U.S. patent application number 15/779652 was filed with the patent office on 2018-09-13 for method of removing co2 from a contaminated hydrocarbon stream.
The applicant listed for this patent is SHELL OIL COMPANY. Invention is credited to Raimo Edwin Gregor POORTE, Michiel Gijsbert VAN AKEN, Laurens Joseph Arnold Marie VAN CAMPEN, Helmar VAN SANTEN.
Application Number | 20180259251 15/779652 |
Document ID | / |
Family ID | 55077330 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180259251 |
Kind Code |
A1 |
POORTE; Raimo Edwin Gregor ;
et al. |
September 13, 2018 |
METHOD OF REMOVING CO2 FROM A CONTAMINATED HYDROCARBON STREAM
Abstract
The present invention provides a method to separate CO2 from a
contaminated hydrocarbon-containing stream. The method comprises
obtaining a multiphase contaminated hydrocarbon-containing stream
(100) containing at least a vapour phase, a liquid phase and a
solid phase, creating a slurry stream (120) from the multiphase
stream. The slurry stream is fed to a crystallization chamber
comprising CO2 seed particles. A liquid hydrocarbon stream (170) is
obtained from the crystallization chamber (91) and a concentrated
slurry (140) is obtained. The concentrated slurry (140) is removed
from the crystallization chamber (91) by means of an extruder
(142), thereby obtaining solid CO2. A feedback stream (141) is
obtained from the solid CO2 comprising CO2 seed particles having an
average size greater than 100 micron. The feedback stream (141) is
passed into the crystallization chamber (91).
Inventors: |
POORTE; Raimo Edwin Gregor;
(Rijswijk, NL) ; VAN AKEN; Michiel Gijsbert; (The
Hague, NL) ; VAN CAMPEN; Laurens Joseph Arnold Marie;
(Amsterdam, NL) ; VAN SANTEN; Helmar; (Amsterdam,
NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHELL OIL COMPANY |
HOUSTON |
TX |
US |
|
|
Family ID: |
55077330 |
Appl. No.: |
15/779652 |
Filed: |
December 1, 2016 |
PCT Filed: |
December 1, 2016 |
PCT NO: |
PCT/EP2016/079403 |
371 Date: |
May 29, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 2215/04 20130101;
F25J 2245/90 20130101; F25J 2210/04 20130101; F25J 2245/02
20130101; Y02C 20/40 20200801; B01D 43/00 20130101; B01D 2257/504
20130101; F25J 2270/04 20130101; F25J 1/0202 20130101; F25J 3/067
20130101; F25J 2220/66 20130101; F25J 3/061 20130101; B01D 53/002
20130101; B01D 2256/245 20130101; F25J 1/0037 20130101; F25J 1/004
20130101; F25J 2240/02 20130101; Y02C 10/12 20130101; F25J 1/0035
20130101; F25J 2205/20 20130101; F25J 2230/60 20130101; F25J 3/0635
20130101; F25J 2205/10 20130101; F25J 2230/30 20130101; F25J
2205/84 20130101; F25J 1/0022 20130101; F25J 2235/60 20130101; F25J
2270/88 20130101 |
International
Class: |
F25J 3/06 20060101
F25J003/06; F25J 1/00 20060101 F25J001/00; F25J 1/02 20060101
F25J001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2015 |
EP |
15197896.2 |
Claims
1. A method to separate CO2 from a contaminated
hydrocarbon-containing stream; the method comprising (a) providing
a multiphase contaminated hydrocarbon-containing stream, from the
contaminated hydrocarbon-containing stream, the multiphase
contaminated hydrocarbon-containing stream containing at least a
liquid phase and a solid phase, wherein the solid phase comprises
CO2 particles; (b1) feeding a slurry stream obtained from the
multiphase contaminated hydrocarbon-containing stream to a
crystallization chamber, the crystallization chamber comprising
seed particles, the seed particles comprising CO2; (b2) obtaining a
liquid hydrocarbon stream from the crystallization chamber, thereby
forming a concentrated slurry in the crystallization chamber; (b3)
removing the concentrated slurry from the crystallization chamber
by means of an extruder and obtaining a CO2 enriched solid product
and a methane enriched liquid hydrocarbon stream from the
extruder.
2. The method according to claim 1, wherein the method further
comprises (b4) obtaining a CO2 feedback stream from the CO2
enriched solid product obtained in (b3), the feedback stream
comprises CO2, (b5) feeding back the CO2 feedback stream to a
feedback inlet, the feedback inlet being in the crystallization
chamber or at a position upstream of the crystallization chamber to
provide seed particles.
3. The method according to claim 2, wherein the seed particles
provided in (b5) have an average size greater than 20 micron.
4. The method according to claim 2, wherein (b4) comprises
obtaining a CO2 feedback stream comprising CO2 seed particles and
(b5) comprises passing the feedback stream (141) into the
crystallization chamber (91) to provide the seed particles to the
crystallization chamber.
5. The method according to claim 2, wherein (b4) comprises breaking
the solid CO2 obtained in (b3) to form the seed particles.
6. The method according to claim 2, wherein (b4) comprises adding a
carrier fluid, such as a liquid natural gas stream, to the feedback
stream.
7. The method according to claim 2, wherein (b4) comprises heating
at least part of the CO2 enriched solid product thereby creating a
liquid CO2 enriched stream, and forming the feedback stream from at
least part of the liquid CO2 enriched stream, the CO2 seed
particles being formed from the liquid CO2 enriched stream.
8. The method according to claim 7, wherein (b5) comprises spraying
the liquid CO2 enriched stream into a feedback position thereby
creating seed particles.
9. The method according to claim 7, wherein (b5) comprises
processing the liquid CO2 enriched stream to form the CO2 seed
particles and feeding back the CO2 seed particles by passing the
CO2 seed particles to the crystallization chamber or to a position
upstream of the crystallization chamber to provide seed
particles.
10. The method according to claim 1, wherein the method comprises
combining the methane enriched liquid hydrocarbon stream and the
liquid hydrocarbon stream obtained in step (b2).
11. The method according to claim 1, wherein (b2) further comprises
subjecting the liquid hydrocarbon stream obtained from the
crystallization chamber, to a polishing treatment to obtain a
polished liquid hydrocarbon stream and a residue stream, wherein
the method further comprises passing the polished liquid
hydrocarbon stream to the LNG storage tank.
12. The method according to claim 1, wherein the extruder comprises
a housing, the housing comprising at least one opening for
discharging the methane enriched liquid hydrocarbon stream.
13. The method according to claim 1, wherein step (a) comprises
(a1) providing a contaminated hydrocarbon-containing gas stream;
(a2) cooling the contaminated hydrocarbon-containing gas stream in
a first heat exchanger thereby obtaining a cooled contaminated
hydrocarbon-containing stream; (a3) cooling the cooled contaminated
hydrocarbon-containing stream in an expander thereby obtaining a
partially liquefied stream; (a4) separating the partially liquefied
stream in a separator thereby obtaining a gaseous stream and a
liquid stream; (a5) expanding the liquid steam obtained in step
(a4) thereby obtaining the multiphase contaminated
hydrocarbon-containing stream, the multiphase contaminated
hydrocarbon-containing stream containing at least a vapour phase, a
liquid phase and a solid phase, wherein the solid phase comprises
CO2 particles.
14. The method according to claim 1, wherein the method further
comprises (d) passing the gaseous stream obtained in step (a4)
through the first heat exchanger thereby obtaining a heated gaseous
stream); and (e) compressing the heated gaseous stream thereby
obtaining a compressed gas stream; and (f) combining the compressed
gas stream obtained in step (e) with the contaminated
hydrocarbon-containing gas stream provided in step (a1).
15. The method according to claim 1, wherein the extruder exerts an
extrusion force which pushes the solid phase particles present in
the concentrated slurry together to form larger CO2 particles, CO2
chunks or a (semi) continuous solid CO2 product stream, and the
extrusion force squeezes out the liquid present in the concentrated
slurry, e.g. via holes or filters in the housing of the
extruder.
16. A system for separating CO2 from a contaminated
hydrocarbon-containing stream; the system comprising a conduit
suitable for carrying a multiphase contaminated
hydrocarbon-containing stream, the multiphase contaminated
hydrocarbon-containing stream containing at least a liquid phase
and a solid phase, wherein the solid phase comprises CO2 particles,
a solid-liquid separator comprising a crystallization chamber, the
crystallization chamber comprising a slurry inlet being in fluid
communication with the conduit to receive a slurry stream obtained
from the multiphase contaminated hydrocarbon-containing stream, a
fluid outlet for discharging a liquid hydrocarbon stream from the
crystallization chamber, a concentrated slurry outlet, an extruder
being in fluid communication with the crystallization chamber via
the concentrated slurry outlet to receive concentrated slurry from
the crystallization chamber and discharge a CO2 enriched solid
product and a methane enriched liquid hydrocarbon stream.
17. System The system according to claim 16, wherein the
crystallization chamber comprises an overhead venting outlet.
18. System The system according to claim 16, wherein the slurry
inlet is formed by a downcomer with a discharge opening, the
solid-liquid separator comprises a weir having an upper edge
positioned at a level gravitational above or below the discharge
opening, wherein the fluid outlet for discharging the liquid
hydrocarbon stream from the crystallization chamber is positioned
at an opposite side of the weir than the discharge opening of the
downcomer.
19. The system according to claim 16, wherein the system comprises
a seed particle forming device, such as a scraper, arranged to
obtain seed particles from the solid CO2 obtained from the
extruder, the seed particles having an average size greater than
100 micron.
20. System The system according to claim 16, wherein the extruder
comprises holes or filters in a housing of the extruder through
which the methane enriched liquid hydrocarbon stream is obtained.
Description
[0001] The present invention relates to a method to separate CO2
from a contaminated hydrocarbon-containing stream.
[0002] Methods of liquefying hydrocarbon-containing gas streams are
well known in the art. It is desirable to liquefy a
hydrocarbon-containing gas stream such as natural gas stream for a
number of reasons. As an example, natural gas can be stored and
transported over long distances more readily as a liquid than in
gaseous form, because it occupies a smaller volume and does not
need to be stored at high pressures. Typically, before being
liquefied, the contaminated hydrocarbon-containing gas stream is
treated to remove one or more contaminants (such as H.sub.2O,
CO.sub.2, H.sub.2S and the like) which may freeze out during the
liquefaction process or are undesirable in the product.
[0003] WO2014/166925 describes a method of liquefying a
contaminated hydrocarbon-containing gas stream, the method
comprising at least the steps of:
[0004] (1) providing a contaminated hydrocarbon-containing gas
stream;
[0005] (2) cooling the contaminated hydrocarbon-containing gas
stream in a first heat exchanger thereby obtaining a cooled
contaminated hydrocarbon-containing stream;
[0006] (3) cooling the cooled contaminated hydrocarbon-containing
stream in an expander thereby obtaining a partially liquefied
stream;
[0007] (4) separating the partially liquefied stream in a separator
thereby obtaining a gaseous stream and a liquid stream;
[0008] (5) expanding the liquid steam obtained in step (4) thereby
obtaining a multiphase stream, the multiphase stream containing at
least a vapour phase, a liquid phase and a solid phase;
[0009] (6) separating the multiphase stream in a separator thereby
obtaining a gaseous stream and a slurry stream;
[0010] (7) separating the slurry stream in a solid/liquid separator
thereby obtaining a liquid hydrocarbon stream and a concentrated
slurry stream;
[0011] (8) passing the gaseous stream obtained in step (4) through
the first heat exchanger thereby obtaining a heated gaseous stream;
and
[0012] (9) compressing the heated gaseous stream thereby obtaining
a compressed gas stream; and
[0013] (10) combining the compressed gas stream obtained in step
(9) with the contaminated hydrocarbon-containing gas stream
provided in step (1).
[0014] The method as described in WO2014/166925 allows liquefying a
contaminated hydrocarbon-containing gas stream with a relatively
low equipment count, thereby providing a simple and cost-effective
method of liquefying a contaminated hydrocarbon-containing gas
stream, in particular a methane-containing contaminated gas stream
such as natural gas.
[0015] The contaminant may be CO2. The solubility of CO2 in
liquefied natural gas is very low. So, the method according to
WO2014/166925 doesn't remove the CO2 in the gaseous phase, but by
expansion over a valve, leading to a rapid oversaturation of the
liquids, leading to solid CO2 formation. The particles are allowed
to reach equilibrium and may then be removed with the use of a
cyclone, settler, filter or a combination thereof.
[0016] However, as the CO2 particles typically have a relatively
small size, flow assurance and separation problems are likely to
occur. This could result in solid CO2 residue in the product or in
clogging causing operational instabilities.
[0017] Furthermore, the waste stream may be a mix of CO2 and
valuable hydrocarbons. The handling of the fine-grained slurry
makes separation difficult and may lead to a significant loss of
valuable hydrocarbons and thus a loss of value.
[0018] Other methods for removing gaseous contaminants from a gas
stream comprising gaseous contaminants, including CO2, are known
from the prior art, such as WO2010/023238 and U.S. Pat. No.
3,376,709.
[0019] U.S. Pat. No. 3,376,709 describes separation of acid gases
from natural gas by solidification by a process which comprises
providing the feed natural gas at conditions of pressure and
temperature as to constitute a liquid solution, reducing the
pressure on the solution to provide a mixture consisting of solid,
liquid and vapor phases, immediately contacting the mixture with
liquid natural gas containing solid acid gas particles and removing
solid acid gas particles therefrom. According to U.S. Pat. No.
3,376,709 the size of the solid acid gas particles is typically
from about 0.001 to about 2 microns. As already mentioned above,
the handling of fine-grained slurry makes separation difficult and
may lead to a significant loss of value.
[0020] It is an object of the present invention to at least
partially overcome at least one of these problems.
[0021] One or more of the above or other objects are achieved
according to the present invention by a method to separate CO2 from
a contaminated hydrocarbon-containing stream (10); the method
comprising
[0022] (a) providing a multiphase contaminated
hydrocarbon-containing stream (100) from the contaminated
hydrocarbon-containing stream (10), the multiphase contaminated
hydrocarbon-containing stream (100) containing at least a liquid
phase and a solid phase, wherein the solid phase comprises CO2
particles;
[0023] (b1) feeding a slurry stream (120) obtained from the
multiphase contaminated hydrocarbon-containing stream (100) to a
crystallization chamber (91), the crystallization chamber (91)
comprising seed particles, the seed particles comprising CO2;
[0024] (b2) obtaining a liquid hydrocarbon stream (170) from the
crystallization chamber (91), thereby forming a concentrated slurry
(140) in the crystallization chamber (91);
[0025] (b3) removing the concentrated slurry (140) from the
crystallization chamber (91) by means of an extruder (142) and
obtaining a CO2 enriched solid product and a methane enriched
liquid hydrocarbon stream (147) from the extruder (142).
[0026] According to a further aspect there is provided a system for
separating CO2 from a contaminated hydrocarbon-containing stream;
the system comprising
a conduit (100) suitable for carrying a multiphase contaminated
hydrocarbon-containing stream, the multiphase contaminated
hydrocarbon-containing stream containing at least a liquid phase
and a solid phase, wherein the solid phase comprises CO2 particles,
a solid-liquid separator (9) comprising a crystallization chamber
(91), the crystallization chamber (91) comprising [0027] a slurry
inlet (120) being in fluid communication with the conduit (100) to
receive a slurry stream obtained from the multiphase contaminated
hydrocarbon-containing stream, [0028] a fluid outlet (174) for
discharging a liquid hydrocarbon stream (170) from the
crystallization chamber (91), [0029] a concentrated slurry outlet
(145), an extruder (142) being in fluid communication with the
crystallization chamber (91) via the concentrated slurry outlet
(145) to receive concentrated slurry (140) from the crystallization
chamber (91) and discharge a CO2 enriched solid product and a
methane enriched liquid hydrocarbon stream (147).
[0030] The use of an extruder allows an efficient way of removing
the concentrated slurry (140) from the crystallization chamber
(91), while at the same time a relatively pure CO2 enriched solid
product and a relatively pure methane enriched liquid hydrocarbon
stream (147) are obtained separately from each other.
[0031] The CO2 enriched solid product may also be referred to as a
CO2 enriched compact product, and vice versa.
[0032] The concentrated slurry comprises a liquid phase and a solid
phase, formed by a plurality of CO2 particles. The extruder
functions to remove the concentrated slurry out of the
crystallization chamber, compact the solids in the concentrated
slurry (140) and also functions as separator, at is separates the
solid phase from the liquid phase (creating the CO2 enriched solid
product and the methane enriched liquid hydrocarbon stream).
[0033] An extruder removes the concentrated slurry by exerting a
mechanical force (extrusion force) which pushes the solid phase
particles present in the concentrated slurry together to form
larger CO2 particles, CO2 chunks or a (semi) continuous solid CO2
product stream, which can be relatively easy separated from the
liquid. At the same time, the extrusion force squeezes out the
liquid present in the concentrated slurry, e.g. via holes or
filters in the housing of the extruder.
[0034] Any type of suitable extruder may be used, in particular a
screw extruder.
[0035] Preferably, the extruder comprises an extruder outlet 155
and the extruder is orientated such that the extruder outlet 155 is
at a gravitational lower level of the extruder.
[0036] It will be understood that the above method is applied in a
continuous manner wherein the different steps are performed
simultaneously. This also applies for the embodiments described
below. Where in this text the word step or steps is used or
numbering is used (like b1, b2), this is not done to imply a
specific order in time. The steps may be applied in any suitable
order, in particular including simultaneously.
[0037] Hereinafter the invention will be further described with
reference to the following non-limiting drawings:
[0038] FIGS. 1a-1b schematically depict embodiments of a method and
system to separate CO2 from a contaminated hydrocarbon-containing
stream, and
[0039] FIG. 2 schematically depicts an embodiment of a method and
system for performing a method of liquefying a contaminated
hydrocarbon-containing gas stream using the embodiment depicted in
FIG. 1b.
[0040] For the purpose of this description, same reference numbers
refer to same or similar components.
[0041] FIGS. 1a and 1b depict a method and system to separate CO2
from a contaminated hydrocarbon-containing stream.
[0042] First, a contaminated hydrocarbon-containing gas stream 10
is provided. Although the contaminated hydrocarbon-containing gas
stream is not particularly limited, it preferably is a methane-rich
gas stream such as natural gas.
[0043] According to a preferred embodiment, the contaminated
hydrocarbon-containing gas stream 10 comprises at least 50 mol %
methane, preferably at least 80 mol %. Preferably, the hydrocarbon
fraction of the contaminated hydrocarbon-containing gas stream 10
comprises especially at least 75 mol % of methane, preferably at
least 90 mol %. The hydrocarbon fraction in the natural gas stream
may suitably contain from between 0 and 25 mol % of
C.sub.2+-hydrocarbons (i.e. hydrocarbons containing 2 or more
carbon atoms per molecule), preferably between 0 and 20 mol % of
C.sub.2-C.sub.6 hydrocarbons, more preferably between 0.3 and 18
mol % of C.sub.2-C.sub.4 hydrocarbons, especially between 0.5 and
15 mol % of ethane.
[0044] The contaminant comprises CO2 and possibly comprises further
contaminants, such as H.sub.2S, H.sub.2O, C.sub.6+ hydrocarbons,
aromatic compounds.
[0045] The amount of contaminant in the contaminated
hydrocarbon-containing gas stream 10 is suitably between 0.5 and 50
mol %, typically above 1.0 mol % and below 20 mol %.
[0046] The amount of CO2-contaminant in the contaminated
hydrocarbon-containing gas stream is typically between 0.02 mol
%-15 mol % of the contaminated hydrocarbon-containing gas stream,
preferably in the range 0.02 mol %-5 mol %, more preferably in the
range 0.1 mol %-5 mol %, and even more preferably in the range 0.2
mol %-3 mol %, e.g. 2 mol %.
[0047] From the contaminated hydrocarbon-containing gas stream 10 a
multiphase contaminated hydrocarbon-containing stream 100 is
obtained. This is only schematically depicted in FIGS. 1a and 1b as
this may be done in different ways as will be appreciated by the
skilled person. A more detailed example will be described below
with reference to FIG. 2.
[0048] The multiphase contaminated hydrocarbon-containing stream
100 contains at least a liquid phase and a solid phase, the solid
phase comprising CO2 particles, the CO2 particles typically having
an average size smaller than 50 micron, for instance smaller than
20 micron. The multiphase contaminated hydrocarbon-containing
stream 100 may further comprise a vapour phase.
[0049] Downstream of the valve, at lower pressure and temperature,
the multiphase contaminated hydrocarbon-containing stream 100 is
oversaturated with CO2. The CO2 in excess over the solubility will
escape the liquid phase by crystallizing into a solid phase,
forming a stable system at prevailing conditions. The formation of
solid particles will start rapidly, but a certain amount of time is
required before the system approaches steady state conditions,
dependent on CO2 concentration, pressure and temperature, as can be
appreciated by the person skilled in the art.
[0050] FIGS. 1a-1b further show an optional separator 7 (shown with
dashed lines), a solid-liquid separator 9 comprising a
crystallization chamber 91, an extruder 140 and a feedback conduit
141.
[0051] In case the multiphase contaminated hydrocarbon-containing
stream 100 comprises a liquid phase, a solid phase and no vapour
phase, the multiphase contaminated hydrocarbon-containing stream
100 may be passed directly to the solid-liquid separator 9 as
slurry stream 120. A slurry comprises a liquid and a solid
phase.
[0052] In case the multiphase contaminated hydrocarbon-containing
stream 100 comprises a liquid phase, a solid phase and also a
vapour phase, the method may comprise
[0053] (a') separating the multiphase contaminated
hydrocarbon-containing stream (100) in a separator (7) thereby
obtaining a gaseous stream (110) and a slurry stream (120).
[0054] The slurry stream may then be passed on to the solid-liquid
separator 9.
[0055] The separator 7 may comprise an inlet being in fluid
communication with the conduit (100) to receive multiphase
contaminated hydrocarbon-containing stream, the separator (7)
further comprising a first outlet for a gaseous stream (110) and a
second outlet for a slurry stream (120).
[0056] Although the separator 7 and solid-liquid separator 9 are
shown and described as separate vessels connected by a down-comer
123, it will be understood that the separator 7 and solid-liquid
separator 9 may also be embodied as a single vessel comprising
separator 7 and solid-liquid separator 9.
[0057] The separator (7) as used in step (a') may be a cyclone
separator or a horizontal gravity based separator vessel. In a
cyclone separator, the stream is brought in rotation such that the
heavier components are forced outwardly and can be separated from
the lighter components to form the gaseous stream (110) and a
slurry stream (120).
[0058] Any suitable type of cyclone separator may be used aimed for
gas/liquid separation, including a (Gasunie) cyclone or an open
vertical vessel with a tangential inlet.
[0059] According to an embodiment the crystallization chamber (91)
is a gravity based separator vessel. The gravity based separator
vessel may be an open vessel.
[0060] Preferably the gravity based separator vessel is positioned
vertically, but a horizontal gravity based separator vessel may be
used as well. The terms vertical and horizontal are used here to
refer to the orientation of the longitudinal body axis, such as the
cylindrical body axis of the vessel.
[0061] The slurry stream 120 obtained from the multiphase
contaminated hydrocarbon-containing stream 100 (either directly or
via separator 7) is fed into the crystallization vessel 91 at the
top via a slurry inlet 120. The crystallization chamber 91 may
comprise a stirring device to prevent the slurry from solidifying
completely and/or to favour conditions to optimize crystal
growth.
[0062] The slurry inlet 120 is formed by a down-comer 123 having a
discharge opening 124, which, in use, is submerged into the slurry
contained in the crystallization vessel 91. Alternatively, the
down-comer 123 has its discharge opening 123 positioned below or
above the slurry contained in the crystallization vessel.
[0063] Liquid is separated from the crystallization vessel 91 over
a weir 92 and is discharged as liquid hydrocarbon stream 170. The
discharge opening 124 of the down-comer 123 may be positioned at a
gravitational level above or below a top edge of the weir 92.
[0064] According to an embodiment the slurry inlet (120) is formed
by a downcomer 123 with a discharge opening (124), the solid-liquid
separator (9) comprises a weir (92) having an upper edge positioned
at a level gravitational above or below the discharge opening
(124), wherein the fluid outlet (174) for discharging the liquid
hydrocarbon stream (170) from the crystallization chamber (91) is
positioned at an opposite side of the weir (92) than the discharge
opening (124) of the downcomer (124).
[0065] The weir separates liquid hydrocarbon from the slurry and
the solid CO2 particles.
[0066] The feedback conduit 141 may debouche in the crystallization
chamber 91 at a level below the upper edge of the weir 92.
[0067] According to an embodiment, step (b2) comprises passing the
liquid hydrocarbon stream (170) to a LNG storage tank. Passing the
liquid hydrocarbon stream 170 to the LNG storage tank may be done
by a pump 171. The liquid hydrocarbon stream 170 obtained from the
crystallization chamber 91 in step (b2) may comprise small
CO2-particles, e.g. having an average size smaller than 10 micron.
Optionally, these particles may be removed in a polishing step, as
described in more detail below.
[0068] In step b3, the extruder (142) exerts a mechanical force
(extrusion force) on the concentrated slurry (140) to move
concentrated slurry (140) out of the crystallization chamber (91)
thereby obtaining the CO2 enriched solid product. The CO2 enriched
solid product may in fact be a stream of compacted CO2 particles,
compacted CO2 chunks or a (semi) continuous solid CO2 product
stream. The CO2 enriched solid product may further comprise a
remainder of other process substances such as hydrocarbons.
[0069] The extrusion force drives the concentrated slurry through
an opening or die to compact or densify the concentrated slurry,
thereby obtaining the CO2 enriched solid product. Due to the
extrusion force exerted by the extruder (142) the CO2 particles
group together to form the solid product, which may obtained as a
continuous CO2 enriched solid product stream.
[0070] By the extrusion force exerted, the liquid present in the
concentrated slurry is squeezed out of the concentrated slurry 140
thereby obtaining a methane enriched liquid hydrocarbon stream
147.
[0071] Any suitable extruder may be used, including axial end plate
extruders, radial screen extruders, rotary cylinder extruders, ram
and piston type extruders and screw extruders.
[0072] The extruder 142 is preferably a screw extruder. Screw
extruders employ a screw (actuator) to exert the extrusion force on
the concentrated slurry 140 to move concentrated slurry 140 out of
the crystallization chamber 91.
[0073] A screw extruder 142 comprises a screw positioned in a drum
(housing). The screw comprises a helical ridge wrapped around a
shaft. The drum is formed by a cylindrical wall. The longitudinal
axes of the screw and the drum are aligned. The cylindrical wall
comprises one or more filters.
[0074] Rotation of the screw employs a force to drive the
concentrated slurry and densify the CO2 particles thereby obtaining
the CO2 enriched solid product, while the liquid present in the
concentrated slurry is squeezed out of the drum via the one or more
filters or openings in the drum wall to obtain the methane
enriched
[0075] According to an embodiment, the method further comprises
[0076] (b4) obtaining a CO2 feedback stream (141) from the CO2
enriched solid product obtained in (b3), the feedback stream (141)
comprises CO2,
[0077] (b5) feeding back the CO2 feedback stream (141) by passing
the CO2 feedback stream (141) to the crystallization chamber (91)
or to a position upstream of the crystallization chamber (91) to
provide the seed particles.
[0078] The seed particles may be provided to the crystallization
chamber directly, or may be provided to the crystallization chamber
(91) indirectly by feeding back the CO2 feedback stream (141) to a
position upstream of the crystallization chamber 91, in particular
to separator 7 or to multiphase contaminated hydrocarbon-containing
stream (100). The CO2 feedback stream may comprise the CO2 seed
particles (FIG. 1a) or may comprise liquid CO2 where the CO2 seed
particles are created upon re-introduction of the feedback stream
(FIG. 1b), as will be explained in more detail below.
[0079] In the crystallization chamber 91 a concentrated slurry 140
is formed by removing a liquid hydrocarbon stream 170 and allowing
the CO2 to crystallize. The concentrated slurry comprises less
liquid and larger CO2 particles than the slurry stream 120 obtained
from the multiphase contaminated hydrocarbon-containing stream
100.
[0080] This process is facilitated by providing CO2 seed particles
by means of the CO2 feedback stream 141.
[0081] According to an embodiment, the seed particles provided in
(b5) have an average size greater than 20 micron.
[0082] The seed particles provided in step (b5) may have an average
size greater than 50, or even greater than 100 micron.
[0083] By introducing relatively large seed particles in the
crystallization vessel via the CO2 feedback stream 142, the
crystallization process is facilitated and accelerated and as a
result, relatively large CO2 particles form in the concentrated
slurry 140, which can relatively easily be removed from the
crystallization chamber using the extruder.
[0084] The feedback stream that is used to feed seed particles to
the crystallization vessel comprises seed particles having an
average size greater than 20 micron. Preferably the average size of
the seed particles in the feedback stream 141 is in the range 20
micron-20 mm, more preferably in the range 20 micron-1 mm and more
preferably in the range 50 micron-200 micron.
[0085] In order to optimize the crystallization process the seed
particles are preferably kept small to maximize the surface
available for crystallization. However, this would result in
relatively small CO2 particles being formed that do not settle
easily and are relatively difficult to separate. It has been found
that in combination with the extruder, seed particles having an
average size as indicated, provide a good balance between
crystallization speed (kg/s) on the one hand and ease of separation
on the other hand.
[0086] The term micron is used in this text in line with common
practice: 1 micron equals 1.times.10.sup.-6 metre.
[0087] According to an embodiment (b4) comprises obtaining a CO2
feedback stream comprising CO2 seed particles and (b5) comprises
passing the CO2 feedback stream (141) into the crystallization
chamber (91) to provide the seed particles to the crystallization
chamber (91). This embodiment is shown in FIG. 1a.
[0088] According to this embodiment the CO2 feedback stream
comprises seed particles having an average size greater than 20
micron. Preferably the average size of the seed particles in the
feedback stream 141 is in the range 20 micron-20 mm, more
preferably in the range 20 micron-1 mm and more preferably in the
range 50 micron-200 micron.
[0089] According to an embodiment (b4) comprises breaking the solid
CO2 obtained in (b3) to form the seed particles. The system may
comprise a seed particle forming device, such as a scraper,
chopper, die or palleting device, arranged to obtain seed particles
from the solid CO2 obtained from the extruder, the CO2 seed
particles. The seed particle forming device may be operated in a
vapour atmosphere.
[0090] A scraper may be used in step (b3) arranged to scrape CO2
seed particles from the solid CO2 obtained from the extruder to
create a CO2 feedback stream comprising seed particles having the
above indicated size. The scraper or breaker 148 may be positioned
directly downstream of an extruder outlet 155.
[0091] According to an embodiment (b4) comprises adding a carrier
fluid, such as a liquid natural gas stream, to the feedback stream
(141).
[0092] In order to transport the seed particles, the seed particles
may be suspended in a carrier fluid. The carrier fluid may be a
carrier liquid or a carrier gas. Preferably the carrier fluid is a
liquid natural gas stream.
[0093] By adding a carrier fluid to the feedback stream a suspended
feedback stream is obtained.
[0094] The carrier fluid may comprise a portion of the liquefied
natural gas as produced in the overall process. The liquefied
natural gas stream added to the feedback stream may be obtained
from the liquid hydrocarbon stream 170 obtained from the
crystallization chamber 91 in step b2. The liquefied natural gas
stream added to the feedback stream may also be obtained from the
polished liquid hydrocarbon stream 170', as will be discussed in
more detail below.
[0095] Depending on the particle size, the volumetric fraction of
the seed particles in the suspended feedback stream is in the range
30-70%, preferably in the range 40-60%. According to an alternative
embodiment, as depicted in FIG. 1b, the CO2 feedback stream
comprises liquid CO2 which is fed back by spray-cooling, thereby
forming seed particles.
[0096] According to an embodiment step (b4) comprises heating at
least part of the CO2 enriched solid product thereby creating a
liquid CO2 enriched stream, and forming the feedback stream (141)
from at least part of the liquid CO2 enriched stream.
[0097] The extruder 142 compresses the concentrated slurry and
increases the pressure to form the CO2 enriched solid product.
Next, the CO2 enriched solid product is heated to create a liquid
CO2 enriched stream, of which a part is taken to form the CO2
feedback stream. The CO2 seed particles may be formed from the
liquid CO2 enriched stream. According to this embodiment, no
carrier fluid is needed.
[0098] Heating may be done by one or more heaters 150. As shown in
FIG. 1a, the heater 150' may be positioned downstream of the
extruder to heat the part of the CO2 enriched solid product not
being passed to the feedback stream 141. According to the
embodiment shown in FIG. 1b, the heater 150 may be integrated into
the extruder 142 or being positioned adjacent to the extruder 142.
The heaters are preferably positioned close to or at the extruder
outlet 155.
[0099] The extruder 142 may be a screw extruder 142 comprising a
screw 151 being positioned in a barrel 152, the barrel comprising a
cylindrical wall surrounding the screw. The heaters 150 may be
integrated in the wall of the barrel at a position at or towards
the discharge extruder outlet 155.
[0100] According to an embodiment step (b5) comprises spraying the
liquid CO2 enriched stream into a feedback position thereby
creating seed particles.
[0101] Spraying may be done by introducing the liquid CO2 enriched
stream via one or more spraying nozzles 158. Upon entering the
vessel, the liquid CO2 droplets expand to a state where the liquid
phase does not exist. Almost all CO2 will solidify. Due to the high
local CO2 concentration, the resulting CO2 solid size will be
closely correlating to the CO2 droplet size. By adjusting the
droplet sizes produced by the spray nozzle, the seed particle size
can be adjusted to the preferred value.
[0102] The spraying nozzles comprise a plurality of nozzle
openings. By selecting the amount of nozzle openings and size of
the nozzle openings the size of the CO2 droplets and thus of the
CO2 seed particles provided may be controlled.
[0103] According to an embodiment step (b5) further comprises
processing the liquid CO2 enriched stream to form the CO2 seed
particles and feeding back the CO2 seed particles by passing the
CO2 seed particles to the crystallization chamber (91) or to a
position upstream of the crystallization chamber (91) to provide
seed particles.
[0104] Instead of spraying liquid CO2 into the crystallization
chamber or a position upstream, the liquid CO2 stream may be
converted into a stream comprising of solid CO2 parcels and a
transport medium, such as liquid or gaseous hydrocarbons. For this
pelleting, typically an expansion step into gas/solid is deployed,
followed by compression into pellets of the desired size.
[0105] As indicated above, the liquid hydrocarbon stream 170
obtained from the crystallization chamber 91 in (b2) may comprise
small CO2-particles.
[0106] In order to separate such CO2 particles from the liquid
hydrocarbon stream 170, according to an embodiment, (b2) further
comprises subjecting the liquid hydrocarbon stream (170) obtained
from the crystallization chamber to a polishing treatment (172) to
obtain a polished liquid hydrocarbon stream (170') and a residue
stream (175), wherein method further comprises [0107] passing the
polished liquid hydrocarbon stream (170') to the LNG storage tank
and [0108] optionally, recycling the residue stream (175) to the
crystallization vessel, e.g. by combining the residue stream (175)
with the feedback stream (141).
[0109] The optional polishing treatment serves the purpose of
removing any remaining small solids from the liquid hydrocarbon
stream (170), in particular any residual CO2 particles that may
have ended up in the liquid hydrocarbon stream. The polished liquid
hydrocarbon stream comprises less CO2 particles than the liquid
hydrocarbon stream as obtained from the crystallization chamber
91.
[0110] The residue stream 175 may be recycled, such as by combining
the residue stream 175 with one of the multiphase contaminated
hydrocarbon-containing stream 100, the feedback stream, the
concentrated slurry stream obtained from the crystallization
chamber 91. The residue stream may function as carrier fluid for
the feedback stream. The residue stream 175 may also be recycled by
introducing the residue stream 175 into one of the separator 7, the
crystallization vessel 91 or any other suitable vessel or stream
upstream of separator 7.
[0111] The polishing treatment may be any kind of suitable
polishing treatment, including passing the liquid hydrocarbon
stream through a filter, such as a band filter or HEPA filter, or
passing the liquid hydrocarbon stream through static separation
equipment, such as (parallel) desanding cyclones or one or more
(parallel) hydroclones 172, from which the residue stream is
obtained from the one or more bottom streams and the polished
liquid hydrocarbon stream is obtained by combining the one or more
top streams.
[0112] Passing the liquid hydrocarbon stream 170 to the LNG storage
tank may comprise passing the liquid hydrocarbon stream through a
pressure reduction stage, e.g. formed by a throttle vale 173 and/or
an end flash vessel.
[0113] According to an embodiment, the method further comprises
obtaining a venting stream (121) from the crystallization chamber
(91).
[0114] The separator 7 and the solid-liquid separator 9 may operate
at substantial equal pressure. In embodiments wherein the downcomer
120, in use, does not allow vapour or gas to flow from the
solid-liquid separator 9 to the separator 7, a vent line (121) may
be provided to allow such a flow. This is in particular the case in
embodiments wherein the downcomer debouches under the liquid or
slush level in the solid-liquid separator 9.
[0115] The crystallization chamber (91) may comprise an overhead
venting outlet (122).
[0116] A venting conduit may be provided which is with one end in
fluid communication with the venting outlet and with an other end
in fluid communication with the separator 7 to feedback the venting
stream to the separator.
[0117] The venting outlet is preferably positioned in a top part of
the crystallization chamber.
[0118] Gas may escape from the slurry stream after having been fed
to the crystallization chamber. The venting stream may be passed to
the separator (7) of step (a') via the venting conduit.
Alternatively, the venting stream may be combined with the gaseous
stream 110 obtained in (a').
[0119] At the bottom of the crystallization vessel 91, a connection
is made to the extruder, in particular a screw extruder. Connection
between the extruder and the crystallization vessel can be made by
any method known in the art.
[0120] According to an embodiment a portion of the concentrated
slurry (140) removed from the crystallization chamber (91) not
being part of the feedback stream (141) is liquefied by heating (by
means of a heater downstream of the extruder 142 or by means of an
integrated heater (integrated into the extruder) thereby obtaining
a liquefied concentrated stream (144) and the liquefied
concentrated stream (144) is
passed to a distillation column to obtain a hydrocarbon enriched
top stream and a CO2 enriched bottom stream , or passed to a carbon
capture storage, or passed to a geological storage for CO2 passed
to a flash vessel to obtain a gaseous hydrocarbon enriched top
stream and a liquid CO2 enriched bottom stream from the flash
vessel, or passed through a membrane unit to obtain a CO2 enriched
stream that is vented and a hydrocarbon enriched stream which is
recycled upstream in the process or that can be discharged
separately.
[0121] The gaseous hydrocarbon enriched top stream obtained from
the flash vessel may be combined with a fuel gas stream.
[0122] As indicated above, in step (b3) the concentrated slurry 140
is removed from the crystallization chamber 91 by means of an
extruder 142, thereby obtaining solid CO2. The term concentrated
slurry is used to indicate that the density and viscosity of the
concentrated slurry is higher than the density and viscosity of the
slurry as comprised by the slurry stream received from separator
7.
[0123] The extruder is in fluid communication with a lower part of
the crystallization chamber 91, preferably with a lowest part of
the crystallization chamber 91 such that under the influence of
gravity, the extruder receives a relatively dense portion of the
concentrated slurry 140.
[0124] The extruder mechanically forces the concentrated slurry 140
out of the crystallization chamber 91, pushing the CO2 particles
together and pushing liquids out of the concentrated slurry
creating solid CO2, preferably in the form of a continuous solid
CO2 stream and a methane enriched liquid hydrocarbon stream
147.
[0125] According to an embodiment the extruder comprises a housing,
the housing comprising at least one opening for discharging the
methane enriched liquid hydrocarbon stream (147). The housing
comprises an extruder outlet 155 for discharging the CO2 enriched
solid product and at least one opening for discharging the methane
enriched liquid hydrocarbon stream (147). The one or more openings
may comprise filters allowing the methane enriched liquid
hydrocarbon through but not allowing the CO2 enriched solid product
through.
[0126] Step (b3) then comprises obtaining the methane enriched
liquid hydrocarbon stream (147) from the extruder (142) via the at
least one opening for discharging the methane enriched liquid
hydrocarbon stream (147).
[0127] The housing forms a flow path from an extruder inlet being
in fluid communication with a concentrated slurry outlet (145) of
the crystallization chamber (91) to the extruder outlet (155), the
extruder comprising an actuator being at least partially positioned
in the housing to mechanically push the concentrated slurry (140)
from the crystallization chamber (91) towards the extruder outlet,
wherein the housing comprises one openings for discharging the
methane enriched liquid hydrocarbon stream (147).
[0128] The at least one opening for discharging the methane
enriched liquid hydrocarbon stream (147) is preferably in fluid
communication with a conduit carrying the liquid hydrocarbon stream
(170) obtained in step (b2) from the crystallization chamber 91,
the method thus comprising combining the methane enriched liquid
hydrocarbon stream (147) and the liquid hydrocarbon stream (170)
obtained in step (b2) from the crystallization chamber 91.
[0129] FIG. 2 shows an embodiment of how the method and system as
described above with reference to FIG. 1b may be embedded in a
process/liquefaction scheme generally referred to with reference
number 1.
[0130] The process scheme 1 comprises a compressor 2, a heat
exchanger 3 ("the first heat exchanger"), an expander 4, a first
separator 5, a JT-valve 6, a second separator 7, an LNG storage
tank 11, further compressors 13 and 14, a second heat exchanger 15,
an expander 16 and an optional methanol separator 17. The process
scheme may comprise further heat exchangers in addition to the
first heat exchanger 3 and second heat exchanger 15.
Preferably, the first heat exchanger 3 and second heat exchanger 15
are separate heat exchangers.
[0131] During use of the process scheme 1, a contaminated
hydrocarbon-containing gas stream 10 is provided which is
compressed in compressor 2. The compressed contaminated
hydrocarbon-containing gas stream 20 is cooled (as stream 30) in
the first heat exchanger 3 thereby obtaining a cooled contaminated
hydrocarbon-containing gas stream 40. The first heat exchanger 3 is
(like the second heat exchanger 15) an indirect heat exchanger;
hence no direct contact between the streams takes place, but only
heat exchanging contact.
[0132] As shown in the embodiment of FIG. 2, the cooled
contaminated hydrocarbon-containing stream 40 is passed to the
methanol separator 17 to separate methanol (as stream 50) that has
been previously injected (e.g. into stream 20) to prevent hydrate
formation. After the methanol separator 17, the (methanol-depleted)
cooled contaminated hydrocarbon-containing gas stream is further
cooled as stream 60 in the expander 4 thereby obtaining a partially
liquefied stream 70. This partially liquefied stream 70 is
separated in separator 5 thereby obtaining a gaseous stream 80 and
a liquid stream 90. The liquid steam 90 is expanded in JT-valve 6
thereby obtaining the multiphase contaminated
hydrocarbon-containing stream 100 as described above which is
passed to the separator 7.
[0133] The gaseous stream 80 is passed through the first heat
exchanger 3 thereby obtaining a heated gaseous stream 270; if
desired some inerts (such as N.sub.2) may be removed from the
heated gaseous stream 270 as (minor) stream 280. As stream 80 is
used to cool the stream 30, this is an "auto-refrigeration"
step.
[0134] The heated gaseous stream 270 is compressed in compressor 13
thereby obtaining a compressed gas stream 220. Part 230 of the
compressed gas stream 220 is combined with the contaminated
hydrocarbon-containing gas stream 20.
[0135] As can be seen in the embodiment of FIG. 2, a part 240 of
the compressed gas stream 220 is passed through the second heat
exchanger 15 (and cooled therein) thereby obtaining a cooled
compressed gas stream 250. The cooled compressed gas stream 250 is
expanded in expander 16 thereby obtaining an expanded an expanded
gas stream 260. Subsequently, the expanded gas stream 260 is
combined with the gaseous stream 80 to form stream 265.
[0136] Furthermore, in the embodiment of FIG. 2, the gaseous stream
110 is passed as stream 190 through the second heat exchanger 15
thereby obtaining a second heated gaseous stream 200. The second
heated gaseous stream 200 is compressed in compressor 14 thereby
obtaining a second compressed gas stream 210; this second
compressed gas stream 210 is combined with the heated gaseous
stream 270 (to form stream 215).
[0137] Also, a boil-off gas stream 180 is obtained from the LNG
storage tank 11 which may be combined with the gaseous stream 110
obtained from separator 7 (in step (a')).
[0138] So, according to an embodiment, step (a) comprises
[0139] (a1) providing a contaminated hydrocarbon-containing gas
stream (10, 20);
[0140] (a2) cooling the contaminated hydrocarbon-containing gas
stream (20) in a first heat exchanger (3) thereby obtaining a
cooled contaminated hydrocarbon-containing stream (40);
[0141] (a3) cooling the cooled contaminated hydrocarbon-containing
stream (40) in an expander (4) thereby obtaining a partially
liquefied stream (70);
[0142] (a4) separating the partially liquefied stream (70) in a
separator (5) thereby obtaining a gaseous stream (80) and a liquid
stream (90);
[0143] (a5) expanding the liquid steam (90) obtained in step (a4)
thereby obtaining the multiphase contaminated
hydrocarbon-containing stream (100), the multiphase contaminated
hydrocarbon-containing stream (100) containing at least a liquid
phase and a solid phase, wherein the solid phase comprises CO2
particles. The multiphase contaminated hydrocarbon-containing
stream (100) may comprise a vapour phase.
[0144] The liquid hydrocarbon product stream obtained in step (a4)
may contain more CO.sub.2 than the partially liquefied stream, such
as at least 250 ppm-mol, and may comprise more C.sub.5+, such as at
least 0.1 mol %.
[0145] According to an embodiment, the method further comprises
[0146] (d) passing the gaseous stream (80) obtained in step (a4)
through the first heat exchanger (3) thereby obtaining a heated
gaseous stream (270); and
[0147] (e) compressing the heated gaseous stream (270) thereby
obtaining a compressed gas stream (220); and
[0148] (f) combining the compressed gas stream (220) obtained in
step (e) with the contaminated hydrocarbon-containing gas stream
(20) provided in step (a1).
[0149] The person skilled in the art will readily understand that
many modifications may be made without departing from the scope of
the invention. For instance, where the word step or steps is used
it will be understood that this is not done to imply a specific
order. The steps may be applied in any suitable order, including
simultaneously.
* * * * *