The fractionator is the core distillation unit of air separation. It uses two-stage distillation of upper and lower columns+main condensing evaporator. The operation is divided into four stages: start-up liquid accumulation, steady-state operation, load increase and decrease, and shutdown disposal.
The third stage of start-up: first slowly cool the tower body, the cooling rate is ≤ 10 ℃/h, and the cold end of the main heat exchanger reaches -172 ℃; Then add the expansion machine cold liquid, and it is qualified if the liquid oxygen level of the main cold rises to 1400 – 1600mm; Finally, adjust the purity. The core operation is V1 liquid air throttle valve and V2 liquid nitrogen throttle valve. Follow the principle of "first move V2 and then move V1, 1/8 turn each time, and then adjust after 30 minutes of observation". When V2 is turned on, the oxygen purity will increase and the nitrogen purity will decrease. On the contrary, the nitrogen purity will increase and the oxygen purity will decrease. The final oxygen purity is ≥ 99.6%, and the nitrogen oxygen content is ≤ 10ppm.
Steady state operation control: the lower tower pressure is 0.45 – 0.50mpa, the upper tower pressure is 0.12 – 0.14MPa, the main cooling liquid level is 1200 – 1500mm, and the minimum load is not less than 70% of the design. Discharge the main cooling non condensable gas in each shift, test the liquid oxyacetylene and total carbon regularly, and discharge it immediately if it exceeds the standard. The load increase and decrease shall follow the principle of "one full increase and one full decrease", and the air compressor, expander and throttle valve shall be adjusted synchronously. The single adjustment interval shall be ≥ 30 minutes to prevent flooding and purity fluctuation.
Shutdown and abnormality: short term cold insulation shutdown to retain the liquid in the tower and system pressure; For long-term shutdown, the whole tower shall be heated and thawed, and the temperature rise shall be ≤ 10 ℃/h. In case of power failure, water supply interruption, main cooling hydrocarbon exceeding the standard, and a large number of cold box leakage, emergency shutdown is required. Common abnormalities: low oxygen purity shut down V2 make-up liquid level, low nitrogen purity slightly open V2 to stabilize the pressure, and immediately reduce the load to check freezing blockage or flooding when the tower resistance rises.
Red line of operation: it is strictly forbidden to adjust the flow valve in a large and fast way, strictly control the temperature and speed change rate, and the safe discharge of liquid oxygen in the main cooling is the key to explosion prevention.
