Method and apparatus for liquefying co2

Abstract

A CO2 liquefaction apparatus includes a chamber (S), means for bringing into direct contact a first liquid stream rich in CO2 (L1) and a first gaseous stream (V2) 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 transport means (B) comprising a liquid CO2 storage to the contacting means to receive the condensed gas rich in CO2 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.

Description

[0001] The present invention relates to a method and apparatus for the liquefaction of CO2.

[0002] When liquid CO2 is sent from CO2 separation and / or liquefaction units to a storage facility, thermal inputs can cause 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 through vaporization of the liquid (known as "boil-off gas" or "BOG"). CO2 vapors are also present in means of transport that include or consist of liquid CO2 storage, such as trucks, trains, or ships; these vapors can be shared with the storage during the refueling of the transport vehicle. It is also desirable to recover any remaining gaseous CO2 from 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 generation of vapor and / or to seek to liquefy the CO2 vapors present in means of transport.

[0003] This problem is discussed in the report "Pre-feasibility study for CO2 pipeline and storage" by Amager Resource Center, October 2020. 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), with the storages being positioned near means of transport (a port for example). State of the art

[0004] In the cryogenic industry, it is typical to subcool the liquid produced by a liquefier in order to prevent its vaporization during transport.

[0005] It is also typical to install liquefaction units for gases that evaporate in liquid storage tanks located near the storage facilities. In the case of CO2, refrigeration units using ammonia, propane, or propylene are commonly employed for this purpose.

[0006] In the natural gas liquefaction industry, the use of a gas-liquid contactor upstream of storage tanks is well known to those skilled in the art. The subcooled liquid produced is brought into contact with the vapors generated in the storage tanks to liquefy them by direct contact. It is also known to liquefy the vapors directly within the storage tanks through contact between the liquid produced and the surrounding gas.

[0007] 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. Problem solved by the invention

[0008] Heat inputs are highly dependent on the operating conditions of the storage tank and its associated loading units. In operation without loading or unloading, heat inputs are limited to the pipes surrounding the tank and the tank itself. These heat inputs are very stable, generating a small and consistent amount of evaporated gas over time. However, during loading (for example, of a ship), pumps are suddenly activated, other pipes are used, and the ship is connected to the storage tank, releasing the carbon dioxide vapors it contains, which are generally at a temperature above 0°C. These systems generate additional heat inputs that can be more than twice the value of the heat inputs during normal operation without loading or 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. Description of the invention

[0009] The invention consists of leveraging the capacity of a CO2 production unit to produce subcooled liquid CO2 at marginal cost and in a flexible manner. It involves combining storage with a CO2 production unit whose outlet temperature varies according to the storage operating mode.

[0010] In particular, when the storage facility is operating 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). For example, in the case of a storage facility operating at 16 bar, the CO2 temperature at the outlet of the CO2 production unit will be between -27°C and -40°C.

[0011] When CO2 vapors from a means of transport, such as a ship, are sent to storage, they increase the pressure in the storage, so it is necessary to reduce the temperature of the liquid CO2 feeding the storage in order to compensate for the pressure increase.

[0012] Preferably, the liquid CO2 is pumped to a higher level in the storage tank, above the liquid level, to create a scrubbing effect that condenses some of the gaseous CO2 present. When a liquid CO2 transport ship is loaded, for example, the CO2 will be 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.

[0013] The storage can be, for example, a liquid storage with a gaseous headspace into which the gas to be liquefied and the liquid from the liquefaction and / or separation device are injected, this liquid being at the temperature required to liquefy the gas.

[0014] Alternatively, the storage can be a tower where the gas to be liquefied is brought into contact with the liquid from the liquefaction and / or separation unit, this liquid being at the temperature required to liquefy the gas. The liquid from the tower can then be transferred to another storage facility and returned to the means of transport from which the gas to be liquefied originated, or to another means of transport.

[0015] According to one object of the invention, a CO2 liquefaction apparatus is provided, comprising: An enclosure; Means for directly contacting 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 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 includes i) means for detecting the flow rate of 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 sent or to be sent in the means for sending the first gaseous flow and / or iii) means for detecting the pressure in the enclosure and iv) means for regulating 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 pressure of the contacting means.

[0016] Depending on other optional characteristics: The enclosure is designed to store liquid and does not contain any solid means to facilitate mass exchange. The contacting means consist of a gaseous headspace formed above the liquid level when the apparatus is in operation. The means for sending the first liquid stream are connected to send the first liquid stream above an arrival point of the first gaseous stream. The enclosure is a scrubbing tower having a tank, in which the contacting means are located within the scrubbing tower. These contacting means consist of means for facilitating heat and mass transfer above the tank and are connected to receive the first liquid stream at a level of the tower above the arrival point of the first gaseous stream. The tank of the tower is connected to a CO2 storage tank to which liquid is sent. The first CO2-rich liquid stream is a liquid other than a tank liquid of the enclosure.

[0017] 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 part 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, characterized in that: i) the temperature of the first CO2-rich liquid stream is increased if the flow rate and / or temperature of the first CO2-rich gas stream decreases and / or if the pressure in the enclosure decreases and the temperature of the first CO2-rich liquid stream is decreased if the flow rate and / or temperature of the first gas stream increases and / or if the pressure in the enclosure increases and / or ii) the temperature of the first CO2-rich liquid stream is increased in anticipation of a reduction in the flow rate and / or temperature of the first CO2-rich gas stream and / or the pressure in the enclosure and the temperature of the first CO2-rich liquid stream is reduced in anticipation of an increase in the flow rate and / or temperature of the first gas stream and / or the pressure in the enclosure.

[0018] 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 contacting means is sufficient to liquefy at least part of the first gaseous stream; the temperature of the first liquid stream is modified by dividing it into two variable fractions, one of the fractions is cooled, the other 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 withdrawn from a CO2 separation or liquefaction apparatus by distillation and / or partial condensation to send it to the contacting means.

[0019] 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.

[0020] According to other optional aspects: The first CO2-rich liquid stream is initiated by a signal indicating the arrival of the transport means and / or the planned connection of the transport means within a specified timeframe. No first liquid stream is sent to the containment if no flow of the first gaseous stream is sent to the containment or if no flow of the first gaseous stream is planned to be sent to the containment within a given timeframe. No gas is withdrawn from the containment. The first CO2-rich liquid stream is a liquid other than a tank liquid from the containment. The first CO2-rich liquid stream is sent to the contact means directly from a CO2 separation unit. The first liquid stream is subcooled in a heat exchanger of the CO2 separation unit.

[0021] 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. The contacting devices must be sufficiently cold to reliquefy the gas upon arrival (thus overcoming the thermal inertia of the pipes, storage, etc.); 2. The pressure in the contacting devices must drop before the gas arrives, knowing that the gas's arrival will necessarily increase the pressure when it is introduced into the contacting devices. This allows, even if the gas is not reliquefied instantaneously, for its reliquefaction to be slowed down or even stored in the contacting devices without reaching the maximum pressure of the enclosure containing the contacting devices, and therefore prevents its loss during the time required for reliquefaction (for example, by escaping through a safety vent pipe).

[0022] It should be noted that the means of contact can consist of features that facilitate contact, such as trays or bulk or structured packing. However, the means of contact can also simply consist of an empty space, such as the gas space above a liquid in a storage tank, where a liquid and a gas can mix simply by being together in the same space.

[0023] 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 account for the system's thermal inertia. This allows the system to be ready to liquefy additional evaporated gases from a transport storage tank at the time of connection with the transport vehicle, for example. This anticipation can therefore be planned in advance, for instance, upon the imminent arrival of a transport vehicle, such as a ship. Similarly, to optimize the energy consumption of the CO2 production unit, subcooling can be limited at the end of the loading phase, in advance of the initial phase, to take advantage of the system's thermal inertia, as it is still cold.

[0024] The subcooling of CO2 on the side of the CO2 production unit can be achieved in the following way: The liquid CO2 produced is separated into two fractions. The first fraction is subcooled in a heat exchanger to a first temperature, for example, the lowest temperature required (for loading / unloading operations), or even lower (down to the lowest temperature the liquefier can reach). The second fraction bypasses at least part of the heat exchanger via a control valve, is therefore not completely subcooled, and is at a second temperature higher than the first. It is then 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 rate ratio between the first and second fractions. In normal operation without loading / unloading, the valve is open to reheat the second fraction and thus limit subcooling.During operation involving loading / unloading, it closes at least partially.

[0025] The invention will be described in more detail with reference to the figures where: FIG.1 schematically represents a process according to the invention. FIG.2 schematically represents a process according to the invention.

[0026] FIG.1This illustrates a CO2 storage apparatus with a thermally insulated chamber S containing liquid CO2, in which gaseous CO2 is generated, for example, by heat inlets. The liquid stored in chamber S comes from a CO2 liquefier or CO2 separator CC in which a CO2-containing stream is liquefied and / or separated by partial condensation and / or distillation and / or solidification, forming a stream 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 chamber S, via distribution means, into the gaseous space above the liquid level. The liquid can also be sent to other levels of chamber S; for example, subcooled liquid L2 is sent to a lower level of chamber S. The liquid descending in chamber S encounters the gas formed at the top of chamber S.The gas is thus liquefied at least partially and the liquid formed falls back into the enclosure S.

[0027] Occasionally, liquid L3 is sent from the tank in enclosure S to another element B, which could be a liquid CO2 storage unit belonging to a means of transport, for example, a ship, train, tanker truck, pipeline, or railcar. Element B could be a pipeline that constitutes a means of transporting CO2 and allows for its temporary storage.

[0028] Upon arrival at component 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 component B at a temperature above that of the liquid CO2 can also generate gaseous CO2.

[0029] The storage S includes a gas vent line, potentially to air V1, 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.

[0030] In order not to lose the gaseous CO2 V2 from the means of transport B, this gas V2 is sent to storage S at a level below the arrival of liquid L1 as the first gaseous flow rich in CO2, so that it is liquefied by direct contact with liquid L1.

[0031] It is also possible to introduce gas V2 into the storage tank through pipe V1. The gas is then washed by the first CO2-rich liquid stream L1.

[0032] The liquid from device CC can be introduced into the storage through a single opening but preferably is sent to different places at the same level of the enclosure S in order to wet a larger surface of the enclosure S. Thus we see that liquid L2 is introduced at a lower level of the storage S than liquid L1.

[0033] The process uses means to modify the temperature of the washing liquid L1, L2 sent to the chamber S. These can take several forms, the simplest, illustrated here, consisting of bypassing a portion 1A of the liquid around the heat exchanger so that a variable fraction of the liquid is cooled in the exchanger, the remainder that has not been cooled being mixed with the variable fraction to form liquid L1. The larger the fraction 1A, the higher the temperature of the liquid L1, L2.

[0034] In a basic variant, a pressure sensing device (PIC) measures the pressure within the enclosure. When this pressure exceeds a threshold, it regulates the temperature of liquid L1, for example, by closing valve 2 to prevent liquid 1A from bypassing the subcooling system. This reduces the temperature of liquids L1 and L2. Thus, the temperature of liquids L1 and / or L2 is reduced when an increase in gas flow rate and / or gas temperature is anticipated, ensuring that the cooling capacity supplied to storage S is sufficient to liquefy the gas. Similarly, when the gas flow rate and / or temperature increases, the pressure within enclosure S rises, and reducing the temperature of liquid L1 limits or even eliminates this pressure increase.

[0035] Similarly, the temperature of liquid L1 decreases when a reduction in gas flow and / or a reduction in the temperature of gas V1 is expected, for example when the arrival of a means of transport B is expected but before gas V2 arrives in storage.

[0036] 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 gaseous flow sent or to be sent to storage S.

[0037] 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 chamber S drops, and an increase in the temperature of liquid L1 limits or even cancels out this pressure drop.

[0038] Since the overall system has a certain thermal inertia, it is recommended to reduce the temperature of 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 liquid L1 is reduced in anticipation of the arrival of gas V2.

[0039] FIG.2This figure illustrates a variant of the process comprising a contacting tower K, which is a tower containing trays or bulk or structured packings as contacting means. This tower is located between apparatus CC and the storage tank to receive the first CO2-rich liquid stream L1 from apparatus CC and the first CO2-rich gas stream V2 from a transport means B. As in the previous figure, the gas is liquefied by direct contact with the liquid L1, but in this figure, it enters at the bottom of tower K and rises in the tower, encountering the liquid descending the tower. The gas V2 is thus liquefied, and the liquid formed in tank L2 is sent to a storage tank S. The tank liquid L3 from storage S is pressurized by a pump P2 to supply the transport means B.

[0040] Alternatively, tower K can also be used to liquefy the gas V1 formed in storage S, for example, by heat inputs. Gases V1 and V2 are mixed to form a gas V' which arrives at the bottom of tower K. Alternatively, some of the liquid from unit CC can be sent directly to storage S, with only a portion of the liquid feeding the top of tower K.

[0041] The V1 gas passes through a valve (not shown) as in the FIG.1 which regulates the pressure of storage S. A PIC pressure detector (not shown) in tower K regulates the opening of valve 2.

Claims

1. CO2 liquefaction apparatus comprising: • A chamber (S, K) • Means for directly contacting a first CO2-rich liquid stream (L1) and a first CO2-rich gas stream (V2, V') arranged within the chamber in order to condense at least a portion of the first gas stream, forming CO2-rich condensed gas • Means for connecting a means of transport (B) comprising or consisting of a liquid CO2 storage tank to the contacting means in order to receive the CO2-rich condensed gas from the contacting means • Means for sending the first liquid stream to the contacting means • Means for sending the first gas stream to the contacting means from a liquid CO2 storage tank or the liquid CO2 storage tank of the means of transport characterized in thatIt includes 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 solid means to promote mass exchange and the means of making contact 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 (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 in which the enclosure (K) is a washing tower having a tank and in which 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 (L1) 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. Apparatus according to any one of the preceding claims wherein the first CO2-rich liquid stream (L1) is a liquid other than a tank liquid of the enclosure.

6. A 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 portion 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 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. characterized in thati) the temperature of the first CO2-rich liquid stream (L1) is increased if the flow rate and / or temperature of the first gaseous CO2 flow rate decreases and / or if the pressure in the enclosure decreases and the temperature of the first CO2-rich liquid stream is reduced if the flow rate and / or temperature of the first gaseous flow rate increases and / or if the pressure in the enclosure increases and / or ii) the temperature of the first CO2-rich liquid stream is increased in anticipation of a reduction in the flow rate and / or temperature of the first gaseous CO2 flow rate and / or the pressure in the enclosure and the temperature of the first CO2-rich liquid stream is reduced in anticipation of an increase in the flow rate and / or temperature of the first flow rate and / or the pressure in the enclosure.

7. A method according to claim 6 in which the temperature of the first liquid stream (L1) 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 part of the first gaseous stream.

8. A method according to any one of claims 6 or 7 in which the temperature of the first liquid stream (L1) is modified by dividing it into two variable fractions (1, 1A), 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.

9. Method according to any one of claims 6 to 8 wherein the first CO2-rich liquid stream (L1) and another CO2-rich liquid (L2) are sent to different levels of the enclosure (S).

10. A method according to any one of claims 6 to 9 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.

11. A method according to any one of claims 6 to 10 wherein the first CO2-rich liquid stream (L1) is a liquid other than a tank liquid of the enclosure.

12. Method according to claim 11 wherein the first CO2-rich liquid stream (L1) is sent to the contact means directly from a CO2 separation device (CC).

13. Method according to claim 12 wherein the first liquid stream is subcooled in a heat exchanger of the CO2 separation apparatus (CC).

14. Method of putting into operation an apparatus according to any one of claims 1 to 5 or a method according to any one of claims 6 to 13 in which the first liquid stream rich in CO2 (1, L1) is sent to the contacting means before sending the first gaseous stream rich in CO2 and before sending liquid from the contacting means to the CO2 storage of the means of transport (B).

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