The operating principles of Circulating Fluidized Bed (CFB) boilers involve a significant amount of heat accumulation, which forms the thermal inertia of the boiler and hinders the improvement of its variable load response rate. This study aims to characterize the thermal inertia of CFB boilers by evaluating the change in the boiler’s heat accumulation corresponding to the change in unit power generation. The thermal inertia of a 330 MW CFB boiler was determined through the collection of operating data under four different operating conditions of 30%, 50%, 75%, and 100% load. The study proposes to substitute the existing refractory material with a metal grille to reduce the thermal inertia of the boiler. The effect of the metal grille on heat transfer was confirmed through verification on a 440 t/h CFB boiler, and its performance change and thermal inertia reduction were further predicted. The results indicate that over 50% of the total thermal inertia of CFB boilers originates from the refractory material. The use of metal grille in place of refractory material improved heat transfer in the furnace, resulting in a decrease of the furnace chamber temperature by 13°C in the 330 MW CFB boiler. This reduction of thermal inertia by 30%–35% will facilitate faster load lifting and lowering of the boiler, fulfilling the requirement for flexible peaking.
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