No desiccant is perfect or best for all applications. In some applications the desiccant choice is determined primarily by economics. Sometimes the process conditions control the desiccant choice. Many times the desiccants are interchangeable and the equipment designed for one desiccant can often be operated effectively with another product. Table 8-4 illustrates the most common …
Read More…Category: Design Considerations
Solid Bed Dehydrator – Moisture Content of Inlet Gas
An important variable that determines the size of a given desiccant bed is the relative saturation of the inlet gas. This variable is the driving force that affects the transfer of water to the adsorbent. If saturated gas (100% relative humidity) is being dried, higher useful capacities can be expected for most desiccants than when …
Read More…Solid Bed Dehydrator – Pressure Drop
Towers are sized for a design pressure drop of about 5 psi through the desiccant. The pressure drop can be estimated by: Pressure drops of greater than approximately 8 psi are not recommended.
Read More…Solid Bed Dehydrator – Bed Height to Diameter Ratio
In its simplest form, an adsorber is normally a cylindrical tower filled with a solid desiccant. The depth of the desiccant may vary from a few feet to 30 ft or more. The vessel diameter may be from a few inches to 10 or 15 ft. A bed height to diameter (L/D) ratio of higher …
Read More…Solid Bed Dehydrator – Gas Velocities
Generally, as the gas velocity during the drying cycle decreases, the ability of the desiccant to dehydrate the gas increases. At lower actual velocities, drier effluent gases will be obtained. Consequently, it would seem desirable to operate at minimum velocities to fully use the desiccant. However, low velocities require towers with large cross-sectional areas to …
Read More…Solid Bed Dehydrator – Cycle Time
Most adsorbers operate on a fixed drying cycle time and, frequently, the cycle time is set for the worst conditions. However, the adsorbent capacity is not a fixed value; it declines with usage. For the first few months of operation, a new desiccant has a very high capacity for water removal. If a moisture analyzer …
Read More…Solid Bed Dehydrator – Pressure
Generally, the adsorption capacity of a dry bed unit decreases as the pressure is lowered. If the dehydrators are operated well below the design pressure, the desiccant will have to work harder to remove the water and to maintain the desired effluent dew point. With the same volume of incoming gas, the increased gas velocity, …
Read More…Solid Bed Dehydrator – Temperature
Adsorption plant operation is very sensitive to the temperature of the incoming gas. Generally, the adsorption efficiency decreases as the temperature increases. The temperature of the regeneration gas that commingles with the incoming wet gas ahead of the dehydrators is also important. If the temperature of these two gas streams differs more than 15°F to …
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