During the cold operation process after the fault shutdown of the air separation unit, after the air compressor system, air precooling system and molecular sieve purification system are put into normal operation, start the supercharger, at the same time lower the column to boost the pressure, and lower the column to boost the pressure at the same time. The boosting process should be slow to prevent the upper column overpressure. When controlling the upper column pressure, the temperature of the carbon steel pipeline should be ensured to be ≥ - 30 ℃, and the main column backflow nitrogen can be used to flow out of the discharge valve of the subcooler The discharge valve of the main column backflow sewage nitrogen out of the subcooler shall be coordinated and adjusted.
After the system pressurization, start the expander system. If the liquid level of the lower main cooler is still at full scale, in order to speed up the operation of the lower main cooler as soon as possible, part of the main cooler liquid oxygen can be properly discharged to a higher level than that in normal operation. In the process of purification, it is necessary to increase the opening of the valve of liquid nitrogen returning to the lower column and the valve of liquid nitrogen throttling into the upper column, so as to speed up the main cooling work. The increase of the main cooling heat load is conducive to the rapid improvement of oxygen purity.
The liquid oxygen of air separation unit is pumped out from the liquid oxygen storage tank and sent to the main heat exchanger for heat exchange. Liquid oxygen should be sent to the main heat exchanger in proportion according to the amount of processing air. The speed should be controlled and the change of oxygen purity should be paid close attention to, so as to prevent the cooling capacity from entering the unit too fast and affect the recovery time of oxygen purity. The common process organization form of liquid oxygen pump is adopted. As long as there is a certain amount of liquid oxygen in the storage tank, liquid oxygen can be introduced into the cold box after the end of aeration, so as to accelerate the rectification, shorten the qualified time of oxygen and nitrogen purity, and the effect of energy saving is very obvious.
