U.S. patent application number 13/120410 was filed with the patent office on 2011-08-11 for process for removing gaseous contaminants from a feed gas stream comprising methane and gaseous contaminants.
Invention is credited to Diki Andrian, Rick Van Der Vaart.
Application Number | 20110192190 13/120410 |
Document ID | / |
Family ID | 40428001 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110192190 |
Kind Code |
A1 |
Andrian; Diki ; et
al. |
August 11, 2011 |
PROCESS FOR REMOVING GASEOUS CONTAMINANTS FROM A FEED GAS STREAM
COMPRISING METHANE AND GASEOUS CONTAMINANTS
Abstract
The invention provides 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 first temperature
at which liquid phase contaminant is formed as well as a methane
enriched gaseous phase; 3) separating the two phases obtained in
step 2) by means of a first gas/liquid separator; 4) cooling the
methane enriched gaseous phase obtained in step 3) at least party
by means of an external refrigerant to a second temperature at
which liquid phase contaminant is formed as well as a methane
enriched gaseous phase; and 5) separating the two phases obtained
in step 4) by means of a second gas/liquid separator. The invention
further concerns a device for carrying out the present process, the
purified gas stream, and a process for liquefying a feed gas
stream.
Inventors: |
Andrian; Diki; (Rijswijk,
NL) ; Van Der Vaart; Rick; (Rijswijk, NL) |
Family ID: |
40428001 |
Appl. No.: |
13/120410 |
Filed: |
September 11, 2009 |
PCT Filed: |
September 11, 2009 |
PCT NO: |
PCT/EP2009/061795 |
371 Date: |
March 22, 2011 |
Current U.S.
Class: |
62/617 |
Current CPC
Class: |
F25J 2220/66 20130101;
C10L 3/10 20130101; F25J 2215/04 20130101; B01D 2258/06 20130101;
C10L 3/102 20130101; F25J 3/061 20130101; B01D 2257/504 20130101;
F25J 2270/60 20130101; F25J 3/067 20130101; B01D 2256/24 20130101;
F25J 3/0635 20130101; Y02C 20/40 20200801; B01D 53/002 20130101;
F25J 2270/12 20130101; F25J 2270/66 20130101; Y02C 10/12 20130101;
B01D 2257/304 20130101 |
Class at
Publication: |
62/617 |
International
Class: |
F25J 3/00 20060101
F25J003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 23, 2008 |
EP |
08164892.5 |
Claims
1. 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 first temperature at which liquid phase
contaminant is formed as well as a methane enriched gaseous phase;
3) separating the two phases obtained in step 2) by means of a
first gas/liquid separator; 4) cooling the methane enriched gaseous
phase obtained in step 3) at least partly by means of an external
refrigerant to a second temperature at which liquid phase
contaminant is formed as well as a methane enriched gaseous phase;
and 5) separating the two phases obtained in step 4) by means of a
second gas/liquid separator.
2. A process according to claim 1, in which at least one of the
first and second gas/liquid separators comprises a centrifugal
which comprises a bundle of parallel channels that are arranged
within a spinning tube parallel to an axis of rotation of the
spinning tube.
3. A process according to claim 1, in which the first and/or second
gas/liquid separator comprises a housing with a gas inlet for
contaminated gas at one end of the vessel, a separating body, a gas
outlet for purified gas at the opposite end of the housing and a
contaminants outlet downstream of the separating body wherein the
separating body comprises a plurality of ducts over a part of the
length of the axis of the housing, which ducts have been arranged
around a central axis of rotation, in which apparatus the
separating body has been composed of a plurality of perforated
discs wherein the perforations of the discs form the ducts.
4. A gas separation system, comprising: a) a housing comprising a
first, second and third separation section for separating liquid
from a gas mixture, wherein the second separation section is
arranged below the first separation section and above the third
separation section, the respective separation sections are in
communication with each other, and the second separation section
comprises a rotating coalescer element; b) tangentially arranged
inlet means to introduce the mixture into the first separation
section; c) means to remove liquid from the first separation
section; d) means to remove liquid from the third separation
section; and e) means to remove a gaseous stream, lean in liquid,
from the third separation section.
5. A process according 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.
6. A process according to claim 5, in which the natural gas stream
comprises between 1 and 90 vol % of carbon dioxide, and between 0.1
and 60 vol % of hydrogen sulphide.
7. A process claim 1, in which the feed gas stream comprises
between 20 and 80 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 150 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 9, wherein the expansion is done
using at least two expansion devices and the operating parameters
of the expansion devices are chosen such that the liquefied acidic
contaminants have a certain droplet size distribution.
11. A process claim 1, in which the feed gas stream is cooled in
steps 2) and 4) to a temperature between -30 and -80.degree. C.,
preferably between -40 and -65.degree. C.
12. A process claim 1, in which the pressure applied in step 4) is
higher than the pressure applied in step 2), and in which the
second temperature in step 4) is lower than the first temperature
in step 2).
13. A process according claim 1, in which the external refrigerant
has a higher molecular weight than the methane enriched gaseous
phase to be cooled.
14. A process according to claim 1, in which the first and/or
second gas/liquid separator comprises a gas/liquid inlet at an
intermediate level, a liquid outlet arranged below the gas/liquid
inlet and a gas outlet arranged above the gas/liquid inlet, in
which vessel a normally horizontal coalescer is present above the
gas/liquid inlet and over the whole cross-section of the vessel and
in which vessel a centrifugal liquid separator is arranged above
the coalescer and over the whole cross-section of the vessel, the
liquid separator comprising one or more swirl tubes.
15. (canceled)
Description
[0001] The present invention concerns a process for the removal of
gaseous contaminants from a feed gas stream which comprises methane
and gaseous contaminants, in particular the removal of gaseous
contaminants such as carbon dioxide and hydrogen sulphide from a
natural gas.
[0002] Methane comprising gas streams produced from subsurface
reservoirs, especially natural gas, associated gas and coal bed
methane, usually contain contaminants as carbon dioxide, hydrogen
sulphide, carbon oxysulphide, mercaptans, sulphides and aromatic
sulphur containing compounds in varying amounts. For most of the
applications of these gas streams, the contaminants needs to be
removed, either partly or almost completely, depending on the
specific contaminant and/or the use. Often, the sulphur compounds
need to be removed into the ppm level, carbon dioxide sometimes
into ppm level, e.g. LNG applications, or down to 2 or 3 vol.
percent, e.g. for use as heating gas. Higher hydrocarbons may be
present, which, depending on the use, may be recovered.
[0003] Processes for the removal of carbon dioxide and sulphur
compounds are know in the art. These processes include absorption
processes using e.g. aqueous amine solutions or adsorption
processes using e.g. molecular sieves. These processes are
especially suitable for the removal of contaminants, especially
carbon dioxide and hydrogen sulphide, that are present in
relatively low amounts, e.g. up till several vol %.
[0004] In WO 2006/087332, a method has been described for removing
contaminating gaseous components, such as carbon dioxide and
hydrogen sulphide, from a natural gas stream. In this method a
contaminated natural gas stream is cooled in a first expander to
obtain an expanded gas stream having a temperature and pressure at
which the dewpointing conditions of the phases containing a
preponderance of contaminating components, such a carbon dioxide
and/or hydrogen sulphide are achieved. The expanded gas stream is
then supplied to a first centrifugal separator to establish the
separation of a contaminants-enriched liquid phase and a
contaminants-depleted gaseous phase. The contaminants-depleted
gaseous phase is then passed via a recompressor, an interstage
cooler, and a second expander into a second centrifugal separator.
The interstage cooler and the second expander are used to cool the
contaminants-depleted gaseous phase to such an extent that again a
contaminants-enriched liquid phase and a further
contaminants-depleted gaseous phase are obtained which are
subsequently separated from each other by means of the second
centrifugal separator. In such a method energy recovered from the
first expansion step is used in the compression step, and air,
water and/or an internal process stream is used in the interstage
cooler.
[0005] A disadvantage of this known method is that the use of a
recompressor, interstage cooler and an expander between the two
centrifugal separators affects the hydrocarbon efficiency of the
separation process, which hydrocarbon efficiency is a measure of
the fuel gas consumption and the hydrocarbon loss in the liquid
phase contaminant streams during the process.
[0006] It has now been found that in an integrated process for
removing gaseous contaminants from a gas stream the hydrocarbon
efficiency can be considerably improved when between a first and a
second gas/liquid separation the contaminants-depleted gaseous
phase is at least partly cooled by means of an external refrigerant
which allows an excellent separation of gaseous contaminants,
whereas the use of an expander between the first and second
gas/liquid separation can be avoided.
[0007] Thus, the present invention concerns a process for removing
gaseous contaminants from a feed gas stream which comprises methane
and gaseous contaminants, which process comprises:
1) providing the feed gas stream; 2) cooling the feed gas stream to
a first temperature at which liquid phase contaminant is formed as
well as a methane enriched gaseous phase; 3) separating the two
phases obtained in step 2) by means of a first gas/liquid
separator; 4) cooling the methane enriched gaseous phase obtained
in step 3) at least partly by means of an external refrigerant to a
second temperature at which liquid phase contaminant is formed as
well as a methane enriched gaseous phase; and 5) separating the two
phases obtained in step 4) by means of a second gas/liquid
separator.
[0008] Suitably, the feed gas stream is a natural gas stream in
which the gaseous contaminants are carbon dioxide and/or hydrogen
sulphide.
[0009] The natural gas stream suitably comprises between 1 and 90
vol % of carbon dioxide, preferably between 5 and 80 vol % of
carbon dioxide.
[0010] The natural gas stream suitably comprises between 0.1 to 60
vol % of hydrogen sulphide, preferably between 20 and 40 vol % of
hydrogen sulphide.
[0011] The feed gas stream to be used in accordance with the
present invention comprises between 20 and 80 vol % of methane.
[0012] Suitably, 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 150 bara, preferably
between 80 and 120 bara.
[0013] The raw feed gas stream may be pre-treated to partially or
completely remove water and optionally some heavy hydrocarbons.
This can for instance be done by means of a pre-cooling cycle,
against an external cooling loop or a cold internal process stream.
Water may also be removed by means of pre-treatment with molecular
sieves, e.g. zeolites, or silica gel or alumina oxide or other
drying agents such as glycol, MEG, DEG or TEG, or glycerol. 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 0.0001
vol %.
[0014] The cooling in step 2) of the feed gas stream may be done by
methods known in the art. For instance, cooling may be done against
an external cooling fluid. In the case that the pressure of the
feed gas is sufficiently high, cooling may be obtained by expansion
of the feed gas stream.
[0015] Combinations may also be possible. A suitable method to cool
the feed gas stream is done by nearly isentropic expansion,
especially by means of an expander, preferably a turbo expander or
laval nozzle. Another suitable method is to cool the feed gas
stream by isenthalpic expansion, preferably isenthalpic expansion
over an orifice or a valve, especially over a Joule-Thomson
valve.
[0016] Preferably, the expansion is done using at least two
expansion devices and the operating parameters of the expansion
devices are chosen such that the liquefied contaminants in the
cooled stream have a certain droplet size distribution. The use of
at least two expansion devices allows the control of the droplet
size distribution of condensed contaminants.
[0017] In a preferred embodiment the feed gas stream is pre-cooled
before expansion. This may be done against an external cooling loop
or against a cold process stream, e.g. liquid contaminant.
Preferably the gas stream is pre-cooled before expansion to a
temperature between 15 and -35.degree. C., preferably between
10.degree. C. and -20.degree. C. Pre-cooling may be done against
internal process streams. Especially when the feed gas stream has
been compressed, the temperature of the feed gas stream may be
between 100 and 150.degree. C. In that case air or water cooling
may be used to decrease the temperature first, optionally followed
by further cooling.
[0018] Another suitable cooling method is heat exchange against a
cold fluidum, especially an external refrigerant, e.g. a propane
cycle, an ethane/propane cascade or a mixed refrigerant cycle,
optionally in combination with an internal process loop, suitably a
carbon dioxide stream (liquid or slurry), a cold methane enriched
stream or washing fluid.
[0019] Suitably the feed gas stream is cooled in steps 2) and 4) to
a temperature between -30 and -80.degree. C., preferably between
-40 and -65.degree. C. At these temperatures liquid phase
contaminant will be formed.
[0020] Suitably, the pressure applied in step 4) can be higher than
the pressure applied in step 2).
[0021] Preferably, the second temperature in step 4) is lower than
the first temperature in step 2).
[0022] Preferably, the second temperature in step 4) is up to
20.degree. C. lower than the first temperature in step 2). More
preferably, the second temperature is between 5 and 10.degree. C.
lower than the first temperature in step 2).
[0023] The cooling in step 4) can be carried out by means of an
internal process stream such as a stream of liquid phase
contaminant which is separated from the methane enriched gaseous
phase in step 3).
[0024] In accordance with the present invention the cooling of the
methane enriched gaseous phase in step 4) can suitably at least
partly be done by means of an external refrigerant.
[0025] Preferably, the external refrigerant to be used in step 4)
has a higher molecular weight than the methane enriched gaseous
phase to be cooled. Suitable examples of such cooling medium
include ethane, propane and butane. Preferably, the cooling medium
comprises ethane and/or propane.
[0026] More preferably, the external refrigerant to be used
comprises a propane cycle, an ethane/propane mixed refrigerant or
an ethane/propane cascade. Such an ethane/propane cascade is
described in more detail hereinbelow.
[0027] The cooling in step 4) can suitably be partly done by means
of an external refrigerant and partly by means of an internal
process stream, e.g. a stream of liquid phase contaminant which is
separated from the methane enriched gaseous phase in step 3).
[0028] The cooling in step 4) as, for instance, done by use of an
external refrigerant can very attractively replace the sequence of
the recompressor, interstage cooler and the expander which is used
between the two centrifugal separators as described in WO
2006/087332, improving the hydrocarbon efficiency of the separation
process.
[0029] In another embodiment of the present invention the methane
enriched gaseous phase obtained in step 3) is recompressed in one
or more compression steps before step 4) is carried out.
[0030] In another embodiment of the present invention the methane
enriched gaseous phase obtained in step 3) is firstly cooled by
means of an interstage cooler before the cooling in step 4) is
carried out.
[0031] In yet another embodiment of the present invention, the
methane enriched gaseous phase obtained in step 3) is firstly
recompressed in one or more compression steps, than cooled by means
of an interstage cooler, and subsequently cooled in step 4).
[0032] Suitably, such an interstage cooler will be based on a
internal process stream and air or water cooling.
[0033] Suitably, in the case liquid is formed inside the cooler,
this cooler is designed in such a way that liquid is effectively
removed form the cooling device without impairing heat
transfer.
[0034] In the one or more compression steps suitably energy is used
that is recovered in step 2).
[0035] In the process according to the present invention a variety
of gas/liquid separators can suitably be used in steps 3) and 5),
such as, for instance, rotating centrifuges or cyclones.
[0036] In steps 3) and 5) use can be made of different types or
similar types of gas/liquid separators. Suitably, in steps 3) and
5) is made of similar types of gas/liquid separators.
[0037] Suitable gas/liquid separators to be used in accordance with
the present invention have, for instance, been described in WO
2008/082291, WO 2006/087332, WO 2005/118110, WO 97/44117, WO
2007/097621 and WO 94/23823, which documents are hereby
incorporated by reference.
[0038] Typically, the gas/liquid separator requirements in step 3)
are more stringent than the requirements in step 5) since
homogeneous droplet nucleation after expansion does produce smaller
droplets than heterogeneous nucleation in a heat exchanger, cooled
by an external process stream.
[0039] In a preferred embodiment of the present invention, the
first and/or second gas/liquid separator comprises a gas/liquid
inlet at an intermediate level, a liquid outlet arranged below the
gas/liquid inlet and a gas outlet arranged above the gas/liquid
inlet, in which vessel a normally horizontal coalescer is present
above the gas/liquid inlet and over the whole cross-section of the
vessel and in which vessel a centrifugal liquid separator is
arranged above the coalescer and over the whole cross-section of
the vessel, the liquid separator comprising one or more swirl
tubes.
[0040] When using a vertical gas/liquid separator vessel, the
process only needs a relatively small area.
[0041] According to a preferred embodiment, the gas/liquid inlet
comprises an admittance with a supply and distribution assembly
extending horizontally in the separator vessel. In its most simple
form, the inlet is a simple pipe, having a closed end and a number
of perforations evenly distributed over the length of the pipe.
Optionally, the pipe may have a tapered or conical shape. One or
more cross pipes may be present to create a grid system to
distribute the gas-liquid mixture more evenly over the
cross-section of the vessel. Preferably, the assembly includes a
chamber, e.g. a longitudinal box-like structure, connected to the
gas inlet and having at least one open vertical side with a grid of
guide vanes disposed one behind each other, seen in the direction
of the flow. By means of this supply and distribution assembly, the
gas is evenly distributed by the guide vanes over the cross-section
of the column, which brings about an additional improvement of the
liquid separation in the coalescer/centrifugal separator
combination. A further advantage is that the supply and
distribution assembly separates from the gas any slugs of liquid
which may suddenly occur in the gas stream, the separation being
effected by the liquid colliding with the guide vanes and falling
down inside the column. Suitably, the box structure narrows down in
the direction of the flow. After having been distributed by the
vanes over the column cross-section, the gas flows up to the
coalescer.
[0042] In a preferred embodiment the longitudinal chamber has two
open vertical sides with a grid of guide vanes.
[0043] Suitable gas/liquid inlets are those described in e.g. GB
1,119,699, U.S. Pat. No. 6,942,720, EP 195,464, U.S. Pat. No.
6,386,520 and U.S. Pat. No. 6,537,458. A suitable, commercially
available gas/liquid inlet is a Schoepentoeter.
[0044] There are numerous horizontal coalescers available,
especially for vertical columns. A well-known example of a mist
eliminator is the demister mat. All of these are relatively tenuous
(large permeability) and have a relatively large specific
(internal) surface area. Their operation is based on drop capture
by collision of drops with internal surfaces, followed by drop
growth on these surfaces, and finally by removal of the grown drop
either by the gas or by gravity.
[0045] The horizontal coalescer can have many forms which are known
per se and may, for example, consist of a bed of layers of gauze,
especially metal or non-metal gauze, e.g. organic polymer gauze, or
a layer of vanes or a layer of structured packing. Also
unstructured packings can be used and also one or more trays may be
present. All these sorts of coalescers have the advantage of being
commercially available and operating efficiently in the column
according to the invention. See also Perry's Chemical Engineers'
Handbook, Sixth edition, especially Chapter 18. See also EP
195464.
[0046] The centrifugal liquid separator in one of its most simple
forms may comprise a horizontal plate and one or more vertical
swirl tubes extending downwardly from the plate, each swirl tube
having one or more liquid outlets below the horizontal plate at the
upper end of the swirl tube. In another form, the centrifugal
liquid separator comprises one or more vertical swirl tubes
extending upwardly from the plate, each swirl tube having one or
more liquid outlets at the upper end. The plate is provided with a
downcomer, preferably a downcomer that extends to the lower end of
the separator vessel.
[0047] In a preferred embodiment of the invention, the centrifugal
liquid separator comprises two horizontal trays between which
vertical open-ended swirl tubes extend, each from an opening in the
lower tray to some distance below a coaxial opening in the upper
tray, means for the discharge of secondary gas and of liquid from
the space between the trays outside the swirl tubes, and means
provided in the lower part of the swirl tubes to impart to the
gas/liquid a rotary movement around the vertical axis.
[0048] The liquid separator is also preferably provided with
vertical tube pieces which project down from the coaxial openings
in the upper tray into the swirl tubes and have a smaller diameter
than these latter. This arrangement enhances the separation between
primary gas on the one hand and secondary gas and liquid on the
other hand, since these latter cannot get from the swirl tubes into
the openings in the upper tray for primary gas.
[0049] According to a preferred embodiment, the means for
discharging the secondary gas from the space between the trays
consist of vertical tubelets through the upper tray, and the means
for discharging liquid from the space between the trays consist of
one or more vertical discharge pipes which extend from this space
to the bottom of the column. This arrangement has the advantage
that the secondary gas, after having been separated from liquid in
the said space between the trays, is immediately returned to the
primary gas, and the liquid is added to the liquid at the bottom of
the column after coming from the coalescer, so that the secondary
gas and the liquid removed in the centrifugal separator do not
require separate treatment.
[0050] In order to improve even further the liquid separation in
the centrifugal separator, openings are preferably provided in
accordance with the invention at the top of the swirl tubes for
discharging liquid to the space between the trays outside the swirl
tubes. This has the advantage that less secondary gas is carried to
the space between the trays. A suitable, commercially available
centrifugal separator is a Shell Swirltube deck.
[0051] In a preferred embodiment, the separation vessel comprises a
second normally horizontal liquid coalescer above the centrifugal
liquid separator and over the whole cross-section of the vessel.
This has the advantage that any droplets still present in the gas
stream are removed. See for a further description hereinabove.
Preferably, the second coalescer is a bed of one or more layers of
gauze, especially metal or non-metal gauze, e.g. organic polymer
gauze. In another preferred embodiment, the second normally
horizontal liquid coalescer is situated above the secondary gas
outlets, for instance in the way as described in EP 83811,
especially as depicted in FIG. 4.
[0052] In a most preferred embodiment, a first and/or second
separator is used comprising:
a) a housing comprising a first, second and third separation
section for separating liquid from the mixture, wherein the second
separation section is arranged below the first separation section
and above the third separation section, the respective separation
sections are in communication with each other, and the second
separation section comprises a rotating coalescer element; b)
tangentially arranged inlet means to introduce the mixture into the
first separation section; c) means to remove liquid from the first
separation section; d) means to remove liquid from the third
separation section; and e) means to remove a gaseous stream, lean
in liquid, from the third separation section.
[0053] In the present invention the first and/or second gas/liquid
separator may suitably comprise a centrifugal separator which
comprises a bundle of parallel channels that are arranged within a
spinning tube parallel to an axis of rotation of the spinning
tube.
[0054] Suitably, in the present process the centrifugal separator
is spinned by introducing a swirling gas stream into the spinning
tube.
[0055] Preferably, the centrifugal separator to be used in
accordance with the present invention comprises a housing with a
gas inlet for contaminated gas at one end of the vessel, a
separating body, a gas outlet for purified gas at the opposite end
of the housing and a contaminants outlet downstream of the
separating body or upstream and downstream of the separating body,
wherein the separating body comprises a plurality of ducts over a
part of the length of the axis of the housing, which ducts have
been arranged around a central axis of rotation, in which apparatus
the separating body has been composed of a plurality of perforated
discs wherein the perforations of the discs form the ducts.
[0056] It will be appreciated that the discs can be easily created
by drilling or cutting a plurality of perforations into the
relatively thin discs. By attaching several discs to together these
discs form a separating body. By aligning the perforations ducts
are obtained.
[0057] It is now also very easy to attach the discs such that the
perforations are not completely aligned. By varying the number and
nature of the non-alignment of the perforations the resulting ducts
can be given any desired shape. In such cases not only ducts are
obtainable that are not completely parallel to the central axis of
rotation, but also ducts that form a helix shape around the axis of
rotation. So, in this way very easily the preferred embodiment of
having non-parallel ducts can be obtained. Hence it is preferred
that the perforations of the discs have been arranged such that the
ducts are not parallel to the central axis of rotation or form a
helix shape around the axis of rotation.
[0058] Further, it will be appreciated that it is relatively easy
to increase or decrease the diameter of the perforations. Thereby
the skilled person has an easy manner at his disposal to adapt the
(hydraulic) diameter of the ducts, and thereby the Reynolds number,
so that he can easy ascertain that the flow in the ducts is laminar
or turbulent, just as he pleases. The use of these discs also
enables the skilled person to vary the diameter of the duct along
the axis of the housing. The varying diameter can be selected such
that the separated liquid or solid contaminants that are collected
against the wall of the duct will not clog up the duct completely,
which would hamper the operation of the apparatus.
[0059] The skilled person is also now enabled to maximise the
porosity of the separating body. The easy construction of the discs
allows the skilled person to meticulously provide the disc with as
many perforations as he likes. He may also select the shape of the
perforations. These may have a circular cross-section, but also
square, pentagon, hexagon, octagon or oval cross-sections are
possible. He may therefore minimise the wall thickness of the
separating body and the wall thicknesses of the ducts. He is able
to select the wall thicknesses and the shape of the ducts such that
the surface area that is contributed to the cross-section of the
separating body by the walls is minimal. That means that the
pressure drop over the separating body can be minimised.
[0060] The apparatus can have a small or large number of ducts.
Just as explained in the prior art apparatuses the number of ducts
suitably ranges from 100 to 1,000,000, preferably from 500 to
500,000. The diameter of the cross-section of the ducts can be
varied in accordance with the amount of gas and amounts and nature,
e.g., droplet size distribution, of contaminants and the desired
contaminants removal efficiency. Suitably, the diameter is from
0.05 to 50 mm, preferably from 0.1 to 20 mm, and more preferably
from 0.1 to 5 mm. By diameter is understood twice the radius in
case of circular cross-sections or the largest diagonal in case of
any other shape.
[0061] The size of the apparatus and in particular of the
separating body may vary in accordance with the amount of gas to be
treated. In EP-B 286 160 it is indicated that separating bodies
with a peripheral diameter of 1 m and an axial length of 1.5 m are
feasible. The separating body according to the present invention
may suitably have a radial length ranging from 0.1 to 5 m,
preferably from 0.2 to 2 m. The axial length ranges conveniently
from 0.1 to 10 m, preferably, from 0.2 to 5 m.
[0062] The number of discs may also vary over a large number. It is
possible to have only two discs if a simple separation is needed
and/or when the perforations can be easily made. Other
considerations may be whether parallel ducts are desired, or
whether a uniform diameter is wanted. Suitably the number of discs
varies from 3 to 1000, preferably from 4 to 500, more preferably
from 4 to 40. When more discs, are used the skilled person will
find it easier to gradually vary the diameter of the ducts and/or
to construct non-parallel ducts. Moreover, by increasing or
decreasing the number of discs the skilled person may vary the duct
length. So, when the conditions or the composition of the gas
changes, the skilled person may adapt the duct length easily to
provide the most optimal conditions for the apparatus of the
present invention. The size of the discs is selected such that the
radial diameter suitably ranges from 0.1 to 5 m, preferably from
0.2 to 2 m. The axial length of the discs may be varied in
accordance with construction possibilities, desire for varying the
shape etc. Suitably, the axial length of each disc ranges from
0.001 to 0.5 m, preferably from 0.002 to 0.2 m, more preferably
from 0.005 to 0.1 m.
[0063] Although the discs may be manufactured from a variety of
materials, including paper, cardboard, and foil, it is preferred to
manufacture the discs from metal or ceramics. Metals discs have the
advantage that they can be easily perforated and be combined to
firm sturdy separating bodies. Dependent on the material that needs
to be purified a suitable metal can be selected. For some
applications carbon steel is suitable whereas for other
applications, in particular when corrosive materials are to be
separated, stainless steel may be preferred. Ceramics have the
advantage that they can be extruded into the desired form such as
in honeycomb structures with protruding ducts.
[0064] Typically, the ceramics precursor material is chosen to form
a dense or low-porosity ceramic. Thereby the solid or liquid
contaminants are forced to flow along the wall of the ducts and
not, or hardly, through the ceramic material of the walls. Examples
of ceramic materials are silica, alumina, zirconia, optionally with
different types and concentrations of modifiers to adapt its
physical and/or chemical properties to the gas and the
contaminants.
[0065] The discs may be combined to a separating body in a variety
of ways. The skilled person will appreciate that such may depend on
the material from which the discs have been manufactured. A
convenient manner is to attach the discs to a shaft that provides
the axis of rotation. Suitable ways of combining the discs include
clamping the discs together, but also gluing them or welding them
together can be done. Alternatively, the discs may be stacked in a
cylindrical sleeve. This sleeve may also at least partly replace
the shaft. This could be convenient for extruded discs since no
central opening for the shaft would be required. It is preferred to
have metal discs that are welded together.
[0066] In a preferred embodiment of the invention, the methane
enriched gaseous phase obtained in accordance with the present
invention is further purified, e.g. by extraction of remaining
acidic components with a chemical solvent, e.g. an aqueous amine
solution, especially aqueous ethanolamines, such as DIPA, DMA,
MDEA, etc., or with a physical solvent, e.g. cold methanol, DEPG,
NMP, etc.
[0067] The contaminated gas stream is continuously provided,
continuously cooled and continuously separated.
[0068] The present invention also relates to a device (plant) for
carrying out the process as described above, as well as the
purified gas stream obtained by the present process. In addition,
the present invention concerns a process for liquefying a feed gas
stream comprising purifying the feed gas stream by means of the
present process, followed by liquifying the purified feed gas
stream by methods known in the art.
[0069] The invention will be further illustrated by means of the
following Figures.
[0070] Referring to FIG. 1, natural gas via a conduit 1 is passed
through an expansion means 2, whereby a stream is obtained
comprising liquid phase contaminant and a methane enriched gaseous
phase. The stream flows via a conduit 3 into a gas/liquid separator
4 wherein the two phases are separated from each other. The liquid
phase contaminant is recovered via a conduit 5, whereas the methane
enriched gaseous phase is passed via a conduit 6 into a heat
exchanger 7. In heat exchanger 7 ethane is used as an external
refrigerant whereby the ethane is cooled by means of an
ethane/propane cascade 8 as depicted in more detail in FIG. 2. The
methane enriched gaseous phase is cooled in the heat exchanger 7 to
a temperature whereby a liquid phase contaminant and an methane
enriched gaseous phase are formed. The stream which comprises these
two phases is then passed via a conduit 9 into a gas/liquid
separator 10 from which a further enriched methane enriched gaseous
phase is recovered via a conduit 11 and liquid phase contaminant is
recovered via a conduit 12.
[0071] In FIG. 2 the heat exchanger 7 is shown using ethane that is
cooled by means of an ethane/propane cascade which comprises an
ethane loop and a propane loop. In the ethane loop an ethane stream
is passed via a conduit 13 into an expander 14 (e.g. a turbine
expander or a Joule-Thomson valve), and the cooled ethane stream so
obtained is passed via a conduit 15 into the heat exchanger 7. A
stream of warm ethane is then passed from the heat exchanger 7 to a
recompressor 16 via a conduit 17 to increase the pressure of the
ethane stream. The compressed stream of ethane obtained from
recompressor 16 is then passed via a conduit 18 into a heat
exchanger 19 wherein the ethane stream is cooled and at least
partly condensed. Via the conduit 13 the ethane stream is then
recycled to the expander 14. In the propane loop a propane stream
is passed via a conduit 20 into an expander 21 (e.g. a turbine
expander or a Joule-Thomson valve), and the cooled propane stream
so obtained is passed via a conduit 22 into the heat exchanger 19
of the ethane loop. A stream of warm propane is then passed from
the heat exchanger 19 via a conduit 23 into a recompressor 24 to
increase the pressure of the propane stream. The compressed stream
of propane obtained from recompressor 24 is then passed via a
conduit 25 into heat exchanger 26 wherein the propane stream is
cooled and at least partly condensed by means of water or air. Via
the conduit 20 the propane stream is then recycled to the expander
21.
[0072] In FIG. 3 a suitable gas/liquid separator is shown for use
in steps 3) and 5) of the present process. Both the gas/liquid
separators 4 and 10 as shown in FIG. 1 can be of this type. The
stream comprising liquid phase contaminant and a methane enriched
gaseous phase is passed via the conduit 3 (or the conduit 9) into
the gas/liquid separator 4 (or the gas/liquid separator 10) via
supply and distribution assembly 27. Most of the liquid will flow
down to the lower end of the separator and leave the separator via
the liquid outlet 5. The gaseous stream comprising larger and
smaller droplets will flow upwards via liquid coalescer 28,
centrifugal separator 29 and a second liquid coalescer 30 to the
top of the separator vessel, and leave the separator vessel via the
gas outlet 6.
[0073] In FIG. 4 another suitable gas/liquid separator is shown for
use in steps 3) and 5) of the present process. Both the gas/liquid
separators 4 and 10 as shown in FIG. 1 can be of this type. The
stream comprising liquid phase contaminant and a methane enriched
gaseous phase is passed via the conduit 3 (or the conduit 9) to a
gas inlet 31 in a housing 32 of the gas/liquid separator 4 (or the
gas/liquid separator 10). The housing 32 further comprises a
separating body 33 which shows a large number of ducts 34 which are
arranged around a shaft 35, which provides an axis of rotation.
Separating body 33 has been composed of six discs 33a, 33b, 33c,
33d, 33e and 33f that have been combined by welding or gluing. In
the rotating separating body droplets of carbon dioxide and/or
hydrogen sulphide are separated from the natural gas. The separated
contaminants are discharged from the housing via a contaminants
outlet 36 which has been arranged downstream of the separating body
33, and via the discharge conduit 5. Purified natural gas leaves
housing 32 via the gas outlet 6 arranged at the opposite end of the
housing 32.
* * * * *