Understand what it really costs to cycle fossil-fired units

Abstract

Competition among generating facilities, including non-utility generators, and the presence of a utility`s own nuclear power plants, have caused more and more fossil-fired units designed for base-load operation to be converted to some type of cycling operation. Cycling, as used here, refers to operating modes that respond to changes in system load requirements, including load following, low-load cycling, and on/off. The last comprises: (1) hot restart within 24 hours of shutting down - the mode that is least damaging to equipment; (2) warm starts following downtimes of 24 to 120 hours; and (3) cold starts 120 hours or longer after shutdown, the most damaging mode of all. Cycling almost always lead to early component failures and higher costs. Unfortunately, the real costs of cycling - in terms of additional maintenance requirements, equivalent forced outage rates (EFOR), and increases in system production costs - are not well understood. Analyzing these effects and applying the results can save between 10 million dollars and 200 million dollars when evaluated over the life cycle of a typical 600 MW coal-fired power plant in a 4000-MW utility system. 4 figs., 3 tabs.