Accident Handling 6: Circulating fluidized bed boilers – when is an emergency shutdown necessary?

Answer: 1. The boiler is severely short of water, and the water level disappears from the drum gauge. 2. When the boiler is severely overfilled, with the water level exceeding the visible level above the drum level gauge. 3. When the boiler’s tubes burst and normal water level cannot be maintained. 4. When the fuel burns in the flue behind the combustion chamber, causing the exhaust temperature to rise abnormally. 5. When all water level gauges are damaged. 6. When the steam and water pipes of the boiler burst, posing a threat to the safety of equipment and personnel. 7. When the combustion chamber cokes up, as well as the primary return material, making normal operation impossible. 8. When the pressure exceeds the operating pressure, the safety door does not operate, and at the same time the vent cannot be opened.

The boiler must be shut down urgently in the following situations to avoid greater losses: (1) When the boiler is severely overfilled with water (the water level in the drum exceeds the visible part above the gauge). (2) When the boiler is severely short of water (the drum water level disappears). (3) Explosion of the furnace tubes and damage to the steam-water system pipes, preventing the maintenance of the drum water level. (4) When all level gauges are damaged and the boiler operator is unable to monitor the drum water level. (5) The fuel undergoes secondary combustion in the flue, causing the exhaust temperature to rise abnormally. (6) Bursting of boiler steam and water pipes, posing a threat to human safety and equipment safety ； When cracks occur in the furnace chamber, posing a risk of collapse, or when the crossbeams turn red hot. (7) When the boiler steam pressure exceeds the operating pressure of the safety valve but the safety valve does not operate, and at the same time the exhaust valve to the atmosphere cannot be opened. (8) When the MFT should operate but fails to do so. (9) When the boiler water wall or other heating surfaces in the furnace burst, causing a large amount of steam-water mixture to flow into the bed material and resulting in a sharp drop in bed temperature. (10) The J-valve return hopper is severely clogged. The material level in the hopper rises rapidly, the negative pressure at the inlet of the cyclone separator decreases, while the negative pressure at the outlet increases; the hopper stops returning material at this point. (11) All operator stations of the Distributed Control System (DCS) have failed, and there are no reliable backup means for operation monitoring. (12) Power failure to the thermal control instruments prevents monitoring and adjusting of key operating parameters. (13) A severe fire occurred within the boiler unit, posing a direct threat to the safe operation of the boiler.

For circulating fluidized bed boiler units, an emergency shutdown must be carried out when the following situations occur to avoid greater losses: (1) When the boiler is severely overfilled with water (the water level in the drum exceeds the visible part above the gauge). (2) When the boiler is severely short of water (the drum water level disappears). (3) Explosion of the furnace tubes and damage to the steam-water system pipes, preventing the maintenance of the drum water level. (4) When all level gauges are damaged and the boiler operator is unable to monitor the drum water level. (5) The fuel undergoes secondary combustion in the flue, causing the exhaust temperature to rise abnormally. (6) Bursting of boiler steam and water pipes, posing a threat to human safety and equipment safety ； When cracks occur in the furnace chamber, posing a risk of collapse, or when the crossbeams turn red hot. (7) When the boiler steam pressure exceeds the operating pressure of the safety valve but the safety valve does not operate, and at the same time the exhaust valve to the atmosphere cannot be opened. (8) When the MFT should operate but fails to do so. (9) When the boiler water wall or other heating surfaces in the furnace burst, causing a large amount of steam-water mixture to flow into the bed material and resulting in a sharp drop in bed temperature. (10) The J-valve return hopper is severely clogged. The material level in the hopper rises rapidly, the negative pressure at the inlet of the cyclone separator decreases, while the negative pressure at the outlet increases; the hopper stops returning material at this point. (11) All operator stations of the Distributed Control System (DCS) have failed, and there are no reliable backup means for operation monitoring. (12) Power failure to the thermal control instruments prevents monitoring and adjusting of key operating parameters. (13) A severe fire occurred within the boiler unit, posing a direct threat to the safe operation of the boiler.

(1) The boiler is severely overfilled with water. (2) The boiler is severely underwatered. (3) Tube rupture on the heating surface and damage to the steam-water system pipes, preventing the maintenance of the drum water level. (4) When all level gauges are damaged and it is impossible to monitor the drum level. (5) The fuel undergoes secondary combustion in the flue, causing the exhaust temperature to rise abnormally. (6) Bursting of boiler steam and water pipes, posing a threat to human safety and equipment safety ； When cracks occur in the furnace chamber, posing a risk of collapse, or when the crossbeams turn red hot. (7) When the boiler steam pressure exceeds the operating pressure of the safety valve but the safety valve does not operate, and at the same time the exhaust valve to the atmosphere cannot be opened. (8) When the MFT should operate but fails to do so. (9) When the boiler water wall or other heating surfaces in the furnace burst, causing a large amount of steam-water mixture to flow into the bed material and resulting in a sharp drop in bed temperature. (10) Severe blockage and coking of the U-shaped return conveyor ； Severe ash accumulation in the separator or interruption of feedback. (11) All operator stations of the Distributed Control System (DCS) have failed. (12) Power failure to the thermal control instruments prevents monitoring and adjusting of key operating parameters. (13) A severe fire has broken out in the boiler’s material bin and cannot be extinguished, posing a direct threat to the safe operation of the boiler. (14) Severe failures occur in the main rotating equipment (induced draft fans, primary fans, feeders, etc.), posing a threat to the safety of the equipment and personnel.

1) The boiler is severely overfilled with water. 2) The boiler is severely underwatered. 3) All level gauges are damaged, preventing monitoring of the drum level. 4) Severe tube failures in the furnace water wall or water cooling screens, preventing the maintenance of a normal water level in the steam drum. 5) When the main feedwater pipeline, superheater, and main steam pipeline burst, posing a threat to the safety of equipment and personnel. 6) Interruption of boiler reheat steam. 7) When the pressure exceeds the operating value of the safety valve and the safety valve fails to open, while the primary and secondary bypasses as well as the superheater to atmosphere vent valves (PCV valves) are insufficient to relieve the pressure. 8) When the boiler shuts down and cannot be restarted. 9) When re-ignition occurs in the tail flue, causing the exhaust gas temperature to exceed 200°C. 10) When an explosion in the furnace or flue causes severe damage to the equipment. 11) A fire broke out within the boiler unit area, posing a direct threat to the safe operation of the boiler. 12) When the thermal protection reaches the tripping condition, the protection fails to operate. 13) All thermal control power supplies are disconnected, making it impossible to monitor or control the boiler operation. 14) Emergency shutdown on the mechanical side and electrical side.