Because the molecular sieve adsorbent has strict requirements on the temperature of the adsorption medium, its inlet temperature must be lower than 15 ℃ to work normally, generally 8 ~ 15 ℃, and it is very difficult to cool the air to the temperature range required by molecular sieve with ordinary cooling water.

If the molecular sieve adsorption purification process does not use the freezing precooling system, it will inevitably lead to the increase of molecular sieve inlet temperature. It can be seen from the theoretical calculation that every 1 ℃ increase in the gas medium temperature will increase the molecular sieve load by about 5%. Therefore, if possible, make full use of the cooling capacity and dryness of nitrogen to cool the cooling water to the lowest temperature in the water cooling tower.

In addition, in order to counteract the increase of load caused by temperature rise, it is necessary to improve the design of molecular sieve purification. For example, increase the adsorption capacity of molecular sieve, change the tank structure from horizontal to vertical, shorten the purification cycle, and reduce the heating and cold blowing time of molecular sieve.

The advantages and disadvantages of this measure are as follows:

1) It reduces the one-time design investment of the refrigerator cooling system, but increases the investment of the purification system;

2) The production of pure nitrogen should be reduced so that there is enough polluted nitrogen to cool the water;

3) The cross-sectional area of the vertical tank is small, which makes the air distribution more uniform;

4) The height of molecular sieve bed is increased, the resistance of molecular sieve is increased, and the energy consumption of oxygen product is increased;

5) With the change of season, the gas temperature through the molecular sieve bed changes greatly, which makes the air separation production unstable.