DEAR Cryogenic air separation unit.If the resistance of the cold section increases, it is carbon dioxide freezing; if the resistance of the hot section increases, it is water freezing; if the resistance of the whole heat exchanger increases, it is both freezing, or molecular sieve powder is blocked; the abnormal operation of the refrigerator causes the temperature of the chilled water to rise, and the air cannot be cooled to the normal temperature.For cold equipment, when the temperature does not rise above 0 ℃, do not blow it with wet air. The blowing procedure is to clean the pipes outside the tower to prevent impurities from entering the tower; the air heat exchanger inside the tower is firstly blown, then the lower tower is blown, and finally the upper tower and the liquid oxygen and liquid nitrogen discharge system are blown.DEAR Cryogenic air separation unit.The higher the air pressure into the device, the greater the power consumption of the air compressor, and the higher the requirements for the safety and strength of the pipeline and equipment. Moreover, with the increase of pressure, the increase of cooling capacity also decreases. Therefore, the maximum pressure of small high-pressure oxygen generator is generally not more than 20MPa, and in normal production, the working pressure should be reduced as much as possible. When the temperature of air entering the unit increases, the cooling capacity of throttling effect decreases slightly.
DEAR Cryogenic air separation unit.In other words, because part of the liquid gasification needs heat absorption, the temperature after throttling will decrease. Generally, the gasification rate y of saturated liquid in air separation column can reach 17% ~ 18% after throttling. The subcooler uses the low temperature gas from the upper tower to cool the saturated liquid from the lower tower, so that the temperature is lower than the saturation temperature.Before the liquid appears in the start-up stage of the air separation unit, the lowest temperature is generated by the expander, and the temperature in the distillation column can not be lower than the temperature after expansion. However, liquid appears in the lower tower, and when the saturated liquid throttles to the upper tower, the pressure decreases, part of it gasifies, and the temperature also decreases to the saturation temperature corresponding to the upper tower pressure. For example, when the liquid nitrogen at - 177 ℃ on the top of the lower tower is throttled to the upper tower, the temperature can be reduced to - 193 ℃.
DEAR Cryogenic air separation unit.First of all, the preparation work before heating should be done well: 1) discharge the liquid in the tower; 2) remove the flowmeter and thermometer at the outlet of oxygen, nitrogen and fraction; remove the upper and lower joints of liquid air and liquid oxygen level gauge; 3) close the main inlet valve of high-pressure air, section-1 valve, oxygen and nitrogen product delivery valve, and the main inlet valve of heating; 4) open the inlet and outlet valves of expander 5) open all through valves, throttle valves, analysis valves, blow off valves, upper and lower valves of liquid level gauge, Pressure Gauge Valves and heating valves on the shell of fractionator; 6) top up the distilled water of heating furnace.When the temperature of the backflow gas out of the accumulator decreases, the temperature difference at the hot end will be larger. The cooling capacity absorbed by positive flow air is more than that absorbed by return flow and positive flow air, so the temperature of air out of the accumulator decreases, resulting in the reduction of temperature difference at the cold end.
The oxygen content of liquid oxygen and liquid air in the air separation unit is high, which will cause the oxygen concentration to increase in local range after evaporation in the air. If there is a fire, there is a risk of combustion and explosion. A large amount of liquid oxygen was discharged into the trench in a chemical fertilizer plant, and the electric welding spark caused an explosion injury accident. Therefore, it is strictly forbidden to discharge the liquid into the trench at will, and it should be discharged into the liquid evaporation tank or special low temperature resistant metal discharge pit through pipeline.In our daily life, we can see that a cup of hot water will naturally cool to the ambient temperature, and a piece of ice will naturally melt into water in the environment above 0 ℃. But water doesn't spontaneously drop to a lower temperature than the surrounding air and freeze. These phenomena show a basic law of nature: heat can only be transferred spontaneously from high-temperature objects to low-temperature objects, but the opposite process cannot be carried out spontaneously.
