Transcript Final Stages NGL Separation - EO-206-Gas

Fractionation Unit Overview
3 Towers: Deethanized,
Depropanizer, and Debutanizer

NGL’s are fed to this unit from cryogenic unit.
• Remember natural gas liquids contains an ethane, propane,
butane all mixture.

The first column is the deethanizer.
• Why? Because ethane will be removed from the other products
and will exit out the top of this tower.
• How? NGL’s enter the deethanizer tower where they will be
heated up by a reboiler just enough to vaporize ethane.

The reboiler transfers heat via steam or hot oil;
dependant on the plant configuration. (Usually hot
oil)
• Reboiler heats the NGL’s just enough to vaporize ethane
allowing it to travel up the tower. The ethane vapor leaves the
top of this tower to a condenser.
 The
condenser uses cooling water for the
removal of heat from the ethane causing
it to condense.
 Liquid ethane flows to the reflux
drum. Where some ethane is sent back
to the column as reflux while some leaves
the system as product.
 Again, the purpose of reflux is to improve
product purity by prohibiting other
products from leaving with the ethane.

What doesn’t get vaporized is going to travel out
of the bottom of the deethanizer tower.
• Propane and Butane are still present in the NGL stream

This botttom feed travels to the Depropanizer
vessel.
• The depropanizer operates in the same manner as the
previous tower. (higher temperature)
• A reboiler supplies just enough heat to vaporize propane
from the NGL mixture.

Propane escapes from the top as vapor and
travels to an Air Cooled heat exchanger.
 The
Air Cooled heat exchanger is another
form of a condenser used to liquefy
propane vapors into a liquid state.
 This air cooled heat exchanger utelizes a
fan to move air across the tubes cooling the
propane vapors and allowing them to
condense.
 The condensed vapors (liquid) flow to a
reflux drum where some product is sent
back to depropanizer as reflux while some
is sent out as product.
 The
remaining NGL stream leaving the
bottom of the Depropanizer contains butane
and natural gasoline which will be
separated by the Debutanizer tower.
• The butane leaves the top of this column and natural
gasoline exits the bottom.
• The NGL steam is heated in the debutanizer by a
reboiler.
• Butane vaporizes and travels up and out the top of
this column.
 Butanes
vapors enter an air cooled heat
exchanger.
 This
heat exchanger condenses the butane;
causing it to liquefy.
• The liquid butane product flows to the reflux drum
where some product can sent back to the column as
reflux and some can be sent out of the system as
product.
 Butane
product can be further refined in
some plants.
• It can be sold as butane product or it can be to a
butane splitter tower or deisobutanizer.
• Which separates butane from isobutene in a similar
fasion.
 The
Bottom’s product of the debutanizer
is natural gasoline.
• Natural Gasoline is a product of this unit as
well.
 Our
discussion today has centered
around the process of fractionation.
• Remember: Fractionation columns are very
similar to distillation towers. The key difference
being that the vaporization points within a
fraction tower are much tighter than the
vaporization points in a distillation tower.
 The
towers on this page are the
Dethanizer, Depropanizer and
Debutanizer. The Dethanizer has ethane
leaving the top, the Depropanizer has
propane going exiting the top and the
Debutanizer has butane leaving the
top. So, each tower is named for what
product is exiting it as an overhead
product and not a bottoms product.