A.2.1 Brief description of equipment
A power plant has two condensing steam turbine generator sets installed, with a single unit capacity of 135MW. The boiler ash discharge method is pneumatic ash conveying. The ash removal system is equipped with four screw air compressors, with air compressor specifications of 110kW, water-cooled units, and exhaust volume of 20m³/min
A.2.2 Fault phenomenon
After the air compressor was shut down for 2 months, when it was restarted, the motor overcurrent could not be started, and the air compressor rotor was "stuck" and could not be turned manually. After checking the air compressor and oil pipeline, it was found that there was a maltose-like light-colored colloid on the air compressor rotor, and there was also a maltose-like light-colored colloid on the bottom of the oil and gas barrel and the oil pipeline.
A.2.3 Cause Analysis
(1) The lubricating oil of the air compressor has been used for about 4000 hours, and the service life of the air compressor oil is 6000 hours. The color of the lubricating oil has not changed significantly, and the carbon deposit caused by the lubricating oil exceeding its service life has been ruled out.
(2) Inspection of the main engine and pipelines revealed that the carbon deposit contained ash. The air compressor is located in a dusty geographical location, and the air filter of the air compressor has accumulated a lot of dust, indicating that a large amount of dust has entered the lubricating oil system before the air compressor was shut down. The dust particles inhaled with the air make the oil thicker, which prolongs the passage time of the oil through the hot parts of the exhaust system, increases the time of the oil oxidation reaction, and thus accelerates the speed of carbon deposit formation.
(3) Checking the air compressor operation record, the air compressor temperature before shutdown was above 90℃, and the operating temperature of the air compressor has increased significantly compared with the past. Temperature is the main factor causing oil oxidation. For every 10°C increase in temperature, the oxidation rate doubles.
(4) After the air compressor has been shut down for a long time, the lubricating oil, which has become thick and has a tendency to deposit carbon, gradually floats on the machine parts and causes serious gelling and carbon deposits.
A.2.4 Treatment method
Remove the air compressor and connecting pipes, open the oil and gas barrel; Clean the oil; Use carbon deposit cleaning agent to soak the air compressor main unit and the removed pipes for 24 hours. After soaking, flush the pipes and check the flushing effect. If the carbon deposits are completely removed, they can be reinstalled. If the vibration exceeds the standard during the trial operation, check the oil supply and check if the bearings are worn if necessary. It is impossible to completely clean the oil system of the air compressor with carbon deposits at one time. Therefore, the interval between the next oil change should be shorter than usual to prevent carbon deposits from occurring again.
A.2.5 Preventive measures
(1) Clean and replace the air filter element strictly in accordance with the requirements, especially when the working environment has a lot of ash.
(2) Control the temperature of the air compressor to about 75 °C during normal operation. If high temperature is found, find the cause and eliminate it in time.
(3) The air compressor should be switched regularly and long-term shutdown is prohibited.
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