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A common accident in circulating fluidized bed boilers is leakage in the water wall tubes. The following is a summary of the phenomena associated with water wall leakage and the measures taken to address it, in the hope that it will be useful to everyone. Phenomenon: 1. The bed pressure drops; maintaining normal output from the cold slag machine will not ensure a proper bed pressure. 2. The flue gas temperature drops behind the leakage point; if the leakage point is located in the furnace, the temperature at the thermocouple sensor located next to the leakage point is significantly lower than the temperatures at other sensors. 3. The deviation between the total amount of feedwater and cooling water and the steam generation volume increases. 4. The furnace pressure rises, resulting in an increase in the output of the induced draft fan dampers. 5. When the leakage increases, water will flow out from the accident slag discharge pipe, and phosphates can be detected in this flowing water. 6. If the leakage point is in the dense-phase zone of the furnace, an abnormal noise can be heard at the leakage site outside the furnace. Remedial measures: 1. Stop coal feeding and operate the secondary coal feeder in idle mode. 2. Stop returning ash and maintain normal operation of the cold slag machine to discharge the bed material. Once the bed temperature drops to 500°C, increase the output of the slag cooler. At the same time, monitor the slag discharge from the cooler; if water is detected in the discharged slag, stop the cooler and use the emergency slag discharge pipe instead. A baffle should also be installed in the slag outlet pipe of the cooler to prevent furnace water from entering the slag conveyor. 3. After all the bed material has been discharged, stop the fan; keep the manual shut-off valves on the emergency slag discharge pipe and the continuous slag discharge pipe fully open to allow water to flow out, thereby emptying the slag stored in the air-cooled slag discharger. Also, remove the blind flaps covering the drainage holes at the bottom of the ignition burner to allow water to flow out. 4. Stop feeding water once the wall temperature of the drum drops to 130°C; the entire amount of boiler water can be drained once the drum’s wall temperature falls to 85°C. 5. Open the inspection cover plates at the heads of the primary and secondary coal feeders to release the water vapor from the furnace. 6. The furnace manhole door can be opened only after the furnace temperature drops to 80°C. Last edited by ssbayf on 2008-1-12 at 16:20.]