How to shut down a circulating fluidized bed boiler?

(1) Switch the boiler main control to manual mode. (2) Gradually reduce the coal feed rate, as well as the volume of primary and secondary air and the intake air volume, in order to lower the heat load. (3) Depending on the decrease in steam temperature, shut off or reduce the amount of cooling water. (4) Pressure drop rate: The average decrease shall not exceed 0.1 MPa/min. (5) Cooling rate: The average temperature drop of flue gas in the furnace shall not exceed 1°C/min ； The main steam temperature should not drop by more than 1°C per minute. (6) During the descent phase, special attention should be paid to combustion adjustment to maintain a superheat temperature of the steam above 50°C. (7) During the process of cooling and reducing pressure, adjust the combustion in a timely manner to ensure a uniform decrease in steam temperature and pressure; sudden drops are not allowed. (8) When the steam flow rate drops to 300 t/h or 100 t/h, a full blowdown should be carried out once. (9) Reduce the unit to its minimum stable load and maintain it for about 30 minutes to allow the refractory material inside the cyclone separator to cool down gradually. Additionally, the wall temperature of the heated surfaces in the cyclone separator may increase; at that point, the exhaust valve on the collector box of the cyclone separator can be opened to vent air. (10) When the boiler load drops below 10% of the rated load, open the drain valves located on the outlet header of the high-temperature superheater as well as on the main steam pipes. It is important to control the cooling rate of the boiler; as long as steam is still being generated during this period, these drain valves must not be closed. (11) The limestone feeding system is shut down. (12) When the electrical load drops to zero, shut down the furnace, close the shut-off valves at all fuel hopper outlets, and empty the burner of all coal. (13) After the boiler is shut down, the primary and secondary fans, the coal feeding pressure fan, and the exhaust fan shall continue to operate for 5 minutes before being stopped, in order to purge any combustible materials inside the furnace. (14) Close the fluidization air baffle of the cold slag holder, and close the air supply valve J on the slag inlet pipe of the cold slag holder. (15) Shut down the electrostatic precipitator. (16) Shut down the coal feeding system, and stop the operation of the primary and secondary fans, the coal feeding pressure booster fan, and the exhaust fan ； The J-valve fan should continue to operate; to prevent damage to the J-valve components, the J-valve fan can be stopped only when the J-valve is cooled below 260°C.

The shutdown procedure for a circulating fluidized bed boiler is: (1) Switch the boiler’s main control to manual mode. (2) Gradually reduce the coal feed rate, as well as the volume of primary and secondary air and the intake air volume, in order to lower the heat load. (3) Depending on the decrease in steam temperature, shut off or reduce the amount of cooling water. (4) Pressure drop rate: The average decrease shall not exceed 0.1 MPa/min. (5) Cooling rate: The average temperature drop of flue gas in the furnace shall not exceed 1°C/min ； The main steam temperature should not drop by more than 1°C per minute. (6) During the descent phase, special attention should be paid to combustion adjustment to maintain a superheat temperature of the steam above 50°C. (7) During the process of cooling and reducing pressure, adjust the combustion in a timely manner to ensure a uniform decrease in steam temperature and pressure; sudden drops are not allowed. (8) When the steam flow rate drops to 300 t/h or 100 t/h, a full blowdown should be carried out once. (9) Reduce the unit to its minimum stable load and maintain it for about 30 minutes to allow the refractory material inside the cyclone separator to cool down gradually. Additionally, the wall temperature of the heated surfaces in the cyclone separator may increase; at that point, the exhaust valve on the collector box of the cyclone separator can be opened to vent air. (10) When the boiler load drops below 10% of the rated load, open the drain valves located on the outlet header of the high-temperature superheater as well as on the main steam pipes. It is important to control the cooling rate of the boiler; as long as steam is still being generated during this period, these drain valves must not be closed. (11) The limestone feeding system is shut down. (12) When the electrical load drops to zero, shut down the furnace, close the shut-off valves at all fuel hopper outlets, and empty the burner of all coal. (13) After the boiler is shut down, the primary and secondary fans, the coal feeding pressure fan, and the exhaust fan shall continue to operate for 5 minutes before being stopped, in order to purge any combustible materials inside the furnace. (14) Close the fluidization air baffle of the cold slag holder, and close the air supply valve J on the slag inlet pipe of the cold slag holder. (15) Shut down the electrostatic precipitator. (16) Shut down the coal feeding system, and stop the operation of the primary and secondary fans, the coal feeding pressure booster fan, and the exhaust fan ； The J-valve fan should continue to operate; to prevent damage to the J-valve components, the J-valve fan can be stopped only when the J-valve is cooled below 260°C.

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