According to a DEAR air separation user, during the operation of a set of air separation plant that has been in operation for 5 years, it is found that under the condition that the inlet guide vane does not change, the expansion air volume of the expander gradually decreases, and the rotation speed of the expander gradually decreases, the outlet pressure of the booster end of the expander rises from 0.76MPa to 0.8MPa, the inlet temperature rises from - 110 ° C to - 95 ° C, and the working condition of the chilled water pump is poor.
According to the situation reported by the user, DEAR air separation sent technicians to the site in time, switched 2# standby expanders immediately according to the situation on the site, and checked the faulted 1# expander. By closing the inlet and outlet valves of the aftercooler of 1# expander booster, it is found that there is always gas discharged from the exhaust valve on the water side of the cooler after water drainage, so as to determine the leakage of the cooler.
Because the water pressure of the cooler is basically the same as the air pressure, water is carried on the air side during operation, and it is frozen on the charge air channel of the main heat exchanger and the inlet filter of the expander, which results in poor heat exchange effect of the main heat exchanger channel, temperature rise at the inlet of the expander and decrease of the expansion air volume.
After determined the cause of failure, the 1# expander after supercharging cooler is disassembled and inspected, and two heat exchange tubes (made of carbon steel) are found to be leaking. Then we blocked the leaking heat exchange tubes. After pressure test, they meet the use conditions. After reassembly, they are temporarily restored to use.
In order to fundamentally solve the problem and prevent the leakage from happening again, it is recommended that the user replace the tube bundle of the aftercooler, change the carbon steel heat exchange tube which is easy to be corroded into the stainless steel heat exchange tube; in operation, reasonable operation steps are formulated to ensure that the pressure at the gas side is always higher than that at the water side. The acidity, alkalinity and hardness of the chilled water should be tested regularly, and the water supplement amount of the water cooling column should be increased regularly. The dry expansion air is used to take the water on the booster channel of the main heat exchanger to the inlet filter of the expander, and the water is taken out of the device by heating the expander.
Through the above operation and improvement, the normal operation function of the equipment is restored, and the shutdown and heating of the air separation plant are avoided.
