The Absorption Method

This process is similar to adsorption by dehydration. The natural gas is passed through an absorption tower and brought into contact with the absorption oil that soaks up a large amount of the NGLs (EIA 2006). The oil containing NGLs exits the absorption tower through the bottom. The rich oil is fed into lean oil stills, and the mixture is heated to a temperature above the boiling point of the NGLs and below that of the oil. The oil is recycled and NGLs are cooled and directed to an absorption tower. This process allows recovery of up to 75% of butanes and 85-90% of pentanes and heavier molecules from the natural gas stream. If the refrigerated oil absorption method is used, propane recovery can reach up to 90%. Extraction of the other, heavier NGLs can reach close to 100% using this process. Alternatively, the fractioning tower can also be used where boiling temperatures vary from the individual hydrocarbons in the natural gas stream. The process occurs in stages as the gas stream rises through several towers where heating units

C3 + hydrocarbons

C3 + hydrocarbons

pipeline

Figure 12.8 Membrane system for NGL recovery and dew point control (redrawn from MTR 2007).

pipeline

Figure 12.8 Membrane system for NGL recovery and dew point control (redrawn from MTR 2007).

raise the temperature of the stream, causing the various liquids to separate and exit into specific holding tanks (EIA 2006).

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