Zero flaring during the startup of a liquid natural gas plant

Abstract

Techniques for reducing flaring of natural gas when starting up a liquified natural gas (LNG) plant are described. In one example, a feed of natural gas can be provided as input to a sequence of processing units of the LNG plant, where the processing units generate processed fluids based on the feed of natural gas. The processed fluids can be transmitted through recycling components that transform the processed fluids into a recycled stream of natural gas. The recycled stream of natural gas can then be transmitted back to one or more inlets of the processing units, to thereby recycle the natural gas rather than flare the natural gas.

Description

TITLE OF THE INVENTION: ZERO FLARING DURING THE STARTUP OF A LIQUID NATURAL GAS PLANTCross-Reference to Related Applications

[0001] This application claims priority under 35 U.S.C. § 119(e) to French Application No. 2404418, titled “ZERO FLARING DURING THE STARTUP OF A LIQUID NATURAL GAS PLANT” and filed on April 26, 2024, to French Application No. 2409495 filed on September 6, 2024 and to United Kingdom Application No. 2415191.2, filed on October 16, 2024, the entirety of each of which is hereby incorporated by reference herein.Background

[0002] A liquefied natural gas (LNG) plant is a facility that cools natural gas to -260°F (-162°C), turning it into a liquid for easier storage and transportation. The process involves removing impurities from the gas, then cooling it to its liquefaction point. LNG is stored in insulated tanks and can be transported via ships or trucks. At its destination, it is pressurized and reheated back into a gas for distribution and use.

[0003] An LNG plant can include numerous components (or units) working together to process the natural gas. For example, an LNG plant can include feed gas treatment components to remove impurities such as mercury, water, carbon dioxide, sulfur compounds and heavy hydrocarbons from the natural gas. An LNG plant can also include liquification units that cool the natural gas to its liquefaction temperature using processes like refrigeration or expansion cooling. An LNG plant can also include storage tanks, which are insulated tanks that store the liquified natural gas at extremely low temperatures (e.g., -260°F) and LNG ship loading stations.

[0004] The feed gas treatment components can include inlet separators, distillation columns that separate liquids and solids from the incoming natural gas stream. The feed gas treatment components can also include an Acid Gas Removal Unit (AGRU) that removes acidic gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S) from the natural gas stream. The feed gas treatment components can further include a Dehydration Unit that removes water vapor from the natural gas to prevent ice formation and corrosion in downstream equipment. Other feed gas treatment components caninclude a Mercury Removal Unit that removes trace amounts of mercury from the natural gas to prevent damage to downstream equipment, and a Hydrocarbon Treatment Unit to remove additional impurities or hydrocarbons that could freeze or interfere with the liquification process.

[0005] During the startup of an LNG plant, natural gas is often flared for various reasons. For example, natural gas may be flared for safety reasons to help ensure that any uncombusted gas is safely disposed of, reducing the risk of leaks or buildup of combustible gases within the plant. Additionally, natural gas may be flared for operational stability because flaring allows operators to maintain stable operating conditions by disposing of excess gas that cannot be processed or utilized in other units during the startup phase. This helps reaching the proper operating parameter and performance of the units, as well as preventing fluctuations in pressure and temperature within the plant, which could otherwise disrupt the startup process. Further, in many jurisdictions, regulations require the flaring of excess natural gas during startup and shutdown periods to minimize emissions of greenhouse gasses and other pollutants. When it comes to the very first startup of an LNG plant, flaring can last for weeks or even months in the worstcase scenario.Summary

[0006] One example of the present disclosure can include a method for starting up a liquified natural gas (LNG) plant. The method can comprise the steps of: a) providing a feed of natural gas as input to a sequence of processing units of the LNG plant, wherein the processing units generate processed fluids based on the feed of natural gas; b) transmitting the processed fluids through recycling components that transform the processed fluids into a recycled stream of natural gas; and c) transmitting the recycled stream of natural gas back to one or more inlets of the processing units, to thereby recycle the natural gas rather than flare the natural gas.

[0007] One or more examples can include the method of the previous paragraph, wherein the recycling components can include mixing drums that combine outputs from two or more of the processing units together. The mixing drums can include a warm drain drum and a cold drain drum.

[0008] One or more examples can include the method of any previous paragraph, further comprising transmitting a first portion of the recycled stream of natural gas from the warm drain drum to a first processing section of the LNG plant. A second portion of the recycled stream of natural gas can also be transmitted from the cold drain drum to a second processing section of the LNG plant. The cold drain drum can be downstream of the warm drain drum.

[0009] One or more examples can include the method of any previous paragraph, further comprising providing the first portion of the recycled stream of natural gas to a first set of process units of the first processing section. The first set of process units can extend from a gas inlet of the LNG plant to a Natural Gas Liquid (NGL) Recovery Unit. The second portion of the recycled stream of natural gas can also be provided to a second set of process units of the second processing section. The second set of process units can be downstream the NGL Recovery Unit.

[0010] One or more examples can include the method of any previous paragraph, wherein first vapor fluids passed through the first processing section are mixed and recycled back for reprocessing. Second vapor fluids passed through the second processing section can also be mixed and recycled back for reprocessing.

[0011] One or more examples can include the method of any previous paragraph, further comprising mixing a first set of outputs of the processing units in the warm drain drum, prior to transmitting first mixed content of the warm drain drum to the first processing section. A second set of outputs of the processing units can also be mixed in the cold drain drum, prior to transmitting second mixed content of the cold drain drum to the second processing section.

[0012] One or more examples can include the method of any previous paragraph, wherein the recycling components mix and compress the processed fluids from the processing units such that the recycled stream of natural gas has a composition, temperature, and / or pressure that is substantially similar to the feed of natural gas, so that the recycled stream of natural gas is compatible with the processing units during a subsequent recycling phase.

[0013] One or more examples can include the method of any previous paragraph, further comprising providing a set of outputs from a set of processing units of the firstprocessing section to the warm drain drum by transmitting the set of outputs through one or more compressors to the warm drain drum. The one or more compressors can be fluidically coupled between the set of processing units and the warm drain drum.

[0014] One or more examples can include the method of any previous paragraph, further comprising providing a set of outputs from a set of processing units of the second processing section to the cold drain drum by transmitting the set of outputs through one or more compressors to the cold drain drum. The one or more compressors can be fluidically coupled between the set of processing units and the cold drain drum.

[0015] One or more examples can include the method of any previous paragraph, further comprising transmitting an input gas through a bypass line of a Dehydration Unit to a Regeneration Gas Compressor of the Dehydration Unit, without the input gas passing through dehydration driers of the Dehydration Unit.

[0016] One or more examples can include the method of any previous paragraph, further comprising collecting fluid in a Natural Gas Liquid (NGL) reinjection drum of a Fractionation Unit for recycling.

[0017] One or more examples can include the method of any previous paragraph, further comprising transmitting an input gas through a bypass line of the Fractionation Unit to the NGL reinjection drum, without the input gas passing through a Deethanizer and / or a Depropanizer.

[0018] One or more examples can include the method of any previous paragraph, further comprising repeating steps b) and c) at least until the processing units are operating according to at least one predefined operating criterion.

[0019] Another example of the present disclosure can include a liquified natural gas (LNG) plant comprising a sequence of processing units that receive a feed of natural gas as input; and a plurality of recycling components fluidically coupled to the processing units. The recycling components can receive processed fluids from the processing units and transform the processed fluids into a recycled stream of natural gas. The recycling components can further transmit the recycled stream of natural gas back to one or more inlets of the processing units, to thereby recycle the natural gas rather than flare the natural gas.

[0020] One or more examples can include the LNG plant of the previous paragraph, wherein the recycling components can include mixing drums that combine outputs from two or more of the processing units together. The mixing drums can include a warm drain drum and a cold drain drum. The cold drain drum can be downstream of the warm drain drum.

[0021] One or more examples can include the LNG plant of any previous paragraph, further comprising a first processing section and a second processing section. The warm drain drum can be fluidically coupled to the first processing section. The cold drain drum can be fluidically coupled to the second processing section. The recycling components can transmit a first portion of the recycled stream of natural gas from the warm drain drum to the first processing section. The recycling components can transmit a second portion of the recycled stream of natural gas from the cold drain drum to the second processing section.

[0022] One or more examples can include the LNG plant of any previous paragraph, wherein the first processing section can include a first set of process units from a gas inlet of the LNG plant to a Natural Gas Liquid (NGL) Recovery Unit. The second processing section can include a second set of process units downstream the NGL Recovery Unit.

[0023] One or more examples can include the LNG plant of any previous paragraph, wherein the recycling components can mix and compress the processed fluids from the processing units such that the recycled stream of natural gas has a composition, temperature, and / or pressure that is substantially similar to the feed of natural gas, so that the recycled stream of natural gas is compatible with the processing units during a subsequent recycling phase.

[0024] One or more examples can include the LNG plant of any previous paragraph, wherein the sequence of processing units can comprise a Dehydration Unit that includes a first bypass line that transmits an input gas to a Regeneration Gas Compressor of the Dehydration Unit, without the input gas passing through dehydration driers of the Dehydration Unit. The sequence of processing units can also comprise a Fractionation Unit that includes a Natural Gas Liquid (NGL) reinjection drum. The NGL reinjection drum can collect fluids from the Fractionation Unit for recycling. TheFractionation Unit can include a second bypass line that transmits an input gas to the NGL reinjection drum without the input gas passing through a Deethanizer and / or a Depropanizer.

[0025] One or more examples can include the LNG plant of any previous paragraph, further comprising one or more compressors fluidically coupled between the processing units and the warm drain drum. The one or more compressors can include a Dehydration Unit Regeration Gas Compressor, a Native CO2 Compressor(s), a Boost Compressor of a Natural Gas Liquid (NGL) Recovery Unit, or a Flare Recovery Unit Compressor.Brief Description of the Drawings

[0026] FIG. 1 shows a block diagram of an example of a liquid natural gas plant configured to recycle fluid during a startup phase according to some aspects of the present disclosure.

[0027] FIG. 2 shows a process flow diagram of an example of a Dehydration Unit with dehydration bypass according to some aspects of the present disclosure.

[0028] FIG. 3 shows a process flow diagram of an example of a warm drain drum mixing fluids from the regeneration and CO2 compressor before being recycled upstream, according to some aspects of the present disclosure.

[0029] FIG. 4A and FIG.4B show block diagrams of examples of configurations for an Acid Gas Removal Unit, both when there is no power generation (4A) and when there is power generation (4B) at the LNG plant, according to some aspects of the present disclosure.

[0030] FIG. 5A and FIG.5B show block diagrams of examples of configurations for the startup of the Dehydration Unit, both when there is no power generation (5A) and when there is power generation (5B) at the LNG plant, according to some aspects of the present disclosure.

[0031] FIG. 6 shows a process flow diagram of an example of the flow pattern for a Dehydration Unit according to some aspects of the present disclosure.

[0032] FIG. 7A and FIG.7B show block diagrams of examples of configurations for the startup of an NGL Recovery Unit, both when there is no power generation (7A) andwhen there is power generation (7B) at the LNG plant, according to some aspects of the present disclosure.

[0033] FIG. 8 shows a process flow diagram of an example of the flow pattern for the NGL Recovery Unit according to some aspects of the present disclosure.

[0034] FIG. 9A, FIG. 9B and FIG. 9C show block diagrams of examples of configurations for the startup of a Liquefaction Unit when LNG storage is warm, both when there is no power generation (9A) and when there is power generation (9B-9C) at the LNG plant, according to some aspects of the present disclosure.

[0035] FIG. 10 shows a process flow diagram of an example of using a cold drain drum (e.g., cryogenic drain drum) for the start of the Liquefaction Unit, according to some aspects of the present disclosure.

[0036] FIG. 11 A, FIG. 11 B and FIG. 11 C show block diagrams of examples of configurations for the startup of the Liquefaction Unit when LNG storage is cold, both when there is no power generation (11 A) and when there is power generation (11 B-11 C) at the LNG plant, according to some aspects of the present disclosure.

[0037] FIG. 12A, FIG. 12B and FIG. 12C show block diagrams of examples of configurations for the startup of the Liquefaction Unit when no refrigerant is available, both when there is no power generation (12A) and when there is power generation (12B- 12C) at the LNG plant, according to some aspects of the present disclosure.

[0038] FIG. 13 shows a process flow diagram of an example of a Fractionation Unit configuration in which a Depenthanizer is arranged to receive the input gas first, according to some aspects of the present disclosure.

[0039] FIG. 14 shows a process flow diagram of an example of a fractionation unit in which a Deethanizer and Depropanizer is bypassed, according to some aspects of the present disclosure.

[0040] FIG. 15 shows a process flow diagram of an example of Depenthanizer / condensate stabilizer startup with recycling to condensate off-spec storage, according to some aspects of the present disclosure.

[0041] FIGS. 16A and FIG. 16B show block diagrams of examples of configurations for the startup of the Depenthanizer, both when there is no powergeneration (16A) and when there is power generation (16B) in the LNG plant, according to some aspects of the present disclosure.

[0042] FIG. 17 A and FIG. 17B show block diagrams of examples of configurations for the startup of the Deethanizer and Depropanizer, both when there is no power generation (17A) and when there is power generation (17B) in the LNG plant, according to some aspects of the present disclosure.

[0043] FIG. 18 shows a process flow diagram of an example of a Fractionation Unit’s recycle scheme, according to some aspects of the present disclosure.Detailed Description

[0044] Certain aspects and features of the present disclosure relate to recycling fluid (e.g., natural gas) used during the startup phase of a liquified natural gas (LNG) plant, instead of flaring the natural gas, to thereby reduce the amount of flaring. In particular, the amount of flaring may be reduced to zero or near zero. This is achieved through a fluid recycling scheme that is integrated into the existing equipment of the LNG plant, so that no additional equipment is needed. The techniques described herein can be applied to various different plant configurations, such a full electric plant with electric power import, a full electric plant with power generation on site, or a plant that may or may not have liquefaction refrigerant available. The techniques described herein can also be applied during a first startup of the LNG plant (e.g., LNG storage warm) or a subsequent startup.

[0045] A key cause of flaring during the startup process is that units are normally started sequentially, and the natural gas provided to each unit needs to be disposed of by flaring until the next unit is ready to receive it. Such flaring can lead to large CO2 emissions. A typical first start-up period can also be quite long (e.g., 4 months), with continuous flaring taking place during this time. Under these conditions, it is common to operate the facility at turndown (typically 40% flow), which is all flared. Conversely, by using techniques described herein, there is very little or no flaring. A small amount of flaring may occur for LNG storage cooldown or if the Liquefaction Unit is started up in an LNG plant that lacks power generation on site, but the flared flow is still much lower (e.g., 10% flow) and the duration of flaring is significantly reduced, for example to 10 days orless. When comparing these two options, 98% CO2 emission savings can be achieved using the techniques described herein.

[0046] Conventionally, there are many difficulties with attempting to reduce flaring during the startup of an LNG plant. During startup, the units are still not running under normal conditions, so the natural gas can vary in quality and conditions, such as composition, pressure, and temperature. An LNG plant may also handle multiple different fluids that need to be managed separately to avoid any problems. There also needs to be a location at which the fluids can be disposed of until LNG can be sent to storage, without flaring. Additionally, recycling compressors or pumps may be needed to perform the recycling, but they are not normally provided in the plant. And because of cost constraints, it may not be possible to add such new compressors and pumps to the plant’s design. Recycled fluids may also need to be made compatible with the requirements of the unit where it is recycled to, for example in terms of composition, pressure, and / or temperature.

[0047] There are also other challenges associated with attempting to reduce flaring during the startup of an LNG plant. For example, after being processed, a recycled fluid may also need to be restored to its original condition (e.g., the condition it was in prior to processing), so as not to disturb the unit to which it is returned. For instance, various aspects of the gas quality such as its composition, pressure, and / or temperature may be changed when passing through a unit. To recycle the fluid without impacting the operation of the units, the original condition at the inlet of the unit may need to be restored before recycling. Additionally, LNG plants can have different configurations and specificities depending on projects. As a result, start-up requirements and sequence can be different between plants. For instance, a fully electrified plant with no power generation on site would be different than a plant with power generation on site.

[0048] To help overcome one or more of the above challenges, some examples of the present disclosure can reuse existing components in an LNG plant for the purpose of recycling the fluids. For example, any of the following existing compressors in the LNG plant may be used to assist with fluid recycling:• Dehydration Unit Regeneration Gas Compressor• Native CO2 Compressor• Natural Gas Liquid (NGL) Unit Booster Compressor• End Flash Gas Compressor and Boil Off Gas (BOG) Compressor

[0049] Also, to restore the original composition of the natural gas (e.g., the condition it was in before it was processed during startup), the different fluids that were separated in the units may need to be mixed back gain. Mixing drums can be used for this purpose. For example, the existing drain drums in the LNG plant can be used for this purpose. Liquid drains and vapor recycling can be sent to these drums, from which noflaring management can be accomplished.

[0050] More specifically, an LNG facility is typically provided with two drain drums. One is used for the warm end of the facility and the other is used for cold end the facility. Two drums are used because cold fluids cannot be mixed with warm and wet fluids. Some examples herein can take advantage of the two existing drums to segregate the different fluids and recycle them to the correct location. For the warm section, the Dehydration Unit Regeneration Gas Compressor, the Native CO2 compressor, and / or the NGL Unit Booster Compressor can be used to recover the processed gas and to compress it, before returning it to the warm section drain drum, where the different fluids can be mixed back together and recycled to the process afterwards. To implement this functionality, the warm drain drum can be operated at process (high) pressure. For the cold section, the different fluids can change in pressure and temperature during the start-up of the cold units. It may be desirable for their condition to be stabilized before being recycled back to the process. To that end, the processed fluids can be sent to the cryogenic drain drum, which may be operated at low pressure. Then the gas can be sent to the End Flash Gas Compressor and / or the BOG compressor where it can be compressed again. The advantage in doing so is that the gas is warmed up again when compressed.

[0051] An additional consideration is that start-up activity should be well prepared for in advance. It may be advantageous to emphasize operator training with an Operating Training Simulator and dynamic commissioning activities (e.g., starting equipment with dummy fluids). Also, it may be desirable to increase the number of qualified personnel and the number of control stations in the control room to allow more panel operators to act simultaneously.

[0052] As described herein, a new configuration of existing components in an LNG plant can be provided to achieve a system where different streams can be successfullyrecovered and recycled. The recycling can be sustained (e.g., repeated) at least until one or more predefined criteria are satisfied. For example, the recycling can be sustained until the processing units are individually or collectively operating according to one or more predefined operating criteria. In some such examples, the recycling can be sustained until some or all of the processing units are operating in accordance with their own respective criteria. In other examples, the recycling can be sustained until the processing units are collectively operating according to a predetermined overall operating criterion such that the flaring is minimized, as opposed to flaring during the complete startup sequence. Additionally, the recycling can be sustained as long as necessary to resolve problems or perform other tasks. For instance, if an issue occurs, the plant can stay in a hold condition without flaring until the issue is resolved. This implies that the upstream units (where the gas is recycled) are not upset or disturbed by the recycling.

[0053] As noted above, to implement the recycling process, the existing drain drums can be used as recycling and mixing drums. For instance, the warm drain drum for the warm section and the cryogenic drain drum for the cold section can be reused for this purpose. Because these two equipment items are normally already present in all facilities, they can be reused to serve the additional purpose of reducing flaring during the start-up procedure with few modifications.

[0054] These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements but, like the illustrative examples, should not be used to limit the present disclosure.

[0055] Turning now to FIG. 1 , shown is a block diagram of an example of a liquid natural gas plant 100 configured to recycle fluid during a startup phase according to some aspects of the present disclosure. The liquid natural gas plant 100 can be conceptualized as having a “warm side” and a “cold side.” The warm side can refer to the left half of the diagram, including components 102-108, 120, 122, 124, and 126, because the natural gas is maintained at a warmer temperature through those components. The warm side can also be referred to herein as a “first processing section,” because it is a first section of the LNG plant 100 that has processing units. The warm side can include some or all ofthe processing units from a gas inlet of the LNG plant 100 up to (but not including) a NGL Recovery Unit 110. The cold side can refer to the right half of the diagram, including components 110-1 18, 128, 130, and 132, because the natural gas is maintained at a cooler temperature through those components than in the warm side. The cold side can also be referred to herein as a “second processing section,” because it is a second section of the LNG plant 100 that has processing units. The cold side can include some or all of the processing units downstream of the NGL Recovery Unit 110 and including the NGL Recovery Unit 110 itself.

[0056] The warm side can include inlet facilities 102 fluidically coupled to a Mercury Removal Unit 104. The Mercury Removal Unit 104 can be configured to remove mercury from a natural gas input into the LNG plant 100. The Mercury Removal Unit 104 can be fluidically coupled to an Acid Gas Removal (AGR) Unit 106 configured to remove acid from the natural gas. The AGR Unit 106 can be fluidically coupled to a Dehydration Unit 108 configured to remove water from the natural gas. This may be important because water vapor can cause corrosion, freeze in cold temperatures, and decrease efficiency. The AGR Unit 106 may also be fluidically coupled to a compressor 120 (e.g., Native CO2 Compressor) configured to compress carbon dioxide from the AGR Unit 106. The compressed carbon dioxide may then be transmitted through a fluidic connection to a first Flare Gas Recovery Unit (FGRU) 122, also referred to herein as the “warm FGRU,” to assist in the recycling process described in greater detail later. Also included in the warm side may be a first drain drum 124, also referred to herein as a “warm drain drum,” and an Off-Spec Condensate Storage Unit 126, both of which may also be used in the recycling process as described in greater detail later. For example, the warm drain drum 124 may be used as a mixing drum to mix fluidic components together during the recycling process.

[0057] As noted above, the liquid natural gas plant 100 can include a cold side. The cold side can include a Natural Gas Liquids (NGL) Recovery Unit 110, which is fluidically coupled to the Dehydration Unit 108. The NGL Recovery Unit 1 10 can be configured to produce natural gas liquids and condensates from the treated natural gas. Examples of the natural gas liquids may include ethane, propane, and butanes. The NGL Recovery Unit 110 can be fluidically coupled to a Fractionation Unit 128 and aLiquefaction Unit 112. The Fractionation Unit 128 can include a Demethanizer, Deethanizer, a Depropanizer, and a Debutanizer to separate and recover methane, ethane, propane, butanes, respectively, and any higher boiling hydrocarbons. The Liquefaction Unit 112 can condense the natural gas into a liquid. The Liquefaction Unit 112 may condense the natural gas into a liquid at essentially atmospheric pressure by using refrigeration to cool it to a low temperature, such as -162°C. The Liquefaction Unit 112 can be fluidically coupled to an LNG Storage Unit 114 for storing the liquefied natural gas. The LNG Storage Unit 114 can be fluidically coupled to a compressor, such as the BOG Compressor 116, which in turn may be fluidically coupled to a Nitrogen Removal Unit (NRU) 118 in examples involving power import. The NRU 118 can be configured to remove nitrogen from the liquified natural gas before it is used in a downstream process. Also included in the cold side can be a second FGRU 130, also referred to herein as the “cold FGRU,” and a second drain drum 132, also referred to herein as a “cold drain drum” or “cryogenic drain drum.” These components may facilitate the recycling process as described in greater detail below. For example, the cold drain drum 132 may be used as a mixing drum to mix fluidic components together during the recycling process.

[0058] As shown in FIG. 1 , recycling is achieved through transmissions of natural gas and other fluids to and from the first drain drum 124, as well as through transmissions of natural gas and other fluids to and from the second drain drum 132. In particular, the first drain drum 124 can be fluidically coupled to the Dehydration Unit 108 and receive regeneration gas from the Dehydration Unit 108. The first drain drum 124 can also be fluidically coupled to the NGL Recovery Unit 110 and receive lean gas from the NGL Recovery Unit 110. The first drain drum 124 may be further fluidically coupled to the second drain drum 132 and receive recycled liquids from the second drain drum 132. The first drain drum 124 can mix these fluid components together to generate a recycled gas that has is similar in terms of composition, pressure, temperature, or any combination thereof to the original gas input to the AGR Unit 106. Additionally or alternatively, the recycled gas from the first drain drum 124 can be mixed with compressed CO2 from the compressor 120, depending on the needs of the system. In some examples, the first drain drum 124 can be fluidically coupled to the Off-Spec Condensate Storage Unit 126. Thewarm drain drum 124 can transmit the recycled gas to the Off-Spec Condensate Storage Unit 126 for further storage.

[0059] The second drain drum 132 can be used for a similar purpose on the cold side. For example, the second drain drum 132 can be fluidically coupled to the Fractionation Unit 128 and receive flash gas and natural gas liquids from the Fractionation Unit 128. In some examples, the Fractionation Unit 128 can be fluidically coupled to the Off-Spec Condensate Storage Unit 126 for storing liquids. The second drain drum 132 can also be fluidically coupled to the Liquefaction Unit 1 12 and receive cold gas from the Liquefaction Unit 112. The second drain drum 132 can mix these fluid components together to generate a recycled gas that has is similar in terms of composition, pressure, temperature, or any combination thereof to the original gas input to the NGL Recovery Unit 110. The second drain drum 132 can transmit this recycled gas to the first drain drum 124 and / or the compressor 116. From the compressor 116, the compressed recycled gas can be returned to the NGL Recovery Unit 110 as input for a subsequent treatment cycle.

[0060] By using the first drain drum 124 on the warm side and the cold drain drum 132 on the cold side to mix fluid components together, after the natural gas has been treated by one or more of the process units (e.g., units 102-112, 128), the drain drums 124, 132 can generate a recycled gas is substantially similar to the original natural gas that was input to one or more of the process units. This may allow the recycled gas to be input into the process units again for a subsequent treatment cycle without damaging or otherwise negatively affecting the operation of the process units during the subsequent treatment cycle. Because the same stream of natural gas can now be recycled without negatively affecting the process units, it can be repeatedly used without the need for flaring.

[0061] Various components described above and elsewhere herein may be referred to as “recycling components,” because they are used to facilitate the recycling process. For example, the warm FGRU 122, the warm drain drum 124, the Off-Spec Condensate Storage Unit 126, the cold FGRU 130, and the cold drain drum 132 may be considered recycling components, since they perform steps during the recycling process to help recycle the natural gas. Additionally, various compressors described herein, such as the BOG compressor 1 16, may be considered recycling components if they are usedduring the recycling process.

[0062] Now that an overview of recycling process and recycling components has been provided, further details about the operation of some of the individual process units during the recycling process will be further explained below.Dehydration Unit

[0063] Turning now to the Dehydration Unit 108, FIG. 2 shows a process flow diagram of an example of a Dehydration Unit 108 with bypass line for a dehydration bypass according to some aspects of the present disclosure. The Dehydration Unit 108 can be fluidically coupled to the AGR Unit 106 to receive an input gas, which may be an off-spec gas. The input gas can be transmitted through an inlet gas cooler before being sent to a drier separator 204. The drier separator 204 can be fluidically coupled through a series of valves to one or more dehydration driers, such as a first dehydration drier 206, a second dehydration drier 208, and a third dehydration drier 210. Under normal operating conditions, the input gas can be transmitted through the series of dehydration driers 206- 210, a regeneration gas heater 216, and a regeneration gas preheater 218. From there, the treated gas may be transmitted to a regeneration gas air cooler 212, which can cool the regeneration gas and transmit the cooled gas to a regeneration gas separator 214. The regeneration gas separator 214 can separate the gas components of the regeneration gas and transmit one or more of said components to a regeneration gas compressor 220, also referred to herein as a Dehydration Regeneration Gas Compressor, which can compress the regeneration gas.

[0064] During the recycling process described herein, the compressor 220 can be reused, in addition to the first and second drain drums, to help implement the recycling process. In particular, when starting all process units upstream of the compressor 220, instead of flaring, a bypass line can send the used gas directly to the compressor 220. Since the compressor 220 is located on the process route downstream of the dehydration driers 206-210, the dehydration driers 206-210 can be bypassed since they might not be compatible for accepting untreated gas. Thus, the new bypass route depicted by a dashed line in FIG. 2 can be activated via a valve 222, so that the dehydration driers 206-210 can be bypassed. As a result, the untreated gas can be sent directly to the compressor 220, without being transmitted through the dehydration driers 206-210. From the compressor220, the gas can be sent to the warm drain drum, which can be pressurized, before being returned to the process upstream. In doing so, no flaring occurs.

[0065] Further details about the warm drain drum 124 are shown in FIG. 3. In particular, FIG. 3 shows an example of the warm drain drum 124 mixing fluids from the regeneration gas compressor 220 of FIG. 2 and the native CO2 compressor 120 of FIG. 1 before being recycled upstream. The recycling may be achieved as shown via the dashed line in FIG. 3, by transmitting the recycled gas from the warm drain drum 124 to the AGR Unit 106. More details about the AGR Unit 106 will now be described below.Acid Gas Removal Unit

[0066] Turning to FIGS. 4A-B, shown are block diagrams of examples of configurations of liquified natural gas plants 400, 402 for starting up an AGR Unit 106 according to some aspects of the present disclosure. FIG. 4A shows an example in which there is no power generation at the liquified natural gas plant. FIG. 4B shows an example in which there is power generation at the liquified natural gas plant. The AGR Unit 106 can remove the acid gas (typically CO2) from the process stream.

[0067] When the AGR Unit 106 is being started, recycling the same gas may be acceptable at first. However, as time passes, the gas may start containing less and less CO2. Towards the end, it may be troublesome to send it back to the inlet of AGR Unit 106 as it can lead to emulsion or foaming. To prevent this issue, it is possible to mix the acid gas that was separated from the feed gas back into the recycled gas, using the warm drain drum 124 as a mixing drum for start-up. For example, a line from the native CO2 compressor 120 to the warm drain drum 124 can be installed and the native CO2 compressor 120 may be started up in advance, so that it is ready in advance (e.g., as part of dynamic commissioning using CO2 bottles). It will be appreciated that, in some cases, the discharge pressure of the native CO2 compressor 120 may be too high compared to the operating pressure of the warm drain drum 124. If the gas is taken from the last stage discharge, the pressure may need to be let down, which can cause the temperature to drop dramatically. To prevent this, the native CO2 compressor 120 can be of variable speed or the gas can be extracted from an intermediate stage, rather than the last stage, of the CO2 compressor 120. When this setup is applied, it may be desirable for the startup flow not to exceed the capacity of the regeneration gas compressor of the DehydrationUnit 108 (e.g., regeneration gas compressor 220 of FIG. 2), which may be, for example, 7-10% flow. Thus, the AGR Unit 106 can be started up with a lower flow. Some examples of startup flow rates are shown in FIGS. 4A-B, whereby the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the AGR Unit 106. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the AGR Unit 106.Dehydration Unit

[0068] Turning now to FIGS. 5A-B, shown are block diagrams of examples of configurations of liquified natural gas plants 500, 502 for starting up a Dehydration Unit 108 according to some aspects of the present disclosure. FIG. 5A shows an example in which there is no power generation at the liquified natural gas plant. FIG. 5B shows an example in which there is power generation at the liquified natural gas plant.

[0069] As shown in FIGS. 5A-B, when starting the Dehydration Unit 108, the recycle loop that was described for the AGR Unit 106 startup can be continued for the Dehydration Unit 108 as well; only this time, the gas coming from the AGR Unit 106 can be confirmed to be on specification (“on-spec”) for CO2 and it can start passing through the dehydration drier beds instead of bypassing them. The Dehydration Unit 108 can stay in recycling mode until the dry gas is confirmed and the NGL Recovery Unit 110 is defrosted / pressurized, and it is ready to receive the gas. This can provide enough time to test the drier sequence, and regenerate the driers one after the other, as many times as necessary. Similar to FIGS. 4A-B, in FIGS. 5A-B, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the Dehydration Unit 108. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the Dehydration Unit 108.

[0070] Within the Dehydration Unit 108, certain valves can be activated to establish a flow pattern through the Dehydration Unit 108 during startup. One example of such a flow pattern is shown in FIG. 6. Thicker lines (dashed and solid) can represent active flowpaths during the startup operation of the Dehydration Unit 108. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the Dehydration Unit 108. As shown, an active flow path may transmit gas through the inlet gas cooler and the drier separator 204 into a first dehydration drier 206 and a second dehydration drier 208. The gas may be transmitted from the first dehydration drier 206 and the second dehydration drier 208 through the regeneration gas preheater 218 and the regeneration gas heater 216 before entering a third dehydration drier 210. From the third dehydration drier 210, the gas can be transmitted to the regeneration gas air cooler 212 and then the regeneration gas separator 214, before entering the regeneration gas compressor 220. Finally, the regeneration gas compressor 220 can transmit the recycled gas to the warm drain drum (e.g., the first drain drum 124 of FIG. 1 ).NGL Recovery Unit

[0071] Turning now to FIGS. 7A-B, shown are block diagrams of examples of configurations of liquified natural gas plants 700, 702 for starting up a NGL Recovery Unit 110 according to some aspects of the present disclosure. FIG. 7A shows an example in which there is no power generation at the liquified natural gas plant. FIG. 7B shows an example in which there is power generation at the liquified natural gas plant. Like prior figures, in FIGS. 7A-B, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the NGL Recovery Unit 110. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the NGL Recovery Unit 110.

[0072] Before starting any cold or cryogenic unit, it is often desirable to remove water moisture in advance from the lines and equipment, to avoid water freezing and equipment blockages. This is usually done by passing dry gas in the lines and equipment. This operation is often called defrosting. The dry gas absorbs the water and is then disposed of. Common practice is to flare this gas because it is low pressure and cannot be recycled easily. Natural gas is often selected as the dry gas for defrosting fluid because once it is warmed up (e.g., to 55°C / 60°C) it is very efficient in removing water and allows the equipment to reach the dryness level required. However, this implies flaringhydrocarbons, which leads to CO2 emissions. If the entire defrost process is performed using natural gas, it leads to the use of a larger amount of gas and therefore flaring. In some examples, it is possible to start defrosting with dry air or dry nitrogen. If dry air is used first, then it can be continued with dry nitrogen to inert the units. Another advantage of using inert fluids is that the defrosting activity can be started well in advance of the facility start-up and gas-in. This removes safety constraints and defrosting activity can be carried out several weeks before. Then, final defrosting using dry natural gas takes much less time. Additionally, instead of flaring the natural gas used for defrosting, in some examples the natural gas can be sent to a cold FGR Unit, such as cold FGRU 130 of FIG. 1 . If the flow capacity of the cold FGR Unit is limited, the defrost flow may be reduced and the time needed for defrosting may be increased. If the defrost gas is moisturized when used, the defrost gas can also be sent to a warm FGRU, such as warm FGRU 122, from which the gas can be recycled to the upstream units.

[0073] After the unit defrosting is completed, to start the NGL Recovery Unit 1 10, the NGL Recovery Unit 110 can be pressurized and the flow can be gradually established through the NGL Recovery Unit 110. First, a small flow can be used to progressively cool down the NGL Recovery Unit 1 10 to a normal operating temperature. The flow can then be gradually increased as the NGL Recovery Unit 110 cools down. Once the flow is established, the lean gas that is leaving the NGL Recovery Unit's 1 10 Booster Compressor (e.g., booster compressor 802 of FIG. 8) can be recycled back into the process in a similar fashion to previous units. It can be routed back into the warm drain drum 124, where it can be mixed with native CO2, regeneration gas from Dehydration Unit 108, and finally be transmitted into the inlet of the AGR Unit 106 again. This way, the NGL Recovery Unit 110 can stay in recycle mode until it is stabilized.

[0074] Since no new rich gas is being introduced to the NGL Recovery Unit 110, excess liquid production at the bottom of the Demethanizer column (e.g., Demethanizer 804 of FIG. 8) of the NGL Recovery Unit 110 is also prevented. This means the Fractionation Unit 128 does not need to be started up immediately. One potential problem that can arise from lack of liquid production is the inability to start the Demethanizer Reboiler (e.g., Demethanizer Reboiler 806 of FIG. 8). In case the Demethanizer Column is liquid free, and that the reboiler is not started, the bottom of the Demethanizer Columnmay cool down below acceptable temperatures. However, filling the Demethanizer Column bottom with butane before the unit start-up, and starting the reboiler in advance, can eliminate this problem.

[0075] Within the NGL Recovery Unit 110, certain valves can be activated to establish a flow pattern through the NGL Recovery Unit 110 during startup. One example of such a flow pattern is shown in FIG. 8. Thicker lines (dashed and solid) can represent an active flow path during the startup operation of the NGL Recovery Unit 110. Thinner lines can represent an inactive flow path through which no fluid may flow during the startup operation of the NGL Recovery Unit 1 10. In this example, feed gas can enter a NGL cold box 808 and flow to a low temperature separator 810, whereby it can be separated. A first portion of the feed gas can be transmitted to a top of the Demathanizer Column 804 and a second portion of the feed gas can be transmitted to a middle portion of the Demethanizer 804. The Demethanizer 804 can be configured to remove methane from the feed gas. A Demethanizer Reboiler 806 can be coupled to the Demethanizer 804 for providing heat to the bottom of the Demathanizer Column 804. The top of the Demethanizer 804 can be flu idically coupled to the NGL cold box 808, which can receive the demethanized gas from the Demathanizer Column 804 and transmit it to a booster compressor 802. A booster compressor can be a specialized type of air compressor that increases the pressure of an input gas (e.g., up to 1000 bar). The booster compressor 802 can then transmit the pressurized gas to the warm drain drum (e.g., the first drain drum 124 of FIG. 1 ).Liquefaction Unit

[0076] Turning now to the Liquefaction Unit 112, when the Liquefaction Unit 112 is started using the recycling mode, there may be no or very little liquid production at the NGL Recovery Unit 110. This implies that the Fractionation Unit 128 may not need to be started before the Liquefaction Unit 112 start-up and, thus, the refrigerant components needed by the Liquefaction Unit’s 112 refrigeration systems may not be produced. So, refrigerant needed for the Liquefaction Unit 112 can be taken from refrigerant storage as available.

[0077] In some examples, the Liquefaction Unit 112 can be started up when LNG storage 1 14 is warm. In some such examples, liquified natural gas can be used to cooldown the LNG storage tanks, but if not available, it is possible to use gas from the Liquefaction Unit 112 that is progressively getting colder as the Liquefaction Unit 112 is being started to gradually cool down the equipment without causing thermal shock. During start-up of the Liquefaction Unit 112, cold gas can be produced and can be used for this purpose if the two units are started-up simultaneously. The gas or the flash gas recovered from LNG storage 114 can then be routed to the BOG Compressor 116 instead of being sent to the flare. The destination of the gas from the BOG Compressor 1 16 can depend on the facility configuration, and in particular, on the presence or absence of a power generation unit in the LNG plant 100. Some examples of such configurations are shown in FIGS. 9A-C. FIG. 9A shows a block diagram of an example of a configuration for the startup of the Liquefaction Unit when LNG storage 114 is warm and when there is no power generation at the LNG plant 100. FIGS. 9B-C show block diagrams of examples of a configuration for the startup of the Liquefaction Unit 112 when LNG storage 114 is warm and when there is power generation at the LNG plant 100. Like prior figures, in FIGS. 9A-C, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the Liquefaction Unit 112. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the Liquefaction Unit 112.

[0078] Additionally, in some examples the Liquefaction Unit 112 can be started up when LNG storage 114 is cold. In some such examples, the startup procedure can be slightly different when it is being done after a prior shutdown (e.g., it is not the first startup of the plant). In particular, the LNG storage tanks may be too cold to receive the warm gas that is being produced by the Liquefaction Unit 112 at the beginning. To avoid thermal shock of the different items, a new destination for the “cold gas” generated by the Liquefaction Unit 1 12 can be used. The cold drain drum 132 can be used as a recycling point in this case, since it is designed to receive gas that is getting progressively colder. One example of this is shown in FIG. 10. As shown, a valve 1002 can be activated to establish a flow path (dashed line) from the Main Cryogenic Heat Exchanger (MCHE) 1004 to the cold drain drum 132. From the cold drain drum 132, the gas can be transmittedto the End Flash Gas compressor (if any) or / and the BOG Compressor 116, and the destination from there can be depend on the presence or absence of a power generation unit at the LNG plant 100, as described above. Note that the flow configuration can change as the start-up is progressing. The gas leaving the Liquefaction Unit 112 can gradually become colder and, when it reaches cold enough temperature, liquids are formed in the cold drain drum 132. Then the flow can be diverted to the normal route towards the LNG storage 114, for example by deactivating the first valve 1002 and / or activating a second valve 1006.

[0079] Some examples of the abovementioned flows are shown in FIGS. 1 1 A-C. FIG. 11 A shows a block diagram of an example of a configuration for the startup of the Liquefaction Unit 1 12 when LNG storage 1 14 is cold and when there is no power generation at the LNG plant 1100. FIGS. 1 1 B-C show block diagrams of examples of a configuration for the startup of the Liquefaction Unit 112 when LNG storage 114 is cold and when there is power generation at the LNG plants 1 104-1106. Like prior figures, in FIGS. 11 A-C, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the Liquefaction Unit 112. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the Liquefaction Unit 112.

[0080] In some examples, the Liquefaction Unit 112 can be started up when no refrigerant is available. In some such examples, refrigerants may need to be produced from the Fractionation Unit 128. So, a feed forward gas-in flow to the facility may be established to bring in the refrigerant from the gas needed for their production. The refrigerants can therefore be produced progressively, in parallel of the startup of the Liquefaction Unit 112. The refrigerants can be injected into the refrigeration loop progressively as they are being produced. Some examples of this process are shown in FIGS. 12A-C. FIG. 12A shows a block diagram of an example of a configuration for the startup of the Liquefaction Unit 112 when no refrigerant is available and when there is no power generation at the LNG plant 1200. FIGS. 12B-C show block diagrams of examples of a configuration for the startup of the Liquefaction Unit 112 when there is no refrigerantavailable and when there is power generation at the LNG plant 1202-1204. Like prior figures, in FIGS. 12A-C, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the Liquefaction Unit 112. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the Liquefaction Unit 112.Fractionation Unit

[0081] Turning now to the Fractionation Unit 128, the start-up sequence of the Fractionation Unit 128 can depend on the unit’s configuration. In some examples, to minimize flaring, a configuration can be used in which the Depenthanizer column can be installed first. One example of such a configuration is shown in FIG. 13. In this example, the Fractionation Unit 128 is configured such that the Depenthanizer 1302 is configured to receive the input gas prior to the Deethanizer 1304 and the Depropanizer 1306. This arrangement can allow for operating the Depenthanizer 1302 alone, without the Deethanizer 1304 and the Depropanizer 1306 in service. In some such cases, the Deethanizer 1304 and the Depropanizer 1306 can be bypassed using a bypass line. An example of bypassing the Deethanizer 1304 and the Depropanizer 1306 is shown in FIG. 14. In this example, the natural gas liquids recovered at the top of the Depenthanizer 1302 can be sent to an NGL reinjection drum 1402, from which they can be recycled to the process. This can be achieved by activating a bypass valve 1404, which causes the enclosed portion of the figure (e.g., the Deethanizer 1304 and the Depropanizer 1306) to be bypassed.

[0082] It is usual practice to start the fractionation columns in sequence. In the beginning of startup, the column condensers may have trouble condensing to column overhead flow due to presence of too light components that cannot condense. Therefore, liquids are not generated inside reflux drums 1406-1410. The vapors inside the reflux drums 1406-1410 are normally flared during this period. In particular, it can take some time to stabilize each column and liquids will start eventually accumulating inside. However, these are off-spec, and the next column cannot receive them. Also, in this case, these liquids may need to be disposed of anyway in order not to trip the level alarms. Inthat situation, usual practice is to send them to the Flare Knockout Drums where they will eventually flash and be flared. As a result, the main sources of flaring are typically the flash gas from the reflex drums 1406-1410 of the columns, and the liquids from the Deethanizer 1304 and Depropanizer 1306. To help overcome these issues, in some examples the Depenthanizer 1302 can be started up such that, when it receives liquids that are formed in the Demethanizer of the NGL Recovery Unit 110 (Demethanizer 804 of FIG. 8), the liquids collected on the column overhead bypass the Deethanizer 1304 and Depropanizer 1306 and go directly into the Off-Spec Condensate Storage 126. One example of the above process is shown in FIG. 15, which shows recycling to Off-Spec Condensate Storage 126. Similarly, the liquids collected at the bottom of the Depenthanizer 1302 can be first sent to the Off-Spec Condensate Storage 126. Once the Depenthanizer 1302 is operating normally, and the products overhead and bottom are confirmed to be on-spec, the different products streams can be aligned to the correct destination. Condensate can be sent to condensate storage, and the liquid overhead can be sent to the NGL reinjection drum. From there, it can be pumped into the feed gas stream at the inlet of the Liquefaction Unit 112. In doing so, this bypasses the Deethanizer 1304 and the Depropanizer 1306 that are not started. Flashed vapor from Condensate Stabilizer Reflux Drum, which is likely to contain C5+ / BTEX, can be transmitted to an FGRU (e.g., cold FGRU 130 of FIG. 1 ) to avoid flaring.

[0083] FIGS. 16A-B show block diagrams of examples of configurations for the startup of the Depenthanizer 1302, both when there is no power generation (FIG. 16A) and when there is power generation (FIG. 16B) in the LNG plant 1600-1602. Like prior figures, in FIGS. 16A-C, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths through which fluid flows during the startup operation of the Depenthanizer 1302. Thinner lines can represent inactive flow paths through which no fluid may flow during the startup operation of the Depenthanizer 1302.

[0084] In some examples, the Deethanizer 1304 and the Depropanizer 1306 can be started up such that, once the Depenthanizer 1302 column’s overhead stream is confirmed to not contain BTX (a mixture of benzene, touline, and xylene), it can be slowlysent to the Deethanizer 1304. After some time, the flow to the Depropanizer 1306 also becomes possible. The liquids accumulated in the column bottoms of the Deethanizer 1304 and Depropanizer 1306 can first be sent to the NGL Reinjection Drum 1402. A cooler can be used to cool them down prior to arriving at the drum 1402. The off-spec liquids can be accumulated inside the NGL Reinjection Drum 1402 at first, but it is likely that the volume of the drum may not be sufficient to contain them throughout the entire start-up procedure. At a certain point, a new destination may therefore be required for draining. The cold drain drum 132 can once again be used as a recycling point in this case. A heater can be present inside the cold drain drum 132 to vaporize the liquids. The vapor generated can be low pressure, in which case the vapor may not be recycled to the process without first going through the BOG Compressor 1 16. The destination after the BOG Compressor 116 can depend on the capacity and discharge pressure of the BOG Compressor 116.

[0085] FIGS. 17A-B show block diagrams of examples of configurations for the startup of the Deethanizer 1304 and Depropanizer 1306, both when there is no power generation (FIG. 17A) and when there is power generation (FIG. 17B) in the LNG plant 1700-1702. Like prior figures, in FIGS. 17A-B, the percentages can reflect examples of the flow rates into the corresponding components, though the actual flow rates used in practice may depend on the particularities of such components. Thicker lines (dashed and solid) can represent active flow paths. Thinner lines can represent inactive flow paths. The lighter components inside the recycled liquids can vaporize, while the heavier components can remain liquid. By installing a pump, it is possible to route these liquids into the warm drain drum 124, as the cold drain drum 132 may be unable to contain all the liquids until the Fractionation Unit 128 is stabilized. From the warm drain drum 124, a pump can send liquids to the Off-Spec Condensate Storage 126, which is normally big and can contain the liquids until the start-up is finalized. After the start-up is complete and the Fractionation Unit 128 is stabilized, these liquids can be returned to the inlet of the Condensate Stabilizer via an existing connection.

[0086] One example of the Fractionation Unit’s overall recycling scheme 1800 is shown in FIG. 18. The dashed lines can represent the abovementioned flow paths. For example, as shown, the liquids accumulated in the column bottoms of the Deethanizer1304 and Depropanizer 1306 can first be sent to the NGL Reinjection Drum 1402. A cooler can be used to cool them down prior to arriving at the drum 1402. The off-spec liquids can be accumulated inside the NGL Reinjection Drum 1402 and then transmitted to the cold drain drum 132, which can be used as a recycling point in this case. The liquids in the cold drain drum 132 can then be transmitted to the warm drain drum 124. Vapor in the cold drain drum 132 can be transmitted to an FGRU and / or the Bog Compressor 116 via one or more fluidic connections. From the warm drain drum 124, the liquids can be transmitted to Off-Spec Condensate Storage 126. Vapor in the warm drain drum 124 can be transmitted to an FGRU via a fluidic connection.

[0087] The foregoing description of the disclosure, including illustrated aspects and examples has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art without departing from the scope of this disclosure. Aspects and features from each disclosed example may be combined with any other example.

Claims

Claims1 . A method for starting up a liquified natural gas (LNG) plant, the method comprising the steps of: a) providing a feed of natural gas as input to a sequence of processing units of the LNG plant, wherein the processing units generate processed fluids based on the feed of natural gas; b) transmitting the processed fluids through recycling components that transform the processed fluids into a recycled stream of natural gas; and c) transmitting the recycled stream of natural gas back to one or more inlets of the processing units, to thereby recycle the natural gas rather than flare the natural gas.

2. The method of claim 1 , wherein the recycling components include mixing drums that combine outputs from two or more of the processing units together, the mixing drums including a warm drain drum and a cold drain drum.

3. The method of claim 2, further comprising: transmitting a first portion of the recycled stream of natural gas from the warm drain drum to a first processing section of the LNG plant; and transmitting a second portion of the recycled stream of natural gas from the cold drain drum to a second processing section of the LNG plant, the cold drain drum being downstream of the warm drain drum.

4. The method of claim 3, further comprising: providing the first portion of the recycled stream of natural gas to a first set of process units of the first processing section, wherein the first set of process units extend from a gas inlet of the LNG plant to a Natural Gas Liquid (NGL) Recovery Unit; and providing the second portion of the recycled stream of natural gas to a second set of process units of the second processing section, wherein the second set of process units are downstream the NGL Recovery Unit.

5. The method of claim 3, wherein first vapor fluids passed through the first processing section are mixed and recycled back for reprocessing, and wherein second vapor fluids passed through the second processing section are mixed and recycled back for reprocessing.

6. The method of claim 3, further comprising: mixing a first set of outputs of the processing units in the warm drain drum, prior to transmitting first mixed content of the warm drain drum to the first processing section; and mixing a second set of outputs of the processing units in the cold drain drum, prior to transmitting second mixed content of the cold drain drum to the second processing section.

7. The method of claim 1 , wherein the recycling components mix and compress the processed fluids from the processing units such that the recycled stream of natural gas has a composition, temperature, and / or pressure that is substantially similar to the feed of natural gas, so that the recycled stream of natural gas is compatible with the processing units during a subsequent recycling phase.

8. The method of claim 3, further comprising providing a set of outputs from a set of processing units of the first processing section to the warm drain drum by transmitting the set of outputs through one or more compressors to the warm drain drum, wherein the one or more compressors are fluidically coupled between the set of processing units and the warm drain drum.

9. The method of claim 3, further comprising providing a set of outputs from a set of processing units of the second processing section to the cold drain drum by: transmitting the set of outputs through one or more compressors to the cold drain drum, wherein the one or more compressors are fluidically coupled between the set of processing units and the cold drain drum.

10. The method of claim 1 , further comprising transmitting an input gas through a bypass line of a Dehydration Unit to a Regeneration Gas Compressor of the Dehydration Unit, without the input gas passing through dehydration driers of the Dehydration Unit.11 . The method of claim 1 , further comprising: collecting fluid in a Natural Gas Liquid (NGL) reinjection drum of a Fractionation Unit for recycling.

12. The method of claim 11 , further comprising: transmitting an input gas through a bypass line of the Fractionation Unit to the NGL reinjection drum, without the input gas passing through a Deethanizer and / or a Depropanizer.

13. The method of claim 1 , further comprising repeating steps b) and c) at least until the processing units are operating according to at least one predefined operating criterion.

14. A liquified natural gas (LNG) plant comprising: a sequence of processing units that receive a feed of natural gas as input; and a plurality of recycling components fluidically coupled to the processing units, wherein the recycling components receive processed fluids from the processing units and transform the processed fluids into a recycled stream of natural gas, wherein the recycling components further transmit the recycled stream of natural gas back to one or more inlets of the processing units, to thereby recycle the natural gas rather than flare the natural gas.

15. The LNG plant of claim 14, wherein the recycling components include mixing drums that combine outputs from two or more of the processing units together, the mixing drums including a warm drain drum and a cold drain drum, wherein the cold drain drum is downstream of the warm drain drum.

16. The LNG plant of claim 15, further comprising a first processing section and a second processing section, and wherein: the warm drain drum is fluidically coupled to the first processing section; the cold drain drum is fluidically coupled to the second processing section; the recycling components transmit a first portion of the recycled stream of natural gas from the warm drain drum to the first processing section; and the recycling components transmit a second portion of the recycled stream of natural gas from the cold drain drum to the second processing section.

17. The LNG plant of claim 16, wherein the first processing section includes a first set of process units from a gas inlet of the LNG plant to a Natural Gas Liquid (NGL) Recovery Unit, and wherein the second processing section includes a second set of process units downstream the NGL Recovery Unit.

18. The LNG plant of claim 15, wherein the recycling components mix and compress the processed fluids from the processing units such that the recycled stream of natural gas has a composition, temperature and / or pressure that is substantially similar to the feed of natural gas, so that the recycled stream of natural gas is compatible with the processing units during a subsequent recycling phase.

19. The LNG plant of claim 15, wherein the sequence of processing units comprise: a Dehydration Unit that includes a first bypass line that transmits an input gas to a Regeneration Gas Compressor of the Dehydration Unit, without the input gas passing through dehydration driers of the Dehydration Unit; and a Fractionation Unit that includes a Natural Gas Liquid (NGL) reinjection drum, wherein the NGL reinjection drum collects fluids from the Fractionation Unit for recycling, and wherein the Fractionation Unit includes a second bypass line that transmits an input gas to the NGL reinjection drum without the input gas passing through a Deethanizer and / or a Depropanizer.

20. The LNG plant of claim 15, further comprising one or more compressors flu idically coupled between the processing units and the warm drain drum, wherein the one or more compressors include a Dehydration Unit Regeration Gas Compressor, a Native CO2 Compressor(s), a Boost Compressor of a Natural Gas Liquid (NGL) Recovery Unit, or a Flare Recovery Unit Compressor.

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