Air cooling tower is also a hybrid heat exchanger. In order to make the cooling water fully contact and strongly mix with the air to enlarge the heat transfer area and strengthen the heat transfer, the "stuffing Tower" or "sieve plate Tower" are usually used ". Also can use hollow spray tower.
The stuffing Tower is a round container made of steel, which is filled with stuffing (porcelain ring, or plastic ring, etc ). The cooling water sprays down from the tower top and is mixed with the bottom-up flowing air for heat and mass exchange. Air transmits heat to cooling water to lower the temperature itself and raise the water temperature. In order to prevent the air from dripping out of the water, the upper part of the tower is usually equipped with laxige ring (or stainless steel wire mesh) stuffing separator (also called capture layer) and mechanical water separator (inertial separation ). The cooling water sprayed out by the spraying device flows downward along the stuffing layer through the distributor, and there is an overflow ring of redistributing water at a certain distance in the stuffing layer, do not cause water to directly downstream along the container wall and affect the heat transfer effect. The cooling water with increased temperature is led out from the lower part, sent to the cooling tower of water or discharged (for open-type system), and the air after cooling is discharged from the top of the tower and sent to the air separation tower or molecular sieve adsorber. The disadvantage of the stuffing Tower is that the stuffing is easy to be blocked by scale, and it is difficult to clean and replace the stuffing into large blocks.
The sieve tower is similar to the sieve tower of the distillation tower, but the number of the boards is relatively small (generally about 5 pieces), and the diameter of the sieve hole and the space between the holes are relatively large (the aperture is about 5mm, and the space between the holes is about 9mm ). The cooling water is sprayed out from the top through the spraying device, and flows down layer by layer along the tower plate through the sieve hole. The air flows back from the bottom of the tower through the sieve hole, and the air is bulged up. Gas-liquid two-phase strenuous movement on the sieve plate, forming a foam layer, increasing the gas-liquid contact area and the degree of disturbance, making the gas-liquid have a good heat and mass transfer, and the effect is better than that of the stuffing tower.
There is neither stuffing nor sieve plate in the hollow tower. Cooling water is sprayed downward by the spraying device layer by layer, air flows from bottom to top, and gas and liquid are mixed directly. It is simpler than packing tower and sieve tower, with small size, small resistance and better cooling effect. The hollow tower has high requirements on the spraying device and water quality, and the water sprayed out must be well atomized to make the gas-liquid fully contact.
At present, the air cooling tower of large air separation plant in our country adopts the upper section as the stuffing tower, which is equipped with new plastic rings; the lower section is the sieve Tower (the aperture is 12mm, and the space is 24mm), which has achieved good results. The heat transfer temperature difference of the top is only 0.5 ℃, and the problem of scaling is completely solved.
There are also non-mixed (tubular) air cooling towers in nitrogen-water precooler of the air separation plant, which are combined with the last cooler of the air compressor. For example, the air cooling tower of 6500 m 3/h air separation plant in France.
