NATURAL GAS DEHYDRATION AT HYDRAULIC FRACTURING SITES USING TRIETHYLENE GLYCOL (TEG)
With
all the compressor stations being built in the United States to help transport
the natural gas to the point of destination, we often here the term glycol
dehydration unit. Natural gas contains a
certain amount of water. That water must
be removed, along with other constituents, prior to be allowed to enter the
pipeline. This is to prevent pipeline
corrosion and mechanical damage to downstream equipment.
Triethylene
glycol (TEG) is the predominant liquid desiccant employed to remove water vapor
from natural gas streams.
Most
natural gas producers use Triethylene glycol (TEG) to remove water from the
natural gas stream in order to meet the pipeline quality standards. This process is required to prevent hydrates
formation at low temperatures or corrosion problems due to the presence of
carbon dioxide or hydrogen sulfide (regularly found in natural gas).
Dehydration,
or water vapor removal, is accomplished by reducing the inlet water dew point
(temperature at which vapor begins to condense into a liquid) to the outlet dew
point temperature which will contain a specified amount of water.
Absorption
of water vapor in the TEG is the common method. The wet gas is brought into contact with dry
glycol in an absorber in a packed or tray section. Water vapor is absorbed in the glycol and
consequently, its dew point reduces. The
wet rich glycol then flows from the lower section of the absorber to a
regeneration system in which the entrained gas is separated and fractionated in
a column and reboiler. The dry gas exits
at the top of the absorber. The heating
allows boiling off the absorbed water vapor and the water dry lean glycol is
cooled (via heat exchange) and pumped back to the absorber.
Rich
glycol passes through a reflux coil in the reboiler still, preheats in a
glycol/glycol exchanger and then enters the flash tank. In the flash tank,
hydrocarbons and dissolved gas are separated from the rich glycol. The rich
glycol exits the flash tank and passes through a charcoal filter, sock filter,
and is subsequently preheated in another glycol/glycol exchanger prior to
entering the reboiler through the reboiler still column. The rich glycol is
heated to approximately 400°F as water is boiled off and exits through the vent
atop the reboiler still.
Lean
glycol is cooled prior to being pumped through a glycol/gas heat exchanger and
into the absorber to continue the process. Water removal depends on several
factors such as: gas pressure and temperature, gas composition, glycol
circulation rate, glycol purity and efficiency of glycol to gas contact.
CONDENSATE
STABILIZATION
Many
natural gas fields, such as the hydraulic fracturing fields of North Dakota,
also produce a light hydrocarbon liquid product (condensate) along with the gas.
For this liquid to be shipped safely in
atmospheric pressure trucks and to avoid high vaporization losses, the liquid
is stabilized using heat and a fraction tower to set the liquid vapor pressure
within acceptable limits. The light products removed from the heavier liquid
can be used as fuel and/or many other uses. The stabilized liquid is cooled
before going to storage tanks.
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Engineering, Consulting & Forensics (MECF)
Providing
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Services
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Tel.:
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E-mail:
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