Influence of Thermal Inertia of Refractory Material in Furnace on the Peak Regulating Rate of Circulating Fluidized Bed Boiler

The influence of thermal inertia of the furnace refractory on the peak regulation characteristics of a 300 MW circulating fluidized bed boiler (CFB) was studied by using a numerical calculation method. Based on the actual operation conditions of the boiler, the calculation results reveal that the thermal inertia of refractory is affected by its thermal conductivity and the thickness. Specifically, the thermal inertia of refractory decreases with the increasing thermal conductivity and decreasing refractory thickness. As a consequence, the time that required for the refractory to reach heat equilibrium decreases from 5 812 s to 3 426 s if the thermal conductivity of refractory increases from 1 W/(m⋅K) to 15 W/(m⋅K), while it increases from 3 267 s to 7 771 s if the thickness of refractory material increases from 30 mm to 90 mm. Practically in the presence of the traditional refractory in the CFB dense phase zone, the time required to achieve heat equilibrium state becomes 82, 65 and 60 min when the load of this CFB boiler rises from 50% to 100% with a rate of 1%/min, 2%/min and 3%/min. For a refractory with higher thermal conductivity, the equilibrium response time will be reduced to 65, 46 and 40 min, correspondingly. According to the calculation results, a formula for the heat absorption rate of refractory material was obtained. In addition, the influencing coefficient of the thermal inertia of refractory on coal feeding was also defined and calculated.