All low pressure air separation units are usually equipped with nitrogen water precoolers. It mainly uses the unsaturation of nitrogen in sewage to evaporate part of water. As the water evaporates, it absorbs the latent heat of vaporization to lower the temperature of the cooling water, which is then used to cool the treated air and lower the temperature of the air entering the column. Therefore, it includes air cooling column and water cooling column.
The basic purpose of setting up nitrogen precooler is to reduce the air temperature entering the air separation column and avoid the temperature fluctuation greatly. Because the inlet air temperature directly affects the operation conditions of the switching heat ex-changer and distillation column, as well as the economy of the whole air separation unit. In the design, the air temperature entering the column is usually set at 30 ° C. When the inlet temperature of the column is higher than the design index during operation, the throttling cooling capacity of compressed air will be reduced, and the temperature difference and heat load at the heat end of the switching heat ex-changer will increase, which will lead to increased cooling loss and energy consumption.
Secondly, in the air cooling column (spray cooling column), air and water contact directly, not only for heat exchange but also for washing, so as to remove dust in the air and dissolve some corrosive impurities, so as to avoid corrosion of aluminum alloy material of plate fin switch heat ex-changer and prolong its service life. Due to the large volume of the air cooling column, it can also buffer the air, and the air compressor is not easy to over-pressure when switching.
For the process of adsorption and purification, the adsorption capacity of molecular sieve is related to temperature. The lower the temperature, the greater the adsorption capacity. For a certain size of the adsorber, the working time may be very long, or for a certain adsorption time, the designed adsorber volume may be very small, so the air needs to be precooled to the lowest possible temperature. In the nitrogen water precooler, the cooling capacity of nitrogen is fully recovered and utilized to cool the air.
