Dynamic characteristics of active stock in a circulating fluidized bed boiler based on unsteady state conditions

Abstract During rapid load increase and decrease in circulating fluidized bed (CFB) units, the presence of a large amount of bed material, including incompletely combusted carbon residue and incompletely reacted calcium‐based desulphurizers, affects both the load change rate and pollutant emissions of the boiler. Therefore, the rational utilization of active stock within the boiler plays an important role in improving the heat release rate and increasing the load response rate. Using a 350 MW supercritical CFB boiler as the research object, numerical simulations were conducted on the load increase and decrease processes of the CFB boiler. Dynamic models of active carbon residue stock and active limestone were constructed to analyze the active stock during load increase and decrease processes. The results show that during the load increase from 175 to 350 MW, the coal feed rate is the main factor affecting the active carbon residue stock. The combustion rate of active carbon residue is lower than the coal feed rate, resulting in an increasing trend in active carbon residue stock, ranging from 6801.51 to 17,491.03 kg. During the load decrease from 350 to 300 MW, the active carbon residue stock decreases sharply, from 15,883.58 to 11,188.43 kg. During the load increase, there is a negative correlation between SO 2 concentration and active limestone stock. As the load increases from 208 to 280 MW, the SO 2 concentration rises from 1978.96 to 4951.94 mg/m 3 , while the active limestone stock decreases from 2223.65 to 1675.40 kg.