Management of vapor generated from warming of liquefied gas

Abstract

A method for managing BOG comprising providing one or more receiving tanks, each receiving tank comprises a condensation reserve amount of liquefied gas and a bottom distribution header. The header comprises a length of at least 10% of a length of the receiving tank and (ii) a plurality of openings arranged along the length of the distribution header. At least one opening is arranged per meter along the length of the bottom distribution header. The method further comprises providing boil-off-gas (BOG) to at least one receiving tank via the plurality of openings of the header; recondensing the BOG in the at least one receiving tank using the condensation reserve amount of liquefied gas; and terminating the provision of the BOG before pressure of the at least one receiving tank exceeds a pressure threshold of that tank.

Description

SP3180MANAGEMENT OF VAPOR GENERATED FROM WARMING OF LIQUEFIED GASField of the Invention

[0001] The present specification generally relates to the field of managing vapor generated from warming of liquefied gas.Background of the Invention

[0002] This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of any prior art.

[0003] Generally, it is commercially important to liquefy various types of gases, such as hydrogen, carbon dioxide, and natural gas for more convenient storage and transport. A fundamental reason for the liquefaction of gas is that liquefaction results in a volume reduction, thereby making it possible to store and transport large volumes the liquefied gas in containers at low or even atmospheric pressure, in an economical manner, and thereby to provide a technically sound and safe solution, in situations where pipeline transport is not practical or economically feasible.

[0004] As the liquefied gas, such as liquefied natural gas (LNG), is stored for transport at a cryogenic temperature, approximately -163° C for LNG, at ambient pressure, at least a portion of the liquefied gas evaporates over time, thereby generating what is called boil-off gas (BOG), whenever the temperature of the stored liquefied gas is lower than the surrounding environmental temperature. This occurs because, although storage tanks are thermally insulated, heat is continually transferred from the outside (environment) to the storage tank and to its content (liquefied gas), which generates BOG in the storage tank, which in turn increases the pressure of the storage tank. If the BOG or increased pressure is not managed, the pressure may continue to increase and potentially exceed a safety threshold level.

[0005] Another way BOG is generated is when the storage tank needs to be cooled to a temperature suitable for storing a liquefied gas. One way to cool the storage tank is to continually provide it with a stream of liquefied gas until the desired tank wall temperature is reached. During the cool down process, BOG gas is generated in the storage tank and is typically discharged fromSP3180 the tank to manage the increasing tank pressure. To continue the tank cooldown process, liquefied gas is continuously provided at a flow rate that meets the tank allowed cooldown rate, until the desired temperature is achieved.

[0006] For instance, US 11698169B2 discloses a compressor on a ship for receiving boil-off gas and supplying pressurized boil-off gas to an engine at a relatively higher pressure and a boil- off gas recovery system for recovery of boil off gas.

[0007] WO2017114815A1 discloses a sub-cooler fluidly connected to the fuel gas storage tank, and a consumer; pumping the liquefied fuel gas from the fuel gas storage tank into the subcooler to create subcooled liquefied fuel gas; and introducing the subcooled liquefied fuel gas into the fuel gas storage tank. The subcooled liquefied fuel gas may be sprayed into a vapor space of the fuel gas storage tank.

[0008] Generally, the discharged BOG can be used to fuel an engine, if available, burned, or it can be reliquefied. These have their drawbacks, such as the generation of environmental emissions, the waste of useful energy in the case of flaring, limited capacity such as to fuel an engine particularly for the relatively large amount of BOG that is typically generated during cool down, and the consumption of extra energy and equipment for reliquefaction. Accordingly, there is still a need for ways to manage boil-off gas (vapor generated from warming of liquefied gas). Summary of the Invention

[0009] According to one aspect, there is provided a method for managing BOG comprising: providing one or more receiving tanks, where each receiving tank comprises a condensation reserve amount of liquefied gas; a bottom distribution header comprising (i) a length of at least 10%, preferably at least 20%, more preferably at least 30%, and most preferably at least 40%, a length of the receiving tank and (ii) a plurality of openings arranged along the length of the distribution header wherein at least one opening, preferably at least five openings, more preferably at least 10 openings, being located per meter along the length of the bottom distribution header. The method further comprises providing boil-off-gas (BOG) to at least one receiving tank via the plurality of openings of the bottom distribution header; recondensing the BOG in the at least one receiving tank using the condensation reserve amount of liquefied gas; and terminating the provision of the BOG to the at least one receiving tank via the plurality of openings before pressure of the at least one receiving tank exceeds a pressure threshold of that tank.SP3180

[0010] Optionally, the method further comprises providing the BOG to the at least one receiving tank according to a selected ratio of (i) an amount of condensation reserve to (ii) a selected BOG flow rate at which the BOG is provided, wherein the ratio is at most 1 m3condensation reserve to 1 kg / h BOG being provided, more preferably at most 0.5 m3condesnation reserve to 1 kg / h BOG, and most preferably at most 0.2 m3condensation reserve to 1 kg / h BOG.

[0011] Optionally, the method further comprise selecting a ratio of (i) an amount of condensation reserve to (ii) a selected BOG flow rate at which the BOG is provided to the condensation reserve; estimating progress of the selected ratio over a period of time during which BOG is provided to generate a model of the selected ratio; calculating an actual ratio of the amount of condensation reserve to an actual BOG flow rate over time while the BOG is provided to the condensation reserve; and comparing the actual ratio with the model of the selected ratio overtime.

[0012] Optionally, the method further comprises providing an estimate of pressure increase of the at least one tank over time based at least on starting conditions of condensation reserve amount, starting temperature of the condensation reserve, duration of time that the BOG is provided, and a selected BOG flow rate; comparing measured pressure values of the at least one tank over time while receiving the BOG at the selected flow rate against the estimate of pressure; and adjusting the selected flow rate if the measured pressure value deviates from the estimate beyond a desired amount.

[0013] Optionally, the liquefied gas is LNG, hydrogen, or carbon dioxide. Optionally, the pressure threshold is up to 90% of the Maximum Allowable Working Pressure (MAWP) of the at least one receiving tank. Optionally, the condensation reserve amount is spread across two or more receiving tanks. Optionally, the condensation reserve amount is with respect to the at least one receiving tank. Optionally, the storage tank is located on one ship and the at least one receiving tank is located on another ship. Optionally, the BOG is generated from cooling down of a storage tank (104) to a temperature below - 10 degrees C using a liquefied gas, wherein the liquefied gas used for the cool down being the same type of gas as the liquefied gas in the receiving tank. Optionally, the BOG is generated from cooling the storage tank to a temperature capable of storing an amount of the liquefied gas. Optionally, the BOG is generated from cooling down the storage tank from a temperature of greater than - 10 degrees C . Optionally, the one or more receiving tanks further comprises a drop-down line in fluid connection with the bottom distribution header.Brief Description of the DrawingsSP3180

[0014] FIG. 1 illustrates an exemplary fluid flow arrangement between two ships, according to aspects disclosed herein.

[0015] FIG. 2A illustrates a portion of one ship that is further illustrated in FIG. 2B.

[0016] FIG. 2B illustrates further details of an arrangement to provide BOG inside the designated portion in FIG. 2A, according to aspects disclosed herein.

[0017] FIG. 3 illustrates an exemplary plot of estimated ratios over time for providing BOG, according to aspects disclosed herein.

[0018] FIG. 4 illustrates an exemplary plot of estimated pressures over time for providing BOG, according to aspects disclosed herein.Detailed Description of the Invention

[0019] The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. References to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the art, are within the spirit and scope of the invention.

[0020] Although the description herein provides numerous specific details that are set forth for a thorough understanding of illustrative embodiments, it will be apparent to one skilled in the art that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and / or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow.

[0021] In addition, when like elements are used in one or more figures, identical reference characters will be used in each figure, and a detailed description of the element will be provided only at its first occurrence. Some features or components of the systems or processes described herein may be omitted in certain depicted configurations in the interest of clarity.SP3180

[0022] According to one aspect, there is provided a method for managing boil-off gas (BOG). The method comprises estimating an amount of boil-off gas (BOG) of a liquefied gas to be generated. The liquefied gas can be any liquefied gas, including natural gas (LNG), liquefied carbon dioxide (LCO2), liquefied hydrogen (LH2), liquefied petroleum gas (LPG), and others. The to-be-generated BOG can come from various instances known to one of ordinary skill in which liquefied gas is vaporized. One such instance is cooling down of a storage tank of a liquefied gas from a temperature that is higher than a storage temperature down, such as greater than - 10 degrees C, to a desired temperature capable of storing an amount of the liquefied gas, which can vary depending on the type of liquefied gas. For example, if the liquefied gas is LNG, then the final cool down temperature is in a range of -80°C to -140°C. References to cool down or a particular liquefied gas (e.g., LNG) are intended for illustrative purposes of a particular example of a source of BOG of a particular liquefied gas and not intended to limit the methods disclosed herein.

[0023] Cool-down (or cool down) is the process to bring a cargo containment system (such as a storage tank and associated components, including valves and pipes) to a temperature that does not cause excessive boil-off during loading and prevents thermal shock to the primary containment system (such as storage tank, which can be storage for transport and / or for use as fuel). During cool down, the liquefied gas to be stored (for instance, LNG) is provided to the tank that needs cooling, usually via a spray header and spray nozzles. The conditions of the to-be-cooled tanks (primarily relatively higher temperature not capable of storing the liquefied gas, such as greater than -10 degrees C) vaporises the sprayed liquefied gas and starts to cool the tank, thereby generating BOG, which needs to be managed as noted herein. The liquefied gas is provided during cool down until the tank reaches a desired temperature, preferably a temperature capable of storing an amount of the liquefied gas (“storage temperature”). After which, the liquefied gas can continue to be provided, at least a portion (up to all) of which remains in the tank as a liquid for storage (which is also known as bunkering - for transport and / or fuel). A typical cool down process to cool an LNG storage tank down to a storage temperature can take a long time, such as around 20 hours or more, depending at least on the starting temperature, pressure rating, and storage capacity (size) of the tank. The rate of cool down (and correspondingly rate of liquefied gas being provided for cool down or “send-out rate”) is typically designed to minimize thermal shock and, potentially even, mechanical damage to the tanks, as well as to maintain the generated BOG that remainsSP3180 within the tanks in a respective acceptable range. A typical LNG cool down process can also generate a relatively large amount of BOG, such as at least 10 tons although it is understood that other amounts, including less than 10 tons can be involved depending on the specific cool down needs. That is, the total amount of BOG generated per operation varies because it is influenced by several factors, including the customer tank size, wall thickness, pre-cooldown starting temperature and cooldown end temperature. In a typical cooldown process, the rate of BOG that needs to be managed can be around 500 kg / hr or higher and the duration for managing BOG at such rate can be around at least 24 hours to 38 hours. It is understood that the methods disclosed herein can be used to manage BOG that gets generated from any suitable applications (such as cooldown and bunkering operations, and vapor coming from a ship or from shore), not just from cooldown. Cooldown is specifically highlighted as an exemplary application of embodiments of the methods disclosed herein because of the amount of BOG that gets generated.

[0024] Cool down and bunkering usually (but not necessarily) takes place between two ships, with the bunkering ship providing the liquefied gas to a customer ship for both cool down and bunkering, as shown in FIG. 1. In a typical scenario, customer ship 102 can be a liquefied gas transport ship (such as an LNG ship) that comprises one or more storage tanks 104 for storing such liquefied gas. If storage tanks 104 are empty and / or have a temperature above the temperature suitable for storage of liquefied gas, prior to being able to store any liquefied gas, it needs to be cooled down, preferably to a temperature capable of storing the liquefied gas. Bunkering ship 106 can provide the liquefied gas for cool down, and preferably filling up the storage tanks 104 pursuant to a customer’s order. Bunkering ship 106 comprises storage tanks (which can be 108 or other tanks not shown) that has at least an adequate amount of liquefied gas for the cool down, and / or to fulfil any additional orders for liquefied gas. During cool down of at least one storage tank 104 (and up to all applicable storage tanks 104 that needs to be cooled down), liquefied gas is provided to storage tank 104, which may be via liquefied gas line 110 if that arrangement is selected. At least a portion of the BOG that gets generated is provided back to one or more storage tanks 108 via BOG link 112 for management, which as described herein is the condensation of the BOG back to liquefied gas using the existing amount of liquefied gas in the respective storage tank 108. As used herein, the term “condensation” and “recondensation” are used interchangeably. Although FIG. 1 depicts two ships, it is understood that the principles described with respect to FIG. 1 can be applied to scenarios in which the storage tanks 104 are located on land, rather thanSP3180 on a ship, or in which storage tanks 108 are located on land, or a combination of both. It is also understood that the principles described herein can apply to various scenarios beyond cool down to manage BOG that is generated, such as when storage tanks 104 already contains an amount of liquefied gas but needs to be filled up.

[0025] Referring to FIG. 2 (meaning FIGS. 2A and 2B), each storage tank 108 (receiving tanks) that receives BOG for recondensation comprises an amount of the liquefied gas (e.g., LNG) 114 (or recondensation reserve) to absorb the heat from any provided BOG to recondense it back into liquefied gas. Storage tank 108 further comprises a bottom distribution header 116 disposed at the bottom of storage tank 108, and a drop-down line 118. A suitable distribution header comprises a length and a plurality of (two or more) openings 122 arranged along the length to provide the fluid into the tank. Optionally, the same existing infrastructure for filling can be used to receive BOG for condensation, which can reduce costs associated with installing new equipment. The distribution header can be located at the bottom of the tank (which would be considered bottom filling when liquefied gas is provided) and / or top of the tank (which would be considered top filling). Reference to “at the bottom” of a storage tank is understood by one of ordinary skill to include near the bottom of the tank, such as a position at 50% of the height of the tank or below, such as 40%, 30%, 20%, 10%, etc. the height of the tank. For instance, a suitable location “at the bottom” of storage tank 108 is anywhere at 50% of the height of tank 108 at 122 or below, meaning a position between the 50% mark of 124 and the actual bottom 126.

[0026] A storage tank typically has an opening at the top for filling. For bottom filling operations, bottom distribution header 116 is fluidly connected to drop-down line 118 for the fluid to be provided from the top of tank 108 to bottom distribution header 116. Drop-down line 118 be fluidly connected to a manifold through which BOG is provided from tank 104. Optionally and preferably, storage tank 108 already comprises bottom distribution header 116 for filling tank 108 with liquefied natural gas. Bottom distribution header 116 has a length 120 that is at least 10%, preferably at least 40%, more preferably at least 60%, and most preferably at least 75% the length of storage tank 108. Distribution header 116 comprises a plurality of openings 122 arranged along the length 120 of the distribution header 116. Optionally, there is at least one opening 122, preferably at least five openings, more preferably at least 10 openings, being arranged per meter of the length 120 of the distribution header 116. Optionally, the plurality of openings 122 has a diameter of 50 mm or smaller, preferably 25 mm or smaller, and most preferably 10 mm or smaller.SP3180

[0027] The BOG is provided in a manner that maintains the pressure of tank 108 at or below a pressure threshold, preferably the pressure threshold is a pressure rating of tank 108. As the BOG, enters tank 108 via openings 122 of bottom distribution header 116 as bubbles, which condense as they rise through the liquefied gas 114 in tank 108. It is understood that the BOG can also at least partially, including fully, condense while in line 118 and undergoing thermal exchange with the liquefied gas in tank 108 as it travels to openings 122. A relatively slower flow rate of BOG (or BOG management rate) means the BOG spends relatively more time in line 108, which results in more condensation in 108, versus a relatively higher flow rate of BOG which would lead to more condensation in 114. The BOG is provided to tank 108 in a manner that maintains an acceptable BOG condensation rate. If the BOG condensation rate in tank 108 is below the acceptable rate, the BOG bubbles will not fully condense and at least a portion remains in vapor form as they move through the liquefied gas column. The uncondensed vapor potion exits the liquid column (liquefied gas) and if left unmanaged, will accumulate as vapor at the top (vapor space) of tank 108, which can lead to increased tank pressure beyond the pressure threshold, an example of which is the pressure rating for tank 108. Optionally, the pressure threshold is up to 90% of the Maximum Allowable Working Pressure (MAWP) of the second storage tank, which is tank 108 with respect to at least FIG. 2.

[0028] It has been found that properties of bubbles of BOG exiting the openings 122 can influence the BOG condensation rate. In particular, it has been found that relatively smaller sized BOG bubbles tend to condense faster, which improves the mixing dynamics in tank 108. Optionally and preferably to provide for smaller sized BOG bubbles, bottom distribution header 116 has at least one, including any combination, such as all, of the following: one or more, most preferably, ten (10) or more openings 122 per meter of the length 120 of header 116, where length 120 is at least 75% the length of tank 108, and each opening 122 has a diameter of 10 mm or less.

[0029] As such, methods disclosed herein allow for faster condensation for the amount of gas per bubble) to provide for the desired properties of BOG bubbles, and thus, the BOG condensation rate in that tank by providing a system with any one of (i) the number of openings (more openings results in relatively more bubbles), the length 120 (longer length results in relatively more bubbles), and diameter of openings 122 (smaller diameter results in relatively smaller sized bubbles. These features are often, but not necessarily, associated with the configurations of the distribution header 116, so they are usually selected before cooldown begins.SP3180

[0030] It is understood that the condensation capacity of liquefied gas 114 can also influence the BOG condensation rate. The condensation capacity of the liquefied gas 114 is an inherent property that largely depends on the starting temperature of such liquefied gas. Preferably, having more volume of liquefied gas at a lower temperature generally correlates to being able to condense more BOG relatively speaking. Preferably, the temperature of the liquefied gas is as close to its atmospheric pressure saturation point as practically feasible. For example, that temperature is - 161 degrees C if the liquefied gas is LNG.

[0031] If desired, the total amount of liquefied gas reserved for condensation can be determined before starting a cool down operation as known by one of ordinary skills, such as taking into consideration available liquefied gas and amounts reserved for cool down and other relevant factors, including cooldown specifications by a particular customer. The total amount of liquefied gas reserved for condensation can be contained in one tank 108 or spread across a plurality of tanks 108. If the total amount of liquefied gas reserved for condensation is spread across a plurality of tanks 108, then there is a total amount of condensation reserve (amount of liquefied gas 114 reserved for condensation) and an individual amount of condensation reserve in a particular tank.

[0032] Accordingly, the present disclosure provides a method for managing BOG comprising providing one or more receiving tanks, where each receiving tank comprises a recondensation reserve amount of liquefied gas; a bottom distribution header comprising (i) a length of at least 10%, preferably at least 20%, more preferably at least 30%, and most preferably at least 40%, a length of the second storage tank and (ii) a plurality of openings arranged along the length of the distribution header where at least one opening, preferably at least 5 openings, more preferably at least 10 openings, being arranged per meter of the length (120) of the bottom distribution header.

[0033] The method further comprises providing boil-off-gas (BOG) to at least one receiving tank via the plurality of openings of the bottom distribution header, where the BOG being generated from cooling down of a storage tank to a temperature below - 10 degrees C using a liquefied gas, where the liquefied gas used for the cool down being the same type of gas as the liquefied gas in the receiving tank. The BOG is recondensed in the receiving tank by the recondensation reserve amount. The recondensation process is stopped before pressure of the receiving tank exceeds its pressure threshold.SP3180

[0034] Optionally and preferably, the amount of BOG that can be provided to the (total or individual, as context dictates) condensation reserve while complying with the pressure threshold of a particular tank can be monitored throughout the operation. For instance, it can be provided according to a ratio of (i) the amount of (total or individual) condensation reserve to (ii) a selected BOG flow rate, based on starting conditions as applicable. Preferably, the ratio is at most 1 m3condensation reserve amount to 1 kg / h BOG being provided, more preferably at most 0.5 m3condensation reserve to 1 kg / h BOG, and most preferably at most 0.2 m3condensation reserve to 1 kg / h BOG. For instance, if tank 108 has 100 m3of LNG at -160 degrees C (with a corresponding saturation pressure of 0.2 bar g) reserved for condensation, then BOG can be provided at a rate of at least 100 kg / h (ratio of 1) and up to 500 kg / h (ratio of 0.2) before the pressure threshold of that tank 108 is reached.

[0035] This ratio can help guide the operation by ensuring the operation progresses as anticipated at least by monitoring measured (or actual) operational parameters, such as condensation reserve and BOG flow rate to ensure they are equal or higher than the predetermined ratio. For example, FIG. 3 shows three exemplary plots that fall within the provided ratio of at most 1 m3liquefied condensation reserve gas to 1 kg / h BOG being provided, more preferably at most 0.5 m3liquefied gas to 1 kg / h BOG, and most preferably at most 0.2 m3liquefied gas to 1 kg / h BOG, which is within the capabilities of one of ordinary skills to determine and generate based on the information provided herein, including known starting conditions and the provided ratio. As can be seen, FIG. 3 indicates a pressure threshold of 90% MAWP and when that it is anticipated that the threshold would be reached. As the measured (or actual) operational parameters of condensation reserve and BOG flow rate can be plotted are acquired over time, they can be plotted in the same graph to monitor the progress of the cool down operation. It is preferred that the measured plot falls within the two outer lines and near or around a selected preferred ratio, which is 0.5 in this illustrative instance in FIG. 3. As such, the methods disclosed herein allow for management of BOG by recondensing it by providing it to the condensation reserve via a manner that is designed to improve properties of the BOG bubbles to positively influence the BOG condensation rate, and further optionally allow for predicting the progress of the BOG recondensation process (using the provided ratios) to respect the pressure rating of the equipment involved.SP3180

[0036] Accordingly, the method can optionally further comprise selecting a ratio of (i) an amount of condensation reserve to (ii) a selected BOG flow rate at which the BOG is provided to the condensation reserve; estimating progress of the selected ratio over a period of time during which BOG is provided to generate a model of the selected ratio; calculating an actual ratio of the amount of condensation reserve to an actual BOG flow rate over time while the BOG is provided to the condensation reserve; and comparing the actual ratio with the model of the selected ratio over time.

[0037] In addition, with known starting conditions such as the condensation reserve amount, starting temperature of the condensation reserve, cool down duration, the methods disclosed herein further provide for predicting the pressure progress over time at a selected BOG recondensation rate (optionally and preferably consistent with the disclosures herein, including the provided ratio), in light of the starting conditions. For instance, a chart can be generated to show estimated temperatures of the liquefied gas 114 in the receiving tank 108 at various times during the cooldown or bunkering process at a certain BOG flowrate or amount being provided. Optionally, the chart can show, additionally or alternatively, the predicted tank vapor space pressure at various times throughout the process that generates the BOG. For instance, FIG. 4 provides an example of such model or estimate. In particular, FIG. 4 is a model or estimate where LNG is the liquefied gas for which BOG is being managed and the condensation reserve is also LNG. The amount of LNG condensation reserve is 1620 m3, with a starting temperature of LNG saturated at -160°C, and the condensation BOG rate (or BOG flow rate) is constant at 3200 kg / h (with an average temperature of 25°C) for 15 hours. With the model as shown in FIG. 4, the tank vapor pressure of the receiving tank 108 can be measured and its progress monitored against the predicted model or estimate.

[0038] As such, optionally, the methods can further comprise the steps of monitoring at least one of the temperatures of the LNG in receiving tank 108 and the tank vapor space pressure at various times throughout the BOG-generating process so that these values can be compared against the estimated or modelled values. That is, the method can optionally further comprise - providing an estimate of pressure increase of the at least one tank (108) over time based at least on starting conditions of condensation reserve amount, starting temperature of the condensation reserve, duration of time that the BOG is provided, and a selected BOG flow rate; comparing measured pressure values of the at least one tank over time while receiving the BOG at the selected flow rateSP3180 against the estimate of pressure; and adjusting the selected flow rate if the measured pressure value deviates from the estimate beyond a desired amount.

[0039] Suitable ways and equipment to measure the temperature of the liquefied gas in the tank and / or tank vapor space pressure are known to one of ordinary skills. Predicted values can be provided in suitable increments, such as at least every minute, in order to improve operational resolution. Preferably, temperature and / or pressure measurements can be done at the same increments as the predicted values, or for practical reasons, be collected and provided every 10 minutes, or preferably every 5 minutes, to help to captured are delta between the predicted and measured value that enables a timely correction in the operational parameters, as known to one of ordinary skill.

[0040] Measured values that are higher than the estimated pressure (such as at least 1% higher) indicates that the pressure threshold may be reached sooner than anticipated, and mitigating steps may be needed. Examples of mitigating steps include reducing the amount of BOG management rate (that is, the amount of BOG being provided to the tank), providing the BOG to another tank 108, and potentially even stopping the cooldown or bunkering process to stop generating BOG if no other alternative BOG managing methods is available.

[0041] While not shown, it is understood that a vapor manifold crossover can be part of the infrastructure to allow the BOG to crossover from the vapor piping system to a liquid piping system and enter at least drop-down line 118 to be provided to tank 108 via bottom distribution header 116. In scenarios in which liquefied gas 114 is LNG, tank 108 is preferably a type C LNG storage tanks, which are a type of cargo containment system that is suitable for fluids stored at higher pressures. The LNG stored in type C tanks, may be stored at a saturation pressure, anywhere from 0 bar g to 6 bar g (or higher, depending on the size of the tank). LBVs (i.e., Bunker Vessels) will typically store LNG between 0 - 1 bar g saturation pressure and may have a MAWP in the range of 3 - 6 bar g (higher or lower MAWPs are also possible).

[0042] While not shown, it is understood that a computer program can be used to control and / or implement some, including all, aspects of the methods described herein. This computer program may be referred to as a controller. For instance, the computer program can be used to control the pump discharge pressure and flow, the system operating pressure via the manipulation of the flow control valve opening percentage, among others. A suitable computer program includes one that is executed by a data processor. As used herein, reference to a computer program is intended toSP3180 be equivalent to a reference to a program element and / or a computer readable medium containing instructions for controlling a computer system to coordinate the performance of the above described method. The computer program may be implemented as computer readable instruction code by use of any suitable programming language, such as, for example, JAVA, C++, and may be stored on a computer-readable medium (removable disk, volatile or nonvolatile memory, embedded memory / processor, etc.). The instruction code is operable to program a computer or any other programmable device to carry out the intended functions. The computer program may be available from a network, such as the World Wide Web, from which it may be downloaded. The various aspects described herein may be realized by means of a computer program respectively software; however, they may also be realized by means of one or more specific electronic circuits respectively hardware. Furthermore, the invention may also be realized in a hybrid form, i.e. in a combination of software modules and hardware modules. Additionally or alternatively, any or all aspects of the methods described herein can be performed manually by one or more human operator with relevant operational knowledge of the facility.

[0043] While specific embodiments have been described herein, it is understood that such descriptions are not intended to limit the described embodiments. Instead, any combination of the features and elements provided above, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Furthermore, although embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages described herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s).

Claims

SP3180CLAIMS1. A method for managing BOG comprising:- providing one or more receiving tanks (108), wherein each receiving tank comprises- a condensation reserve amount of liquefied gas;- a bottom distribution header (116) comprising (i) a length (120) of at least 10%, preferably at least 20%, more preferably at least 30%, and most preferably at least 40%, a length of the receiving tank (120) and (ii) a plurality of openings (122) arranged along the length (120) of the distribution header (116), and wherein at least one opening (122), preferably at least 5 openings (122), more preferably at least 10 openings (122), being arranged per meter along the length (120) of the bottom distribution header (116);- providing boil-off-gas (BOG) to at least one receiving tank (108) via the plurality of openings (122) of the bottom distribution header (116);- recondensing the BOG in the at least one receiving tank (108) using the condensation reserve amount of liquefied gas; and- terminating the provision of the BOG to the at least one receiving tank (108) via the plurality of openings (122) before pressure of the at least one receiving tank (108) exceeds a pressure threshold of that tank (108).

2. The method of claim 1, further comprising:- providing the BOG to the at least one receiving tank according to a selected ratio of (i) an amount of condensation reserve to (ii) a selected BOG flow rate at which the BOG is provided, wherein the ratio is at most 1 m3condensation reserve to 1 kg / h BOG being provided, more preferably at most 0.5 m3condensation reserve to 1 kg / h BOG, and most preferably at most 0.2 m3condensation reserve to 1 kg / h BOG.

3. The method of claim 2, further comprising:- selecting a ratio of (i) an amount of condensation reserve to (ii) a selected BOG flow rate at which the BOG is provided to the condensation reserve;- estimating progress of the selected ratio over a period of time during which BOG is provided to generate a model of the selected ratio;SP3180- calculating an actual ratio of the amount of condensation reserve to an actual BOG flow rate over time while the BOG is provided to the condensation reserve; and- comparing the actual ratio with the model of the selected ratio over time.

4. The method of claim 2 or 3, further comprising:- providing an estimate of pressure increase of the at least one tank (108) over time based at least on starting conditions of condensation reserve amount, starting temperature of the condensation reserve, duration of time that the BOG is provided, and a selected BOG flow rate;- comparing measured pressure values of the at least one tank (108) over time while receiving the BOG at the selected flow rate against the estimate of pressure; and- adjusting the selected flow rate if the measured pressure value deviates from the estimate beyond a desired amount.

5. The method of any one of the preceding claims, wherein the liquefied gas is LNG, hydrogen, or carbon dioxide.

6. The method of any one of the preceding claims, wherein the pressure threshold is up to 90% of the Maximum Allowable Working Pressure (MAWP) of the at least one receiving tank (108).

7. The method of any one of the preceding claims, wherein the amount condensation reserve is spread across two or more receiving tanks (108).

8. The method of any one of claims 1 - 6, wherein the amount of condensation reserve is with respect to the at least one receiving tank (108).

9. The method of any one of the preceding claims, wherein the storage tank (104) being located on one ship and the at least one receiving tank (108) being located on another ship.

10. The method of any one of the preceding claims, wherein the BOG is generated from cooling storage tank (104) from a temperature of greater than -10 degrees C.SP318011 . The method of any one of the preceding claims, wherein the BOG is generated from cooling storage tank (104) to a temperature capable of storing an amount of the liquefied gas.

12. The method of any one of the preceding claims, wherein the one or more receiving tanks (108) further comprises a drop-down line (118) in fluid connection with the bottom distribution header (116).

13. The method of any one of the preceding claims, wherein the BOG being generated from cooling down of a storage tank (104) to a temperature below - 10 degrees C using a liquefied gas, wherein the liquefied gas used for the cool down being the same type of gas as the liquefied gas in the receiving tank (108).

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