In order to accumulate the liquid as soon as possible after the appearance of the liquid, we should prepare as much cold as possible and reduce the cold loss as much as possible. Therefore, the following points should be paid attention:
1) the high pressure should be maintained at the highest pressure allowed by the air compressor, and be stable as far as possible to produce more cooling capacity;
2) use the cooling amount reasonably. That is to say, master the gas distribution that enters into the expansion machine and passes through the high pressure air throttle valve (section-1 valve. Specifically, it is to strictly control the temperature. Too much gas flows through the expansion machine, and the temperature drops too low behind the expansion machine and before the section-1 valve, which will enlarge the temperature difference at the hot end, increase the cold loss and waste the cold volume. At the same time, the amount of gas passing through the joint-1 valve is relatively less, so the amount of liquid empty generated will also decrease, and the liquid oxygen level is not easy to rise. On the contrary, if the gas volume through the expansion machine is too small, the gas volume through the joint-1 Valve will increase relatively. Due to the reduction of cold production, the temperature after heat exchange will rise, and the gas after the joint-1 valve cannot be liquefied, the temperature of the lower tower rises, which is not conducive to the rise of the liquid oxygen level. According to general experience, the temperature (T3) before the joint-1 valve should be controlled at-155 ~ -165℃ is appropriate, which is also the focus of this stage;
3) medium pressure (lower tower) pressure should be as low as possible to increase the differential pressure before and after expansion and increase the refrigerating capacity. At this time, the liquid air and liquid nitrogen throttle valve should be fully open;
4) low pressure (upper tower) pressure should be raised appropriately, and oxygen outlet valve should be closed a little bit less. In order to increase the liquefaction temperature of oxygen and reduce the liquid evaporation of the upper tower with throttling. Therefore, once the liquid empty appears, the oxygen outlet valve should be shut down to about 30% of the normal flow. At the same time, in order to set up the rectification working condition as soon as possible in the lower tower, improve the purity of nitrogen on the top of the lower tower and narrow the temperature difference of main cooling, when adjusting the working condition of the lower tower, the liquid nitrogen throttle is closed faster than the liquid-air throttle. Low pressure is generally controlled at 0.045 ~ 0.05MPa. However, the oxygen flow should not be shut down too small, otherwise the oxygen interlayer of the heat exchanger will not work, and the thermal load of the nitrogen interlayer is too large, which will increase the incomplete loss of the heat exchange;
5) with the change of the flow of the backflow gas, the distribution of the high pressure air flow should be changed timely to prevent the temperature difference of the hot end from expanding.
