GPSA Ch. 16 GPA 2140

Calculation Mode:

Design Rate

Design: Size ethane recovery plant from feed gas conditions and target recovery.

Feed Gas Conditions

Inlet Gas Flow

MMSCFD

Inlet Temperature

°F

Inlet Pressure

psig

Gas Specific Gravity

Feed Composition (mol%)

Methane (C₁)

Ethane (C₂)

Propane (C₃)

iso-Butane (iC₄)

n-Butane (nC₄)

Pentane+ (C₅+)

CO₂

N₂

Process Parameters

Process Type

Target C₂ Recovery

Expander Efficiency

Compressor Efficiency

Residue Gas Pressure

psig

Demethanizer Type

Existing Equipment

Existing Expander HP

Existing Demethanizer Diameter

Existing Demethanizer Trays

trays

Typical Ethane Recovery Operating Conditions

Parameter	Range
Demethanizer Pressure	350–450 psig
Expander Outlet Temp	−130 to −150°F
C₂ Recovery (GSP)	85–95%
C₂ Recovery (Conv.)	40–60%
Expander Efficiency	78–87%

Engineering Basis

Turboexpander Isentropic Work:

W_exp = m · (h_in − h_out,s) · η_exp

Where m = mass flow rate, h_in = inlet enthalpy, h_out,s = isentropic outlet enthalpy, η_exp = expander isentropic efficiency.

C₂ Recovery Efficiency:

η_C2 = (C₂ in NGL product) / (C₂ in feed gas) × 100%

Recovery efficiency depends on process configuration: GSP > CRR > ISS > Conventional JT.

Gas Subcooled Process (GSP): Splits the chilled gas into two streams — one feeds the demethanizer top as reflux (subcooled liquid), the other is expanded through the turboexpander. This configuration achieves 85–95% ethane recovery.

Demethanizer Sizing: Column diameter sized from vapor/liquid traffic. Number of theoretical stages determined by required separation sharpness between C₁ and C₂.

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Ethane Recovery Results

C₂ Recovery

C₃+ Recovery -

Process Type -

Shrinkage -

Turboexpander

Expander Power -

Expander Outlet Temp -

Expander Outlet Press -

Recompressor Power -

Net Compression HP -

Demethanizer Column

Diameter -

Trays / Stages -

Column Height -

Reboiler Duty -

Operating Pressure -

Product Rates

Residue Gas -

NGL (C₂+) Product -

Ethane Product -

C₃+ Product -

Design Guidelines

GSP Process: Gas Subcooled Process achieves 85–95% ethane recovery by splitting chilled gas into reflux and expander streams. Most common for high C₂ recovery.

CRR Process: Cold Residue Recycle can achieve 92–97% C₂ recovery by recycling a portion of cold residue gas as additional reflux.

Ethane Rejection: Plants can be operated in ethane rejection mode (C₃+ recovery only) when ethane prices are unfavorable.

Ethane Recovery Process Calculator