Three air heater basket samples were received for failure analysis. The samples were specified as 22 gauge, a proprietary low-alloy corrosion-resistant steel (LACR). These baskets typically last at least 10 years or more, depending upon conditions within the unit. These failed within two years of service. Approximately a year ago, the plant started injecting activated carbon in the flue gas and calcium bromide (CaBr2) in the coal steam to help with mercury removal.

The air heater consists of four stages (1 hot, 2 intermediate and 1 cold end). The failed samples were removed from the cold end stage. The flue gas inlet temperature to the air heater is about 780 °F and the exit temperature is about 290 °F. The air enters about 70 °F and leaves at 691 °F. The cold end basket temperature triggered an alarm, sometimes suggesting the temperature may have dropped below the acid dew point corrosion point. However, with the addition of CaBr2, there may be potential for this to also be condensed or deposited. There is no SCR system in the unit for NOx control. The sulfur content in the coal is about 0.3%. There is a sootblower that cleans these baskets as needed to keep them free of ash pluggage. There is a concern that there may be a small amount of water sprayed at the beginning of the sootblower cycle from condensation in the soot blower pipe.

For more information email us at contact@davidnfrench.com or speak with us directly at 502-955-9847.