What are the operating steps for the hot start of a circulating fluidized bed boiler?

Chapter 7 of NFPA85 details hot start-up

1. Pre-startup checks: ① Check that the drum water level is at the normal level； ②All systems such as fuel, limestone, slag removal, and return material should be prepared for operation. 2. Start the following fans in accordance with the cold-start procedure: J-valve fan, suction fan, secondary fan, primary fan, and coal-dosing pressurization fan, to establish an air flow rate and maintain bed pressure; the fluidization speed must not be lower than 1.2 m/s, the furnace negative pressure should be at –100 Pa, and the combustion air flow rate should be set to 25% of the maximum continuous output (MCR) condition. 3. Start the coal feeder to supply coal to the furnace. When beginning coal supply, the amount of coal fed must be small and gradual, while increasing the amount of combustion air at the same time. 4. Adjust the return feeder bypass valve to control the amount of ash returned, thereby maintaining bed pressure and bed temperature. 5. If, after establishing an air flow in the furnace and feeding coal, the bed temperature drops rapidly and falls below 650°C, hot-starting should be stopped and a cold-start should be carried out. 6. If too much fuel is supplied to the fluidized bed, it results in incomplete combustion of the fuel; as a consequence, the bed temperature rises rapidly and the oxygen level drops quickly. Therefore, no more fuel should be added to the furnace until the fluidized bed reaches a stable state. If there is a tendency for the bed temperature to rise rapidly and exceed 950°C, the following steps should be taken before the temperature reaches 950°C: 1) Reduce the air supply to the bed in order to slow down the combustion process. 2) The trends in oxygen level and bed temperature indicated instability in the unit; the dampers of the primary air duct at the furnace bottom were closed to create a oxygen-deficient combustion condition. 7. If the bed temperature does not rise 5 minutes after coal is fed, it indicates that the hot-start attempt has failed; in this case, coal feeding should be stopped, and purging should be carried out again so that the boiler can start up in a normal cold-start mode. 8. After coal is fed, the heat load inside the furnace increases, and the steam temperature and pressure rise gradually; subsequent operations are the same as those for a cold start.