NGL · Gas Plant
Turboexpander NGL Recovery
The cold section of the plant: exchangers, a turboexpander and a demethanizer tower that condense the ethane and heavier hydrocarbons out of the gas.
What it does
The gas is chilled against the cold sales gas and refrigeration, then expanded through the turboexpander, which drops its temperature further and drives a recompressor. The demethanizer separates methane overhead, which becomes sales gas, from the NGL at the bottom. Simpler plants use only mechanical refrigeration to recover propane and heavier.
Basics
| Main parts | Cold box exchangers, separators, turboexpander, demethanizer |
| Expander also drives | Sales gas recompressor |
| Top product | Methane rich sales gas |
| Bottom product | NGL to fractionation |
Common failures
- Hydrate or ice formation in the cold section
Troubleshooting
- Symptom
- Expander trips or cold box pressure drop rises
- Likely cause
- Water slipped from the dehydration
- What to check
- Check the mol sieve outlet moisture and thaw the section per procedure