Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF REMOVING CO2 FROM
A CONTAMINATED HYDROCARBON STREAM
The present invention relates to a method to
separate CO2 from a contaminated hydrocarbon-containing
stream.
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 H20, CO2, HS and the like) which may freeze out
during the liquefaction process or are undesirable in the
product.
W02014/166925 describes a method of liquefying a
contaminated hydrocarbon-containing gas stream, the
method comprising at least the steps of:
(1) providing a contaminated hydrocarbon-containing
gas stream;
(2) cooling the contaminated hydrocarbon-containing
gas stream in a first heat exchanger thereby obtaining a
cooled contaminated hydrocarbon-containing stream;
(3) cooling the cooled contaminated hydrocarbon-
containing stream in an expander thereby obtaining a
partially liquefied stream;
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(4) separating the partially liquefied stream in a
separator thereby obtaining a gaseous stream and a liquid
stream;
(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;
(6) separating the multiphase stream in a separator
thereby obtaining a gaseous stream and a slurry stream;
(7) separating the slurry stream in a solid/liquid
separator thereby obtaining a liquid hydrocarbon stream
and a concentrated slurry stream;
(8) passing the gaseous stream obtained in step (4)
through the first heat exchanger thereby obtaining a
heated gaseous stream; and
(9) compressing the heated gaseous stream thereby
obtaining a compressed gas stream; and
(10) combining the compressed gas stream obtained in
step (9) with the contaminated hydrocarbon-containing gas
stream provided in step (1).
The method as described in W02014/166925 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.
The contaminant may be CO2. The solubility of CO2 in
liquefied natural gas is very low. So, the method
according to W02014/166925 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
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equilibrium and may then be removed with the use of a
cyclone, settler, filter or a combination thereof.
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.
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.
Other methods for removing gaseous contaminants from
a gas stream comprising gaseous contaminants, including
CO2, are known from the prior art, such as W02010/023238
and US3376709.
US3376709 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
US3376709 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.
It is an object of the present invention to at least
partially overcome at least one of these problems.
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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
(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;
(bl) 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;
(b2) obtaining a liquid hydrocarbon stream (170)
from the crystallization chamber (91), thereby forming a
concentrated slurry (140) in the crystallization chamber
(91);
(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).
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,
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- a solid-liquid separator (9) comprising a
crystallization chamber (91), the crystallization chamber
(91) comprising
- 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,
- a fluid outlet (174) for discharging a liquid
hydrocarbon stream (170) from the crystallization
chamber (91),
- 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).
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.
The CO2 enriched solid product may also be referred
to as a CO2 enriched compact product, and vice versa.
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).
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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.
Any type of suitable extruder may be used, in
particular a screw extruder.
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.
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 bl,
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.
Hereinafter the invention will be further described
with reference to the following non-limiting drawings:
Fig.'s la - lb schematically depict embodiments of a
method and system to separate CO2 from a contaminated
hydrocarbon-containing stream, and
Fig. 2 schematically depicts an embodiment of a
method and system for performing a method of liquefying a
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contaminated hydrocarbon-containing gas stream using the
embodiment depicted in Fig. lb.
For the purpose of this description, same reference
numbers refer to same or similar components.
Fig. la and lb depict a method and system to
separate CO2 from a contaminated hydrocarbon-containing
stream.
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.
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 C2+-hydrocarbons (i.e. hydrocarbons
containing 2 or more carbon atoms per molecule),
preferably between 0 and 20 mol% of C2-C6 hydrocarbons,
more preferably between 0.3 and 18 mol% of C2-C4
hydrocarbons, especially between 0.5 and 15 mol% of
ethane.
The contaminant comprises CO2 and possibly comprises
further contaminants, such as H2S, H20, C6+ hydrocarbons,
aromatic compounds.
The amount of contaminant in the contaminated
hydrocarbon-containing gas stream 10 is suitably between
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0.5 and 50 mol%, typically above 1.0 mol% and below 20
mol%.
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%.
From the contaminated hydrocarbon-containing gas
stream 10 a multiphase contaminated hydrocarbon-
containing stream 100 is obtained. This is only
schematically depicted in Fig.'s la and lb 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.
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.
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,
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pressure and temperature, as can be appreciated by the
person skilled in the art.
Fig.'s la - lb 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.
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.
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
(a') separating the multiphase contaminated
hydrocarbon-containing stream (100) in a separator (7)
thereby obtaining a gaseous stream (110) and a slurry
stream (120).
The slurry stream may then be passed on to the
solid-liquid separator 9.
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).
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.
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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).
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.
According to an embodiment the crystallization
chamber (91) is a gravity based separator vessel. The
gravity based separator vessel may be an open vessel.
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.
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.
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
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123 has its discharge opening 123 positioned below or
above the slurry contained in the crystallization vessel.
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.
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).
The weir separates liquid hydrocarbon from the slurry
and the solid CO2 particles.
The feedback conduit 141 may debouche in the
crystallization chamber 91 at a level below the upper
edge of the weir 92.
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.
In step b3, the extruder (142) exerts a mechanical
force (extrusion force) on the concentrated slurry (140)
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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.
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.
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.
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.
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.
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
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the drum are aligned. The cylindrical wall comprises one
or more filters.
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
According to an embodiment, the method further
comprises
(b4) obtaining a CO2 feedback stream (141) from the
CO2 enriched solid product obtained in (b3), the feedback
stream (141) comprises CO2,
(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.
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. la) or may comprise
liquid CO2 where the CO2 seed particles are created upon
re-introduction of the feedback stream (Fig. lb), as will
be explained in more detail below.
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
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particles than the slurry stream 120 obtained from the
multiphase contaminated hydrocarbon-containing stream
100.
This process is facilitated by providing CO2 seed
particles by means of the CO2 feedback stream 141.
According to an embodiment, the seed particles
provided in (b5) have an average size greater than 20
micron.
The seed particles provided in step (b5) may have an
average size greater than 50, or even greater than 100
micron.
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.
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.
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
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crystallization speed (kg/s) on the one hand and ease of
separation on the other hand.
The term micron is used in this text in line with
common practice: 1 micron equals 1x10-6 metre.
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. la.
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.
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.
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.
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According to an embodiment (b4) comprises adding a
carrier fluid, such as a liquid natural gas stream, to
the feedback stream (141).
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.
By adding a carrier fluid to the feedback stream a
suspended feedback stream is obtained.
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.
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. lb, the CO2 feedback stream comprises
liquid CO2 which is fed back by spray-cooling, thereby
forming seed particles.
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.
The extruder 142 compresses the concentrated slurry
and increases the pressure to form the CO2 enriched solid
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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.
Heating may be done by one or more heaters 150. As
shown in Fig. la, 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. lb,
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.
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.
According to an embodiment step (b5) comprises
spraying the liquid CO2 enriched stream into a feedback
position thereby creating seed particles.
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.
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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 CO2seed particles provided may be
controlled.
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.
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.
As indicated above, the liquid hydrocarbon stream
170 obtained from the crystallization chamber 91 in (b2)
may comprise small CO2-particles.
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
- passing the polished liquid hydrocarbon stream (170')
to the LNG storage tank and
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- optionally, recycling the residue stream (175) to the
crystallization vessel, e.g. by combining the residue
stream (175) with the feedback stream (141).
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.
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.
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.
Passing the liquid hydrocarbon stream 170 to the LNG
storage tank may comprise passing the liquid hydrocarbon
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stream through a pressure reduction stage, e.g. formed by
a throttle vale 173 and/or an end flash vessel.
According to an embodiment, the method further
comprises obtaining a venting stream (121) from the
crystallization chamber (91).
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.
The crystallization chamber (91) may comprise an
overhead venting outlet (122).
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.
The venting outlet is preferably positioned in a top
part of the crystallization chamber.
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').
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.
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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.
The gaseous hydrocarbon enriched top stream obtained
from the flash vessel may be combined with a fuel gas
stream.
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.
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
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under the influence of gravity, the extruder receives a
relatively dense portion of the concentrated slurry 140.
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.
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.
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).
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).
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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.
Fig. 2 shows an embodiment of how the method and
system as described above with reference to Fig. lb may
be embedded in a process/liquefaction scheme generally
referred to with reference number 1.
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.
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.
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As shown in the embodiment of Figure 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.
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 N2) 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.
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.
As can be seen in the embodiment of Figure 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.
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Furthermore, in the embodiment of Figure 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).
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')).
So, according to an embodiment, step (a) comprises
(al) providing a contaminated hydrocarbon-containing
gas stream (10, 20);
(a2) cooling the contaminated hydrocarbon-containing
gas stream (20) in a first heat exchanger (3) thereby
obtaining a cooled contaminated hydrocarbon-containing
stream (40);
(a3) cooling the cooled contaminated hydrocarbon-
containing stream (40) in an expander (4) thereby
obtaining a partially liquefied stream (70);
(a4) separating the partially liquefied stream (70)
in a separator (5) thereby obtaining a gaseous stream
(80) and a liquid stream (90);
(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.
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The liquid hydrocarbon product stream obtained in
step (a4) may contain more CO2 than the partially
liquefied stream, such as at least 250 ppm-mol, and may
comprise more Cs+, such as at least 0.1 mol%.
According to an embodiment, the method further
comprises
(d) passing the gaseous stream (80) obtained in step
(a4) through the first heat exchanger (3) thereby
obtaining a heated gaseous stream (270); and
(e) compressing the heated gaseous stream (270)
thereby obtaining a compressed gas stream (220); and
(f) combining the compressed gas stream (220)
obtained in step (e) with the contaminated hydrocarbon-
containing gas stream (20) provided in step (al).
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.
