In the past the material return valve in a 330MW circulating fluidized bed boiler was repeatedly choked because of a lot of recycling ashes

which seriously affected the unit’s reliability and economy. But otherwise the material return valve was choked recently when the boiler BT action which was resulted from the low vacuum protection occurred. Then how to find out the real reason is introduced in this paper. Focused on the correctness of the boiler BT protection action logic

the trip sequence and trip time of the different fans after the boiler BT action occurred were restored by recalling the accident record of the DCS system. The key reason is that the induced fan and the high pressure fluidized fan tripped in the wrong order and the jump stop of the high-pressure fluidized fan delayed 20 s than that of the first order fan. Based on the results of this research

some recommendations for improvement

training and revised logical measures were brought forward

which similarly can be used to prevent the choking of the return valve in larger-scale circulating fluidized bed.