Effects of Different Fuel Specifications and Operation Conditions on the Performance of Coated and Uncoated Superheater Tubes in Two Different Biomass-Fired Boilers

Fireside corrosion is a serious concern in biomass firing power plants such that the efficiency of boilers is limited by high temperature corrosion. Application of protective coatings on superheater tubes is a possible solution to combat fireside corrosion. The current study investigates the corrosion performance of coated tubes compared to uncoated Esshete 1250 and TP347H tubes, which were exposed in two different biomass-fired boilers for one year. Data on the fuel used, temperature of the boilers, and temperature fluctuations are compared for the two boilers, and how these factors influence deposit formation, corrosion, and the stability of the coatings is discussed. The coatings (Ni and Ni2Al3) showed protective behavior in a wood-fired plant where the outlet steam temperature was 520 °C. However, at the plant that fired straw with an outlet steam temperature of 540 °C and where severe thermal cycling took place, both the Ni and Ni2Al3 coatings failed. This highlights the differences between the two biomass plants and demonstrates that a coating solution has to be tailored to the operation conditions of a specific boiler.