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Oil Purification Still Calculator

GPSA Ch. 16

Oil Purification Still Calculator
Sizes oil purification (stripping) stills for lean oil absorption plants. The still removes absorbed NGL (C₃+) from demethanized rich oil, regenerating lean oil for recirculation to the absorber. Supports reboiler-only and steam stripping configurations per GPSA Ch. 16.
GPSA Ch. 16 ASME VIII
Calculation Mode:
Design: Size oil purification still from oil flow, NGL loading, and stripping requirements.

Oil Feed

GPM
°F
g/mol

NGL Loading

% (gal NGL/gal oil)

Column Parameters

psig
°F
%
%
in
%

Steam Stripping

lb/gal oil

Typical Oil Purification Still Parameters

ParameterTypical Range
Still Pressure30–75 psig
Reboiler Temperature350–450°F
Theoretical Stages4–12
NGL Retention Target1–3%
Steam Rate0.3–1.0 lb/gal
Oil Loss0.02–0.10%

Engineering Basis

Stripping Efficiency:

ηstrip = (NGLin − NGLout) / NGLin × 100%

Typical stripping efficiency 85–98% depending on stages, temperature, and steam usage. Steam stripping allows lower reboiler temperatures while maintaining high NGL recovery.

Function: The oil purification still strips absorbed NGL (C₃+) from demethanized rich oil, producing lean oil for recirculation to the absorber and NGL product from the overhead.

Design Guidelines

Reboiler Temperature: Keep below 400°F for most oils. Steam stripping allows lower reboiler temperatures (350–380°F) while maintaining high NGL recovery.
Oil Degradation: Monitor oil color, viscosity, and flash point. Dark oil indicates thermal cracking. Makeup oil rate typically 0.02–0.10% of circulation.
Steam Stripping: Improves stripping at lower temperatures. Typical steam rate 0.3–1.0 lb steam per gallon oil. Requires overhead water separation.

Frequently Asked Questions

What is an oil purification still?

An oil purification (stripping) still removes absorbed NGL (Cā‚ƒ+) from demethanized rich oil, regenerating lean oil for recirculation to the absorber in lean oil absorption plants. It is sized per GPSA Ch. 16.

What configurations does the still calculator support?

The calculator supports both reboiler-only and steam stripping configurations. Steam stripping provides additional driving force for light component removal and is used when higher lean oil purity is required per GPSA Ch. 16.

How is reboiler duty calculated for the still?

Reboiler duty is determined from the heat required to vaporize absorbed NGL components from the rich oil, plus sensible heat and heat losses. The calculator computes duty based on oil flow rate, NGL loading, and operating temperatures.

What outputs does the oil purification still calculator provide?

The calculator provides column diameter, number of trays, reboiler duty, NGL product rate, steam requirements (if applicable), lean oil quality, and estimated vessel weight per ASME VIII and GPSA Ch. 16.