In the air separation unit, the function of air cooling column is to reduce the temperature of air compressed by air compressor. Air cooling column is a kind of hybrid heat exchange equipment. In order to increase the heat transfer area, make the cooling water fully contact with the air and mix completely to enhance the heat transfer effect, the air cooling column usually adopts several structural forms such as packed column, sieve plate column or hollow spray column.
The air cooling column in the form of packed column is made of steel container equipment. Ceramic ring or plastic ring is used as filler in the column and filled in layers. In order to prevent the cooling water from flowing down the inner wall of the container and affecting the heat transfer effect, an overflow ring for redistributing water is set between the packing layers. In order to prevent the air from carrying water out of the air cooling column, a ring type trap layer and water separator are set at the top of the column. The cooling water is sprayed from the top of the column to exchange heat and mass with the flowing air from bottom to top, so as to reduce the air temperature. The disadvantage of packed column is that the packing surface is easy to scale and block, and it is not easy to clean and replace.
The air cooling column with sieve tray column is similar to the distillation column in the form of sieve tray column. However, the number of tray in air cooling column is small, and the diameter and spacing of sieve holes are larger. The cooling water from the top of the column and the air rising from the bottom of the column are contacted on the tray. The foam layer increases the gas-liquid contact area and disturbance degree, and strengthens the heat and mass transfer of the gas and liquid. The effect of mass transfer is better than that of packed column.
There is no packing and tray in the hollow spray column. The cooling water directly contacts with the air from the spray device. The structure is simple and the cooling effect is good, but the requirements for the spray device and water quality are high.
At present, most of the domestic air separation units generally choose the upper packed column and the lower sieve plate column, which can reduce the heat transfer temperature difference at the top and thoroughly solve the problem of scaling on the packing surface. Good results have been achieved.
