DEAR Liquid air separation unit.When the full low pressure oxygen generator encounters an emergency power failure, the first task is to quickly open the vent valve at the end of the air compressor and close the valve of the air entering the rectification tower, so as to avoid the failure of the check valve at the outlet of the air compressor causing the compressed air to reverse and burn the bearing.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 ℃)For 1000m3 / h such a small low-pressure air separation plant, when producing gaseous products, the required expansion air volume has reached 28% of the processing air volume, and it can not all enter the tower to participate in distillation. If some liquid products are to be produced, more expansion air will be needed, and more expansion air will be bypassed to the heat exchanger.
It should be noted that the latent heat of evaporation of 1 kg liquid oxygen is not equal to that of condensation of 1 kg gaseous nitrogen. At the above temperature, the gasification latent heat of oxygen is 207 kJ / kg, and the condensation latent heat of nitrogen is 168 kJ / kg. Therefore, after the heat is transferred from gas nitrogen to liquid oxygen, the condensation amount of nitrogen is about 1.23 times of the evaporation amount of oxygen.In normal operation, the surface pressure of the main cooling liquid oxygen surface at the bottom of the upper tower is about 0.04MPa, and the evaporation latent heat of oxygen is 6700kj / KMOL; the condensation pressure of gas nitrogen is about 0.48mpa, and the condensation latent heat of nitrogen is 4815kj / KMOL. The latent heat of condensation of nitrogen is less than that of evaporation of oxygen, that is to say, the cooling capacity required to condense 1 mmol of gaseous nitrogen into liquid nitrogen is less than that released by evaporation of 1 mmol of liquid oxygen.
DEAR Liquid air separation unit.Adjust the purity of liquid air and liquid nitrogen. The lower column distillation is the foundation of the upper column. The change of liquid air and liquid nitrogen extraction quantity will affect the purity of liquid air and liquid nitrogen and the reflux ratio of upper column distillation section. If the amount of liquid nitrogen removed is too small, although the nitrogen purity is very high, but the reflux liquid supplied to the distillation section is too small, the nitrogen purity will be reduced.When the liquid level of condensing evaporator is too high, part of liquid oxygen can be discharged. This can not only make the liquid level drop rapidly, but also remove some impurities, which is conducive to safe operation. If the equipment is equipped with argon tower, the liquid oxygen level should be raised in advance to accumulate cold capacity, and then the argon tower should be started.With the increase of cooling capacity and the same amount of backflow air, the cooling capacity will be insufficient, so the temperature in the middle will rise. For the group with high temperature in the middle, turn down the air inlet stop valve (or diaphragm butterfly valve) to reduce the air throughput. Due to the sufficient cooling capacity, the temperature in the middle can be reduced. Attention should be paid to keep the total amount of air unchanged.
