Abstract: The formation and exfoliation of oxide skin on the high temperature heating surfaces have become a worldwide problem that may threaten the secure operation of electric power generating units. It is widely agreed that the formation and exfoliation of oxide skin may be accelerated by the plasma igniter for boiler startup. In fact, the oxide skin formation and exfoliation are indeed related to the startup and shutdown rates of the boilers. In this paper, the detailed analysis on this problem is conducted from the aspects of boiler startup and shutdown methods, the initial and succeeding loading rates and operational adjustment. Based on the experience on hundreds of boilers that are equipped with plasma igniter in pulverized coal burners, especially in supercritical and ultra supercritical units, if the startup process satisfies the temperature and pressure rising curves and the initial and succeeding loading rates as well as the operation style are appropriate, the formation and exfoliation of oxide skin in the tubes of high temperature heating surfaces will not be accelerated.

Key words: boiler, plasma igniter, high temperature heating surface, tube material, steam, high temperature oxidation skin, growing and shedding behavior, boiler start up