least once every 72 hours after lighting off to ensure that any residual contaminants are expelled and to maintain optimal water quality and boiler performance.

By adhering to this timeframe, you help prevent scale build-up and corrosion, which can be detrimental in boiler operation, extending the life of the equipment, and promoting safe and efficient operations.

The other options reflect intervals that are either too short or too extended based on standard practices, thus not aligning with the maintenance guidelines established for post-cleaning procedures.