For the full low pressure unit, the expansion can only be increased, which affects the distillation condition of the upper column and reduces the average purity of nitrogen. Therefore, when the expansion air flow into the tower is limited and the cooling capacity is insufficient, the argon fraction can only be reduced.DEAR Air separation unit.In the cold state, the deformation and leakage of each part should be checked in detail. The location of the leakage point can be judged according to the frosting condition, and should be marked. After freezing, the flange screws should be tightened again to make up for the screw relaxation caused by different thermal expansion coefficient at low temperature. However, attention should also be paid not to screw too tightly to prevent excessive prestress.In order to avoid the increase of hydrocarbon concentration in liquid oxygen, according to the material balance, it is necessary to extract part of liquid oxygen from the main cooler and extract part of hydrocarbon from the main cooler. The minimum amount of liquid oxygen extracted is equal to 1% of the gas oxygen output, and then gasified separately.
For the medium pressure air separation unit, the low temperature air from the main heat exchanger enters the lower tower by throttling expansion to ensure that the air entering the tower has a certain moisture content. For the expansion of cryogenic liquid, the energy loss of liquid throttling is small, and there is no significant difference between expander expansion and throttling expansion. The structure and operation of throttling valve are much simpler than expander. Therefore, throttling expansion is adopted when the liquid from lower tower expands to upper tower.The ability of a substance lower than the ambient temperature to absorb heat. This kind of low temperature is obtained at a certain cost, that is, the compressed gas consumes work and then expands after being compressed. If this part of cooling capacity is not recycled, it is called cooling capacity loss.The more water is allowed to evaporate, the more evaporation latent heat is absorbed, and the lower the temperature of cooling water out of the cooling tower. Therefore, the higher the temperature at the outlet of the sewage nitrogen, the better the cooling effect of the water cooling tower. Of course, the outlet temperature of sewage nitrogen can not be higher than the inlet temperature of water.
The structure of water cooling tower for large air separation plant in China is as follows: packed tower. In the early stage, it was equipped with ceramic lacigo ring, which had good heat transfer effect and little resistance. However, when it is used in the self cleaning low-pressure process, because the switching system is switched every few minutes, the air flow has a great impact on the porcelain ring during the switching venting, which is easy to cause the porcelain ring damage and increase the resistance. There are also plastic rings to increase strength.Forced valve is driven by air pressure to open and close the piston valve. The fault includes two aspects: the fault in the cylinder and the fault in the valve body. The fault in the cylinder is mainly caused by the slow switching action, the valve is not easy to open or close tightly. This is caused by too low air pressure, too dirty air or too large pipeline resistance.The mechanical water is carried out with the air and enters the molecular sieve purifier or the switching heat exchanger, which destroys the normal operation of the device. The causes of this failure are as follows: the screen hole of the sieve plate is partially blocked. The spray water of the air cooling tower flows down through the cross flow sieve plate and constantly contacts with the air.
