U.S. patent application number 13/003547 was filed with the patent office on 2011-06-30 for process for removing a gaseous contaminant from a contaminated gas stream.
Invention is credited to Diki Andrian, Rick Van Der Vaart.
Application Number | 20110154856 13/003547 |
Document ID | / |
Family ID | 40090334 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110154856 |
Kind Code |
A1 |
Andrian; Diki ; et
al. |
June 30, 2011 |
PROCESS FOR REMOVING A GASEOUS CONTAMINANT FROM A CONTAMINATED GAS
STREAM
Abstract
The invention provides a process for removing one or more
gaseous contaminants from a contaminated feed gas stream, the
process comprising 1) providing the contaminated feed gas stream,
2) cooling the contaminated feed gas stream to a temperature at
which liquid contaminant is formed as well as a contaminant
depleted gaseous phase, and 3) separating the two phases by
introducing them into a gas/liquid separator vessel, comprising 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. The contaminated gas stream can be a
methane-containing gas stream, especially a natural gas stream, or
a gas stream from a gasification or combustion process. The
invention further provides a device for carrying out the process as
well as the purified gas stream.
Inventors: |
Andrian; Diki; (Rijswijk,
NL) ; Van Der Vaart; Rick; (Rijswijk, NL) |
Family ID: |
40090334 |
Appl. No.: |
13/003547 |
Filed: |
July 3, 2009 |
PCT Filed: |
July 3, 2009 |
PCT NO: |
PCT/EP09/58403 |
371 Date: |
March 8, 2011 |
Current U.S.
Class: |
62/618 |
Current CPC
Class: |
F25J 2215/04 20130101;
Y02C 20/40 20200801; F25J 3/067 20130101; C10L 3/102 20130101; Y02C
10/12 20130101; B01D 45/16 20130101; B01D 46/0031 20130101; F25J
2270/90 20130101; F25J 2205/10 20130101; F25J 3/0635 20130101; C10L
3/10 20130101; F25J 3/061 20130101; B01D 50/002 20130101 |
Class at
Publication: |
62/618 |
International
Class: |
F25J 3/08 20060101
F25J003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2008 |
EP |
08160067.8 |
Claims
1. A process for removing one or more gaseous contaminants from a
contaminated feed gas stream, the process comprising 1) providing
the contaminated feed gas stream, 2) cooling the contaminated feed
gas stream to a temperature at which liquid contaminant is formed
as well as a contaminant depleted gaseous phase, and 3) separating
the two phases by introducing them into a gas/liquid separator
vessel, comprising 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.
2. Process according to claim 1, in which the gas inlet comprises
an admittance with a supply and distribution assembly extending
horizontally in the separator vessel, the assembly consisting of 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.
3. Process according to claim 1, in which the horizontal coalescer
consists of one or more layers of gauze.
4. Process according to claim 1, in which the horizontal coalescer
consists of a layer of vanes.
5. Process according to claim 1, in which the horizontal coalescer
consists of a layer of structured packing.
6. Process according claim 1, in which 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 a 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.
7. Process according to claim 6, in which in the separation vessel
a second normally horizontal liquid coalescer is present above the
centrifugal liquid separator and over the whole cross-section of
the vessel, wherein the second coalescer is arranged to remove
liquids from the secondary gas.
8. Process according to claim 7, in which the second coalescer is a
bed of one or more layers of gauze.
9. A process according to claim 1, in which the gaseous
contaminants are acidic gaseous contaminants, comprising carbon
dioxide or hydrogen sulphide, wherein the natural gas stream
comprises between 5 and 80 vol % of methane.
10. A process according to claim 1, in which the contaminated gas
stream has a temperature between -20 and 150.degree. C., and a
pressure between 10 and 150 bara.
11. A process according to claim 1, in which the cooling is done by
isenthalpic expansion.
12. A process according to claim 11, in which the feed gas stream
is pre-cooled to a temperature between 15 and -35.degree. C. before
expansion.
13. A process according to claim 1, in which the cooling is done by
heat exchange against a cold fluidum.
14. A process according to claim 1, in which the contaminated gas
stream is cooled to a temperature between -30 and -80.degree.
C.
15. (canceled)
Description
[0001] The invention relates to a process for removing one or more
gaseous contaminants, such as carbon dioxide or hydrogen sulphide,
from a contaminated gas stream containing methane, especially a
natural gas stream. The invention further relates to a device for
carrying out the process and to the purified gas stream obtainable
by the process.
[0002] The removal of acidic gaseous contaminants, especially
carbon dioxide and/or hydrogen sulphide, from methane containing
gas streams has been described in several publications.
[0003] In WO 2004/070297 a process for removing gaseous
contaminants from a natural gas stream is described. In this
process, water is removed from the feed gas stream by cooling, the
cooling resulting in methane hydrate formation. This step is
followed by separation of the hydrates and further cooling of the
remaining gas stream, resulting in the formation of solid acidic
contaminants. After separation of the solid acidic contaminants a
cleaned natural gas stream is obtained. Heating is used to convert
the solid contaminants into a slurry or liquid. The slurry or
liquid is removed from the separation zone. Usually special
measures are necessary to remove also the smallest solid particles
from the gas stream.
[0004] In WO 2003/062725 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.
[0005] In WO 2007/030888 a process is described similar to the
process described in WO 2004/070297, followed by washing the
cleaned natural gas stream with methanol.
[0006] In U.S. Pat. No. 4,533,372 a cryogenic process is described
for the removal of carbon dioxide and/or hydrogen sulphide from
natural gas by treating the feedstream in a distillation zone and a
controlled freezing zone.
[0007] There is still a need for a further improved process to
remove carbon dioxide and/or hydrogen sulphide from natural gas
streams. It is especially desired to design a relatively simple
process, not requiring any rotating equipment, not requiring
cryogenic distillation processes, not requiring the handling of
solid particles or liquid/solid slurries and only having a minimum
plot space requirement (footprint).
[0008] The process according to the present invention comprises no
more than two steps requiring relatively simple equipment only. In
the first step the contaminated gas stream containing methane is
cooled until liquid contaminants condense, followed by a simple
gas/liquid separator, not needing any rotating equipment and not
needing any energy for a distillation section.
[0009] Thus, the process provides a process for removing one or
more gaseous contaminants from a contaminated feed gas stream, the
process comprising 1) providing the contaminated feed gas stream,
2) cooling the contaminated feed gas stream to a temperature at
which liquid contaminant is formed as well as a contaminant
depleted gaseous phase, and 3) separating the two phases by
introducing them into a gas/liquid separator vessel, comprising 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.
[0010] The process is a rather easy and uncomplicated process. It
actually comprises only a cooling step, followed by a simple
gas/liquid separation step, the separation step not involving any
moving equipment and not comprising any energy consuming steps.
When using a vertical gas/liquid separator vessel, the process can
be performed in a device only needing a relatively small plot
space.
[0011] 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 waves 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. In a preferred embodiment the longitudinal chamber has
two open vertical sides with a grid of guide vanes. Suitable
gas/liquid inlets are 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 inlet device.
[0012] There are numerous horizontal coalescers available,
especially for vertical columns. A well-known example of a
coalescer is a wire mesh. All of these are relatively tenuous
(large permeability) and have a relatively large specific
(internal) plot space. 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.
[0013] 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.
[0014] 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.
[0015] In a preferred embodiment, 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
The second coalescer is arranged to remove liquids from the
secondary gas. This has the advantage that any droplets still
present in the secondary gas are removed as described 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.
[0020] The contaminated gas stream may be any gas stream containing
acidic contaminants.
[0021] Suitably, the contaminated gas stream is a methane
containing gas stream, for instance from natural sources as natural
gas, associated gas or coal bed methane or from industrial sources
as refinery streams or synthetic sources as Fischer-Tropsch streams
or from biological sources as anaerobic waste or manure
fermentation. The amount of methane present may vary over a wide
range, e.g. from 3 to 90 vol %, preferably 5 and 80 vol % methane,
more preferably between 10 and 75 vol %.
[0022] The contaminated gas stream may also be a syngas stream
comprising carbon dioxide, a flue gas stream or a gas stream
obtained after combustion of coal. Syngas is a mixture of carbon
monoxide and hydrogen. A syngas stream comprising carbon dioxide is
generally obtained after converting part or most of the carbon
monoxide to carbon dioxide in a so-called water gas shift
reaction.
[0023] The acidic contaminants in the feedstream are especially
carbon dioxide and hydrogen sulphide, although also carbonyl
sulphide (COS), carbon disulphide (CS2), mercaptans, sulphides and
aromatic sulphur compounds may be present. Beside acidic
contaminants, also inerts may be present, for instance nitrogen and
noble gases as argon and helium. The amount of acidic contaminants
present in the feed gas may vary over a wide range. The amount of
carbon dioxide in the feed gas is suitably between 15 and 90 vol %,
preferably between 20 and 75 vol %. The amount of hydrogen sulphide
in the feed gas is suitably between 5 and 55 vol %, preferably
between 10 and 45 vol %.
[0024] The cooling of the feed gas 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. 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 one or more
Joule-Thomson valves. Preferably, more than one expander is used,
as this enables influencing the droplet size and/or droplet size
distribution.
[0025] 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 acidic 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 cooling may be used
to decrease the temperature first, optionally followed by further
cooling.
[0026] 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 contaminant
depleted stream or washing fluid or in which the cooling is done by
compression, cooling and expansion.
[0027] Suitably the feed gas stream is cooled to a temperature
between -30 and -80.degree. C., especially between -40 and
-60.degree. C. At these temperatures liquids will be formed.
[0028] The raw feed gas stream may be pre-treated to partially or
completely remove 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 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. Water may also be removed by means of washing with
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 0.01 vol %.
[0029] The feedstream for the process of the invention, optionally
pretreated as described above, will suitably have a pressure
between 10 and 120 bara, or even up till 160 bara. Especially, the
feedstream has a pressure between 15 and 70 bara, preferably
between 20 and 50 bara. The feedstream, preferably pretreated,
suitably has a temperature between -30 and 150.degree. C., suitably
between -20 and 70.degree. C., preferably between 0 and 50.degree.
C.
[0030] In a preferred embodiment of the invention, the contaminant
depleted gaseous phase 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.
[0031] The contaminated gas stream is continuously provided,
continuously cooled and continuously separated.
[0032] The invention is further explained by FIG. 1. In FIG. 1 a
device is shown for carrying out the process of the present
invention. A dry feed stream (water content 20 ppm, 60 bara) flows
via pipe 1 to turbo-expander 2. In the expander the temperature
drops to -45.degree. C. The feed gas comprises 40 vol % of carbon
dioxide, 2 vol % of ethane and 58 vol % of methane. The resulting
gas/liquid mixture is introduced into vertical gas/liquid separator
3 via supply and distribution assembly 4. Most of the liquid will
flow down to the lower end of the separator and leave the separator
via liquid outlet 5. The gaseous stream comprising larger and
smaller droplets will flow upwards via liquid coalescer 6,
centrifugal separator 7 and a second liquid coalescer 8 to the top
of the separator vessel, and leave the separator vessel via gas
outlet 9.
* * * * *