Incident Handling 44: What are the phenomena that occur when a circulating fluidized bed boiler shuts down?

1. The temperature of the fluidized bed drops sharply, and the temperature of the flue gas also decreases； 2. Drop in steam temperature and pressure ； 3. The combustion chamber becomes dark and the flame is no longer visible ； 4. The oxygen level indication rises significantly.

(1) The bed temperature and flue gas temperature drop sharply. (2) The bed pressure begins to drop, and the particle concentration in the furnace decreases significantly. (3) The furnace interior darkens, the flame becomes invisible, and the oxygen level indicator rises rapidly. (4) The main steam temperature and pressure drop rapidly. (5) If the power circuit of the turbine’s digital electro-hydraulic control system (DEH) is not activated, the active power of the generator drops rapidly. (6) If the drum level control is not activated automatically, the level will first drop and then rise.

Phenomenon: ① The temperature of the fluidized bed drops sharply, and the flue gas temperature also decreases. ②The steam temperature and pressure drop. ③The combustion chamber darkened, and the flame could no longer be seen. ④The oxygen level indicator shows a significant increase.

1. Negative pressure rises significantly, and oxygen levels increase sharply. 2. The bed temperature, as well as the steam temperature and pressure, drop sharply. 3. Drop in wind chamber pressure, bed pressure difference, and furnace pressure difference

Answer: The phenomena that occur when a circulating fluidized bed boiler shuts down include the following: (1) A sharp drop in bed temperature and flue gas temperature. (2) The bed pressure begins to drop, and the particle concentration in the furnace decreases significantly. (3) The furnace interior darkens, the flame becomes invisible, and the oxygen level indicator rises rapidly. (4) The main steam temperature and pressure drop rapidly. (5) If the power circuit of the turbine’s digital electro-hydraulic control system (DEH) is not activated, the active power of the generator drops rapidly. (6) If the drum level control is not activated automatically, the level will first drop and then rise. Take the following measures: (1) Immediately stop the operation of all coal feeders and switch all automatic controls to manual adjustment. (2) Start the oil guns above and below the bed to rapidly increase the bed temperature, thereby facilitating combustion. (3) Appropriately reduce the air volume according to the situation, adjust the amount of circulating ash, and discharge some ash if necessary. (4) Reduce the water supply volume, control the drum water level at -30 mm, and closely monitor the water level. (5) Based on the downward trend in steam temperature, reduce or shut off the desuperheating water, and activate the drain valve and vent steam to cool the superheater. (6) If there is a fault in the coal feeding system, it should be repaired as soon as possible; if the system is blocked, it should be cleared promptly. (7) If the bed temperature meets the conditions for hot start, a hot start should be carried out immediately; once the steam temperature and pressure reach the rated values, the turbine can be restarted. (8) If the bed temperature does not meet the conditions for hot start, purging must be performed followed by operation according to the cold start procedure. It is strictly prohibited to feed coal blindly, as this can lead to secondary combustion or furnace explosions, resulting in serious damage to the equipment. After the boiler shuts down, operators should promptly determine the cause; it is strictly forbidden to rely on luck and try to maintain the unit’s load by increasing the coal supply in order to raise the bed temperature. The above handling steps must be strictly followed to ensure the safe operation of the equipment.