U.S. patent application number 13/143474 was filed with the patent office on 2012-02-09 for process and appartus for removing gaseous contaminants from gas stream comprising gaseous contaminants.
Invention is credited to Cornelius Johannes Schellekens, Helmar Van Santem.
Application Number | 20120031143 13/143474 |
Document ID | / |
Family ID | 41165123 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120031143 |
Kind Code |
A1 |
Van Santem; Helmar ; et
al. |
February 9, 2012 |
PROCESS AND APPARTUS FOR REMOVING GASEOUS CONTAMINANTS FROM GAS
STREAM COMPRISING GASEOUS CONTAMINANTS
Abstract
An apparatus and process for removing gaseous contaminants from
a feed gas comprising methane and gaseous contaminants, in which
the feed gas is cooled to obtain a slurry comprising solid
contaminant, liquid contaminant and a methane enriched gaseous
phase. The slurry is introduced into a separation device from which
the methane enriched gaseous phase is removed. The slurry is
diluted with liquid contaminant and passed through a heat exchanger
wherein solid contaminant is melted into liquid contaminant. A
stream comprising liquid contaminant is removed from the separation
device at a position below the slurry level in the separation
device by means of a pump and at least part of the removed liquid
contaminant is recovered as a stream product and at least part is
recycled and introduced into the separation device to dilute the
slurry inside the separation device.
Inventors: |
Van Santem; Helmar;
(Amsterdam, NL) ; Schellekens; Cornelius Johannes;
(Amsterdam, NL) |
Family ID: |
41165123 |
Appl. No.: |
13/143474 |
Filed: |
January 6, 2010 |
PCT Filed: |
January 6, 2010 |
PCT NO: |
PCT/EP2010/050070 |
371 Date: |
September 16, 2011 |
Current U.S.
Class: |
62/617 |
Current CPC
Class: |
B01D 53/1462 20130101;
F25J 2210/70 20130101; F25J 3/0675 20130101; F25J 3/067 20130101;
F25J 2245/02 20130101; B01D 53/263 20130101; F25J 2240/40 20130101;
F25J 2220/66 20130101; F25J 3/0625 20130101; F25J 2220/64 20130101;
F25J 2240/60 20130101; C10L 3/10 20130101; F25J 2270/66 20130101;
B01D 2257/304 20130101; F25J 2215/04 20130101; B01D 53/1431
20130101; Y02C 20/40 20200801; F25J 3/061 20130101; F25J 2205/20
20130101; B01D 53/261 20130101; F25J 2270/60 20130101; C10L 3/102
20130101; Y02C 10/12 20130101; B01D 53/75 20130101; B01D 2257/7022
20130101; B01D 2258/06 20130101; F25J 3/0635 20130101; F25J 2240/02
20130101; B01D 53/002 20130101; F25J 2270/12 20130101; F25J 2290/42
20130101; B01D 2256/24 20130101; B01D 53/265 20130101 |
Class at
Publication: |
62/617 |
International
Class: |
F25J 3/00 20060101
F25J003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 8, 2009 |
EP |
09150250.0 |
Claims
1. A for removing gaseous contaminants from a feed gas stream which
comprises methane and gaseous contaminants, the process comprising:
1) providing the feed gas stream; 2) cooling the feed gas stream to
a temperature at which a slurry is formed which comprises solid
contaminant, liquid phase contaminant and a methane enriched
gaseous phase; 3) introducing the slurry as obtained in step 2)
into the top part or intermediate part of a cryogenic separation
device; 4) removing from the top part of the separation device a
stream which comprises the methane enriched gaseous phase; 5)
introducing a stream comprising liquid phase contaminant into the
intermediate part or the bottom part of the separation device or
both to dilute the slurry which has been introduced into the
separation device in step 3); 6) passing the diluted slurry as
obtained in step 5) through a heat exchanger which is arranged
inside the separation device, whereby at least part of the solid
contaminant present in the diluted slurry is melted into liquid
phase contaminant; 7) removing from the separation device by means
of a pump, preferably an eductor, a stream comprising liquid phase
contaminant, which pump is situated below the heat exchanger and
arranged outside or inside the separation device or partly inside
or outside the separation device; 8) removing a stream comprising
liquid phase contaminant from the separation device at a position
below the slurry level in the separation device; 9) separating the
stream of liquid phase contaminant obtained in step 8) into a
liquid product stream and a recirculation stream which is used as a
motive fluid in the eductor in the case that an eductor is used;
and 10) introducing into the separation device as described above
in step 5) at least part of the stream as removed in step 7) and at
least part of the recirculation stream as obtained in step 9).
2. A process according to claim 1, in which the pump, is arranged
outside the separation device and communicates with the separation
device.
3. A process according to claim 1 in which the feed gas stream is a
natural gas stream in which the gaseous contaminants are carbon
dioxide and/or hydrogen sulphide and/or C.sub.2+ hydrocarbons.
4. A process according to claim 3, in which the natural gas stream
comprises between 5 and 50 vol % of hydrogen sulphide.
5. A process according to claim 3 or 4, in which the natural gas
stream comprises between 5 and 90 vol % of carbon dioxide.
6. A process according to claim 1 in which the feed gas contains
between 0 and 25 vol % of C.sub.2+ hydrocarbons.
7. A process according to claim 1 in which the feed gas stream
comprises between 75 and 100 vol % of methane.
8. A process according to claim 1 in which the feed gas stream in
step 1) has a temperature between -20 and 150.degree. C.,
preferably between -10 and 70.degree. C., and a pressure between 10
and 250 bara, preferably between 80 and 120 bara.
9. A process according to claim 1 in which the cooling in step 2)
is done by isenthalpic expansion.
10. A process according to claim 1 in which the feed gas stream is
cooled in step 2) to a temperature between -40 and -100.degree.
C.
11. A process according to claim 1 in which substantially all the
solid contaminant present in the slurry of contaminants is melted
in step 6).
12. A process according to claim 1 in which in step 5) the stream
comprising liquid phase contaminant or the slurry contaminants
stream is introduced into the separation device at a level which is
lower than the level at which the methane enriched gaseous phase is
removed from the separation device in step 4).
13. A cryogenic separation device for carrying out the process
according to claim 1, which separation device comprises a top part,
an intermediate part and a bottom part; means to introduce a slurry
which comprises solid contaminant, liquid phase contaminant and a
methane enriched gaseous phase into the top or intermediate part of
the separation device; means to remove a methane enriched gaseous
phase from the top part of the separation device; means for
introducing a stream comprising liquid phase contaminant into the
top or intermediate part of the separation device to dilute the
slurry inside the separation device; a heat exchanger arranged
inside the separation device; a pump, which is arranged at a level
which is below the level at which the heat exchanger is arranged
for removing a stream comprising liquid phase contaminant from the
separation device; means to remove a stream comprising liquid phase
contaminant from the intermediate or bottom part of the separation
device; and means to separate liquid phase contaminant removed from
the intermediate or bottom part into a liquid product stream and a
recirculation stream for use as a motive fluid in the eductor in
the case an eductor is used, in which the pump is arranged outside
the separation device and communicates with the separation
device.
14. A Purified gas stream obtained by a process according to claim
1.
15. A process for liquefying a feed gas stream comprising purifying
the feed gas stream according to claim 1, followed by liquefying
the feed gas stream by methods known in the art.
Description
[0001] The present invention concerns a process for removing
gaseous contaminants, especially carbon dioxide and/or hydrogen
sulphide, from a feed gas stream comprising methane and gaseous
contaminants. The invention further comprises a cryogenic
separation device to carry out the process, as well as products
made in the process.
[0002] The removal of acid contaminants, especially carbon dioxide
and/or hydrogen sulphide, from methane containing gas streams has
been described in a number of publications.
[0003] In WO 03/062725 a process is described for the removal of
freezable species from a natural gas stream by cooling a natural
gas stream to form a slurry of solid acidic contaminants in
compressed liquefied natural gas. The solids are separated from the
liquid by means of a cyclone. It will be clear that a complete
separation of the liquid from the solids is not easily
achieved.
[0004] In U.S. Pat. No. 4,533,372 a cryogenic process is described
for the removal of carbon dioxide and other acidic gases from
methane-containing gas by treating the feed stream in a
distillation zone and a controlled freezing zone. This is a rather
complicated process requiring very specific equipment.
[0005] In U.S. Pat. No. 3,398,544 the removal of acid contaminants
from a natural gas stream is described by cooling to liquefy the
stream and to partly solidify the stream, followed by expansion and
separation of cleaned gas and liquid streams from the solids. Solid
contaminants need to be removed from the separation vessel, which
is a complicated process when the loss of natural gas liquid is to
be minimized.
[0006] In WO 2004/070297 a process for removing contaminants from a
natural gas stream has been described. In a first step, water is
removed from the feed gas stream. This is especially done by
cooling the feed gas stream resulting in methane hydrate formation,
followed by removal of the hydrates. Further cooling results in the
formation of solid acidic contaminants. After separation of the
solid acidic contaminants a cleaned natural gas stream is obtained.
It is preferred to convert the solid contaminant into a liquid by
heating the solids.
[0007] A problem of the process as described in WO 2004/070297 is
the removal of the contaminants in a reliable way from the
separation vessel, as well as the removal of a pure liquid only,
free from solid particles. In this respect it is observed that the
continuous stream of solid particles in the described process will
occasionally result in the formation of a thick layer of solid
material on top of the heat exchanger. Furthermore, a layer of
solid material may built up on the bottom of the vessel since solid
CO.sub.2 has a high density compared to the liquid stream. In
addition, this could result in uneven distribution of the heat
input required for melting and could result in hot gas plumes
forming from the liquid decreasing the clean natural gas stream
quality. Also, it is important to withdraw a pure liquid stream
from the vessel, in order to avoid blockages in the piping system
and/or heat exchangers, as well as damages of pumps and other
devices.
[0008] Object of the present invention is to provide an improved
cryogenic separation process which attractively deals with the
above-indicated problems.
[0009] Surprisingly it is now been found that this can be
established by means of a particular sequence of process steps
wherein use is made of a pump, especially an eductor device, a heat
exchanger arranged outside the separation device and the
recirculation of liquid phase contaminant obtained from the heat
exchanger.
[0010] Accordingly, the present invention relates to a process for
removing gaseous contaminants from a feed gas stream which
comprises methane and gaseous contaminants, the process
comprising:
1) providing the feed gas stream; 2) cooling the feed gas stream to
a temperature at which a slurry is formed which comprises solid
contaminant, liquid phase contaminant and a methane enriched
gaseous phase; 3) introducing the slurry as obtained in step 2)
into the top part or intermediate part of a cryogenic separation
device; 4) removing from the top part of the separation device a
stream which comprises the methane enriched gaseous phase; 5)
introducing a stream comprising liquid phase contaminant into the
intermediate part or the bottom part of the separation device or
both; to dilute the slurry which has been introduced into the
separation device in step 3); 6) passing the diluted slurry as
obtained in step 5) through a heat exchanger which is arranged
inside the separation device, whereby at least part of the solid
contaminant present in the diluted slurry is melted into liquid
phase contaminant; 7) removing from the separation device by means
of a pump, preferably an eductor, a stream comprising liquid phase
contaminant, which pump is situated below the heat exchanger and
arranged outside or inside the separation device or partly inside
or outside the separation device; 8) removing a stream comprising
liquid phase contaminant from the separation device at a position
below the slurry level in the separation device; 9) separating the
stream of liquid phase contaminant obtained in step 8) into a
liquid product stream and a recirculation stream which is used as a
motive fluid in the eductor in the case that an eductor is used;
and 10) introducing into the separation device as described above
in step 5) at least part of the stream as removed in step 7) and at
least part of the recirculation stream as obtained in step 9).
[0011] The present invention uses a recirculation loop of a liquid
or slurry stream over the separation device. To achieve the
circulation stream, a liquid or slurry stream is withdrawn
downstream of the internal heat exchanger by means of a pump,
preferably an eductor, and at least part of the obtained stream is
recirculated to the zone above the heat exchanger. Thus, a
continuously moving slurry phase is obtained, minimizing any
blockages in the separation vessel. Further, a fully liquid stream
is withdrawn, especially from the slurry zone above the heat
exchanger. Thus, the risk of blockages in pipelines or heat
exchangers after the separation device is minimal, and no damages
will occur to any devices having moving parts, as pumps.
[0012] It is further observed that when pure liquid stream is
withdrawn from the space above the heat exchanger, a relatively
cold liquid stream is obtained, thus maintaining a high amount of
exchangeable cold in the product stream. The absence of solid
particles in the product stream also minimizes any forms of erosion
in the pipelines and other pieces of equipment.
[0013] It is observed that the liquid phase contaminant as
described in step 7) above, as well as the liquid phase contaminant
as described in step 9) above, may contain some vapor and/or flash
gas, e.g. up till 10 wt %, especially up till 5 wt %, more
especially up till 2 wt %, of the total liquid phase
contaminant.
[0014] Suitably, the feed gas stream to be used in accordance with
the present invention is a natural gas stream in which the gaseous
contaminants are carbon dioxide and/or hydrogen sulphide and/or
C.sub.2+-hydrocarbons.
[0015] The amount of the hydrocarbon fraction in the feed gas
stream is suitably from 10 to 85 mol % of the gas stream,
preferably from 25 to 80 mol %. The hydrocarbon fraction of the
natural gas stream comprises especially at least 75 mol % of
methane, preferably 90 mol %. The hydrocarbon fraction in the
natural gas stream may suitably contain from 0 to 20 mol %,
suitably from 0.1 to 10 mol %, of C.sub.2-C.sub.6 compounds. The
gas stream may also comprise up to 20 mol %, suitably from 0.1 to
10 mol % of nitrogen, based on the total gas stream.
[0016] The amount of carbon dioxide in the gas stream is suitably
from 10 to 90 vol %, preferably from 20 to 75 vol %, and/or the
amount of hydrogen sulphide in the gas stream is suitably from 5 to
40 vol % of the gas stream, preferably from 20 to 35 vol %. Basis
for these amounts is the total volume of hydrocarbons, hydrogen
sulphide and carbon dioxide. It is observed that the present
process is especially suitable for gas streams comprising large
amounts of sour contaminants, e.g. 10 vol % or more, suitably from
15 to 90 vol %, and is especially suitable for gas streams
comprising carbon dioxide as contaminant.
[0017] In the process according to the present invention the feed
gas stream in step 1) has suitably a temperature between -20 and
150.degree. C., preferably between -10 and 70.degree. C., and a
pressure between 10 and 250 bara, preferably between 80 and 120
bara.
[0018] The feed gas stream may be pre-treated for partial or
complete removal of water and optionally some heavy hydrocarbons.
This can for instance be done by means of a pre-cooling cycle,
against an external cooling loop, a cold internal process stream,
or a cold LNG stream. Water may also be removed by means of
pre-treatment with molecular sieves, e.g. zeolites, aluminium oxide
or silica gel or other drying agents. Water may also be removed by
means washing with glycol, MEG, DEG or TEG, or glycerol. Other
processes for forming methane hydrates or for drying natural gas
are also possible. The amount of water in the gas feed stream is
suitably less than 1 vol %, preferably less than 0.1 vol %, more
preferably less than 0.01 vol %. Water may also be removed by
hydrate formation in the way as described in WO2004/070297.
Suitably, water is removed until the amount of water in the natural
gas stream comprises at most 50 ppmw, preferably at most 20 ppmw,
more preferably at most 1 ppmw of water, based on the total feed
gas stream.
[0019] The cooling in step 2) of the present process can suitably
be done by isenthalpic expansion, preferably isenthalpic expansion
over an orifice or a valve, especially a Joule-Thomson valve, or in
which the cooling is done by nearly isentropic expansion,
especially by means of an expander, preferably a turbo expander or
a laval nozzle. A valve is in particular preferred.
[0020] In step 2) the feed gas stream is suitably cooled to a
temperature between -40 and -100.degree. C., preferably between -50
and -80.degree. C.
[0021] Suitably, the feed gas stream is pre-cooled to a temperature
between 15 and -45.degree. C., preferably between 5 and -25.degree.
C., before expansion.
[0022] Suitably, such a pre-cooling of the feed gas stream is done
by heat exchange against a cold fluidum, especially an external
refrigerant, e.g. a propane cycle, an ethane/propane cascade or a
mixed refrigerant cycle, or an internal process loop, suitably a
carbon dioxide of hydrogen sulphide stream, or a cold methane
stream.
[0023] Preferably, the present process is carried out in such a way
that substantially all the solid contaminant present in the diluted
slurry of contaminants is melted into liquid phase contaminant in
step 6). With the phrase "substantially" is meant that at least 95%
of the solid contaminant present in the diluted slurry is melted,
especially at least 98%. More preferably, all the solid contaminant
present in the diluted slurry of contaminants is melted in step
6).
[0024] Suitably, between 0 and 90 vol % of the liquid phase
contaminant which is removed from the separation device in step 7)
is introduced in the separation device as described in step 5),
preferably between 5 and 80 vol % of the liquid phase contaminant
as removed in step 7). It is also possible to introduce all liquid
phase contaminant removed in step 7) in the separation device as
described in step 5).
[0025] In step 8) the stream comprising liquid phase contaminant is
suitably removed from the separation device at a position above the
heat exchanger.
[0026] In the present invention solid contaminant will mainly
comprise carbon dioxide, whereas liquid phase contaminant will
usually comprise both carbon dioxide and hydrogen sulphide. A small
amount of hydrocarbons may be present.
[0027] Preferably, the pump is arranged outside the separation
device and the pump communicates with the separation device.
Preferably, the pump is an eductor.
[0028] Eductors, also referred to as siphons, exhausters, ejectors
or jet pumps, are as such well-known and have extensively been
described in the prior art. Reference herein to an eductor is to a
device to pump produced solid and liquid CO2 slurry from the
separator to the heat exchanger. The eductor is suitably designed
for use in operations in which the head pumped against is low and
is less than the head of the fluid used for pumping. For a
description of suitable eductors, also referred to as eductors or
jet pumps, reference is made to Perry's Handbook for Chemical
Engineering, 8th edition, chapter 10.2. In accordance with the
present invention any type of eductor can be used. The eductor is
preferably a liquid jet solid pump.
[0029] Preferably, the eductor is arranged inside the separation
device or partly inside and outside the separation device.
[0030] Suitably, a housing can be positioned around the eductor,
enabling the eductor to be removed from the separation device. Such
a housing can, for instance, be a vessel like containment, e.g. a
pipe, that can be isolated from the process through valves.
[0031] In another embodiment of the present invention the eductor
is arranged outside the separation device. Such an embodiment can
be useful in situations in which the eductor in use needs to be
repaired or replaced.
[0032] The eductor can be of such a size that it fits completely in
the separation device or it may cover the entire diameter of the
separation device, usually a vessel. However, it may also extend at
two locations through the internal wall of the separation
device.
[0033] More preferably, the eductor is arranged below the central
bottom part of the separation device.
[0034] Suitably, in step 10) between 25 and 95 vol % of the stream
of liquid phase contaminant removed from the separation device in
step 9) is used as a motive fluid in the eductor, preferably
between 30 and 85 vol % of the stream of liquid phase contaminant
removed from the separation device in step 9).
[0035] In general, the methane enriched gaseous phase is removed
from the top part of the cryogenic separation device at a high
level, preferably at the top of the reactor.
[0036] The outlet for the methane enriched gaseous phase will
usually be above the level at which the stream of liquid phase
contaminant obtained from the heat exchanger is introduced into the
separation device in step 5).
[0037] The cooling process as described in step (2) of the present
process is preferably carried out at a close distance, e.g. up to a
few meters, preferably at most 1 m, to the separator vessel. It may
also be done inside the separation vessel, thus minimizing any
problems due to the transport of the solid particles. The
separation device is suitably a vessel which comprises a vertical
cylindrical housing. The diameter may vary from 1 to 10 meter, or
even more, the height may vary from 3 to 35 meters or even more. In
general, the slurry level in the separation vessel will vary
between 30 and 70% of the height of the vessel. The temperature of
the slurry is suitably about 1 to 45.degree. C. higher than the
temperature of the contaminated gas stream on introduction is the
separator vessel, preferably 3 to 40.degree. C.
[0038] The heat exchanger preferably uses a process stream to
supply the heat for melting the solid contaminants. A suitable
process stream is the methane enriched gaseous phase.
[0039] A suitable internal structure to remove the stream
comprising liquid phase contaminant from the separation device in
step 9) is a conical section or a cylindrical section that is
closed at the upper end. Also a standpipe may be used with a closed
upper end to prevent solids transport with this liquid stream. In
addition, filters may be used, suitably equipped with heat tracing
to prevent blockage.
[0040] The content of contaminants in the methane enriched gaseous
phase as removed from the separation device in step 4) is suitably
less than 10 vol %, preferably less than 5 vol %. The content of
methane in the contaminants product stream is suitably less than 2
wt %, preferably less than 1 wt %, based on total weight of the
stream.
[0041] The feed gas stream provided in step 1) of the present
process can suitably have been subjected to one or more
purification processes in which gaseous contaminants are removed
from a feed gas stream, before step 2) of the present process is
carried out.
[0042] Such a purification process can suitably comprise the steps
of:
a) providing a feed gas stream; b) cooling the feed gas stream to a
temperature at which liquid phase contaminant is formed as well as
a methane enriched gaseous phase; and c) separating the two phases
obtained in step 2) by means of a gas/liquid separator.
[0043] Suitably, steps a) and b) can be repeated twice or three
times before step 2) in accordance with the present invention is
carried out. Such a process has, for instance been described in WO
2006/087332 which is hereby incorporated by reference. Hence, the
feed gas stream can be subjected to a number of combinations of
subsequent cooling and separation steps, before step 2) of the
present invention is carried out.
[0044] Suitably, after step a) the methane enriched gaseous phase
can be recompressed in one or more compression steps before step 2)
in accordance with the present invention is carried out.
[0045] In another embodiment of the invention the feed gas stream
may between steps 1) and 2) be cooled to a temperature at which at
least part of the feed gas stream is present in the liquid phase,
the cooled feed stream so obtained may be separated by means of a
cryogenic distillation into a bottom stream rich in liquid phase
contaminant and lean in methane and into a top stream rich in
methane and lean in gaseous contaminant, and the feed gas stream so
obtained may then be subjected to the remaining steps 2)-10) of the
process according to the present invention.
[0046] The cryogenic distillation section to be used in the
cryogenic distillation is as such known in the art.
[0047] Suitably, the feed gas stream is cooled to a temperature
between -10 and -50.degree. C., preferably between -20 and
-40.degree. C. before introduction into the cryogenic distillation
section.
[0048] Suitably, the bottom temperature of the cryogenic
distillation section is between -15 and 35.degree. C., preferably
between -5 and 30.degree. C. A reboiler may be present to supply
heat to the column.
[0049] Suitably, the top temperature of the cryogenic distillation
section is between -70 and -40.degree. C., preferably between -60
and -30.degree. C. In the top of the cryogenic distillation column
a condenser may be present, to introduce cold into the column.
[0050] In order to reach gas line specifications or LNG
specifications for the methane stream, the methane enriched gaseous
phase obtained in step 4) may further be purified, in an additional
cryogenic distillation process using a cryogenic distillation
section which is as such known in the art.
[0051] Suitably, in such an additional cryogenic distillation
process the bottom temperature of the cryogenic distillation
section is between -30 and 10.degree. C., preferably between -10
and 5.degree. C. A reboiler may be present to supply heat to the
distillation section.
[0052] Suitably, the top temperature of the cryogenic distillation
section is between -110 and -80.degree. C., preferably between -100
and -90.degree. C. In the top of the cryogenic distillation section
a condenser may be present, to provide reflux and a liquefied (LNG)
product.
[0053] As an alternative, further purification of the methane
enriched gaseous phase may be accomplished by absorption with a
suitable absorption liquid. Suitable absorbing liquids may comprise
chemical solvents or physical solvents or mixtures thereof.
[0054] A preferred absorbing liquid comprises a chemical solvent
and/or a physical solvent, suitably as an aqueous solution.
[0055] Suitable chemical solvents are primary, secondary and/or
tertiary amines, including sterically hindered amines.
[0056] A preferred chemical solvent comprises a secondary or
tertiary amine, preferably an amine compound derived from
ethanolamine, more especially DIPA, DEA, MMEA
(monomethyl-ethanolamine), MDEA (methyldiethanolamine) TEA
(triethanolamine), or DEMEA (diethyl-monoethanolamine), preferably
DIPA or MDEA. It is believed that these chemical solvents react
with acidic compounds such as CO2 and H2S.
[0057] Suitable physical solvents include tetramethylene sulphone
(sulpholane) and derivatives, amides of aliphatic carboxylic acids,
N-alkyl pyrrolidone, in particular N-methyl pyrrolidine, N-alkyl
piperidones, in particular N-methyl piperidone, methanol, ethanol,
ethylene glycol, polyethylene glycols, mono- or di(C1-C4)alkyl
ethers of ethylene glycol or polyethylene glycols, suitably having
a molecular weight from 50 to 800, and mixtures thereof. The
preferred physical solvent is sulfolane. It is believed that CO2
and/or H2S are taken up in the physical solvent and thereby
removed.
[0058] Other treatments of the methane enriched gaseous phase may
include a further compression, when the purified gas is wanted at a
higher pressure. If the amounts of acidic contaminants in the
purified gas are undesirably high, the purified gas may be
subjected to one or more repetitions of the present process.
[0059] It is an advantage of the present process enables
purification of natural gas comprising substantial amounts of
acidic contaminants, resulting in purified natural gas comprising
low levels of contaminants, especially of sulphur contaminants. The
production of LNG from such natural gas, which would be very
difficult if not impossible by conventional processes, is made
possible. Thus, the invention also provides LNG obtained from
liquefying purified natural gas obtained by the process. The LNG
thus-obtained typically has very low concentrations of contaminants
other than natural gas.
[0060] In general, the top part of the separation device will
comprise the top quarter length of the device. The bottom part will
comprise the lower quarter up till the lower half of the length of
the device. The intermediate part will comprise the remaining.
[0061] The present invention also relates to a cryogenic separation
device for carrying out the process according to the present
process, which separation device comprises a top part, an
intermediate part and a bottom part; means to introduce a slurry
which comprises solid contaminant, liquid phase contaminant and a
methane enriched gaseous phase into the top or intermediate part of
the separation device; means to remove a methane enriched gaseous
phase from the top part of the separation device; means for
introducing a stream comprising liquid phase contaminant into the
top or intermediate part of the separation device to dilute the
slurry inside the separation device; a heat exchanger arranged
inside the separation device; a pump, preferably an eductor, which
is arranged inside or outside the separation device or partly
inside and outside the separation device at a level which is below
the level at which the heat exchanger is arranged for removing a
stream comprising liquid phase contaminant from the separation
device; means to remove a stream comprising liquid phase
contaminant from the intermediate or bottom part of the separation
device; and means to separate liquid phase contaminant removed from
the intermediate or bottom part into a liquid product stream and a
recirculation stream for use as a motive fluid in the eductor in
the case an eductor is used.
[0062] Preferably, the slurry pump, preferably an eductor, is
arranged outside and communicates with the separation device.
Preferably, the pump, preferably an eductor is arranged below the
separation device. More preferably, it is arranged below the
central bottom part of the separation device.
[0063] The process is also suitable for the removal in general of
carbon dioxide from carbon dioxide comprising streams, especially
(partial)oxidation flue gas streams, more especially streams
comprising (beside carbon dioxides) hydrogen, carbon monoxide,
nitrogen and/or oxygen, for instance boiler flue gas streams
(usually comprising mainly carbon dioxide, nitrogen and oxygen),
partial oxidation process streams (usually containing mainly carbon
dioxide, carbon monoxide, hydrogen and optionally nitrogen), steam
methane reforming process streams (usually comprising hydrogen,
carbon dioxide and carbon monoxide.
[0064] In the event that the contaminant-rich stream mainly
comprises carbon dioxide and is therefore a CO2-rich stream,
preferably CO2-rich stream is further pressurised and injected into
a subterranean formation, preferably for use in enhanced oil
recovery or for storage into an aquifer reservoir or for storage
into an empty oil reservoir. It is an advantage that a liquid
CO2-rich stream is obtained, as this liquid stream requires less
compression equipment to be injected into a subterranean formation.
Preferably, at least 90%, more preferably at least 95% and most
preferably at least 98% of the solid acidic contaminants are
melted. In this way a liquid stream of contaminants is obtained,
which can be easily transported further.
[0065] The present invention further relates to a purified gas
stream obtained by a process according to the present
invention.
[0066] The present invention also relates to a process for
liquefying a feed gas stream comprising purifying the feed gas
stream in accordance with the present invention, followed by
liquefying the feed gas stream by methods known in the art.
[0067] The invention will be further illustrated by means of FIG.
1. In FIG. 1, a natural gas is passed via a conduit 1 through an
expansion means 2, especially a Joule Thomson valve, whereby a
stream is obtained of a slurry which comprises solid contaminant,
liquid phase contaminant and a methane enriched gaseous phase. The
stream of the slurry flows via a conduit 3 into cryogenic
separation vessel 4. A methane enriched gaseous phase is removed
from the separation vessel via a conduit 5. A stream of liquid
phase contaminant is introduced into the separation device via a
conduit 6 to dilute the slurry inside the separation device,
establishing or maintaining a slurry level 7. The diluted slurry
passes then towards a heat exchanger 8. Via a conduit 9 a stream
comprising liquid phase contaminant is removed from the separation
device, whereby part of the stream is recovered as a liquid product
via a conduit 10. Another part of the stream is passed via a
conduit 11 to an eductor 12 where it is used as motive fluid, after
which it is recirculated to the separation device via the conduit
6.
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