Decarbonisation Technology May 2022 Issue

Lean fuel/process gas

Increase lean oil circulation rate with modest hydraulic inprovements, such as pump impeller / motor resizing and absorber internals replacement

Sponge oil (e.g. diesel, naphtha)

Process gas

Gas compressor


Rich oil to air cooler inlet

Make-up lean oil

Cooled lean oil (˜20˚C)

T = ambient

Reux condenser

Process unit

LPG product

Stripped gas

Improve front-end air cooler performance with fan speed increase or wavy ns


Process heat source

Refrigerated cooling water (˜10˚C)



C+ Product


Signicantly increase hydrocarbon recovery with lean oil chiller / cooling water exchangers. Steam-driven chillers are available if there is excess steam available in the facility

Reduce energy consumption by integrating de-ethaniser reboiler heat source with other hot process streams in facility (e.g. debutaniser bottoms)

Figure 3 Typical lean oil recovery process with potential recovery improvement upgrades in green

efficient range or has high recycle flow to prevent surge. Discussing rotor replacement or other modifications with the manufacturer can improve lead to augmented efficiency that improves recovery (by reducing outlet temperature) while reducing compressor horsepower simultaneously • Improving heat integration and recovery – using process heat for column reboiler duty or introducing an economiser in the refrigeration loop can, again, improve energy efficiency and recovery. Improving refrigeration compressor operation by converting to an electric machine or changing compressor parameters (for example, installing automatic unloaders on a reciprocating machine or increasing capacity to reduce chiller pressure) Lean oil separation plants are capable of less overall recovery than cryogenic separation, but this technology usually has significant room for recovery improvement above the original nameplate recovery. Often designed for ~50% propane recovery, these processes are capable of >80% propane recovery with the proper modifications. Lean oil plants work by absorption of heavy hydrocarbons in a packed or trayed absorber column, where a heavy gas is contacted with a liquid lean oil that is ‘lean’ in heavier

hydrocarbons. In the column, the heavy hydrocarbons are more soluble overall in the lean oil, resulting in a richer oil and leaner gas leaving the column. An example schematic is shown in Figure 3 , with the ultimate products being gas, LPG, and C5+ streams. Many opportunities for improvement are available that can elevate recovery to the next level. These are all depicted in green as possible improvements in the schematic and assume the desire to reject ethane while capturing maximum propane and propylene or heavier molecules. Improvements shown include: • Increased lean and sponge oil circulation – increasing absorbent oil circulation up to absorber hydraulic limits, along with absorber internals upgrading as needed, can drastically increase recovery • Reduced lean and sponge oil temperatures or changing solvent composition – use of cooling water or lean oil chilling to maintain lean/sponge oil temperatures around 20°C will generally lead to profitable recovery improvement; substituting with ‘leaner’ lean oil that is devoid of C3-C5 will also augment the equilibrium in the absorber • Advanced heat integration – replacement of steam condensing reboilers with process heat integration (for example, feed/effluent


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