The start-up of the cryogenic air separation unit follows the principle of "auxiliary before main process, and slow progress along the process". The complete hot start-up is divided into eight stages, and the speed and safety red line are strictly controlled throughout the process.
PSSR safety confirmation must be completed before start-up: all utilities (electricity, water, gas and steam) are in place, the oil system and interlock ESD test of the compressor unit are qualified, all drain valves and purge valves of the cold box are closed, the molecular sieve has completed a complete regeneration, and the internal dew point of the cold box is ≤ -60 ℃.
In the start-up phase, the air compressor and booster are put into operation in turn. After no-load start-up, the pressure is increased slowly to prevent surge and overpressure. Then the precooling system was put into operation, and the air temperature at the outlet of the air cooling tower was controlled at 8~12 ℃ to prevent free water from being brought into the purification system. After the molecular sieve purification system is put into operation, strictly monitor the outlet Co ɑ＜ 1ppm, and supply gas to the cold box only after it is qualified.
Cold box air inlet is the core key stage. The pressure rise rate of the lower tower is ≤ 0.05mpa/h, and the temperature drop is ≤ 30 ℃/h, so as to avoid the impact of air flow on the internals of the tower and damage to the pipeline by temperature difference stress. Start the cooling capacity of the booster turbine expansion mechanism, enter the liquid accumulation stage, and the main cooling level gradually rises to the design value. During this period, continue to discharge liquid oxygen and monitor the content of acetylene and total carbon.
In the rectification adjustment stage, gradually establish liquid nitrogen reflux, fine tune the expansion and withdrawal amount, stabilize the pressure and resistance of the upper and lower towers, and after the oxygen purity is ≥ 99.6% and the nitrogen purity is up to standard, vent and then slowly open the product delivery valve to supply gas to the grid, finally raise it to the rated load, and all automatic control loops will automatically turn into normal operation.
