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

The bed temperature before coal is fed should be no lower than the specified value; this temperature can be determined based on the type of fuel – fuels with a high volatility content can allow for a lower temperature, while those with low volatility content require a higher temperature. However, it must not be lower than 650°C; once the bed temperature falls below this value, purging must be carried out again following the cold-start procedure.

What are the conditions for hot startup of a circulating fluidized bed boiler? Answer: The bed temperature before coal is fed must be above the specified value; this temperature can be determined based on the type of fuel used. Fuels with high volatility can require a lower temperature, while fuels with low volatility need a higher temperature. However, it must not be lower than 650°C; once the bed temperature falls below this value, purging must be carried out again following the cold-start procedure. What conditions must the ignition oil system meet before igniting a circulating fluidized bed boiler? Answer: The ignition oil system must meet the following conditions before igniting a circulating fluidized bed boiler: (1) The oil pipelines are operating properly, with no leaks. (2) The oil pressure is stable, and the oil temperature is above 25°C. (3) All solenoid valves and manual valves shall operate correctly, and the closing time of the quick-close valves must be within the specified range. (4) The steam purging system is in good condition; the steam must be free of water, and the pressure and temperature should be within the specified ranges. (5) The flame detection system is functioning properly, and the photosensitive device can accurately reflect the brightness of the flame. (6) The firing gun can move forward and backward to the proper position. (7) The ignition timing control can be performed correctly. What are the operational steps for the hot start of a circulating fluidized bed boiler? Answer: The operational steps for the hot start of a circulating fluidized bed boiler are as follows: (1) Checks before startup: ① Check that the water level in the steam drum 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 booster fan, to establish an air flow rate and maintain bed pressure; the fluidization speed shall not be lower than 1.2 m/s, the furnace negative pressure shall be –100 Pa, and the combustion air flow rate shall be adjusted to 25% of the maximum continuous output (MCR) condition. (3) Start the coal feeder to supply coal to the furnace; when beginning coal feeding, the amount of coal supplied must be small and gradual, while increasing the amount of combustion air. (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 airflow 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 suppress the combustion process. 2) The trends in oxygen level and bed temperature indicated instability in the unit; the damper of the primary air duct at the furnace bottom was 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 has failed; in this case, coal feeding should be stopped, purging should be carried out again, and the boiler should begin a normal cold start. (8) After coal is fed, the heat load in the furnace increases, and the steam temperature and pressure gradually rise; subsequent operations are the same as those for a cold start.

The bed temperature before coal is fed should be no lower than the specified value; this temperature can be determined based on the type of fuel – fuels with a high volatility content can allow for a lower temperature, while those with low volatility content require a higher temperature. However, it must not be lower than 650°C; once the bed temperature falls below this value, purging must be carried out again following the cold-start procedure.