1. Chapter 7 NGL Recovery – Lean-Oil Absorption
Gas Processing I NGT 140
Chapter 7
NGL Recovery – Lean-Oil Absorption
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2. Ch 3
Ch 5
Ch 2
Ch 7 & 8
Ch 10
Ch 4
Ch 6
Ch 9
Ch 2
Ch 9

3. Raw Natural Gas
Hydrocarbons – methane, ethane, propane and butane.
Nonhydrocarbons – nitrogen,helium, carbon dioxide.
Kerosene was in demand and natural gas was burnt off.
A form of gasoline become a by product which then became in demand
Lean oil absorption process was developed to increase production.

4. Lean oil absorption
Lean oil is a hydrocarbon liquid when in contact with natural gas absorbs heavier hydrocarbons.
This allowed for more gas condensate to be recovered.
Permitting more specific natural gas products to be produced.
Lean oil absorption is only one way to separate various products in natural gas.
A less expensive process is by refrigerating the gas to remove the propane and heavier hydrocarbons.

5. Chapter 7 presents the older, but still commonly used, lean oil absorption process.
Chapter 8 covers the newer processes of refrigeration and turboexpansion.

6. Lean-Oil Absorption Primary Systems (Fig. 7.1)
Recovery
Rejection
Separation

7. Lean-Oil Absorption Primary Systems
Recovery
All product to be recovered is removed from the inlet gas by a combination of refrigeration and absorption.
The main piece of equipment is the absorber
Remaining equipment is used to increase the efficiency of the absorber
Absorption oil removes some of the components from the gas
Absorption oil is called lean oil
Absorption works by transferring hydrocarbon molecules from the gas phase to the liquid phase. The liquid phase is rich oil

8. Lean-Oil Absorption Primary Systems
Recovery (continued)
The main piece of equipment in the recovery section is the absorber.
Absorption is a process in which a liquid solvent removes some of the from a gas.
Absorption oil is called lean oil – that is it contains little of the desired hydrocarbons to be extracted from the gas.
Absorption is the transfer of hydrocarbon molecules from the gas phase in the inlet gas to the liquid phase (or rich oil).
A problem is that the lean oil vaporizes more easily in the residue gas.

9. Lean-Oil Absorption Primary Systems
Recovery (continued)
Oil to gas ratio measures how hard the absorber is working.
The ratio is expressed as gallons per minute of lean oil circulated per million cubic feet of gas through the absorber.
In the recovery stage unwanted methane always remains and must be removed.
Absorber – a tower or column used to remove various products or emissions from a natural gas stream, which provides contact between the gas and the absorption oil

10. Lean-Oil Absorption Primary Systems
2. Rejection System

11. Lean-Oil Absorption Primary Systems
2. Rejection System
Gets rid of the methane retained by the recovery system and cannot not be sold as a liquid product
This is called demethanizing
Methane is rejected in two steps
Hot rich-oil flash tank (p. 104)
Rich-oil demethanizer (ROD)(p. 105)
ROD tower – top strips & bottom reasorbs.
Stripper – the process of removing light components in the gas through vaporization.

12. Lean-Oil Absorption Primary Systems
3. Separation System

13. Lean-Oil Absorption Primary Systems
3. Separation System
Fluid from ROD bottoms is fed to the separation system where the product is separated from the lean oil.
Product goes out the top of the still and lean oil out the bottom
This is called distillation
Still – a product condensing facility or vessel in which hydrocarbon distillation is done. Also called a rich-oil fractionator.

14. Lean-Oil Absorption Primary Systems
Figure 7.3
Figure 7.8
Figure 7.12