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Activated Alumina

March 12, 2011

 

Activated alumina is a porous form of aluminum oxide. It has a high surface area which adsorbs vapors without any change in form. Activated alumina will not soften or disintegrate easily when immersed in water.

Dew points to -40°F and lower may be achieved with activated alumina depending on dryer design and operating conditions.

  • The 1/8 (2-5mm) bead is the size most frequently used in regenerative dryers.
  • The 3/16 (4-8mm) bead is used when pressure drop and surface area requirements fall between  •1/8” and 1/4” material. It is suitable for most systems.
  • The 1/4 (5-10mm) bead alumina is used both as a pre-bed material to support large desiccant beds  or as a buffer for silica gel beads. Pressure drop is slightly lower than 1/8” (2-5mm) material.

If size is not known or specified, the 1/8” (2-5mm) size is usually satisfactory. However, if activated alumina is used in a regenerative dryer and the desiccant retaining screens cannot be measured, the 1/4” (5-10mm) size should be used as a bed support (6” layer). If at all possible, obtain a sample material and measure it before ordering.

Benefits :

  1. High adsorption capacity : With high surface area and excellent pore distribution, activated alumina has a high water adsorption capacity. This reduces initial cost, energy consumption and operating costs through smaller bed sizes and/or longer operating cycles.
  2. Low abrasion : Insures less dusting during tower depressurization or loading. Low abrasion means low pressure drop and a reduced chance of plugging the after filter.
  3. Resists liquid water : Water slugging due to upstream failure of after cooler, separators or drain traps will not fracture the alumina beads. The adsorption capacity of the desiccant can be restored after complete regeneration.
  4. High crush strength : High crush strength, which limits dusting, is important during loading of desiccant towers. High crush strength makes alumina effective as a prebed material when used with other types of desiccants.
  5. Uniform bead sizes : Activated alumina is a uniformly sized bead. It provides low pressure drop to minimize channeling and ensures utilization of the full bed column section.

 
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