Molecular Sieve (4A) Dehydration Bed Calculator
Size Type 4A molecular sieve adsorption vessels, calculate required adsorbent mass, bed diameter/height, superficial velocity limits, and regeneration thermal duty for LNG cryogenic pretreatment.
Gas Throughput & Water Load
4A Zeolite Adsorbent Properties
Adsorption Bed Sizing Results
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Frequently Asked Questions
Why is molecular sieve mandatory for LNG liquefaction instead of TEG glycol?
TEG dehydration systems can economically achieve a water dew point of approximately -10°F to -25°F (~2 to 4 lb/MMSCF or ~50 ppmv). In LNG plants where natural gas is chilled to -260°F (-162°C), any water concentration above 0.1 ppmv will freeze into solid ice crystals, blinding plate-fin heat exchangers (MCHE). Type 4A molecular sieve reduces water to sub-0.1 ppmv.
What is Dynamic Water Capacity (DWC) vs Equilibrium Capacity?
Equilibrium capacity is the maximum water a pristine molecular sieve crystal can absorb in a static laboratory beaker (typically 20% to 22% wt). Dynamic Water Capacity (DWC) is the actual usable capacity in a commercial flowing bed (typically 9% to 12% wt) after accounting for hydrothermal aging, coke fouling, and the finite Mass Transfer Zone (MTZ).
How does thermal swing regeneration (TSA) desorb water from 4A zeolites?
Molecular sieve water adsorption is an exothermic physical electrostatic attraction. During the regeneration cycle, a portion of treated dry gas is heated to 450°F to 550°F (230°C to 290°C) and passed upflow through the bed. The intense thermal energy breaks the hydrogen bonds, vaporizing and carrying away the adsorbed water.