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

Abstract

Techniques according to the invention make it possible to reduce natural gas flaring during the start-up of a liquefied natural gas (LNG) plant. In one example, a natural gas supply can be provided as an input to a sequence of processing units in the LNG plant, where the processing units generate treated fluids according to the natural gas supply. The treated fluids can be conveyed through recycling components that convert them into a recycled natural gas stream. The recycled natural gas stream can then be returned to one or more inlets of the processing units, thereby recycling the natural gas rather than flaring it. Figure for the abstract: Fig. 1

Description

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

[0001] CROSS-REFERENCE TO RELATED REQUESTS

[0002] This application claims priority, under Article 119(e) of 35 USC, from French application no. 2,404,418, entitled "ZERO FLARING DURING THE STARTUP OF A LIQUID NATURAL GAS PLANT" (ABSENCE DE TROCHAGE LORS LE DÉMARREMENT D'UNE USINE DE GAZ NATUREL LIQUEFIÉ) and filed on April 26, 2024, the entirety of which is incorporated herein by reference.

[0003] BACKGROUND

[0004] 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 from the gas and 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 pressurized, reheated, and converted back into a gas for distribution and use.

[0005] An LNG plant may include many components (or units) that work together to process natural gas. For example, an LNG plant may include feed gas treatment components to remove impurities such as mercury, carbon dioxide, sulfur compounds, and heavy hydrocarbons 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), and LNG ship loading stations.

[0006] Feed gas treatment components may include inlet separators and distillation columns that separate liquids and solids from the incoming natural gas stream. Feed gas treatment components may also include an acid gas removal unit (AGRU) that removes acid gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S) from the natural gas stream. 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 natural gas to prevent damage to downstream equipment, and a hydrocarbon pretreatment unit that removes additional impurities or hydrocarbons that may freeze or interfere with the liquefaction process.

[0007] 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 removed, thereby reducing the risk of leaks or the accumulation of combustible gases within the plant. Furthermore, natural gas may be flared to ensure operational stability, as flaring allows operators to maintain stable operating conditions by rapidly removing excess gas that cannot be processed or used in other units during the start-up phase. This helps achieve the proper operating parameters and performance of the units and avoids pressure and temperature fluctuations within the plant, which could otherwise disrupt the start-up process.Furthermore, in many jurisdictions, regulations require the flaring of excess natural gas during start-up 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 in the worst-case scenario.

[0008] SUMMARY

[0009] An example of this description may include a method for starting up a liquefied natural gas (LNG) plant. The method may include the steps of: a) supplying a natural gas feed as input to a sequence of processing units of the LNG plant, in which the processing units generate treated fluids according to the natural gas feed; b) conveying the treated fluids through recycling components that transform the treated fluids into a recycled natural gas stream; and c) returning the recycled natural gas stream to one or more inlets of the processing units, thereby recycling the natural gas rather than flaring it.

[0010] One or more examples may include the process of the preceding paragraph, in which the recycling components may include mixing drums that combine the outputs of two or more processing units. The mixing drums may include a hot purge drum and a cold purge drum.

[0011] One or more examples may comprise the process according to any preceding paragraph, further comprising the transmission of a first portion of the recycled natural gas stream from the hot blowdown drum to a first processing section of the LNG plant. A second portion of the recycled natural gas stream can also be transferred from the cold blowdown drum to a second processing section of the LNG plant. The cold blowdown drum can be located downstream of the hot blowdown drum.

[0012] One or more examples may include the process according to any preceding paragraph, further comprising supplying the first portion of the recycled natural gas stream to a first set of processing units in the first processing section. The first set of processing units may extend from a gas inlet of the LNG plant to a Natural Gas Liquids (NGL) recovery unit. The second portion of the recycled natural gas stream may also be supplied to a second set of processing units in the second processing section. The second set of processing units may be located downstream of the NGL recovery unit.

[0013] One or more examples may comprise the process according to any preceding paragraph, wherein the first steam fluids having passed through the first treatment section are mixed and recycled for reprocessing. The second steam fluids having passed through the second treatment section may also be mixed and recycled for reprocessing.

[0014] One or more examples may comprise the process according to any preceding paragraph, further comprising mixing a first set of outputs from the processing units in the hot purge drum, before transferring the first mixed contents of the hot purge drum to the first processing section. A second set of outputs from the processing units may also be mixed in the cold purge drum, before transferring the second mixed contents of the cold purge drum to the second processing section.

[0015] One or more examples may include the process according to any preceding paragraph, wherein the recycling components mix and compress the treated fluids from the processing units so that the recycled natural gas stream has a composition, temperature and / or pressure substantially similar to the natural gas supply, so that the recycled natural gas stream is compatible with the processing units during a subsequent recycling phase.

[0016] One or more examples may comprise the method according to any preceding paragraph, further comprising supplying a set of outputs from a set of treatment units in the first treatment section to the hot blowdown drum by transmitting the set of outputs through one or more compressors to the hot blowdown drum. The compressor(s) may be fluidly coupled between the set of treatment units and the hot blowdown drum.

[0017] One or more examples may comprise the method according to any preceding paragraph, further comprising supplying a set of outputs from a set of processing units of the second processing section to the cold purge drum by transmitting the set of outputs through one or more compressors to the cold purge drum. The compressor(s) may be fluidly coupled between the set of processing units and the cold purge drum.

[0018] One or more examples may include the process according to any preceding paragraph, further including the transmission of an inlet gas through a bypass line from a dehydration unit to a regeneration gas compressor of the dehydration unit, without the inlet gas passing through the dehydration dryers of the dehydration unit.

[0019] One or more examples may include the process according to any preceding paragraph, further including the collection of fluid in a natural gas liquid (NGL) reinjection drum of a fractionation unit for the purpose of recycling.

[0020] One or more examples may include the process according to any preceding paragraph, further including the transmission of an inlet gas through a bypass line from the fractionation unit to the NGL reinjection drum, without the inlet gas passing through a desethaner and / or a depropanizer.

[0021] One or more examples may include the process according to any preceding paragraph, further including the repetition of steps b) and c) at least until the processing units operate according to at least one predefined operating criterion.

[0022] Another example of the present description may include a liquefied natural gas (LNG) plant comprising a sequence of processing units that receive a natural gas feed as input; and a plurality of recycling components fluidly coupled to the processing units. The recycling components may receive the treated fluids from the processing units and transform the treated fluids into a stream of recycled natural gas. The recycling components may further return the stream of recycled natural gas to one or more inlets of the processing units, thereby recycling the natural gas rather than flaring it.

[0023] One or more examples may include the LNG plant of the preceding paragraph, in which the recycling components may include mixing drums that combine the outputs of two or more processing units. The mixing drums may include a hot purge drum and a drum of Cold drain. The cold drain drum can be located downstream of the hot drain drum.

[0024] One or more examples may comprise the LNG plant according to any preceding paragraph, further comprising a first processing section and a second processing section. The hot blowdown drum may be fluidly coupled to the first processing section. The cold blowdown drum may be fluidly coupled to the second processing section. The recycling components may transmit a first portion of the recycled natural gas stream from the hot blowdown drum to the first processing section. The recycling components may transmit a second portion of the recycled natural gas stream from the cold blowdown drum to the second processing unit.

[0025] One or more examples may comprise the LNG plant according to any preceding paragraph, wherein the first processing section may comprise a first set of processing units extending from a gas inlet of the LNG plant to a natural gas liquid (NGL) recovery unit. The second processing section may comprise a second set of processing units downstream of the NGL recovery unit.

[0026] One or more examples may include the LNG plant according to any preceding paragraph, in which the recycling components mix and compress the treated fluids from the processing units so that the recycled natural gas stream has a composition, temperature and / or pressure substantially similar to the natural gas supply, so that the recycled natural gas stream is compatible with the processing units during a subsequent recycling phase.

[0027] One or more examples may include the LNG plant according to any preceding paragraph, wherein the sequence of processing units may include a dehydration unit comprising a first bypass line that transmits an inlet gas to a regeneration gas compressor of the dehydration unit, without the inlet gas passing through the dehydration unit's dehydration dryers. The sequence of processing units may also include a fractionation unit comprising a natural gas liquid (NGL) reinjection drum. The NGL reinjection drum may collect fluids from the fractionation unit for recycling. The fractionation unit may include a second bypass line that transmits an inlet gas to the NGL reinjection drum without the inlet gas passing through a degasser and / or a depropanizer.

[0028] One or more examples may include the LNG plant according to any preceding paragraph, further comprising one or more coupled compressors fluidly between the processing units and the hot blowdown drum. The compressor(s) may include a regeneration gas compressor from a dehydration unit, one or more native CO2 compressors, a booster compressor from a natural gas liquids (NGL) recovery unit, or a flare recovery unit compressor. Brief description of the drawings

[0029] Fig. 1 shows a functional diagram of an example of a liquefied natural gas plant configured to recycle the fluid during a start-up phase according to certain aspects of this description.

[0030] Fig. 2 shows a process flowchart of an example of a dehydration unit with a dehydration bypass according to certain aspects of the present description.

[0031] Figure 3 shows a process flow diagram of an example of a hot purge drum mixing the fluids from the regeneration and CO2 compressor before their upstream recycling, according to certain aspects of this description.

[0032] [Fig.4A] and [Fig.4B] below show functional diagrams of example configurations for an acid gas removal unit, both when there is no power production (4A) and when there is power production (4B) at the LNG plant, according to certain aspects of this description.

[0033] [Fig.5A] and [Fig.5B] show functional diagrams of example configurations for starting the dehydration unit, both when there is no power production (5A) and when there is power production (5B) at the LNG plant, according to certain aspects of this description.

[0034] Figure 6 shows a process flow diagram of an example of the flow scheme for a dehydration unit according to certain aspects of the present description.

[0035] [Fig.7A] and [Fig.7B] show functional diagrams of example configurations for starting an NGL recovery unit, both when there is no power production (7A) and when there is power production (7B) at the LNG plant, according to certain aspects of this description.

[0036] Fig. 8 shows a process flow diagram of an example of the flow scheme for the NGL recovery unit according to certain aspects of the present description.

[0037] [Fig.9A], [Fig.9B] and [Fig.9C] show functional diagrams of examples of configurations for starting a liquefaction unit when the LNG storage is hot, both when there is no power generation (9A) and when it There is energy production (9B-9C) at the LNG plant, according to certain aspects of this description.

[0038] Fig. 10 shows a process flowchart of an example of the use of a cold purge drum (e.g., a cold purge drum) for starting the liquefaction unit, according to certain aspects of this description.

[0039] [Fig. 11 A], [Fig. 11B] and [Fig. 11C] show functional diagrams of example configurations for starting the liquefaction unit when the LNG storage is cold, both when there is no power production (1 IA) and when there is power production (11B-11C) at the LNG plant, according to certain aspects of this description.

[0040] [Fig.12A], [Fig.12B] and [Fig.12C] show functional diagrams of example configurations for starting 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 certain aspects of this description.

[0041] Figure 13 shows a process flowchart of an example configuration of a fractionation unit in which a depentanizer is designed to first receive the inlet gas, according to certain aspects of the present description.

[0042] Fig. 14 shows a process flowchart of an example of a fractionation unit in which a desethaner and a depropanizer are bypassed, according to certain aspects of the present description.

[0043] Fig. 15 shows a process flowchart of an example of starting up a condensate depentanizer / stabilizer with recycling to an out-of-specification condensate storage facility, according to certain aspects of this description.

[0044] [Fig.10A] and [Fig.10B] show functional diagrams of example configurations for starting the depentanizer, both when there is no power production (16A) and when there is power production (16B) at the LNG plant, according to certain aspects of this description.

[0045] [Fig.17A] and [Fig.17B] show functional diagrams of example configurations for starting the desethaner and the depropanizer, both when there is no power production (17A) and when there is power production (17B) in the LNG plant, according to certain aspects of this description.

[0046] Fig. 18 shows a process flowchart of an example of a recycling scheme of the fractionation unit, according to certain aspects of the present description. DETAILED DESCRIPTION

[0047] 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.

[0048] 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 an average flow rate (typically 40% of the flow), which is entirely flared. Conversely, using the techniques described herein, there is very little or no flaring.A small amount of flaring may occur for cooling LNG storage or if the liquefaction unit is started up in an LNG plant that does not have on-site power generation, but the flared flow is always much smaller (e.g., 10% of the flow) and the flaring duration is considerably reduced, for example, to 10 days or less. When comparing these two options, the techniques described here reduce CO2 emissions by 98%.

[0049] 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 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 until the LNG can be sent to storage without being flared. In addition, compressors or recycling 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.

[0050] 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 on-site power generation would be different from a factory with on-site power generation.

[0051] 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:

[0052] - Regeneration unit regeneration gas compressor

[0053] - Native CO2 compressor

[0054] - Natural gas liquid (NGL) unit booster compressor

[0055] - Final instantaneous steam compressor and evaporation gas compressor (BOG)

[0056] 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.

[0057] More specifically, an LNG installation is typically equipped with two blowdown drums. One is used for the hot end of the installation and the other is used for the cold end. Two drums are used because cold fluids cannot be mixed with hot, humid fluids. Some examples here can take advantage of the two existing drums to separate the different fluids 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 purge 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 (high) pressure. For the cold section, the different fluids may change pressure and temperature during the startup of the cold units. It may be desirable to stabilize their state before recycling them back into the process.To this end, 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 final instantaneous steam compressor and / or the BOG compressor where it can be compressed again. The advantage of doing this is that the gas is reheated during compression.

[0058] 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.

[0059] 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 (e.g., repeated) at least until one or more predefined criteria are met. For example, recycling can be maintained until the processing units operate individually or collectively according to one or more predefined operating criteria. In some such examples, recycling can be maintained until some or all of the processing units operate in accordance with their respective criteria.In other examples, recycling can be maintained until the processing units are collectively operating according to a predetermined overall operating criterion, thus minimizing combustion, as opposed to flaring throughout the entire startup sequence. Furthermore, recycling can be maintained for as long as necessary to troubleshoot or perform other tasks. For example, if a problem arises, the plant can remain in standby mode without flaring until... The problem is solved. This means that the upstream units (where the gas is recycled) are not disturbed or disrupted by the recycling.

[0060] As mentioned 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 both of these pieces of equipment are normally already present in all installations, they can be reused with the additional aim of reducing flaring during the start-up procedure, subject to a few modifications.

[0061] These illustrative examples are given to introduce the reader to the general subject matter presented here and are not intended to limit the scope of the concepts described. The following sections describe various features and additional examples with reference to the drawings in which the same numbers denote the same elements, but, like the illustrative examples, they should not be used to limit this description.

[0062] Looking now at [Fig. 1], a working diagram shows an example of a liquefied natural gas (LNG) plant 100 configured to recycle the fluid during a start-up phase according to certain aspects of this description. The LNG plant 100 can be designed as having a "hot side" and a "cold side." The hot side can refer to the left half of the diagram, including components 102 to 108, 120, 122, 124, and 126, because the natural gas is maintained at a warmer temperature through these components. The hot side can also be called the "first processing section" here, as it is the first section of the LNG plant 100 that includes processing units. The hot side may include all or some of the processing units from a gas inlet of the LNG plant 100 to the LNG recovery unit 110 (but not including the LNG itself).The cold side can refer to the right half of the diagram, including components 110 to 118, 128, 130, and 132, because the natural gas is maintained at a cooler temperature through these components than in the hot side. The cold side can also be called the "second processing section" here, as it is a second section of the LNG 100 plant that includes processing units. The cold side may include all or some of the processing units downstream of the NGL 110 recovery unit, including the NGL 110 recovery unit itself.

[0063] The hot side may include inlet facilities 102 fluidly coupled to a mercury removal unit 104. The mercury removal unit 104 may be configured to remove mercury from a natural gas inlet at the LNG plant 100. The mercury removal unit 104 may be coupled fluidly coupled to an acid gas removal (AGR) unit 106 configured to remove acid from natural gas. The AGR unit 106 can be fluidly coupled to a dehydration unit 108 configured to remove water from natural gas. This can be important because water vapor can cause corrosion, freeze in cold weather, and reduce efficiency. The AGR unit 106 can also be fluidly coupled to a compressor 120 (for example, a native CO2 compressor) configured to compress the carbon dioxide from the AGR unit 106. The compressed carbon dioxide can then be conveyed via a fluid link to a first flare gas recovery unit (FGRU) 122, also referred to herein as the "hot FGRU," to contribute to the recycling process described in more detail later.The hot side may also include a first blowdown drum 124, also referred to herein as the "hot blowdown drum," and an out-of-specification condensate storage unit 126, both of which can also be used in the recycling process, as described in more detail later. For example, the hot blowdown drum 124 can be used as a mixing drum to blend the fluidic components during the recycling process.

[0064] As indicated above, the natural gas liquid plant 100 may include a cold side. The cold side may include a natural gas liquid (NGL) recovery unit 110, which is fluidly coupled to the dehydration unit 108. The NGL recovery unit 110 may be configured to produce natural gas liquids and condensates from the processed natural gas. Ethane, propane, and butanes are examples of natural gas liquids. The NGL recovery unit 110 may be fluidly coupled to a fractionation unit 128 and a liquefaction unit 112. The fractionation unit 128 may include a demethanizer, a deethanizer, a depropanizer, and a starter-generator to separate and recover methane, ethane, propane, butanes, respectively, and all higher boiling point hydrocarbons. Liquefaction unit 112 can condense natural gas into a liquid.The liquefaction unit 112 can condense natural gas into a liquid at essentially atmospheric pressure by using refrigeration to cool it to a low temperature, for example -162 °C. The liquefaction unit 112 can be fluidly coupled to an LNG storage unit 114 to store the liquefied natural gas. The LNG storage unit 114 can be fluidly coupled to a compressor, such as the BOG compressor 116, which in turn can be fluidly coupled to a nitrogen removal unit (NRU) 118 in examples involving energy import. The NRU 118 can be configured to remove nitrogen from the liquefied natural gas before it is used in a downstream process. The cold side can also include a second FGRU 130, also referred to here as the "cold FGRU," and a second blowdown drum 132. also referred to here as a "cold purge drum" or "cryogenic purge drum." These components can facilitate the recycling process as described in more detail below. For example, the 132 cold purge drum can be used as a mixing drum to blend fluidic components during the recycling process.

[0065] As shown in [Fig. 1], recycling is achieved by transferring natural gas and other fluids to and from the first purge drum 124, as well as by transferring natural gas and other fluids to and from the second purge drum 132. In particular, the first purge drum 124 can be fluidly coupled to the dehydration unit 108 and receive regeneration gas from the dehydration unit 108. The first purge drum 124 can also be fluidly coupled to the NGL recovery unit 110 and receive lean gas from the NGL recovery unit 110. The first purge drum 124 can further be fluidly coupled to the second purge drum 132 and receive recycled liquids from the second purge drum 132.The first blowdown drum 124 can mix these fluid components to generate a recycled gas that has a composition, pressure, temperature, or any combination thereof similar to the original gas that entered the AGR unit 106. In addition, or alternatively, the recycled gas from the first blowdown drum 124 can be mixed with compressed CO2 from the compressor 120, as required by the system. In some examples, the first blowdown drum 124 can be fluidly coupled to the non-specification condensate storage unit 126. The hot blowdown drum 124 can then transfer the recycled gas to the non-specification condensate storage unit 126 for further storage.

[0066] The second purge drum 132 can be used for a similar purpose on the cold side. For example, the second purge drum 132 can be fluidly coupled to the fractionation unit 128 and receive instantaneous steam and natural gas liquids from the fractionation unit 128. In some examples, the fractionation unit 128 can be fluidly coupled to the non-specification condensate storage unit 126 for liquid storage. The second purge drum 132 can also be fluidly coupled to the liquefaction unit 112 and receive cold gas from the liquefaction unit 112. The second purge drum 132 can mix these fluid components to generate a recycled gas that has a composition, pressure, temperature, or any combination thereof similar to the original gas that entered the NGL recovery unit 110.The second purge drum 132 can transmit this recycled gas to the first purge drum 124 and / or to the compressor 116. From the compressor 116, the recycled gas. The tablet can be returned to the NGL 110 recovery unit as input for a subsequent treatment cycle.

[0067] By using the first purge drum 124 on the hot side and the cold purge drum 132 on the cold side to mix the fluid components, after the natural gas has been processed by one or more of the processing units (e.g., units 102 to 112, 128), the purge drums 124, 132 can generate a recycled gas that is substantially similar to the original natural gas that was fed into one or more of the processing units. This allows the recycled gas to be re-entered into the processing units for a subsequent processing cycle without damaging or otherwise negatively affecting the operation of the processing units during the subsequent processing cycle. Since the same stream of natural gas can now be recycled without negatively affecting the processing units, it can be used repeatedly without the need for flaring.

[0068] Various components described above and elsewhere in this document may be called "recycling components" because they are used to facilitate the recycling process. For example, the hot FGRU 122, the hot blowdown drum 124, the out-of-specification condensate storage unit 126, the cold FGRU 130, and the cold blowdown drum 132 may be considered recycling components since they perform steps during the recycling process to help recycle natural gas. In addition, various compressors described here, such as the BOG compressor 116, may be considered recycling components if they are used during the recycling process.

[0069] Now that an overview of the recycling process and recycling components has been given, further details on the operation of some of the individual processing units during the recycling process will be explained below.

[0070] Dehydration unit

[0071] Now with regard to the dehydration unit 108, [Fig. 2] shows a process flow diagram of an example of a dehydration unit 108 with a bypass line for dehydration bypass according to certain aspects of this description. The dehydration unit 108 can be fluidly coupled to the AGR unit 106 to receive an inlet gas, which may be an out-of-specification gas. The inlet gas can be passed through an inlet gas cooler before being sent to a separator-dryer 204. The separator-dryer 204 can be fluidly coupled by a series of valves to one or more dehydration dryers, such as a first dehydration dryer 206, a second dehydration dryer 208, and a third dehydration dryer 210. Under normal operating conditions, the inlet gas can be transmitted through the series of dehydration dryers 206 to 210, a regeneration gas heater 216 and a regeneration gas preheater 218. From there, the treated gas can 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 gaseous components of the regeneration gas and transmit one or more of said components to a regeneration gas compressor 220, also referred to here as a dehydration regeneration gas compressor, which can compress the regeneration gas.

[0072] During the recycling process described herein, the compressor 220 can be reused, along with the first and second purge drums, to facilitate the implementation of the recycling process. In particular, when starting up all the processing units upstream of the compressor 220, a bypass line can send the spent gas directly to the compressor 220 instead of flaring it. Since the compressor 220 is located on the processing route downstream of the dehydration dryers 206 to 210, the dehydration dryers 206 to 210 can be bypassed because they may not be able to accept untreated gas. Thus, the new bypass route represented by a dashed line in [Fig. 2] can be activated by means of a valve 222, so that the dehydration dryers 206 to 210 can be bypassed.Therefore, the untreated gas can be sent directly to compressor 220, without passing through dehydration dryers 206 to 210. From compressor 220, the gas can be sent to the hot purge drum, which can be pressurized, before being returned to the upstream process. In this way, there is no flaring.

[0073] Further details of the hot purge drum 124 are illustrated in [Fig. 3]. In particular, [Fig. 3] shows an example of the hot purge drum 124 mixing the fluids from the regeneration gas compressor 220 of [Fig. 2] and the native CO2 compressor 120 of [Fig. 1] before their upstream recycling. Recycling can be achieved, as shown by the dashed line in [Fig. 3], by conveying the recycled gas from the hot purge drum 124 to the AGR unit 106. Further details of the AGR unit 106 are described below.

[0074] Gas removal unit. Acids

[0075] Figures 4A-B show functional diagrams of example liquefied natural gas plant configurations 400, 402 for starting up an AGR unit 106 according to certain aspects of this description. Figure 4A shows an example in which there is no power generation at the liquefied natural gas plant. Figure 4B shows an example in which there is power generation at the liquefied natural gas plant level. The AGR 106 unit can remove acid gas (usually CO2) from the process stream.

[0076] When the AGR 106 unit is started, recycling the same gas may initially be acceptable. However, over time, the gas may begin to contain less and less CO2. Towards the end, returning it to the inlet of the AGR 106 unit may be problematic as it can lead to emulsification or foaming. To avoid this problem, the acidic gas that has been separated from the feed gas can be mixed with the recycled gas, using the hot purge drum 124 as a mixing drum for startup. For example, a line can be installed between the native CO2 compressor 120 and the hot purge drum 124, and the native CO2 compressor 120 can be started in advance so that it is ready beforehand (for example, as part of a dynamic start-up using CO2 cylinders).It should be borne in mind that, in some cases, the discharge pressure of the native CO2 compressor 120 may be too high compared to the operating pressure of the hot purge drum 124. If the gas is drawn from the discharge of the last stage, it may be necessary to reduce the pressure, which can lead to a considerable drop in temperature. To avoid this, the native CO2 compressor 120 can be variable-speed, or the gas can be drawn from an intermediate stage, rather than from the last stage of the CO2 compressor 120. When this configuration is used, it may be desirable for the start-up flow not to exceed the capacity of the regeneration gas compressor of the dehydration unit 108 (for example, the regeneration gas compressor 220 of [Fig. 2]), which could be, for example, a flow of 7 to 10%. Thus, the AGR unit 106 can be started with a lower flow.Some examples of start-up flow rates are shown in [Fig. 4A]-B, where the percentages may reflect examples of flow rates in the corresponding components, although the actual flow rates used in practice may depend on the specific characteristics of such components. The thicker lines (dashed and solid) may represent active flow paths through which fluid flows during the start-up operation of the AGR 106 unit. The thinner lines may represent inactive flow paths through which no fluid can flow during the start-up operation of the AGR 106 unit.

[0077] Dehydration unit

[0078] Figures 5A-B show functional diagrams of example configurations of liquefied natural gas plants 500, 502 for starting up a dehydration unit 108 according to certain aspects of this description. Figure 5A shows an example in which there is no power generation at the level of the liquefied natural gas plant. Figure 5B shows an example of energy production at the liquefied natural gas plant.

[0079] As illustrated in [Fig. 5A]-B, during the start-up of the dehydration unit 108, the recycling loop described for the start-up of the AGR unit 106 can also be continued for the dehydration unit 108. Only then can it be confirmed that the gas from the AGR unit 106 meets the specification for CO2 and can begin to pass through the dehydration dryer beds instead of bypassing them. The dehydration unit 108 can remain in recycling mode until the dry gas is confirmed and the NGL unit 110 is defrosted / pressurized and ready to receive the gas. This provides sufficient time to test the dryer sequence and regenerate the dryers one after the other as many times as necessary. In a similar way to [Fig.4A]-B, in the [Fig.5A]-B, the percentages may reflect examples of flow rates in the corresponding components, although the actual flow rates used in practice may depend on the particularities of such components. The thicker lines (dashed and solid) may represent the active flow paths through which fluid flows during the start-up operation of the dehydration unit 108. The thinner lines may represent the inactive flow paths through which no fluid can flow during the start-up operation of the dehydration unit 108.

[0080] In the dehydration unit 108, certain valves can be activated to establish a flow pattern through the unit during startup. An example of such a flow pattern is shown in [Fig. 6]. The thicker lines (dashed and solid) can represent the active flow paths during the startup of the dehydration unit 108. The thinner lines can represent the inactive flow paths through which no fluid can flow during the startup operation of the dehydration unit 108. As illustrated, an active flow path can convey the gas through the inlet gas cooler and the dryer separator 204 into a first dehydration dryer 206 and a second dehydration dryer 208.The gas can be conveyed from the first dehydration dryer 206 and the second dehydration dryer 208 through the regeneration gas preheater 218 and the regeneration gas heater 216 before entering a third dehydration dryer 210. From the third dehydration dryer 210, the gas can be conveyed to the regeneration gas air cooler 212, then to the regeneration gas separator 214, before entering the regeneration gas compressor 220. Finally, the regeneration gas compressor 220 can convey the recycled gas. to the hot purge drum (for example, the first purge drum 124 of [Fig.l]).

[0081] NGL Recovery Unit

[0082] Figures 7A-B show functional diagrams of example liquefied natural gas plant configurations 700, 702 for starting up an NGL 110 recovery unit according to certain aspects of this description. Figure 7A shows an example in which there is no power generation at the liquefied natural gas plant. Figure 7B shows an example in which there is power generation at the liquefied natural gas plant. As in the preceding figures, in Figures 7A-B, the percentages may reflect example flow rates in the corresponding components, although the actual flow rates used in practice may depend on the specific characteristics of such components. The thicker lines (dotted and solid) may represent the active flow paths through which the fluid flows during the startup operation of the NGL 110 recovery unit.The thinner lines may represent inactive flow paths through which no fluid can flow during the startup operation of the NGL 110 recovery unit.

[0083] Before starting any refrigeration or cryogenic unit, it is often desirable to remove moisture from the lines and equipment to prevent freezing and equipment blockage. This is generally done by passing dry gas through the lines and equipment. This operation is often called defrosting. 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 flaring. In some examples, it is possible to begin defrosting with dry air or dry nitrogen. If dry air is used initially, dry nitrogen can then be used to inert the units. Another advantage of using inert fluids is that the defrosting activity can begin well before the system starts up and the gas arrives. This eliminates safety constraints, and the defrosting activity can be carried out several weeks in advance. Subsequently, the final defrosting with dry natural gas takes much less time. Furthermore, 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 a cold FGRU 130 of [Fig. 1]. If the capacity... If the flow rate from the cold FGR unit is limited, the defrost flow rate may be reduced and the defrosting time may be increased. If the defrost gas is humidified during use, it can also be sent to a hot FGR unit, such as a hot FGR 122, from which the gas can be recycled to upstream units.

[0084] Once the unit has defrosted, to start the NGL 110 recovery unit, the NGL 110 recovery unit can be pressurized and flow can be gradually established through it. Initially, a small flow can be used to gradually cool the NGL 110 recovery unit to a normal operating temperature. The flow can then be gradually increased as the NGL 110 recovery unit cools. Once the flow is established, the lean gas leaving the booster compressor of the NGL 110 recovery unit (e.g., booster compressor 802 of [Fig. 8]) can be recycled back into the process in the same way as in the previous units.It can be returned to the hot purge drum 124, where it can be mixed with native CO2, the regeneration gas from the dehydration unit 108, and finally return to the inlet of the AGR unit 106. In this way, the NGL recovery unit 110 can remain in recycling mode until it is stabilized.

[0085] Since no new rich gas is introduced into the NGL 110 recovery unit, excessive liquid production at the bottom of the digester column (e.g., digester 804 of [Fig. 8]) of the NGL 110 recovery unit is also avoided. This means that the fractionation unit 128 does not need to be started immediately. A potential problem that can result from a lack of liquid production is the inability to start the digester reboiler (e.g., digester reboiler 806 of [Fig. 8]). If the digester column is free of liquid, and the reboiler is not started, the bottom of the digester column may cool below acceptable temperatures. However, filling the bottom of the demethanizer column with butane before starting the unit, and starting the reboiler in advance, can eliminate this problem.

[0086] In the NGL 110 recovery unit, certain valves can be activated to establish a flow pattern through the unit during startup. An example of such a flow pattern is shown in [Fig. 8]. The thicker lines (dashed and solid) can represent an active flow path during the startup operation of the NGL 110 recovery unit. The thinner lines can represent an inactive flow path through which no fluid can flow during the unit's startup operation. NGL 110 recovery. In this example, the feed gas can enter a cold box of NGL 808 and flow to a low-temperature separator 810, where it can be separated. A first portion of the feed gas can be conveyed to the upper part of the column of the digester 804, and a second portion of the feed gas can be conveyed to the middle part of the digester 804. The digester 804 can be configured to remove methane from the feed gas. A reboiler of the methanizer 806 can be coupled to the methanizer 804 to provide heat to the bottom of the methanizer column 804. The upper part of the methanizer 804 can be fluidly coupled to the cold box of NGL 808, which can receive the demethanized gas from the methanizer 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 inlet gas (e.g., up to 1000 bar). The booster compressor 802 can then transmit the pressurized gas to the hot blowdown drum (e.g., the first blowdown drum 124 in [Fig. 1]).

[0087] Liquefaction unit

[0088] With regard to the liquefaction unit 112, when the liquefaction unit 112 is started in recycling mode, there may be little or no liquid production at the NGL recovery unit 110. This means that the fractionation unit 128 may not need to be started before the liquefaction unit 112 starts, and consequently, the refrigerant components required for the refrigerant systems of the liquefaction unit 112 may not be produced. Thus, the refrigerant used for the liquefaction unit 112 can be drawn from the available refrigerant storage.

[0089] In some examples, the liquefaction unit 112 can be started when the LNG storage 114 is hot. In some examples, the liquefied natural gas can be used to cool the LNG storage tanks, but if it is not available, the gas from the liquefaction unit 112, which gradually cools down 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 112, cold gas is produced and can be used for this purpose if both units are started simultaneously. The gas or instantaneous steam recovered from the 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 116 compressor may depend on the configuration of the installation, and more specifically on the presence or absence of a power generation unit in the LNG 100 plant. Some examples of such configurations are illustrated in [Fig.9A]-C. [Fig.9A] shows a diagram. Functional diagrams of an example configuration for starting the liquefaction unit when the LNG 114 storage is hot and there is no power generation at the LNG 100 plant. Figures 9B-C show functional diagrams of example configurations for starting the liquefaction unit 112 when the LNG 114 storage is hot and there is power generation at the LNG 100 plant. As in the previous figures, in Figures 9A-C, the percentages may reflect example flow rates in the corresponding components, although the actual flow rates used in practice may depend on the specific characteristics of such components. The thicker lines (dashed and solid) may represent the active flow paths through which the fluid flows during the start-up operation of the liquefaction unit 112.The thinner lines may represent inactive flow paths through which no fluid can flow during the start-up operation of liquefaction unit 112.

[0090] In addition, in some examples the liquefaction unit 112 can be started when the LNG storage 114 is cold. In some examples, the start-up procedure may be slightly different when it is carried out after a previous shutdown (for example, when it is not the plant's first start-up). In particular, the LNG storage tanks may be too cold to receive the hot gas that is initially produced by the liquefaction unit 112. In order to avoid thermal shock to the various components, a new destination for the "cold gas" generated by the liquefaction unit 112 can be used. The cold blowdown drum 132 can be used as a recycling point in this case, since it is designed to receive gas that is gradually becoming colder. An example is shown in [Fig. 10].As illustrated, a valve 1002 can be activated to establish a flow path (dotted line) from the main cryogenic heat exchanger (MCHE) 1004 to the cold blowdown drum 132. From the cold blowdown drum 132, the gas can be routed to the final instantaneous steam compressor (if equipped) and / or the BOG compressor 116, and the destination from there may depend on the presence or absence of a power generation unit at the LNG plant 100, as described above. It is important to note that the flow configuration may change as startup progresses. The gas exiting the liquefaction unit 112 gradually becomes colder, and when it reaches a sufficiently low temperature, liquids form in the cold blowdown drum 132.The flow can then be diverted back to the normal route towards the LNG 114 storage, for example by deactivating the first valve 1002 and / or activating a second valve 1006.

[0091] Some examples of the aforementioned flows are illustrated in [Fig. IIA]-C. [Fig. IIA] shows a functional diagram of an example configuration for The start-up of liquefaction unit 112 when LNG storage 114 is cold and there is no power generation at LNG plant 1100. Figures [11B]-C show functional diagrams of example configurations for starting liquefaction unit 112 when LNG storage 114 is cold and when there is power generation at LNG plants 1104 to 1106. As in the previous figures, in Figures [11A]-C, the percentages may reflect example flow rates in the corresponding components, although the actual flow rates used in practice may depend on the specific characteristics of such components. The thicker lines (dashed and solid) may represent the active flow paths through which the fluid flows during the start-up operation of liquefaction unit 112.The thinner lines may represent inactive flow paths through which no fluid can flow during the start-up operation of liquefaction unit 112.

[0092] In some examples, the liquefaction unit 112 can be started when no refrigerant is available. In some such examples, it may be necessary to produce refrigerants from the fractionation unit 128. Thus, a gas supply flow to the installation can be established to supply the refrigerant from the gas necessary for its production. The refrigerants can therefore be produced gradually, in parallel with the start-up of the liquefaction unit 112. The refrigerants can be injected into the refrigeration loop gradually as they are produced. Some examples of this process are illustrated in [Fig. 12A]-C. [Fig.[Fig. 12A] shows a functional diagram of an example configuration for starting liquefaction unit 112 when no refrigerant is available and when there is no power generation at LNG plant 1200. [Fig. 12B]-C shows functional diagrams of example configurations for starting liquefaction unit 112 both when no refrigerant is available and when there is power generation at LNG plant 1202 to 1204. As in the previous figures, in [Fig. 12A]-C, the percentages may reflect example flow rates in the corresponding components, although the actual flow rates used in practice may depend on the specific characteristics of such components. The thicker lines (dotted and solid) may represent the active flow paths through which the fluid flows during the start-up operation of the liquefaction unit 112.The thinner lines may represent inactive flow paths through which no fluid can flow during the start-up operation of liquefaction unit 112.

[0093] Splitting unit

[0094] With regard to the fractionation unit 128, the start-up sequence of the fractionation unit 128 may depend on the unit configuration. In some examples, to minimize flaring, it is possible to use a configuration in which the depentanizer column can be installed first. An example of such a configuration is shown in [Fig. 13]. In this example, the fractionation unit 128 is configured so that the depentanizer 1302 is configured to receive the inlet gas before the desethaner 1304 and the depropanizer 1306. This arrangement allows the depentanizer 1302 to operate alone, without the desethaner 1304 and the depropanizer 1306 in operation. In some of these cases, the 1304 degasser and the 1306 depropanizer can be bypassed using a bypass line. An example of bypassing the 1304 degasser and the 1306 depropanizer is shown in [Fig. 14].In this example, the natural gas liquids recovered at the top of the depentanizer 1302 can be sent to an NGL reinjection drum 1402, from which they can be recycled back into the process. This can be achieved by activating a bypass valve 1404, which causes the enclosed portion of the figure (e.g., the desethaner 1304 and the depropanizer 1306) to be bypassed.

[0095] It is common practice to start the fractionation columns sequentially. At the start-up, the column condensers may have difficulty condensing to a column head flow due to the presence of components that are too light to condense. Consequently, liquids are not generated inside reflux drums 1406 to 1410. The vapors inside reflux drums 1406 to 1410 are 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. Similarly, in this case, these liquids may have to be removed anyway to avoid triggering level alarms.In this situation, the usual practice is to send them to the flare separators, where they will eventually evaporate and be flared. Consequently, the main sources of flaring are typically the evaporation gas from the reflux drums 1406 to 1410 of the columns, and the liquids from the degasser 1304 and the depropanizer 1306. To address these issues, in some examples, the depropanizer 1302 can be started up so that, when it receives liquids formed in the degasser of the NGL recovery unit 110 (degasser 804 of [Fig. 8]), the liquids collected at the column head bypass the degasser 1304 and the depropanizer 1306 and go directly into the out-of-specification condensate storage 126. An example. The above process is illustrated in [Fig. 15], which shows the recycling to the out-of-specification condensate storage 126. Similarly, the liquids collected at the bottom of the depentanizer 1302 can be sent first to the out-of-specification condensate storage 126. Once the depentanizer 1302 is operating normally, and the overhead and bottom products are confirmed to be within specifications, the different product streams can be aligned to their correct destinations. The condensate can be sent to the condensate storage, and the overhead liquid 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. This bypasses the deethane decanizer 1304 and the depropanizer 1306, which have not yet started up.The evaporated vapors from the reflux drum of the condensate stabilizer, which are likely to contain C5+ / BTEX, can be conveyed to a (e.g., a cold FGRU 130 of [Fig.1]) to prevent flaring.

[0096] Figures [Fig. 16A]-B show functional diagrams of example configurations for starting the depentanizer 1302, both when there is no power production ([Fig. 10A]) and when there is power production ([Fig. 10B]) in the LNG plant 1600 to 1602. As in the previous figures, in Figures [Fig. 10A]-C, the percentages may reflect examples of flow rates in the corresponding components, although the actual flow rates used in practice may depend on the particularities of such components. The thicker lines (dotted and solid) may represent the active flow paths through which fluid flows during the startup operation of the 1302 depentanizer. The thinner lines may represent the inactive flow paths through which no fluid can flow during the startup operation of the 1302 depentanizer.

[0097] In some examples, the desethaner 1304 and the depropanizer 1306 can be started in such a way that, once it has been confirmed that the headstream of the column of the depropanizer 1302 does not contain BTX (a mixture of benzene, toulin and xylene), it can be slowly sent to the desethaner 1304. After a certain time, the flow to the depropanizer 1306 also becomes possible. The liquids accumulated in the column bottoms of the 1304 desethanester and 1306 depropanizer can first be sent to the NGL 1402 reinjection drum. A chiller can be used to cool them before they reach the 1402 drum. Out-of-specification liquids may accumulate inside the NGL 1402 reinjection drum initially, but the drum volume is unlikely to be sufficient to contain them for the entire duration of the start-up procedure.At a certain point, a new destination may therefore be required for purging. The cold purge drum 132 can again be used as a recycling point in this case. A driver. It may be present inside the cold purge drum 132 to vaporize the liquids. The generated steam may be at low pressure, in which case it cannot be recycled back into the process without first passing through the BOG compressor 116. The destination after the BOG compressor 116 may depend on the capacity and discharge pressure of the BOG compressor 116.

[0098] Figures 17A-B show functional diagrams of example configurations for starting the desethaner 1304 and the depropanizer 1306, both when there is no power production (Fig. 17A) and when there is power production (Fig. 17B) in the LNG plant 1700 to 1702. As in the preceding figures, in Figures 17A-B, the percentages may reflect example flow rates in the corresponding components, although the actual flow rates used in practice may depend on the specific characteristics of such components. Thicker lines (dashed and solid) may represent active flow paths. Thinner lines may represent inactive flow paths. The lighter components within the recycled liquids may vaporize, while the heavier components may remain liquid.By installing a pump, it is possible to convey these liquids to the hot blowdown drum 124, as the cold blowdown drum 132 might not be able to hold all the liquids until the fractionation unit 128 is stabilized. From the hot blowdown drum 124, a pump can send the liquids to the non-specification condensate storage 126, which is normally large and can hold the liquids until startup is complete. Once startup is complete and the fractionation unit 128 is stabilized, these liquids can be returned to the condensate stabilizer inlet via an existing fitting.

[0099] An example of the recycling scheme for the fractionation unit 1800 is illustrated in [Fig. 18]. The dashed lines can represent the aforementioned flow paths. For example, as illustrated, the liquids accumulated in the column bottoms of the desethane 1304 and the depropanizer 1306 can first be sent to the reinjection drum of NGL 1402. A chiller can be used to cool them before they reach the drum 1402. Out-of-specification liquids can be collected in the reinjection drum of NGL 1402 and then transferred to the cold purge drum 132, which can be used as a recycling point in this case. The liquids contained in the cold purge drum 132 can then be transferred to the hot purge drum 124. The steam contained in the cold purge drum 132 can be transferred to an FGRU and / or the BOG compressor 116 via one or more fluid connections.From the hot purge drum 124, liquids can be routed to the condensate storage. out of specification 126. The steam contained in the purge drum 124 can be transmitted to an FGRU via a fluidic link.

[0100] 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.

Claims

Demands

1. A method for starting up a liquefied natural gas (LNG) plant, the method comprising the steps of: a) supplying a natural gas feed as input to a sequence of processing units of the LNG plant, wherein the processing units generate treated fluids according to the natural gas feed; b) conveying the treated fluids through recycling components which transform the treated fluids into a recycled natural gas stream; and c) returning the recycled natural gas stream to one or more inlets of the processing units, thereby recycling the natural gas rather than flaring it.

2. A method according to claim 1, wherein the recycling components comprise mixing drums that combine the outputs of two or more processing units, the mixing drums comprising a hot purge drum and a cold purge drum.

3. A method according to claim 2, further comprising: the transmission of a first part of the recycled natural gas stream from the hot blowdown drum to a first processing section of the LNG plant; and the transmission of a second part of the recycled natural gas stream from the cold blowdown drum to a second processing section of the LNG plant, the cold blowdown drum being located downstream of the hot blowdown drum.

4. A method according to claim 3, further comprising: supplying the first part of the recycled natural gas stream to a first set of processing units in the first processing section, wherein the first set of processing units extends from a gas inlet of the LNG plant to a natural gas liquids (NGL) recovery unit; and supplying the second part of the recycled natural gas stream to a second set of processing units in the second processing section, wherein the second set of processing units is located downstream of the NGL recovery unit.

5. A process according to claim 3, wherein first vapor fluids having passed through the first treatment section are mixed and recycled for reprocessing, and wherein second vapor fluids having passed through the second treatment section are mixed and recycled for reprocessing.

6. A method according to claim 3, further comprising: mixing a first set of outputs from the processing units in the hot purge drum, before transmitting the first mixed contents of the hot purge drum to the first processing section; and mixing a second set of outputs from the processing units in the cold purge drum, before transmitting the second mixed contents of the cold purge drum to the second processing section.

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

8. A method according to claim 3, further comprising supplying a set of outlets from a set of processing units of the first processing section to the hot purge drum by transmitting the set of outlets through one or more compressors to the hot purge drum, wherein the compressor(s) are fluidly coupled between the set of processing units and the hot purge drum.

9. A method according to claim 3, further comprising supplying a set of outlets from a set of processing units of the second processing section to the cold purge drum by: transmitting the set of outlets to the cold purge drum through one or more compressors, wherein the compressor(s) are fluidly coupled between the set of processing units and the cold purge drum.

10. A method according to claim 1, further comprising the transmission of an inlet gas through a bypass line of a dehydration unit to a regeneration gas compressor of the dehydration unit, without the inlet gas passing through the dehydration unit's dehydration dryers.

11. A method according to claim 1, further comprising: the collection of fluid in a natural gas liquid (NGL) reinjection drum from a fractionation unit for the purpose of recycling.

12. A method according to claim 11, further comprising: the transmission of an inlet gas through a bypass line from the fractionation unit to the NGL reinjection drum, without the inlet gas passing through a de-ethanizer and / or a de-propanizer.

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

14. Liquefied natural gas (LNG) plant comprising: a sequence of processing units which receive a supply of natural gas as input; and a plurality of recycling components fluidly coupled to the processing units, wherein the recycling components receive the treated fluids from the processing units and transform the treated fluids into a stream of recycled natural gas, wherein the recycling components further return the stream of recycled natural gas to one or more inlets of the processing units, thereby recycling the natural gas rather than flaring it.

15. LNG plant according to claim 14, wherein the recycling components comprise mixing drums which combine the outputs of two or more processing units, the mixing drums comprising a hot purge drum and a cold purge drum, wherein the cold purge drum is located downstream of the hot purge drum.

16. LNG plant according to claim 15, further comprising a first processing section and a second processing section, and in which: the hot blowdown drum is fluidly coupled to the first processing section; The cold purge drum is fluidly coupled to the second processing section; the recycling components transmit a first part of the recycled natural gas stream from the hot purge drum to the first processing section; and the recycling components transmit a second part of the recycled natural gas stream from the cold purge drum to the second processing unit.

17. LNG plant according to claim 16, wherein the first processing section comprises a first set of processing units from a gas inlet of the LNG plant to a natural gas liquids (NGL) recovery unit, and wherein the second processing section comprises a second set of processing units downstream of the NGL recovery unit.

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

19. LNG plant according to claim 15, wherein the sequence of processing units comprises: a dehydration unit which includes a first bypass line which transmits an inlet gas to a regeneration gas compressor of the dehydration unit, without the inlet gas passing through the dehydration dryers of the dehydration unit; and a fractionation unit which 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 which transmits an inlet gas to the NGL reinjection drum without the inlet gas passing through a de-anaerobic and / or de-propaneizer.

20. LNG plant according to claim 15, further comprising one or more fluidly coupled compressors between the processing units and the hot blowdown drum, wherein the compressor(s) comprise a dehydration unit regeneration gas compressor, one or more native CO2 compressors, a natural gas liquid (NGL) recovery unit booster compressor, or a flare recovery unit compressor.

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