Dehydration · Gas Plant
Molecular Sieve Dehydration
Two or more towers filled with molecular sieve pellets that adsorb water down to very low levels, used ahead of cryogenic NGL recovery.
What it does
Glycol cannot dry the gas enough for the very cold section, where any water would freeze. One tower dries the gas while the other is regenerated with hot gas, and they switch on a timed cycle, typically every 8 to 12 hours for saturated gas.
Basics
| Used ahead of | Low temperature (cryogenic) NGL recovery |
| Arrangement | Two towers, one drying, one regenerating |
| Cycle | Usually 8 to 12 hours for saturated gas |
| Regeneration gas | About 480 to 530 °F |
| Pellets | About 2 to 3 mm diameter |
Common failures
- Water breakthrough that freezes the cold box
Troubleshooting
- Symptom
- Rising pressure drop in the cold section
- Likely cause
- Water breakthrough from a spent or poorly regenerated bed
- What to check
- Check the regeneration temperature and cycle, and the outlet moisture analyzer