Guide: The purpose of boiler flushing is to use the boiler’s self-generated steam to flush out the rust, welding slag, iron filings, ash and grease in the superheater, reheater heating surface pipe and steam pipe. Otherwise, the steam will be supplied to the steam turbine. Produce the following hazards:

　　The purpose of boiler flushing is to use the boiler’s self-generated steam to flush out the rust, welding slag, iron filings, ash and grease in the superheater, reheater heating surface pipe and steam pipe. Otherwise, the steam will be supplied to the steam turbine. Produce the following hazards:

　　(1) The high-speed steam carries debris and hits the turbine blades, forming a large number of pits, which can cause the blade to break in severe cases and cause major accidents.

　　(2) The debris remaining in the superheater will reduce the flow area of the serpentine tube, or even block it, causing the tube to overheat and burst.

　　(3) The silicate impurities in the residue will seriously affect the steam quality.

　　Before flushing the tube, the boiler shall have the conditions for formal start-up. Therefore, the boiler flushing is also the first complete start-up process of the boiler itself. It plays a role in testing equipment, inspecting equipment, and initially grasping the operating characteristics of the equipment, laying the foundation for the smooth trial operation of the equipment.

　　The flushing process of the main steam system is to install a temporary gate valve at the outlet of the boiler steam header, which is discharged through a temporary exhaust pipe in front of the electric isolation door of the main steam system. The flushing pipe of the reheat steam system uses the primary bypass to charge the reheat steam system. The process is: main steam pipe → primary bypass → low temperature section reheater → high temperature reheater → reheat steam outlet header →The temporary exhaust pipe connected in front of the medium-pressure combined valve is discharged.

　　The steam parameters of the pipe flushing are generally: the main steam temperature is 30-50℃ lower than the rated value, the main steam pressure is 30%-60% of the rated value, or even lower, and the steam flow rate is about 1/3 of the rated value. Each flushing time lasts about 15 minutes. The interval between two flushings should be determined according to the time required for the wall temperature to drop below 100°C. This is to allow the debris stuck on the tube wall to be cooled by the tube wall And fall off. In order to test and judge the effect of flushing pipes, an aluminum target plate is installed at the exit of the temporary exhaust pipe. Under normal circumstances, the number of marks per square centimeter of the target plate is less than 0.7, and no more than 3mm. Mark pits are qualified.