Determination of operating energy losses in liquefied gas carriers

Abstract

The present invention relates to a method (10) for determining the operational energy loss (Df, Ds) over time intervals for a liquefied gas carrier equipped with a liquefaction system, the method comprising: (12) calculating the amount of energy consumed by the ship's energy consumption devices; (14) calculating the energy fluctuation (D2) as a function of temperature fluctuations of the liquefied gas; (16) adding the energy fluctuation (D2) to the amount of energy consumed (D1) to generate the actual operational energy loss (Df); and, if the liquefaction system is operating over time intervals, the method comprising: (18) calculating the amount of energy saved by the liquefaction system; and (20) adding the energy saved (D3) to the actual operational energy loss (Df) to generate the estimated operational energy loss (Ds) that would have been observed if the liquefaction system had not been operating.

Description

[Technical Field]

[0001] The present invention relates to the field of liquefied gas carriers, particularly methane tankers, and to equipment for monitoring energy consumption in such vessels. More specifically, the present invention relates to a method for determining data representing operational energy losses in such vessels. [Background technology]

[0002] Such vessels have cargo holds designed to accommodate one or more tanks for transporting gas in liquid form, with capacities ranging from several thousand cubic meters to tens of thousands of cubic meters. In the case of natural gas, the latter is held in the tanks at atmospheric pressure and approximately -163°C. Thus, the tanks are sealed and insulated by a double layer of insulation. However, liquefied natural gas (LNG) tends to evaporate despite the double insulation due to factors such as a drop in gas pressure within the tank and heat flow through the tank walls, so the upper part of each tank, the so-called upper tank space, is filled with gas in vapor form. The latter is generally used as fuel for one or more engines of the vessel. Gas in vapor form that is not used and cannot be held in the tanks is either burned via flares and then released into the atmosphere, or rarely released as is, or reliquefied by the vessel's (re)liquefaction system, the so-called liquefaction system in this application, and returned to the tanks in liquid form at -163°C. Thus, this liquefaction system consumes energy to operate, while enabling the saving of gas, and therefore energy, that would otherwise be lost.

[0003] Estimating the energy balance of the operational losses of liquefied gases during a ship's voyage, the so-called operational BOR (short for "Boil-Off Rate"), is difficult. It particularly depends on the consumption by the ship's engines that reduce the pressure in at least one tank, weather conditions (temperature, swell), the heat resistance of the tanks, and the efficiency of the liquefaction system. Severe weather conditions can cause significant motion in the ship and, therefore, in the liquefied gases in the tanks, which leads to greater evaporation of the liquefied gases than when the ship is sailing in calm waters.

[0004] However, shipowners of such vessels want to know the precise performance of their ships in terms of energy losses during operation, particularly for reasons related to contractual guarantees.

[0005] Currently, shipowners evaluate operational performance using the decrease in the volume of liquefied gas in the tanks, but this method is inaccurate due to fluctuations in the movement of the liquid in the tanks caused by the movement of the ship itself. In addition, this decrease does not distinguish energy losses caused by gas consumption by the ship's engines from other losses.

[0006] Furthermore, the operational performance that is of interest to shipowners should take into account the optimal operating conditions of the vessel, particularly the ship's liquefaction system. However, this liquefaction system, which consumes energy itself, does not always operate during a ship's voyage, and therefore, operational performance measured by methods based on volume fluctuations does not necessarily represent the operational performance that the ship will achieve.

[0007] Prediction methods can provide operational performance that considers the optimal operating conditions for a vessel by using the estimated energy consumption of a vessel at sea as a function of various usage scenarios. However, these prediction methods are complex and ultimately not very accurate, resulting in an insufficient evaluation of the operational performance that a vessel will achieve, and a loss of interest and confidence in the data provided by these methods.

[0008] Therefore, in order to understand the differences in operational performance as a function of the ship's operating conditions, it is necessary to provide accurate operational performance data for liquefied gas carriers equipped with liquefaction systems. [Overview of the project]

[0009] The present invention aims to overcome, at least partially, the shortcomings of the prior art by providing a method for determining data representing the operational energy loss over a certain time interval in a liquefied gas carrier, a corresponding determination apparatus and system, and a computer program, thereby enabling accurate comparison between the active operational performance corresponding to the operating mode of a vessel with the liquefaction system in operation and the passive operational performance corresponding to the operating mode of a vessel with the liquefaction system stopped.

[0010] For this purpose, the present invention provides a method for determining data representing the operational energy loss of a liquefied gas carrier over a certain time interval, wherein this energy is initially stored in the form of liquefied gas and evaporated gas in at least one tank of the vessel, and the vessel is equipped with a system for liquefying evaporated gas, and the determination method is as follows: - A step of calculating first data representing the amount of energy consumed over a time interval as a function of at least one measurement related to the activity of at least one energy-consuming device of the ship, - A step of calculating a second data representing the energy fluctuation of the liquefied gas present in the tank as a function of the temperature fluctuation of the liquefied gas in the tank over a time interval, - The second data is added to the first data to generate data representing the actual operating energy loss on board the vessel. The determination method includes, if the liquefaction system operates over a time interval, - A step of calculating a third data representing the amount of energy saved by the liquefaction system over a time interval, - The third step involves adding the data representing the actual operational energy loss to generate data representing the estimated operational energy loss that would have been observed if the liquefaction system had not been operating. It is characterized by further including the following.

[0011] In this determination method according to the present invention, the first data is a function of one or more measurements, each related to one or more consuming devices of a ship, such as multiple motors, to calculate all the energy consumed by the ship's consuming devices. The measurements are provided by one or more sensors, such as flow meters in the supply piping of the ship's engines.

[0012] Furthermore, if a ship has multiple tanks, the second data point corresponds to the energy fluctuations associated with temperature variations of the liquefied gas in all tanks, and this can be a positive or negative value. In fact, if a ship consumes a large amount of evaporated gas, the pressure of the liquefied gas may decrease, which lowers the temperature of the LNG. In this case, the LNG supplies energy corresponding to a negative second data point. Conversely, if the consumption of evaporated gas is low, the pressure of the liquefied gas may increase, and therefore the temperature of the liquefied gas increases, resulting in the LNG absorbing energy, which corresponds to a positive second data point. Finally, the third data point corresponds to the energy saved in all tanks by the liquefaction system.

[0013] For example, the time intervals over which the first, second, and third data are calculated may correspond to one day or one hour, but these intervals may also be adjusted over the shortest time interval during which the liquefaction system is operating or stopped. In fact, it should be noted that the calculation of the third data and the estimated operating energy loss can also be performed when the liquefaction system is stopped, in which case the third data will simply have a value of zero and the estimated operating energy loss will be equal to the actual operating energy loss.

[0014] As a result of the determination method according to the present invention, the data representing operational energy loss is far more accurate than that of the prior art. In particular, in the calculation of the first data representing the energy consumed by the ship's consuming equipment, measured values ​​are used, and by integrating these measured values ​​over time intervals, it is possible to determine the actual mass of gas leaking from the tank. In contrast, the prior art estimation of mass loss, which is calculated from the results of volume fluctuations, is highly inaccurate because it is biased by the mathematically estimated volume and density data due to the movement of the liquid.

[0015] Furthermore, this determination method makes it possible to compare the actual operating energy loss corresponding to active operating performance and operating modes in which the liquefaction system is active with the estimated operating energy loss corresponding to passive operating performance and operating modes in which the liquefaction system is shut down. This comparison is highly accurate because it is based on the amount of energy saved by the liquefaction system, and its value is precisely calculated based on measured mass rather than estimation. Thus, passive operating performance is estimated in a highly reliable manner, thereby enabling users of the determination method according to the present invention to assess the operating performance that a vessel can actually achieve and to encourage the vessel to operate the liquefaction system more frequently, thus saving energy throughout the vessel's voyage. This method differs from prior art, which is highly unreliable because operating performance under unmet operating conditions is predicted based on estimates of energy savings or energy losses. In particular, estimation of volume loss based on the liquid level in the vessel's tanks is highly unreliable, especially due to the movement of the vessel.

[0016] In one embodiment, the vessel is equipped with a liquefied gas vaporizer, and the method for determining data representing operational energy loss further includes the steps of calculating a fifth data representing the amount of energy of the liquefied gas that is pumped from a tank and planned to pass through the vaporizer over a time interval, and subtracting the fifth data from data representing the actual operational energy loss.

[0017] In another embodiment, the method for determining data representing operating energy losses includes further steps of calculating sixth data representing energy fluctuations in the gas phase of the liquefied gas present in the tank as a function of pressure fluctuations and temperature fluctuations in the tank over a time interval, and adding the sixth data to the data representing the actual operating energy losses.

[0018] In one embodiment of the present invention, each of the first, second, third, fifth, and sixth data, and the data representing the actual operating energy losses and the data representing the estimated operating energy losses, on the one hand, are related to the amount of energy lost over a time interval, and on the other hand, - the amount of energy calculated at the start of the period of use of the determination method, or - the amount of energy loaded onto the ship correspond to the ratio to a reference energy amount selected from either of these.

[0019] The amount of energy loaded onto the ship corresponds to the energy contained immediately after the ship's tanks are filled. Of course, other reference energy amounts can be used. For example, the selected reference energy amount is the amount of energy represented by the liquefied gas loaded onto the ship when the liquefied gas loaded onto the ship is loaded at a predefined percentage of its total loading capacity, such as 100%, 95%, or 90%.

[0020] By using this ratio, the user of the determination method according to the present invention can better grasp the operating energy losses over a time interval.

[0021] Preferably, the determination method according to the present invention includes an additional step of rendering the first, second, and third data, and the data representing the actual operating energy losses and the data representing the estimated operating energy losses, on a human - machine interface. For example, such rendering consists of display on the screen of the interface.

[0022] The present invention also relates to a method for monitoring operating data related to at least one tank of a liquefied gas carrier, characterized by implementing a method for determining data representing the operating energy losses according to the present invention and including a step of calculating fourth data indicating the volume variation of the liquefied gas in the tank over a time interval.

[0023] This last calculation enables the user of the monitoring method according to the present invention to compare the estimated values provided by the prior art with the estimated operating energy losses according to the present invention. This shows the variability of this prior art estimate when compared with the data representing the estimated operating energy losses.

[0024] The present invention also relates to a device for determining data representing operating energy losses, comprising means for implementing the determination method according to the present invention. The determination device implements the determination method according to the present invention in hardware and / or software. The determination device is adapted to collect measurement data from sensors and to enable the implementation of the various steps of the determination method according to the present invention. Thus, it consists, for example, of a shipboard computer, or a computer connected to the ship, or a remote server adapted to receive these data.

[0025] The present invention also relates to a determination system for data representing the operating energy losses of a liquefied gas carrier over a certain time interval, this energy being initially stored in the form of liquefied gas and vapor gas in at least one tank of the ship, the ship being equipped with a vapor gas liquefaction system, and the determination system - first means for calculating first data representing the amount of energy consumed over a time interval as a function of at least one measurement related to the activity of at least one energy-consuming device of the ship; - second means for calculating second data representing the energy variation of the liquefied gas present in the tank as a function of the temperature variation of the liquefied gas in the tank over a time interval; - means for adding the second data to the first data to generate data representing the actual operating energy losses in the ship The decision system includes, - A third means for calculating third data representing the amount of energy saved by the liquefaction system over a time interval when the liquefaction system is operating over a time interval, - An adding means for adding a third data to data representing actual operational energy loss, wherein when the liquefaction system is operating over a time interval, the adding means generates data representing the estimated operational energy loss that would have been observed if the liquefaction system had not been operating. It is characterized by further including the following.

[0026] The decision system according to the present invention is implemented by hardware and / or software. The means of the decision system according to the present invention enable the latter to implement the decision method according to the present invention. Thus, the decision system according to the present invention is, for example, identical to the decision device according to the present invention, or comprises a plurality of remote physical entities, for example, it is formed by a remote server adapted to receive data by and from the ship's onboard computer and, optionally, from terminals connected to this remote server. The remote server may be formed by a plurality of computers connected to each other by one or more communication networks. In another example, the decision system according to the present invention comprises only an onboard computer and terminals connected to this onboard computer. The decision system according to the present invention may further comprise sensors such as a temperature sensor for measuring the temperature of liquefied gas or a flow meter that enables measuring the gas consumption of one or more consuming devices of the ship.

[0027] In one embodiment of the present invention, a ship is equipped with a liquefied gas vaporizer, and the determination system further comprises a fifth means for calculating a fifth data representing the amount of energy of the liquefied gas that is pumped from a tank and planned to pass through the vaporizer over a time interval, and an additional means for subtracting the fifth data from data representing the actual operational energy loss.

[0028] In another embodiment of the present invention, the determination system may further include a sixth means for calculating a sixth data representing the energy fluctuations of the gas phase of the liquefied gas present in the tank as a function of pressure and temperature fluctuations in the tank over a time interval, and an additional means for adding the sixth data to data representing the actual operational energy loss.

[0029] According to preferred features of the determination system according to the present invention, the latter comprises a human-machine interface equipped with display means adapted to provide representations of first, second, third, fifth, and sixth data, as well as data representing actual and estimated operational energy losses, wherein the data representing actual operational energy losses is visualized as the sum of at least two of the first, second, fifth, and sixth data, and as the liquefaction system operates over a time interval, the data representing estimated operational energy losses is visualized in the form of an accumulation of the third data and the data representing actual operational energy losses. In other words, the human-machine interface is adapted to perform an additional step of visually rendering the determination method according to the present invention.

[0030] In one embodiment of the present invention, the representation is a waterfall chart. Such charts are suitable for rendering mathematical relationships between rendered data in an intuitively understandable manner. Of course, one variation may use means such as a table of values, a conventional histogram, or a pie chart.

[0031] In this embodiment of the present invention, the display means is adapted to show data representing the actual operating energy loss at a first position on the waterfall chart when the liquefaction system is operating over a time interval, or at a second position different from the first position on the waterfall chart when the liquefaction system is stopped over a time interval, wherein the data representing the estimated operating energy loss is shown by the display means at the second position when the liquefaction system is operating over a time interval.

[0032] In this embodiment, it is possible to always reserve a first position on the graph for active operation performance and a second position for passive operation performance. In other words, this allows users of the decision system according to the present invention to easily correlate actual operation energy loss with the operating status or shutdown status of the liquefaction system.

[0033] In this embodiment, the rendering of data relates to a time interval or an average value between time intervals. In particular, in this embodiment, the human-machine interface of the decision system according to the present invention further comprises means for selecting at least a portion of the voyage undertaken by the vessel, and means for selecting a first time interval in which the liquefaction system was operated throughout this portion of the voyage, and display means when the first time interval is selected by the user of the decision system, - The average values ​​of the first, second, fifth, and sixth data provided by the means for calculating the data at each first time interval, - The average value of data representing the actual operational energy loss provided by the summing means at each first time interval, - The average value of the third data provided by the third calculation means at each first time interval, - The average value of data representing estimated energy loss provided by the summing means at each first time interval. It will be adapted to display.

[0034] In this embodiment of the present invention, the human-machine interface of the decision system according to the present invention further comprises means for selecting a second time interval in which the liquefaction system was stopped throughout the partial voyage, and display means for when the second time interval is selected by the user of the decision system. - The average values ​​of the first, second, fifth, and sixth data provided by the means for calculating the data at each second time interval, - The average value of data representing the actual operational energy loss, provided by the summing means at each second time interval. The display is adapted to show the following: For example, the means for selecting a first or second interval is a graphical button or graphical tab on a graphical interface rendered by the display means.

[0035] In this embodiment, the rendering of complementary monitoring data allows users of the decision system according to the present invention to correlate with more data in order to better understand the trends in operational energy loss rendered by the human-machine interface. Accordingly, in this embodiment, the human-machine interface includes means for selecting at least one tab relating to operational data concerning liquefied gas, evaporated gas, reliquefied gas, or consumed gas in the tank, and is adapted to display a graph of values ​​corresponding to the selected tab on a display means, where these values ​​are operational data values ​​over one or more time intervals and are recorded in the memory of the decision system. For example, operational data may include: - Flow rate of evaporated gas sent to the liquefaction system over time - Cumulative mass of gas lost over time - Mass of non-cumulative gas lost over time - Density of liquefied gas in the tank over time - Temperature of liquefied gas in the tank over time - Pressure of gas evaporated in the tank over time - Volume of liquefied gas over time - Ship speed over time Select from the following items.

[0036] These data may be instantaneous or related to a predefined time interval.

[0037] The present invention also relates to a monitoring system for operational data relating to at least one tank of a liquefied gas carrier, characterized by comprising a data determination system representing operational energy loss according to the present invention, and means for calculating a fourth data representing volume fluctuations of liquefied gas in the tank over a time interval. Preferably, the display means of the determination system according to the present invention is identical to the display means of the monitoring system according to the present invention, and therefore also renders the fourth data representing energy loss in the tank over a time interval under consideration.

[0038] Finally, the present invention relates to a computer program, and if the program is executed on one or more processors, the program includes program code instructions that perform steps of the determination method according to the present invention.

[0039] The computer program, when executed on a decision device according to the present invention equipped with this processor, runs on a single processor. It runs on multiple processors, for example, in a decision system according to the present invention, where the decision system according to the present invention is composed of multiple remote physical entities, each entity equipped with one of these processors, in particular, the calculation step of the decision method according to the present invention is performed, for example, on a remote server or a computer on board a ship, and the rendering step is performed on a terminal connected to the remote server or the computer on board.

[0040] It should also be noted that the determination method according to the present invention may be performed dynamically during the ship's voyage or statically after the ship has arrived at its destination. Therefore, if the calculation steps of the determination method according to the present invention are performed on a remote server of the determination system according to the present invention, the remote server shall include means for wireless communication with the ship's onboard computer, such as satellite internet communication means, in order to dynamically render data representing the ship's operational energy loss. These wireless communication means may be replaced by data transfer via a physical medium such as a data storage flash drive if rendering is performed only after the ship has arrived at its destination.

[0041] The decision device, decision system, monitoring system, and computer program according to the present invention include similar advantages to the decision method and monitoring method according to the present invention.

[0042] Other features and advantages of the present invention will become more apparent, on the one hand, through the following description and on the other hand, from several embodiments given for non-limiting illustrative purposes with reference to the accompanying schematic diagrams. [Brief explanation of the drawing]

[0043] [Figure 1] One embodiment of the present invention includes steps of a method according to the present invention for determining data representing the operational energy loss over time intervals in a liquefied gas carrier, and steps of a monitoring method for implementing this determination method in this embodiment of the present invention. [Figure 2] This illustrates a decision system according to the present invention, and in this embodiment of the present invention, it comprises means adapted to carry out a decision method according to the present invention. [Figure 3] In this embodiment of the present invention, a graphical interface is shown that enables rendering of data determined by the method in Figure 1 when a ship's liquefaction system operates over a time interval. [Figure 4] Figure 3 shows a graphical interface for when a ship's liquefaction system is shut down over a period of time. [Modes for carrying out the invention]

[0044] In one embodiment of the present invention shown in Figures 1 to 4, the determination method 10 shown in Figure 1 makes it possible to provide data representing the operational energy losses Df, Ds of the vessel 40 shown in Figure 2 over a certain time interval. This determination method 10 is part of a more general method 11 for monitoring operational data related to the tanks 42 of the vessel 40. For example, the selected or predefined time interval is one day, one hour, or a shorter or longer time interval. For example, the time interval corresponds to the period required for the vessel to perform a voyage or partial voyage, as selected by the user of the determination method 10. The vessel 40 is a liquefied gas carrier, and in this embodiment of the present invention, this gas is liquefied natural gas. However, in one variation, this gas is, for example, liquid hydrogen or another type of gas.

[0045] The vessel 40 stores liquefied gas in sealed, insulated tanks 42 at -163°C and near atmospheric pressure. Each tank 42 is filled with liquefied gas up to a liquid level indicated by reference numeral 46, and the space in the tank above this liquid level 46 is called the upper tank space and is filled with evaporated gas. The amount of liquefied gas present in liquid and gaseous forms in the tanks 42 of the vessel 40 represents the amount of energy transported by the vessel 40. This amount of energy decreases as the vessel progresses at sea, due to gas consumption by the vessel's consuming equipment, gas loss due to evaporation, and energy loss associated with fluctuations in the pressure and temperature of the liquefied natural gas, which can be due to various causes such as swells, weather, the heat resistance of the tanks, and gas draw-in by the vessel 40's consuming equipment. Nevertheless, the vessel 40 is equipped with a liquefaction system that allows for the liquefaction of some of the evaporated gas in the upper tank space, thus saving gas loss.

[0046] The determination method 10 according to the present invention is: -This enables the determination of data representing the actual operational energy loss Df, which corresponds to the actual energy loss within a time interval relative to the reference energy described below. In this embodiment of the present invention, this data representing the actual operational energy loss Df is calculated regardless of whether the liquefaction system is operating over the time interval. This time interval may be modified to correspond to a single operating state or a single stopped state of the liquefaction system. -The data representing the estimated operational energy loss Ds is calculated only when the liquefaction system is operating over a time interval, and corresponds to the energy loss over that time interval that would have been observed if the liquefaction system had not been operating over that time interval; this energy loss is also related to the reference energy.

[0047] In this embodiment of the present invention, the determination method 10 is performed by hardware and / or software in a determination system 50, referenced in Figure 2, which represents the operational energy losses Df, Ds described herein, and the steps of the determination method 10 enable the acquisition of data representing the operational energy losses Df, Ds, which will be described later. The determination system 50 is part of a more general system for monitoring operational data related to the tanks of a ship and implements the monitoring method 11 according to the present invention by hardware and / or software.

[0048] The decision system 50 includes an onboard computer 52 that receives measurements from various sensors present within the ship 40, particularly from a temperature sensor 54 that measures the temperature of liquefied gas in a tank 42, and at least one mass flow meter 56 that measures the mass of gas supplied to the ship's consuming equipment over time intervals.

[0049] The determination system 50 also includes a remote server 55, represented as an internet "cloud" 60, which dynamically receives measurements from a temperature sensor 54 and a mass flow meter 56 transmitted by the onboard computer 52 in message m1. To transmit these measurements, the onboard computer 52 includes, for example, means for connecting to a satellite internet. To receive the measurements, the remote server 55 includes, for example, a wired internet connection. For example, the remote server 55 receives measurements from multiple gas carriers and stores them in a database 57. This includes calculation, addition, and summation means to perform the calculation steps of the determination method 10 according to the present invention, enabling the determination of data representing the operating energy losses Df, Ds of the vessel 40 over time intervals, as described later. These means include at least one processor of the server 55 adapted to read the data stored in the database 57.

[0050] The decision system 50 also includes a terminal 58, such as a laptop computer or a multimedia mobile phone, and is equipped with means for displaying data representing the operational energy losses Df, Ds provided by the remote server 55, and these display means particularly include a screen. In this use case of the present invention, the terminal 58 is on a ship 40, but the present invention can also be used on land. Thus, it sends a message m2 to the remote server 55 using satellite internet connectivity means, which includes a request to send data representing the operational energy losses Df, Ds over a time interval. Upon receiving message m2, the remote server 55 sends the data representing the operational energy losses Df, Ds to the terminal 58 in message m3.

[0051] Returning to Figure 1, the determination method 10 includes a first step 12 of calculating a first data D1 representing the amount of energy consumed over a time interval as a function of measurements provided by the mass flowmeter 56. This mass flowmeter 56 provides the total flow rate φ of gas consumption by the ship's consuming devices 44 shown in Figure 2, including the main engine of the ship 40, the auxiliary engine of the ship 40, and flares used to burn unrecovered evaporated gases when the liquefaction system is stopped. Alternatively, multiple mass flowmeters, e.g., one for each consuming device, may be used.

[0052] It should be noted that using a mass flow meter in the consuming device to estimate the mass of gas consumed is more accurate than observing the difference in liquid level over time. In fact, measuring the liquid level can be very noisy due to the movement of the liquid in tank 42.

[0053] When using embodiments of the present invention, the first data D1 is the percentage of energy consumed in a day, and is calculated by the first calculation means of the server 55 as follows.

[0054]

number

[0055] Here -* is the multiplication operator. -t is the duration of the time interval in days. -t1 is the start of the time interval -t2 is the end of the time interval. -φ is the flow rate in kilograms / day supplied by the mass flowmeter 56. -L hv This represents the average value of the latent heat of vaporization of the gas in kilojoules / kilogram at the start and end of the time interval. -N is the reference energy in kilojoules. That is the case.

[0056] For example, the reference energy N is the amount of energy exhibited by the liquefied gas in the tank 42 at the start of the usage period of the determination method 10, which is the same as or earlier than the energy exhibited at the start of the time interval. N=d1*V1*L1 Here, -d1 is the density in kilograms / cubic meter of liquefied gas in tank 42 at the start of the usage period of determination method 10. -V1 is the volume in cubic meters of liquefied gas in the tank 42 at the start of the usage period of the determination method 10. -L1 is the latent heat of vaporization in kilojoules / kilograms of the liquefied gas in tank 42 at the start of the usage period of determination method 10. That is the case.

[0057] Alternatively, the reference energy N can be considered to be equal to the amount of energy stored in tank 42 immediately after filling of tank 42.

[0058] N = d2 * V2 * L2 Here, -d2 is the density in kilograms / cubic meter of liquefied gas in tank 42 immediately after filling. -V2 is the volume in cubic meters of liquefied gas in tank 42 immediately after filling. -L2 is the latent heat of vaporization in kilojoules / kilogram of the liquefied gas in tank 42 immediately after filling. That is the case.

[0059] In yet another variant, if the liquefied gas is pure methane, the reference energy N is considered to be equal to the amount of energy loaded into tank 42 immediately after filling tank 42. N = dm * V2 * Lm Here, -dm represents the density of pure methane in kilograms per cubic meter. -Lm is the latent heat of vaporization of pure methane in kilojoules / kilogram. That is the case.

[0060] It should be noted that in this embodiment, “pure methane” means a gas formed solely from methane, taking impurities into consideration, rather than from a mixture of methane and another gas, such as propane.

[0061] This final variant has the advantage of not depending on the reference energy during the measurement period, but only on the volume of liquefied gas initially loaded onto the ship.

[0062] The second step of the determination method 10 is step 14 to calculate a second data D2 that represents the energy fluctuations associated with the temperature fluctuations of the liquefied gas present in the tank 42, as a function of the temperature fluctuations of the liquefied gas in the tank 42 measured over a time interval.

[0063] This second data point, D2, reflects the energy fluctuations associated with temperature changes within tank 42. When the temperature decreases (for example, due to a decrease in pressure), the energy fluctuations correspond to the amount of energy supplied by the LNG, and when the temperature increases, the energy fluctuations correspond to the amount of energy absorbed by the LNG.

[0064] When using this embodiment of the present invention, the second data D2 is the percentage of energy stored or consumed on the day under consideration, calculated by the second calculation means of the server 55 as follows:

[0065]

number

[0066] Here, -df is the density of liquefied gas in tank 42 in units of kilograms per cubic meter at the end of the time interval. -Vf is the volume in cubic meters of liquefied gas in tank 42 at the end of the time interval. -Cp is the average value of the specific heat (also called specific heat capacity) of the liquefied gas in kilojoules per kilogram of temperature at the beginning and end of the time interval. -T2 is the average value of the temperature measurements in degrees Celsius of the liquefied gas in tank 42 at the end of the time interval. -T1 is the average value of the temperature measurement in degrees Celsius of the liquefied gas in tank 42 at the start of the time interval. That is the case.

[0067] Alternatively, the second data D2 is calculated by summing the energy proportions associated with the temperature fluctuations of the liquefied natural gas, and thus the energy accumulated or lost over a time interval, with these proportions calculated individually for each tank 42. Temperature measurements at the beginning of the time interval and at the end of the time interval are averaged for each tank 42 to obtain data representing the temperature in the tank at the beginning or end of the time interval. Different temperature measurements in one of the tanks 42 at a given point in time are averaged and correspond, for example, to measurements from different temperature sensors spaced along the liquefied gas unloading mast present in each tank 42.

[0068] The third step of the determination method 10 is step 16 of adding the second data D2 to the first data D1, which generates data representing the actual operating energy loss Df in the vessel 40 over a time interval, and the addition step is carried out by the adding means of the server 55 as follows:

[0069] Df = D1 + D2 When using this embodiment of the present invention, the data representing the actual operational energy loss Df corresponds to the ratio of lost energy to the reference energy on the day considered. It corresponds to active operational performance if the liquefaction system was operating on that day, and to passive operational performance if the liquefaction system was shut down on that day.

[0070] The fourth step of the determination method 10 is step 18 of calculating a third data D3 representing the amount of energy saved by the liquefaction system over a time interval. In this use of the present invention, it is assumed that the liquefaction system was operating over a time interval and was therefore able to avoid the loss of a mass of evaporated gas in the tank 42 exceeding the demand of the consumption device 44 by reliquefaction. Otherwise, this mass would likely have been burned by a flare. The fourth step of the determination method 10 is carried out by a third calculation means of the server 55.

[0071] When using this embodiment of the present invention, the third data D3 is the percentage of energy saved on the day considered.

[0072]

number

[0073] Here,

[0074]

number

[0075] This is the daily mass flow rate in kilograms of reliquefied gas by the liquefaction system. This value can be provided by a flow meter connected to the liquefaction system.

[0076] The fifth step of the determination method 10 is step 20, which adds a third data D3 to the data representing the actual operating energy loss Df, providing data representing the estimated operating energy loss Ds, and the fifth step of the determination method 10 is performed by the addition means of the server 55.

[0077] Ds = D3 + Df Therefore, the data representing the estimated operational energy loss Ds corresponds to an estimate of the operational energy loss that would have occurred in one day if the liquefaction system had not been operational. Thus, this corresponds to the passive operational performance estimated retrospectively.

[0078] When used when the liquefaction system is stopped, D3=0=>Ds=Df This is the result.

[0079] Therefore, in the latter case, the data representing the estimated operational energy loss Ds corresponds to the data representing the actual operational energy loss Df, and is no longer an estimate.

[0080] In the case of a vessel 40 equipped with a liquefied gas vaporizer, the method for determining data representing operational energy loss may further include the optional step of calculating a fifth data D5 representing the amount of energy of the liquefied gas that is pumped from the tank and planned to pass through the vaporizer over a time interval, and the step of subtracting the fifth data D5 from data representing the actual operational energy loss Df.

[0081] The fifth data point, D5, corresponds to "Forced BOR." This consists of the amount of energy associated with the mass of the liquefied gas being pumped from the tank and guided through the vaporizer, and is calculated by the fifth calculation means of server 55 as follows:

[0082]

number

[0083] Here -* is the multiplication operator. -t is the duration of the time interval in days. -t1 is the start of the time interval -t2 is the end of the time interval. -Φ is the flow rate in kilograms / day provided by the mass flow meter downstream of the vaporizer. -L hv_LGThis represents the average value of the latent heat of vaporization in kilojoules / kilograms of the liquefied gas at the start and end of the time interval. -N is the reference energy in kilojoules, as explained above. That is the case.

[0084] A method for determining data representing operational energy loss may also include the optional step of calculating a sixth data point D6 representing the energy fluctuations of the gas phase of the liquefied gas present in the tank as a function of pressure and temperature fluctuations within the vessel over a time interval, and adding the sixth data point D6 to data representing the actual operational energy loss Df.

[0085] The sixth data point, D6, corresponds to the "ballast BOR" or "pressure BOR." This is an amount of energy related to the gas phase of the liquefied gas present in the tank, and which fluctuates as a function of the pressure and temperature in the tank over time intervals. As a non-limiting example, this can be calculated by the sixth calculation means of server 55 as follows:

[0086]

number

[0087] △mp represents the mass of evaporated gas that contributes to the pressure increase in the tank, and can be determined based on the law of ideal gases.

[0088]

number

[0089] Here -* is the multiplication operator. -t is the duration of the time interval in days. -t1 is the start of the time interval -t2 is the end of the time interval. -d is the average density in kilograms / cubic meter of liquefied gas in tank 42 over a time interval t. -V is the average volume in cubic meters of the liquefied gas in tank 42 over the time interval t -L hv is the average value of the latent heat of vaporization of the gas in kJ / kg at the start and end of the time interval (L hv (t1), L hv (t2) corresponds to the latent heat of vaporization of the gas at time points t1 and t2 respectively) -R is the universal gas constant of an ideal gas -P(t1), P(t2) are the pressures in the tank at time points t1 and t2 respectively -V BOG (t1), V BOG (t2) is the volume of the gas evaporated in the tank at time points t1 and t2 -T BOG (t1), T BOG (t2) is the temperature of the gas evaporated in the tank at time points t1 and t2 -M BOG (t1), M BOG (t2) is the molar mass of the gas evaporated in the tank at time points t1 and t2 is.

[0090] The calculation of the sixth data D6 contributes to a more accurate determination of the operating energy loss over the selected time interval. The sixth data D6 takes into account the pressure fluctuations in the tank, which may indicate a non-negligible mass loss, especially when the amount of gas in the tank is large during ballast voyages.

[0091] In parallel with these first five steps and the optional steps of the determination method 10 according to the invention, the monitoring method 11 according to the invention performs an additional step 22 of calculating a fourth data D4 representing the energy loss in tank 42 as a function of the volume variation of the liquefied gas over a time interval.

[0092] When using an embodiment of the present invention, D4 is the proportion of energy lost on the day considered and is calculated as follows,

[0093]

Equation

[0094] Here, Vi is the volume in cubic meters of liquefied gas in tank 42 at the start of the time interval.

[0095] Alternatively, D4 may be calculated by replacing the denominator Vi with the volume of liquefied natural gas immediately after loading onto the vessel, or with a predefined percentage, for example, the tank's filled volume at 95% or 98%.

[0096] This calculation yields the magnitude of the total energy loss in tank 42 over a time interval. In reality, this calculation is not accurate because the rate of liquefied gas evaporation depends heavily on the actions of the ship's crew. For example, if the crew decides to sail at high speed, the gas pressure in tank 42 will decrease, which may force the evaporation of the liquefied gas. This will result in a larger rate of liquefied gas evaporation. Conversely, if the crew slows down or the ship stops, the gas demands of different consuming devices will likely be much smaller than the gas released by evaporation from tank 42. Thus, the pressure in tank 42 will increase, and the rate of gas evaporation will decrease.

[0097] This is why the present invention takes into account temperature fluctuations of the liquefied gas, because these temperature fluctuations are closely related to the rate of gas evaporation. If the latter is very large, the temperature of the liquefied gas will almost certainly decrease. On the other hand, if the gas consumption is low, not only the gas pressure in the tank 42 but also the temperature of the liquefied gas should increase.

[0098] The sixth step of the determination method 10, which is common to the monitoring method 11, is step 24, which renders the previously calculated data D1, D2, D3, D4, Ds, Df (and optionally D5, D6) on a graphical interface displayed on the screen of the terminal 58. Of course, in other embodiments of the present invention, this rendering may be performed in other ways, for example, in text or audio format on the terminal 58 or another element of the determination system 50.

[0099] Steps 12–24 do not necessarily have to be performed in the order described, and it should be noted that the first step 12, the second step 14, the fourth step 18, and the sixth step 22 can be performed independently and in parallel with each other. Preferably, steps 12–22 are repeated to provide data corresponding to multiple time intervals, for example, they are performed at the end of each day of the voyage undertaken by the vessel 40.

[0100] Finally, the determination method according to the present invention may include the step of applying a correction factor to one of the data provided by the calculation means in order to take into account relevant physical phenomena that may affect the calculation of the data. For example, in the case of a third data D3 representing the amount of energy saved by the liquefaction system over a time interval, a correction factor can be applied to take into account the fact that if the gas is returned to the tank after liquefaction, some of the liquefied gas may re-evaporate. This re-evaporation contributes to reducing the amount of energy actually saved by the liquefaction system. The correction factor makes it possible to take this effect into account. The effect of re-evaporation can be determined by calculations known to those skilled in the art. The correction factor may be compiled into a table based on calculations performed in advance as a function of the ambient parameters of the tank, or it may be calculated by a calculation means associated with the data when the ambient parameters of the tank are known.

[0101] Figure 3 shows a screenshot 30 of terminal 58, in which the graphical interface is divided into five areas 1 to 5.

[0102] Area 1 is a world map showing the voyage undertaken by ship 40. Graphical buttons on this map allow the user of decision method 10 to select the entire voyage or a portion of it.

[0103] Area 2 displays fixed data related to the voyage and the vessel 40, specifically the "id" field which contains the name of the vessel (in this example, "Messi"), the "ref" field which contains the voyage reference symbol (in this example, "Voyage"), the GPS ("Global Positioning System") coordinates of the departure and arrival points of the voyage, the corresponding distance, the departure and arrival dates, the number of voyage hours, the cargo load of the vessel 40, its density, and an indicator for a loaded voyage or a return voyage using ballast. If the vessel is on a loaded voyage, the indicator is set to "L".

[0104] Area 3 is equipped with graphical tabs that can be selected by the user. When a corresponding graphical tab is selected, a graph can be visualized on Area 3, and this graph is... - Flow rate v1 of evaporative gas in kilograms / hour sent to the liquefaction system over time - The cumulative mass of gas lost over time, v2, corresponds to data representing the actual operational energy loss calculated through a selected portion of the voyage, and is expressed in kilograms of gas, not as a percentage. - The mass flow rate of gas consumed over time v8, for example, data representing the actual operating energy loss calculated for each day of a selected portion of a voyage, expressed in tons per day rather than as a percentage. - Density v7 of liquefied gas in tank 42 over time - Temperature of liquefied gas in tank 42 over time v5 - Pressure v6 of the gas evaporated in tank 42 over time - The volume v4 of liquefied gas in tank 42 over time, and - Speed ​​of ship 40 over time v3 Display.

[0105] In screenshot 30, the user selected the tab corresponding to the flow rate v1 of evaporated gas sent to the liquefaction system through the selected partial voyage. In the graph corresponding to flow rate v1, the liquefaction system operating period, where the gas flow rate to the liquefaction system is not zero, is shown in gray. This is because, in area 4, the user selected graphical button B1 corresponding to the liquefaction system operating period through the selected partial voyage.

[0106] Area 4 includes Waterfall Chart G1, and Waterfall Chart G1 is, - The first histogram bar at the first position represents the mean of the first data D1, labeled "consumed BOR" or "mass BOR," calculated by the determination system 50 during the period when the liquefaction system was operational, for each day of the selected partial voyage. - The second histogram bar at the second position represents the average value of the second data D2, labeled "BOR due to LNG temperature fluctuations" or "rate due to ship adjustments," calculated by the determination system 50 during the period when the liquefaction system was operational, for each day of the selected portion of the voyage. - The sum of the mean values ​​shown in the first position and the mean values ​​shown in the second position, indicated by the third histogram bar in the third position, which is labeled as "Active BOR". -The fourth histogram bar at the fourth position represents the mean of the third data D3, labeled "Reliquefied BOR," calculated by the determination system 50 during the period when the liquefaction system was operational, for each day of the selected partial voyage. - The sum of the total value represented in the third position and the mean value represented in the fourth position, labeled "Passive BOR" by the fifth histogram bar in the fifth position. - The sixth histogram bar at the sixth position represents the average value of the fourth data point D4, labeled "Volume BOR," calculated by the monitoring system during the period when the liquefaction system was operational, for each day of the selected portion of the voyage. Display.

[0107] Therefore, the waterfall chart shows the average daily energy loss or savings for the selected portion of the voyage. Alternatively, the overall energy loss or savings for the selected portion of the voyage can be shown in waterfall chart G2, or the cumulative total of the overall energy loss or savings for the selected portion of the voyage can be shown in waterfall chart G3.

[0108] In the waterfall chart G1, the first bar extends from zero to an extremely high y-coordinate, the second bar extends downward from the extremely high y-coordinate of the first bar to an extremely low y-coordinate, and the third bar extends from the extremely low y-coordinate of the second bar to zero. Thus, the data structure representing the actual operational energy loss Df as the sum of the first data D1 and the second data D2 is visually shown. Note that if the second data D2 represents energy loss rather than energy saving, the extremely high y-coordinate of the first bar may correspond to the extremely low y-coordinate of the second bar.

[0109] Similarly, the fourth bar extends from an extremely low y-coordinate equal to the extremely low y-coordinate of the second bar, up to the extremely high y-coordinate of the third bar, and further up to higher y-coordinates, while the fifth bar extends from a y-coordinate of zero to the high y-coordinate of the fourth bar. Thus, the data structure representing the estimated operational energy loss Ds as the sum of the third data D3 and the actual operational energy loss Df is visually shown.

[0110] Finally, area 5 represents a scale of values ​​ranging from green (indicating low values) to red (indicating high values), with arrows on each bar indicating the measured value. -The first scale E1 displays the ship's speed. -The second scale E2 displays the speed of the main engine of ship 40. -The third scale, E3, displays the pressure inside tank 42.

[0111] In Figure 4, the screenshot 32 of the graphical interface corresponds to the user selecting a tab in area 3 corresponding to the gas flow rate v1 sent to the liquefaction system through the selected partial voyage, and the user selecting a graphical button B2 in area 4 corresponding to the liquefaction system shutdown period through the selected partial voyage.

[0112] Therefore, in the graph corresponding to flow rate v1, periods when the reliquefied gas flow rate is 0 are shown in gray. Furthermore, a new waterfall chart is shown in area 4, which currently consists of only four histogram bars. -At the first position, the first histogram bar, labeled "Consumed BOR" or "Mass BOR," shows the new average value of the first data D1 calculated by the decision system 50 for each day of the selected portion of the voyage in which the liquefaction system was shut down.

[0113] -At the second position, the second bar, labeled "BOR due to LNG temperature fluctuations" or "rate due to ship adjustments," shows the new average value of the second data D2 calculated by the decision system 50 for each day of the selected partial voyage in which the liquefaction system was shut down.

[0114] - In the third position, no bar is present, but the value 0% is displayed, and this value is labeled "Active BOR" in this third position.

[0115] - In the fourth position, there is no bar, but a value of 0% is displayed, which corresponds to zero percent of the energy saved by the liquefaction system. This value is labeled "Reliquefaction BOR" in this fourth position.

[0116] - In the fifth position, the fifth histogram bar, labeled "Passive BOR," shows data representing the sum of the new mean values ​​shown in the first position and the new mean values ​​shown in the second position, and therefore the operational energy loss Df.

[0117] -At position 6, the sixth histogram bar, labeled "Volume BOR," shows the new average value of the fourth data D4 calculated by the monitoring system for each day of the selected portion of the voyage in which the liquefaction system was shut down.

[0118] In this new waterfall chart, the first, second, and fifth bars are arranged similarly to the waterfall chart in Figure 3, visualizing the fact that the fifth bar, representing actual operational energy losses, is composed of the sum of the first bar, representing energy consumption, and the second bar, representing energy fluctuations related to temperature changes in liquefied natural gas.

[0119] Therefore, the data representing the actual operating energy loss Df is shown in the fifth position, and the data representing the estimated operating energy loss Ds is shown in Figure 3. In fact, this fifth position is dedicated to passive operating performance, which corresponds to the operating mode of the vessel 40 when the liquefaction system is stopped. Similarly, the third position is dedicated to active operating performance Dg, which corresponds to the operating mode of the vessel 40 when the liquefaction system is operating. Therefore, this active operating performance Dg is equal to the data representing the actual operating energy loss Df in Figure 3, but equal to the zero value in Figure 4.

[0120] Finally, in area 4, graphical button B3 allows visualization of a waterfall chart showing the average percentage of energy lost or saved per day throughout the entire day of the selected sub-voyage, regardless of whether the liquefaction system was operational or not. In this waterfall chart, a third position on the graph dedicated to active operational performance provides first data representing the actual operational energy loss Df over all time intervals when the liquefaction system was operational, and a fifth position on the graph dedicated to passive operational performance provides second data representing the actual operational energy loss Df over all time intervals when the liquefaction system was operational and stopped. This second representative data is obtained by adding data representing the amount of energy saved by reliquefaction throughout the entire sub-voyage to the first data representing the actual operational energy loss Df.

[0121] The same principle applies when the fifth and sixth data points D5 and D6 are taken into consideration in the determination method of the present invention.

[0122] Naturally, the present invention is not limited to the embodiments described above, and many modifications can be made to these embodiments without departing from the scope of the invention. In particular, the features of different embodiments or variations of the invention considered in this application can be combined to carry out the invention, provided that these embodiments or variations do not contradict each other.

Claims

1. A method (10) for determining data representing the operating energy loss (Df, Ds) of a liquefied gas carrier (40) over a certain time interval, This energy is initially stored in the form of liquefied gas and evaporated gas in at least one tank (42) of the vessel (40), and the vessel (40) is equipped with a liquefaction system for the evaporated gas. The aforementioned determination method (10) is, Step (12) of calculating a first data (D1) representing the amount of energy consumed over the time interval as a function of at least one measurement related to the activity of at least one energy consumption device (44) of the vessel (40), Step (14) of calculating a second data (D2) that represents the energy fluctuation of the liquefied gas present in the tank as a function of the temperature fluctuation of the liquefied gas in the tank (42) over the aforementioned time interval, A step (16) of adding the second data (D2) to the first data (D1), wherein a step (16) of generating data representing the actual operating energy loss (Df) of the vessel (40) Includes, The determination method (10) is determined when the liquefaction system operates over the time interval, Step (18) of calculating a third data (D3) representing the amount of energy saved by the liquefaction system over the aforementioned time interval, A step (20) of adding the third data (D3) to the data representing the actual operating energy loss (Df), wherein a step (20) of generating data representing the estimated operating energy loss (Ds) that would have been observed if the liquefaction system had not been operating is also included. A determination method (10) further comprising:

2. The aforementioned vessel (40) is equipped with a vaporizer for the liquefied gas, The aforementioned method, A step of calculating a fifth data (D5) representing the amount of energy of the liquefied gas that is pumped from the tank and planned to pass through the vaporizer over the time interval, A method for determining data representing operational energy loss according to claim 1 (10), further comprising the step of subtracting the fifth data (D5) from the data representing the actual operational energy loss (Df).

3. The steps include calculating a sixth data (D6) that represents the energy fluctuation of the gas phase of the liquefied gas present in the tank, as a function of the pressure fluctuation and temperature fluctuation in the tank over the aforementioned time interval, A method for determining data representing operational energy loss according to claim 1 or 2 (10), further comprising the step (XX) of adding the sixth data (D6) to the data representing the actual operational energy loss (Df).

4. The first, second, third, fifth, and sixth data (D1, D2, D3, D5, D6) and the data representing the actual operating energy loss (Df) and the data representing the estimated operating energy loss (Ds) are, on the one hand, the amount of energy lost over the aforementioned time interval and, On the other hand, The amount of energy calculated at the start of the usage period of the above determination method (10), or The amount of energy loaded onto the aforementioned vessel (40) Corresponding to the ratio with the reference energy amount selected from any of the following, A method for determining data representing operational energy loss according to any one of claims 1 to 3 (10).

5. A method (11) for monitoring operational data relating to at least one tank (42) of a liquefied gas carrier (40), A monitoring method (11) characterized by performing a method (10) for determining data representing operational energy loss according to any one of claims 1 to 4, and calculating a fourth data (D4) representing the volume fluctuation of the liquefied gas in the tank (42) over the time interval (22).

6. A device (55) for determining data representing operational energy loss, comprising means for carrying out the determination method (10) described in any one of claims 1 to 4 or the monitoring method (11) described in claim 5.

7. A data determination system (50) for a liquefied gas carrier (40) that represents the operational energy loss over a certain time interval, This energy is initially stored in the form of liquefied gas and evaporated gas in at least one tank (42) of the vessel (40), and the vessel (40) is equipped with a liquefaction system for the evaporated gas. The aforementioned decision system (50) A first means for calculating first data (D1) representing the amount of energy consumed over the time interval as a function of at least one measurement value relating to the activity of at least one energy consumption device (44) of the vessel (40), A second means for calculating a second data (D2) representing the energy fluctuation of the liquefied gas present in the tank (42) as a function of the temperature fluctuation of the liquefied gas in the tank (42) over the aforementioned time interval, An adding means for adding the second data (D2) to the first data (D1), the adding means for generating data representing the actual operating energy loss (Df) of the vessel (40) Equipped with, The aforementioned decision system (50) A third means for calculating a third data (D3) representing the amount of energy saved by the liquefaction system over the time interval when the liquefaction system operates over the time interval, Adding means for adding the third data (D3) to the data representing the actual operating energy loss (Df), wherein the adding means generates data representing the estimated operating energy loss (Ds) that would have been observed if the liquefaction system had not been operating, when the liquefaction system was operating over the time interval. A decision system (50) further characterized by having the following features.

8. The aforementioned vessel (40) is equipped with a vaporizer for the liquefied gas, A fifth means for calculating a fifth data (D5) representing the amount of energy of the liquefied gas that is pumped from the tank and planned to pass through the vaporizer over the time interval, The determination system (50) according to claim 7 further comprises an additional subtraction means for subtracting the fifth data (D5) from the data representing the actual operational energy loss (Df).

9. A sixth means for calculating a sixth data (D6) representing the energy fluctuation of the gas phase of the liquefied gas present in the tank, as a function of the pressure fluctuation and temperature fluctuation in the tank over the aforementioned time interval, The determination system (50) according to claim 7 or 8, further comprising additional adding means for adding the sixth data (D6) to the data representing the actual operating energy loss (Df).

10. The system includes a human-machine interface comprising a display means (58) adapted to provide a representation of the first, second, third, fifth, and sixth data (D1, D2, D3, D5, D6), as well as data representing the actual operating energy loss (Df) and estimated operating energy loss (Ds), The data representing the actual operating energy loss (Df) is visualized as the sum of at least two of the first, second, fifth, and sixth data (D1, D2), As the liquefaction system operates over the time interval, the data representing the estimated operational energy loss (Ds) is visualized in the form of a third data (D3) representing the actual operational energy loss (Df) and an accumulation of the data, according to any one of claims 7 to 9 (50).

11. The aforementioned representation is a waterfall chart (4), the decision system (50) according to claim 10.

12. The display means (58) is adapted to display the data representing the actual operating energy loss (Df) at a first position on the waterfall chart (4) when the liquefaction system is operating over the time interval, or at a second position on the waterfall chart (4) that is different from the first position when the liquefaction system is stopped over the time interval. The determination system (50) according to claim 11, wherein the data representing the estimated operating energy loss (Ds) is shown by the display means (58) at the second position if the liquefaction system is operating over the time interval.

13. The human-machine interface of the decision system (50) further comprises means (1) for selecting at least a portion of the voyage performed by the vessel (40), and means (B1) for selecting a first time interval in which the liquefaction system was operating throughout the partial voyage. The display means (58) is activated when the first time interval is selected by the user of the decision system (50). The average value of each of the first, second, fifth, and sixth data (D1, D2, D5, D6) provided by the means for calculating the data at each of the first time intervals, The average value of the data representing the actual operational energy loss (Df) provided by the adding means for each of the first time intervals, The average value of the third data (D3) provided by the third calculation means at each of the first time intervals, The average value of the data representing the estimated energy loss (Ds) provided by the adding means for each of the first time intervals and A determination system (50) according to any one of claims 10 to 12, adapted to represent the following:

14. The human-machine interface of the decision system (50) further comprises means (B2) for selecting a second time interval during which the liquefaction system was stopped throughout the partial voyage. The display means (58) is used when the second time interval is selected by the user of the decision system (50). The average value of each of the first, second, fifth, and sixth data (D1, D2, D5, D6) provided by the means for calculating the data at each of the second time intervals, The average value of the data representing the actual operational energy loss (Df) provided by the adding means for each of the second time intervals and The determination system (50) according to claim 13, which is adapted to display the following.

15. The human-machine interface further comprises means for selecting at least one tab relating to operational data concerning the liquefied gas, evaporated gas, reliquefied gas, or consumed gas in the tank (42), The display means (58) is adapted to display a graph (3) of the values ​​corresponding to the selected tab. The determination system (50) according to any one of claims 10 to 14, wherein the value is a value of the operation data over one or more time intervals and is recorded in the memory of the determination system (50).

16. A monitoring system for operational data relating to at least one tank (42) of a liquefied gas transport vessel, A data determination system (50) for determining operational energy loss according to any one of claims 7 to 15, A monitoring system characterized by comprising means for calculating a fourth data (D4) representing the volume fluctuation of the liquefied gas in the tank (42) over the aforementioned time interval.

17. A computer program, which, when the program is executed on one or more processors, includes program code instructions for performing the steps of the determination method (10) described in any one of claims 1 to 4.

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