A.10.1 Equipment description
A power plant has 2 condensing steam turbine generator sets installed, with a single unit capacity of 300MW. The power plant's instrument gas system is equipped with 3 screw air compressors, with air compressor specifications of 220kW, air-cooled units, and exhaust volume of 36m³/min.
A.10.2 Accident description
The power plant's pneumatic ash conveying system uses micro-positive pressure pneumatic ash conveying, and the control air source uses instrument air source. During the operation of pneumatic ash conveying, the valve switch often fails to be in place. For this reason, the control solenoid valve was replaced many times, and the service manufacturer was contacted to replace the solenoid valve. Later, the manufacturer's technicians came to help find the problem and found that the main reason for the damage to the solenoid valve was the poor quality of the instrument gas, and the gas source contained more oil and water and a small amount of impurities.
A.10.3 Cause Analysis
The reasons for the high oil and water content and small amount of impurities in the gas source are as follows: the three gas tanks in the instrument gas system are all post-gas tanks, that is, the compressed air first passes through the cold dryer and dryer before entering the gas tank to the gas supply main pipe. This design increases the workload of the cold dryer and dryer, and often fails during operation and the filter element is blocked very quickly. Finally, the maintenance personnel had to remove the filter element after the cold dryer. Even so, the drainage volume of the dryer was still large, indicating that the compressed air still contained a lot of water and oil. Therefore, the compressed air entering the gas tank also contained a lot of water and oil.
A.10.4 Preventive measures
(1) Propose a technical improvement plan to change one of the three gas tanks to a front gas tank, that is, the compressed air first passes through the front gas tank, and relies on the expansion and diversion of the gas tank to perform gravity separation and centrifugal separation of the compressed air. After the implementation of this plan, it was proved that the water removal effect of the front gas tank was very good, and almost no water was discharged from the exhaust port of the dryer.
(2) Connect the filter element in series with the air main pipe of the pneumatic ash conveyor, drain and clean it regularly, and focus on preventing impurities in the compressed air pipeline.
