For the activated alumina drying, generally heating regeneration method is applied, and usually hot nitrogen is used for regeneration because of the strong interaction of water and activated alumina and it is difficult to completely desorb the adsorbed water by other methods. The heating and desorption process includes three steps of heating, rinsing, and cooling.The higher the heating temperature, the more complete desorption regeneration.Generally, the activated alumina heating regeneration temperature is between 180 and 350 °C. The temperature of the activated alumina column is generally raised to 280 °C for 4 hours and heating rate is about 50 °C per hour. Since high concentration water vapor at high temperatures can severely damage the structure of the activated alumina, the activated alumina bed must be flushed with nitrogen, air and other suitable gas while heating. The flushing gas should be free of moisture because the amount of water in the flushing gas directly affects the regeneration effect.
The regenerated activated alumina bed must be cooled down before the adsorption operation. When the bed is flushed with the cooling gas, the gas used also should be free of moisture, and the flow direction of the cold gas is the same as the direction of the adsorption cycle. When the activated alumina is used for liquid drying, such as propylene, the liquid of the activated alumina bed should be eliminated without any dead angle. Otherwise, the residual liquid would react or carbonize upon heating, which seriously affects the performance and operating life of the adsorption cycle.
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