Natural Gas Industry - Natural Gas Liquids (NGL) Plant

Natural Gas Industry - Natural Gas Liquids (NGL) Plant
Natural Gas Industry
Natural Gas Liquids (NGL) Plant
Process Gas Chromatograph Application Note
A Natural Gas Liquids (NGL) plant consists of a series of
fractionators whose purpose is to separate a mixture of light
hydrocarbons into various pure products. The NGL Plant typically
consists of a demethanizer, a deethanizer, a depropanizer, a
debutanizer, and a butane splitter. Other arrangements of
columns are possible for NGL Plants and also parallel columns
may be present for higher plant processing capacity.
monoxide and hydrogen). The ethane stream from an NGL Plant
is used as either fuel or as feedstock for chemical production (for
chemical production, the chemical desired is usually ethylene). The
isobutane product of an NGL Plant is usually used as feedstock for
an alkylation unit. The normal butane stream is used as feedstock
to a butamer unit (to make isobutane) or as fuel. The C5+ product
stream is used as a gasoline blending component.
The feed to a NGL Plant consists of a mixture of light hydrocarbons (methane, ethane, propane, isobutane, n-butane and C5+
or gasoline components) from the Natural Gas Plant. The NGL
is fed to the demethanizer where methane is removed (by
fractionation) as an overhead product. The bottoms product,
consisting of ethane and heavier compounds, is the feed to the
deethanizer. In the deethanizer, ethane is removed as an overhead product. Propane and heavier components leaves the
deethanizer as a bottoms product and fed to the depropanizer.
In the depropanizer, propane is removed as an overhead product
and butane and heavier compounds leaves the product and fed
to a debutanizer. In the debutanizer, isobutane and normal
butane are removed as an overhead product and fed to a C4
splitter. C5+ material leaves the debutanizer bottoms product. In
the C4 splitter, isobutane is separated (overhead product) from
the normal butane (bottoms product).
The operating objectives of an NGL Plant are typically a balance of
two objectives:
The methane stream from an NGL Plant is normally used as fuel
(i.e. used for its heating value) or as feedstock to a methane
reformer for the production of synthesis gas (a mixture of carbon
1.To maximize through-put while maintaining product quality.
2.To optimize product specifications versus utilities to maximize economic return.
Process gas chromatographs provide the compositional information
needed for the plant control system to meet these objectives.
Typical GC measurements
The number of gas chromatographs required varies on how many
products the plant wants to extract from the natural gas liquid feed
As mentioned above, the analyzers used in the NGL plant fall into
two categories. The first are those analyzers used for monitoring
the purity of the overhead product streams. The second type of
analyzers used is the column-to-column analyzers that monitor the
efficiency of each tower.
Natural Gas Liquids (NGL) Plant
Analyzer no.
Components measured
Measurement objective
Methane Product
Minimize losses of C2 in Methane Product stream
DeMethanizer Bottoms
C1, C2
Control C1 impurity in the Ethane Product stream
Ethane Product
Minimize losses of C3 in the Ethane Product stream
DeEthanizer Bottoms
C2, C3
Control C2 impurity in the Propane Product stream
Propane Product
DePropanizer Bottoms
C3, iC4
Minimize losses of iC4 in the Propane Product stream
Control C3 impurity in the isoButane Product stream
Minimize losses of iC5 in the n-Butane Product Stream
Control nC4 impurity in the C5+ Product stream
Control iC4 impurity in the n-Butane Product stream
DeButanizer Overhead
DeButanizer Bottoms
C4 Splitter Overhead
iC5, nC4
C4 Splitter Bottoms
Control nC4 impurity in the isoButane Product stream
For more information, please contact:
Siemens Industry, Inc.
7101 Hollister Road
Houston, TX 77040
Siemens Industry, Inc.
3333 Old Milton Parkway
Alpharetta, GA 30005
Subject to change without prior notice
Order No.: PIAAP-00007-0713
Printed in USA
© 2013 Siemens Industry, Inc.
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