Analyze the causes of failures in the return material system during the operation of a circulating fluidized bed boiler

The return material system of circulating fluidized beds has many problems, and the most problematic part is the return material device. Generally, the return material valve adopts an N-shaped structure; although the main material flowing through it are large particles resulting from combustion (coming from the separator), the movement of these particles is influenced by the fluidized air at the bottom of the return material device, giving it fluid-like properties. Under normal operation, the return feeder should take material from the separator, push the partially unburned particle fluid at the bottom into the return feeder, and through its \"N\"-shaped structure, send it back into the furnace for combustion. Because its motion is similar to that of a fluid, fluid analysis can be applied. As long as the static pressure coming from the cyclone separator at the top of the material returner is higher than the static pressure in the furnace, the flow can proceed normally; if this pressure is not achieved, proper material return is not possible. The main reasons for abnormal return material flow are as follows: 1. High-temperature particles adhere to the lining of the return material device, forming coking; over time, large pieces of material are stripped away due to wind erosion. Because these particles are large, they cannot be lifted by the return air flow and thus fall near the outlet of this air flow. Once accumulated there, they affect the speed of the return air flow and impair the fluidization of the return material particles, preventing normal return of the material. 2. There is a problem with the air distribution of the return air itself; the air pressure is insufficient. 3. There are issues with the distribution of primary and secondary air at the furnace location, resulting in excessive static pressure inside the furnace and preventing the return material from entering the furnace properly.

1. The separator assembly bridges or blocks the bell mouth. 2. The casting material of the separator and return feeder has fallen off. 3. Coking inside the return valve. 4. Ash leakage from the air chamber of the return feeder, or blockage or loosening of the small holes in the air caps; the air caps on the return side are installed in the wrong direction. 5. Low return air pressure (leakage in the return air system). 6. Coking and blockage at the return material inlet in the furnace.