U.S. patent application number 16/348186 was filed with the patent office on 2019-09-12 for method for cryogenically separating a natural gas stream.
The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des Procedes Georges Claude. Invention is credited to Nicolas CHANTANT, Vincent FAUCHER, Henri PARADOWSKI, Christophe SZAMLEWSKI, Paul TERRIEN.
Application Number | 20190277566 16/348186 |
Document ID | / |
Family ID | 57583364 |
Filed Date | 2019-09-12 |
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United States Patent
Application |
20190277566 |
Kind Code |
A1 |
TERRIEN; Paul ; et
al. |
September 12, 2019 |
METHOD FOR CRYOGENICALLY SEPARATING A NATURAL GAS STREAM
Abstract
A method for cryogenically separating a natural gas supply
stream into a gas containing the most volatile compounds of the
supply stream, and a liquid product containing the heaviest
compounds at least including the following. Introducing an at least
partially condensed stream into an absorption column at an
introduction stage in the lower part of said absorption column,
thus producing, at the top, a gaseous stream that contains the most
volatile compounds and, the bottom, a liquid product. Introducing
the liquid product into a fractionation column in order to obtain,
in the bottom of the fractionation column, a liquid product that
contains the heaviest compounds of the supply stream and, at the
top of the fractionation column, a distillate that is at least
partially condensed in a second heat exchanger system
Inventors: |
TERRIEN; Paul; (Paris,
FR) ; CHANTANT; Nicolas; (Vincennes, FR) ;
PARADOWSKI; Henri; (Pluvigner, FR) ; SZAMLEWSKI;
Christophe; (Combs la Ville, FR) ; FAUCHER;
Vincent; (Taverney, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Family ID: |
57583364 |
Appl. No.: |
16/348186 |
Filed: |
November 8, 2017 |
PCT Filed: |
November 8, 2017 |
PCT NO: |
PCT/FR2017/053045 |
371 Date: |
May 8, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 3/0645 20130101;
F25J 2230/60 20130101; F25J 2210/60 20130101; F25J 3/0233 20130101;
F25J 2240/02 20130101; F25J 3/064 20130101; F25J 2200/70 20130101;
F25J 2200/04 20130101; F25J 2235/60 20130101; F25J 3/0209 20130101;
F25J 2200/74 20130101; C10G 2400/26 20130101; F25J 3/065 20130101;
F25J 2250/02 20130101; F25J 3/0635 20130101; F25J 3/0242 20130101;
C10G 5/06 20130101; F25J 2200/78 20130101; C10G 2300/1025 20130101;
F25J 2205/10 20130101; F25J 2200/02 20130101; F25J 2205/04
20130101; F25J 3/061 20130101 |
International
Class: |
F25J 3/06 20060101
F25J003/06; C10G 5/06 20060101 C10G005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2016 |
FR |
1660774 |
Claims
1.-5. (canceled)
6. A process for the cryogenic separation of a natural gas feed
stream into a gas containing the most volatile compounds of the
feed stream and into a liquid product containing the heaviest
compounds of the feed stream, comprising at least the following
stages: Stage a): at least partial condensation of a natural gas
feed stream in a first heat-exchange system; Stage b): introduction
of the at least partially condensed stream resulting from stage a)
into an absorption column at an introduction level located in the
lower part of said absorption column, said absorption column
producing, at the top, a gas stream containing the most volatile
compounds and, at the bottom, a liquid product; Stage c):
introduction of the liquid product resulting from stage b) into a
fractionation column in order to obtain, in the fractionation
column bottom, a liquid product containing the heaviest compounds
of the feed stream and, at the fractionation column top, a
distillate, at least partially condensed in a second heat-exchange
system; Stage d): introduction, at a level located in the upper
part of the absorption column, of the gas phase of the condensed
distillate resulting from stage c) as feed stream of the absorption
column; wherein the gas stream produced at the absorption column
top resulting from stage b) is employed in order to condense, in
the second heat-exchange system, the distillate resulting from the
top of the fractionation column.
7. The process according to claim 6, further comprising a stage,
prior to stage d), of condensation of the distillate resulting from
the top of the fractionation column in a third heat-exchange
system.
8. The process as claimed in claim 6, wherein all of the gas stream
produced at the absorption column top resulting from stage b) is
employed in order to condense, in the second heat-exchange system,
the distillate resulting from the top of the fractionation
column.
9. The process as claimed in claim 6, wherein the gas stream
produced at the absorption column top resulting from stage b) is
separated into several streams, at least one of which is employed
in order to condense, in the second heat-exchange system, the
distillate resulting from the top of the fractionation column.
10. The process as claimed in claim 6, wherein the liquid phase of
the condensed distillate resulting from stage c) is used as reflux
at the top of the fractionation column.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a 371 of International PCT Application
No. PCT/FR2017/053045, filed Nov. 8, 2017, which claims priority to
French Patent Application No. 1660774, filed Nov. 8, 2016, the
entire contents of which are incorporated herein by reference.
BACKGROUND
[0002] The present invention relates to a process for the cryogenic
separation of a natural gas feed stream into a gas containing the
most volatile compounds of the feed stream and into a liquid
product containing the heaviest compounds of the feed stream.
[0003] During the exploitation of natural gas deposits, numerous
stages may be provided. A relatively conventional stage after the
drying and the withdrawal of the impurities is the separation of
the liquids associated with the natural gas (NGLs).
[0004] It is often desirable to separate the heavy hydrocarbons, or
more generally the NGL (Natural Gas Liquids), from the natural gas,
for example such as ethane, butane, propane or C5+ and C6+(that is
to say, having at least five carbon atoms and having more than six
carbon atoms) hydrocarbons.
[0005] This stage can have many advantages but often it is a matter
of upgrading various products (ethane, propane, and the like) which
are generally sold at a much higher price than the natural gas
product. It is in particular common to sell hydrocarbons having a
least three carbon atoms as propane, butane and condensate
products.
[0006] Many industrial installations have been described which make
it possible to fractionate gas feedstocks into a residual gas
containing the most volatile compounds of the feedstock and into a
liquid product containing the heaviest compounds of the feedstock,
this being done for the purpose of obtaining, in said liquid
product, a given component of the feedstock with a high degree of
recovery.
[0007] In this regard, mention may be made, for example, of the
recovery of liquefied petroleum gas (hydrocarbons therein having
three or four carbon atoms) from natural or refinery gas, the
recovery of ethane intended in particular to feed steam cracking
units, or the desulfurization and the gasoline extraction of
natural gases by recovery of the sulfur-comprising compounds, such
as carbon oxysulfide and mercaptains Several technologies exist for
producing hydrocarbons having at least three carbon atoms from
natural gas.
[0008] One of the most effective is a process employing a
two-column turbo-expander in which the first column is an absorber
dedicated to forcing the recovery of as much propane as possible
and the second column is a de-ethanizer.
[0009] The condensation of the de-ethanizer top stream is often
carried out in part with the fluid coming from the absorber bottom.
This fluid exits partially evaporated in order to enter the main
exchange line requiring a two-phase introduction.
[0010] This renders the process very complex in order to provide
good distribution in this heat exchanger.
[0011] Such a process is described in the documents U.S. Pat. Nos.
4,690,702 and 5,114,450.
[0012] The inventors of the present invention have thus developed a
solution which makes it possible to solve the problems raised
above.
SUMMARY
[0013] A subject matter of the present invention is a process for
the cryogenic separation of a natural gas feed stream into a gas
containing the most volatile compounds of the feed stream and into
a liquid product containing the heaviest compounds of the feed
stream, comprising at least the following stages: [0014] Stage a):
at least partial condensation of a natural gas feed stream in a
first heat-exchange system; [0015] Stage b): introduction of the at
least partially condensed stream resulting from stage a) into an
absorption column at an introduction level located in the lower
part of said absorption column, said absorption column producing,
at the top, a gas stream containing the most volatile compounds
and, at the bottom, a liquid product; [0016] Stage c): introduction
of the liquid product resulting from stage b) into a fractionation
column in order to obtain, in the fractionation column bottom, a
liquid product containing the heaviest compounds of the feed stream
and, at the fractionation column top, a distillate, at least
partially condensed in a second heat-exchange system; [0017] Stage
d): introduction, at a level located in the upper part of the
absorption column, of the gas phase of the condensed distillate
resulting from stage c) as feed stream of the absorption
column;
[0018] characterized in that the gas stream produced at the
absorption column top resulting from stage b) is employed in order
to condense, in the second heat-exchange system, the distillate
resulting from the top of the fractionation column.
[0019] According to other embodiments, another subject-matter of
the invention is: to A process as defined above, characterized in
that it comprises a stage, prior to stage d), of condensation of
the distillate resulting from the top of the fractionation column
in a third heat-exchange system.
[0020] A process as defined above, characterized in that all of the
gas stream produced at the absorption column top resulting from
stage b) is employed in order to condense, in the second
heat-exchange system, the distillate resulting from the top of the
fractionation column.
[0021] A process as defined above, characterized in that the gas
stream produced at the absorption column top resulting from stage
b) is separated into several streams, at least one of which is
employed in order to condense, in the second heat-exchange system,
the distillate resulting from the top of the fractionation
column.
[0022] A process as defined above, characterized in that the liquid
phase of the condensed distillate resulting from stage c) is used
as reflux at the top of the fractionation column.
[0023] Thus, the solutions of the process which is a subject matter
of the present invention make it possible to dispense with the
two-phase entry, or at least limit to a very high LN (liquid/vapor)
ratio, of the stream withdrawn at the absorption column bottom
before introducing it into a main heat-exchange system prior to its
introduction into the fractionation column.
[0024] Solution A--The single use of the top stream of the
absorption column for condensing the top stream of the
fractionation column in a dedicated exchanger has in particular the
advantages: the suppression of the two-phase entry of the stream
withdrawn at the absorption column bottom into the main exchange
line, and the limitation of the delivery pressure of the pump at
the outlet of the bottom of the absorption column.
[0025] Solution B--Separation of the top fluid of the absorption
column into several streams, at least one of which provides the
condensation in the top condenser of the fractionation column: this
results in a better regulation of the fractionation column top
condenser.
[0026] Solution C--Condensation of the reflux fluid of the
absorption column in a dedicated exchanger by virtue of the top of
the absorption column only: this makes possible a simplification of
the main exchange line.
[0027] The stream of hydrocarbons to be liquefied is generally a
stream of natural gas obtained from natural gas fields, oil
reservoirs or a domestic gas network in which the gas is
distributed via pipelines.
[0028] Generally, the natural gas stream is essentially composed of
methane. Preferably, the feed stream comprises at least 80 mol % of
methane. Depending on the source, the natural gas contains
quantities of hydrocarbons heavier than methane, such as, for
example, ethane, propane, butane and pentane and also certain
aromatic hydrocarbons. The natural gas stream also contains
nonhydrocarbon products, such as H.sub.2O, N.sub.2, CO.sub.2,
H.sub.2S and other sulfur-comprising compounds, mercury and
others.
[0029] The feed stream containing the natural gas is thus
pretreated before being introduced into the heat exchanger making
possible the first stage of cooling of the process which is a
subject matter of the present invention. This pretreatment
comprises the reduction and/or the removal of the undesirable
components, such as CO.sub.2 and H.sub.2S, or other stages, such as
the precooling and/or the pressurization. Given that these measures
are well known to a person skilled in the art, they are not
described in further detail here.
[0030] The expression "natural gas" as used in the present patent
application relates to any composition containing hydrocarbons,
including at least methane. This comprises a "crude" composition
(prior to any treatment or scrubbing) and also any composition
which has been partially, substantially or completely treated for
the reduction and/or removal of one or more compounds, including,
but without being limited thereto, sulfur, carbon dioxide, water,
mercury and certain heavy and aromatic hydrocarbons.
[0031] The heat exchanger can be any heat exchanger, any unit or
other arrangement suitable for making possible the passage of a
certain number of streams, and thus making possible at least one
system for direct or indirect exchange of heat between one or more
liquid coolant lines and one or more feed streams.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] For a further understanding of the nature and objects for
the present invention, reference should be made to the following
detailed description, taken in conjunction with the accompanying
drawings, in which like elements are given the same or analogous
reference numbers and wherein:
[0033] FIG. 1 illustrates the diagram of a process according to the
state of the art as described in the preamble of the present
description.
[0034] FIG. 2 illustrates a diagram of an embodiment of an
implementation of a process according to the invention.
[0035] FIG. 3 illustrates a diagram of a specific embodiment of an
implementation of a process according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] In FIG. 1, a feed stream of natural gas 1 is introduced into
a main heat exchanger 2 in order to be cooled. The gas thus cooled
3 is partially condensed and introduced into a phase separator 4.
The gas phase 5 at the phase separator 4 top is introduced into a
turbine 6 in order to recover the expansion energy and to condense
a portion of the stream 5, and is then introduced into an
absorption column 7 comprising a lower part 7' and an upper part
7''. The liquid phase 8 at this phase separator 4 bottom is
introduced after expansion 9 into the absorption column 7. The
absorption column produces a liquid 10 at the column bottom and a
residual gas 11 at the column top. The liquid 10 is reheated in a
heat exchanger 12 in which it is partially evaporated. The stream
thus reheated 13 is subsequently introduced into the main exchanger
2; this introduction 13 is then strongly a two-phase
introduction.
[0037] At the absorption column 7 top, the residual gas 11, which
contains only the products more volatile than ethane, is reheated
in the main heat exchanger 2; the stream which results therefrom 14
is subsequently compressed and sent to a treatment unit A.
[0038] The stream 13' at the heat exchanger 2 outlet resulting from
the bottom of the absorption column 7 is introduced into a
fractionation column 15. This column 15 produces, at the bottom 16,
a reboiled liquid product 18 using a reboiler 17 in order to obtain
a liquid rich in propane and depleted in ethane. A gas 20 is
produced at the fractionation column 15 top 19. This gas 20 is
condensed in the heat exchanger 12 and the product 21 which exits
from this exchanger 12 is introduced into a phase separator 22. The
gas phase 23 at the top of the phase separator 22 acts as reflux in
the absorption column 7. The liquid 25 at the bottom of the phase
separator 22 acts as reflux 26 at the top of the fractionation
column 15. A pump 30 is necessary to pump the liquid 25.
[0039] The problem related to the two-phase introduction of the
stream 13 into the main heat exchanger 2 is solved by the process
which is a subject matter of the present invention.
[0040] This is because, in FIG. 2, the residual gas 11 at the
absorption column 7 top which contains only the products more
volatile than ethane is reheated in a heat exchanger 27 located
immediately downstream of the top of said column 7. The gas thus
reheated 28 at the outlet of the heat exchanger 27 is then
introduced into the heat exchanger 12 at the top of the
fractionation column before being introduced into the main
exchanger 2 in order to constitute the stream 14 subsequently
compressed and sent to a treatment unit A.
[0041] Unlike what is illustrated in FIG. 1, the liquid stream 10
at the bottom of the absorption column 7 is pumped using a pump 29
and then directly introduced 13 into the main exchanger 2 in order
to form the stream 13' which is sent to the fractionation column
15.
[0042] The advantages of such a process are as follows: Energy
efficiency: the pressure of the absorption column 7 is thus
maximized.
[0043] Simplicity of the exchangers: none of the three heat
exchangers 2, 27, 12 has two-phase introduction; the temperature
differences in cold fluids and hot fluids are reasonable (i.e.,
less than 25-30.degree. C., differences beyond which exchangers of
brazed aluminum type might be damaged).
[0044] Alternatively, other configurations are possible, such as
the following, for example: the heat exchanger 12 can be fitted
inside the fractionation column 15. The exchanger 27 can for its
part be fitted directly above the absorption column 7. The
advantage with respect to installing it on the ground is that of
avoiding a pump for lifting the reflux.
[0045] Another embodiment is represented diagrammatically in FIG.
3. In comparison with the diagram of FIG. 2, the modification
consists of a separation of the fluid 11 at the top of the
absorption column 7 into several streams 11' and 11''. The stream
11' provides the condensation in the condenser 12 at the to
fractionation column 15 top.
[0046] The stream 11' is introduced into the condenser 12 at the
fractionation column 15 top and is then introduced into the main
exchanger 2. The stream 11'' is directly introduced into the main
exchanger 2.
[0047] The bottom liquid 10 of the absorption column 7 is pumped
and then directly introduced into the main exchanger 2.
[0048] A control valve can precisely control the fraction sent to
the top of the fractionation column 15, making possible precise and
effective control of the unit.
Advantage
[0049] Better regulation of the fractionation column 15 top
condenser 12.
[0050] Minimization of the number of items of equipment while
maintaining a single-phase introduction of the liquid 13 from the
absorption column into the heat exchanger 2.
[0051] Alternatively, other configurations are possible, such as
the following, for example: the heat exchanger 12 can be fitted
directly above the absorption column 7. The advantage with respect
to installing it on the ground is that of avoiding a pump for
lifting the reflux.
[0052] In addition to this, the invention can advantageously be
combined with an integration between the columns and the
exchangers. In the case corresponding to FIGS. 2 and 3, a
configuration which makes it possible to integrate, in one and the
same module, the column 15 and the exchanger 12, while avoiding the
use of the pump 30, for example, and while avoiding a shell
dedicated to the exchanger 12 is provided. In that case, said
module is characterized in that a separator is installed directly
above the fractionation column 15, above which separator a
condenser is installed. The condenser is connected to the top of
the fractionation column and to the separator on the condensation
side. The bottom of the separator is connected to the fractionation
column (indirectly with a valve between the two, typically). Module
is thus understood to mean a single structure comprising the column
15, the separator and the heat exchanger 12.
[0053] It will be understood that many additional changes in the
details, materials, steps and arrangement of parts, which have been
herein described in order to to explain the nature of the
invention, may be made by those skilled in the art within the
principle and scope of the invention as expressed in the appended
claims. Thus, the present invention is not intended to be limited
to the specific embodiments in the examples given above.
* * * * *