CO2 liquefaction process and apparatus

Abstract

Title: CO2 Liquefaction Process and Apparatus A CO2 liquefaction apparatus comprises a chamber (S), means for directly contacting a first CO2-rich liquid stream (L1) and a first CO2-rich gas stream (V2) arranged within the chamber to condense at least a portion of the first gas stream, forming CO2-rich condensed gas, means for connecting a transport means (B) comprising a liquid CO2 storage to the contacting means for receiving the CO2-rich condensed gas from the contacting means, means for sending the first liquid stream to the contacting means, and means (1A, 2) for regulating the temperature of the first liquid stream upstream of the contacting means as a function of the pressure of the contacting means. Abstract Figure: FIG. 1

Description

Title of the invention: CO2 liquefaction process and apparatus

[0001] The present invention relates to a CO2 liquefaction process and apparatus.

[0002] When liquid CO2 from CO2 separation and / or liquefaction units is sent to a storage facility, thermal inputs can generate partial vaporization of the CO2. Furthermore, within the storage facility and within the facilities receiving the CO2 (trucks, trains, or ships), thermal inputs will also generate vapors by vaporization of the liquid (known as "boil-off gas" or "BOG"). CO2 vapors are also contained in means of transport, including or consisting of liquid CO2 storage, such as trucks, trains, or ships; these vapors can be shared with the storage facility during the refueling of the means of transport.It is also desirable to recover the gaseous CO2 remaining in the storage tanks of transport vehicles that are not completely empty and are subsequently refilled by a CO2 liquefier or a CO2 capture device. In order to limit CO2 losses and therefore emissions into the atmosphere, it is important to minimize this vapor generation and / or to seek to liquefy the CO2 vapors present in the transport vehicles.

[0003] This problem is discussed in the report "Pre-feasibility study for CO2 pipeline and storage" by Amager Resource Center, October 2020.

[0004] In the case of CO2 capture and sequestration, the distance between the CO2 separation and / or liquefaction units and the storage can be very high (sometimes on the order of several kilometers), the storages being positioned near means of transport (a port for example).

[0005] State of the art

[0006] In the cryogenic industry, it is typical to subcool the liquid produced by a liquefier in order to prevent its vaporization during transport.

[0007] It is also typical to install liquefaction units for gases that evaporate in liquid storage tanks near the storage facilities. In the case of CO2, refrigeration units using ammonia, propane, or propylene are commonly employed for this purpose.

[0008] In the natural gas liquefaction industry, the use of a gas-liquid contactor upstream of storage tanks is known to those skilled in the art. The subcooled produced liquid is brought into contact with the vapors generated in the storage tanks in order to liquefy them by direct contact. It is also known to liquefy the vapors directly in the storage tanks by contact between the produced liquid and their vapor headspace.

[0009] A gaseous or liquid stream rich in CO2 contains at least 60% mol of CO2, at least 70% mol of CO2, at least 80% mol of CO2, or even at least 90% mol of CO2 or even at least 95% mol of CO2.

[0010] Problem solved by the invention

[0011] Heat inputs are extremely dependent on the operating conditions of the storage unit and the associated loading units. Indeed, in operation without loading / unloading the storage unit, heat inputs are limited to the pipes surrounding the storage unit and the storage unit itself. These heat inputs are then very stable, generating a small and stable quantity of evaporated gas over time. However, during loading (of a ship, for example), pumps are suddenly activated, other pipes are used, and the ship is connected to the storage unit, releasing the carbon dioxide vapors it contains, generally at a temperature above 0°C. This equipment generates additional heat inputs that can represent more than twice the value of the heat inputs in normal operation without loading / unloading.Consequently, the volume of evaporated gases requiring liquefaction can suddenly triple compared to normal operation, and the liquefaction unit (refrigeration unit or gas-liquid contactor) must be designed accordingly to handle this additional gas. This necessitates a particularly flexible installation and significant additional costs, especially for refrigeration units where the heat to be dissipated is directly tripled.

[0012] Description of the invention

[0013] The invention consists of taking advantage of the capacity of a CO2 production unit to produce subcooled liquid CO2 at marginal cost and in a flexible manner. It consists of combining storage with a CO2 production unit whose outlet temperature will vary according to the operating mode of the storage.

[0014] In particular, when the storage is in operation without loading / unloading, the CO2 will only be subcooled to compensate for heat inputs from the transfer pipe and the storage unit (which depend on the pipe length and the storage unit size). In the case of a storage unit operated at 16 bar, for example, the temperature of the CO2 exiting the CO2 production unit will be, for example, between -27°C and -40°C.

[0015] When CO2 vapors from a means of transport, such as a ship, are sent to the storage tank, they increase the pressure in the tank. Therefore, it is necessary to reduce the temperature of the liquid CO2 supplying the tank in order to compensate for the pressure increase. Preferably, the liquid CO2 is sent to a higher level in the storage tank, in the gaseous headspace above the liquid level, in order to produce a washing effect that condenses some of the gaseous CO2 present. When a ship transporting liquid CO2 is loaded, for example, the CO2 will subcooled to a lower temperature to compensate for the additional heat input. Using the same example as above, the temperature of the CO2 exiting the CO2 production unit will then be between -40°C and -55°C.

[0016] The storage can be, for example, a liquid storage having a gaseous headspace into which the gas to be liquefied and the liquid from the liquefaction and / or separation apparatus are injected, this liquid being at the temperature required to liquefy the gas.

[0017] Alternatively, the storage can be a tower for bringing the gas to be liquefied into contact with the liquid from the liquefaction and / or separation apparatus, this liquid being at the temperature required to liquefy the gas.

[0018] The liquid from the tower can pass through another storage and can be returned to the means of transport from which the gas to be liquefied originates or to another means of transport.

[0019] According to one object of the invention, a CO2 liquefaction apparatus is provided comprising: • A speaker; • Means of bringing into direct contact a first liquid stream rich in CO2 and a first gaseous stream rich in CO2 arranged in the enclosure in order to condense at least part of the first gaseous stream forming condensed gas rich in CO2; • Means for connecting a means of transport (B) comprising or constituting a liquid CO2 storage to the means of contacting to receive the CO2-rich condensed gas from the means of contacting; • Means of sending the first liquid flow to the means of contacting; • Means of sending the first gaseous flow to the means of contacting from a / the storage of liquid CO2 of the means of transport;

[0020] characterized in that it comprises i. means for detecting the flow rate of the first gas stream sent or to be sent in the means for sending the first gas stream and / or ii. means for detecting the temperature of the first gas stream sent or to be sent in the means for sending the first gas stream and / or iii. means for detecting the pressure in the enclosure and iv. means to regulate the temperature of the first liquid flow upstream of the contacting means as a function of the flow rate and / or temperature of the first gaseous flow and / or the pressure of the contacting means.

[0021] According to other optional features: • the enclosure is designed to store liquid and does not contain solid means to promote mass exchange and the means of contacting are constituted by a space of the gaseous head formed above the liquid level when the apparatus is in operation, the means of sending the first liquid flow being connected to send the first liquid flow above an arrival point of the first gaseous flow. • The enclosure is a washing tower having a tank and in which the means of making contact are located in the washing tower, these means of making contact being made up of means to promote the transfer of heat and mass above the tank and connected to receive the first liquid flow at a level of the tower above the arrival point of the first gaseous flow, the tank of the tower being connected to a CO2 storage to send liquid to it.

[0022] According to another object of the invention, a CO2 liquefaction process is provided in which a first liquid stream rich in CO2 is sent to contacting means in an enclosure; a first gaseous stream rich in CO2 is sent to the contacting means such that the first liquid and gaseous streams mix and at least a portion of the first gaseous stream is condensed; liquid is sent from the contacting means to a transport means comprising or consisting of a liquid CO2 storage unit connected to the contacting means to receive the condensed CO2-rich gas from the contacting means; the first gaseous stream from the liquid CO2 storage unit is formed by partial evaporation above the liquid level in the storage unit due to heat inputs.

[0023] characterized in that: i. The temperature of the first liquid CO2 stream is increased if the flow rate and / or temperature of the first gaseous CO2 stream decreases and / or if the pressure in the enclosure decreases, and the temperature of the first stream is decreased if the flow rate and / or temperature of the first stream increases and / or if the pressure in the enclosure increases and / or ii. the temperature of the first liquid CO2 stream is increased in anticipation of a reduction in the flow rate and / or temperature of the first gaseous CO2 stream and / or pressure of the enclosure and the temperature of the first stream is reduced in anticipation of an increase in the flow rate and / or temperature of the first stream and / or pressure in the enclosure.

[0024] According to other aspects of the invention: • The temperature of the first CO2-rich liquid stream is adjusted according to its flow rate so that the temperature of the means of in contact is sufficient to liquefy at least part of the first gaseous flow; • the temperature of the first liquid stream is modified by dividing it into two variable fractions, one of the fractions is cooled, the other fraction is not cooled and the cooled fraction is mixed with the uncooled fraction, the proportions of the fractions being varied to vary the temperature of the mixture which constitutes the first liquid stream sent to the contacting means; • the first CO2-rich liquid stream and another CO2-rich liquid are sent to different levels of the enclosure; • the first CO2-rich liquid stream is drawn from a CO2 separation or liquefaction apparatus by distillation and / or partial condensation to be sent to the contacting means.

[0025] According to another aspect of the invention, a method is provided for putting into operation an apparatus as described above or a method as described above in which the first liquid flow rich in CO2 is sent to the contacting means before sending the first gaseous flow rich in CO2 and before sending liquid from the contacting means to the CO2 storage of the means of transport.

[0026] According to other optional aspects: • the sending of the first CO2-rich liquid stream is triggered by a signal indicating the arrival of the means of transport and / or the connection of the means of transport scheduled within a period of time; • No first liquid flow is sent to the enclosure if no flow of the first gaseous flow is sent to the enclosure or if no flow of the first gaseous flow is planned to be sent to the enclosure within a given time period; • No gas flow is drawn from the enclosure.

[0027] According to the invention, it is not necessarily necessary to operate the storage at constant pressure. If the arrival of a means of transport to be loaded with liquid CO2, such as a ship, is anticipated, the process according to the invention can pre-cool the means intended for contacting the gas from the means of transport, that is to say, before the gas arriving from the means of transport is present in the contacting means, in order to: 1. be ready to be cold enough in the means of contact to liquefy the gas when it arrives (thus having already overcome the thermal inertia of the pipes, storage etc); 2. so that the pressure drops in the contacting means before the gas arrives, knowing that the arrival of the gas will necessarily cause increasing the pressure when it is introduced into the contacting means. This allows, even if the gas does not reliquefy instantly, at least to slow it down or even store it in the contacting means without reaching the maximum pressure of the enclosure containing the contacting means and therefore to avoid losing it during the time necessary for its reliquefaction (for example by escaping through a safety vent pipe).

[0028] It should be noted that the means of establishing contact may consist of contact-facilitating features, such as trays or loose or structured packing. However, the means of establishing contact may simply consist of an empty space, such as the gaseous space above a body of liquid in a storage tank where a liquid and a gas can mix simply by being together in the same space.

[0029] The temperature change of the liquid to be sent to the contacting means, for example at the outlet of a CO2 production unit, can be anticipated to take into account the thermal inertia of the system and thus be ready to liquefy the additional evaporated gases from a storage tank of a means of transport at the time of connection with the means of transport, for example. This anticipation can therefore be planned in advance, upon the imminent arrival of a means of transport, for example a ship. Similarly, in order to optimize the energy consumption of the CO2 production unit, subcooling can be limited at the end of the loading phase in advance to take advantage of the thermal inertia of the system, which is still cold.

[0030] The subcooling of CO2 on the side of the CO2 production unit can be achieved in the following manner: • The liquid CO2 produced is separated into two fractions. • A first fraction is subcooled in a heat exchanger to a first temperature, for example the lowest temperature required (for the case of loading / unloading), or even lower (down to the lowest temperature that the liquefier can reach). • The second fraction bypasses at least part of the heat exchanger via a regulating valve, therefore is not completely subcooled and is at a second temperature higher than the first temperature and is mixed with the first subcooled fraction to reheat it. • The final subcooling temperature is adjusted by opening or closing the control valve to modify the flow ratio between the first and second fractions. In normal operation without loading / unloading, the valve is open to preheat the second fraction and thus limit subcooling. During loading / unloading operations, it closes at least partially.

[0031] The invention will be described in more detail with reference to the figures where:

[0032] [Fig.1] schematically represents a method according to the invention.

[0033] [Fig.2] schematically represents a method according to the invention.

[0034] [Fig. 1] shows a CO2 storage device with a chamber S containing Liquid CO2, thermally insulated, in which gaseous CO2 is generated, for example, by heat inputs. The liquid stored in enclosure S comes from a CO2 liquefier or a CO2 separation unit CC in which a flow containing CO2 is liquefied and / or separated by partial condensation and / or distillation and / or solidification, forming a flow of liquid CO2 1. This liquid is preferably subcooled by sending it to cool in a heat exchanger E and is then sent as subcooled liquid L1 to the top of enclosure S, by distribution means, into the gaseous space above the liquid level. The liquid can also be sent to other levels of enclosure S; for example, subcooled liquid L2 is sent to a lower level of enclosure S. The liquid descending in enclosure S encounters the gas formed at the top of enclosure S.The gas is thus liquefied at least partially and the liquid formed falls back into the enclosure S.

[0035] Occasionally, liquid L3 is sent from the tank of enclosure S to another element B, which may be a liquid CO2 storage unit forming part of a means of transport, for example, a ship, a train, a tanker truck, a pipeline, or a railcar. Element B may be a pipeline that constitutes a means of transporting CO2 and allows for its temporary storage.

[0036] Upon arrival at element B (or at the time of its connection, in the case of a pipeline), it may contain gaseous CO2 resulting from previous transport. Alternatively, the arrival of liquid CO2 in element B at a temperature above that of the liquid CO2 may also generate gaseous CO2.

[0037] The storage S includes a gas vent line, potentially to air VI, equipped with a valve J allowing gas to be sent to the air if the pressure of the gas head above the liquid level becomes excessive.

[0038] To avoid losing the gaseous CO2 V2 from the transport means B, this gas V2 is sent to storage S at a level below the inlet of liquid L1, so that it is liquefied by direct contact with liquid LL

[0039] It is also possible to introduce the V2 gas into the storage tank through the VL line. The gas is thus washed by the CO2-rich liquid flow LL

[0040] The liquid from the CC device can be introduced into the storage through a single opening, but preferably is directed to different locations at the same level of the enclosure S in order to spray a larger surface area of ​​the enclosure S. Thus, one sees that liquid L2 is introduced at a lower level of storage S than liquid L1.

[0041] The process uses means to modify the temperature of the washing liquid L1, L2 sent to the enclosure S. These can take several forms, the simplest, illustrated here, consisting of short-circuiting a part IA of the liquid around the exchanger so that a variable fraction of the liquid is cooled in the exchanger, the remainder which has not been cooled being mixed with the variable fraction to form the liquid LL. The larger the fraction IA, the greater the temperature of the liquid L1, L2.

[0042] In a basic embodiment, a pressure sensing means PIC measures the pressure in the enclosure and, when this exceeds a threshold, regulates the temperature of the liquid L1, for example by closing valve 2 to prevent the liquid IA from bypassing the subcooling, thus reducing the temperature of the liquid L1, L2

[0043] Thus, the temperature of liquid L1 and / or L2 is reduced when an increase in gas flow rate and / or an increase in gas temperature is anticipated, so that the cooling capacity supplied to storage S is sufficient to liquefy the gas. According to the same principle, when the gas flow rate and / or temperature increases, the pressure in enclosure S rises, and a reduction in the temperature of liquid L1 limits or even eliminates this pressure increase.

[0044] Similarly, the temperature of the liquid L1 decreases when a reduction in the gas flow rate and / or a reduction in the temperature of the gas V1 is expected, for example when the arrival of a means of transport B is expected but before the gas V2 arrives in the storage.

[0045] Instead of or in addition to the pressure detection means PIC, the device may include a flow detection means FIC and / or a temperature detection means TIC to measure the flow rate and / or temperature respectively of the first gas flow sent or to be sent to storage S.

[0046] The same variations are expected if the flow rate and / or temperature of the gas V2 in element B vary. According to the same principle, when the gas flow rate and / or temperature decreases, the pressure in the enclosure S drops, and an increase in the temperature of the liquid L1 limits or even cancels out this pressure drop.

[0047] Since the overall system has a certain thermal inertia, it is recommended to reduce the temperature of the liquid L1 before the flow rate and / or temperature of the gas increases, so that the upper part of the storage tank S is at the correct temperature to ensure liquefaction. Thus, before the arrival of a ship B, for example, the temperature of the liquid L1 is reduced in anticipation of the arrival of the gas V2.

[0048] [Fig. 2] shows a variant of the method comprising a contacting tower T, which is a tower containing trays or bulk or structured packings as contacting means. This tower is located between the CC apparatus and the storage to receive liquid L1 from apparatus CC and gas V2 from transport means B. As in the previous figure, the gas is liquefied by direct contact with liquid L1, but in this figure it enters the bottom of tower T and rises in the tower, encountering the liquid descending the tower. Gas V2 is thus liquefied, and the liquid formed in tank L4 is sent to storage S. The liquid in tank L3 of storage S is pressurized by pump P2 to supply transport means B.

[0049] Alternatively, tower T can also be used to liquefy the gas V1 formed in storage S, for example, through heat inlets. Gases VI and V2 are mixed to form a gas V' which enters the bottom of tower T.

[0050] Alternatively, part of the liquid from the CC device can be sent directly to storage S, only part of the liquid supplying the top of the tower T.

[0051] The gas V1 passes through a valve (not shown) as in [Fig. 1] which regulates the pressure of the storage S. A pressure detector PIC (not shown) of the tower T regulates the opening of the valve 2.

Claims

Demands

1. A CO2 liquefaction apparatus comprising: • A chamber (S,K) • Means for bringing into direct contact a first liquid stream rich in CO2 (L1) and a first gaseous stream (V2, V') rich in CO2 arranged in the chamber in order to condense at least a part of the first gaseous stream forming condensed gas rich in CO2 • Means for connecting a means of transport (B) comprising or consisting of a liquid CO2 storage to the means of contacting in order to receive the condensed gas rich in CO2 from the means of contacting • Means for sending the first liquid stream to the means of contacting • Means for sending the first gaseous stream to the means of contacting from a liquid CO2 storage of the means of transport characterized in that it comprises i.means for detecting the flow rate of the first gaseous flow in the means for sending the first gaseous flow sent or to be sent in the means for sending the first gaseous flow and / or ii. means for detecting the temperature of the first gaseous flow and / or iii. means (PIC) for detecting the pressure in the enclosure and iv. means (1A,2) for regulating the temperature of the first liquid flow upstream of the contacting means as a function of the flow rate and / or the temperature of the first gaseous flow and / or the pressure of the contacting means.

2. Apparatus according to claim 1 in which the means of transport (B) is a boat, a train, a tank truck, a pipeline or a wagon, capable of storing at least temporarily liquid CO2.

3. Apparatus according to claim 1 or 2 in which the enclosure (S) is designed to store liquid and does not contain means solids to promote mass exchange and the means of contacting are constituted by a space of the gaseous sky formed above the liquid level when the apparatus is in operation, the means of sending the first liquid flow (L1) being connected to send the first liquid flow above an arrival point of the first gaseous flow (V2).

4. Apparatus according to any one of the preceding claims wherein the enclosure (K) is a washing tower having a tank and wherein the contacting means are located in the washing tower, these contacting means being constituted by means for promoting the transfer of heat and mass above the tank and connected to receive the first liquid flow (Ll) at a level of the tower above the arrival point of the first gaseous flow (V'), the tank of the tower being connected to a CO2 storage (S, B) to send liquid into it.

5. CO2 liquefaction process in which a first liquid stream (L1) rich in CO2 is sent to contacting means in a chamber (S,K), a first gaseous stream rich in CO2 (V2,V') is sent to the contacting means such that the first liquid and gaseous streams mix and at least a part of the first gaseous stream is condensed, liquid is sent from the contacting means to a transport means (B) comprising or consisting of a liquid CO2 storage connected to the contacting means to receive the condensed CO2-rich gas from the contacting means, the first gaseous stream from the liquid CO2 storage being formed by partial evaporation above the liquid level in the storage due to heat inputs characterized in that: i.the temperature of the first liquid CO2 stream is increased if the flow rate and / or temperature of the first gaseous CO2 stream decreases and / or if the pressure in the enclosure decreases and the temperature of the first stream is reduced if the flow rate and / or temperature of the first stream increases and / or if the pressure in the enclosure increases and / or ii. the temperature of the first liquid CO2 stream is increased in anticipation of a reduction in the flow rate and / or the. temperature of the first flow of gaseous CO2 and / or pressure of the enclosure and we reduce the temperature of the first flow in anticipation of an increase in the flow and / or temperature of the first flow and / or pressure in the enclosure.

6. A method according to claim 5 in which the temperature of the first liquid stream (Ll) rich in liquid CO2 is adapted according to its flow rate so that the temperature of the contacting means is sufficient to liquefy at least a part of the first gaseous stream.

7. A method according to any one of claims 5 or 6 wherein the temperature of the first liquid stream (L1) is modified by dividing it into two variable fractions (1, IA), one of the fractions is cooled, the other fraction is not cooled, and the cooled fraction is mixed with the uncooled fraction, the proportions of the fractions being varied to vary the temperature of the mixture which constitutes the first liquid stream sent to the contacting means.

8. A method according to any one of claims 5 to 7 in which the first CO2-rich liquid stream (L1) and another CO2-rich liquid (L2) are sent to different levels of the enclosure (S).

9. A method according to any one of claims 5 to 8 in which the first CO2-rich liquid stream (1, L1) is withdrawn from a CO2 separation or liquefaction apparatus by distillation and / or partial condensation to be sent to the contacting means.

10. A method of putting into operation an apparatus according to any one of claims 1 to 4 or a method according to any one of claims 5 to 9 in which the first CO2-rich liquid stream (1, L1) is sent to the contacting means before sending the first CO2-rich gas stream to them and before sending liquid from the contacting means to the CO2 storage of the means of transport (B).

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