The pressure of the lower tower is reduced due to the condensation of some gases, so that more air is "sucked in". Therefore, with the rise of the main cooling liquid level, the amount of condensed liquid in the lower tower increases, and the amount of air entering the tower also increases gradually. At this time, gradually turn down the air vent valve to let all the air into the tower.DEAR Liquid air separation unit.In operation, it is very important to record the temperature condition of the accumulator correctly and measure the temperature difference between the hot end and the cold end, which is the basic data to judge whether the operation of the air separation unit is normal. The temperature of the hot end of the accumulator is generally measured by a resistance thermometer. The thermometer should be installed on the outlet pipe between the top of the accumulator and the switching valve, and the closer it is to the top, the better.The state of the air entering the air separation unit is also an important factor affecting the operation cycle. Because the increase of air quantity or air temperature in the unit will increase the load of water removal and the temperature difference of heat exchange. At the cold end, the self clearance is poor and the resistance rises faster. Therefore, the operation cycle will be shortened in high load production, and extended in low load production.
DEAR Liquid air separation unit.If the temperature in the middle is controlled lower, the cold zone will be enlarged and the freezing area of carbon dioxide will be increased, which can reduce the amount of carbon dioxide brought into the distillation column. If the resistance increases little due to the residual ice and solid carbon dioxide, the middle temperature can be reduced appropriately, the temperature difference at the cold end can be reduced, and the switching time can be shortened, so as to strengthen the self-cleaning ability and gradually reduce the resistance in long-term operation.DEAR Liquid air separation unit.If the temperature is increased by 1 ℃, the energy consumption of the air separation unit will increase by about 2%. Lowering the inlet air temperature can not only improve the economy of the air separation plant, but also reduce the saturated moisture content in the air. For example, when the absolute pressure of air is 0.6MPa and the air temperature drops from 40 ℃ to 30 ℃, the saturated moisture content in every 1kg of air will be reduced by about 40%.
For the all low pressure air separation unit which uses freezing method to remove moisture and CO2 from the air, because sufficient backflow gas is needed to carry the frozen moisture and CO2 out of the unit, the pure nitrogen (99.999%) yield is only 1.1 times of the oxygen yield. For the molecular sieve purification air separation process of extracting argon fraction, the yield of pure nitrogen is not subject to the above restrictions.However, at the beginning of the handover, it often goes up instead of down. This phenomenon is not caused by the abnormal phenomenon of the accumulator, nor by the wrong connection of the thermometer. It is often caused by the hysteresis of the platinum resistance thermometer. The length of the lag time is also related to the position of the temperature measuring point and the insertion depth of the thermometer rod. If the probe is inserted deeper, the temperature response is more sensitive. On the contrary, the lag time is longer.DEAR Liquid air separation unit.The temperature drop of air from 0.6MPa throttling to 0.1MPa is only about 1 ℃, while the temperature drop can reach 80 ~ 90 ℃ theoretically through expansion of expander, and the effect of temperature drop is much better than that of throttling. The reason is that the throttling process does not output work, and the decrease of temperature is caused by the increase of molecular potential energy.
