A CONTAMINATED HYDROCARBON STREAM

The present invention relates to a method to separate C02 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 H ₂ 0, C0 ₂ , H ₂ S and the like) which may freeze out during the liquefaction process or are undesirable in the product .

WO2014/166925 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; (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 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.

The contaminant may be C02. The solubility of C02 in liquefied natural gas is very low. So, the method according to WO2014/166925 doesn't remove the C02 in the gaseous phase, but by expansion over a valve, leading to a rapid oversaturation of the liquids, leading to solid C02 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.

However, as the C02 particles typically have a relatively small size, flow assurance and separation problems are likely to occur. This could result in solid

C02 residue in the product or in clogging causing operational instabilities.

Furthermore, the waste stream may be a mix of C02 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 los s of value .

Other methods for removing gaseous contaminants from a gas stream comprising gaseous contaminants, including C02, are known from the prior art, such as WO2010/023238 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. One or more of the above or other objects are achieved according to the present invention by a method to separate C02 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 C02 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 C02 ;

(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 C02 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 C02 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 C02 particles, - 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 C02 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 C02 enriched solid product and a

relatively pure methane enriched liquid hydrocarbon stream (147) are obtained separately from each other.

The C02 enriched solid product may also be referred to as a C02 enriched compact product, and vice versa.

The concentrated slurry comprises a liquid phase and a solid phase, formed by a plurality of C02 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 C02 enriched solid product and the methane enriched liquid hydrocarbon stream) . 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 C02

particles, C02 chunks or a (semi) continuous solid C02 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 C02 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 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 C02 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~Cg 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 C02 and possibly comprises further contaminants, such as H ₂ S, H ₂ 0, C ₆₊ hydrocarbons, aromatic compounds.

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% .

The amount of C02-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 C02 particles, the C02 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 C02. The C02 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 C02 concentration, 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. 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 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 C02 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 C02-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) to move concentrated slurry (140) out of the

crystallization chamber (91) thereby obtaining the C02 enriched solid product . The C02 enriched solid product may in fact be a stream of compacted C02 particles, compacted C02 chunks or a (semi) continuous solid C02 product stream. The C02 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 density the concentrated slurry, thereby obtaining the C02 enriched solid product . Due to the extrusion force exerted by the extruder (142) the C02 particles group together to form the solid product, which may obtained as a continuous C02 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 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 density the C02 particles thereby obtaining the C02 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 C02 feedback stream (141) from the C02 enriched solid product obtained in (b3), the feedback stream (141) comprises C02,

(b5) feeding back the C02 feedback stream (141) by passing the C02 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 C02 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 C02 feedback stream may comprise the C02 seed particles (Fig. la) or may comprise liquid C02 where the C02 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 C02 to crystallize. The concentrated slurry comprises less liquid and larger C02 particles than the slurry stream 120 obtained from the multiphase contaminated hydrocarbon-containing stream 100.

This process is facilitated by providing C02 seed particles by means of the C02 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 C02 feedback stream 142, the crystallization process is facilitated and accelerated and as a result, relatively large C02 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 C02 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.

The term micron is used in this text in line with common practice: 1 micron equals lxlCT ⁶ metre.

According to an embodiment (b4) comprises obtaining a

C02 feedback stream comprising C02 seed particles and (b5) comprises passing the C02 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 C02 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 C02 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 C02 obtained from the extruder, the C02 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 C02 seed particles from the solid C02 obtained from the extruder to create a C02 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. 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 C02 feedback stream comprises liquid C02 which is fed back by spray-cooling, thereby forming seed particles.

According to an embodiment step (b4) comprises heating at least part of the C02 enriched solid product thereby creating a liquid C02 enriched stream, and forming the feedback stream (141) from at least part of the liquid C02 enriched stream.

The extruder 142 compresses the concentrated slurry and increases the pressure to form the C02 enriched solid product. Next, the C02 enriched solid product is heated to create a liquid C02 enriched stream, of which a part is taken to form the C02 feedback stream. The C02 seed particles may be formed from the liquid C02 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 C02 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 C02 enriched stream into a feedback position thereby creating seed particles.

Spraying may be done by introducing the liquid C02 enriched stream via one or more spraying nozzles 158. Upon entering the vessel, the liquid C02 droplets expand to a state where the liquid phase does not exist . Almost all C02 will solidify. Due to the high local C02

concentration, the resulting C02 solid size will be closely correlating to the C02 droplet size. By adjusting the droplet sizes produced by the spray nozzle, the seed particle size can be adjusted to the preferred value. 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 C02 droplets and thus of the C02seed particles provided may be controlled.

According to an embodiment step (b5) further comprises processing the liquid C02 enriched stream to form the C02 seed particles and feeding back the C02 seed particles by passing the C02 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 C02 into the

crystallization chamber or a position upstream, the liquid C02 stream may be converted into a stream

comprising of solid C02 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 C02-particles .

In order to separate such C02 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 - 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 C02 particles that may have ended up in the liquid

hydrocarbon stream. The polished liquid hydrocarbon stream comprises less C02 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 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 . 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 C02 enriched bottom stream , or

- passed to a carbon capture storage, or

- passed to a geological storage for C02

- passed to a flash vessel to obtain a gaseous hydrocarbon enriched top stream and a liquid C02 enriched bottom stream from the flash vessel, or

- passed through a membrane unit to obtain a C02 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 C02.

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 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 C02 particles together and pushing liquids out of the concentrated slurry creating solid C02, preferably in the form of a continuous solid C02 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 C02 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 C02 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) . 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 . 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 N 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.

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. 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 C02 particles. The multiphase contaminated hydrocarbon-containing stream (100) may comprise a vapour phase. The liquid hydrocarbon product stream obtained in step (a4) may contain more C0 ₂ than the partially liquefied stream, such as at least 250 ppm-mol, and may comprise more C ₅₊ , 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 .