After the pipelines, valves in the tower and the air separation units installed on site are completely installed, heated and purged, the start-up refrigeration is carried out without filling the cold insulation material in the cold insulation box, which is called "bare cooling". Therefore, bare cooling is an indispensable process for the equipment installed on site, after installation and before formal test run, which should be given enough attention.DEAR Air separation equipment.The common fault of the automatic valve is that it is not closed tightly, resulting in gas channeling at the middle and low pressure cold end. This is reflected by the increase of air flow and the decrease of pressure. At the same time, the pressure of the low pressure system increases. The failure of automatic valve is also a great threat to the normal production of oxygen generator.The throttling expansion process of the throttle valve and the expansion process of the expander often encountered in the oxygen generator can be regarded as an adiabatic process. After expansion, the pressure decreases. However, the former is irreversible adiabatic expansion, and the entropy value increases before and after expansion.
In this way, continuous refrigeration can be realized. In the oxygen generator, it is also a refrigeration process to reduce the air temperature to the liquefying temperature. Therefore, there must be a compressor at the cost of power consumption. Only in the oxygen generator, air is used as the working medium, and the purpose of cooling is achieved by first compressing and then expanding the air. Then cool the air itself until it reaches the liquefying temperature.DEAR Air separation equipment.The situation at the top of the distillation column is similar to this, gas nitrogen and liquid nitrogen are in the coexistence of saturation state, with the same saturation temperature. However, the saturated liquid and vapor at the same temperature belong to different states. The heat released by saturated steam can be condensed into saturated liquid with constant temperature, which is called "condensation latent heat"; the heat absorbed by saturated liquid can be gasified into saturated steam with constant temperature, which is called "evaporation latent heat". For the same substance, under the same pressure, they are equal in value.
Increase the expansion through the liquefier. One way of expanded gas goes directly to the cold end of the switching heat exchanger, and the other way goes through the liquefier. If the gas flow through the liquefier increases, the cooling capacity is sufficient, and the flow rate increases, the heat transfer can be enhanced, and the liquefaction capacity can be increased. Therefore, the bypass valve should be turned down to let more gas pass through the liquefier.When the molecular sieve adsorber is switched, the first step is to equalize the pressure. Because the pressure equalizing pipe is at the outlet, if the pressure equalizing valve is opened too fast in the pressure equalizing process, it is bound to cause a large fluctuation of air volume, which will affect the stable production of air separation; if the pressure equalizing valve is opened too slowly, it will prolong the service time of molecular sieve, which is not conducive to the adsorption effect.Maintain the water level of the air cooling tower; the water spray volume should not be too large; the water quality should meet the requirements, reduce the inlet water temperature and reduce the scale. In case of water inflow accident, the working condition of the air cooling tower should be dealt with first, the water supply of the water pump should be stopped, the water level of the air cooling tower should be lowered, and the normal working condition should be restored.
DEAR Air separation equipment.About 174kj of cold energy can be recovered by liquefying 1kg of air. If this part of liquid enters the upper tower, it will vaporize completely because the main cooling temperature is still very high. Although part of the cold energy will be transferred to the upper tower, the evaporated steam will pass through the liquefier after leaving the upper tower, and the temperature rise of low temperature gas in the liquefier is limited (for example, from - 189 ℃ to - 175 ℃)The higher the temperature is, the greater the energy the molecule has, the easier it is to get rid of the liquid and gasify, and the higher the corresponding saturation pressure is. A certain temperature and a certain saturation pressure are not independent. Therefore, in the saturated state, the temperature corresponding to the saturation pressure is also called "saturation temperature". Usually, the relationship between saturation temperature and saturation pressure of various substances can be found in the manual.
