Absence of flaring during the start-up of a liquefied natural gas plant

Abstract

The invention relates to a method comprising the implementation of a start-up process for a liquefied natural gas (LNG) plant involving the supply of natural gas through a sequence of processing units of the LNG plant; during the start-up process, the supply of natural gas from the outlets of the processing units to a hot blowdown drum and a cold blowdown drum of the LNG plant; and after the start-up process, the recycling of the natural gas by supplying the natural gas from the hot blowdown drum and the cold blowdown drum to the inlets of the processing units. Abstract figure: Figure 1

Description

Title of the invention: No flaring during the start-up of a liquefied natural gas plant

[0001] BACKGROUND

[0002] A liquefied natural gas (LNG) plant is an installation that cools natural gas to -260 °F (-162 °C), transforming it into a liquid to facilitate storage and transportation. The process involves removing impurities and compressing the gas, then cooling it to its liquefaction point. The LNG is stored in insulated tanks and can be transported by ship or truck. Upon arrival at its destination, it is reheated and converted back into a gas for distribution and use.

[0003] An LNG plant may include many components that work together to liquefy natural gas. For example, an LNG plant may include feed gas treatment components to remove impurities such as water, carbon dioxide, and sulfur compounds from the natural gas. An LNG plant may also include liquefaction units that cool the natural gas to its liquefaction temperature using processes such as refrigeration or expansion cooling. An LNG plant may also include storage tanks, i.e., insulated tanks that store the liquefied natural gas at extremely low temperatures (e.g., -260 °F).

[0004] The feed gas treatment components may include inlet separators that separate liquids and solids from the incoming natural gas stream. The feed gas treatment components may also include an acid gas removal (AGR) unit that removes acid gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S) from the natural gas stream. The feed gas treatment components may also include a dehydration unit that removes water vapor from the natural gas to prevent ice formation and corrosion of downstream equipment.Other feed gas treatment components may include a mercury removal unit that removes traces of mercury from the natural gas to prevent damage to downstream equipment, and a liquefaction pretreatment unit that removes additional impurities that may freeze or interfere with the liquefaction process.

[0005] During the start-up of an LNG plant, natural gas is often flared for various reasons. For example, natural gas may be flared for safety reasons to ensure that any unburned gas is safely disposed of, reducing This reduces the risk of leaks or accumulation of combustible gases within the plant. Furthermore, natural gas can be flared to ensure operational stability, as flaring allows operators to maintain stable operating conditions by quickly removing excess gas that cannot be processed or used during the startup phase. This prevents pressure and temperature fluctuations within the plant that could otherwise disrupt the startup process. In addition, many jurisdictions require the flaring of excess natural gas during startup and shutdown periods to minimize greenhouse gas and other pollutant emissions. During the initial startup of an LNG plant, flaring can last for weeks or even months. DETAILED DESCRIPTION

[0006] Certain aspects and features of this description relate to the recycling of fluid (e.g., natural gas) used during the start-up phase of a liquefied natural gas (LNG) plant, instead of flaring the natural gas, thereby reducing the volume of flaring. In particular, the amount of flaring can be reduced to zero or almost zero. This is achieved through a fluid recycling system that is integrated into the existing equipment of the LNG plant, so that no additional equipment is required. The techniques described herein can be applied to various different plant configurations, such as a complete power plant with imported electricity, a complete power plant with on-site power generation, or a plant that may or may not have a liquefaction refrigerant.The techniques described here can also be applied during an initial start-up of the LNG plant (e.g., hot LNG storage) or a subsequent start-up.

[0007] One of the main causes of flaring during the start-up process is that the units are normally started sequentially and the natural gas supplied to each unit must be flared off until the next unit is ready to receive it. Such flaring can result in significant CO2 emissions. A typical start-up period can also be quite long (e.g., 4 months), with continuous flaring occurring during this time. Under these conditions, it is common to operate the plant at a 40% flow rate, which is entirely flared. Conversely, using the techniques described herein, there is little or no flaring.A small amount of flaring may occur for the cooling of LNG storage or if the liquefaction unit is started in an LNG plant that does not have power generation, but the flared flow is always much smaller (e.g., 10% of the flow) and the . The duration of flaring is considerably reduced, for example to 10 days or less. When comparing these two options, the techniques described here reduce CO2 emissions by 98%.

[0008] Typically, attempts to reduce flaring during the start-up of an LNG plant encounter numerous difficulties. During start-up, the units are not yet operating under normal conditions, so the process fluids (e.g., natural gas) may vary in quality and condition, such as composition, pressure, and temperature. An LNG plant may also process several different fluids that must be handled separately to avoid any problems. A location must also be provided where the fluids can be disposed of without being flared. Furthermore, recycling compressors or pumps may be required to perform recycling, but these are not normally supplied to the plant. And due to financial constraints, it is not always possible to add such new compressors and pumps to the plant design.Recycled fluids may also need to be made compatible with the requirements of the unit where they are recycled, for example in terms of composition, pressure, and / or temperature.

[0009] There are also other challenges associated with attempting to reduce flaring during the start-up of an LNG plant. For example, after being processed, a recycled fluid may also need to be restored to its original state (e.g., the state it was in before processing) so as not to disrupt the unit to which it is returned. For example, various aspects of gas quality, such as its composition, pressure, and / or temperature, may change as it passes through a unit. To recycle the fluid without affecting the operation of the units, it may be necessary to restore it to its original state at the unit inlet before recycling. Furthermore, LNG plants may have different configurations and specifications depending on the project. Therefore, the requirements and start-up sequence may vary from one plant to another.For example, a fully electrified factory without energy production would be different from a factory with energy production.

[0010] To help overcome one or more of the aforementioned challenges, some examples in this description may reuse existing components in an LNG plant for the purpose of fluid recycling. For example, any of the following compressors existing in the LNG plant may be used to assist in fluid recycling: • Regeneration unit regeneration gas compressor • Native CO2 compressor • Natural gas liquid (NGL) unit booster compressor • Evaporative gas compressor (BOG)

[0011] Similarly, to restore the original composition of the natural gas (for example, the state it was in before being processed during startup), it may be necessary to remix the different fluids that were separated in the units. Mixing drums can be used for this purpose. For example, the existing purge drums in the LNG plant can be used for this purpose. Liquid purges and vapor recycling can be sent to these drums, from which flaring-free management can be performed.

[0012] More specifically, an LNG plant is typically equipped with two blowdown drums. One is used for the hot end of the plant and the other is used for the cold end. Two drums are used because cold fluids cannot be mixed with hot, wet fluids. Some examples here can take advantage of the two existing drums to separate the different flows and recycle them to the correct location. For the hot section, the regeneration gas compressor from the dehydration unit, the native CO2 compressor, and / or the NGL unit's booster compressor can be used to recover the treated gas and compress it before returning it to the hot section blowdown drum, where the different fluids can be remixed and subsequently recycled back into the process.To implement this functionality, the hot purge drum can operate at the process pressure (high). In the cold section, the various fluids can change pressure and temperature during the startup of the chilled units. It may be desirable to stabilize their state before recycling them into the process. For this purpose, the treated fluids can be sent to the cryogenic purge drum, which can operate at low pressure. The gas can then be sent to the BOG compressor where it can be compressed again. The advantage of doing this is that the gas is reheated during compression.

[0013] Before starting any refrigeration or cryogenic unit, it is often desirable to remove moisture from the water to prevent freezing and equipment blockage. This is usually done by passing dry gas through the lines and equipment. The dry gas absorbs the water and is then removed. A common practice is to flare this gas because it is at low pressure and cannot be easily recycled. Natural gas is often chosen as the dry gas for the defrosting fluid because, once heated (e.g., from 55°C to 60°C), it very effectively removes water and allows the equipment to reach the required level of dryness. However, this involves flaring hydrocarbons, which results in CO2 emissions. If the entire defrosting process is carried out using natural gas, this results in the use of a larger quantity of gas and therefore more flaring.In some examples, it is possible to start the . Defrosting can be done with dry air or dry nitrogen. If dry air is used initially, dry nitrogen can then be used to render the units inert. Another advantage of using inert fluids is that the defrosting process can begin well before the system starts up and the gas supply arrives. This eliminates safety concerns, and the defrosting can be carried out several weeks in advance. The final defrosting with dry natural gas then takes significantly less time.

[0014] Furthermore, instead of flaring the natural gas used for de-icing, in some examples the natural gas can be sent to a flare recovery unit. If the flow capacity of the flare recovery unit is limited, the de-icing flow can be reduced and the de-icing time can be increased. If the de-icing gas is humidified during use, the de-icing gas can also be sent to a hot flare recovery unit, from which the gas can be recycled to upstream units.

[0015] It should also be taken into account that the start-up activity must be well prepared in advance. It may be advantageous to emphasize operator training using a training simulator and dynamic commissioning activities (for example, starting the equipment with dummy fluids). In addition, it may be desirable to increase the number of qualified personnel and the number of control stations in the control room to allow a larger number of panel operators to work simultaneously.

[0016] As described herein, a new configuration of existing components in an LNG plant can be provided to obtain a system in which different streams can be successfully recovered and recycled. Recycling can be maintained for as long as necessary (for example, if a problem occurs, the plant can remain in standby mode without flaring until the problem is resolved). This means that the upstream units (where the gas is recycled) are not disrupted or disturbed by the recycling. As noted above, to implement the recycling process, existing purge drums can be used as recycling and mixing drums. For example, the hot purge drum for the hot section and the cryogenic purge drum for the cold section can be reused for this purpose.Since these two pieces of equipment are normally already present in all installations, and with a few modifications, they can be reused for the additional purpose of reducing flaring during the start-up procedure.

[0017] An example of a recycling scheme is illustrated in [Fig. 1] below. For comparison, [Fig. 2] and [Fig. 3] show functional diagrams of a typical LNG plant. [Fig. 2] shows an example in which there is no energy production at the LNG plant, while [Fig. 3] shows an example in which there is energy production at the LNG plant. In the figures, the acronym "FGRU" stands for Flare Gas Recovery Unit.

[0018] [Fig. 1] SHOWS A GENERAL OVERVIEW OF THE RECYCLING SCHEME

[0019] [Fig.2] SHOWS A TYPICAL LNG FACILITY WITHOUT ENERGY PRODUCTION

[0020] [Fig.3] SHOWS A TYPICAL LNG INSTALLATION WITH ENERGY PRODUCTION

[0021] It follows from the above that recycling is achieved in certain examples by transfers of natural gas and other fluids to and from a hot purge drum, as well as by transfers of natural gas and other fluids to and from a cold (e.g., cryogenic) purge drum. These fluid transfers are not present in a conventional device.

[0022] In addition to the purge drums, the dehydration regeneration gas compressor can also be reused to assist in the implementation of the recycling process, as described above. When starting up all units upstream of the dehydration regeneration gas compressor, instead of flaring, a routing can be implemented to send the spent gas directly to the regeneration compressor. Since the recording compressor is located on the processing route downstream of the dehydration dryers, the dehydration dryers may need to be bypassed because they might not be compatible with accepting untreated gas. Therefore, a new bypass can be implemented so that the dryers can be bypassed, and the untreated gas sent directly to the regeneration compressor. Figure 4, shown below, is an example of a dehydration bypass.From the regeneration compressor, the gas can be sent to the hot purge drum, which can be pressurized, before being returned to the upstream process. This avoids flaring. Figure 5 below shows an example of a hot purge drum mixing fluids from the regeneration compressor and CO2 before they are recycled upstream.

[0023] [Fig.4] SHOWS THE CIRCUMVENTION OF DEHYDRATION

[0024] [Fig.5] SHOWS A HOT PURGE DRUM MIXING THE Fluids from the regeneration compressor and CO2 before being recycled upstream

[0025] Additional aspects and features of the recycling process will now be described below. In particular, the operation of various units of the LNG plant within the recycling process will now be described and illustrated by additional figures.

[0026] Gas removal unit. Acids

[0027] The LNG plant may also include an acid gas removal unit to remove acid gas (usually CO2) from the process stream. When the acid gas removal unit is started, recycling this same gas may initially be acceptable. However, over time, the gas may begin to contain less and less CO2. Towards the end, it may be problematic to return it to the inlet of the acid gas removal unit because this can lead to emulsification or foaming. To avoid this problem, it is possible to mix the acid gas that has been separated from the feed gas with the recycled gas, using the hot blowdown drum as a mixing drum for startup.For example, a line can be installed between the CO2 compressor and the hot blowdown drum, and the CO2 compressor can be started in advance so that it is ready for dynamic commissioning using CO2 cylinders, for instance. It should be kept in mind that, in some cases, the discharge pressure of the CO2 compressor may be too high compared to the operating pressure of the hot blowdown drum. If the gas is drawn from the top stage discharge, it may be necessary to reduce the pressure, which can lead to a significant drop in temperature. To avoid this, the CO2 compressor can be variable-speed, or the gas can be drawn from an intermediate stage rather than the top stage.When this configuration is applied, it may be desirable for the start-up flow not to exceed the capacity of the regenerative gas compressor (for example, a flow of 7 to 10%). This allows the acid gas removal unit to be started with a lower flow rate. Some existing plants have already developed acid gas removal unit start-ups with minimal natural gas flow, or even with no natural gas flow at all.

[0028] Fig. 6 below shows functional diagrams of example configurations for the acid gas removal unit when there is no power production (top) and when there is power production (bottom) at the LNG plant.

[0029] [Fig.6] SHOWS CONFIGURATIONS FOR STARTING THE ACID GAS REMOVAL UNIT

[0030] Dehydration unit

[0031] During the start-up of the dehydration unit, the recycling loop described for the start-up of the acid gas removal unit can also be continued for the dehydration unit; only then can it be confirmed that the gas from the acid gas removal unit meets the specification for CO2 and can begin to pass through the dryer beds. dehydration instead of bypassing them. The dehydration unit can remain in recirculation mode until the dry gas is confirmed and the NGL unit is defrosted / pressurized and ready to receive the gas. This can provide sufficient time to test the dryer sequence and regenerate the dryers one after another as many times as necessary.

[0032] Figure 7 shows an example of a flow diagram for the unit of dehydration. Fig. 8 shows functional diagrams of example configurations for starting the dehydration unit both when there is no power production (top) and when there is power production (bottom) at the LNG plant.

[0033] [Fig.7] SHOWS A FLOW DIAGRAM OF THE UNIT OF DEHYDRATION

[0034] [Fig.8] SHOWS CONFIGURATIONS FOR STARTING THE DEHYDRATION UNIT

[0035] NGL Unit

[0036] Once the unit has defrosted, to start the NGL unit, the NGL unit can be pressurized and flow can be gradually established through the NGL unit and the pressurization process. Initially, a small flow can be used to gradually cool the NGL unit to its normal operating temperature. The flow can then be gradually increased as the NGL unit cools. Once the flow is established, the lean gas leaving the booster compressor can be recycled back into the process in the same way as in the previous units. It can be returned to the hot blowdown drum, where it can be mixed with native CO2, the regeneration gas from the dehydration unit, and finally return to the inlet of the acid gas removal unit. In this way, the NGL unit can remain in recycling mode until it has stabilized.And since no new rich gas is introduced into the unit, excessive liquid production at the bottom of the digester is also avoided. This means the fractionation unit does not need to be started immediately. A potential problem can arise if there is insufficient liquid production: the digester's reboiler cannot be started. If the column is empty of liquid and the reboiler is not started, the bottom of the column can cool below acceptable temperatures. However, filling the bottom of the digester column with butane and starting the reboiler in advance can eliminate this problem.

[0037] Figure 9 shows an example of a flow diagram for the NGL unit. [Fig. 10] shows functional diagrams of example configurations for the NGL unit start-up both when there is no power production (top) and when there is power production (bottom) at the LNG plant.

[0038] [Fig.9] SHOWS A FLOW DIAGRAM OF THE NGL UNIT

[0039] [Fig. 10] SHOWS CONFIGURATIONS FOR STARTING THE NGL UNIT

[0040] Liquefaction unit

[0041] With regard to the liquefaction unit, when the liquefaction unit is started in recirculation mode, there may be little or no gas at the inlet of the liquefaction unit. Consequently, liquid production is very low at the NGL unit. This implies that it may not be necessary to start the fractionation unit before starting the liquefaction unit. The refrigerant used for the liquefaction unit can be taken from the available refrigerant storage.

[0042] In some examples, the liquefaction unit can be started when the LNG storage is hot. In some examples, the LNG can be used to cool the LNG storage tanks, but if it is not available, the gas from the liquefaction unit, which gradually cools as the unit is started, can be used to gradually cool the equipment without causing thermal shock. During the start-up of the liquefaction unit, cold gas is produced and can be used for this purpose if both units are started simultaneously. The gas or instantaneous vapor recovered from the LNG storage can then be routed to the BOG compressor instead of being sent to the flare. The destination of the gas from the BOG compressor may depend on the plant configuration, and more specifically on the presence or absence of a power generation unit.

[0043] In addition, in some examples the liquefaction unit can be started when the LNG storage is cold. In some such examples, the start-up procedure may be slightly different when performed after a shutdown. In particular, the LNG tanks may be too cold to receive the hot gas produced at the beginning of liquefaction. To avoid thermal shock to the various components, a new destination for the "cold gas" can be used. The cryogenic purge drum can be used as a recycling point in this case, since it is designed to receive gas that is gradually becoming colder. From the cryogenic purge drum, the gas can go to the BOG compressor, and the destination from there will be as in the cases described above. It is important to note that the flow configuration may change as the start-up progresses.The gas exiting the liquefaction chamber gradually becomes colder and when it reaches a sufficiently low temperature, [the gases]... Liquids form in the cryogenic purge drum. Then the flow can be diverted to the normal route towards the LNG storage tanks.

[0044] In some examples, the liquefaction unit can be started even when no refrigerant is available. In some such examples, it may be necessary to produce refrigerants from the fractionation unit. This implies that a gas supply line to the installation can be established to supply the refrigerant from the gas required for its production. The refrigerants can therefore be produced gradually, in parallel with the start-up of the liquefaction unit. The refrigerants can be injected into the refrigeration loop progressively as they are produced.

[0045] Figure 11 shows an example of using the cold purge drum to start the liquefaction unit. Figure 12 shows functional diagrams of example configurations for starting the liquefaction unit when the LNG storage is hot, both when there is no power generation (top) and when there is power generation (middle and bottom) at the LNG plant. Figure 13 shows functional diagrams of example configurations for starting the liquefaction unit when the LNG storage is cold, both when there is no power generation (top) and when there is power generation (middle and bottom) at the LNG plant. Figure 14 shows a functional diagram of an example configuration for starting the liquefaction unit when there is no refrigerant available.

[0046] [Fig. 11] SHOWS THE USE OF THE COLD PURGE DRUM FOR STARTING THE LIQUEFACTION UNIT

[0047] FIG. 12, COMPRISING [Fig. 12A] (TOP AND MIDDLE) AND [Fig. 12B] (BOTTOM) SHOWS CONFIGURATIONS FOR STARTING THE LIQUEFACTION UNIT WITH HOT LNG STORAGE

[0048] FIG. 13, COMPRISING [Fig. 13A] (TOP AND MIDDLE) AND [Fig. 13B] (BOTTOM) SHOWS CONFIGURATIONS FOR STARTING THE LIQUEFACTION UNIT WITH COLD LNG STORAGE

[0049] FIG. 14, COMPRISING [Fig. 14A] (TOP AND MIDDLE) AND [Fig. 14B] (BOTTOM) SHOWS CONFIGURATIONS FOR STARTING THE LIQUEFACTION UNIT WHEN NO REFRIGERANT IS AVAILABLE

[0050] Splitting unit

[0051] The start-up sequence of the fractionation unit may depend on the unit configuration. To minimize flaring, a configuration can be used in which the condensate depentanizer / stabilizer column can be installed first. Figure 15 shows an example of such a configuration. A fractionation unit in which a depentanizer / condensate stabilizer is used first. Then, the desethaner and the depropanizer / debutanizer can be installed (for example, in that order). This arrangement allows the depentanizer to operate alone, without the desethaner and the depropanizer / debutanizer columns in operation. Figure 16 shows an example of a fractionation unit in which a desethaner and a depropanizer / debutanizer are bypassed. The NGLs recovered at the top of the depentanizer can be sent to an LPG reinjection drum, from where they can be recycled back into the process.

[0052] [Fig. 15] SHOWS THE CONFIGURATION OF THE FRACTIONATING UNIT IN WHICH A DEPENTANIZER / CONDENSATE STABILIZER IS FIRST

[0053] [Fig. 16] SHOWS THE CONFIGURATION OF THE FRACTIONATING UNIT WITH THE DEPROPANIZER / DEBUTANASER BYPASSED

[0054] It is common practice to start fractionation columns sequentially. At the start-up, the column condensers may have difficulty condensing due to the presence of components that are too light to condense. Consequently, liquids are not generated inside the reflux drums. The vapor inside the reflux drums is normally flared during this time. In particular, the stabilization of each column can take some time, and liquids eventually begin to accumulate inside. However, they are out of specification, and the next column cannot receive them. These liquids may need to be removed anyway to avoid triggering level alarms. In this case, the usual practice is to send them to the torch separators, where they will eventually evaporate and be flared.Therefore, the main sources of flaring are typically evaporation gas from the column reflux drums, and liquids from the de-ethanizer and depropanizer / debutanizer.

[0055] In some examples, the depentanizer / condensate stabilizer can be started up such that, when it receives liquids formed in the digester, the liquids collected at the top of the column bypass the columns of the digester and depropanizer and go directly to the non-specification condensate storage. Figure 17 shows an example of starting up a depentanizer / condensate stabilizer with recycling to condense the non-specification storage. Similarly, the liquids collected at the bottom of the column can be sent first to the non-specification condensate storage. Once the depentanizer column is operating normally, and the top and bottom products are confirmed to be within specifications, the various streams of Products can be routed to their correct destinations. The condensate can be sent to the condensate storage, and the overhead liquid can be sent to the LPG reinjection drum. From there, it can be pumped into the feed gas stream at the liquefaction unit inlet. This bypasses the degasser and depropanizer, which have not yet started. Evaporated vapors from the condensate stabilizer reflux drum, which are likely to contain C5+ / BTEX, can be routed to a flare gas recovery unit to prevent flaring. Figure 18 shows flow diagrams of example configurations for starting the depropanizer / condensate stabilizer, both when there is no power generation (top) and when there is power generation (bottom) at the LNG plant.

[0056] [Fig. 17] SHOWS THE START-UP OF THE CONDENSATE DEPENTANIZER / STABILIZER WITH RECYCLING TO CONDENSE OUT-OF-SPECIFICATION STORAGE

[0057] [Fig. 18] SHOWS CONFIGURATIONS FOR STARTING THE CONDENSATE DEPENTANIZER / STABILIZER

[0058] In some examples, the desethaner and the depropanizer / debutanizer can be started up such that, once it has been confirmed that the headstream of the debutanizer column does not contain BTX, it can be slowly sent to the desethaner. After a certain time, flow to the depropanizer also becomes possible. Liquids accumulating in the column bottoms of the desethaner and depropanizer can first be sent to the NGL reinjection drum. A chiller can be used to cool them before they reach the drum. Out-of-specification liquids may accumulate inside the NGL reinjection drum initially, but it is likely that the drum's volume will not be sufficient to contain them for the entire duration of the start-up procedure. At some point, therefore, a new destination may be required for purging.The cryogenic purge drum can again be used as a recycling point in this case. A driver can be present inside the cryogenic purge drum to vaporize the liquids. The generated vapor may be at low pressure, in which case the vapor cannot be recycled back into the process without first passing through the BOG compressor. The destination after the BOG compressor may depend on the capacity and discharge pressure of the BOG compressor. Figure 19 shows functional diagrams of example configurations for starting the desethaner and the depropanizer / debutanizer, both when there is no power generation (top) and when there is power generation (bottom) in the LNG plant.

[0059] [Fig. 19] SHOWS CONFIGURATIONS FOR STARTING THE DETHANAZER AND THE DEPROPANIZER / DEBUTANAZER

[0060] The lighter components within the recycled liquids can vaporize, while the heavier components can remain liquid. By installing a pump, it is possible to convey these liquids to the hot purge drum, as the cryogenic drum might not be able to hold all the liquids until the fractionation unit is stabilized. From the hot purge drum, a pump can send the liquids to the out-of-specification condensate drum, which is normally large and can hold the liquids until startup is complete. Once startup is complete and the fractionation unit is stabilized, these liquids can be returned to the condensate stabilizer inlet via an existing fitting. An example of the fractionation unit recycling scheme is shown below in [Fig. 20].

[0061] [Fig.20] IS A RECYCLING SCHEME FOR THE UNIT OF FRACTIONATION

[0062] The foregoing description of the disclosure, including the aspects and examples illustrated, is provided for illustrative and descriptive purposes only and is not intended to be exhaustive or to limit the disclosure to the specific forms disclosed. Many modifications, adaptations, and uses thereof will be obvious to those skilled in the art without departing from the scope of this disclosure. Aspects and features of each disclosed example may be combined with any other example.

[0063] Larger versions of each of the above figures are found in Annex A, which is incorporated herein by way of reference. Examples of demands

Claims

Demands

1. A method comprising: the implementation of a start-up process for a liquefied natural gas (LNG) plant involving the supply of natural gas through a sequence of processing units of the LNG plant; during the start-up process, the supply of natural gas from outlets of the processing units to a hot blowdown drum and a cold blowdown drum of the LNG plant; and after the start-up process, the recycling of natural gas by supplying natural gas from the hot blowdown drum and the cold blowdown drum to the inlets of the processing units.

2. A process according to claim 1, wherein the processing units comprise a first processing unit and a second processing unit, wherein the hot blowdown drum is fluidly coupled to the first processing unit, wherein the cold blowdown drum is fluidly coupled to the second processing unit, and wherein the recycling of natural gas after the start-up process involves: the transmission of a first part of the natural gas from the hot blowdown drum to the first processing unit; and the transmission of a second part of the natural gas from the cold blowdown drum to the second processing unit.

3. A method according to any one of claims 2, wherein the first treatment unit is an acid gas removal unit, and wherein the second treatment unit is a natural gas liquid (NGL) recovery unit.

4. A method according to any one of claims 2 and 3, further comprising: mixing a first additional fluid with the first part of the natural gas in the hot blowdown drum, before transferring the first part of the natural gas from the hot blowdown drum to the first processing unit; and mixing a second additional fluid with the second part of the natural gas in the cold blowdown drum, before transferring the second part of the natural gas from the cold blowdown drum to the second processing unit.

5. A process according to claim 4, wherein the first additional fluid comprises a first gas from a third processing unit of the LNG plant, and wherein the first additional fluid further comprises a second gas from a fourth processing unit of the LNG plant.

6. A process according to claim 5, wherein the third processing unit is a dehydration unit of the LNG plant, and wherein the fourth processing unit is an NGL recovery unit.

7. A method according to any one of claims 4 to 6, wherein the second additional fluid comprises a first gas from a fifth processing unit of the LNG plant, and wherein the second additional fluid further comprises a second gas from a sixth processing unit of the LNG plant.

8. A method according to claim 7, wherein the fifth processing unit is a fractionation unit of the LNG plant, and wherein the sixth processing unit is a liquefaction unit of the LNG plant.

9. A method according to any one of claims 1 to 8, wherein the supply of natural gas from one of the processing units to the hot blowdown drum comprises: the transmission of a portion of the natural gas from the processing unit to the hot blowdown drum via a compressor, wherein the compressor is fluidly coupled between the processing unit and the hot blowdown drum.

10. A method according to claim 9, wherein the treatment unit is an acid gas removal unit.

11. A method according to any one of claims 9 to 10, wherein the compressor is a native CO2 compressor.

12. A liquefied natural gas (LNG) generation system, comprising: an acid gas removal unit for receiving natural gas and removing acidic elements from the natural gas; a compressor fluidly coupled between an outlet of the acid gas removal unit and a drum for transferring the natural gas to the drum; and the drum is fluidly coupled to the compressor, wherein the drum generates a mixture of the natural gas with at least one other gas and supplies the mixture to an inlet of the acid gas removal unit.

13. A system according to claim 12, wherein the drum is a first drum and the natural gas comprises a first part and a second part, the first part being received in the first drum, and further comprising: a natural gas liquid (NGL) recovery unit; a fractionation unit fluidly coupled to an output of the NGL recovery unit; and a second drum which is separate from the first drum, in which the second drum is fluidly coupled to an output of the fractionation unit for: receive the second part of the natural gas coming from the fractionation unit; generate another mixture of the second part of the natural gas with at least one other gas; and supply the mixture to the NGL recovery unit.

14. System according to claim 12, further comprising another compressor fluidly coupled between the second drum and the NGL recovery unit to transfer the mixture to the NGL recovery unit.

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