Determination of operational energy losses in a liquefied gas transport vessel

Abstract

Determining operational energy losses in a liquefied gas transport vessel The invention relates to a method for determining (10) operational energy losses (Df, Ds) over a time interval, of a liquefied gas transport vessel equipped with a liquefaction system, comprising steps of: - calculating (12) an amount of energy consumed (D1) by an energy consumer of the vessel, - calculating (14) an energy variation (D2) as a function of a temperature variation of the liquefied gas, - adding (16) the energy variation (D2) to the amount of energy consumed (D1) resulting in an effective operational energy loss (Df), and when the liquefaction system is activated over the time interval: - calculating (18) an energy saving (D3) by the liquefaction system, and - adding (20) the energy saving (D3) to the effective operational energy loss (Df),resulting in an estimated operational energy loss (Ds) that would have been observed without the activation of the liquefaction system. (Figure 1),

Description

Title of the invention: Determination of operational energy losses in a liquefied gas transport vessel

[0001] The present invention relates to the field of liquefied gas transport vessels, in particular LNG carriers, and to the field of equipment for monitoring energy consumption in these vessels. More specifically, the invention relates to a method for determining data representative of operational energy losses in such a vessel.

[0002] Such a ship has a hold designed to contain one or more tanks for transporting gas in the liquid state, these tanks having a capacity of several thousand or even several tens of thousands of cubic meters. When it comes to natural gas, it is kept in the tanks at approximately -163°C (degrees Celsius), at atmospheric pressure. The tanks are therefore sealed and thermally insulated by a double layer of insulation. However, since liquefied natural gas (LNG) tends to evaporate, for example due to a reduction in the gas pressure in the tanks or a heat flow passing through the tank walls despite the double insulation, the upper part of each tank, called the tank gas ceiling, is filled with gas in the vapor state. This is generally used as fuel for one or more of the ship's engines.The unused gas in vapor state that cannot be kept in the tanks is burned via a flare and then released into the atmosphere, or more rarely released as is, or reliquefied by a (re)liquefaction system on the ship, called a liquefaction system in this application, and returned at -163°C in the liquid state to the tanks. This liquefaction system therefore saves gas, and therefore energy, which would be lost without this system, while itself consuming energy to operate.

[0003] The energy balance of operational losses of evaporated gas during a ship's journey, also called operational BOR (for English "Boil-Off Rate") of a ship, is difficult to estimate. It depends in particular on the consumption of the ship's engines, which reduce the pressure in at least one of the tanks, the weather conditions (temperature, swell), the thermal resistance of the tanks, and the efficiency of the liquefaction system. Difficult weather conditions can cause significant movements of the ship and therefore of the liquefied gas in the tanks, which generates greater evaporation of the liquefied gas than when the ship is sailing in calm waters.

[0004] However, the owners of such vessels are keen to know the precise performance of their vessels in terms of operational energy losses, particularly for reasons of contractual guarantees.

[0005] Currently, shipowners use the reduction in the volume of liquefied gas in the tanks to assess this operational performance, but this method is not precise due in particular to variations in the movements of liquid in the tanks due to the movement of the ship itself. In addition, this reduction does not distinguish between energy losses due to the consumption of gas by the ship's engines and other losses.

[0006] Furthermore, the operational performance of interest to shipowners should take into account the best conditions of use of the ship, and in particular the ship's liquefaction system. However, this liquefaction system, itself an energy consumer, is not always activated on the ship's journey, and therefore the operational performance measured by the volume variation method is often not representative of the operational performance enabled by the ship.

[0007] Predictive methods, using an estimated energy consumption of the ship over a journey based on different usage contexts, can provide operational performance taking into account the best usage conditions of the ship. However, these predictive methods prove to be complex and ultimately imprecise, and result in a poor perception of the operational performance that the ship allows, resulting in a lack of interest and confidence in the data provided by these methods.

[0008] There is therefore a need to provide accurate operational performance of a liquefied gas transport vessel equipped with a liquefaction system, so as to enable an understanding of the differences in operational performance depending on the conditions of use of the vessel.

[0009] The present invention aims to remedy at least in part the drawbacks of the prior art by providing a method for determining data representative of operational energy losses over a time interval, in a liquefied gas transport vessel, a corresponding determination device and system, as well as a computer program, which make it possible to accurately compare an active operational performance corresponding to a mode of use of the vessel in which the liquefaction system is active, with a passive operational performance corresponding to a mode of use of the vessel in which the liquefaction system is deactivated.

[0010] To this end, the invention proposes a method for determining data representative of operational energy losses over a time interval, of a liquefied gas transport vessel, this energy being initially stored in the form of liquefied gas and evaporated gas in at least one tank of the vessel, the vessel being equipped with a system for liquefying the evaporated gas, the determination method comprising stages of: - calculation of a first data item representative of a quantity of energy consumed over the time interval, based on at least one measurement relating to the activity of at least one energy consumer of the ship, - calculation of a second data item representative of a variation in energy of the liquefied gas present in the tank, as a function of a variation in temperature of the liquefied gas in the tank over the time interval, - adding the second data to the first data resulting in data representative of an effective operational energy loss in the ship, the determination method being characterized in that it further comprises, when the liquefaction system is activated over the time interval: - a step of calculating a third data item representative of a quantity of energy saved by the liquefaction system over the time interval, and - a step of adding the third data to the data representative of an actual operational energy loss, resulting in data representative of an estimated operational energy loss which would have been observed without the activation of the liquefaction system.

[0011] In this determination method according to the invention, the first data item is a function of one or more measurements each linked to one or more consumers of the ship, for example several engines, so as to calculate the total energy consumed by the consumers of the ship. The measurements are provided by one or more sensors, for example a flow meter in a supply line of an engine of the ship.

[0012] Furthermore, when the ship has several tanks, the second data item corresponds to a variation in energy linked to a variation in the temperature of the liquefied gas on all the tanks, which can be positive or negative. Indeed, when the ship consumes a lot of evaporated gas, the pressure of the liquefied gas is likely to drop, causing the temperature of the LNG to drop. In this case, the LNG has provided energy, which corresponds to a second negative data item. On the contrary, when little evaporated gas is consumed, the pressure of the liquefied gas is likely to increase and therefore cause the temperature of the liquefied gas to rise, resulting in energy absorption by the LNG, which corresponds to a second positive data item. Finally, the third data item corresponds to the energy saved on all the tanks by the liquefaction system.

[0013] The time interval for which the first, second and third data are calculated corresponds for example to a day, or an hour, this interval being able to be adapted according to the smallest time interval over which the liquefaction system is activated or deactivated. It should be noted in fact that the calculations of the third data and of the estimated operational energy loss can also be carried out when the liquefaction system is deactivated, simply the third data will have the value zero and the estimated operational energy loss will be worth the actual operational energy loss.

[0014] Thanks to the determination method according to the invention, the data representative of the operational energy losses are more precise than in the prior art. In particular, the calculation of the first data representative of the energy consumed by consumers of the ship, uses measurements whose integration over the time interval makes it possible to know a real mass of gas escaping from the tank, unlike an estimate of mass loss of the prior art, calculated using a variation in volume, this estimate being very imprecise because of the movements of liquid which bias the volume and density data estimated mathematically.

[0015] Furthermore, the determination method makes it possible to compare an actual operational energy loss corresponding to an active operational performance and to a mode of use where the liquefaction system is activated, with an estimated operational energy loss corresponding to a passive operational performance and to a mode of use where the liquefaction system is deactivated. This comparison is based on the quantity of energy saved by the liquefaction system, the value of which is not estimated but calculated precisely from a measured mass, and is therefore very precise. Thus the passive operational performance is estimated very reliably, which encourages a user of the determination method according to the invention to assess the operational performance actually enabled by the ship, and to activate the liquefaction system more frequently and therefore to save energy on the ship's journey.This approach differs from the prior art in which operational performance under unfulfilled usage conditions is predicted from estimated energy savings or energy losses, and is therefore much less reliable. In particular, estimates of volume losses from liquid heights in the ship's tanks are very unreliable, particularly due to the ship's movements.

[0016] In one embodiment of the invention, the first, second and third data as well as the data representative of an actual operational loss of energy and the data representative of an estimated operational loss of energy each correspond to a ratio between on the one hand a quantity of energy lost over the time interval and on the other hand a reference quantity of energy chosen from: - a quantity of energy calculated at the start of a period of use of the determination method, or - a quantity of energy charged by the ship.

[0017] The quantity of energy charged by the ship corresponds to an energy contained in the vessel's tank(s) immediately after filling. Other reference energy quantities are of course usable, for example the chosen reference energy quantity is the quantity of energy that the liquefied gas loaded by the vessel would represent if it were loaded to a predetermined percentage of its total cargo, for example 100%, 95%, or 90%.

[0018] The use of this ratio allows a user of the determination method according to the invention to better perceive the operational energy losses over the time interval.

[0019] Preferably, the determination method according to the invention comprises an additional step of restoring the first, second and third data as well as the data representative of an actual operational energy loss and the data representative of an estimated operational energy loss, on a human-machine interface. Such a restoration consists for example of a display on a screen of said interface.

[0020] The invention also relates to a method for monitoring operational data linked to at least one tank of a liquefied gas transport vessel, characterized in that it implements the method for determining data representative of operational energy losses according to the invention, and in that it comprises a step of calculating a fourth data item representative of a variation in the volume of liquefied gas in the tank over the time interval.

[0021] This latter calculation allows a user of the supervision method according to the invention to compare the estimate provided by the prior art with the operational energy loss estimated according to the invention. It shows the variability of this estimate of the prior art in comparison with the data representative of the estimated operational energy loss.

[0022] The invention also relates to a device for determining data representative of operational energy losses, comprising means for implementing the determination method according to the invention. The determination device implements the determination method according to the invention in hardware and / or software. It is capable of recovering measurement data from sensors enabling it to implement the different steps of the determination method according to the invention. It is therefore, for example, an on-board computer of the ship, or a computer connected to it, or even a remote server capable of receiving this data.

[0023] The invention also relates to a system for determining data representative of operational energy losses over a time interval, of a liquefied gas transport vessel, this energy being initially stored in the form of liquefied gas and evaporated gas in at least one tank of the vessel, the vessel being equipped with a system for liquefying the evaporated gas, the determination system comprising: - first means for calculating a first data item representative of a quantity of energy consumed over the time interval, as a function of at least one measurement relating to the activity of at least one energy consumer of the ship, - second means for calculating a second data item representative of a variation in energy of the liquefied gas present in the tank, as a function of a variation in temperature of the liquefied gas in the tank over the time interval, - means for adding the second data to the first data, delivering data representative of an effective operational energy loss in the ship, the determination system being characterized in that it further comprises: - third means for calculating a third data item representative of a quantity of energy saved by the liquefaction system over the time interval, when the liquefaction system is activated over the time interval, and - means for adding the third data item to the data item representing an actual operational energy loss, delivering, when the liquefaction system is activated over the time interval, data item representing an estimated operational energy loss, which would have been observed without the activation of the liquefaction system.

[0024] The determination system according to the invention is implemented in hardware and / or software. The means of the determination system according to the invention enable it to implement the determination method according to the invention. The determination system according to the invention is therefore, for example, identical to the determination device according to the invention, or else comprises several remote physical entities, for example, it is formed of the ship's on-board computer and a remote server capable of receiving data from the ship's on-board computer, and possibly a terminal connected to this remote server.The remote server is possibly formed of several computers connected to each other by one or more communication networks. In another example, the determination system according to the invention comprises only the on-board computer and a terminal connected to this on-board computer. The determination system according to the invention may further comprise sensors such as liquefied gas temperature sensors or flow meters making it possible to measure the gas consumption of one or more consumers of the ship.

[0025] According to a preferred characteristic of the determination system according to the invention, the latter comprises a human-machine interface comprising display means capable of providing a representation of the first, second and third data, as well as data representative of the actual and estimated operational energy losses, in which the data representative of an actual operational energy loss is displayed in the form of a sum between the first and second data and, when the liquefaction system is activated over the time interval, the data representative of an estimated operational energy loss is visualized in the form of a cumulative total of the third data and the data representative of the actual operational energy loss. In other words, this human-machine interface is capable of implementing the additional step of restitution of the determination method according to the invention, in visual form.

[0026] In one embodiment of the invention, said representation is a waterfall graph. Such a graph is well suited to restoring in an immediately understandable manner the mathematical relationships between the restored data. Of course, in an alternative embodiment, other graphic means such as tables of values, conventional histograms or pie charts can be used.

[0027] In this embodiment of the invention, the display means are capable of representing the data representative of the actual operational energy loss in a first location of the waterfall graph when the liquefaction system is activated over the time interval, or in a second location of the waterfall graph, distinct from the first location, when the liquefaction system is deactivated over the time interval, the data representative of an estimated operational energy loss being represented by the display means at the second location when the liquefaction system is activated over the time interval.

[0028] This embodiment makes it possible to always reserve the first location on the graph for active operational performance, and the second location for passive operational performance. In other words, this allows a user of the determination system according to the invention to easily correlate the operational losses of effective energy to a context of activation of the liquefaction system or to a context of deactivation of the liquefaction system.

[0029] In this embodiment, the restitution of the data is linked to a time interval or to an average over time intervals. In particular in this embodiment, the human-machine interface of the determination system according to the invention further comprises means for selecting at least one portion of a journey made by the ship, and means for selecting first time intervals during which the liquefaction system was activated on this portion of the journey, the display means being capable of representing when the first time intervals are selected by a user of the determination system: - an average of the first data delivered by the first calculation means for each of the first time intervals, - an average of second data delivered by the second calculation means for each of the first time intervals, - an average of data representative of operational losses of effective energy delivered by the addition means, for each of the first intervals of time, - an average of third data delivered by the third calculation means for each of the first time intervals, and - an average of representative data of estimated operational energy losses delivered by the addition means for each of the first time intervals.

[0030] In this embodiment of the invention, the human-machine interface of the determination system according to the invention further comprises means for selecting second time intervals during which the liquefaction system was deactivated on this portion of the journey, the display means being capable of representing when the second time intervals are selected by a user of the determination system: - an average of first data delivered by the first calculation means for each of the second time intervals, - an average of second data delivered by the second calculation means for each of the second time intervals, and - an average of data representative of operational losses of effective energy delivered by the adding means for each of the second time intervals. The means for selecting the first or second intervals are, for example, buttons or graphic tabs on the graphic interface rendered by the display means.

[0031] Additional supervision data are returned in this embodiment, allowing a user of the determination system according to the invention to correlate more data in order to better understand the evolution of the operational energy losses returned by the human-machine interface. Thus in this embodiment, the human-machine interface further comprises means for selecting at least one tab linked to an operational data item relating to the liquefied, evaporated, reliquefied or consumed gas in the tanks, capable of causing the display means to display a graph of values ​​corresponding to the selected tab, the values ​​being those of the operational data item over one or more time intervals and being recorded in a memory of the determination system. The operational data item is taken for example from:

[0032] - a flow of evaporated gas sent to the liquefaction system over time, - a cumulative mass of gas lost over time, - a non-cumulative mass of gas lost over time, - a density of the liquefied gas in the tank over time, - a temperature of the liquefied gas in the tank over time, - a pressure of the evaporated gas in the tank over time, - a volume of liquefied gas over time, - a ship speed over time.

[0033] This data can be instantaneous or linked to a predefined time interval.

[0034] The invention also relates to a system for monitoring operational data linked to at least one tank of a liquefied gas transport ship, characterized in that it comprises the system for determining data representative of operational energy losses according to the invention, and in that it comprises means for calculating a fourth data item representative of a variation in the volume of liquefied gas in the tank over the time interval. The display means of the determination system according to the invention are preferably identical to display means of the monitoring system according to the invention, and therefore also restore the fourth data item representative of an energy loss in the tank over the time interval considered.

[0035] The invention finally relates to a computer program comprising program code instructions for executing the steps of the determination method according to the invention, when said program is executed on one or more processors.

[0036] The computer program is executed on a single processor, for example when it is executed in the determination device according to the invention, equipped with this processor. It is executed on several processors, for example in the determination system according to the invention when the latter comprises several remote physical entities each equipped with one of these processors, in particular the calculation steps of the determination method according to the invention are implemented, for example, in a remote server or in the ship's on-board computer, and the restitution step is implemented in a terminal connected to the remote server or to the on-board computer.

[0037] It should also be noted that the determination method according to the invention is implemented dynamically during the ship's journey, or statically once the ship has arrived at its destination. When the calculation steps of the determination method according to the invention are implemented in a remote server of the determination system according to the invention, the remote server therefore comprises means of wireless communication with the ship's on-board computer, for example means of internet communication via satellite, to dynamically restore the data representative of the ship's operational energy losses. These wireless communication means can be replaced by a transfer of data via a physical medium, such as a data storage key, when the restoration is carried out only once the ship has arrived at its destination.

[0038] The determination device according to the invention, the determination system according to the invention, the supervision system according to the invention and the computer program according to the invention, have advantages similar to those of the determination method according to the invention and the supervision method according to the invention.

[0039] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0040] [Fig-1] represents steps of a determination method according to the invention, of data representative of operational energy losses in a liquefied gas transport vessel, over a time interval, in one embodiment of the invention, and steps of a supervision method implementing this determination method, in this embodiment of the invention,

[0041] [Fig.2] represents a determination system according to the invention, in this mode of embodiment of the invention, comprising means capable of implementing the determination method according to the invention,

[0042] [Fig.3] represents a graphical interface allowing the restitution of data from terminated by the methods of [Fig.l], in this embodiment of the invention, when a liquefaction system of the ship was activated over the time interval, and

[0043] [Fig.4] represents the graphical interface of [Fig.3], when the liquefaction system ship quefaction was disabled on the time interval.

[0044] In an embodiment of the invention shown in Figures 1 to 4, a determination method 10 shown [Fig. 1] makes it possible to deliver data representative of operational energy losses Df, Ds over a time interval, of a ship 40 shown [Fig. 2]. This determination method 10 is part of a more general method 11 for supervising operational data linked to the tanks 42 of the ship 40. The chosen or predetermined time interval is, for example, a day, an hour, a shorter or longer time interval. The time interval corresponds, for example, to a period of time necessary for the ship to complete a journey or a portion of a journey, selected by a user of the determination method 10. The ship 40 is a ship transporting liquefied gas, this gas being, in this embodiment of the invention, liquefied natural gas.However, in an alternative embodiment, this gas is, for example, liquid hydrogen or another type of gas.

[0045] The ship 40 stores the liquefied gas at -163°C and at a pressure close to atmospheric pressure in sealed and thermally insulated tanks 42. Each tank 42 is filled with liquefied gas up to the liquid level referenced 46, the space in the tank above this liquid level 46, called the tank gaseous headspace, being filled with evaporated gas. The liquefied gas present in liquid and gaseous form in the tanks 42 of the ship 40, represents a quantity of energy transported by the ship 40. This quantity of energy decreases as the ship travels, due to the consumption of gas by the ship's consumers, gas losses through evaporation and energy losses linked to variations in pressure and temperature of the liquefied natural gas, these variations which may be of various origins such as swell, meteorology, thermal resistance of the tanks, gas draw by the consumers of the ship 40, etc. The ship 40 nevertheless includes a liquefaction system making it possible to liquefy part of the gas evaporated in the gaseous tank ceilings and thus save a loss of gas.

[0046] The determination method 10 according to the invention makes it possible to determine:

[0047] - data representative of an effective operational energy loss Df, cor corresponding to an effective energy loss during the time interval, compared to a reference energy as explained later; this data representative of an effective operational energy loss Df is calculated, in this embodiment of the invention, whether the liquefaction system is active or not over the time interval. This time interval can be modified to correspond to a single active or deactivated state of the liquefaction system; and

[0048] - data representative of an estimated operational energy loss Ds, calculated only when the liquefaction system is active over the time interval, and corresponding to an energy loss during the time interval, which would have been observed if the liquefaction system had not been activated over the time interval, this energy loss also relating to a reference energy.

[0049] In this embodiment of the invention, the determination method 10 is implemented in hardware and / or software in a system 50 for determining data representative of operational energy losses Df, Ds, referenced [Fig.2] and now described, the steps of the determination method 10 allowing the obtaining of data representative of operational energy losses Df, Ds being described next. The determination system 50 is part of a more general system for supervising operational data linked to the tanks of the ship, implementing in hardware and / or software the supervision method 11 according to the invention.

[0050] The determination system 50 comprises an on-board computer 52, which receives measurements from various sensors present in the ship 40, in particular temperature sensors 54 of the liquefied gas in the tanks 42 and at least one mass flow meter 56 measuring the mass of gas sent to the consumers of the ship during the time interval.

[0051] The determination system 50 also comprises a remote server 55 represented in the internet “cloud” 60, which dynamically receives measurements from the temperature sensors 54 and the mass flow meter 56, sent by the on-board computer 52 in an ml message. For sending these measurements, the on-board computer 52 comprises, for example, means of connection to the internet by satellite. For receiving the measurements, the remote server 55 comprises, for example, a wired internet connection. remote server 55 receives for example measurements from several gas transport vessels and stores them in a database 57. It comprises calculation, addition and addition means, making it possible to implement the calculation steps of the determination method 10 according to the invention and to determine the data representative of operational energy losses Df, Ds of the vessel 40 over the time interval, as described later. These means comprise at least one processor of the server 55, capable of reading data stored in the database 57.

[0052] The determination system 50 also comprises a terminal 58, for example a portable personal computer or a multimedia mobile telephone, comprising means for displaying data representative of operational energy losses Df, Ds provided by the remote server 55, these display means comprising in particular a screen. This terminal 58 is, in this example of use of the invention, on the ship 40, but can also use the invention on land. It therefore uses means of connection to the internet by satellite to send a message m2 to the remote server 55, this message m2 containing a request to send data representative of operational energy losses Df, Ds over the time interval. Upon receipt of the message m2, the remote server 55 sends in a message m3, the data representative of operational energy losses Df, Ds to the terminal 58.

[0053] Returning to [Fig. 1], the determination method 10 comprises a first step 12 of calculating a first data item DI representative of a quantity of energy consumed over the time interval, as a function of a measurement provided by the mass flow meter 56. This mass flow meter 56 provides a total flow rate q> of gas consumption by the consumers 44 of the ship, represented in [Fig. 2] and including in particular the main engines of the ship 40, the auxiliary engines of the ship 40 and a flare burning unrecovered evaporated gas, used when the liquefaction system is deactivated. As a variant, several mass flow meters are used, for example one per consumer.

[0054] It should be noted that using mass flow meters of the consumers to estimate a mass of gas consumed is more accurate than observing the difference in liquid level over the time interval. Indeed, the liquid level measurements can be very noisy due to the movements of liquid in the tanks 42.

[0055] In a case of use of the embodiment of the invention, the first data DI is a percentage of energy consumed over a day, calculated as follows, by first calculation means of the server 55:

[0056] DI = ^dt*Lhv *100 N*t

[0057] With:

[0058] - * the multiplication operator

[0059] -1 the duration of the time interval in days,

[0060] - tl the start of the time interval,

[0061] -12 the end of the time interval,

[0062] - q> the flow rate supplied by the mass flow meter 56 in kilograms per day,

[0063] - Lhv an average of latent heat of vaporization of the gas between the beginning and the end of the time interval, in kilojoules per kilogram, and

[0064] - N a reference energy in kilojoules.

[0065] The reference energy N is for example the quantity of energy represented by the liquefied gas in the tanks 42 at the start of a period of use of the determination method 10, identical to the start of the time interval or earlier:

[0066] N = ^1*V1*L1

[0067] where

[0068] - dl is the density in kilograms per cubic meter of the liquefied gas in the tanks 42 at the start of the period of use of the determination method 10,

[0069] - VI is the volume in cubic meters of liquefied gas in the tanks 42 at the start of the period of use of the determination method 10, and - L1 is the latent heat of vaporization of the liquefied gas in the tanks 42 at the start of the period of use of the determination method 10, in kilojoules per kilogram.

[0070] Alternatively, the reference energy N is taken equal to the quantity of energy loaded into the tanks 42 immediately after the end of their filling:

[0071] N = ^2^V2*Z2

[0072] where

[0073] - d2 is the density in kilograms per cubic meter of the liquefied gas in the tanks 42 just after filling them,

[0074] - V2 is the volume in cubic meters of liquefied gas in the tanks 42 just after their filling, and - L2 is the latent heat of vaporization of the liquefied gas in the tanks 42 just after they are filled, in kilojoules per kilogram.

[0075] In yet another variant, the reference energy N is taken equal to the quantity of energy loaded into the tanks 42 just after their filling, in the case where the liquefied gas would be pure methane:

[0076] N = ^m*V2*Em

[0077] where

[0078] - dm is the density of pure methane in kilograms per cubic meter, and - Lm is the latent heat of vaporization of pure methane, in kilojoules per kilogram.

[0079] It should be noted that in this embodiment, the term “pure methane” means that the gas is not formed from a mixture of methane with another gas such as propane for example, but is formed solely from methane, with the exception of impurities.

[0080] This latter variant has the advantage of not making the reference energy dependent on the measurement period but only on the volume of liquefied gas initially loaded into the ship.

[0081] A second step of the determination method 10 is a calculation step 14 of a second data item D2, representative of an energy variation linked to the temperature variation of the liquefied gas present in the tanks 42, as a function of temperature variations of the liquefied gas in the tanks 42 measured over the time interval.

[0082] This second data D2 reflects a variation in energy linked to the temperature changes in the tanks 42, and corresponds to a negative variation in energy if the temperature has dropped (for example due to a reduction in pressure) and therefore to a quantity of energy supplied by the LNG, or, if the temperature has increased, to a positive variation in energy and therefore to a quantity of energy absorbed by the LNG.

[0083] In the case of use of this embodiment of the invention, the second data D2 is a percentage of energy stored or taken over the day considered, calculated as follows, by second calculation means of the server 55:

[0084] D2 = *100 N*t with :

[0085] - df is the density in kilograms per cubic meter of the liquefied gas in tanks 42 to the end of the time interval,

[0086] - Vf is the volume in cubic meters of liquefied gas in the tanks 42 at the end of the time interval,

[0087] - Cp is an average of the specific heat (also called heat capacity mass) of the liquefied gas between the start and end of the time interval, in kilojoules per kilogram per degree Celsius,

[0088] - T2 is an average of temperature measurements, in degrees Celsius, of the liquefied gas in tanks 42 at the end of the time interval, and

[0089] - Tl is an average of temperature measurements, in degrees Celsius, of the liquefied gas in tanks 42 at the beginning of the time interval.

[0090] As a variant, the second data D2 is calculated by summing energy percentages linked to the variation in temperature of the liquefied natural gas, therefore to energy stored or lost over the time interval, these percentages being calculated individually on each of the tanks 42. The temperature measurements at the start of the time interval on the one hand, and at the end of the time interval on the other hand, are averaged for each tank 42 in order to have data representative of the temperature in the tank at the start or at the end of the time interval. The different temperature measurements in one of the tanks 42 at a given time, and which are averaged, correspond for example to measurements taken by different temperature sensors spaced along a liquefied gas unloading mast, present in each tank 42.

[0091] A third step of the determination method 10 is a step 16 of adding the second data D2 to the first data DI resulting in the data representative of an effective operational energy loss Df in the ship 40 over the time interval, the adding step being implemented by adding means of the server 55:

[0092] Df=Dl + D2

[0093] In the case of use of this embodiment of the invention, the data representative of an effective operational energy loss Df corresponds to a percentage of energy lost compared to a reference energy, on the day considered. It corresponds to an active operational performance if the liquefaction system was activated on this day, or to a passive operational performance if the liquefaction system was deactivated on this day.

[0094] A fourth step of the determination method 10 is a calculation step 18 of a third data item D3 representative of a quantity of energy saved by the liquefaction system over the time interval. It is assumed, in this case of use of the invention, that the liquefaction system was activated over the time interval, and therefore made it possible not to lose a mass of evaporated gas in the tanks 42 which was greater than the needs of the consumers 44, by reliquefying it. This mass would probably have been burned by the flare in the opposite case. The fourth step of the determination method 10 is implemented by third calculation means of the server 55.

[0095] The third data D3 is, in the case of use of this embodiment of the invention, a percentage of energy saved over the day considered:

[0096] D3= 00^ *100 you, you N*t

[0097] where 0 is the mass flow rate in kilograms per day of reliquefied gas through the liquefaction system. A flow meter connected to the liquefaction system provides this value.

[0098] A fifth step of the determination method 10 is a step 20 of adding the third data D3 to the data representative of an effective operational energy loss Df, providing the data representative of an estimated operational energy loss Ds, the fifth step of the determination method 10 being implemented by addition means of the server 55:

[0099] Ds = D3 + Df

[0100] The data representative of an estimated operational energy loss Ds corresponds therefore to an estimate of the operational energy loss that would have occurred during the day if the liquefaction system had not been activated. It therefore corresponds to a passive operational performance estimated a posteriori.

[0101] In a use case where the liquefaction system is deactivated, we have:

[0102] D3 = 0 => Ds = Df

[0103] In the latter case, the data representative of an estimated operational energy loss Ds therefore corresponds to the data representative of an effective operational energy loss Df, and no longer to an estimate.

[0104] In parallel with these first five steps of the determination method 10 according to the invention, the supervision method 11 according to the invention implements an additional step 22 of calculating a fourth data item D4 representative of a loss of energy in the tanks 42 as a function of a variation in the volume of liquefied gas over the time interval.

[0105] In the case of use of the embodiment of the invention, D4 is a percentage of energy lost over the day considered, calculated as follows:

[0106] D4 = (^7K100

[0107] where Vi is the volume in cubic meters of liquefied gas in the tanks 42 at the start of the time interval.

[0108] Alternatively, D4 can be calculated by replacing Vi in the denominator with a volume of liquefied natural gas just after loading the ship, or with a volume of filling of the tanks to a predetermined percentage, for example 95% or 98%.

[0109] This calculation gives an order of magnitude of the total energy loss in the tanks 42 over the time interval. Indeed, this calculation is not precise because the quantity of liquefied gas evaporated depends strongly on the operations of the ship's crew. For example, if the crew decides to go at a high speed, the gas pressure in the tanks 42 may drop, thus forcing the evaporation of the liquefied gas. In this way, the quantity of liquefied gas evaporated will be greater. Conversely, if the crew slows down, or if the ship is stopped, the gas requirements of the various consumers will very probably be less than the gas emitted by the tanks 42 by evaporation. Thus, the pressure will rise in the tanks 42 and the quantity of gas evaporated will be lower.

[0110] This is why the invention considers the temperature variation of the liquefied gas, because this temperature variation is closely linked to the quantity of gas evaporated. If the latter is very large, then the temperature of the liquefied gas will most likely drop. On the other hand, if the gas consumption is low, the temperature of the liquefied gas should rise as well as the gas pressure in the tanks 42.

[0111] A sixth step of the determination method 10, common to the method of su pervision 11, is a step 24 of restitution of the data Dl, D2, D3, D4, Ds, Df previously calculated on a graphical interface displayed on a screen of the terminal 58. Of course in other embodiments of the invention, this restitution can be done differently, for example in a textual or vocal manner on the terminal 58 or on another element of the determination system 50.

[0112] It should be noted that steps 12 to 24 are not necessarily executed in the order described, the first step 12, the second step 14, the fourth step 18 and the sixth step 22 being able in particular to be carried out independently and therefore in parallel with each other. Steps 12 to 22 are preferably repeated to provide data corresponding to several time intervals, for example they are executed at the end of each day of a journey made by the ship 40.

[0113] [Fig.3] shows a screenshot 30 of terminal 58, showing the graphical interface divided into five zones 1 to 5.

[0114] Zone 1 is a world map on which the route taken by the ship 40 is represented. A graphic button on this map allows a user of the determination method 10 to select all or a portion of the route.

[0115] Zone 2 displays fixed data linked to the journey and to the ship 40, in particular under the heading "id" the name of the boat ("Messi" in this example of use), under the heading "ref" a reference of the journey ("Voyage" in this example of use), GPS coordinates (according to the English "Global Positioning System") of the starting point and the arrival point of the journey, the corresponding distance, a corresponding departure date and arrival date, the duration in hours of the journey, as well as the capacity of the ship 40, its density and an indicator of a loaded voyage or return using a ballast, the indicator being at "L" if the ship is on a loaded voyage.

[0116] Zone 3 includes graphic tabs selectable by the user, making it possible to view on zone 3, when the corresponding graphic tab is selected, a graphic representing:

[0117] - a flow rate vl of evaporated gas sent to the liquefaction system over time, in kilograms per hour, - a cumulative mass of gas v2 lost over time, corresponding to data representative of an effective operational energy loss calculated on the selected portion of the journey in kilograms of gas rather than as a percentage, - a mass flow rate of gas consumed v8 over time, corresponding for example to data representative of operational losses of effective energy calculated for each day of the selected portion of the journey in tonnes per day rather than in percentages, - a density v7 of the liquefied gas in the tanks 42 over time, - a temperature v5 of the liquefied gas in the tanks 42 over time, - a pressure v6 of the evaporated gas in the tanks 42 over time, - a volume v4 of liquefied gas in the tanks 42 over time, and - a speed v3 of the ship 40 over time.

[0118] In screen copy 30, the user has selected the tab corresponding to the flow rate vl of evaporated gas sent to the liquefaction system during the selected portion of the journey. On the graph corresponding to the flow rate vl, the periods corresponding to an activation of the liquefaction system, for which the gas flow rate sent to the liquefaction system is non-zero, are grayed out. This is due to the fact that in zone 4, the user has selected a graphic button B1 corresponding to the periods of activation of the liquefaction system on the selected portion of the journey.

[0119] Zone 4 includes a waterfall chart G1 representing:

[0120] - by a first histogram bar at a first location, an average the first DI data calculated by the determination system 50 for each day of the selected journey portion, during which the liquefaction system was active, called “consumed BOR” or “mass BOR”,

[0121] - by a second histogram bar at a second location, a average of the second D2 data calculated by the determination system 50 for each day of the selected portion of the journey, during which the liquefaction system was active, called “BOR due to the variation in temperature of the LNG” or “rate due to the conditioning of the vessel”,

[0122] - by a third histogram bar in a third location, the sum between the average represented at the first location and the average represented at the second location, called “active BOR”,

[0123] - by a fourth histogram bar in a fourth location, a average of the third data D3 calculated by the determination system 50 for each day of the selected portion of the journey, during which the liquefaction system was active, called “reliquefied BOR”,

[0124] - by a fifth histogram bar in a fifth location, the sum between the sum represented in the third location and the average represented in the fourth location, called “passive BOR”, and

[0125] - by a sixth histogram bar in a sixth location, an average fourth D4 data calculated by the supervision system for each day of the selected portion of the journey, during which the liquefaction system was active, called “volumetric BOR”.

[0126] The waterfall graph therefore represents average percentages of energy losses or gains per day for the selected portion of the journey. Alternatively, it represents percentages of energy losses or gains over the entire selected portion of the journey, on a waterfall graph G2, or a cumulative sum of losses or energy gains over the entire selected portion of the journey, on a G3 waterfall graph.

[0127] In the waterfall chart Gl, the first bar extends from a zero ordinate to a high end ordinate, the second bar extends from the high end ordinate of the first bar to a low end ordinate, and the third bar extends from the low end ordinate of the second bar to a zero ordinate. Thus the construction of the data representative of an effective operational energy loss Df as the sum between the first data DI and the second data D2 is visually represented. It should be noted that the high end ordinate of the first bar can become a low end ordinate of the second bar when the second data D2 is representative of an energy loss rather than an energy gain.

[0128] Similarly, the fourth bar extends from a low end ordinate equal to the low end ordinate of the second bar and also to a high end ordinate of the third bar, to a high end ordinate, and the fifth bar extends from a zero ordinate to the high end ordinate of the fourth bar. Thus the construction of the data representative of an estimated operational energy loss Ds as the sum between the third data D3 and the effective operational energy loss Df is visually represented.

[0129] Finally, zone 5 represents value scales ranging from green for low values ​​to red for high values, with an arrow on each bar showing the measured value:

[0130] - on a first scale El the speed of the ship is represented,

[0131] - on a second scale E2, the speed of the main engines of the ship 40 is re presented, and

[0132] - on a third scale E3 the pressure in the tanks 42 is represented.

[0133] In [Fig.4], a screenshot 32 of the graphical interface corresponds to the case where the user has selected in zone 3, the tab corresponding to the gas flow rate vl sent to the liquefaction system during the selected portion of the journey, and where the user has selected in zone 4, a graphic button B2 corresponding to the periods of deactivation of the liquefaction system on the selected portion of the journey.

[0134] As a result, on the graph corresponding to the flow rate vl, the periods for which the reliquefied gas flow rate is zero are grayed out. In addition, a new waterfall graph is represented in zone 4 and now only has four histogram bars:

[0135] - On the first location, a first histogram bar named “BOR consumed” or “mass BOR”, represents a new average of first DI data calculated by the determination system 50 for each day of the selected journey portion, during which the liquefaction system was deactivated,

[0136] - On the second location, a second bar named “BOR due to the “LNG temperature variation” or “rate due to vessel conditioning”, represents a new average of second D2 data calculated by the determination system 50 for each day of the selected journey portion, during which the liquefaction system was deactivated,

[0137] - On the third location, no bar is present but the value 0% is displayed, this value being named “active BOR” on this third location,

[0138] - On the fourth location, no bar is present but the value 0% and displayed, corresponding to a zero percentage of energy saved by the liquefaction system, this value being called “reliquefied BOR” on this fourth location,

[0139] - On the fifth location, a fifth histogram bar named “Passive BOR” represents the sum between the new average represented on the first location and the new average represented on the second location, and therefore the data representative of an operational energy loss Df, and

[0140] - On the sixth location, a sixth histogram bar named “BOR volumetric” represents a new average of fourth D4 data calculated by the supervision system for each day of the selected journey portion, during which the liquefaction system was deactivated.

[0141] On this new waterfall graph the first, second and fifth bars are arranged in a similar manner to the waterfall graph of [Fig.3], to visualize the fact that the fifth bar representative of an effective operational energy loss is constructed as the sum between the first bar representative of consumed energy and the second bar representative of an energy variation linked to the change in temperature of the liquefied natural gas.

[0142] The data representative of an effective operational energy loss Df is therefore represented at the fifth location, where the data representative of an estimated operational energy loss Ds was represented in [Fig.3]. Indeed, this fifth location is dedicated to a passive operational performance, corresponding to an operating mode of the ship 40 in which the liquefaction system is deactivated. Similarly, the third location is dedicated to an active operational performance Dg, corresponding to an operating mode of the ship 40 in which the liquefaction system is active. As a result, this active operational performance Dg is equal to the data representative of the effective operational energy loss Df in [Fig.3], but is equal to the zero value in [Fig.4].

[0143] Finally in zone 4, a graphic button B3 allows you to view a graphic in waterfall showing average percentages of energy lost or gained per day, over all days of the selected section of the journey, whether the liquefaction system is active or not.On this waterfall graph, the third location of the graph dedicated to an active operational performance will provide a first data item representative of an effective operational energy loss Df over all the time intervals for which the liquefaction system was active, and the fifth location of the graph dedicated to a passive operational performance will provide a second data item representative of an effective operational energy loss Df over all the time intervals for which the liquefaction system was active and inactive, this second representative data item being obtained by adding the data item representative of the energy saved by reliquefaction over the entire portion of the journey, to the first data item representative of an effective operational energy loss Df.

[0144] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, the characteristics of the different embodiments or variants of the invention envisaged in this application can be combined to achieve the invention, to the extent that these embodiments or variants are not incompatible with each other.

Claims

Claims

1. Method for determining (10) data representative of operational energy losses (Df, Ds) over a time interval, of a ship (40) for transporting liquefied gas, this energy being initially stored in the form of liquefied gas and evaporated gas in at least one tank (42) of the ship (40), the ship (40) being equipped with a system for liquefying the evaporated gas, the determination method (10) comprising steps of: - calculation (12) of a first data item (Dl) representative of a quantity of energy consumed over the time interval, as a function of at least one measurement relating to the activity of at least one consumer (44) of energy of the ship (40), - calculation (14) of a second data item (D2) representative of a variation in energy of the liquefied gas present in the tank, as a function of a variation in temperature of the liquefied gas in the tank (42) over the time interval, - addition (16) of the second data (D2) to the first data (Dl) resulting in data representative of an effective operational energy loss (Df) in the ship (40), the determination method (10) being characterized in that it further comprises, when the liquefaction system is activated over the time interval: - a step of calculating (18) a third data item (D3) representative of a quantity of energy saved by the liquefaction system over the time interval, and - a step of adding (20) the third data (D3) to the data representative of an effective operational energy loss (Df), resulting in data representative of an estimated operational energy loss (Ds) which would have been observed without the activation of the liquefaction system.

2. Method for determining (10) data representative of operational energy losses according to claim 1, in which the first, second and third data (Dl, D2, D3) as well as the data representative of an effective operational energy loss (Df) and the data representative of an estimated operational energy loss (Ds) each correspond to a ratio between on the one hand a quantity of energy lost over the time interval and on the other hand a quantity of energy of reference chosen from: - a quantity of energy calculated at the start of a period of use of the determination method (10), or - a quantity of energy loaded by the ship (40).

3. Method for supervising (11) operational data linked to at least one tank (42) of a ship (40) for transporting liquefied gas, characterized in that it implements the method for determining (10) data representative of operational energy losses according to claim 1 or 2, and in that it comprises a step of calculating (22) a fourth data item (D4) representative of a variation in the volume of liquefied gas in the tank (42) over the time interval.

4. Device (55) for determining data representative of operational energy losses, comprising means for implementing the determination method (10) according to claim 1 to 2, or the supervision method (11) according to claim 3.

5. System for determining (50) data representative of operational energy losses over a time interval, of a ship (40) for transporting liquefied gas, this energy being initially stored in the form of liquefied gas and evaporated gas in at least one tank (42) of the ship (40), the ship (40) being equipped with a system for liquefying the evaporated gas, the determination system (50) comprising: - first means for calculating a first data item (D1) representative of a quantity of energy consumed over the time interval, as a function of at least one measurement relating to the activity of at least one energy consumer (44) of the ship (40), - second means for calculating a second data item (D2) representative of a variation in energy of the liquefied gas present in the tank (42), as a function of a variation in temperature of the liquefied gas in the tank (42) over the time interval,- means for adding the second data item (D2) to the first data item (Dl), delivering data representative of an effective operational energy loss (Df) in the ship (40), the determination system (50) being characterized in that it further comprises: - third means for calculating a third data item (D3) representative of a quantity of energy saved by the liquefaction system over the time interval, when the liquefaction system is activated over the time interval, and, - means for adding the third data (D3) to the data representative of an effective operational energy loss (Df), delivering, when the liquefaction system is activated over the time interval, data representative of an estimated operational energy loss (Ds) which would have been observed without the activation of the liquefaction system.

6. Determination system (50) according to the preceding claim, comprising a human-machine interface comprising display means (58) capable of providing a representation of the first, second and third data (Dl, D2, D3), as well as data representative of the actual (Df) and estimated (Ds) operational energy losses, in which the data representative of an actual operational energy loss (Df) is displayed in the form of a sum between the first and second data (Dl, D2) and, when the liquefaction system is activated over the time interval, the data representative of an estimated operational energy loss (Ds) is displayed in the form of a cumulative total of the third data (D3) and the data representative of the actual operational energy loss (Df).

7. Determination system (50) according to the preceding claim, wherein the representation is a waterfall graph (4).

8. Determination system (50) according to the preceding claim, in which the display means (58) are capable of representing the data representative of the actual operational energy loss (Df) in a first location of the waterfall graph (4) when the liquefaction system is activated over the time interval, or in a second location of the waterfall graph (4), distinct from the first location, when the liquefaction system is deactivated over the time interval, the data representative of an estimated operational energy loss (Ds) being represented by the display means (58) at the second location when the liquefaction system is activated over the time interval.

9. Determination system (50) according to any one of claims 6 to 8, in which the human-machine interface of the determination system (50) further comprises means (1) for selecting at least a portion of a journey made by the ship (40), and means (B1) for selecting first time intervals during which the liquefaction system was activated on this portion of journey, the display means (58) being capable of representing when the first time intervals are selected by a user of the determination system (50): - an average of first data (Dl) delivered by the first calculation means for each of the first time intervals, - an average of second data (D2) delivered by the second calculation means for each of the first time intervals, - an average of data representative of effective operational energy losses (Df) delivered by the addition means for each of the first time intervals, - an average of third data (D3) delivered by the third calculation means for each of the first time intervals, and - an average of data representative of estimated operational energy losses (Ds) delivered by the addition means for each of the first time intervals.

10. Determination system (50) according to the preceding claim, in which the human-machine interface of the determination system (50) further comprises means (B2) for selecting second time intervals during which the liquefaction system was deactivated on this portion of the journey, the display means (58) being capable of representing when the second time intervals are selected by a user of the determination system (50): - an average of first data (D1) delivered by the first calculation means for each of the second time intervals, - an average of second data (D2) delivered by the second calculation means for each of the second time intervals, and - an average of data representative of operational losses of effective energy (Df) delivered by the addition means for each of the second time intervals.

11. Determination system (50) according to any one of claims 6 to 10, in which the human-machine interface further comprises means for selecting at least one tab linked to an operational data item relating to the liquefied, evaporated, reliquefied or consumed gas in the tanks (42), capable of causing the display means (58) to display a graph (3) of values ​​corresponding to the selected tab, the values ​​being those of the operational data item over one or more time intervals and being recorded in a memory of the determination system (50).

12. System for monitoring operational data linked to at least one tank (42) of a liquefied gas transport vessel, characterized in that it comprises the system for determining (50) data representative of operational energy losses according to any one of claims 5 to 11, and in that it comprises means for calculating a fourth data item (D4) representative of a variation in the volume of liquefied gas in the tank (42) over the time interval.

13. A computer program comprising program code instructions for performing the steps of the determining method (10) according to claim 1 or 2, when said program is executed on one or more processors.