WO2024122139A1 - In-tank liquefied gas composition inferring method - Google Patents

Abstract

This in-tank liquefied gas composition inferring method is for inferring the composition of a liquefied gas including a plurality of components in a tank where the liquefied gas is stored. The in-tank liquefied gas composition inferring method comprises: a step for acquiring reference information for inferring the composition of a liquefied gas in a tank at a first time point; a step for setting first time point composition information regarding the composition of the liquefied gas at the first time point on the basis of the reference information acquired in the step for acquiring the reference information; a step for acquiring information regarding an outflow of the liquefied gas in the tank between the first time point and a second time point different from the first time point; and a step for inferring second time point composition information regarding a composition of the liquefied gas at the second time point on the basis of the first time point composition information set in the step for setting the first time point composition information and the outflow of the liquefied gas acquired in the step for acquiring the information regarding the outflow of the liquefied gas in the tank.

Description

Method for estimating the composition of liquefied gas in a tank

The present disclosure relates to a method for estimating the composition of liquefied gas in a tank.
This application claims priority based on Japanese Patent Application No. 2022-193891, filed on December 5, 2022, the contents of which are incorporated herein by reference.

In a tank that stores liquefied gas such as liquefied natural gas or liquefied petroleum gas, the liquefied gas evaporates in the tank due to heat input from the outside, generating boil-off gas. When the tank is installed on a ship, the boil-off gas may be used, for example, as fuel for the main engine installed on the ship.
For example, Patent Literature 1 discloses a tank state estimation method that acquires information on the state inside a tank at the start point of a target section on a route, and calculates the state inside the tank at the end point of the section, assuming that the heat input to the tank in the section is used to vaporize the liquefied gas in the tank. In this tank state estimation method, the amount of heat inside the tank is estimated as the state inside the tank.

International Publication No. 2018/189789

However, if a tank is not provided with a device for re-liquefying the boil-off gas, it may be necessary to discharge the gas in the tank to the outside of the tank and consume it as fuel for the main engine or incinerate it in order to suppress an increase in tank pressure. However, if the liquefied gas is composed of multiple components, the components with lower boiling points among these multiple components will evaporate before the components with higher boiling points to become boil-off gas, so discharging the gas in the tank to the outside of the tank will change the composition of the liquid in the tank. In other words, when the gas or liquid in the tank is supplied to the outside of the tank, the composition of these gases and liquids will change over time. For example, when the liquid in the tank is used as fuel for a combustion device installed on the ship, a change in the composition of the fuel supplied from the tank may affect the combustion state of the fuel in the combustion device.
However, the method disclosed in Patent Document 1 does not allow the composition of the liquefied gas in the tank to be known, and therefore requires sampling the liquefied gas in the tank and analyzing the composition. Sampling the liquefied gas and analyzing the composition are time-consuming and laborious.

The present disclosure has been made to solve the above problems, and aims to provide a method for estimating the composition of liquefied gas in a tank that can easily grasp the composition of the liquefied gas stored in the tank.

In order to solve the above problems, the method for estimating the composition of liquefied gas in a tank according to the present disclosure is a method for estimating the composition of the liquefied gas in a tank that stores liquefied gas containing multiple components. The method for estimating the composition of the liquefied gas in the tank includes a step of acquiring reference information, a step of setting first time point composition information, a step of acquiring information regarding the outflow amount of the liquefied gas in the tank, and a step of estimating second time point composition information. The step of acquiring reference information acquires reference information for estimating the composition of the liquefied gas in the tank at a first time point. The step of setting first time point composition information sets first time point composition information regarding the composition of the liquefied gas at the first time point based on the reference information acquired in the step of acquiring reference information. The step of acquiring information regarding the outflow amount of the liquefied gas in the tank acquires information regarding the outflow amount of the liquefied gas in the tank between a second time point different from the first time point and the first time point. In the step of estimating the second time point composition information, second time point composition information regarding the composition of the liquefied gas at the second time point is estimated based on the first time point composition information set in the step of setting the first time point composition information and the outflow amount of the liquefied gas acquired in the step of acquiring information regarding the outflow amount of the liquefied gas in the tank.

The method for estimating the composition of liquefied gas in a tank according to the present disclosure is a method for estimating the composition of the liquefied gas in a tank that stores liquefied gas containing multiple components. The method for estimating the composition of the liquefied gas in the tank includes a step of acquiring first reference time composition information, a step of acquiring outflow amount information, and a step of estimating third time composition information. In the step of acquiring the first reference time composition information, first reference time composition information regarding the composition of the liquefied gas set at a past first reference time is acquired. In the step of acquiring the outflow amount information, outflow amount information regarding the outflow amount of the liquefied gas in the tank between a third time point different from the first reference time point and the first reference time is acquired. In the step of estimating the third time composition information, third time composition information regarding the composition of the liquefied gas at the third time point is estimated based on the first reference time composition information acquired in the step of acquiring the first reference time composition information and the outflow amount information acquired in the step of acquiring outflow amount information regarding the outflow amount of the liquefied gas in the tank between the third time point and the first reference time.

The method for estimating the composition of liquefied gas in a tank according to the present disclosure is a method for estimating the composition of the liquefied gas in a tank storing liquefied gas containing multiple components. The method for estimating the composition of the liquefied gas in the tank includes a step of acquiring second reference time composition information, a step of acquiring inflow volume information and outflow volume information, a step of acquiring inflow liquefied gas composition information, and a step of estimating fourth time composition information. In the step of acquiring second reference time composition information, second reference time composition information regarding the composition of the liquefied gas set at a past second reference time is acquired. In the step of acquiring inflow volume information and outflow volume information, inflow volume information regarding the inflow volume of the liquefied gas into the tank and outflow volume information regarding the outflow volume between a fourth time point different from the second reference time point and the second reference time point are acquired. In the step of acquiring inflow liquefied gas composition information, inflow liquefied gas composition information regarding the composition of the liquefied gas that has flowed into the tank is acquired. In the step of estimating the fourth time point composition information, the fourth time point composition information regarding the composition of the liquefied gas at the fourth time point is estimated based on the second reference time point composition information acquired in the step of acquiring the second reference time point composition information, the inflow volume information and the outflow volume information acquired in the step of acquiring inflow volume information regarding the inflow volume of liquefied gas into the tank and outflow volume information regarding the outflow volume between the fourth time point and the second reference time point, and the inflow liquefied gas composition information acquired in the step of acquiring the inflow liquefied gas composition information.

The disclosed method for estimating the composition of liquefied gas in a tank makes it easy to determine the composition of the liquefied gas stored in the tank.

FIG. 1 is a side view of a float equipped with a method for estimating the composition of a liquefied gas in a tank according to an embodiment of the present disclosure. FIG. 1 is a diagram illustrating a hardware configuration of a liquefied gas composition estimation device according to an embodiment of the present disclosure. FIG. 1 is a functional block diagram of a liquefied gas composition estimation device according to an embodiment of the present disclosure. FIG. 1 is a chart showing different uses of methods for estimating the composition of liquefied gas in a tank according to embodiments of the present disclosure. 1 is a flowchart showing the steps of a first liquefied gas composition estimation method as a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure. 1 is a flowchart showing the steps of a second liquefied gas composition estimation method as a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure. 13 is a flowchart showing the steps of a third liquefied gas composition estimation method as a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure.

Hereinafter, a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 7. FIG.
(Overall configuration of the vessel)
As shown in FIG. 1, the method for estimating the composition of liquefied gas in a tank according to this embodiment is carried out on a ship equipped with a combustion device that burns or incinerates boil-off gas as fuel.
As shown in Fig. 1, the ship 1 of this embodiment includes at least a hull 2, a superstructure 4, a combustion device 9, a tank 10, and a liquefied gas composition estimation device 60 that estimates the composition of the liquefied gas in the tank 10. Note that the ship 1 of this embodiment will be described as an example of a ship that can navigate using a main engine or the like. The type of the ship 1 is not limited to a specific type of ship. Examples of the type of the ship 1 include a liquefied gas carrier, a ferry, a RORO ship, a car carrier, a passenger ship, and the like.

The hull 2 has a pair of side panels 5A, 5B and a bottom 6 that form its outer hull. The side panels 5A, 5B each have a pair of side panel shells that form the starboard and port sides, respectively. The bottom 6 has a bottom panel shell that connects the side panels 5A, 5B. The pair of side panels 5A, 5B and the bottom 6 give the outer hull 2 a U-shape in cross section perpendicular to the bow-stern direction FA.

The hull 2 further comprises an upper deck 7, which is a full-length deck located at the topmost level. The superstructure 4 is formed on this upper deck 7. Accommodation areas and the like are provided within the superstructure 4. In the ship 1 of this embodiment, for example, a cargo carrying area (hold) 8 is formed closer to the bow 2a in the bow-stern direction FA than the superstructure 4.

The combustion device 9 is a device that generates thermal energy by burning fuel, and is provided inside the hull 2. Examples of the combustion device 9 include an internal combustion engine used in the main engine for propelling the ship 1, an internal combustion engine used in the power generation equipment that supplies electricity to the ship, and a boiler that generates steam as a working fluid.

The tanks 10 are arranged in the hull 2. In this embodiment, the tanks 10 are cylindrical and extend horizontally, and a plurality of tanks 10 are arranged side by side in the bow-stern direction FA within the cargo carrying area 8. However, there are no limitations on the shape, number, or arrangement of the tanks 10. For example, the tanks 10 can be arranged on the exposed deck. Furthermore, for example, the tanks 10 may be spherical, rectangular, etc.

The tank 10 stores therein a liquefied gas containing multiple components. Examples of liquefied gas containing multiple components include LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas), which are liquefied gases liquefied at low temperatures. In this embodiment, LNG will be used as an example of a liquefied gas containing multiple components.

The liquefied gas in the tank 10 evaporates due to heat input from the outside, becoming boil-off gas. The liquid of the liquefied gas in the tank 10 and the boil-off gas generated in the tank 10 are supplied to the combustion device 9 as fuel in the combustion device 9, or sent to an incineration device (not shown) for incineration.

(Hardware configuration diagram)
FIG. 2 is a diagram illustrating a hardware configuration of a liquefied gas composition estimation device according to an embodiment of the present disclosure.
2, the liquefied gas composition estimation device 60 is a computer including a central processing unit (CPU) 61, a read only memory (ROM) 62, a random access memory (RAM) 63, a storage 64, and a signal transmission/reception module 65. The signal transmission/reception module 65 receives detection signals from, for example, a pressure sensor that detects the pressure inside the tank 10, a temperature sensor that detects the temperature inside the tank 10, etc. (neither of which are shown).

(Function block diagram)
3 is a functional block diagram of a liquefied gas composition estimation device according to an embodiment of the present disclosure. As shown in Fig. 3, a CPU 61 of a liquefied gas composition estimation device 60 executes a program stored in advance in a storage device such as a ROM 62 or a storage 64 to realize each of the components of an information acquisition unit 71, an in-tank change amount acquisition unit 72, a composition estimation unit 73, and an information storage unit 74.

The information acquisition unit 71 acquires tank composition information regarding the composition of the liquefied gas in the tank 10 at each point in time. The information acquisition unit 71 acquires detection data, for example, from a pressure sensor that detects the pressure inside the tank 10 and a temperature sensor that detects the temperature inside the tank 10, based on the detection signal received by the signal transmission/reception module 65.

The tank internal change amount acquisition unit 72 acquires the amount of change in the liquefied gas in the tank 10 between multiple points in time.
The composition estimation unit 73 estimates composition information regarding the composition of the liquefied gas in the tank 10 based on the composition information in the tank at multiple points in time acquired by the information acquisition unit 71 and the amount of change in the liquefied gas in the tank 10 acquired by the tank change amount acquisition unit 72.

The information storage unit 74 stores various pieces of information required when the liquefied gas composition estimation device 60 executes the process of estimating the composition of the liquefied gas in the tank 10. The information storage unit 74 stores, for example, information such as the number, volume, heat retention performance, and amount of heat input from the outside of the tank 10 as specification information of the tank 10. The information storage unit 74 also stores various estimation results obtained by repeatedly executing the process of estimating the composition of the liquefied gas in the tank 10.

(Procedure for estimating the composition of liquefied gas in a tank)
FIG. 4 is a chart showing how to use different methods for estimating the composition of a liquefied gas in a tank according to an embodiment of the present disclosure.
The method S10 for estimating the composition of a liquefied gas in a tank in this embodiment includes a first method S10A for estimating the composition of a liquefied gas, a second method S10B for estimating the composition of a liquefied gas, and a third method S10C for estimating the composition of a liquefied gas.

The first liquefied gas composition estimation method S10A is executed in a state A1 in which the composition of the liquefied gas in the tank 10 is unknown. The first liquefied gas composition estimation method S10A is also executed in a state in which no liquefied gas flows into the tank 10 from the outside, for example, while the ship 1 is sailing. Here, an example of the state A1 in which the composition of the liquefied gas in the tank 10 is unknown is a state after new liquefied gas is injected into the tank 10 from a state in which no liquefied gas is stored in the tank 10 (for example, a state in which all the liquefied gas has been discharged, etc.).

The second liquefied gas composition estimation method S10B is executed in state A2 where the composition of the liquefied gas in the tank 10 is estimated and known. For example, after the composition of the liquefied gas stored in the tank 10 is estimated by the first liquefied gas composition estimation method S10A, the second liquefied gas composition estimation method S10B estimates the composition of the liquefied gas based on the estimation result. In addition, the second liquefied gas composition estimation method S10B is executed in a state where no liquefied gas flows into the tank 10 from the outside, for example, while the ship 1 is sailing.

The third liquefied gas composition estimation method S10C is executed when the composition of the liquefied gas in the tank 10 is known and when liquefied gas is being supplied from the outside into the tank 10 or immediately after the supply. For example, in the case of a ship 1 fueled by liquefied gas, the method is executed in a state A3 during refueling with liquefied gas, that is, during so-called bunkering.

FIG. 5 is a flowchart showing the steps of a first liquefied gas composition estimation method as a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure.
As shown in Figure 5, the first liquefied gas composition estimation method S10A of this embodiment includes a step S11 of acquiring reference information, a step S12 of setting first point-in-time composition information, a step S13 of acquiring outflow volume information regarding the outflow volume of liquefied gas in the tank, a step S14 of estimating second point-in-time composition information, a step S15 of acquiring a state quantity of the liquefied gas in the tank at the second point in time, a step S16 of estimating the state quantity of the liquefied gas in the tank from the second point-in-time composition information, and a step S17 of determining an error of the estimated value.

In step S11 of acquiring reference information, reference information is acquired for estimating the composition of the liquefied gas in the tank 10 at a first point in time T1 (see FIG. 4). Here, the first point in time T1 is an arbitrary point in time during state A1 in which the composition of the liquefied gas in the tank 10 is unknown. The first point in time T1 is a point in time that has passed a certain amount of time since the start of use of the tank 10 at point T0, and is a point in time when liquefied gas is stored in the tank 10.

An example of reference information for estimating the composition of the liquefied gas in the tank 10 is the state quantity of the tank 10 at the first time point T1. The state quantity of the tank 10 is, for example, at least one of the pressure, temperature, density, etc., inside the tank 10. In this embodiment, the pressure and temperature inside the tank 10 are used as the reference information acquired in step S11. The pressure and temperature inside the tank 10 are acquired, for example, from a pressure sensor, a temperature sensor, etc. installed in the tank 10.

In step S12 of setting the first time point composition information, the first time point composition information regarding the composition of the liquefied gas at the first time point T1 is set based on the reference information acquired in step S11 of acquiring the reference information.

Specifically, in step S12, the liquid composition of the liquefied gas in the tank 10 at the first time T1 is assumed. The liquid composition of the liquefied gas in the tank 10 at the first time T1 may be assumed by using, for example, the amount of boil-off gas (the ratio to the liquefied gas that is liquid) generated in the tank 10 from the liquefied gas supplied to the tank 10 after the start of use time T0 to the first time T1 as a variable, or the liquid composition of a random set of numerical values may be assumed by using random numbers. Here, the liquefied gas stored in the tank 10 can be supplied from a land-based liquefied gas supply facility, a tanker truck, a bunker ship, etc. The supply side, such as a land-based liquefied gas supply facility, analyzes the liquefied gas to be supplied to the tank 10 in advance, etc., to determine the liquid composition of the liquefied gas.
In step S12, when it is determined that the error is not within the set range by step S17 for determining the error of the estimated value, which will be described later, the liquid composition of the liquefied gas in the tank 10 at the first time point T1 is again assumed to be a different set of values. Note that multiple liquid compositions of the liquefied gas in the tank 10 at the first time point T1 may be assumed.

Next, in step S12, the assumed values of the state quantities of the liquefied gas at the assumed liquid composition of the liquefied gas are calculated. For example, the liquid density of the liquefied gas can be calculated from the assumed values of the pressure and temperature of the liquefied gas as the state quantity of the liquefied gas at the assumed liquid composition of the liquefied gas.

In step S12, the first time composition information is set based on the calculated assumed value of the state quantity of the liquefied gas in the tank 10 at the first time T1 and the actual measured value of the state quantity of the liquefied gas in the tank 10 at the first time T1 obtained in step S11. As described above, in step S11 of this embodiment, detection data of the pressure and temperature of the liquefied gas is obtained as the state quantity of the liquefied gas in the tank 10 at the first time T1. Therefore, in this step S12, the density of the liquefied gas in the tank 10 at the first time T1 is calculated based on the detection data of the pressure and temperature of the liquefied gas in the tank 10 at the first time T1 obtained in step S11. Then, in this step S12, the calculated assumed value of the density of the liquefied gas in the tank 10 at the first time T1 is compared with the density of the liquefied gas based on the actual measured value of the liquefied gas in the tank 10 at the first time T1.

In step S12, a liquid composition of the liquefied gas is further searched for and estimated by an appropriate optimization method such that the error between the assumed value of the state quantity of the liquefied gas in the tank 10 at the first time T1 calculated and the state quantity of the liquefied gas based on the actual measurement value of the liquefied gas in the tank 10 at the first time T1 is sufficiently small or zero. For example, if the error between the assumed value of the density of the liquefied gas in the tank 10 at the first time T1 and the density of the liquefied gas based on the actual measurement value of the liquefied gas in the tank 10 at the first time T1 is within a preset allowable error range, the assumed value may be set as the first time composition information. In addition, if there are multiple assumed values of the state quantity of the liquefied gas in the tank 10 at the first time T1 within the allowable error range, the assumed value with the smallest error from the actual measurement value of the state quantity of the liquefied gas in the tank 10 at the first time T1 among these multiple assumed values may be set as the first time composition information.

In step S13 of acquiring outflow amount information regarding the outflow amount of liquefied gas in the tank, outflow amount information regarding the outflow amount of liquefied gas in the tank 10 between the first point in time T1 and a second point in time T2 different from the first point in time T1 is acquired. Here, the second point in time T2 different from the first point in time T1 may be after the first point in time T1 or may be before the first point in time T1. In this embodiment, the second point in time T2 is, for example, the start point in time T0 of use, which is before the first point in time T1.

The outflow of liquefied gas in the tank 10 between the second point in time T2 and the first point in time T1 occurs, for example, by supplying the liquefied gas liquid in the tank 10 to the combustion device 9 as fuel. In addition, the outflow of liquefied gas in the tank 10 between the second point in time T2 and the first point in time T1 also occurs, for example, by discharging boil-off gas generated by the evaporation of the liquefied gas in the tank 10 to the outside of the tank 10.

The amount of liquefied gas flowing out of the tank 10 between the second point in time T2 and the first point in time T1 may be calculated based on specification information about the tank 10 pre-stored in the information storage unit 74, or measurement data may be used. Examples of specification information about the tank 10 include the number of tanks 10, the volume of the tank 10, the thermal insulation performance of the tank 10, and the amount of heat input from the outside to the tank 10. The amount of heat input from the outside to the tank 10 can be obtained based on, for example, the thermal insulation performance of the tank 10 and data such as the air temperature.

The outflow volume information regarding the outflow volume of liquefied gas in the tank obtained in step S13 may be, for example, the outflow volume of liquefied gas in the tank 10 itself between the first point in time T1 and a second point in time T2 different from the first point in time T1, or other information (e.g., heat quantity) that correlates with the outflow volume of liquefied gas may be obtained and the outflow volume may be calculated from this information.
In addition, the outflow volume information regarding the outflow volume of liquefied gas in the tank obtained in step S13 may be, for example, the consumption volume in a combustion device 9 that consumes the liquefied gas flowing out from within the tank 10, which may be obtained from a data logger or the like installed on the ship 1.

In step S14 of estimating second time composition information, second time composition information regarding the composition of the liquefied gas at the second time T2 is estimated based on the first time composition information set in step S12 and the outflow amount information regarding the outflow amount of the liquefied gas acquired in step S13. Specifically, in step S14, the amount of change in the composition ratio of the multiple components constituting the liquefied gas between the second time T2 and the first time T1 is calculated based on the first time composition information at the first time T1 set in step S12 and the outflow amount of the liquefied gas in the tank 10 between the second time T2 and the first time T1 acquired in step S13. In step S14, for example, the liquid composition of the liquefied gas in the tank 10 at the second time T2 is estimated based on the first time composition information at the first time T1 set in step S12 and the calculated amount of change in the composition ratio of the multiple components constituting the liquefied gas between the second time T2 and the first time T1.

In step S15 of acquiring the state quantity of the liquefied gas in the tank at the second time point, the state quantity of the liquefied gas in the tank 10 at the second time point T2 is acquired. Specifically, for example, the actual measured values of the pressure and temperature of the liquefied gas acquired from a pressure sensor, a temperature sensor, etc. installed in the tank 10 are acquired as the state quantity of the liquefied gas in the tank 10 at the second time point T2.

In step S16 of estimating the state quantity of the liquefied gas in the tank from the second time point composition information, the state quantity of the liquefied gas in the tank 10 at the second time point T2 is estimated from the second time point composition information estimated in step S14. Specifically, estimates of other state quantities of the liquefied gas at the second time point T2 are calculated based on the second time point composition information estimated in step S14 and the actual measured value of the state quantity of the liquefied gas in the tank 10 at the second time point T2 acquired in step S15. In this embodiment, for example, the density of the liquefied gas at the second time point T2 is calculated as an estimate of the state quantity of the liquefied gas at the second time point T2 based on the liquid composition of the liquefied gas at the second time point T2 estimated in step S14 and the pressure and temperature of the liquefied gas in the tank 10 at the second time point T2.

In step S17, it is determined whether or not an error between the estimated value of the state quantity (e.g., density) of the liquefied gas at the second time T2 calculated in step S16 and another state quantity of the liquefied gas in the tank 10 at the second time T2 calculated from the actual measurement value of the state quantity of the liquefied gas in the tank 10 at the second time T2 acquired in step S15 is within a preset range. If the error between the estimated value of the state quantity of the liquefied gas in the tank 10 at the second time T2 calculated from the actual measurement value of the state quantity of the liquefied gas in the tank 10 at the second time T2 acquired in step S15 is within the preset range (Yes in step S17), the composition of the liquefied gas in the tank 10 at the first time T1 based on the first time point composition information set in step S12 is adopted as an estimation result of the composition of the liquefied gas in the tank 10 in the first liquefied gas composition estimation method S10A in this embodiment.
On the other hand, if the result of the above judgment is that the error between the estimated value of the state quantity of the liquefied gas in the tank 10 at the second point in time T2 calculated and the actual measured value of the state quantity of the liquefied gas in the tank 10 at the second point in time T2 obtained in step S15 is not within the set range (No in step S17), return to step S12 and repeat the processing from step S13 onwards by further changing the assumption of the liquid composition of the liquefied gas in the tank 10 at the first point in time T1.

FIG. 6 is a flowchart showing the steps of a second liquefied gas composition estimation method as a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure.
As shown in Figure 6, the second liquefied gas composition estimation method S10B of this embodiment includes a step S21 of acquiring outflow volume information regarding the outflow volume of liquefied gas in the tank between the third point in time T3 and the first reference point in time Ts1, and a step S22 of estimating the third point in time composition information.

The second liquefied gas composition estimation method S10B is performed in state A2 (see FIG. 4) where the composition of the liquefied gas in the tank 10 is known by executing the first liquefied gas composition estimation method S10A, or by measuring the composition of the liquefied gas in the tank 10 by sampling. In the first liquefied gas composition estimation method S10A, as described above, the composition of the liquefied gas in the tank 10 at the first time point T1 based on the first time point composition information set in step S12 is adopted as the estimated result of the composition of the liquefied gas in the tank 10.

In step S21, which acquires outflow volume information regarding the outflow volume of liquefied gas in the tank, the outflow volume of liquefied gas in the tank 10 between a third point in time T3, which is different from the first point in time T1 and the second point in time T2, and a first reference point in time Ts1 is acquired. Here, the third point in time T3 is a point in time after the first reference point in time Ts1. In this embodiment, the first reference point in time Ts1 is set to the first point in time T1 at which the most recent estimated result of the liquid composition of the liquefied gas is adopted.

The outflow of liquefied gas in the tank 10 between the third time point T3 and the first reference time point Ts1 (first time point T1) occurs, for example, by supplying the liquefied gas liquid in the tank 10 to the combustion device 9 as fuel. In addition, the outflow of liquefied gas in the tank 10 between the third time point T3 and the first reference time point Ts1 also occurs, for example, by discharging boil-off gas generated by the evaporation of the liquefied gas in the tank 10 to the outside of the tank 10.

The amount of liquefied gas flowing out of the tank 10 between the third point in time T3 and the first reference point in time Ts1 may be calculated, for example, based on specification information about the tank 10 pre-stored in the information storage unit 74, or measurement data may be used. Examples of specification information about the tank 10 include the quantity of the tanks 10, the volume of the tanks 10, the thermal insulation performance of the tanks 10, and the amount of heat input from the outside to the tank 10. The amount of heat input from the outside to the tank 10 can be obtained, for example, based on data such as the thermal insulation performance of the tank 10 and the air temperature outside the tank 10.

The outflow amount information regarding the outflow amount of liquefied gas in the tank obtained in step S21 may be, for example, the outflow amount of liquefied gas in the tank 10 itself between the third time point T3 and the first reference time point Ts1, or other information (e.g., heat amount) that correlates with the outflow amount of liquefied gas may be obtained and the outflow amount may be calculated from this information. In addition, the outflow amount information regarding the outflow amount of liquefied gas in the tank 10 obtained in step S21 may be, for example, the amount of liquefied gas consumed in the combustion device 9 or the like that consumes the liquefied gas outflowing from the tank 10, obtained from a data logger or the like installed on the ship 1.

In step S22 of estimating the third time point composition information, the third time point composition information relating to the composition of the liquefied gas at the third time point T3 is estimated based on the first time point composition information (first reference time point composition information) at the first time point T1, which is the first reference time point Ts1, and the outflow amount information relating to the outflow amount of the liquefied gas between the third time point T3 and the first reference time point Ts1 obtained in step S21. Specifically, in step S22, the amount of change in the composition ratio of the multiple components that make up the liquefied gas between the third time point T3 and the first reference time point Ts1 is calculated based on the first time point composition information at the first time point T1, which is the first reference time point Ts1, and the outflow amount of the liquefied gas in the tank 10 between the third time point T3 and the first reference time point Ts1 obtained in step S21. In step S22, the liquid composition of the liquefied gas in the tank 10 at the third time T3, for example, is estimated based on the first time point composition information at the first time point T1, which is the first reference time point Ts1, and the calculated change in the composition ratio of the multiple components that make up the liquefied gas between the third time point T3 and the first reference time point Ts1. In this way, the liquid composition of the liquefied gas in the tank 10 at the third time point T3 estimated in step S22 is used as the estimation result in the second liquefied gas composition estimation method S10B in this embodiment.

FIG. 7 is a flowchart showing the steps of a third liquefied gas composition estimation method as a method for estimating the composition of liquefied gas in a tank according to an embodiment of the present disclosure.
As shown in Figure 7, the third liquefied gas composition estimation method S10C of this embodiment includes a step S31 of acquiring inflow volume information regarding the inflow volume of liquefied gas in the tank between the fourth point in time T4 and the second reference point in time Ts2 and outflow volume information regarding the outflow volume of liquefied gas in the tank, a step S32 of acquiring inflow liquefied gas composition information, and a step S33 of estimating the fourth point in time composition information.

In step S31, inflow information on the inflow amount of the liquefied gas in the tank 10 and outflow information on the outflow amount of the liquefied gas in the tank are acquired. Inflow information on the inflow amount of the liquefied gas in the tank 10 and outflow information on the outflow amount of the liquefied gas in the tank 10 between a fourth time point T4, which is different from the first time point T1, the second time point T2, and the third time point T3, and the second reference time point Ts2 are acquired. Here, the fourth time point T4 is a time point during so-called bunkering, or immediately after bunkering, in which liquefied gas is supplied from the outside into the tank 10 after the second reference time point Ts2. The fourth time point T4 is a time point after the first reference time point Ts1. In this embodiment, the second reference time point Ts2 is set to the third time point T3, which employs the most recent estimated result of the liquid composition of the liquefied gas. The second reference time point Ts2 is not limited to the third time point T3, and may be another time point such as the first time point T1 or the second time point T2.
The inflow amount of liquefied gas in the tank 10 between the fourth time point T4 and the second reference time point Ts2 can be obtained, for example, based on measurement data of the flow rate of the liquefied gas supplied to the tank 10. The outflow amount of liquefied gas in the tank 10 between the fourth time point T4 and the second reference time point Ts2 may be calculated, for example, based on specification information regarding the tank 10 pre-stored in the information storage unit 74, or may use the measurement data.

In step S32 of acquiring inflow liquefied gas composition information, inflow liquefied gas composition information is acquired regarding the composition of the liquefied gas that has flowed into the tank 10 between the fourth time point T4 and the second reference time point Ts2 (third time point T3). This inflow liquefied gas composition information may be information on the liquid composition of the liquefied gas supplied to the tank 10 provided by a liquefied gas supply facility, for example. Note that the inflow liquefied gas composition information may be estimated by reusing past actual values.

In step S33 of estimating the fourth time point composition information, the fourth time point composition information regarding the composition of the liquefied gas at the fourth time point T4 is estimated based on the third time point composition information (second reference time point composition information) at the third time point T3, which is the second reference time point Ts2, the inflow volume information regarding the inflow volume of liquefied gas and the outflow volume information regarding the outflow volume of liquefied gas in the tank 10 between the fourth time point T4 and the second reference time point Ts2 acquired in step S31, and the inflow liquefied gas composition information acquired in step S32.

Specifically, in step S33 of estimating the fourth time point composition information, the amount of change in the multiple components constituting the liquefied gas between the fourth time point T4 and the third time point T3 is calculated based on the third time point composition information at the third time point T3, which is the second reference time point Ts2, the inflow amount of the liquefied gas in the tank 10 between the fourth time point T4 and the second reference time point Ts2 (third time point T3) acquired in step S31 and the outflow amount of the liquefied gas in the tank 10 between the fourth time point T4 and the second reference time point Ts2 (third time point T3), and the inflow liquefied gas composition information acquired in step S32. Then, in step S33 of estimating the fourth time point composition information, for example, the liquid composition of the liquefied gas in the tank 10 at the fourth time point T4 is estimated based on the third time point composition information at the third time point T3 and the calculated amount of change in the multiple components constituting the liquefied gas between the fourth time point T4 and the third time point T3. In this way, the liquid composition of the liquefied gas in the tank 10 at the fourth time point T4 estimated in step S33 is adopted as the estimated result in the third liquefied gas composition estimation method S10C in this embodiment.

(Action and Effect)
In the method S10 for estimating the composition of liquefied gas in a tank in the above embodiment, second-point-in-time composition information regarding the composition of the liquefied gas at the second point-in-time T2 is estimated based on first-point-in-time composition information of the liquefied gas obtained at the first point-in-time T1 and the amount of liquefied gas flowing out of the tank 10 between the second point-in-time T2 and the first point-in-time T1.
Therefore, the composition of the liquefied gas stored in the tank 10 can be easily grasped without measuring the composition of the liquefied gas in the tank 10.

In addition, in the above embodiment, the liquid composition of the liquefied gas in the tank 10 at the first point in time T1 is assumed, and first point in time composition information regarding the liquid composition of the liquefied gas at the first point in time T1 can be set based on an assumed value of the state quantity of the liquefied gas calculated from the assumed liquid composition of the liquefied gas and the actual state quantity of the liquefied gas in the tank 10 at the first point in time T1.

In addition, in the above embodiment, the liquid composition of the liquefied gas in the tank 10 at the first time point T1 is assumed, and among the assumed values of the state quantities in the assumed liquid composition of the liquefied gas, the difference between the assumed value of the state quantity and the state quantity of the liquefied gas in the tank 10 at the first time point T1 is within a preset range and is set as the first time point composition information. This makes it possible to select from the assumed liquid compositions of the liquefied gas one that is close to the composition of the liquefied gas in the tank 10 at the first time point T1, thereby improving the estimation accuracy of the assumed liquid composition of the liquefied gas.

In addition, in the above embodiment, by estimating the state quantity of the liquefied gas at the second time point T2 and comparing the estimated value of the state quantity of the liquefied gas at the second time point T2 with the actual state quantity of the liquefied gas in the tank 10 at the second time point T2, it is possible to obtain an estimate of the state quantity of the liquefied gas at the second time point T2 that falls within a preset error range. Therefore, based on the estimate of this state quantity, it is possible to obtain a probable estimated composition, i.e., probable second time point composition information and first time point composition information.

In addition, in the above embodiment, if a leakage of liquefied gas occurs in the tank 10 between the third time point T3 and the first reference time point Ts1 (second time point T2), by acquiring leakage amount information regarding the leakage amount of liquefied gas in the tank 10, it is possible to estimate third time point composition information regarding the composition of the liquefied gas at the third time point T3 based on the first time point composition information (first reference time point composition information) and the leakage amount information.

In addition, in the above embodiment, if liquefied gas flows into the tank 10 and flows out of the tank 10 between the fourth time point T4 and the second reference time point Ts2 (third time point T3), inflow volume information regarding the amount of liquefied gas flowing into the tank 10 and outflow volume information regarding the amount of liquefied gas flowing out of the tank 10 are acquired, and fourth time point composition information regarding the composition of the liquefied gas at the fourth time point T4 can be estimated based on the third time point composition information (second reference time point composition information), the inflow volume information, and the outflow volume information.

Other Embodiments
Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like that do not deviate from the gist of the present disclosure are also included.
In the above embodiment, in step S11 and the like, the pressure and temperature inside the tank 10 are acquired as the state quantities of the tank 10, and the density of the liquefied gas is calculated from these pressures and temperatures, but this is not limited to the above. For example, the composition of the liquefied gas may be estimated by calculating the temperature of the liquefied gas from the pressure inside the tank 10 and the density of the liquefied gas. Furthermore, information on even more parameters may be acquired as the state quantities of the liquefied gas inside the tank 10, and the composition of the liquefied gas may be estimated from this information.

In addition, in step S12 of the above embodiment, an assumed value to be used in subsequent processing is selected from multiple assumed values of the state quantity (density) of the liquefied gas in the tank 10 at the first time point T1 using an appropriate optimization method, but the specific method may be any method.

In addition, in the second liquefied gas composition estimation method S10B of the above embodiment, the second point in time T2 is used as the first reference point in time Ts1, but the first reference point in time Ts1 may be any other point in time, not limited to the second point in time T2, as long as it is prior to the third point in time T3.
Similarly, in the third liquefied gas composition estimation method S10B of the above embodiment, the third point in time T3 is used as the second reference point in time Ts2, but the second reference point in time Ts2 may be any other point in time, not limited to the third point in time T3, as long as it is prior to the fourth point in time T4.

In the above embodiment, the tank 10 provided on the ship 1 is described as an example, but the tank 10 may also be a tank installed on land.

<Additional Notes>
The method S10 for estimating the composition of liquefied gas in a tank described in the embodiment can be understood, for example, as follows.

(1) A method S10 for estimating the composition of liquefied gas in a tank according to a first aspect is a method S10 for estimating the composition of liquefied gas in a tank 10 storing liquefied gas containing multiple components, and includes: a step S11 for acquiring reference information for estimating the composition of the liquefied gas in the tank 10 at a first point in time T1; a step S12 for setting first point-in-time composition information regarding the composition of the liquefied gas at the first point in time T1 based on the reference information acquired in the step S11 for acquiring the reference information; a step S13 for acquiring information regarding the outflow amount of liquefied gas in the tank between a second point in time T2 different from the first point in time T1 and the first point in time T1; and a step S14 for estimating second point-in-time composition information regarding the composition of the liquefied gas at the second point in time based on the first point-in-time composition information set in the step S12 for setting first point-in-time composition information and the outflow amount of liquefied gas acquired in the step S13 for acquiring information regarding the outflow amount of liquefied gas in the tank.
Examples of the reference information include state quantities such as pressure, temperature, and density of the liquefied gas, and the composition of the liquefied gas.
The second point in time T2, which is different from the first point in time T1, may be a point in time before the first point in time T1, or may be a point in time after the first point in time T1.

This method S10 for estimating the composition of liquefied gas in a tank estimates second-time point composition information regarding the composition of the liquefied gas at the second time point T2 based on first-time point composition information of the liquefied gas obtained at the first time point T1 and the amount of liquefied gas flowing out of the tank 10 between the second time point T2 and the first time point T1, so that the composition of the liquefied gas stored in the tank 10 can be easily grasped without analyzing the composition of the liquefied gas in the tank 10.

(2) A method S10 for estimating the composition of liquefied gas in a tank according to a second aspect is the method S10 for estimating the composition of liquefied gas in a tank of (1), in which in step S11 of acquiring the reference information, a state quantity of the liquefied gas in the tank 10 at the first point in time T1 is acquired as the reference information, and in step S12 of setting the first point in time composition information, a liquid composition of the liquefied gas in the tank 10 at the first point in time T1 is assumed, an assumed value of the state quantity at the assumed liquid composition of the liquefied gas is calculated, and the first point in time composition information is set based on the calculated assumed value of the state quantity and the state quantity of the liquefied gas in the tank 10 at the first point in time T1.
Examples of the state quantities of a liquefied gas include the pressure, temperature, and density of the liquefied gas.

This allows the liquid composition of the liquefied gas in the tank 10 at the first point in time T1 to be assumed, and first point in time composition information regarding the liquid composition of the liquefied gas at the first point in time T1 to be set based on an assumed value of the state quantity of the liquefied gas calculated from the assumed liquid composition of the liquefied gas and the actual state quantity of the liquefied gas in the tank 10 at the first point in time T1.

(3) The method S10 for estimating the composition of liquefied gas in a tank according to the third aspect is the method S10 for estimating the composition of liquefied gas in a tank according to (2), and in step S12 for setting the first time point composition information, multiple liquid compositions of the liquefied gas in the tank 10 at the first time point T1 are assumed, and among the multiple assumed values of the state quantity for each of the multiple assumed liquid compositions of the liquefied gas, one in which the difference between the assumed value of the state quantity and the state quantity of the liquefied gas in the tank 10 at the first time point T1 is within a preset range is identified, and the liquid composition of the liquefied gas corresponding to the identified assumed value of the state quantity is set as the first time point composition information.

As a result, by selecting from among multiple assumed liquid compositions of the liquefied gas the one closest to the composition of the liquefied gas in the tank 10 at the first time point T1, the accuracy of the assumed liquid composition of the liquefied gas can be improved.

(4) The method S10 for estimating the composition of liquefied gas in a tank according to the fourth aspect is any one of the methods S10 for estimating the composition of liquefied gas in a tank according to (1) to (3), and further includes a step S15 for acquiring the state quantity of the liquefied gas in the tank at the second time point, a step S16 for estimating the state quantity of the liquefied gas in the tank 10 at the second time point T2 based on the second time point composition information estimated in the step S14 for estimating the second time point composition information, and a step S17 for determining an error in the estimated value of the state quantity of the liquefied gas in the tank 10 at the second time point T2 by comparing the estimated value of the state quantity of the liquefied gas in the tank 10 at the second time point T2 estimated in the step S16 for estimating the state quantity of the liquefied gas in the tank 10 at the second time point T2 with the state quantity of the liquefied gas in the tank 10 at the second time point T2 acquired in the step S15 for acquiring the state quantity of the liquefied gas in the tank 10 at the second time point T2.

This allows the state quantity of the liquefied gas in the tank 10 at the second time point T2 to be estimated based on the second time point composition information. In addition, by comparing the estimated value of the state quantity of the liquefied gas at the second time point T2 estimated in step S16 with the state quantity of the liquefied gas in the tank 10 at the second time point T2 acquired in step S15, it is possible to obtain an estimated value of the state quantity of the liquefied gas at the second time point T2 that falls within a preset error range, and therefore it is possible to obtain a probable estimated composition based on this estimated value of the state quantity, i.e., the probable second time point composition information estimated in step S14 and the first time point composition information set in step S12.

(5) The method S10 for estimating the composition of liquefied gas in a tank according to the fifth aspect is any one of the methods S10 for estimating the composition of liquefied gas in a tank according to (1) to (4), and includes a step S12 for acquiring first reference time composition information regarding the composition of the liquefied gas at a past first reference time Ts1, a step S21 for acquiring outflow volume information regarding the outflow volume of the liquefied gas in the tank 10 between a third time T3 different from the first reference time Ts1 and the first reference time Ts1, and a step S22 for estimating third time composition information regarding the composition of the liquefied gas at the third time T3 based on the first reference time composition information acquired in the step S12 for acquiring the first reference time composition information and the outflow volume information acquired in the step S21 for acquiring outflow volume information regarding the outflow volume of the liquefied gas in the tank 10 between the third time T3 and the first reference time Ts1.

As a result, if a leak of liquefied gas occurs in the tank 10 between the third point in time T3 and the first reference point in time Ts1, it is possible to obtain leak volume information regarding the amount of liquefied gas leaked from the tank 10, and it is therefore possible to estimate third point in time composition information regarding the composition of the liquefied gas at the third point in time T3 based on the first reference point in time composition information and the leak volume information.

(6) The method S10 for estimating the composition of liquefied gas in a tank relating to the sixth aspect is the method S10 for estimating the composition of liquefied gas in a tank according to (5), and includes a step S31 of acquiring second reference time composition information regarding the composition of the liquefied gas set at a past second reference time Ts2, a step S32 of acquiring inflow volume information regarding the inflow volume of liquefied gas into the tank 10 between a fourth time T4 different from the second reference time Ts2 and the second reference time Ts2, and a step S33 of acquiring inflow liquefied gas composition information regarding the composition of the liquefied gas that has flowed into the tank 10. and a step S33 of estimating fourth time point composition information relating to the composition of the liquefied gas at the fourth time point T4 based on the second reference time point composition information acquired in step S22 of acquiring the second reference time point composition information, the inflow volume information acquired in step S31 of acquiring inflow volume information relating to the inflow volume of the liquefied gas into the tank 10 between the fourth time point T4 and the second reference time point Ts2, and the inflow liquefied gas composition information acquired in step S32 of acquiring the inflow liquefied gas composition information.

As a result, if liquefied gas flows into the tank 10 between the fourth time point T4 and the second reference time point Ts2, inflow volume information regarding the inflow volume of liquefied gas into the tank 10 can be obtained, and fourth time point composition information regarding the composition of the liquefied gas at the fourth time point T4 can be estimated based on the second reference time point composition information and the inflow volume information.

(7) The method S10 for estimating the composition of liquefied gas in a tank according to the seventh aspect is a method S10 for estimating the composition of liquefied gas in a tank 10 storing liquefied gas containing multiple components, and includes a step S12 for acquiring first reference time composition information regarding the composition of the liquefied gas set at a past first reference time Ts1, a step S21 for acquiring outflow volume information regarding the outflow volume of the liquefied gas in the tank 10 between a third time T3 different from the first reference time Ts1 and the first reference time Ts1, and a step S22 for estimating third time composition information regarding the composition of the liquefied gas at the third time T3 based on the first reference time composition information acquired in the step S12 for acquiring the first reference time composition information and the outflow volume information acquired in the step S21 for acquiring outflow volume information regarding the outflow volume of the liquefied gas in the tank 10 between the third time T3 and the first reference time Ts1.

As a result, if a leak of liquefied gas occurs in the tank 10 between the third time point T3 and the first reference time point Ts1, it is possible to obtain leak volume information regarding the amount of liquefied gas leaked from the tank 10, and it is therefore possible to estimate third time point composition information regarding the composition of the liquefied gas at the third time point T3 based on the first reference time point composition information and the leak volume information. Therefore, it is possible to easily grasp the composition of the liquefied gas stored in the tank 10 without analyzing the composition of the liquefied gas in the tank 10.

(8) The method S10 for estimating the composition of liquefied gas in a tank relating to the eighth aspect is a method S10 for estimating the composition of liquefied gas in a tank 10 storing liquefied gas containing multiple components, and includes a step S31 of acquiring second reference time composition information regarding the composition of the liquefied gas set at a past second reference time Ts2, a step S32 of acquiring inflow volume information regarding the amount of liquefied gas flowing into the tank 10 and outflow volume information regarding the amount of liquefied gas flowing out of the tank between a fourth time T4 different from the second reference time Ts2 and the second reference time Ts2, and an inflow liquefied gas composition information regarding the composition of the liquefied gas that has flowed into the tank 10. The method includes a step S32 of acquiring information, and a step S33 of estimating fourth time point composition information related to the composition of the liquefied gas at the fourth time point T4 based on the second reference time point composition information acquired in the step S22 of acquiring the second reference time point composition information, the inflow volume information and the outflow volume information acquired in the step S31 of acquiring inflow volume information related to the inflow volume of the liquefied gas into the tank 10 and outflow volume information related to the outflow volume of the liquefied gas in the tank between the fourth time point T4 and the second reference time point Ts2, and the inflow liquefied gas composition information acquired in the step S32 of acquiring the inflow liquefied gas composition information.

As a result, if inflow and outflow of liquefied gas occurs into and from the tank 10 between the fourth point in time T4 and the previous second reference point in time Ts2, inflow volume information regarding the inflow volume of liquefied gas in the tank 10 and outflow volume information regarding the outflow volume can be obtained, and fourth point in time composition information regarding the composition of the liquefied gas at the fourth point in time T4 can be estimated based on the second reference point in time composition information, the inflow volume information, and the outflow volume information. Therefore, the composition of the liquefied gas stored in the tank 10 can be easily grasped without analyzing the composition of the liquefied gas in the tank 10.

The disclosed method for estimating the composition of liquefied gas in a tank makes it easy to determine the composition of the liquefied gas stored in the tank.

Reference Signs List 1 Ship 2 Hull 2a Bow 4 Superstructure 5A, 5B Ship side 6 Ship bottom 7 Upper deck 8 Cargo carrying compartment 9 Combustion device 10 Tank 60 Composition estimation device 61 CPU
62...ROM
63...RAM
64...Storage 65...Signal transmission/reception module 71...Information acquisition unit 72...In-tank change amount acquisition unit 73...Composition estimation unit 74...Information storage unit A1 to A3...Status FA...Bow-stern direction S10...Method for estimating composition of liquefied gas in tank S11...Step of acquiring reference information S12...Step of setting composition information at first point in time S13...Step of acquiring outflow amount information regarding the outflow amount of liquefied gas in the tank S14...Step of estimating composition information at second point in time S15...Step of acquiring state amount of liquefied gas in the tank at the second point in time S16...Step of estimating state amount of liquefied gas in the tank from composition information at second point in time Step S17: determining an error in the estimated value Step S21: acquiring outflow amount information regarding the outflow amount of liquefied gas in the tank between the third time point and the first reference time Step S22: estimating third time point composition information Step S31: acquiring inflow amount information regarding the inflow amount of liquefied gas in the tank between the fourth time point and the second reference time Step S32: acquiring inflow liquefied gas composition information Step S33: estimating fourth time point composition information T0: start of use time T1: first time point T2: second time point T3: third time point T4: fourth time point Ts1: first reference time point Ts2: second reference time

Claims (8)

1. A method for estimating a composition of a liquefied gas in a tank storing the liquefied gas containing multiple components, comprising the steps of:
   obtaining reference information for estimating a composition of the liquefied gas in the tank at a first time;
   A step of setting first time point composition information regarding a composition of the liquefied gas at the first time point based on the reference information acquired in the step of acquiring the reference information;
   acquiring information about an outflow amount of liquefied gas in the tank between a second time point different from the first time point and the first time point;
   a step of estimating second point-in-time composition information regarding the composition of the liquefied gas at the second point in time based on the first point-in-time composition information set in a step of setting first point-in-time composition information and the outflow amount of the liquefied gas acquired in a step of acquiring information regarding the outflow amount of the liquefied gas in the tank.
2. In the step of acquiring the reference information,
   As the reference information, a state quantity of the liquefied gas in the tank at the first time point is acquired;
   In the step of setting the first time point composition information,
   A method for estimating the composition of liquefied gas in a tank as described in claim 1, which assumes a liquid composition of the liquefied gas in the tank at the first time point, calculates an assumed value of a state quantity at the assumed liquid composition of the liquefied gas, and sets the first time point composition information based on the calculated assumed value of the state quantity and the state quantity of the liquefied gas in the tank at the first time point.
3. In the step of setting the first time point composition information,
   A plurality of liquid compositions of the liquefied gas in the tank at the first time point are assumed;
   Among the assumed values of the state quantity for each of the multiple assumed liquid compositions of the liquefied gas, a difference between the assumed value of the state quantity and the state quantity of the liquefied gas in the tank at the first time point is identified within a preset range;
   The method for estimating a composition of a liquefied gas in a tank according to claim 2 , further comprising the step of: setting a liquid composition of the liquefied gas corresponding to the identified assumed value of the state quantity as the first time point composition information.
4. acquiring a state quantity of the liquefied gas in the tank at the second time point;
   A step of estimating a state quantity of the liquefied gas in the tank at the second time point based on the second time point composition information estimated in the step of estimating the second time point composition information;
   The method for estimating the composition of liquefied gas in a tank as described in claim 1 or 2, further comprising a step of determining an error in the estimated value of the state quantity of the liquefied gas in the tank at the second time point by comparing the estimated value of the state quantity of the liquefied gas in the tank at the second time point estimated in the step of estimating the state quantity of the liquefied gas in the tank at the second time point with the state quantity of the liquefied gas in the tank at the second time point acquired in the step of acquiring the state quantity of the liquefied gas in the tank at the second time point.
5. Obtaining first reference time point composition information regarding a composition of the liquefied gas at a first reference time point in the past;
   Acquiring outflow amount information regarding an outflow amount of the liquefied gas in the tank between a third time point different from the first reference time point and the first reference time point;
   3. The method for estimating the composition of liquefied gas in a tank as described in claim 1 or 2, comprising a step of estimating third time point composition information regarding the composition of the liquefied gas at the third time point based on the first reference time point composition information acquired in the step of acquiring the first reference time point composition information, and the outflow volume information acquired in the step of acquiring outflow volume information regarding the outflow volume of liquefied gas in the tank between the third time point and the first reference time point.
6. Obtaining second reference time point composition information regarding a composition of the liquefied gas set at a second reference time point in the past;
   Acquiring inflow amount information regarding an inflow amount of liquefied gas into the tank between a fourth time point different from the second reference time point and the second reference time point;
   obtaining inflow liquefied gas composition information relating to a composition of the liquefied gas flowing into the tank;
   a step of estimating fourth time point composition information regarding the composition of the liquefied gas at the fourth time point based on the second reference time point composition information acquired in the step of acquiring the second reference time point composition information, the inflow volume information acquired in the step of acquiring inflow volume information regarding the amount of liquefied gas inflow into the tank between the fourth time point and the second reference time point, and the inflow liquefied gas composition information acquired in the step of acquiring the inflow liquefied gas composition information.
7. A method for estimating the composition of a liquefied gas in a tank storing the liquefied gas containing multiple components, comprising:
   Obtaining first reference time point composition information regarding a composition of the liquefied gas set at a first reference time point in the past;
   Acquiring outflow amount information regarding an outflow amount of the liquefied gas in the tank between a third time point different from the first reference time point and the first reference time point;
   a step of estimating third time point composition information regarding the composition of the liquefied gas at the third time point based on the first reference time point composition information acquired in a step of acquiring the first reference time point composition information, and the outflow volume information acquired in a step of acquiring outflow volume information regarding the outflow volume of the liquefied gas in the tank between the third time point and the first reference time point.
8. A method for estimating the composition of a liquefied gas in a tank storing the liquefied gas containing multiple components, comprising:
   Obtaining second reference time point composition information regarding a composition of the liquefied gas set at a second reference time point in the past;
   Acquiring inflow amount information regarding the inflow amount of liquefied gas into the tank and outflow amount information regarding the outflow amount of liquefied gas in the tank between a fourth time point different from the second reference time point and the second reference time point;
   obtaining inflow liquefied gas composition information relating to a composition of the liquefied gas flowing into the tank;
   a step of estimating fourth time point composition information regarding the composition of the liquefied gas at the fourth time point based on the second reference time point composition information acquired in the step of acquiring the second reference time point composition information, the inflow volume information and the outflow volume information acquired in the step of acquiring inflow volume information regarding the amount of liquefied gas inflowing into the tank and outflow volume information regarding the amount of liquefied gas outflowing in the tank between the fourth time point and the second reference time point, and the inflow liquefied gas composition information acquired in the step of acquiring the inflow liquefied gas composition information.

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