GPSA Ch. 16
| Process Type | C₃ Recovery | Cold Sep. Temp |
|---|---|---|
| Turboexpander | 95–99% | −120 to −140°F |
| JT Valve | 70–85% | −40 to −80°F |
| Mech. Refrigeration | 80–90% | −20 to −40°F |
| Lean Oil Absorption | 60–80% | 80–100°F |
Isentropic Expansion (Turboexpander):
Where T1, P1 = inlet conditions, P2 = column pressure, k = ratio of specific heats, ηexp = isentropic efficiency. Lower temperatures drive higher C₃+ recovery.
Joule-Thomson Expansion:
Where μJT = Joule-Thomson coefficient (°F/psi), ΔP = pressure drop across the valve. No work recovery — lower efficiency than turboexpander.
Recovery Efficiency: Recovery depends on cold separator temperature, which is set by expansion ratio and inlet conditions. Ethane rejection is achieved by operating the demethanizer to keep C₂ in the overhead with methane.
Column Sizing: Demethanizer column diameter sized from vapor/liquid traffic using Fair’s flooding correlation at the design flood fraction.
Understand propane recovery process design, turboexpander vs. JT valve trade-offs, and NGL plant optimization