GPSA · Plant Processing of Natural Gas Ch. 3 · Solid Desiccant Dehydration
Comprehensive coverage of silica gel adsorption, regeneration cycles, and comparison with molecular sieves.
It designs silica gel dehydration systems per GPSA Section 20, calculating bed sizing, L/D ratio, pressure drop using the Ergun equation, regeneration heat duty, and cycle times.
Silica gel dehydration systems can dry natural gas to a -40°F dew point as calculated by this tool.
The calculator uses the Ergun equation to calculate pressure drop through the silica gel bed.
Silica gel dehydration can achieve outlet dewpoints down to -40°F, making it suitable for pipeline specifications and moderate dehydration applications. For deeper dehydration below -40°F, molecular sieve is typically required.
Regular density silica gel has 6-8 wt% dynamic capacity at 100°F and 800 psia. High capacity types achieve 10-12 wt%, while indicating silica gel (with color change indicator) has reduced capacity of 5-6 wt% due to the indicator additive.
Key design parameters include L/D ratio of 2:1 to 4:1 for good flow distribution, superficial velocity of 20-40 ft/min to avoid fluidization, maximum pressure drop of 5 psi for clean bed, and a 1.25× safety factor for mass transfer zone losses.
Silica gel is regenerated by heating to 350-450°F for 2-4 hours followed by cooling for 2-3 hours to below 120°F. Regeneration gas flows counter-current to adsorption direction at 5-15% of feed flow rate. Typical on-stream cycle time is 8-16 hours.