WO2021123685A1

WO2021123685A1 - Method for estimating and adjusting an energy balance of a gas in liquid form contained in a tank

Info

Publication number: WO2021123685A1
Application number: PCT/FR2020/052560
Authority: WO
Inventors: Bernard Aoun; Pavel BORISEVICH; Romain NARME
Original assignee: Gaztransport Et Technigaz
Priority date: 2019-12-20
Filing date: 2020-12-18
Publication date: 2021-06-24
Also published as: FR3105462B1; JP2023507467A; FR3105462A1; CN115135921A; EP4078014A1; KR20220119654A

Abstract

The present invention relates to a method (5) for estimating and adjusting an energy balance of a gas in liquid form contained in at least one tank of a floating structure intended to deliver said gas in liquid form to a given place of destination, the floating structure comprising a system (8) for supplying fuel to a consumer of the floating structure (1) capable of carrying out a function of condensation of a gas phase generated from the gas in liquid form and a function of cooling the gas in liquid form, characterized in that the estimating and adjusting method (5) comprises a plurality of steps leading to the adjustment of operating plans of the condensation and cooling functions so that the energy balance of the gas in liquid form complies with the requirements of the place of destination on arrival.

Description

Title of the invention: Method for estimating and adjusting an energy balance of a gas in liquid form contained in a tank

The present invention relates to the field of transporting natural gas, and more particularly to the field of regulating the temperature of said natural gas during such transport.

In order to more easily transport and / or store gas in liquid form, such as natural gas in liquid form, over long distances, the gas is usually liquefied by cooling it to cryogenic temperatures, for example - 163 ° C to atmospheric pressure, in order to obtain liquefied natural gas, commonly known by the acronym “LNG”, or “LNG” for “Liquefied Natural Gas”. This liquefied natural gas is then loaded into specialized storage tanks of the floating structure.

However, the connected tanks are never perfectly thermally insulated so that natural evaporation of the gas is inevitable, this phenomenon being called BOG, acronym for Boil-Off Gas. The storage tanks of the floating structure thus comprise both natural gas in liquid form and natural gas in gaseous form, the gaseous phase of natural gas forming the vessel head.

In a known manner, at least part of the natural gas present in the tank in gaseous form can be used to supply an engine intended to meet the energy needs for the operation of the floating structure, in particular for its propulsion and / or its production of water. electricity for on-board equipment. To this end, it is in particular known to circulate natural gas in the gaseous state through at least one natural gas treatment system, so as to allow its heating and its compression, said system comprising a heat exchanger. used as a superheater and a compressor, both placed upstream of the engine.

It is also known to configure the natural gas treatment system so that it can allow the condensation of a part taken from the natural gas in the state. gaseous. The condensation of natural gas may in particular be required when the quantity of natural gas evaporated in the tank is too large in relation to the operating energy needs of the floating structure, the natural gas treatment system then allows the evaporated natural gas to be condensed. present in the tank in order to return it to the liquid state. Such a liquefaction system can in particular be implemented when the floating structure is stopped and the consumption of gaseous natural gas by its engine or engines is zero, or almost zero.

An essential data to take into account for this type of transport is the state of natural gas in liquid form when the floating structure arrives at its destination to unload its cargo. In fact, the stations for receiving natural gas in liquid form have requirements with regard to the characteristics of the natural gas in liquid form delivered, such as the temperature or the saturation pressure of said natural gas in liquid form. The manager of the facility at the place of destination can therefore refuse the unloading of the cargo of natural gas in liquid form if it does not comply with the requirements of the place of destination. Since temperature is a variable factor which changes significantly during transport, the major risk taken during this type of transport is that the natural gas in the liquid state arrives at its destination at a saturation pressure and / or a temperature which does not meet the criteria expected by the manager of the facility at the place of destination, thus implying a potential rejection or downgrading of the cargo.

Cargo temperature management raises two issues directly related to a buoyancy consumer fuel supply system. The first problem concerns the cooling function of the power system. Lowering the temperature and / or the saturation pressure of natural gas in liquid form is superfluous if this leads to a very large deviation from the requirements of the place of destination. In this situation, the cooling function of the power system is overused and leads to unnecessary power consumption. The second problem concerns the condensing function of the power system. When the condensation function is active, the surplus gas phase generated from the gas in liquid form reverts to the liquid phase and returns to the transport tank. However, the gas in condensed liquid form may have a higher temperature than the gas in liquid form present in the vessel. The return of the gas in liquid form condensed in the tank can therefore lead to a general increase in the temperature of the gas in liquid form present in the tank, thus leading to the risk that the gas cargo in liquid form no longer meets the requirements of the place. of destination and resulting in refusal of delivery. Conversely, the inactivity of the condensing function of the supply system leads to the elimination of the surplus of the gas phase generated from the gas in liquid form, for example by combustion or by release into the air, and therefore a waste. of cargo.

The general problem is therefore to find a balance between the condensing and cooling functions of the supply system so that the cargo meets the requirements of the place of destination, but in turn limiting the energy consumption due to the disposal. of the gas phase generated from the gas in liquid form and / or the overconsumption of the cooling function of the supply system. The present invention therefore proposes to optimize the use of the liquefaction system so as to guarantee that the cargo on delivery will be below the acceptance criterion by the place of destination, without however deviating too much from this criterion, so as to avoid road overconsumption related to the cooling function of the power system.

In this regard, the invention consists of a method for estimating and adjusting an energy balance of a gas in liquid form contained in at least one vessel of a floating structure intended to deliver said gas in liquid form to a given place of destination, the floating structure comprising a system for supplying fuel to a consumer of the floating structure keen to implement a function of condensing a gas phase generated from the gas in liquid form and / or a function of cooling gas in liquid form, characterized in that the estimation and adjustment method comprises the following steps:

- a step A of calculating the maximum authorized temperature of the gas in liquid form contained in the tank on arrival at the place of destination, from the maximum saturation pressure requirements of gas in liquid form at the place of destination and characteristics of the gas in liquid form contained in the tank,

a step B of establishing a first operating plan of the function of condensation of the gas phase generated from the gas in liquid form operated by the supply system until the arrival at the place of destination, said first operating plan being established from an estimate of a surplus of gas phase generated from the gas in liquid form in the vessel during a journey,

a step C of establishing a second operating plan for the cooling function of gas in liquid form operated by the supply system until arrival at the place of destination, said second operating plan being established from the estimate of the surplus gas phase generated from the gas in liquid form during the journey,

- a step D of calculating an energy balance of the gas in liquid form at an instant t from the temperature of the gas in liquid form contained in the vessel and the properties of the gas in liquid form contained in the vessel,

- a step E of calculating a maximum energy balance from the maximum authorized temperature of the gas in liquid form, calculated in step A, and the characteristics of the gas in liquid form contained in the tank,

- a step F of estimating the energy balance of the gas in liquid form contained in the vessel at the arrival of the journey from the operating plans for the condensation and cooling functions determined in steps B and C and from the energy balance of the gas in liquid form at time t, determined in step D,

- a step G of adjusting the first operating plan and / or the second operating plan, a step H of implementing the supply system according to the operating plans for the condensation and cooling functions of gas in liquid form adjusted in step G.

The floating structure may for example be a transport vessel capable of storing and / or transporting gas in liquid form, for example natural gas in liquid form, or LNG. The fuel supply system of a consumer of the floating structure ensures the management of the gaseous phase generated from the gas in liquid form forming in the tank by using it wisely for the supply of one or more several consumers such as a propulsion engine of the floating structure, or an electric generator thereof. At the same time, the fuel supply system of a consumer of the floating structure is able to manage a state of the gas in liquid form contained in the tank, thanks to its cooling function and its condensing function. The term "fuel supply system of a consumer of the floating structure" is hereinafter simplified to "supply system".

The estimation and adjustment process regulates the characteristics of the gas in liquid form so that a cargo of gas in liquid form is delivered to the place of destination having a saturation pressure of the gas in liquid form in accordance with the requirements of the destination, while minimizing the energy consumption required for temperature regulation. The term energy balance is used to denote a numerical data obtained by a calculation which may result from a plurality of physical constants of the gas, such as the saturation pressure of the gas in liquid form or the temperature of the gas in liquid form, or else from the energy supplied or taken by the cooling or condensing functions of the power supply system. The estimation and adjustment process can be initiated before a departure from the floating structure and / or during the journey between a starting point of the floating structure, for example a gas liquefaction terminal, and the place of the destination to which the cargo of gas in liquid form is delivered. The tank containing the gas in liquid form is a tank which conforms and is suitable for the transport of such a cargo, and it may for example be a tank with primary and secondary membranes, each of the membranes being thermally insulated.

The estimation and adjustment process begins with step A which generally consists in determining the conditions for accepting the gas cargo in liquid form by the place of destination, more particularly the maximum authorized temperature of the vessel. gas in liquid form contained in the tank on arrival. It is however possible to reason in terms of the saturation pressure of the gas in liquid form or another value linked to the pressure and / or to the temperature. The calculation of such a target value not to be exceeded depends on the saturation pressure requirements of the gas in liquid form and on the temperature of the gas in liquid form at the place of destination and on the constant characteristics of the gas. Thus, it is understood that the requirement of the terminal receiving gas in liquid form is intended to prevent massive vaporization of natural gas during its transfer between the ship and the terminal by imposing conditions for acceptance of the cargo. The maximum permitted temperature of the gas in liquid form contained in the tank on arrival depends on the properties of the gas in liquid form transported, namely the total mass of gas in liquid form and the specific heat capacity of the gas in liquid form. These two data can for example be provided by any document relating to the cargo, such as a technical sheet, and can be taken into account by the supply system, for example by means of a control monitor.

The maximum authorized temperature of the gas in liquid form contained in the tank on arrival calculated by the estimation and adjustment process also depends on the maximum saturation pressure requirements of the gas in liquid form determined by the plant manager. of the place of destination. Such data is also known by means of any source of information provided by the place of destination and can also be recorded in the power supply system in a manner identical to what has been described previously. Steps B and C consist of setting up an operating plan for each function of the power system. By operating plan, it is necessary to understand a progress of the activity of each of the functions during the journey allowing to reach the place of destination. Each of the functions, namely the condensing function and the cooling function, is either active or inactive and the power system can switch from one mode to the other. The operating plan for each of the functions therefore determines the active and inactive sequences of each of the functions during the journey, which result in heating or cooling of the cargo, as the case may be.

When the condensing and cooling functions are qualified as active, it means that the power system is allowed to perform its condensing and / or cooling functions. Conversely, when the condensing and cooling functions are qualified as inactive, it means that the supply system is not authorized to implement its condensing and / or cooling functions. When the cooling function is active, the supply system is allowed to cool the gas in liquid form provided that there is presence of gas phase generated from the gas in liquid form. When the condensation function is active, the supply system is able to condense the gas in liquid form provided that there is presence of surplus gas phase generated from the gas in liquid form.

When the condensation function is active, the temperature of the gas in liquid form contained in the tank may tend to increase. Regarding the cooling function, this causes a lowering of the temperature when activated. The temperature varies differently when the two functions act simultaneously, or can vary naturally depending on the environmental conditions during the journey. It is understood, however, that the major temperature variations occurring during the journey depend on the activation of the operating plans implemented during steps B and C of the estimation and adjustment process.

The operating plans for the condensing or cooling functions of the supply system are therefore flowcharts determining at what time t during the journey each of the functions must be activated or deactivated. It is also possible that the operating plan consists of maintaining active or inactive one or the other of the functions and this during the entire journey.

Each of these operating plans is determined from the estimate of the excess gas phase generated from the gas in liquid form during the journey. The gas phase generated from the gas in liquid form emanates from the transport tank either naturally or in a forced manner. This gaseous phase can subsequently be used to supply the floating structure, for example the engine for propelling the floating structure, or a generator supplying the floating structure with electricity. The gas phase generated from the gas in liquid form not used to supply the floating structure represents the surplus gas phase generated from the gas in liquid form. When the condensing function and the cooling function act simultaneously, it means that there is an excess gas phase generated from the gas in liquid form circulating in the supply system.

The presence of excess gas phase generated from the gas in liquid form can be detected by a system third party to the management system of the invention or directly through the estimation and adjustment method according to the invention.

Step D of the estimation and adjustment process consists in calculating the energy balance of the gas in liquid form at time t, that is to say from data measured at time t. Step D is independent of steps B and C and can thus take place simultaneously or prior to steps B and C. The calculation of the energy balance during step D depends on the total mass of gas in liquid form and on the specific heat capacity of the gas in liquid form, constants used during step A, as well as the average temperature of the gas in liquid form contained in the vessel at time t. More specifically, the energy balance of gas in liquid form is calculated from the following formula:

Be = mGas x Cp x T Be being the energy balance of the gas in liquid form at time t, mGas being the total mass of the gas in liquid form, Cp being the mass heat capacity of the gas in liquid form and T being the temperature of the gas in liquid form at l 'instant t.

The temperature of the gas in liquid form can be measured by at least one temperature sensor arranged in the tank. Said temperature is then taken into account during the calculation of step D. The temperature can be addressed in the form of an average, for example if several temperature sensors are installed in the tank, or if the floating structure comprises several tanks, each being provided with one or more temperature sensors. The energy balance of the gas in liquid form at time t calculated during this step D is used during the rest of the estimation and adjustment process.

Step E consists of calculating an energy balance similar to the energy balance calculated in step D, but the energy balance of step E is the maximum energy balance, relating to the maximum authorized temperature of the gas in liquid form. calculated in step A. The calculation of the maximum energy balance calculated during step E is independent of the energy balance of the gas in liquid form at time t calculated in step D. Steps D and E can therefore be performed simultaneously or one after the other in any order. The maximum energy balance is calculated from the total mass of gas in liquid form, gas in liquid form, the mass heat capacity of gas in liquid form, and the maximum permitted temperature of gas in liquid form. Thus, the calculation performed in step E is similar to the calculation performed in step D, with the maximum allowable temperature of the gas in liquid form instead of the temperature measured in the tank of the floating structure.

During step F, the estimation and adjustment method calculates an estimate of an energy balance of the gas in liquid form contained in the tank on arrival. In other words, the estimation and adjustment method makes it possible to predict the characteristics of the gas in liquid form contained in the vessel on arrival of the floating structure at its place of destination, in particular the energy balance thereof. To estimate the energy balance of the gas in liquid form contained in the vessel at the arrival of the path, the estimation and adjustment process uses the energy balance of the gas in liquid form at time t calculated during stage D, as well as the operating plans for the cooling and condensing functions of the supply system calculated in stages B and C. The energy balance of the gas in liquid form at time t calculated during the step D constitutes a starting point for the estimation in terms of the saturation pressure of the gas in liquid form and of the temperature of the gas in liquid form. The operating plans for the cooling and condensing functions calculated in steps B and C are also part of the estimate, as they influence the temperature of the gas in liquid form contained in the vessel as mentioned previously. From these three data, the estimation and adjustment process is able to determine the energy balance of the gas in liquid form once the floating structure has arrived at the place of destination, taking into account the operating plans of the functions. of cooling and condensation established previously. The energy balance of gas in liquid form encompassing a plurality of characteristics, it is also possible to reason in terms of saturation pressure of gas in liquid form, temperature or quantity of heat exchange. By thus estimating the energy balance of the cargo on arrival, it is possible to adjust the operating plans so that the saturation pressure of the gas in liquid form on arrival makes it admissible.

Step G then consists of an adjustment of the operating plans according to a comparison between the maximum energy balance calculated in step E and the estimate of the energy balance of the gas in liquid form contained in the tank at the arrival of the path calculated in step F. As a function of said comparison, the first operating plan of the condensation function and / or the second operating plan of the cooling function can be adjusted. The adjustment may consist of stopping one and / or the other of the functions, the stopping being able to be instantaneous or programmed after a certain period of time. One and / or the other of the functions can also be put into operation or put back into operation, also instantaneously or programmed. Thus, the first operating plan of the condensation function and / or the second operating plan of the cooling function are modified on the basis of the data calculated or estimated during steps E and F. Stage H consists of the implementation of the adjusted operating plans. In other words, the power system no longer takes into account the operating plans established during stages B and C, which are replaced by the operating plans adjusted during stage G. The adjusted operating plans are replaced by the operating plans adjusted during stage G. transmitted to the supply system at the end of the course of the estimation and adjustment process. The supply system can therefore implement the cooling and / or the condensation of the gas in liquid form, keep them active or deactivate them, and this according to the respective adjusted operating plans which have been transmitted to it.

According to one characteristic of the invention, step G consists of activating the condensation function as long as the estimate of the energy balance of the gas in liquid form contained in the vessel at the arrival of the path, calculated at step F, is less than the maximum energy balance calculated in step E. When the estimate of the energy balance of the gas in liquid form contained in the vessel at the arrival of the path is less than the maximum energy balance, this means that at Upon arrival of the journey, the cargo of gas in liquid form will, for example, be at a saturation pressure of the gas in liquid form below the prerequisites defined by the place of destination. If this situation arises during the journey, there is no inconvenience in adjusting the operating plans of the functions of the supply system so as to allow and control an increase in the temperature of the gas in liquid form contained in the gas. tank. Thus, if this is not already the case, the adjustment of the first operating plan of the condensation function can consist in keeping the latter active throughout the journey. The excess gas phase generated from the gas in liquid form is therefore fully condensed instead of possibly being eliminated. There is therefore no loss of gas in liquid form contained in the tank, except for the gas phase generated from the gas in liquid form and used to feed the floating structure.

In this situation, the condensing function is active. In other words, the supply system is allowed to condense the excess gas phase generated from the gas in liquid form in the presence of the latter. The condensation of gas in liquid form can vary in terms of activity, depending on the need to manage the gas. surplus gas phase generated from the gas in liquid form. The condensation of the gas in liquid form can, for example, take place in a more sustained manner in the event of an excess of gas phase generated from the gas in liquid form in the tank, in order to reduce the pressure within the latter.

According to one characteristic of the invention, step G consists of stopping the cooling function at an estimated instant dr which guarantees that the estimate of the energy balance of the gas in liquid form contained in the tank at the arrival of the path , calculated in step F, is less than the maximum energy balance calculated in step E. After the adjustment of the first operating plan of the condensation function which consists in maintaining it around the length of the path, it is possible that the estimate of the energy balance of the gas in liquid form on arrival is still lower than the requirements of the place of destination. It is therefore possible to adjust the second operating plan for the cooling function so that this last evening is deactivated at the estimated time dr. Such an adjustment saves the energy consumed by the cooling function during the time it is deactivated. This causes a rise in the temperature of the gas in liquid form contained in the vessel, because the gas in liquid form is no longer cooled by the cooling function. This is why the estimated instant dr when the cooling function is stopped is established so that the gas in liquid form contained in the tank increases in temperature but this increase does not lead to the requirements being exceeded at the moment when the gas in liquid form will be delivered to the place of destination upon arrival of the journey.

To do this, the estimation and adjustment process will successively repeat the adjustment of the second operating plan of the cooling function and step F, even the step of estimating the energy balance of the gas under liquid form contained in the tank on arrival. The adjustment of the second operating plan of the cooling function consists in determining the estimated instant dr, taking the arrival at the place of destination as the target. The estimated instant dr is then determined as being before a certain period of time with respect to the arrival, for example several days or hours. The estimation and adjustment process then recalculates the estimate of the energy balance gas in liquid form contained in the tank on arrival, this time taking into account the new adjustment of the second operating plan of the cooling function, i.e. stopping it by example several days or hours before arrival at the place of destination. If the estimate of the energy balance of the gas in liquid form contained in the tank on arrival is no longer less than the maximum energy balance calculated in step E, then the estimation and adjustment process continues normally with step H. If the estimate of the energy balance of the gas in liquid form contained in the tank on arrival is still less than the maximum balance, the estimation and adjustment process then repeats the adjustment of the second plane d operation of the cooling function by further anticipating the estimated time dt by, for example, several days or hours before arrival at the place of destination. Then, the estimate of the energy balance of the gas in liquid form contained in the tank on arrival is again calculated by taking into account the new adjustment. Thus, as long as the estimate of the energy balance of the gas in liquid form contained in the tank on arrival is less than the maximum energy balance, the estimated instant dt is postponed in time. This loop makes it possible to determine the estimated instant dt closest to the current instant t, and thus to deactivate the cooling function as soon as possible in order to save as much energy as possible. Once the final estimated instant dt has been determined, the estimation and adjustment process continues with step H.

According to one characteristic of the invention, step G consists of stopping the condensation function as long as the estimation of the energy balance of the gas in liquid form contained in the vessel at the arrival of the path, calculated at step F, is greater than the maximum energy balance calculated in step E. When the estimate of the energy balance of the gas in liquid form contained in the vessel at the arrival of the journey is greater than the maximum energy balance, this means that the cargo of gas in liquid form will be at a saturation pressure of gas in liquid form too high compared to the requirements of the place of destination upon arrival of the floating structure. In order to avoid such a situation, it is advisable to limit any action causing a rise in the temperature of the gas in liquid form contained in the tank. Thus, the first operating plan of the condensing function is adjusted in order to cause a shutdown of the condensing function of the power system. at a given time of summer when the energy balance of the gas in liquid form contained in the tank exceeds the maximum energy balance. The condensation function can optionally be reactivated if the estimate of the energy balance of the gas in liquid form contained in the vessel at the arrival of the path again becomes less than the maximum energy balance thereafter.

According to one characteristic of the invention, step G consists of activating the cooling function as long as the estimation of the energy balance of the gas in liquid form contained in the vessel at the arrival of the path, calculated in step F, is greater than the maximum energy balance calculated in step E. In this situation, it is essential to reduce the temperature of the gas in liquid form contained in the tank. Thus, at the same time as the first operating plan of the condensing function is adjusted so that it is deactivated at the given time of t, the second operating plan of the cooling function is also adjusted. so that the cooling function is active until the arrival of the floating structure at the place of destination, with the aim that the saturation pressure of the gas in liquid form meets the requirements of the place of destination.

In this situation, the cooling function is therefore active. In other words, the supply system is allowed to cool the gas in liquid form contained in the tank. The feed system cools the gas in liquid form at the highest possible activity relative to a configuration of said feed system.

According to one characteristic of the invention, the estimation and adjustment method is repeated by iteration from step B and during the journey of the floating structure. The journey time of the floating structure between its point of departure and the place of destination varies depending on the delivery, but the journey can last several days or even several weeks. The estimate can for example be distorted in the medium or long term by environmental conditions, such as the weather or the state of the sea for maritime transport. Thus, in order to achieve the desired objective, the estimation and adjustment process must be repeated regularly during the journey. As a result, the estimation and adjustment process can for example be configured to start at a regular time interval, for example every six hours. Step A is based on a calculation depending on fixed values. It is therefore not necessary to repeat this step after having launched the estimation and adjustment process for the first time. The estimation and adjustment method is therefore repeatable by iteration from the step of establishing the first operating plan of the condensation function of the power supply system.

According to one characteristic of the invention, the estimation and adjustment method comprises an additional step D ', carried out simultaneously with step D, of calculating the energy balance of the gas in liquid form at time t at from the performance of the condensation and cooling functions from the start of the floating structure and up to the instant t and from an energy balance of the gas in liquid form at an instant t calculated during a earlier iteration. The calculation of the energy balance of the gas in liquid form at time t carried out at step D 'no longer takes into account the temperature of the gas in liquid form contained in the tank at time t measured for example by the temperature sensor. temperature, but an energy balance of the gas in liquid form at time t calculated previously. In other words, step D ’is only executed if the estimation and adjustment process has already been carried out for the first time. Advantageously, the energy balance of gas in liquid form at time t is calculated from the energy balance of gas in liquid form at an earlier time t, i.e. the energy balance of gas in liquid form from the previous one iteration of the estimation and adjustment process, which may have been calculated during step D or D ′.

The calculation of the energy balance of the gas in liquid form at time t during step D 'also takes into account the performance of the condensation and cooling functions from the start of the floating structure and up to the instant t. For the condensation function, this corresponds to data relating to the heat transmitted to the tank and leading to a general increase in the temperature of the latter, illustrated for example by a temperature differential at the inlet and outlet of an exchanger. of heat ensuring the function of condensation. For the cooling function, this corresponds to data relating to the cold transmitted to the tank and resulting in a general decrease in the temperature thereof, illustrated for example by a temperature differential at the inlet and outlet of a heat exchanger providing the cooling function.

According to one characteristic of the invention, the energy balance of gas in liquid form at time t kept for step F is the highest among the energy balance of gas in liquid form at time t calculated at step D and the energy balance of the gas in liquid form at time t calculated in step D ′. In other words, when the estimation and adjustment method subsequently reaches step F, that is to say the step of estimating the energy balance of the gas in liquid form contained in the vessel estimated on arrival, c ' is the energy balance of the gas in liquid form contained in the vessel at time t having the highest value among the result obtained in step D and the result obtained in step D 'which is used for the estimation of step F. The energy balance of the gas in liquid form at time t having the highest value is considered to be the most pessimistic result. The objective being not to exceed the maximum energy balance of the place of destination, the energy balance of the gas in liquid form should be kept at the highest time t as a safety measure.

According to one characteristic of the invention, the estimation and adjustment method comprises an additional step A 'of selecting a safety margin for the maximum energy balance of the gas in liquid form as a function of the characteristics of the path of the structure. floating, step E being carried out taking into account said safety margin. In order to be certain that the floating structure does not arrive at the place of destination with a cargo of gas in liquid form whose energy balance is greater than the requirements of said place of destination, it is possible to take into account a safety margin to virtually reduce the value of the maximum energy balance. Thus, during step E, the calculation of the maximum energy balance is always calculated as a function of the maximum authorized temperature of the gas in liquid form calculated in step A, but also by taking into account the safety margin. A secure maximum energy balance is then obtained, with a value lower than the actual maximum energy balance. During the rest of the estimation and adjustment process, the first operating plane of the condensing function and the second operating plane of the cooling function are adjusted according to the comparison between the estimate of the energy balance of the gas in liquid form contained in the tank at the arrival of the journey and a virtual maximum energy balance, that is to say which takes into account the safety margin. The safety margin thus guarantees the certainty of remaining below the actual maximum energy balance.

The safety margin can be chosen according to different parameters. For example, the longer the journey, the more preferable it is to select a high safety margin. A high safety margin is also recommended in the event of a lack of information about the weather conditions during the journey. The safety margin can for example be entered manually through the control monitor, or it can be programmed to be variable over time.

Since the safety margin is used for the calculation of step E, step A ’is therefore prior to step E during the estimation and adjustment process.

According to a feature of the invention, step A ’is repeated by iteration during the path of the floating structure. The repetition of step A ’may be independent of the repetition of the estimation and adjustment process, or it may be part of it. Stage A ’can also be initiated manually, for example following the occurrence of an unforeseen meteorological phenomenon. It may then be wise to manually increase the value of the safety margin to alleviate the uncertainty due to said meteorological phenomenon.

According to a feature of the invention, the safety margin decreases as the floating structure approaches the place of destination. In other words, the closer the floating structure is to its destination, the lower the safety margin needs to be. It is therefore possible to program a degressive safety margin over time.

According to one characteristic of the invention, the floating structure is equipped with at least one motor supplied at least partially by the gas phase generated from the gas in liquid form, the estimation of the surplus of gas phase generated from the gas in liquid form. liquid during the journey being established from an image value of the heat inputs into the tank and from an estimate of the engine consumption. As has been said previously, the floating structure may be able to use the gaseous phase generated from the gas in liquid form, or even to create it, for example to supply its propulsion engine and / or its electricity generator. The gas phase generated from the gas in liquid form not used for these various functions corresponds to the surplus gas phase generated from the gas in liquid form. The latter needs to be estimated in quantity so that steps B and C of the estimation and adjustment process, that is to say the steps of establishing operating plans for the condensation and cooling functions of the power system, can be unwound. The image value of the heat inputs into the tank may for example depend on the tank model used and therefore be available as a technical characteristic of the tank. The image value of heat inputs into the tank can also be estimated using sensors.

The consumption of the engine can be estimated if the floating structure is equipped with a module making it possible to define a route plan for the journey to the place of destination.

If this is not the case, the consumption of the motor can be estimated from the average speed of the floating structure on the remaining path, the latter depending on the remaining distance to be covered and the time remaining to reach instead of destination.

The surplus gas phase generated from the gas in liquid form can thus be estimated through a source external to the estimation and adjustment process, and for example be entered through the control monitor in order to be taken into account during the course of the estimation and adjustment process. This surplus can then be quantified in tonnes / hour.

The invention also covers a system for managing an energy balance of a gas in liquid form contained in at least one tank of a floating structure, implementing the estimation and adjustment method as described above, said management system comprising at least one system for supplying fuel to a consumer of the floating structure and at least one computer having the function of estimating a quantity of surplus gas phase generated from the gas in liquid form during of a path of the floating structure. Such a system for managing the energy balance comprises the system for supplying fuel to a consumer of the floating structure implementing the condensation and cooling functions, and allows the estimation and adjustment process to be carried out. In order to ensure the smooth running of the estimation and adjustment process, in particular steps B and C respectively establishing the first operating plan of the gas phase condensation function generated from the gas in liquid form and the second operating plan for the cooling function of gas in liquid form operated by the supply system, the computer can transmit the estimate of the quantity of surplus gas phase generated from the gas in liquid form, essential for proceeding with the steps B and C. The energy balance management system can also include the control monitor mentioned above.

The invention also covers a floating structure for the transport of gas in liquid form comprising a system for managing the energy balance of said gas as described above.

Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several exemplary embodiments given by way of indication and not limiting with reference to the appended schematic drawings on the other hand, in which : [fig 1] is a schematic representation of a floating structure loaded with gas in liquid form and making a journey to a place of destination,

[fig 2] is a schematic representation of an embodiment of a gas temperature management system in liquid form according to the invention,

[fig 3] is a schematic representation of a process for estimating and adjusting an energy balance of gas in liquid form according to the invention, when the latter is launched for the first time, [fig 4] is a schematic representation of an unfolding of the method for estimating and adjusting the energy balance of gas in liquid form according to the invention, when the latter is launched by iteration,

[fig 5] is a general diagram illustrating a fuel supply system for a consumer of the floating structure capable of carrying out a plurality of commands according to the estimation and adjustment process,

[fig 6] is a diagram of the supply system according to a first specific embodiment,

[fig 7] is a diagram of the supply system according to a second specific embodiment,

[fig 8] is a curve representing the evolution of the energy balance of gas in liquid form as a function of time as well as the operating plans of the condensation and cooling functions, in a situation where said energy balance of gas in liquid form is estimated to be too low on arrival,

[fig 9] is a curve representing the evolution of the energy balance of gas in liquid form as a function of time as well as the adjusted operating plans of the condensation and cooling functions, to alleviate the situation mentioned in figure 8,

[fig 10] is a curve representing the evolution of the energy balance of gas in liquid form as a function of time as well as the operating plans for condensation and cooling functions, in a situation where said energy balance of gas in liquid form is estimated to be too high on arrival,

[fig 11] is a curve representing the evolution of the energy balance of gas in liquid form as a function of time as well as the adjusted operating plans of the condensation and cooling functions, to alleviate the situation mentioned in figure 10,

[fig 12] is a curve representing a first example of the evolution of a value of a safety margin as a function of time, [fig 13] is a curve representing a second example of the evolution of the value of the safety margin as a function of time.

In order to visualize the context in which the invention falls, FIG. 1 represents a floating structure 1 heading towards a place of destination 2 along a path 3. The floating structure 1 represented here is a transport vessel, for example. an LNG carrier. The floating structure 1 transports a cargo of gas in liquid form in order to deliver it to the place of destination 2. In order to ensure such transport, the floating structure 1 comprises at least one tank 9.

The place of destination 2 is a terminal intended to receive the gas in liquid form contained in the tank 9 of the floating structure 1. When the latter reaches the place of destination 2, the gas in liquid form is discharged for example into a tank 40.

Destination 2, however, imposes requirements on the characteristics of the gas in liquid form. The requirements of the place of destination 2 may vary depending on the manager of the facility to which the place of destination 2 is attached, and mainly relate to the characteristics of the gas in liquid form, for example its saturation pressure and / or its temperature.

If the gas in liquid form contained in the vessel 9 of the floating structure 1 does not meet these saturation pressure requirements of the gas in liquid form, the cargo of gas in liquid form can potentially be refused by the manager of the installation of the place of destination 2.

In order to avoid this, the cargo of gas in liquid form should be closely monitored throughout Route 3. Route 3 has a variable distance and can last several days or even weeks depending on the distance from a loading location to the destination. place of destination 2 and the speed of the floating structure 1.

FIG. 2 schematically represents a management system 4 of an energy balance of the gas in liquid form contained in the tank of the floating structure. The energy balance of the gas in liquid form corresponds to a datum including various characteristics of said gas, such as its temperature, its saturation pressure, its total mass of gas in liquid form or its specific heat capacity, for example. The management system 4 comprises a control unit 41 having in memory a method for estimating and adjusting the energy balance of the gas in liquid form contained in the tank of the floating structure. The control unit 41 is thus able to initiate the estimation and adjustment process 5 in a regular and automated manner and / or following a manual control exerted for example by means of a control monitor 6. It is also possible to enter data manually through the control monitor 6, for example characteristics of the gas in liquid form transported, or any other information useful for the progress of the estimation and adjustment process 5 as will be specified thereafter.

The management system 4 also includes a system 8 for supplying fuel to a consumer of the floating structure. The feed system 8 has the function of condensing and / or cooling the gas in liquid form contained in the tank and is able to adjust one or the other of these functions by activating or deactivating the latter. The adjustment of the condensing and cooling functions of the power system 8 depends on the result of the estimation and adjustment process 5. Thus, when the latter ends, the control box 41 sends a signal to the system of. power supply 8, said signal indicating the adjustments to be made by the power supply system 8.

The management system 4 also includes a calculator 7. The function of the calculator 7 is to estimate a quantity of surplus gas phase generated from the gas in liquid form during the journey of the floating structure. The gas phase generated from the gas in liquid form occurs naturally within the tank of gas in liquid form, or it can be forced. The estimate of excess gas phase generated from the gas in liquid form is calculated by estimating the consumption of the motor of the floating structure and by an image value of the heat entering the tank. The computer 7 and the control unit 41 can be part of the same control unit or else be independent of each other.

The estimation of the consumption of the motor of the floating structure can be made by entering a route plan in the control monitor 6 which transmits the information. to the computer 7, or else by calculating an average speed of the floating structure from the distance remaining between a position of the floating structure and the place of destination and the time remaining to reach it. The calculation of the average speed of the floating structure can also be carried out by entering data into the control monitor 6 which transmits the information to the computer 7.

The image value of the heat inputs into the tank can correspond to a design value of the heat inputs into the tank, or also to an estimate of the heat inputs into the tank. The design value of the heat inputs into the tank depends on the model of the tank used for transport and can be given to computer 7 through the control monitor 6. The estimate of the heat inputs into the tank can also be communicated by sensors included in said tank.

Once the excess gas phase generated from the gas in liquid form during the journey is estimated by the computer 7, the latter transmits the result to the control unit 41. The surplus gas phase generated from the gas in liquid form to the course of the journey is a datum allowing the course of the estimation and adjustment process 5 as will be described hereinafter.

FIG. 3 is a schematic representation of the method for estimating and adjusting the energy balance of gas in liquid form according to the invention. This diagram represents the flow of the estimation and adjustment process 5 when it is launched for the first time during the journey to the place of destination. The estimation and adjustment process 5 can be started a first time before the start or at the start of the floating structure. In FIG. 3, the solid arrows represent the course of each of the steps of the estimation and adjustment method 5, and the dotted arrows correspond to a data transmission between two steps of the estimation and adjustment method 5. or between an element of the system for managing the energy balance of gas in liquid form and a step of the estimation and adjustment process 5.

When the estimation and adjustment process 5 is launched for the first time, it begins with a step A which makes it possible to calculate the maximum authorized temperature of the gas in liquid form contained in the tank on arrival at the place of destination. The calculation of step A depends on certain constant characteristics of the gas in liquid form such as the total mass of gas in liquid form and the specific heat capacity of the latter. Such characteristics depend on the type of gas in liquid form being transported and are known in one way or another to the personnel of the floating structure. Thus, the total mass of gas in liquid form and the specific heat capacity of gas in liquid form can be entered or preselected through the control monitor 6 and transmitted for the calculation of step A of the estimation process. and adjustment 5. The calculation of step A also depends on the maximum saturation pressure requirements of the gas in liquid form at the place of destination. As these requirements vary according to the place of destination, the maximum saturation pressure value required of the gas in liquid form is known as soon as the place of destination is known. The saturation pressure requirements of the gas in liquid form can be entered through the control monitor 6 or be known, for example by means of a database listing all the places of destination authorized for reception and the unloading of gas in liquid form.

Once the calculation of step A has been carried out, the estimation and adjustment process 5 can go directly to a step B, or else go through an intermediate step A ’. Step A ’consists of determining a safety margin in order to be sure that the energy balance of the gas in liquid form is lower than the requirements of the place of destination on arrival. Thus, step A 'is not essential for the smooth running of the estimation and adjustment process 5 which can dispense with the safety margin to perform all the calculations and estimations, but nevertheless contributes to the 'optimization of the adjustment of the energy balance of gas in liquid form. The safety margin can be determined automatically from the route plan and / or weather conditions, or manually via the command monitor 6. The safety margin is used for a calculation during a step E. L 'step A' can therefore take place at any time prior to step E.

Step B of the estimation and adjustment process 5 occurs after step A or step A '. Step B consists of establishing the first operating plan for the condensing of the power supply system 8. The first operating plan of the condensing function of the power supply system 8 indicates over time at which point in the journey the condensing function remains active or inactive and when the latter s 'activates or deactivates. The establishment of the first operating plan depends on the amount of surplus gas phase generated from the gas in liquid form during the journey. It is in fact understood that, for example, if it is determined that no surplus gas phase generated from the gas in liquid form is generated during the journey, the supply system does not have a gas phase generated from the gas phase. gas in liquid form to be condensed and therefore does not need to be active during the journey. Such a surplus may result from a case where the consumer of the floating structure is shut down, the natural evaporation of the gas in liquid form continuing to occur. The surplus gas phase generated from the gas in liquid form is estimated by the computer 7 which therefore transmits the information to the control unit so that the estimation and adjustment process 5 can perform step B.

A stage C takes place in parallel or successively with stage B. Stage C is based on the same principle as stage B, since it allows the establishment of the second operating plan of the cooling function of the system d power supply 8. As for step B, the second operating plan of the cooling function of the power supply system 8 indicates over time at which point in time during the journey the cooling function remains active or inactive and at when the latter is activated or deactivated. The establishment of the second operating plan also depends on the quantity of surplus gas phase generated from the gas in liquid form during the journey, estimated by the computer 7. The estimate of surplus gas phase generated from the gas under liquid form is therefore taken into account for steps B and C.

The estimation and adjustment method 5 then continues with a step D which calculates an energy balance of the gas in liquid form at an instant t. FIG. 3 showing the course of the estimation and adjustment process 5 during its first launch, the instant t corresponds here to the time of departure or before the departure of the floating structure. For the calculation of the energy balance of gas in liquid form at time t, the estimation and adjustment method 5 needs the characteristics of the gas in liquid form, in particular used during step A for the calculation of the maximum authorized temperature of the gas in liquid form contained in the tank on arrival, such as the total mass of gas in liquid form of gas in liquid form, or the specific heat capacity of gas in liquid form. These characteristics can be provided by the control monitor 6, just as for step A. The calculation of the energy balance of the gas in liquid form at time t also requires the average temperature of the gas in liquid form contained in the tank. at time t. The average temperature of the gas can be measured, for example, by means of a temperature sensor located in the tank. It is therefore the supply system 8 which supplies the average temperature in the tank and which transmits this to the control unit so that the estimation and adjustment method 5 can perform the calculation of step D.

Once step D has been completed, the estimation and adjustment method 5 continues with step E which consists in calculating a maximum energy balance. The maximum energy balance corresponds to the limit of the requirements of the place of destination that the energy balance of the gas in liquid form contained in the tank must not exceed, otherwise the cargo will be refused once the floating structure has arrived at the place of destination. . The energy balance of gas in liquid form can however exceed this limit of the maximum energy balance during the journey without consequences, but must imperatively fall under this maximum energy balance before the floating structure reaches the place of destination. It is understood that the maximum energy balance is a target for adjusting the energy balance of the gas in liquid form contained in the tank during the journey.

For this calculation of the maximum energy balance during step E, the estimation and adjustment method 5 needs the characteristics of the gas in liquid form and of the maximum authorized temperature of the gas in liquid form contained in the tank at l. 'arrival calculated during step A. The data provided and the calculations performed during step A can therefore be transmitted for the calculation of step E. If the estimation and adjustment method 5 has carried out the 'step A', in other words if the safety margin has been determined and selected, said safety margin is also transmitted for be taken into account for the calculation of the maximum energy balance. Thus, the maximum energy balance calculated during step E corresponds to the actual maximum energy balance in the absence of a safety margin, or to a virtual maximum energy balance, lower than the actual maximum energy balance due to the taking into account of the safety margin in the calculation.

The next step of the estimation and adjustment process 5 is a step F ensuring the estimation of the energy balance of the gas in liquid form contained in the vessel at the end of the journey. Step F makes it possible to determine, while keeping the operating plans for the condensation and cooling functions established during steps B and C, what will be the energy balance of the gas in liquid form contained in the vessel at the arrival of the path. . To make such an estimate, the calculation is based on the energy balance of the gas in liquid form at time t calculated during step D, as well as on the operating plans for the condensation and cooling functions established during steps B and C. These latter having been established for the entire path during steps B and C, the estimation and adjustment method 5 can then estimate the evolution of the energy balance of the gas in liquid form during this step F, the condensation and cooling functions being able to vary said energy balance of the gas in liquid form depending on whether they are active or inactive and when they are activated and deactivated. The energy balance of the gas in liquid form contained in the tank on arrival can therefore be determined from these data.

The estimation and adjustment method 5 then continues with a step G which ensures the adjustment of the operating plans of the condensing and cooling functions of the supply system 8. These adjustments are carried out as a function of a comparison between the maximum energy balance calculated during step E and the estimate of the energy balance of the gas in liquid form contained in the tank on arrival, calculated in step F. As a reminder, the estimate of the energy balance gas in liquid form contained in the tank on arrival calculated during step F is based on the operating plans for the condensation and cooling functions established during steps B and C. Step G therefore makes it possible to modify this estimate of the energy balance of the gas in liquid form contained in the tank on arrival by adjusting the operating plans for the condensing and cooling functions.

If the estimate of the energy balance of the gas in liquid form contained in the tank on arrival is greater than the maximum energy balance, this means that the cargo of gas in liquid form will be on arrival at a saturation pressure of the gas under excessive liquid form in relation to the maximum requirements of the place of destination. The operating plans for the condensation and cooling functions must therefore be adjusted in order to reduce the temperature of the gas in liquid form contained in the vessel and by analogy the energy balance of the gas in liquid form.

If the estimate of the energy balance of the gas in liquid form contained in the tank on arrival is less than the maximum energy balance, this means that the cargo of gas in liquid form will be on arrival in compliance with the requirements of the place of destination, but it is nevertheless possible to make adjustments allowing an increase in the temperature of the gas in liquid form contained in the tank if these prove to be useful in terms of energy saving. The operating plans for the condensation and cooling functions must therefore be adjusted in order to allow an increase in the temperature of the gas in liquid form contained in the tank and by analogy of the energy balance of the gas in liquid form.

Step G therefore determines the optimal adjustments of the operating plans for the condensing and cooling functions of the power system 8 to best meet the situation. Examples of adjustments to operating plans will be presented below.

The estimation and adjustment method 5 finally ends with a step H, implementing the operating plans adjusted during step G. Step H marks the end of the estimation and adjustment method. 5 and sends the adjusted operating plans of the condensing and cooling functions to the power system 8 for the latter to implement. The details of the operation of the power system 8 will be presented below. FIG. 4 is a schematic representation of the estimation and adjustment method 5 of the energy balance of gas in liquid form during its repetition by iteration, that is to say when the estimation and adjustment method 5 is started during the journey after having been launched for the first time according to FIG. 3. Most of the steps of the estimation and adjustment process 5 are similar to what has been described previously, and reference will therefore be made to the description of Figure 3 for explanations relating to them. As in FIG. 3, the solid arrows represent the course of each of the steps of the estimation and adjustment process 5, and the dotted arrows correspond to a transmission of data between two steps of the estimation and adjustment process. adjustment 5 or between an element of the system for managing the energy balance of gas in liquid form and a step of the estimation and adjustment process 5.

When the estimation and adjustment process 5 is repeated by iteration, it is no longer useful to initiate step A. Indeed, the result of the calculation of step A, that is to say that of the maximum authorized temperature of the gas in liquid form contained in the tank on arrival, is invariable over time. The result of step A being however used for the calculation of step E, said result must however be kept during the journey, for example by means of a memory of the control unit.

Step A ’of selecting the safety margin is also not repeated. The safety margin may however be caused to vary, and this independently of the progress of the estimation and adjustment process 5, or because it has been configured to vary over time when the estimation process and adjustment 5 was started the first time, either because it was changed manually through the control monitor 6. The variation of the safety margin is the reason why step E is kept within the estimation and adjustment method 5 since it is a factor liable to vary over time for the calculation of step E.

The estimation and adjustment method 5, when the latter is repeated by iteration, therefore begins with step B. Steps B and C take place as when the estimation and adjustment method is first launched. 5, the amount of phase surplus gas generated from the gas in liquid form always being calculated and supplied by the computer 7.

Step D also takes place identically to what has been described above. On the other hand, a step D 'takes place, in parallel with step D, which also calculates the energy balance of the gas in liquid form at time t, but according to a calculation different from that of step D. The calculation the energy balance of the gas in liquid form at the instant t of step D 'is made from an energy balance of the gas in liquid form at an earlier instant t, calculated during a previous iteration of the process of estimation and adjustment 5, as well as from the performance of the condensation and cooling functions from the start of the floating structure. The energy balance of the gas in liquid form at an earlier instant t can be recovered for example from the buffer memory of the control unit. The performance of the condensing and cooling functions results in the heat transfer carried out by the condensing function and cold transfer carried out by the cooling function to the gas cargo in liquid form. The performance of the condensing and cooling functions can therefore be measured by sensors located at the level of the elements of the supply system 8 ensuring the condensation and cooling of the gas in liquid form, which transmits these data to the control box for application during of step D '.

After calculating the energy balances of the gas in liquid form at time t in steps D and D ’, only the energy balance of the gas in liquid form at time t having the highest value is kept. The latter is considered to have the most pessimistic value, the priority being to remain below the maximum energy balance calculated subsequently.

The remainder of the estimation and adjustment process 5 then proceeds in accordance with what has been described in FIG. 3. Once the estimation and adjustment process 5 has been completed, the adjustments of the operating plans of the functions. of condensation and cooling are transmitted to the power system 8, and the estimation and adjustment process 5 can again be repeated directly from step B according to the setting of the control box. Advantageously, the housing of The control is configured to repeat the estimation and adjustment process 5 at regular intervals throughout the journey, according to the sequence of FIG. 4, for example once a day or every six hours.

Figure 5 is a general representation of the supply system 8 providing the functions of condensing and cooling gas in liquid form. In general, the supply system 8 interacts with the tank 9 as well as with a set of consumers.

The supply system 8 is suitable for managing the temperature of the gas in liquid form in the tank 9. To do this, the supply system 8 comprises a liquid inlet 81 and a gas inlet 82. The liquid inlet 81 links the supply system 8 to the tank 9, and is able to suck the gas in liquid form 13, for example by means of a gas pump in liquid form 26. The gas inlet 82 extends from a vessel top which may include a certain quantity of gas phase 14 generated from the gas in liquid form to the supply system 8. The gas phase 14 generated from the gas in liquid form can be sucked for example by a compressor 27 in order to be driven to the supply system 8.

The supply system 8 also includes a gas outlet 83 which extends from the supply system 8 to the set of consumers. By way of example, the consumers can be a propulsion engine 16, an electric generator 17, a combustion chamber 18 or a degassing mat 28. The propulsion engine 16 makes it possible to advance the floating structure during the journey and is suitable for being supplied by the gas phase 14 generated from the gas in liquid form. The electric generator 17 ensures the supply of electricity to the floating structure, for example the lighting or the on-board network of the floating structure and more generally any entity requiring an electrical supply. The gas phase 14 generated from the gas in liquid form therefore serves as fuel for one and / or the other of these consumers. Thus, for example in the event of an excess of gas phase 14 generated from the gas in liquid form, the supply system 8 can suck the gas phase 14 generated from the gas in liquid form into the gas inlet 82. The gas phase 14 generated from the gas under liquid form can then be processed by the supply system 8 and then exit the latter through the gas outlet 83, for example with the aim of supplying the propulsion motor 16 or the electric generator 17.

The gas phase 14 generated from the gas in liquid form and not used for powering the propulsion engine 16 or the electric generator 17 represents the surplus gas phase 14 generated from the gas in liquid form. This surplus gaseous phase 14 generated from the gas in liquid form can wander burnt by the combustion chamber 18 or wander released into the atmosphere by the degassing mat 28.

Surplus gas phase 14 generated from the gas in liquid form can also be returned to supply system 8 through bypass 84 to be condensed by it. This being done, the gas in condensed liquid form returns to the tank 9 through a liquid outlet 85 of the supply system 8.

If there is a need for cooling the gas in liquid form 13, the latter is sucked by the gas pump in liquid form 26 and circulates within the liquid inlet 81 to the supply system 8 where it is cooled there. . The cooled liquid gas 13 then returns to the vessel 9 through the liquid outlet 85.

Figure 6 is a schematic representation of a first embodiment of the supply system 8 providing the functions of condensing and cooling gas in liquid form.

As in FIG. 5, the supply system 8 manages the temperature of the tank 9. The tank 9 is at least partially filled with a certain quantity of gas in liquid form 13. The tank top can also include a certain amount of gas phase 14 generated from the gas in liquid form. The tank 9 also comprises at least the gas pump in liquid form 26. The tank 9 also comprises a first temperature sensor 10. It is from this first temperature sensor 10 that the average temperature of the gas in liquid form 13 is measured and transmitted to the control unit for the calculation of step D of the estimation and adjustment process. For the example of FIG. 6, the first temperature sensor 10 of the tank 9 reads the temperature of the gas in liquid form which surround it. If the floating structure comprises a plurality of tanks 9 each comprising a first temperature sensor 10, the temperatures are averaged and then sent to the control unit.

As indicated above, the condensing function of the feed system 8 allows the excess gas phase 14 generated from the gas in liquid form to be condensed. To do this, the gas phase 14 generated from the gas in liquid form from the tank 9 is sucked by the compressor 27 located outside the tank and constituting a gas phase circuit 15. The gas phase circuit 15 transports the gas. gas phase 14 generated from the gas in liquid form which extends until it emerges at the level of the propulsion engine 16 and / or the electric generator 17 with the aim of being used as fuel by the latter.

The gas phase 14 generated from the gas in liquid form and not used for supplying the propulsion engine 16 or the electric generator 17 represents the surplus gas phase 14 generated from the gas in liquid form and circulates within a circuit surplus 19. The surplus circuit 19 allows the circulation of the surplus gas phase 14 generated from the gas in liquid form to a first heat exchanger 11. It is the first heat exchanger 11 which performs the condensation function. of the surplus gas phase 14 generated from the gas in liquid form, and this thanks to a heat exchange between a first pass 111 and a second pass 112. The first pass 111 is crossed by the surplus gas phase 14 generated from the gas in liquid form which is then cooled by the second pass 112, so that the surplus gas phase 14 generated from the gas in liquid form condenses and changes to the liquid state. It is thus understood that when the condensation function of the supply system 8 is active, the surplus gas phase 14 generated from the gas in liquid form is directed to the first heat exchanger 11 via the surplus circuit 19. If the condensing function of the feed system 8 is inactive, then the excess gas phase generated from the gas in liquid form is directed to the combustion chamber 18 to be burnt or else to the degassing mat 28 to be released into the 'atmosphere. In order to condense the surplus of gas phase 14 generated from the gas in liquid form, a fluid having a temperature lower than the state change temperature of the surplus gas phase 14 generated from the gas in liquid form circulates within the second pass 112.

Once the surplus gas phase 14 has been generated from the gas in liquid form condensed by the first heat exchanger 11, the condensed gas circulates in a condensed gas circuit 20 to a return circuit 21 which directs the condensed gas towards the tank

9.

Regarding the cooling function of the supply system 8, the gas in liquid form 13 contained in the tank 9 is first of all sucked by the gas pump in liquid form 26. The gas in liquid form 13 sucked in by the gas pump. gas in liquid form 26 circulates to a second heat exchanger 12. It is the second heat exchanger 12 which performs the function of cooling the gas in liquid form 13, and this thanks to a heat exchange between a third pass 121 and a fourth pass 122. The gas in liquid form 13 sucked by the gas pump in liquid form 26 circulates in the second heat exchanger 12 through the fourth pass 122 and is cooled. In order to cool the gas in liquid form 13 which is already at a very low temperature, a fluid of a temperature lower than the gas in liquid form 13 circulates within the third pass 121. The third pass 121 may be part of a refrigerant circuit external to the supply system 8, and not shown in FIG. 6. The external refrigerant circuit may for example form part of a system of the vacuum evaporator type.

Subsequently, after having been cooled by the second heat exchanger 12, the cooled gas in liquid form 13 returns to the tank 9 through the return circuit 21. Thus, the cooled gas in liquid form 13 makes it possible to generally cool down. the tank 9, the temperature of the gas in liquid form 13 being cooled below the temperature of the gas in liquid form 13 remaining in the tank 9.

The heat exchanges of the first heat exchanger 11 and of the second heat exchanger 12 are measured by a plurality of temperature sensors. So the power system 8 comprises two second temperature sensors 24, each located at the inlet and outlet of the first heat exchanger 11, and two third temperature sensors 25, each located at the inlet and outlet of the second heat exchanger 12. By calculating a temperature difference between the outputs and the inputs of each of the heat exchangers, it is possible to measure the heat input into the tank 9 thanks to the second sensors of the heat exchanger. temperature 24 and the cold input into the tank 9 thanks to the third temperature sensors 25. The heat input and the cold input are data used for the calculation of the execution of the condensing and cooling functions of the tank. supply system 8, the said executions serving for the calculation of the energy balance of the gas in liquid form at the instant t of step D ′ of the estimation and adjustment process. These data are therefore sent to the control unit by the power supply system 8.

At the end of the estimation and adjustment process, the power supply system 8 receives the adjusted operating plans for the condensing and cooling functions. The power supply system 8 then modifies its operation according to the adjusted operating plans, being able to program the activation or deactivation of one and / or the other of the condensation and cooling functions.

Fig. 7 schematically shows a second embodiment of the power system 8. Compared to the first embodiment shown in Fig. 6, only the implementation of the cooling function of the power system 8 is different. Reference will therefore be made to the description of FIG. 6 for any part of the power supply system 8 common to the two embodiments.

In this second embodiment of the supply system 8, the latter implements its cooling function in combination with a function of supplying consumers of the floating structure. Indeed, when the gas phase 14 generated from the gas in liquid form is sucked into the gas phase circuit 15, the latter passes through the second exchanger 12, circulating within the third pass 121. The gas in liquid form 13 contained in the tank 9 is for its part first sucked by the gas pump in liquid form 26 and then circulates through the fourth pass 122 located within the second heat exchanger 12. The heat exchange taking place between the third pass 121 and the fourth pass 122 makes it possible both to increase the temperature of the gas phase 14 generated from the gas in liquid form in order to that this is adequate to supply the propulsion motor 16 and / or the electric generator 17, but also to sub-cool the gas in liquid form 13 sucked by the gas pump in liquid form 26. Subsequently, after having been cooled by the second heat exchanger 12, the cooled gas in liquid form 13 circulates in a cooled gas circuit 23, up to the return circuit 21 which directs the gas in liquid form 13 cooled into the tank 9.

Thus, the gas in cooled liquid form 13 returns to the tank 9 and makes it possible to cool the latter overall, the temperature of the gas in cooled liquid form 13 being lower than the temperature of the gas in liquid form 13 remaining in the tank 9.

The gas in liquid form 13 circulates in this way if the cooling function is active. The supply system 8 therefore allows the condensing and cooling functions to be active or inactive simultaneously, insofar as there is presence of gas phase 14 generated from the gas in liquid form for the cooling function and surplus gas phase 14 generated from the gas in liquid form for the condensation function.

Figures 8 to 11 show a curve showing the evolution of the energy balance of the gas in liquid form contained in the tank as a function of time, that is to say during the path of the floating structure, and as a function of operating plans for the condensation and cooling functions shown in the upper part of each of Figures 8 to 11. Figures 8 and 9 correspond respectively to an estimate and an adjustment following a situation where the estimate of the energy balance of the gas under liquid form on arrival is less than the maximum energy balance. FIGS. 10 and 11 correspond respectively to an estimate and an adjustment following a situation where the estimate of the energy balance of gas in liquid form is greater than the maximum energy balance. For each of FIGS. 8 to 11, the initial situation presented is the launching of the estimation and adjustment process at an instant t during the journey of the floating structure between the departure 50 and the arrival 51.

Each of the curves of the energy balance as a function of time in Figures 8 to 11 includes an actual maximum energy balance 32, and the virtual maximum energy balance 33, that is, which takes into account the safety margin. The virtual maximum energy balance 33 is less than the actual maximum energy balance 32, the difference depending on the value of the safety margin. The actual maximum energy balance 32 is only present as an indication, because for each of the figures, the adjustment of the energy balance of the gas in liquid form contained in the tank is done according to the virtual maximum energy balance 33. The balance real maximum energy 32 is constant over time. Advantageously, the virtual maximum energy balance 33 gradually approaches the actual maximum energy balance over time, but for reasons of clarity, the virtual maximum energy balance 33 is also represented as being constant over time in FIGS. 8 to 11. .

FIGS. 8 to 11 also each represent the curves of the first operating plane 36 of the condensation function and of the second operating plane 37 of the cooling function over time. The ordinates of the operating plan curves have only two positions: a 0 position and a 1 position. When the operating plans are in position 0, this means that the associated functions are inactive. When the operating plans are in position 1, it means that the associated functions are active, which therefore allows the condensation and / or cooling of the gas in liquid form through the supply system. For each of the situations, it is assumed that the two operating planes are basic in position 1 throughout the journey, that is to say that the condensation and cooling functions are authorized throughout the journey.

FIG. 8 therefore represents a first situation during the journey of the floating structure. Thus, at time t, the estimation and adjustment method is launched, and the energy balance of the gas in liquid form at time t 38 is obtained during step D or D 'of the method of estimation and adjustment, either from the temperature of the gas in liquid form contained in the tank, or from the performance of the condensation and cooling functions from the start 50. It is possible to observe the evolution of the energy balance of the gas in liquid form contained in the tank from the start 50 and up to the instant t, the change corresponding to a measured energy balance 34. The measured energy balance 34 is shown in solid lines because it has already been measured in real time from the start 50, the first measurement corresponding to a balance starting energy 30, determined when the estimation and adjustment process was started for the first time. The change in the energy balance of the gas in liquid form after time t is dotted and represents a forecast energy balance 35 which is therefore evaluated by the estimation and adjustment process, more precisely during step F and from the energy balance of the gas in liquid form at time t 38. The estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 therefore corresponds to an estimate of the value of the energy balance when the floating structure arrives at the finish 51 if the operating plans as presented in FIG. 8 are maintained until this arrival 51.

It can be seen in FIG. 8 that without adjusting the operating plans of the estimation and adjustment method according to the invention, the estimation of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 is less than the virtual maximum energy balance 33, calculated during step E of the estimation and adjustment process. The gas in liquid form contained in the tank therefore meets the requirements of the place of destination. However, it is possible to adjust the operating plans in order to limit the energy consumption of the power supply system.

FIG. 9 represents a curve implementing step G of the estimation and adjustment method according to the invention, with operating plans adjusted with respect to those presented in FIG. 8. The estimation and adjustment method The adjustment always takes place at the instant t and after the observation that the estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 was less than the virtual maximum energy balance 33. The estimation process and adjustment therefore adjusts operating plans to ensure energy savings. Thus, although this is already the case in the example presented, the first operating plane 36 of the condensation function is adjusted to be kept active, either in position 1, until the arrival 51 of the journey. The excess gas phase generated from the gas in liquid form is therefore fully condensed, which does not lead to losses of the cargo.

Furthermore, the estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 being less than the virtual maximum energy balance 33, it is also possible to deactivate the cooling function at an estimated instant dt during of the journey. To determine the estimated instant dt, the estimation and adjustment method implements one or more iterations in which the adjustment of the second operating plan 37 of the cooling function and the recalculation of the cooling function alternate successively. estimation of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51. Here, the adjustment of the second operating plan 37 of the cooling function consists in selecting an instant when the cooling function is deactivated in taking arrival 51 as the target. The iterations continue as long as the estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 is less than the virtual maximum energy balance 33, the selected instant at which the cooling function is deactivated being at each new occurrence more and more prior to the previous one, and the calculation of the estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 being carried out each time with the new adjustment of the second operating plan 37 of the previously determined cooling function. These iterations thus make it possible to determine the optimum estimated instant dt so that the estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 does not exceed the virtual maximum energy balance 33, but while deactivating the Cooling function as early as possible in order to save maximum energy.

Once the estimated time dt has been obtained, the estimation and adjustment process adjusts the second operating plan 37 of the cooling function and transmits it to the supply system. The second adjusted operating plane 37 of the cooling function can be seen in figure 9, where it can be seen that the cooling function goes to position 0 as a result of the adjustment, causing it to be deactivated at the estimated time dt. Thus, between the estimated instant dt and the arrival 51, the cooling function is kept deactivated. Knowing this, and given that the condensation function is still active, the temperature of the gas in liquid form contained in the tank, and by analogy the energy balance of the gas in liquid form contained in the tank, presents a more significant increase between l 'estimated instant dt and arrival 51 as on the curve of FIG. 8. The estimated instant dt, thanks to the iterations of the estimation and adjustment process mentioned above, is however calculated so as to cause an increase in l estimation of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 but without the latter exceeding the virtual maximum energy balance 33 on arrival 51 at the place of destination.

The gas in liquid form contained in the tank therefore always meets the requirements of the place of destination, but energy savings are made between the estimated time dt and arrival 51 since the cooling function is deactivated during this period. time consuming and therefore does not need to be supplied with energy. The estimation and adjustment process therefore made it possible to limit the waste of energy while maintaining the gas in liquid form in accordance with the requirements of the place of destination.

FIG. 10 still represents the curve of the evolution of the energy balance of the gas in liquid form contained in the tank over time, but this time in the opposite situation to FIGS. 8 and 9. In fact, according to the estimation process and d 'adjustment, during the instant t of the journey, the energy balance of the gas in liquid form at the instant t 38 is calculated, then the estimation and adjustment process calculates the estimate of the energy balance 31 of the gas in the form liquid contained in the tank on arrival 51 from the energy balance of the gas in liquid form at time t 38. As can be seen in FIG. 10, the estimation of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 is greater than the virtual maximum energy balance 33, and even the actual maximum energy balance 32, despite the constant activation of the cooling function throughout the journey as evidenced by the second plan of operation 37 of the cooling function visible on the a figure 10. In this situation, upon arrival 51, and if the operating plans of the condensing and cooling functions are not adjusted, the gas in liquid form contained in the vessel will not meet the requirements of the place of destination, resulting in the refusal of the cargo by the latter. To avoid this, it is essential to lower the saturation pressure of the gas in liquid form contained in the tank, leading to a decrease in the energy balance of the gas in liquid form contained in the tank as well, in order to meet the requirements of the place of destination. upon arrival 51. A given instant of t is indicated in FIG. 10 and corresponds to the instant when the forecast energy balance 35 exceeds the virtual maximum energy balance 33, that is to say the instant from which the energy balance of the gas in liquid form contained in the tank no longer meets the requirements of the place of destination.

The adjustments necessary to alleviate the situation mentioned in FIG. 10 are shown in FIG. 11. Thus, if this is not already the case, the estimation and adjustment method adjusts the second operating plan 37 of the control function. cooling so that the latter is active until the arrival 51 of the journey.

As mentioned previously, the main factor causing an increase in the temperature of the gas in liquid form contained in the tank as well as in the energy balance thereof is due to the condensation of the surplus gas phase generated from the gas in the form liquid. Indeed, although the latter is condensed in order to pass in liquid form, the temperature of the condensed gas is higher than the temperature of the gas in liquid form contained in the tank. The return of the condensed gas to the tank therefore leads in the long run to an increase in the temperature of the gas in liquid form contained in the tank. The best way to stop such a rise in temperature is therefore to implement the first operating plan 36 adjusted for the condensation function so that the latter is deactivated.

Thus the estimation and adjustment method adjusts the first operating plane 36 of the condensation function. The condensation function is therefore programmed to be deactivated at the given instant of t, that is to say at the moment when the estimated energy balance 34 reaches the virtual maximum energy balance 33. The estimation and evaluation process adjustment thus allows the condensing function to be kept active as long as possible. At the given time of summer, the condensation function is deactivated. The increase in the energy balance of the gas in liquid form contained in the tank is then stopped, by deactivating the condensation function, but also by keeping the cooling function in operation. The estimate of the energy balance 31 of the gas in liquid form contained in the tank on arrival 51 is therefore maintained at the level of the virtual maximum energy balance 33, which corresponds to the requirements of the place of destination. In this configuration, between the given time of summer and the arrival 51, the surplus gas phase generated from the gas in liquid form is no longer condensed by the supply system.

FIG. 12 represents a first example of a curve of the evolution of the safety margin 60 as a function of time, from the start 50 to the finish 51. This first example shows a safety margin 60 which decreases over time. In other words, the closer the floating structure is to the place of destination, the more the safety margin 60 decreases and therefore the closer the virtual maximum energy balance approaches the actual maximum energy balance, given that the virtual maximum energy balance is recalculated at each step E by iterations of the estimation and adjustment process with the safety margin 60 which decreases as the floating structure approaches its destination.

The value of the safety margin can also depend on the amount of information that the personnel of the floating structure have concerning the trip, for example the meteorological conditions during this one or the sea conditions. Higher safety 60 may be indicated if there is no information regarding the trip conditions.

FIG. 13 represents a second example of the evolution of the safety margin 60 over time. At the start of this journey, the safety margin 60 decreases over time, just as in the previous figure. However, it is possible that an unforeseen event 61 may occur. Event 61 can be a natural phenomenon, for example a meteorological phenomenon such as a storm or fog, likely to slow down the speed of the floating structure. Event 61 can also be a mechanical incident, for example a failure of the floating structure, capable of immobilizing the latter for a not insignificant period of time. Such an event 61 therefore lengthens the travel time to the place of destination. In this situation, the safety margin 60 as it was programmed at the start 50 is no longer adequate for the journey. It is therefore possible to reprogram the safety margin 60 in order to adapt it to the consequences of the event 61, that is to say the slowing down or immobilization of the floating structure in the above examples. In FIG. 13, the safety margin 60 is increased when the event 61 has occurred, then decreases again over time. This modification guarantees a safety concerning the virtual maximum energy balance and makes it possible to avoid errors which could potentially lead to the refusal of the gas cargo in liquid form upon arrival at the place of destination.

Of course, the invention is not limited to the examples which have just been described and numerous modifications can be made to these examples without departing from the scope of the invention.

The invention, as it has just been described, achieves the goal it had set itself, and makes it possible to propose a method for estimating and adjusting an energy balance of a gas in the form of liquid contained in a tank of a floating structure so that the said energy balance of the gas in liquid form complies with the requirements of a place of destination where the delivery of the gas in liquid form is intended, while adjusting consumption as much as possible energy from the power system. Variants not described here could be implemented without departing from the context of the invention, as long as, according to the invention, they include a method of estimating the fit according to the invention.

Claims

1- Estimation and adjustment method (5) of an energy balance of a gas in liquid form (13) contained in at least one tank (9) of a floating structure (1) intended to deliver said gas in liquid form (13) at a given place of destination (2), the floating structure (1) comprising a fuel supply system (8) to a consumer of the floating structure (1) capable of putting into operation performs a function of condensing a gas phase (14) generated from the gas in liquid form and / or a function of cooling the gas in liquid form (13), characterized in that the estimation and adjustment method ( 5) comprises the following steps: a step A of calculating the maximum authorized temperature of the gas in liquid form contained in the vessel on arrival at the place of destination, from the maximum saturation pressure requirements of gas in liquid form the place of destination (2) and the characteristics of the gas in liquid form contained in the tank, a step B to establish ssement of a first operating plan (36) of the function of condensation of the gas phase (14) generated from the gas in liquid form operated by the supply system (8) up to the inlet (51) at the destination (2), said first operating plan (36) being established from an estimate of a surplus gas phase (14) generated from the gas in liquid form in the vessel (9) during of a path (3), a step C of establishing a second operating plan (37) of the gas cooling function in liquid form (13) operated by the supply system (8) until on arrival (51) at the place of destination (2), said second operating plan (37) being established from the estimate of the surplus gas phase generated from the gas in liquid form during the journey (3 ), a step D of calculating an energy balance of the gas in liquid form at an instant t (38) from the temperature of the gas in liquid form (13) contained in the tank (9) and properties of the gas in liquid form (13) contained in the tank (9), a step E of calculating a maximum energy balance (32, 33) from the maximum authorized temperature of the gas in liquid form (13) calculated in step A, and the characteristics of the gas in liquid form (13) contained in the tank (9), a step F of estimating the energy balance (31) of the gas in liquid form contained in the tank at the arrival (51) of the path (3) from the operating plans (36,

37) of the condensation and cooling functions determined in steps B and C and of the energy balance of the gas in liquid form at time t (38), determined in step D, a step G of adjusting the first plane d 'operation (36) and / or the second operating plan (37), a step H of implementing the power supply system (8) according to the operating plans (36, 37) of the condensation and cooling functions. cooling of the gas in liquid form (13) adjusted in step G.

2- A method of estimating and adjusting (5) the energy balance according to the preceding claim, wherein step G consists of activating the condensation function as long as the estimation of the energy balance (31) of the gas under liquid form contained in the tank at the arrival (51) of the path (3), calculated in step F, is less than the maximum energy balance (32, 33) calculated in step E.

3- A method of estimating and adjusting (5) the energy balance according to any one of the preceding claims, wherein step G consists of stopping the cooling function at an estimated time dt which guarantees that the estimate of the energy balance (31) of the gas in liquid form contained in the tank at the arrival (51) of the path (3), calculated in step F, is less than the maximum energy balance (32, 33) calculated at l 'step E.

4- A method of estimating and adjusting (5) the energy balance according to claim 1, wherein step G consists of stopping the condensation function as long as the estimation of the energy balance (31) of the gas under liquid form contained in the tank at the arrival (51) of the path (3), calculated in step F, is greater than the maximum energy balance (32, 33) calculated in step E.

5- A method of estimating and adjusting (5) the energy balance according to claim 1 or 4, wherein step G consists of activating the cooling function as long as the estimation of the energy balance (31) of the gas in liquid form contained in the tank at the arrival (51) of the path (3), calculated in step F, is greater than the maximum energy balance (32, 33) calculated in step E. 6. Estimation and adjustment method (5) according to any one of the preceding claims, repeated by iteration from step B and during the path (3) of the floating structure (1).

7- Estimation and adjustment method (5) according to claim 6, comprising an additional step D ', carried out simultaneously with step D, of calculating the energy balance of the gas in liquid form at the instant t (38) from the performance of the condensation and cooling functions from the start (50) of the floating structure (1) and up to the instant t and from an energy balance of the gas in the form liquid at an instant t (38) calculated during a previous iteration.

8- Estimation and adjustment method (5) according to claim 7, wherein the energy balance of the gas in liquid form at time t (38) kept for step F is the highest among the energy balance. gas in liquid form at time t (38) calculated in step D and the energy balance of gas in liquid form at time t (38) calculated in step D '.

9- A method of estimating and adjusting (5) according to any one of claims 1 to 5, comprising an additional step A 'of selecting a safety margin (60) of the maximum energy balance (32, 33) gas in liquid form (13) as a function of the characteristics of the path (3) of the floating structure (1), step E being carried out taking into account said safety margin (60).

10. Estimation and adjustment method (5) according to claim 9, wherein step A ’is repeated by iteration during the path (3) of the floating structure (1).

11- A method of estimation and adjustment (5) according to claim 9 or 10, wherein the safety margin (60) decreases as the floating structure (1) approaches the place of destination (2).

12- Estimation and adjustment method (5) according to any one of the preceding claims, in which the floating structure (1) is equipped with at least one motor (16) supplied at least partially by the gas phase. (14) generated from the gas in liquid form, the estimate of the surplus gas phase generated from the gas in liquid form during the path (3) being established from an image value of the heat inputs into the tank (9) and an estimate of the consumption of the engine (16).

13- Management system (4) of an energy balance of a gas in liquid form (13) contained in at least one tank (9) of a floating structure (1), implementing the estimation method and adjustment (5) according to any one of the preceding claims, said management system (4) comprising at least one system (8) for supplying fuel to a consumer of the floating structure (1) and at least a calculator (7) having the function of estimating an amount of surplus gas phase (14) generated from the gas in liquid form during a path (3) of the floating structure (1).

14- Floating structure (1) for transporting gas in liquid form (13) comprising a management system (4) of the energy balance of said gas according to the preceding claim.