U.S. patent number 3,846,993 [Application Number 05/111,330] was granted by the patent office on 1974-11-12 for cryogenic extraction process for natural gas liquids.
This patent grant is currently assigned to Phillips Petroleum Company. Invention is credited to Bruce L. Bates.
United States Patent |
3,846,993 |
Bates |
November 12, 1974 |
CRYOGENIC EXTRACTION PROCESS FOR NATURAL GAS LIQUIDS
Abstract
A process for the cryogenic extraction of natural gas liquids
through the vaporization and direct heat exchange of liquefied
natural gas with a wet natural gas.
Inventors: |
Bates; Bruce L. (Bartlesville,
OK) |
Assignee: |
Phillips Petroleum Company
(Bartlesville, OK)
|
Family
ID: |
22337879 |
Appl.
No.: |
05/111,330 |
Filed: |
February 1, 1971 |
Current U.S.
Class: |
62/625 |
Current CPC
Class: |
F25J
3/0214 (20130101); F25J 3/0209 (20130101); F25J
3/0238 (20130101); F25J 3/0233 (20130101); F25J
2260/10 (20130101); F25J 2200/70 (20130101); F25J
2205/30 (20130101); F25J 2200/02 (20130101); F25J
2270/904 (20130101); F25J 2205/04 (20130101); F25J
2210/62 (20130101) |
Current International
Class: |
F25J
1/00 (20060101); F25J 3/02 (20060101); F25J
1/02 (20060101); F25j 003/06 (); F25j 003/02 () |
Field of
Search: |
;62/17,20,23,24,27,28,29,43,40 ;208/340 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sofer; Jack
Claims
What I claim is:
1. A process for the extraction of ethane and heavier hydrocarbons
from a wet natural gas containing methane, ethane and propane and
the vaporization of a portion of a liquefied natural gas containing
methane, ethane and propane, comprising:
passing a first stream of the liquefied natural gas and a second
stream of the wet natural gas into a mixing zone so as to vaporize
a portion of the liquefied natural gas and condense a portion of
the wet natural gas;
removing from the mixing zone a third stream comprising the
vaporized liquefied natural gas and the wet natural gas which is
not condensed;
removing from the mixing zone a fourth stream comprising the
condensed wet natural gas and the liquefied natural gas which is
not vaporized;
passing the fourth stream to a demethanizer;
removing a fifth stream comprising methane from the demethanizer;
and
removing a sixth stream from the demethanizer comprising
hydrocarbons in the fourth stream heavier than methane.
2. The process of claim 1 wherein the third stream is passed in
indirect heat exchange relationship with the second stream.
3. The process of claim 2 wherein the second stream is removed from
a pipeline, and at least a portion of the third stream and at least
a portion of the fifth stream are returned to the pipeline.
4. The process of claim 3 wherein said wet natural gas comprises
about 95 percent methane.
5. The process of claim 1 wherein the ratio of liquefied natural
gas to the wet natural gas is in the range of about 10 to about 20
percent by volume.
Description
This invention relates to a process for the removal of natural gas
liquids through cryogenic extraction. In another aspect, this
invention relates to a process for vaporizing liquefied natural gas
by direct heat exchange with a wet natural gas stream.
Particularly, this invention relates to a process for the
utilization of liquefied natural gas as a heat sink for cryogenic
extraction purposes.
It is increasingly the practice to liquefy natural gas for
convenient transport to places where it can be utilized. On
arrival, liquefied natural gas is vaporized and used as fuel or for
other purposes. At the same time, the considerable expense of
liquefying the natural gas in the first instance can be partially
recovered by utilizing the liquefied natural gas as a heat sink,
namely by utilizing the cold inherent in the liquefied natural gas
which is made available for use in the course of the vaporization
process.
Various methods for liquefying gases such as natural gases,
principally methane, and the like, have either been proposed or
used. Vaporizing liquefied natural gases after transporting or
storing them at atmospheric pressure is not a simple matter. If
part of the liquefied gas is burned to supply all of the heat
required to vaporize the gas, up to 2 percent by volume of the gas
can be required as fuel. Further, it is impractical to heat the
liquefied gas with air by means of air fin heat exchangers because
of the heavy frost formed during the heating steps. Thus, it can be
seen that there is a distinct need for a practical and economical
process for vaporizing the liquefied gas at the place of
utilization and also to recover and utilize the refrigeration
obtainable during the vaporization process.
It is an object of this invention to provide an economical and
efficient process for the separation of natural gas liquids from
pipeline natural gas and liquefied natural gas sources. It is
another object of this invention to provide a process for the
efficient vaporization of liquefied natural gas utilizing the
liquefied natural gas as a heat sink for the above cryogenic
extraction.
Other aspects and objects of this invention will hereinafter appear
in the examples and claims included hereinbelow. Accordingly, the
problems discussed above, associated with the prior art methods of
vaporizing liquefied gases, are resolved by the practice of the
present invention.
The process of this invention also involves a cryogenic extraction
method for separating components of natural gas streams and more
particularly, a method of separating: (1) methane and varying
amounts of ethane, (2) ethane and/or propane and higher boiling
point hydrocarbon constituents, and (3) heavier hydrocarbons found
in natural gas pipeline streams. Many processes have been developed
and numerous plants constructed to accomplish the separation set
forth above. These processes principally involve external
refrigeration, cooling by expansion of natural gas, and/or solvent
absorption. The aforementioned separation processes known to the
art have failed to utilize or recognize the possibility of
separating natural gas liquids through cryogenic extraction by the
blending of liquefied natural gas with pipeline natural gas.
In accordance with the present invention, there is provided an
improved process for the cryogenic extraction of natural gas
liquids and for the vaporization of liquefied natural gas. In
practicing my invention, a wet natural gas source, for example,
from a pipeline stream is chilled by direct heat exchange with
liquefied natural gas within a suitable vessel which not only
vaporizes the liquefied natural gas but performs a cryogenic
extraction of natural gas liquids. The resulting lean natural gas
stream is taken from the mixing tank and returned to the natural
gas transmission pipeline. The natural gas liquids resulting from
the cryogenic extraction process are removed to a demethanizer
wherein separated methane is either used for plant fuel or returned
to the natural gas transmission pipeline. The natural gas liquids
are removed from the demethanizer equipment for further
fractionation separation and storage.
The present invention will now be illustrated by the following
calculated example, wherein reference is made to the accompanying
drawing which is a flow diagram for practicing the invention.
Example
A wet natural gas stream 1 under a pressure of about 850-1000 psia
and an ambient temperature consisting of methane, 95 mole percent;
ethane, 3 mole percent; propane, 0.65 mole percent; hydrocarbons of
at least 4 carbon atoms per molecule representing in total 0.15
mole percent; carbon dioxide, 0.80 mole percent; and nitrogen, 0.40
mole percent; enters the system at a constant rate of one million
cubic feet per day (mcfd). The pipeline gas flows through a gas
line 2 and passes into the warm side of heat exchanger 3. The
pipeline gas possesses an approximate combustion energy level of
1,035 BTU per cubic foot. The thus cooled, wet pipeline natural gas
stream flows into a mixing and natural gas liquids collector
apparatus 7 wherein it is contacted directly with a liquefied
natural gas stream 5. The liquefied natural gas stream 5 is under
an equivalent pressure as that of the pipeline gas, at a
temperature of about -258.degree.F and consists of methane, 88 mole
percent; ethane, 11 mole percent; and propane, 1 mole percent. The
liquefied natural gas stream 5 as described above enters the mixing
apparatus 7 at a rate of 142,128 mcfd with the gas possessing an
approximate combustion energy level of 1,108 BTU per cubic foot.
The liquefied natural gas is mixed with the wet pipeline natural
gas in apparatus 7 wherein direct heat exchange and cryogenic
extraction occurs. In the mixing and natural gas liquids collector
apparatus 7, the liquefied natural gas is vaporized at least in
part and the wet natural gas is condensed at least in part,
resulting in a cryogenic extraction of the natural gas liquids
comprising from about 3 to about 35 mole percent of both the wet
and the liquefied natural gas streams. The resulting lean gas
leaves the mixing and natural gas liquids collector apparatus 7
through line 9, and separated natural gas liquids leave the mixing
and natural gas liquids collector apparatus 7 through line 11. The
lean natural gas flows through line 9 to the heat exchanger 3
wherein it passes into the cold side of the heat exchanger 3. The
lean natural gas is compressed in compressor 21 and is returned
through line 23 to the natural gas transmission pipeline 25.
The natural gas liquids resulting from the cryogenic extraction are
transferred through line 11 to a demethanizer 13 wherein methane is
removed through line 17 with ethane and heavier hydrocarbons being
removed through line 15 to fractionation treatment and storage. The
methane resulting from the demethanizer 13 flows through line 17
and is either fed through a plant fuel outlet 18 for plant
consumption or continues to compressor 19 before being returned to
the natural gas transmission pipeline 25. The natural gas
transmission pipeline 1 has a valve means 24 for regulating
pipeline flow as offset by plant requirements.
Exemplary of the above system would include a calculated example
having a liquefied natural gas (LNG) volume of 142,128 mcfd
compared to one million mcfd of wet natural gas. The ratio by
volume of LNG to wet natural gas would be 142,128 as compared to
one million; therefore, the LNG represents 14.2 percent by volume
of the total feed. Altering the ratio of LNG to wet natural gas
feed will alter the percentage of the various hydrocarbons actually
recovered. This ratio could vary over a fairly wide range from
about 10 to about 20 percent by volume.
The following extractions would be possible with the conditions as
described hereinabove and are established for exemplary purposes:
ethane, 75 percent; propane 95 percent; butane 98 percent; pentanes
+99 percent; wherein the percentages are based on percent by
volume. Economics and other needs will allow some reduction in the
percentages of ethane and propane recovered. The invention permits
the recovery of natural gas liquids not only in the feed gas but
also in the LNG stream. The calculated figures, based on conditions
disclosed and with extraction levels as shown above, are: total
extraction shrink from feed gas stream and LNG stream = 46,836
mcfd; total feedgas + LNG = 1,142,128 mcfd; volume percent NGL
recovered to feedgas = LNG = 4.1 percent.
It will be apparent that the embodiments shown are only exemplary
and that various modifications can be made in the construction and
arrangement of this disclosure within the scope of my invention as
defined by the appended claims.
* * * * *