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

Description

[0001] The present invention relates to the field of natural gas transport, and more particularly to the field of temperature regulation of said natural gas during such transport.

[0002] In order to more easily transport and / or store liquid gas, such as liquid natural gas, over long distances, the gas is generally liquefied by cooling it to cryogenic temperatures, for example -163°C at 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 on the floating structure.

[0003] However, such tanks are never perfectly thermally insulated, so natural evaporation of the gas is inevitable, a phenomenon known as BOG, an acronym for Boil-Off Gas. The storage tanks of the floating structure therefore contain both natural gas in liquid form and natural gas in gaseous form, with the gaseous phase of the natural gas forming the tank head.

[0004] In a known manner, at least a portion of the natural gas present in the tank in gaseous form can be used to power an engine designed to meet the operating energy needs of the floating structure, in particular for its propulsion and / or its production of electricity for the on-board equipment. For this purpose, it is known in particular to circulate the natural gas in the gaseous state through at least one natural gas treatment system, so as to allow it to be heated and compressed, said system comprising a heat exchanger used as a superheater and a compressor, both placed upstream of the engine.

[0005] It is also known to configure the natural gas treatment system so that it can allow the condensation of a portion of the natural gas taken from the gaseous state. The condensation of the natural gas may be required in particular when the quantity of natural gas evaporated in the tank is too large compared to the operating energy requirements of the floating structure, the natural gas treatment system then allows the evaporated natural gas present in the tank to be condensed in order to return it to the tank in 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(s) is zero, or almost zero.

[0006] An essential factor to consider for this type of transport is the state of the liquid natural gas when the floating structure arrives at its destination to unload its cargo. Indeed, the receiving stations for liquid natural gas have requirements regarding the characteristics of the delivered liquid natural gas, such as the temperature or saturation pressure of the said liquid natural gas. The facility manager at the destination location may therefore refuse to unload the cargo of liquid natural gas if it does not comply with the requirements of the destination location.Since temperature is a variable factor that changes significantly during transport, the major risk taken during this type of transport is that the natural gas in liquid state arrives at its destination at a saturation pressure and / or a temperature that does not correspond to the criteria expected by the facility manager at the destination, thus implying a potential refusal or downgrading of the cargo.

[0007] Cargo temperature management raises two issues directly related to a fuel supply system for a floating structure consumer. The first issue concerns the cooling function of the supply system. Lowering the temperature and / or saturation pressure of liquid natural gas is unnecessary if it leads to a very high deviation from the requirements at the destination. In this situation, the cooling function of the supply system is used excessively and results in unnecessary energy consumption.

[0008] The second issue concerns the condensation function of the supply system. When the condensation function is active, the excess gas phase generated from the liquid gas returns to the liquid phase and returns to the transport tank. However, the condensed liquid gas may have a higher temperature than the liquid gas present in the tank. The return of the condensed liquid gas to the tank may therefore cause an overall increase in the temperature of the liquid gas present in the tank, thus leading to the risk that the liquid gas cargo may no longer comply with the requirements of the destination place and resulting in refusal of delivery.Conversely, inactivity of the condensation function of the supply system results in the elimination of the surplus gas phase generated from the gas in liquid form, for example by combustion or by release into the air, and therefore a waste of the cargo.

[0009] The general problem is therefore to find a happy medium between the condensation and cooling functions of the supply system so that the cargo complies with the requirements of the destination, but while limiting the energy consumption due to the elimination of the gaseous 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 destination, without deviating too much from this criterion, so as to avoid any overconsumption linked to the cooling function of the supply system. An example of a management system is described in document WO 2018 / 189789.

[0010] In this respect, the invention consists of a method 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 destination location, the floating structure comprising a system for supplying fuel to a consumer of the floating structure capable of implementing a function of condensing a gaseous phase generated from the gas in liquid form and / or a function of cooling the gas in liquid form, characterized in that the estimation and adjustment method comprises the following steps: a step A of calculating the maximum permitted temperature of the gas in liquid form contained in the tank upon arrival at the destination location, based on the maximum saturation pressure requirements of the gas in liquid form at the destination location and the characteristics of the gas in liquid form contained in the tank, a step B of establishing a first operating plan for the condensation function of the gaseous phase generated from the gas in liquid form operated by the supply system until arrival at the destination location, said first operating plan being established from an estimate of a surplus of gaseous phase generated from the gas in liquid form in the tank during a journey, a step C of establishing a second operating plan for the cooling function of the gas in liquid form operated by the supply system until arrival at the destination location,said second operating plan being established from the estimation 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 a time t from the temperature of the gas in liquid form contained in the tank and the properties of the gas in liquid form contained in the tank, 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 tank at the end of the journey from the operating plans of the condensation and cooling functions determined in steps B and C and 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 of the functions of condensation and cooling of the gas in liquid form adjusted in step G.,

[0011] 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 to supply one or more consumers such as a propulsion engine of the floating structure, or an electric generator thereof. In parallel with this, the fuel supply system of a consumer of the floating structure is capable of managing a state of the gas in liquid form contained in the tank, thanks to its cooling function and its condensation function. The term "fuel supply system of a consumer of the floating structure" is subsequently simplified to "supply system".

[0012] The estimation and adjustment method makes it possible to regulate the characteristics of the gas in liquid form so that a cargo of gas in liquid form is delivered to the destination place with a saturation pressure of the gas in liquid form conforming to the requirements of the destination place, while minimizing the energy consumption necessary for temperature regulation. The term energy balance is used to designate a numerical data obtained by a calculation which can 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 from the energy supplied or removed by the cooling or condensation functions of the supply system.The estimation and adjustment process may be initiated before a departure from the floating structure and / or during the journey between a departure point of the floating structure, for example a gas liquefaction terminal, and the destination where the cargo of gas in liquid form is delivered. The tank containing the gas in liquid form is a tank that is compliant and suitable for the transport of such a cargo, and may for example be a tank with primary and secondary membranes, each of the membranes being thermally insulated.

[0013] The estimation and adjustment process begins with step A, which generally consists of determining the conditions for acceptance of the cargo of gas in liquid form by the destination, more specifically the maximum authorized temperature of the gas in liquid form contained in the tank upon arrival. However, it is possible to reason in terms of saturation pressure of the gas in liquid form or another value related to pressure and / or temperature. The calculation of such a target value not to be exceeded depends on the requirements for saturation pressure of the gas in liquid form and the temperature of the gas in liquid form at the destination and constant characteristics of the gas. Thus, it is clear that the requirement of the terminal receiving the gas in liquid form is intended to avoid massive vaporization of the natural gas during its transfer between the ship and the terminal by imposing conditions for acceptance of the cargo.

[0014] The maximum permissible temperature of the liquid gas contained in the tank upon arrival depends on the properties of the transported liquid gas, namely the total mass of liquid gas and the specific heat capacity of the liquid gas. These two data can be provided, for example, by any cargo document, such as a technical data sheet, and can be taken into account by the supply system, for example by means of a control monitor.

[0015] The maximum permissible temperature of the liquid gas contained in the tank at the inlet calculated by the estimation and adjustment method also depends on the maximum saturation pressure requirements of the liquid gas determined by the facility manager at the destination location. Such data is also known through any information source provided by the destination location and can also be recorded in the supply system in a manner identical to that described above.

[0016] Steps B and C consist of establishing an operating plan for each of the functions of the fuel system. An operating plan is understood to mean a sequence of activity for each of the functions during the journey to reach the destination. Each of the functions, namely the condensation function and the cooling function, is either active or inactive, and the fuel system can switch from one mode to the other. The operating plan for each of the functions therefore determines active and inactive sequences for each of the functions during the journey, which result in heating or cooling of the cargo, as appropriate.

[0017] When the condensation and cooling functions are described as active, this means that the supply system is authorized to implement its condensation and / or cooling functions. Conversely, when the condensation and cooling functions are described as inactive, this means that the supply system is not authorized to implement its condensation and / or cooling functions. When the cooling function is active, the supply system is authorized to cool the gas in liquid form provided that there is a gaseous 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 a surplus of gaseous phase generated from the gas in liquid form.

[0018] 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 the temperature to drop when activated. The temperature varies differently when the two functions act simultaneously, or may vary naturally depending on the environmental conditions during the journey. However, it is understood 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.

[0019] The operating plans for the condensation or cooling functions of the power system are therefore flowcharts determining at what time t of the journey each of the functions must be activated or deactivated. It is also possible for the operating plan to consist of keeping one or other of the functions active or inactive for the entire journey.

[0020] Each of these operating plans is determined by estimating the excess gas phase generated from the liquid gas during the journey. The gas phase generated from the liquid gas emanates from the transport tank either naturally or forcibly. This gas phase can then be used to power 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 liquid gas not used to power the floating structure represents the excess gas phase generated from the liquid gas. When the condensation function and the cooling function operate simultaneously, this means that there is excess gas phase generated from the liquid gas circulating within the supply system.

[0021] The presence of excess gas phase generated from the gas in liquid form can be detected by a system outside the management system of the invention or directly by means of the estimation and adjustment method according to the invention.

[0022] Step D of the estimation and adjustment method consists of calculating the energy balance of the gas in liquid form at time t, i.e. from data measured at time t. Step D is independent of steps B and C and can therefore take place simultaneously with or before steps B and C. The calculation of the energy balance during step D depends on the total mass of gas in liquid form and 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 tank at time t. More specifically, the energy balance of the gas in liquid form is calculated from the following formula: Be = mGaz × Cp × T

[0023] Be being the energy balance of the gas in liquid form at time t, mGaz being the total mass of the gas in liquid form, Cp being the specific heat capacity of the gas in liquid form and T being the temperature of the gas in liquid form at time t.

[0024] The temperature of the gas in liquid form can be measured by at least one temperature sensor placed 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 placed 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.

[0025] Step E consists of calculating an energy balance similar to the energy balance calculated in step D, but the energy balance in step E is the maximum energy balance, relative to the maximum permitted temperature of the gas in liquid form calculated in step A. The calculation of the maximum energy balance calculated in 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 carried out simultaneously or one after the other in any order. The maximum energy balance is calculated from the total mass of gas in liquid form, the specific heat capacity of the gas in liquid form, and the maximum permitted temperature of the gas in liquid form.Thus, the calculation carried out in step E is similar to the calculation carried out in step D, with the maximum permitted temperature of the gas in liquid form instead of the temperature measured in the tank of the floating structure.

[0026] In step F, the estimation and adjustment method calculates an estimate of an energy balance of the gas in liquid form contained in the tank upon 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 tank upon arrival of the floating structure at its destination, in particular its energy balance. To estimate the energy balance of the gas in liquid form contained in the tank upon arrival of the journey, the estimation and adjustment method uses the energy balance of the gas in liquid form at time t calculated in step D, as well as the operating plans of the cooling and condensation functions of the supply system calculated in steps B and C.The energy balance of the gas in liquid form at time t calculated in step D constitutes a starting point for the estimation in terms of saturation pressure of the gas in liquid form and temperature of the gas in liquid form. The operating plans of the cooling and condensation functions calculated in steps B and C are also part of the estimation, because they influence the temperature of the gas in liquid form contained in the tank 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 destination location, taking into account the operating plans of the cooling and condensation functions established previously.Since the energy balance of gas in liquid form encompasses a variety of characteristics, it is also possible to reason in terms of the saturation pressure of the gas in liquid form, temperature, or the amount of heat exchange. By estimating the energy balance of the cargo on arrival, operating plans can be adjusted so that the saturation pressure of the gas in liquid form on arrival makes it acceptable.

[0027] Step G then consists of an adjustment of the operating plans based on 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 end of the journey calculated in step F. Based on 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 can consist of a shutdown of one and / or the other of the functions, the shutdown 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 restarted, 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 from the data calculated or estimated during steps E and F.

[0028] Step H involves implementing the adjusted operating plans. In other words, the feed system no longer takes into account the operating plans established in steps B and C, which are replaced by the operating plans adjusted in step G. The adjusted operating plans are transmitted to the feed system at the end of the estimation and adjustment process. The feed system can therefore implement the cooling and / or condensation of the gas in liquid form, keep them active or deactivate them, depending on the respective adjusted operating plans transmitted to it.

[0029] According to a 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 tank at the arrival of the journey, calculated in step F, is lower 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 tank at the arrival of the journey is lower than the maximum energy balance, this means that at the 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 lower than the prerequisites defined by the destination location. If this situation occurs during the journey, there is no disadvantage in adjusting the operating plans of the functions of the supply system so as to authorize and control an increase in the temperature of the gas in liquid form contained in the tank.Thus, if this is not already the case, the adjustment of the first operating plan of the condensation function can consist of keeping the latter active throughout the journey. The surplus gas phase generated from the gas in liquid form is therefore fully condensed instead of possibly being eliminated. There are therefore no losses of gas in liquid form contained in the tank, except for the gas phase generated from the gas in liquid form and used to supply the floating structure.

[0030] In this situation, the condensation function is active. In other words, the supply system is allowed to condense the excess gas phase generated from the gas in liquid form if it is present. The condensation of the gas in liquid form can vary in terms of activity, depending on the need to manage the excess gas phase generated from the gas in liquid form. For example, the condensation of the gas in liquid form can be more sustained in the event of excess gas phase generated from the gas in liquid form in the tank, in order to reduce the pressure within the tank.

[0031] According to a characteristic of the invention, step G consists of stopping the cooling function at an estimated time dt which guarantees that the estimate of the energy balance of the gas in liquid form contained in the tank at the arrival of the journey, calculated in step F, is lower than the maximum energy balance calculated in step E. After adjusting the first operating plan of the condensation function which consists of maintaining it throughout the journey, it is possible that the estimate of the energy balance of the gas in liquid form at arrival is always lower than the requirements of the destination location. It is therefore possible to adjust the second operating plan of the cooling function so that the latter is deactivated at the estimated time dt. Such an adjustment makes it possible to save the energy consumed by the cooling function during the period of time when it is deactivated.This causes the liquid gas in the tank to rise in temperature, as the liquid gas is no longer cooled by the cooling function. Therefore, the estimated time dt at which the cooling function is stopped is set so that the liquid gas in the tank increases in temperature but this increase does not cause the requirements to be exceeded at the time the liquid gas is delivered to the destination at the end of the journey.

[0032] To do this, the estimation and adjustment method will successively repeat the adjustment of the second operating plan of the cooling function and step F, i.e. the step of estimating the energy balance of the gas in liquid form contained in the tank upon arrival. The adjustment of the second operating plan of the cooling function consists of determining the estimated time dt, taking the arrival at the destination location as the target. The estimated time dt is then determined to be prior to a certain period of time relative to the arrival, for example several days or hours. The estimation and adjustment method then recalculates the estimate of the energy balance of the gas in liquid form contained in the tank upon arrival, this time taking into account the new adjustment of the second operating plan of the cooling function, i.e. the stopping of the latter for example several days or hours before arrival at the destination location.If the estimate of the energy balance of the gas in liquid form contained in the tank upon arrival is no longer lower 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 upon arrival is still lower than the maximum balance, the estimation and adjustment process then repeats the adjustment of the second operating plan of the cooling function by further anteriorizing the estimated time dt by, for example, several days or hours before arrival at the destination. Then, the estimate of the energy balance of the gas in liquid form contained in the tank upon arrival is recalculated 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 upon arrival is lower than the maximum energy balance, the estimated time dt is pushed back in time.This loop allows to determine the estimated time dt closest to the current time t, and thus to deactivate the cooling function as early as possible in order to save maximum energy. Once the final estimated time dt has been determined, the estimation and adjustment process continues with step H.

[0033] According to a characteristic of the invention, step G consists of stopping the condensation function as long as the estimate of the energy balance of the gas in liquid form contained in the tank at the arrival of the journey, calculated in 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 tank 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 the gas in liquid form that is too high compared to the requirements of the destination location at the arrival of the floating structure. In order to avoid such a situation, it is appropriate to limit any action leading to an increase in the temperature of the gas in liquid form contained in the tank.Thus, the first operating plan of the condensation function is adjusted to cause a shutdown of the condensation function of the feed system at a given time t where the energy balance of the gas in liquid form contained in the tank exceeds the maximum energy balance. The condensation function can possibly be reactivated if the estimate of the energy balance of the gas in liquid form contained in the tank at the end of the journey becomes lower than the maximum energy balance thereafter.

[0034] According to a characteristic of the invention, step G consists of activating the cooling function as long as the estimate of the energy balance of the gas in liquid form contained in the tank at the arrival of the journey, 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 condensation function is adjusted so that it is deactivated at the given time 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 destination location, and this with the aim of ensuring that the saturation pressure of the gas in liquid form meets the requirements of the destination location.

[0035] In this situation, the cooling function is therefore active. In other words, the feed system is allowed to cool the liquid gas contained in the tank. The feed system cools the liquid gas with the highest possible activity compared to a configuration of said feed system.

[0036] According to a feature 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 starting point and the destination location is variable depending on the delivery, but the journey may last several days or even several weeks. The estimation may, 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 method must be repeated regularly during the journey. Therefore, the estimation and adjustment method may, for example, be configured to start at a regular time interval, for example every six hours.

[0037] Step A is based on a calculation dependent on fixed values. It is therefore not necessary to repeat this step after launching the estimation and adjustment process for the first time. The estimation and adjustment process is therefore repeatable by iteration from the step of establishing the first operating plan for the condensation function of the power system.

[0038] According to a 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 from the execution of the condensation and cooling functions from the departure of the floating structure and up to time t and from an energy balance of the gas in liquid form at time t calculated during a previous iteration. The calculation of the energy balance of the gas in liquid form at time t carried out in step D' no longer takes into account the temperature of the gas in liquid form contained in the tank at time t recorded for example by the temperature sensor, 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 method has already been implemented a first time.Advantageously, the energy balance of the gas in liquid form at time t is calculated from the energy balance of the gas in liquid form at a previous time t, i.e. the energy balance of the gas in liquid form resulting from the previous iteration of the estimation and adjustment method, which may have been calculated during step D or D'.

[0039] The calculation of the energy balance of the gas in liquid form at time t during step D' also takes into account the execution of the condensation and cooling functions from the departure of the floating structure until time t. For the condensation function, this corresponds to data relating to the heat transmitted to the tank and resulting in a general increase in its temperature, illustrated for example by a differential in the temperature at the inlet and outlet of a heat exchanger performing the condensation function. For the cooling function, this corresponds to data relating to the cold transmitted to the tank and resulting in a general decrease in its temperature, illustrated for example by a differential in the temperature at the inlet and outlet of a heat exchanger performing the cooling function.

[0040] According to a characteristic of the invention, the energy balance of the gas in liquid form at time t retained for step F is the highest among the energy balance of the gas in liquid form at time t calculated in step D and the energy balance of the gas in liquid form àthe time t calculated in step D'. In other words, when the estimation and adjustment process subsequently reaches step F, i.e. the step of estimating the energy balance of the gas in liquid form contained in the tank estimated on arrival, it is the energy balance of the gas in liquid form contained in the tank 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 destination location, it is advisable to keep the energy balance of the gas in liquid form at the highest time t as a safety measure.

[0041] According to a feature of the invention, the estimation and adjustment method comprises an additional step A' of selecting a safety margin of the maximum energy balance of the gas in liquid form as a function of the characteristics of the journey of the floating structure, 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 destination place with a cargo of gas in liquid form whose energy balance is higher than the requirements of said destination place, 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 taking into account the safety margin.A safe 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 plan for the condensation function and the second operating plan for the cooling function are adjusted based on the comparison between the estimated energy balance of the gas in liquid form contained in the tank at the end of the journey and a virtual maximum energy balance, i.e. one that takes into account the safety margin. The safety margin thus guarantees the certainty of remaining below the actual maximum energy balance.

[0042] The safety margin can be selected based on various parameters. For example, the longer the journey, the higher the safety margin. A high safety margin is also recommended if there is a lack of weather information during the journey. The safety margin can, for example, be entered manually via the control monitor or programmed to vary over time.

[0043] 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.

[0044] According to a feature of the invention, step A' is repeated by iteration during the journey of the floating structure. The repetition of step A' may be independent of the repetition of the estimation and adjustment method, or may be part of it. Step A' may also be triggered manually, for example following the occurrence of an unforeseen meteorological phenomenon. It may then be advisable to manually increase the value of the safety margin to compensate for the uncertainty due to said meteorological phenomenon.

[0045] According to a feature of the invention, the safety margin decreases as the floating structure approaches the destination location. In other words, the closer the floating structure gets to its destination location, the lower the safety margin needs to be. It is therefore possible to program a decreasing safety margin over time.

[0046] According to a characteristic of the invention, the floating structure is equipped with at least one engine powered at least partially by the gaseous phase generated from the gas in liquid form, the estimate of the surplus gaseous phase generated from the gas in liquid form during the journey being established from an image value of the heat inputs in the tank and an estimate of the consumption of the engine. As stated 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 power its propulsion engine and / or its electricity generator. The gaseous phase generated from the gas in liquid form not used for these different functions corresponds to the surplus gaseous 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, i.e. the steps of establishing operating plans for the condensation and cooling functions of the supply system, can take place. The image value of the heat inputs into the tank can, for example, depend on the tank model used and therefore be available as a technical characteristic of the tank. The image value of the heat inputs into the tank can also be estimated using sensors.

[0047] Engine consumption can be estimated if the floating structure is equipped with a module that allows a route plan to be defined for the journey to the destination. If this is not the case, engine consumption can be estimated from the average speed of the floating structure over the remaining journey, the latter depending on the remaining distance to be covered and the time remaining to reach the destination.

[0048] The surplus gas phase generated from the gas in liquid form can thus be estimated via a source external to the estimation and adjustment process, and for example be entered via the control monitor in order to be taken into account during the execution of the estimation and adjustment process. This surplus can then be quantified in tonnes / hour.

[0049] 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 previously, said management system comprising at least one system for supplying fuel to a consumer of the floating structure and at least one calculator having the function of estimating a quantity of surplus gas phase generated from the gas in liquid form during a journey of the floating structure.

[0050] Such an energy balance management system includes the fuel supply system of a consumer of the floating structure implementing the condensation and cooling functions, and allows the estimation and adjustment process to be carried out.

[0051] In order to ensure the smooth running of the estimation and adjustment process, in particular steps B and C establishing respectively the first operating plan for the condensation function of the gas phase generated from the gas in liquid form and the second operating plan for the cooling function of the 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 carrying out steps B and C. The energy balance management system can also include the control monitor mentioned above.

[0052] The invention also covers a floating structure for transporting gas in liquid form comprising a system for managing the energy balance of said gas as described previously.

[0053] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which: [ fig 1 ] is a schematic representation of a floating structure loaded with gas in liquid form and making a journey towards a destination, [ fig 2 ] is a schematic representation of an embodiment of a liquid gas temperature management system according to the invention, [ fig 3 ] is a schematic representation of a sequence of a method for estimating and adjusting an energy balance of gas in liquid form according to the invention, when it is launched for the first time, [ fig 4 ] is a schematic representation of a sequence of the method for estimating and adjusting the energy balance of gas in liquid form according to the invention, when it is launched by iteration, [ fig 5 ] is a general diagram illustrating a fuel supply system for a consumer of the floating structure capable of executing a plurality of commands according to the estimation and adjustment method, [ fig 6 ] is a diagram of the power supply system according to a first specific embodiment, [ fig 7 ] is a diagram of the power supply system according to a second specific embodiment, [ fig 8 ] is a curve representing the evolution of the energy balance of the 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 the 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 the gas in liquid form as a function of time as well as the adjusted operating plans of the condensation and cooling functions, to overcome the situation mentioned in figure 8 , [ fig 10 ] is a curve representing the evolution of the energy balance of the gas in liquid form as a function of time as well as the operating plans of condensation and cooling functions, in a situation where said energy balance of the 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 the gas in liquid form as a function of time as well as the adjusted operating plans of the condensation and cooling functions, to overcome 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.

[0054] In order to visualize the context in which the invention is made, the figure 1 represents a floating structure 1 heading towards a destination location 2 along a route 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 for the purpose of delivering the latter to the destination location 2. In order to ensure such transport, the floating structure 1 comprises at least one tank 9.

[0055] Destination location 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 destination location 2, the gas in liquid form is discharged, for example, into a tank 40. Destination location 2, however, imposes requirements concerning the characteristics of the gas in liquid form. The requirements of destination location 2 may vary depending on the facility manager to which destination location 2 is attached, and mainly concern characteristics of the gas in liquid form, for example its saturation pressure and / or its temperature.

[0056] If the liquid gas contained in tank 9 of floating structure 1 does not meet these liquid gas saturation pressure requirements, the liquid gas cargo may potentially be refused by the facility manager at destination location 2.

[0057] To avoid this, the cargo of gas in liquid form must be closely monitored throughout the journey 3. Journey 3 has a variable distance and can last several days or even weeks depending on the distance between a loading location and the destination location 2 and the speed of the floating structure 1.

[0058] There figure 2 schematically represents a management system 4 for 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 data encompassing 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 box 41 having in memory a method for estimating and adjusting 5 the energy balance of the gas in liquid form contained in the tank of the floating structure. The control box 41 is thus able to initiate the estimation and adjustment method 5 in a regular and automated manner and / or following a manual command exercised for example by means of a control monitor 6.It is also possible to manually enter data via 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 later.

[0059] The management system 4 also comprises a system 8 for supplying fuel to a consumer of the floating structure. The function of the supply system 8 is to condense and / or cool the gas in liquid form contained in the tank and is capable of adjusting one or other of these functions by activating or deactivating them. The adjustment of the condensation and cooling functions of the supply system 8 depends on the result of the estimation and adjustment method 5. Thus, when the latter is completed, the control box 41 sends a signal to the supply system 8, said signal indicating the adjustments to be made by the supply system 8.

[0060] The management system 4 also includes a computer 7. The computer 7 has the function of estimating 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 gas tank in liquid form, or can be forced. The estimate of surplus gas phase generated from the gas in liquid form is calculated using an estimate of the consumption of the engine of the floating structure and an image value of the heat inputs into the tank. The computer 7 and the control box 41 can be part of the same control unit or can be independent of each other.

[0061] The estimation of the consumption of the engine of the floating structure can be done by entering a route plan into the control monitor 6 which transmits the information to the computer 7, or by calculating an average speed of the floating structure from the remaining distance between a position of the floating structure and the destination location and the time remaining to reach it. The calculation of the average speed of the floating structure can also be done by entering data into the control monitor 6 which transmits the information to the computer 7.

[0062] The image value of the heat inputs into the tank may 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 tank used for transport and may be given to the computer 7 via the control monitor 6. The estimate of the heat inputs into the tank may also be communicated by sensors included in said tank.

[0063] Once the surplus 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 box 41. The surplus gas phase generated from the gas in liquid form during the journey is data allowing the estimation and adjustment method 5 to run as will be described later.

[0064] There figure 3 is a schematic representation of the method for estimating and adjusting 5 the energy balance of gas in liquid form according to the invention. This diagram represents the progress of the estimation and adjustment method 5 when it is launched for the first time during the journey to the destination location. The estimation and adjustment method 5 can be launched for the first time before departure or upon departure from the floating structure. On the figure 3 , the solid arrows represent the progress of each of the steps of the estimation and adjustment method 5, and the dotted arrows correspond to a transmission of data 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 method 5.

[0065] When the estimation and adjustment method 5 is launched for the first time, it begins with a step A which makes it possible to calculate the maximum permitted temperature of the gas in liquid form contained in the tank upon arrival at the 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 thereof. Such characteristics depend on the type of gas in liquid form transported and are known in one way or another by the personnel of the floating structure. Thus, the total mass of gas in liquid form and the specific heat capacity of the gas in liquid form can be entered or preselected via the control monitor 6 and transmitted for the calculation of step A of the estimation and adjustment method 5.The calculation of step A also depends on the maximum saturation pressure requirements of the liquid gas at the destination location. Since these requirements vary depending on the destination location, the maximum saturation pressure value required for the liquid gas is known once the destination location is known. The saturation pressure requirements for the liquid gas can be entered via the control monitor 6 or can be known, for example, via a database listing all destination locations authorized to receive and unload liquid gas.

[0066] Once the calculation of step A has been carried out, the estimation and adjustment method 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 certain that the energy balance of the gas in liquid form is lower than the requirements of the destination place on arrival. Thus, step A' is not essential for the proper performance of the estimation and adjustment method 5 which can do without the safety margin to carry out all the calculations and estimations, but nevertheless contributes to the optimization of the adjustment of the energy balance of the gas in liquid form. The safety margin can be determined automatically from the route plan and / or the weather conditions, or manually by means of the control monitor 6. The safety margin is used for a calculation during a step E.Step A' can therefore take place at any time prior to step E.

[0067] Step B of the estimation and adjustment method 5 occurs after step A or step A'. Step B consists of establishing the first operating plan for the condensation function of the supply system 8. The first operating plan for the condensation function of the supply system 8 indicates over time at what instant of the journey the condensation function remains active or inactive and at what instant the latter is activated or deactivated. The establishment of the first operating plan depends on the quantity of surplus gas phase generated from the gas in liquid form during the journey. It is 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 has no gas phase generated from the gas in liquid form to condense 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 of gas phase generated from the gas in liquid form is estimated by the computer 7 which therefore transmits the information to the control box so that the estimation and adjustment method 5 can carry out step B.

[0068] A step C takes place in parallel or successively with step B. Step C is based on the same principle as step B, since it allows the establishment of the second operating plan for the cooling function of the supply system 8. As for step B, the second operating plan for the cooling function of the supply system 8 indicates over time at what time during the journey the cooling function remains active or inactive and at what time 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 in liquid form is therefore taken into account for steps B and C.

[0069] The estimation and adjustment process 5 then continues with a step D which calculates an energy balance of the gas in liquid form at a time t. figure 3 representing the progress 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 the gas in liquid form at the instant t, the estimation and adjustment process 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 the gas in liquid form, or the specific heat capacity of the 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 the instant t also needs the average temperature of the gas in liquid form contained in the tank at the instant t.The average temperature of the gas can be measured, for example, using a temperature sensor located in the tank. It is therefore the supply system 8 which provides the average temperature in the tank and transmits it to the control box so that the estimation and adjustment method 5 can perform the calculation of step D.

[0070] Once step D is completed, the estimation and adjustment process 5 continues with step E, which consists of calculating a maximum energy balance. The maximum energy balance corresponds to the limit of the requirements of the destination location 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 arrives at the destination location. The energy balance of the gas in liquid form may, however, exceed this limit of the maximum energy balance during the journey without consequences, but must imperatively return below this maximum energy balance before the floating structure reaches the destination location. 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.

[0071] 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 the maximum authorized temperature of the gas in liquid form contained in the tank at the arrival calculated during step A. The data provided and the calculations carried out during step A can therefore be transmitted for the calculation of step E. If the estimation and adjustment method 5 has carried out step A', in other words if the safety margin has been determined and selected, said safety margin is also transmitted to 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 inclusion of the safety margin in the calculation.

[0072] The next step of the estimation and adjustment method 5 is a step F ensuring the estimation of the energy balance of the gas in liquid form contained in the tank at the end of the journey. Step F makes it possible to determine, while retaining the operating plans of the condensation and cooling functions established during steps B and C, what the energy balance of the gas in liquid form contained in the tank will be at the end of the journey. To make such an estimation, 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 of the condensation and cooling functions established during steps B and C.The latter having been established for the entire journey 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.

[0073] The estimation and adjustment process 5 then continues with a step G which ensures the adjustment of the operating plans of the condensation and cooling functions of the supply system 8. These adjustments are made based on 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 of the gas in liquid form contained in the tank on arrival calculated during step F is based on the operating plans of 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 of the condensation and cooling functions.

[0074] If the estimated energy balance of the liquid gas contained in the tank upon arrival is higher than the maximum energy balance, this means that the liquid gas cargo will arrive at a saturation pressure of the liquid gas that is excessive compared to the maximum requirements at the destination. The operating plans for the condensation and cooling functions must therefore be adjusted to reduce the temperature of the liquid gas contained in the tank and, by analogy, the energy balance of the liquid gas.

[0075] If the estimated energy balance of the liquid gas contained in the tank upon arrival is lower than the maximum energy balance, this means that the cargo of liquid gas will be in compliance with the requirements of the destination upon arrival, but that it is nevertheless possible to make adjustments allowing an increase in the temperature of the liquid gas contained in the tank if these prove useful in terms of energy savings. The operating plans for the condensation and cooling functions must therefore be adjusted to allow an increase in the temperature of the liquid gas contained in the tank and, by analogy, the energy balance of the liquid gas.

[0076] Step G therefore determines the optimal adjustments to the operating plans of the condensation and cooling functions of the power system 8 to best respond to the situation. Examples of the adjustments to the operating plans will be presented later.

[0077] 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 condensation and cooling functions to the power system 8 so that the latter can implement them. The details of the operation of the power system 8 will be presented later.

[0078] There figure 4 is a schematic representation of the estimation and adjustment process 5 of the energy balance of the gas in liquid form during its repetition by iteration, that is to say when the estimation and adjustment process 5 is launched during the journey after having been launched a first time according to the figure 3 . Most of the steps in the estimation and adjustment process 5 are similar to what has been described previously, and reference will therefore be made to the description of the figure 3 for explanations concerning these. Just as for the figure 3 , the solid arrows represent the progress of each of the steps of the estimation and adjustment method 5, and the dotted arrows correspond to a transmission of data 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 method 5.

[0079] 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 is 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 box.

[0080] Step A' of selecting the safety margin is also not repeated. The safety margin may, however, vary independently of the course of the estimation and adjustment method 5, either because it was set to vary over time when the estimation and adjustment method 5 was first launched, or because it was manually modified via the control monitor 6. The variation of the safety margin is the reason why step E is maintained within the estimation and adjustment method 5 since it is a factor that may vary over time for the calculation of step E.

[0081] The estimation and adjustment method 5, when repeated by iteration, therefore begins with step B. Steps B and C take place as when the estimation and adjustment method 5 is first launched, the quantity of surplus gas phase generated from the gas in liquid form always being calculated and provided by the calculator 7.

[0082] Step D also takes place in an identical manner to what was described previously. However, 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 of the energy balance of the gas in liquid form at time t of step D' is done from an energy balance of the gas in liquid form at a previous time t, calculated during a previous iteration of the estimation and adjustment method 5, as well as from the executions of the condensation and cooling functions since the departure of the floating structure. The energy balance of the gas in liquid form at a previous time t can be recovered for example from the buffer memory of the control box.The executions of the condensation and cooling functions are the origin of heat transfer carried out by the condensation function and cold transfer carried out by the cooling function to the cargo of gas in liquid form. The executions of the condensation 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 this data to the control box for application during step D'.

[0083] 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 with the highest value is retained. The latter is considered to have the most pessimistic value, the priority being to remain below the maximum energy balance calculated subsequently.

[0084] The rest of the estimation and adjustment process 5 then takes place in accordance with what was described in figure 3 . Once the estimation and adjustment method 5 is completed, the adjustments of the operating plans of the condensation and cooling functions are transmitted to the power system 8, and the estimation and adjustment method 5 can again be repeated directly from step B depending on the setting of the control box. Advantageously, the control box is configured to repeat the estimation and adjustment method 5 at regular intervals throughout the route, depending on the progress of the figure 4 , for example once a day or every six hours.

[0085] There figure 5 is a general representation of the supply system 8 ensuring the functions of condensation and cooling of the gas in liquid form. Generally speaking, the supply system 8 interacts with the tank 9 as well as with a set of consumers.

[0086] The feed system 8 is capable of managing the temperature of the gas in liquid form in the tank 9. To do this, the feed system 8 comprises a liquid inlet 81 and a gas inlet 82. The liquid inlet 81 connects the feed system 8 to the tank 9, and is capable of sucking in 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 tank ceiling that may comprise a certain quantity of gaseous phase 14 generated from the gas in liquid form to the feed system 8. The gaseous phase 14 generated from the gas in liquid form can be sucked in for example by a compressor 27 in order to be conducted to the feed system 8.

[0087] The power supply system 8 also comprises a gas outlet 83 which extends from the power supply system 8 to the set of consumers. By way of example, the consumers may be a propulsion engine 16, an electric generator 17, a combustion chamber 18 or a degassing mast 28. The propulsion engine 16 makes it possible to move the floating structure forward during the journey and is capable of being powered by the gaseous phase 14 generated from the gas in liquid form. The electric generator 17 provides the electricity supply 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 power supply. The gaseous 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 gaseous phase 14 generated from the gas in liquid form, the supply system 8 can suck the gaseous phase 14 generated from the gas in liquid form into the gas inlet 82. The gaseous phase 14 generated from the gas in liquid form can then be treated by the supply system 8 and then exit the latter via the gas outlet 83, for example for the purpose of supplying the propulsion engine 16 or the electric generator 17.

[0088] The gaseous phase 14 generated from the gas in liquid form and not used to power the propulsion engine 16 or the electric generator 17 represents the surplus gaseous phase 14 generated from the gas in liquid form. This surplus gaseous phase 14 generated from the gas in liquid form can be burned by the combustion chamber 18 or be released into the atmosphere by the degassing mat 28.

[0089] The surplus gas phase 14 generated from the liquid gas can also return to the feed system 8 via a bypass 84 in order to be condensed by the latter. This being done, the condensed liquid gas returns to the tank 9 via a liquid outlet 85 of the feed system 8.

[0090] If the liquid gas 13 needs to be cooled, it is drawn in by the liquid gas pump 26 and circulates through the liquid inlet 81 to the feed system 8 where it is cooled. The cooled liquid gas 13 then returns to the tank 9 via the liquid outlet 85.

[0091] There figure 6 is a schematic representation of a first embodiment of the supply system 8 ensuring the functions of condensation and cooling of the gas in liquid form.

[0092] Just like for the figure 5 , the supply system 8 ensures the management of 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 ceiling may also comprise a certain quantity 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 box for the calculation of step D of the estimation and adjustment method. For the example of the figure 6 , the first temperature sensor 10 of the tank 9 records the temperature of the gas in liquid form which surrounds it. If the floating structure comprises a plurality of tanks 9 each comprising a first temperature sensor 10, an average of the temperatures is taken and then sent to the control box.

[0093] As previously indicated, the condensation function of the supply system 8 makes it possible to condense the surplus gas phase 14 generated from the gas in liquid form. To do this, the gas phase 14 generated from the gas in liquid form in the tank 9 is sucked in by the compressor 27 located outside the tank and constituting a gas phase circuit 15. The gas phase circuit 15 transports the gas phase 14 generated from the gas in liquid form which extends until it opens at the propulsion engine 16 and / or the electric generator 17 for the purpose of being used as fuel by the latter.

[0094] The gas phase 14 generated from the gas in liquid form and not used to power 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 surplus circuit 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 ensures the function of condensing the surplus gas phase 14 generated from the gas in liquid form, 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, and this so that the surplus gas phase 14 generated from the gas in liquid form condenses and passes into 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 condensation function of the supply system 8 is inactive, then the surplus gas phase generated from the gas in liquid form is directed to the combustion chamber 18 to be burned or to the degassing mat 28 to be released into the atmosphere. In order to condense the surplus 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.

[0095] 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 to the tank 9.

[0096] Concerning the cooling function of the supply system 8, the liquid gas 13 contained in the tank 9 is first sucked in by the liquid gas pump 26. The liquid gas 13 sucked in by the liquid gas pump 26 circulates to a second heat exchanger 12. It is the second heat exchanger 12 which ensures the cooling function of the liquid gas 13, thanks to a heat exchange between a third pass 121 and a fourth pass 122. The liquid gas 13 sucked in by the liquid gas pump 26 circulates in the second heat exchanger 12 via the fourth pass 122 and is cooled. In order to cool the liquid gas 13 which is already at a very low temperature, a fluid with a temperature lower than the liquid gas 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 the . figure 6 The external refrigerant circuit can, for example, be part of a vacuum evaporator type system.

[0097] Subsequently, after having been cooled by the second heat exchanger 12, the cooled gas in liquid form 13 returns to the tank 9 via the return circuit 21. Thus, the cooled gas in liquid form 13 makes it possible to generally cool the tank 9, the temperature of the cooled gas in liquid form 13 being lower than the temperature of the gas in liquid form 13 remaining in the tank 9.

[0098] The heat exchanges of the first heat exchanger 11 and the second heat exchanger 12 are measured by a plurality of temperature sensors. Thus, the supply 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 outlets and the inlets of each of the heat exchangers, it is possible to measure the heat input into the tank 9 using the second temperature sensors 24 and the cold input into the tank 9 using the third temperature sensors 25.The heat input and the cold input are data used for calculating the execution of the condensation and cooling functions of the supply system 8, said executions being used for calculating the energy balance of the gas in liquid form at time t of step D' of the estimation and adjustment method. These data are therefore sent to the control box by the supply system 8.

[0099] At the end of the estimation and adjustment process, the power supply system 8 receives the adjusted operating plans for the condensation and cooling functions. The power supply system 8 then modifies its operation according to the adjusted operating plans by being able to program the activation or deactivation of one and / or the other of the condensation and cooling functions.

[0100] There figure 7 schematically represents a second embodiment of the power supply system 8. Compared to the first embodiment presented in figure 6 , only the implementation of the cooling function of the power supply system 8 is different. We will therefore refer to the description of the figure 6 for any part of the power supply system 8 common to both embodiments.

[0101] In this second embodiment of the supply system 8, the latter implements its cooling function in combination with a function of supplying the consumers of the floating structure. Indeed, when the gaseous phase 14 generated from the gas in liquid form is sucked into the gaseous phase circuit 15, it passes through the second exchanger 12, circulating within the third pass 121. The gas in liquid form 13 contained in the tank 9 is 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 gaseous phase 14 generated from the gas in liquid form so that it is adequate to power the propulsion engine 16 and / or the electric generator 17, but also to sub-cool the gas in liquid form 13 sucked in by the gas in liquid form pump 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, and this up to the return circuit 21 which directs the cooled gas in liquid form 13 into the tank 9.

[0102] Thus, the cooled gas in liquid form 13 returns to the tank 9 and allows the latter to be cooled overall, the temperature of the cooled gas in liquid form 13 being lower than the temperature of the gas in liquid form 13 remaining in the tank 9.

[0103] The gas in liquid form 13 circulates in this way if the cooling function is active. The supply system 8 therefore allows the condensation and cooling functions to be active or inactive simultaneously, to the extent that there is the 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.

[0104] THE figures 8 à 11 represent a curve of 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 journey of the floating structure, and as a function of the operating plans of the condensation and cooling functions represented in the upper part of each of the figures 8 à 11 . THE figures 8 And 9correspond respectively to an estimate and an adjustment following a situation where the estimate of the energy balance of the gas in liquid form on arrival is lower than the maximum energy balance. figures 10 And 11 correspond respectively to an estimate and an adjustment following a situation where the estimate of the energy balance of the gas in liquid form is greater than the maximum energy balance.

[0105] For each of the figures 8 à 11 , the initial situation presented is the launch of the estimation and adjustment process at a time t during the journey of the floating structure between departure 50 and arrival 51.

[0106] Each of the curves of the energy balance as a function of time of the figures 8 à 11 includes a real maximum energy balance 32, and the virtual maximum energy balance 33, i.e. which takes into account the safety margin. The virtual maximum energy balance 33 is lower than the real maximum energy balance 32, the difference depending on the value of the safety margin. The real maximum energy balance 32 is only present for information purposes, because for each of the figures, the adjustment of the energy balance of the gas in liquid form contained in the tank is made according to the virtual maximum energy balance 33. The real maximum energy balance 32 is constant over time. Advantageously, the virtual maximum energy balance 33 gradually approaches the real maximum energy balance over time, but for reasons of clarity, the virtual maximum energy balance 33 is also represented as being constant over time on the figures 8 à 11 .

[0107] THE figures 8 à 11 also each represent the curves of the first operating plane 36 of the condensation function and the second operating plane 37 of the cooling function over time. The ordinates of the curves of the operating planes only have two positions: a position 0 and a position 1. When the operating planes are in position 0, this means that the associated functions are inactive. When the operating planes are in position 1, this means that the associated functions are active, which consequently authorizes the condensation and / or cooling of the gas in liquid form by means of the supply system. For each of the situations, it is assumed that the two operating planes are basically in position 1 throughout the entire journey, that is to say that the condensation and cooling functions are authorized throughout the journey.

[0108] There figure 8 therefore represents a first situation during the journey of the floating structure. Thus, at time t, the estimation and adjustment process 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 estimation and adjustment process, either from the temperature of the gas in liquid form contained in the tank, or from the execution 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 time t, the evolution corresponding to a measured energy balance 34. The measured energy balance 34 is represented in solid lines because it has already been measured in real time since the start 50, the first measurement corresponding to a starting energy balance 30, determined when the estimation and adjustment process was launched for the first time.The evolution of 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 at arrival 51 therefore corresponds to an estimate of the value of the energy balance when the floating structure reaches arrival 51 if the operating plans as presented on the . figure 8 are maintained until this arrival 51.

[0109] It is noted on the figure 8 that without adjustment of the operating plans of the estimation and adjustment method according to the invention, the estimate of the energy balance 31 of the gas in liquid form contained in the tank at arrival 51 is lower than the virtual maximum energy balance 33, calculated during step E of the estimation and adjustment method. The gas in liquid form contained in the tank therefore meets the requirements of the destination location. It is nevertheless possible to adjust the operating plans in order to limit the energy consumption of the supply system.

[0110] There figure 9 represents a curve implementing step G of the estimation and adjustment method according to the invention, with operating plans adjusted in relation to those presented in figure 8 . The estimation and adjustment process always takes place at time t and after the observation that the estimate of the energy balance 31 of the gas in liquid form contained in the tank at arrival 51 was lower than the virtual maximum energy balance 33. The estimation and adjustment process therefore adjusts the operating plans in order to guarantee energy savings. Thus, although this is already the case in the example presented, the first operating plan 36 of the condensation function is adjusted to be kept active, i.e. in position 1, until arrival 51 of the journey. The surplus gas phase generated from the gas in liquid form is therefore fully condensed, which does not result in losses of the cargo.

[0111] Furthermore, the estimate of the energy balance 31 of the gas in liquid form contained in the tank at the arrival 51 being lower than the virtual maximum energy balance 33, it is also possible to deactivate the cooling function at an estimated time dt during the journey. To determine the estimated time dt, the estimation and adjustment method implements one or more iterations where the adjustment of the second operating plan 37 of the cooling function and the recalculation of the estimate of the energy balance 31 of the gas in liquid form contained in the tank at the arrival 51 alternate successively. Here, the adjustment of the second operating plan 37 of the cooling function consists of selecting a time when the cooling function is deactivated by taking the 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 at the arrival 51 is less than the virtual maximum energy balance 33, the selected time at which the cooling function is deactivated being at each new occurrence increasingly earlier than the previous one, and the calculation of the estimate of the energy balance 31 of the gas in liquid form contained in the tank at the arrival 51 being carried out each time with the new adjustment of the second operating plan 37 of the cooling function determined previously. These iterations thus make it possible to determine the optimal estimated time dt so that the estimate of the energy balance 31 of the gas in liquid form contained in the tank at the 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.

[0112] Once the estimated time dt is obtained, the estimation and adjustment method adjusts the second operating plan 37 of the cooling function and transmits it to the power system. The adjusted second operating plan 37 of the cooling function is visible on the figure 9 , where we can see that the cooling function goes to position 0 following the adjustment, causing it to be deactivated at the estimated time dt. Thus, between the estimated time dt and 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, shows a more significant increase between the estimated time dt and arrival 51 than on the curve of the figure 8 . The estimated instant dt, thanks to the iterations of the estimation and adjustment process mentioned previously, is however calculated so as to cause an increase in the estimate of the energy balance 31 of the gas in liquid form contained in the tank at arrival 51 but without the latter exceeding the maximum virtual energy balance 33 at arrival 51 at the destination location.

[0113] The liquid gas contained in the tank therefore always meets the requirements of the destination location, but energy savings are made between the estimated time dt and arrival 51 since the cooling function is deactivated during this time and therefore does not need to be supplied with energy. The estimation and adjustment process therefore made it possible to limit energy waste while maintaining the liquid gas in compliance with the requirements of the destination location.

[0114] There figure 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 figures 8 And 9 . Indeed, according to the estimation and adjustment method, 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 method calculates the estimate of the energy balance 31 of the gas in liquid form contained in the tank at the arrival 51 from the energy balance of the gas in liquid form at the instant t 38. As can be seen on the figure 10 , the estimate of the energy balance 31 of the gas in liquid form contained in the tank at arrival 51 is higher than the maximum virtual energy balance 33, and even the maximum real energy balance 32, and this despite the constant activation of the cooling function throughout the journey as evidenced by the second operating plan 37 of the cooling function visible on the figure 10 .

[0115] In this situation, upon arrival 51, and if the operating plans for the condensation and cooling functions are not adjusted, the liquid gas contained in the tank will not meet the requirements of the destination, resulting in the cargo being rejected by the destination. To avoid this, it is essential to lower the saturation pressure of the liquid gas contained in the tank, resulting in a lower energy balance of the liquid gas contained in the tank as well, in order to meet the requirements of the destination upon arrival 51. A given time t is indicated on the figure 10 and corresponds to the moment when the forecast energy balance 35 exceeds the virtual maximum energy balance 33, i.e. the moment from which the energy balance of the gas in liquid form contained in the tank no longer complies with the requirements of the destination location.

[0116] The adjustments necessary to address the situation mentioned in figure 10 are represented in figure 11 . Thus, if this is not already the case, the estimation and adjustment method adjusts the second operating plan 37 of the cooling function so that the latter is active until the arrival 51 of the journey.

[0117] As mentioned above, the main factor leading to an increase in the temperature of the liquid gas contained in the tank and its energy balance is due to the condensation of the excess gas phase generated from the liquid gas. Indeed, although the latter is condensed in order to pass into liquid form, the temperature of the condensed gas is higher than the temperature of the liquid gas contained in the tank. The return of the condensed gas to the tank therefore leads to an increase in the temperature of the liquid gas contained in the tank over time. The best way to stop such a temperature increase is therefore to implement the first operating plan 36 adjusted for the condensation function so that the latter is deactivated.

[0118] Thus the estimation and adjustment method adjusts the first operating plan 36 of the condensation function. The condensation function is therefore programmed to be deactivated at the given time t, that is to say at the time when the estimated energy balance 34 reaches the virtual maximum energy balance 33. The estimation and adjustment method thus makes it possible to keep the condensation function active for as long as possible. At the given time t, the condensation function is deactivated. The increase in the energy balance of the gas in liquid form contained in the tank is then stopped, thanks to the deactivation of the condensation function, but also thanks to the maintenance of the cooling function in activity. The estimate of the energy balance 31 of the gas in liquid form contained in the tank at the arrival 51 is therefore maintained at the level of the virtual maximum energy balance 33, which corresponds to the requirements of the destination location.In this configuration, between the given time t and arrival 51, the surplus gas phase generated from the gas in liquid form is no longer condensed by the supply system.

[0119] There figure 12 represents a first example of a curve of the evolution of the safety margin 60 as a function of time, from departure 50 to arrival 51. This first example presents a decreasing safety margin 60 over time. In other words, the closer the floating structure gets to the destination location, the more the safety margin 60 decreases and consequently the closer the virtual maximum energy balance gets to the real 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 gets closer to its destination.

[0120] The value of the safety margin may also depend on the amount of information that the personnel of the floating structure have about the journey, for example the weather conditions during the journey or the sea conditions. Thus a higher safety margin 60 may be indicated if there is no information about the conditions of the journey.

[0121] There figure 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 may 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 may also be a mechanical incident, for example a breakdown of the floating structure, likely to immobilize the latter for a significant period of time. Such an event 61 therefore lengthens the journey time to the destination. In this situation, the safety margin 60 as 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 event 61, i.e. the slowing down or immobilization of the floating structure in the examples above. On the . figure 13 , the safety margin 60 is increased at the time when event 61 occurred, then decreases again over time. This modification ensures safety regarding the virtual maximum energy balance and helps avoid errors that could potentially lead to the refusal of the liquid gas cargo upon arrival at the destination.

[0122] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0123] The invention, as just described, achieves the aim it set itself, and makes it possible to propose a method for estimating and adjusting an energy balance of a gas in liquid form contained in a tank of a floating structure so that said energy balance of the gas in liquid form complies with the requirements of a destination location where the delivery of the gas in liquid form is intended, while at the same time adjusting the energy consumption of the supply system as best as possible. Variants not described here could be implemented without departing from the context of the invention, provided that, in accordance with the invention, they comprise a method for estimating and adjusting the energy balance in accordance with the invention.

Claims

1. Method for estimating and adjusting (5) 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) to a given place of destination (2), the floating structure (1) 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 (14) generated from the gas in liquid form and / or a function of cooling the gas in liquid form (13), characterized in that the estimating and adjusting method (5) 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, based on the maximum saturation pressure requirements of gas in liquid form of the place of destination (2) and the characteristics of the gas in liquid form contained in the tank, - a step B of establishing a first operating plan (36) for the condensation function of the gas phase (14) generated from the gas in liquid form carried out by the supply system (8) until the arrival (51) at the place of destination (2), said first operating plan (36) being established from an estimate of an excess gas phase (14) generated from the gas in liquid form in the tank (9) during a journey (3), - a step C of establishing a second operating plan (37) for the cooling function of the gas in liquid form (13) carried out by the supply system (8) until arrival (51) at the place of destination (2), said second operating plan (37) being established from the estimate of the excess 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 a time t (38) from the temperature of the gas in liquid form (13) contained in the tank (9) and the 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 on arrival (51) from the journey (3) from the operating plans (36, 37) of 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 (38), determined in step D, - a step G of adjusting the first operating plan (36) and / or the second operating plan (37), - a step H of implementing the supply system (8) according to the operating plans (36, 37) of the condensation and cooling functions of the gas in liquid form (13) adjusted in step G.

2. Method for estimating and adjusting (5) the energy balance according to the preceding claim, wherein step G consists in activating the condensation function as long as the estimated energy balance (31) of the gas in liquid form contained in the tank (51) on arrival (3) from the journey, calculated in step F, is less than the maximum energy balance (32, 33) calculated in step E.

3. Method for estimating and adjusting (5) the energy balance according to one of the preceding claims, wherein step G consists in stopping the cooling function at an estimated time dt that guarantees that the estimated energy balance (31) of the gas in liquid form contained in the tank on arrival (51) from the journey (3), calculated in step F, is less than the maximum energy balance (32, 33) calculated in step E.

4. Method for estimating and adjusting (5) the energy balance according to claim 1, wherein step G consists in stopping the condensation function as long as the estimated energy balance (31) of the gas in liquid form contained in the tank on arrival (51) from the journey (3), calculated in step F, is greater than the maximum energy balance (32, 33) calculated in step E.

5. Method for estimating and adjusting (5) the energy balance according to claim 1 or 4, wherein step G consists in activating the cooling function as long as the estimated energy balance (31) of the gas in liquid form contained in the tank on arrival (51) from the journey (3), calculated in step F, is greater than the maximum energy balance (32, 33) calculated in step E.

6. Method for estimating and adjusting (5) the energy balance according to one of the preceding claims, repeated by iteration starting from step B and during the journey (3) of the floating structure (1).

7. Method for estimating and adjusting (5) the energy balance 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 time t (38) from the execution of the condensation and cooling functions from the departure (50) of the floating structure (1) and until time t and from an energy balance of the gas in liquid form at time t (38) calculated during an earlier iteration.

8. Method for estimating and adjusting (5) the energy balance according to claim 7, wherein the energy balance of the gas in liquid form at time t (38) conserved for step F is the highest among the energy balance of the gas in liquid form at time t (38) calculated in step D and the energy balance of the gas in liquid form at time t (38) calculated in step D'.

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

10. Method for estimating and adjusting (5) the energy balance according to claim 9, wherein step A' is repeated by iteration during the journey (3) of the floating structure (1).

11. Method for estimating and adjusting (5) the energy balance according to claim 9 or 10, wherein the safety margin (60) decreases as the floating structure (1) approaches the place of destination (2).

12. Method for estimating and adjusting (5) the energy balance according to one of the preceding claims, wherein the floating structure (1) is equipped with at least one engine (16) powered at least partially by the gas phase (14) generated from the gas in liquid form, the estimation of the excess gas phase generated from the gas in liquid form liquid during the journey (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. System (4) for managing an energy balance of a gas in liquid form (13) contained in at least one tank (9) of a floating structure (1), implementing the estimating and adjusting method (5) according to one of the preceding claims, said management system (4) comprising at least one fuel supply system (8) for a consumer of the floating structure (1) and at least one computer (7) having the function of estimating a quantity of excess gas phase (14) generated from the gas in liquid form during a journey (3) of the floating structure (1).

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