What issues should be considered when reducing the load of a circulating fluidized bed boiler during shutdown?

1. The coal feed rate should be gradually reduced in accordance with the rate of load reduction; at the same time, coordination with the operation of the turbine is necessary to reduce the load in a uniform manner, ensuring that the reduction in load and the decrease in coal feed rate occur simultaneously. This prevents a sharp drop in bed temperature, which could lead to an excessively low bed temperature and trigger the boiler’s MFT mechanism, thereby preventing the boiler from being shut down according to the prescribed procedure. 2. Depending on the oxygen level, reduce the amount of secondary air first. 3. Gradually reduce the primary air volume based on the bed pressure and bed temperature. 4. During the process of cooling and pressure reduction, it is necessary to closely monitor the expansion of each component and record the expansion values in a timely manner. 5. If it is not necessary to use up all the bed material, it should be kept at a sufficient thickness to prevent it from becoming too thin after a long period of time during the next startup.

Chapter 7 of NFPA 85, which deals with circulating fluidized bed systems, covers all the requirements regarding startup, operation, and shutdown in detail