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

Abstract

The invention relates to a method (5) for estimating and regulating the energy balance of liquid gas contained in at least one tank of a floating structure, the floating structure being used to transport said liquid gas to a given destination, the floating structure comprising a system (8) for supplying fuel to consumers of the floating structure (1), the system being able to perform a function of condensing the gaseous phase produced from the liquid gas and a function of cooling the liquid gas, characterised in that the estimation and regulation method (5) comprises a plurality of steps leading to the regulation of the operating plans of the condensation and cooling functions so that the energy balance of the liquid gas complies with the requirements for reaching the destination.

Description

Technical Field

[0001] The present invention relates to the field of transporting natural gas and more particularly to the field of regulating the temperature of said natural gas during such transportation. Background Art

[0002] In order to more easily transport and / or store liquid gas, such as liquid natural gas, over long distances, the gas is usually liquefied by cooling it to cryogenic temperatures, such as 163°C at atmospheric pressure, to obtain liquefied natural gas, often abbreviated to "LNG". The liquefied natural gas is then loaded into special tanks in floating structures.

[0003] However, such tanks are never completely insulated and therefore boil-off of the gas is inevitable, a phenomenon known as BOG, short for Boil-Off Gas. Thus, the tanks of the floating structures contain both liquid and gaseous natural gas, the gas phase of which forms the top of the tank.

[0004] In a known manner, at least part of the natural gas present in gaseous form in tanks can be used to supply engines designed to meet the operational energy needs of the floating structure, in particular for its propulsion and / or its generation of electricity for onboard equipment. To this end, it is particularly known to circulate the gaseous natural gas through at least one natural gas processing system so as to allow its heating and compression, said system comprising a heat exchanger acting as superheater and compressor, both situated upstream of the engines.

[0005] It is also known to construct a natural gas processing system so that it can allow condensation of a portion of the natural gas taken from the gaseous state. Condensation of the natural gas may be particularly necessary when the amount of natural gas boiled off in the tank is too large compared to the operating energy requirements of the floating structure; the natural gas processing system can then condense the boiled off gas in the tank so as to return it to the tank in the liquid state. Such a liquefaction system can be implemented in particular when the floating structure is stopped and its engines have zero or almost zero consumption of the gaseous natural gas.

[0006] For this type of transport, an important data item to consider is the state of the LNG when the floating structure arrives at the destination to unload the cargo. In fact, the station receiving the LNG has requirements for the characteristics of the delivered LNG, such as the temperature or saturation pressure of said LNG. Therefore, the facility manager at the destination may refuse to unload the LNG cargo if the LNG does not meet the requirements of the destination. Since temperature is a variable factor that can change significantly during transportation, the main risk in this type of transportation is that the saturation pressure and / or temperature of the LNG when it arrives at the destination may not meet the standards expected by the facility manager at the destination, which means that the cargo may be rejected or downgraded.

[0007] The management of cargo temperature presents two issues that are directly related to the fuel supply system of the floating structure's consumers. The first issue concerns the cooling function of the supply system. This is redundant if lowering the temperature and / or saturation pressure of the liquefied natural gas would result in a significant deviation from the requirements at the destination. In this case, the cooling function of the supply system is overused, resulting in unnecessary energy consumption.

[0008] The second problem is the condensation function of the supply system. When the condensation function is activated, 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. Therefore, the return of the liquid condensed gas to the tank causes a general increase in the temperature of the liquid gas present in the tank, resulting in the risk that the liquid gas cargo no longer meets the requirements of the destination and leads to the rejection of delivery. Conversely, the deactivation of the condensation function of the supply system leads to the elimination of the excess gas phase generated from the liquid gas, for example by combustion or by release into the air, and thus leads to the waste of cargo.

[0009] The general problem is therefore to find a balance between the condensation and cooling functions of the supply system so that the cargo meets the requirements of the destination, but at the same time limits the energy consumption due to the elimination of the gas phase produced by the liquid gas and / or excessive consumption of the cooling function of the supply system. Therefore, the present invention proposes to optimize the use of the liquefaction system to ensure that, at the time of delivery, the cargo will be below the acceptance criteria of the destination, but not deviating too much from this criteria to avoid any excessive consumption related to the cooling function of the supply system. Summary of the invention

[0010] The invention thus comprises a method for estimating and regulating the energy balance of a liquid gas contained in at least one tank of a floating structure intended to transport said liquid gas to a given destination, the floating structure comprising a system for supplying fuel to consumers of the floating structure, the system being able to perform a function of condensation of the gaseous phase produced from the liquid gas and / or a function of cooling the liquid gas, characterised in that the method for estimation and regulation comprises the following steps:

[0011] - Step A, calculating the maximum allowable temperature of the liquid gas contained in the tank upon arrival at the destination based on the maximum saturation pressure requirement of the liquid gas at the destination and the characteristics of the liquid gas contained in the tank,

[0012] - a step B of establishing a first operating plan for the supply system to perform the function of condensation of the gaseous phase produced from the liquid gas until reaching the destination, said first operating plan being established on the basis of an estimate of the excess gaseous phase produced from the liquid gas in the tank during the journey,

[0013] - step C of establishing a second operating plan for the supply system to perform the cooling function of the liquid gas until reaching the destination, said second operating plan being established according to an estimate of the excess gas phase produced from the liquid gas during the journey,

[0014] - step D, calculating the energy balance of the liquid gas at time t based on the temperature of the liquid gas contained in the tank and the properties of the liquid gas contained in the tank,

[0015] - a step E of calculating the maximum energy balance according to the maximum permissible temperature of the liquid gas calculated in step A and the characteristics of the liquid gas contained in the tank,

[0016] - a step F of estimating the energy balance of the liquid gas contained in the tank at the arrival point of the journey, according to the operating plans of the condensation and cooling functions determined in steps B and C, and according to the energy balance of the liquid gas at time t determined in step D,

[0017] - Step G, adjusting the first operation plan and / or the second operation plan,

[0018] - Step H, implementing the supply system according to the operating plan of the condensation and cooling functions of the liquid gas regulated in step G.

[0019] The floating structure may be, for example, a transport vessel capable of storing and / or transporting liquid gas, such as liquid natural gas or LNG. The fuel supply system of the consumers of the floating structure ensures the management of the gas phase resulting from the liquid gas formed in the tanks by judicious use thereof to supply one or several consumers, such as the propulsion engines of the floating structure or its generators. At the same time, the fuel supply system of the consumers of the floating structure is able to manage the state of the liquid gas contained in the tanks, thanks to its cooling and condensing functions. The term "fuel supply system of the consumers of the floating structure" is subsequently simplified to "supply system".

[0020] The estimation and regulation method regulates the properties of the liquefied gas so that the liquefied gas cargo is delivered to the destination at the saturation pressure of the liquefied gas according to the requirements of the destination while minimizing the energy consumption required for temperature regulation. The term "energy balance" is used to represent numerical data obtained by calculation, which can be derived from multiple physical constants of the gas, such as the saturation pressure of the liquid gas or the temperature of the liquid gas, or even from the energy supplied or obtained by the cooling or condensing function of the supply system. The estimation and regulation method can be started before leaving the floating structure and / or during the journey between the starting point of the floating structure (such as a gas liquefaction terminal) and the destination to which the liquefied gas cargo is transported. The tank containing the liquid gas is a compliant tank suitable for transporting such cargo, and it can be, for example, a tank with a primary membrane and a primary membrane, each of which is thermally insulating.

[0021] The estimation and regulation method starts with a step A which generally consists in determining the conditions for acceptance of liquid gas cargoes at the destination and, more specifically, the maximum permissible temperature of the liquid gas contained in the tanks upon arrival. However, the reasoning may be based on the saturation pressure of the liquid gas or another value related to pressure and / or temperature. The calculation of this target value not to be exceeded depends on the saturation pressure requirement of the liquid gas and the temperature of the liquid gas at the destination and the constant characteristics of the gas. It is therefore clear that the requirements of the terminal receiving the liquid gas are intended to avoid a significant evaporation of the gas during the transmission between the ship and the terminal by imposing conditions on the acceptance of the cargo.

[0022] The maximum permissible temperature of the liquid gas contained in the tank upon arrival depends on the properties of the liquid gas transported, i.e. the total mass of the liquid gas and the specific heat capacity of the liquid gas. These two pieces of data may, for example, be provided by any document associated with the cargo, such as a technical data sheet, and may be taken into account by the supply system, for example by means of a control monitor.

[0023] The maximum permissible temperature of the liquid gas contained in the tank upon arrival calculated by the estimation and adjustment method also depends on the maximum saturation pressure requirement of the liquid gas determined by the facility manager at the destination. This data can also be known by any information source provided by the destination and can also be recorded in the supply system in the same manner as described above.

[0024] Steps B and C consist in establishing an operating plan for each function of the supply system. An "operating plan" must be understood as a progression of activation states of each of the functions during a journey that allows reaching the destination. Each of the functions, namely the condensing function and the cooling function, is either active or inactive, and the supply system can switch from one mode to another. Thus, the operating plan for each function determines the activation and inactivation sequence of each function during the journey, which results in heating or cooling of the cargo as appropriate.

[0025] When the condensation and cooling function is identified as activated, this means that the supply system is authorized to perform its condensation and / or cooling function. On the contrary, when the condensation and cooling function is defined as inactive, this means that the supply system is not authorized to perform its condensation and / or cooling function. When the cooling function is activated, the supply system is authorized to cool the liquid gas as long as there is a gas phase generated by the liquid gas. When the condensation function is activated, the supply system is able to cool the liquid gas as long as there is an excess gas phase generated by the liquid gas.

[0026] When the condensation function is activated, the temperature of the liquid gas contained in the tank may increase. The activation of the cooling function results in a decrease in temperature. When both functions are active at the same time, the temperature varies differently or may vary naturally depending on the environmental conditions during the journey. However, it is understood that the main temperature variations that occur during the journey depend on the activation of the operating plans implemented in steps B and C of the estimation and regulation method.

[0027] The operating plan of the condensing or cooling function of the supply system is therefore a flow chart determining at which time t of the journey each of the functions must be activated or deactivated. The operating plan may also include keeping one or another function activated or inactivated throughout the journey.

[0028] Each of these operation plans is determined according to an estimate of the excess gas phase generated from the liquid gas during the journey. The gas phase generated from the liquid gas is emitted from the transport tanks naturally or in a forced manner. This gas phase can then be used to supply the floating structure, for example an engine allowing the floating structure to be propelled, or a generator to power the floating structure. The gas phase generated from the liquid gas that is not used to supply the floating structure represents the excess gas phase generated from the liquid gas. When the condensation function and the cooling function are active simultaneously, this means that an excess gas phase is generated from the liquid gas circulating in the supply system.

[0029] The presence of an excess of gaseous phase produced by liquid gas can be detected by a system external to the management system of the invention or directly by the estimation and regulation method according to the invention.

[0030] Step D of the estimation and regulation method consists in calculating the energy balance of the liquid gas at time t, that is to say, from the data measured at time t. Step D is independent of steps B and C and can therefore be carried out simultaneously or before steps B and C. The calculation of the energy balance during step D depends on the total mass of the liquid gas and the specific heat capacity of the liquid gas, the constants used during step A and the average temperature of the liquid gas contained in the tank at time t. More specifically, the energy balance of the liquid gas is calculated by the following formula:

[0031] Be=mGas×Cp×T

[0032] Be is the energy balance of the liquid gas at time t, mGas is the total mass of the liquid gas, Cp is the specific heat capacity of the liquid gas, and T is the temperature of the liquid gas at time t.

[0033] The temperature of the liquid gas can be measured by at least one temperature sensor arranged in the tank. Said temperature is then taken into account during the calculations of step D. For example, if several temperature sensors are placed in the tank, or if the floating structure comprises several tanks, each provided with one or more temperature sensors, the temperature can be processed in the form of an average value. The energy balance of the liquid gas at time t calculated during this step D is used in the rest of the estimation and regulation method.

[0034] Step E comprises calculating an energy balance similar to the energy balance calculated in step D, but the energy balance of step E is a maximum energy balance, related to the maximum permissible temperature of the liquid gas calculated in step A. The maximum energy balance calculated during step E is calculated independently of the energy balance of the liquid gas at time t calculated in step D. Thus, steps D and E may be performed simultaneously, or one after the other in any order. The maximum energy balance is calculated from the total mass of the liquid gas, the specific heat capacity of the liquid gas and the maximum permissible temperature of the liquid gas. Thus, the calculations performed in step E are similar to those performed in step D, using the maximum permissible temperature of the liquid gas instead of the temperature measured in the tank of the floating structure.

[0035] During step F, the estimation and regulation method calculates the estimated energy balance of the liquid gas contained in the tanks at the time of arrival. In other words, the estimation and regulation method makes it possible to predict the characteristics of the liquid gas contained in the tanks, in particular its energy balance, when the floating structure arrives at its destination. To estimate the energy balance of the liquid gas contained in the tanks at the arrival point of the journey, the estimation and regulation method uses the energy balance of the liquid gas at time t calculated during step D, and the operation plan of the cooling and condensing functions of the supply system calculated in steps B and C. The energy balance of the liquid gas at time t calculated during step D constitutes the starting point for the estimation according to the saturation pressure of the liquid gas and the temperature of the liquid gas. The operation plans of the cooling and condensing functions calculated in steps B and C are also part of the estimation, since they affect the temperature of the liquid gas in the above-mentioned tanks. From these three data, once the floating structure has arrived at its destination, the estimation and regulation method is able to determine the energy balance of the liquid gas, taking into account the operation plans of the cooling and condensing functions previously established. Since the energy balance of the liquid gas contains several characteristics, it can also be inferred according to the saturation pressure of the liquid gas, the temperature or the amount of heat exchange. By estimating the energy balance of the cargo on arrival in this way, the operational plan can be adjusted so that the saturation pressure of the liquid gas on arrival is acceptable.

[0036] Then, step G comprises adjusting the operating plan based on a comparison between the maximum energy balance calculated in step E and the estimate of the energy balance of the liquid gas contained in the tank at the arrival point of the journey calculated in step F. According to said comparison, the first operating plan of the condensing function and / or the second operating plan of the cooling function can be adjusted. This adjustment can include stopping one and / or the other function, which can be instantaneous or changed to after a certain time. One and / or the other of these functions can also be put into operation or restarted immediately or in a predetermined manner. Thus, the first operating plan of the condensing function and / or the second operating plan of the cooling function are modified according to the data calculated or estimated during steps E and F.

[0037] Step H consists in implementing the adjusted operating plan. In other words, the supply system no longer takes into account the operating plans established during steps B and C, which are replaced by the operating plans adjusted during step G. After completing the estimation and adjustment method, the adjusted operating plan is transmitted to the supply system. Thus, the supply system can implement the cooling and / or condensation of the liquid gas, maintain their activation or deactivate them according to the respective adjusted operating plan transmitted to it.

[0038] According to a characteristic of the invention, step G activates the condensation function as long as the estimated energy balance of the liquid gas contained in the tank at the point of arrival of the journey, calculated in step F, is less than the maximum energy balance calculated in step E. When the estimated energy balance of the liquid gas contained in the tank at the point of arrival of the journey is less than the maximum energy balance, this means that, at the point of arrival of the journey, the liquid gas cargo will, for example, be at a saturation pressure of the liquid gas below the prerequisite defined by the destination. If this situation occurs during the journey, there is no disadvantage in adjusting the operating plan of the supply system function so as to allow and control the temperature increase of the liquid gas contained in the tank. Therefore, if this is not already the case, the adjustment of the first operating plan of the condensation function may consist in keeping the first operating plan activated throughout the journey. Thus, the excess gas phase generated by the liquid gas is completely condensed, instead of being possibly eliminated. Thus, there is no loss of liquid gas contained in the tank, except for the gas phase generated from the liquid gas and the gas phase used to supply the floating structure.

[0039] In this case, the condensation function is in an active state. In other words, if liquid gas is present, the supply system is authorized to condense excess gas phase generated from the liquid gas. The condensation of the liquid gas may vary in terms of activation state based on the need to manage the excess gas phase generated by the liquid gas. The condensation of the liquid gas may occur in a more continuous manner, for example, in the case where the liquid gas in the tank generates excess gas phase, in order to reduce the pressure in the tank.

[0040] According to one feature of the invention, step G consists in stopping the cooling function at an estimated time dt which ensures that the estimated energy balance of the liquid gas contained in the tank at the point of arrival of the journey, calculated in step F, is less than the maximum energy balance calculated in step E. After the regulation of the first operating plan of the condensing function consists in maintaining this first operating plan throughout the journey, the estimated energy balance of the liquid gas at the time of arrival may always be lower than the requirements of the destination. Therefore, the second operating plan of the cooling function can be adjusted so that the latter is deactivated at the estimated time dt. This regulation makes it possible to save the energy consumed by the cooling function during its deactivation. Since the liquid gas is no longer cooled by the cooling function, this leads to an increase in the temperature of the liquid gas contained in the tank. This is why the estimated time dt when the cooling function is stopped is established so that the temperature of the liquid gas contained in the tank increases, but this increase does not lead to an excess of the requirements when the liquid gas will be delivered to the destination at the point of arrival of the journey.

[0041] To this end, the estimation and regulation method will continuously repeat the adjustment of the second operating plan for the cooling function and step F, i.e. the step of estimating the energy balance of the liquid gas contained in the tank on arrival. The adjustment of the second operating plan for the cooling function consists in determining an estimated time dt, taking the arrival at the destination as a target. The estimated time dt is then determined as a certain amount of time before relative to the arrival point, for example a few days or hours. The estimation and regulation method then recalculates the estimated energy balance of the liquid gas contained in the tank on arrival, this time taking into account the new adjustment of the second operating plan for the cooling function, that is to say, stopping it, for example, a few days or hours before the arrival at the destination. If the estimated energy balance of the liquid gas contained in the tank on arrival is no longer less than the maximum energy balance calculated in step E, the estimation and regulation method then continues normally with step H. If the estimated energy balance of the liquid gas contained in the tank on arrival is still lower than the maximum balance, the estimation and regulation method then repeats the adjustment of the second operating plan for the cooling function by further predicting the estimated time dt, for example a few days or hours before the arrival at the destination. Then, the estimated energy balance of the liquid gas contained in the tank on arrival is calculated again by taking into account the new adjustment. Thus, the estimated time dt is delayed as long as the estimated energy balance of the liquid gas contained in the tank upon arrival is less than the maximum energy balance. This loop makes it possible to determine the estimated time dt closest to the current time t and therefore deactivate the cooling function as quickly as possible in order to save as much energy as possible. Once the final estimated time dt has been determined, the estimation and regulation method continues with step H.

[0042] According to one feature of the invention, step G consists in stopping the condensing function as long as the estimated energy balance of the liquid gas contained in the tank at the point of arrival of the journey, calculated in step F, is greater than the maximum energy balance calculated in step E. When the estimated energy balance of the liquid gas contained in the tank at the point of arrival of the journey is greater than the maximum energy balance, this means that the liquid gas cargo will be at a saturation pressure of the liquid gas that is too high with respect to the requirements of the floating structure to reach the destination. In order to avoid this, it is recommended to limit any action that causes an increase in the temperature of the liquid gas in the tank. Therefore, the first operating plan for the condensing function is adjusted so as to shut down the condensing function of the supply system at a given time d't - when the energy balance of the liquid gas contained in the tank exceeds the maximum energy balance. The condensing function may be reactivated if the estimated energy balance of the liquid gas contained in the tank at the point of arrival of the journey again becomes lower than the maximum energy balance thereafter.

[0043] According to one feature of the invention, step G activates the cooling function as long as the estimated energy balance of the liquid gas contained in the tank at the arrival point of the journey, calculated in step F, is greater than the maximum energy balance calculated in step E. In this case, it is necessary to reduce the temperature of the liquid gas contained in the tank. Therefore, while the first operating plan of the condensing function is adjusted so that it is deactivated at a given time d't, the second operating plan of the cooling function is also adjusted so that the cooling function is activated until the floating structure reaches the destination so that the saturation pressure of the liquid gas meets the requirements of the destination.

[0044] Therefore, in this case, the cooling function is active. In other words, the supply system is authorized to cool the liquid gas contained in the tank. The supply system cools the liquid gas according to the highest possible activity relative to the configuration of said supply system.

[0045] According to one feature of the invention, the estimation and regulation method is repeated during the journey of the floating structure by iterations starting from step B. The journey time of the floating structure between its departure point and its destination varies according to the delivery, but the journey can last several days or even weeks. For example, in the medium or long term, environmental conditions (such as weather or sea conditions for marine transport) may distort the estimates. Therefore, in order to achieve the desired goal, the estimation and regulation method must be repeated regularly during the journey. As a result, the estimation and regulation method can, for example, be parameterized to be started at regular time intervals, for example every six hours.

[0046] Step A is based on a calculation dependent on fixed values. Therefore, after starting the estimation and regulation method for the first time, it is not necessary to repeat this step. The estimation and regulation method is therefore repeatable by iteration starting from the step of establishing a first operating plan for the condensing function of the supply system.

[0047] According to one characteristic of the invention, the estimation and regulation method comprises an additional step D', performed simultaneously with step D, of calculating the energy balance of the liquid gas at time t, according to the execution of the condensation and cooling functions from the departure of the floating structure until time t, and according to the energy balance of the liquid gas at time t calculated during an earlier iteration. The calculation of the energy balance of the liquid gas at time t performed in step D' no longer takes into account the temperature of the liquid gas contained in the tank at time t, for example recorded by a temperature sensor, but the energy balance of the liquid gas at time t calculated previously. In other words, step D' is only performed if the estimation and regulation method has been implemented for the first time. Advantageously, the energy balance of the liquid gas at time t is calculated from the energy balance of the liquid gas at a previous time t, i.e. the energy balance of the liquid gas from a previous iteration of the estimation and regulation method, which may have been calculated during step D or D'.

[0048] During step D', the calculation of the energy balance of the liquid gas at time t also takes into account the performance of the condensation and cooling functions from the departure of the floating structure until time t. For the condensation function, this corresponds to data related to the amount of heat transferred to the tank and resulting in an overall increase in its temperature, for example illustrated by the temperature difference at the inlet and outlet of the heat exchanger performing the condensation function. For the cooling function, this corresponds to data related to the amount of cold transferred to the tank and resulting in an overall decrease in the tank temperature, for example illustrated by the temperature difference at the inlet and outlet of the heat exchanger performing the cooling function.

[0049] According to one feature of the invention, of the energy balance of the liquid gas at time t calculated in step D and of the energy balance of the liquid gas at time t calculated in step D', the energy balance of the liquid gas at time t saved for step F is the highest. In other words, when the estimation and regulation method subsequently reaches step F, i.e. the step of estimating the energy balance of the liquid gas contained in the tank to be estimated at arrival, the energy balance of the liquid gas contained in the tank at time t having the highest value of the result obtained in step D and of the result obtained in step D' is used for the estimation of step F. The energy balance of the liquid gas at time t having the highest value is considered the most pessimistic result. Since the goal is not to exceed the maximum energy balance at the destination, it is recommended to keep the energy balance of the liquid gas at the highest time t as a safety measure.

[0050] According to one feature of the invention, the estimation and regulation method comprises an additional step A' of selecting a safety margin for the maximum energy balance of the liquid gas according to the characteristics of the journey of the floating structure, step E being performed taking into account said safety margin. In order to ensure that the floating structure does not arrive at the destination with a cargo of liquid gas having an energy balance higher than that required at said destination, the safety margin can be taken into account so as to actually reduce the value of the maximum energy balance. Thus, during step E, the maximum energy balance is always calculated according to the maximum permissible temperature of the liquid gas calculated in step A, but also taking into account the safety margin. A safe maximum energy balance is then obtained, whose value is lower than the real maximum energy balance. During the rest of the estimation and regulation method, the first operating plan for the condensing function and the second operating plan for the cooling function are adjusted according to a comparison between the estimated energy balance of the liquid gas contained in the tank at the arrival point of the journey and a virtual maximum energy balance, that is to say, the virtual maximum energy balance taking into account the safety margin. Thus, the safety margin guarantees the certainty of remaining below the real maximum energy balance.

[0051] The safety margin can be selected according to different parameters. For example, the longer the journey, the better it is to select a high safety margin. If there is a lack of weather information during the journey, a higher safety margin is also advisable. The safety margin can be manually entered, for example via a control monitor, or can even be programmed to vary over time.

[0052] Since the safety margin is used for the calculation of step E, step A′ precedes step E in the estimation and adjustment method.

[0053] According to one feature of the invention, step A' is repeated by iteration during the journey of the floating structure. The repetition of step A' can be independent of the repetition of the estimation and regulation method, or form part of the latter. Step A' can also be triggered manually, for example after the appearance of an unforeseen meteorological phenomenon. It is then advisable to manually increase the value of the safety margin to overcome the uncertainty caused by said meteorological phenomenon.

[0054] According to one feature of the invention, as the floating structure approaches its destination, the safety margin decreases. In other words, the closer the floating structure is to its destination, the lower the safety margin should be. Thus, a safety margin that decreases over time can be programmed.

[0055] According to one feature of the invention, the floating structure is equipped with at least one engine powered at least in part by the gas phase produced by the liquid gas, an estimate of the excess gas phase produced from the liquid gas during the journey being established according to the image value of the heat input into the tank and the estimate of the engine consumption. As previously mentioned, the floating structure is able to use the gas phase produced by the liquid gas, or even produce the gas phase, for example to power its propulsion engine and / or generator. The gas phase produced by the liquid gas that is not used for these different functions corresponds to the excess gas phase produced by the liquid gas. The latter needs to be estimated in quantity so that steps B and C of the estimation and regulation method can be carried out, i.e. the steps of establishing the operating plan of the condensing and cooling functions of the supply system. The image value of the heat input into the tank can, for example, depend on the tank model used and can therefore serve as a technical characteristic of the tank. The image value of the heat input into the tank can also be estimated using sensors.

[0056] If the floating structure is equipped with a module that enables the definition of a route plan for the journey to the destination, the engine consumption can be estimated. If this is not the case, the engine consumption can be estimated from the average speed of the floating structure during the remaining journey, the latter depending on the remaining travel distance and the remaining time to reach the destination.

[0057] Therefore, the excess gas phase produced by the liquid gas can be estimated by a source external to the estimation and regulation method and input, for example, by a control monitor, in order to be taken into account during the estimation and regulation method. This excess can be quantified in tons / hour.

[0058] The invention also covers a system for managing the energy balance of liquid gas contained in at least one tank of a floating structure, the system implementing the estimation and regulation method as previously described, the management system comprising at least one fuel supply system for consumers of the floating structure and at least one computer having the function of estimating the amount of excess gas phase produced by the liquid gas during the journey of the floating structure.

[0059] This energy balance management system comprises a fuel supply system for consumers of the floating structure implementing condensing and cooling functions and allows the operation of estimation and regulation methods.

[0060] In order to ensure smooth operation of the estimation and regulation method, in particular steps B and C of establishing respectively a first operating plan for the condensation function of the gas phase produced by the liquid gas and a second operating plan for the cooling function of the liquid gas performed by the supply system, the computer may transmit an estimate of the excess gas phase produced by the liquid gas, which is essential for the execution of steps B and C. The energy balance management system may also include the above-mentioned control monitor.

[0061] The invention also comprises a floating structure for transporting liquid gas, comprising a system for managing the energy balance of said gas as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Other characteristics and advantages of the invention will emerge from the following description and from several exemplary embodiments, which are given for illustrative purposes and not limiting with reference to the accompanying schematic drawings, in which:

[0063] [ Figure 1 ] is a schematic diagram of a floating structure carrying liquid gas and moving to a destination.

[0064] [ Figure 2 ] is a schematic diagram of an embodiment of a system for managing the temperature of a liquid gas according to the present invention,

[0065] [ Figure 3 ] is a schematic diagram of a sequence when the method for estimating and regulating the energy balance of a liquid gas according to the present invention is activated for the first time,

[0066] [ Figure 4 ] is a schematic diagram of a sequence when the method for estimating and adjusting the energy balance of liquid gas according to the present invention is activated by iteration

[0067] [ Figure 5 ] is a general diagram showing a fuel supply system for consumers of a floating structure capable of executing multiple commands according to an estimation and regulation method,

[0068] [ Figure 6 ] is a schematic diagram of a supply system according to a first specific embodiment,

[0069] [ Figure 7 ] is a schematic diagram of a supply system according to a second specific embodiment,

[0070] [ Figure 8 ] is a curve representing the variation of the energy balance of the liquid gas as a function of time and of the operating schedule of the condensation and cooling functions, in which case said energy balance of the liquid gas is estimated to be too low upon arrival,

[0071] [ Fig. 9 ] is a curve showing the variation of the energy balance of the liquid gas as a function of time and the adjustment of the operating schedule for the condensation and cooling functions to overcome Figure 8 The situation mentioned in

[0072] [ Fig.10 ] is a curve representing the variation of the energy balance of the liquid gas as a function of time and of the operating schedule of the condensation and cooling functions, in which case said energy balance of the liquid gas is overestimated at the time of arrival,

[0073] [ Fig.11 ] is a curve showing the variation of the energy balance of the liquid gas as a function of time and the adjustment of the operating schedule for the condensation and cooling functions to overcome Fig.10 The situation mentioned in

[0074] Fig.12 is a curve showing a first example of the variation of the value of the safety margin as a function of time,

[0075] [ Fig.13 ] is a curve showing a second example of the change in the safety margin value as a function of time. DETAILED DESCRIPTION

[0076] To visualize the environment in which the present invention is applicable, Figure 1 A floating structure 1 is shown advancing towards a destination 2 by following a journey 3. The floating structure 1 shown here is a transport ship, for example an LNG carrier. The floating structure 1 transports liquid gas cargo with the aim of delivering the latter to the destination 2. To ensure this transport, the floating structure 1 comprises at least one tank 9.

[0077] The destination 2 is a terminal intended to receive the liquid gas contained in the tank 9 of the floating structure 1. When the latter arrives at the destination 2, the liquid gas is discharged, for example, into the storage 40. However, the destination 2 places requirements on the characteristics of the liquid gas. The requirements of the destination 2 may vary according to the manager of the facility to which the destination 2 is attached, and mainly concern the characteristics of the liquid gas, such as its saturation pressure and / or its temperature.

[0078] If the liquid gas contained in the tank 9 of the floating structure 1 does not meet these saturation pressure requirements for the liquid gas, the liquid gas cargo may be rejected by the facility manager of the destination 2 .

[0079] To avoid this, the liquid gas cargo must be closely monitored throughout the journey. The journey 3 is of variable distance and can last several days, or even weeks, depending on the distance between the loading location and the destination 2 and the speed of the floating structure 1.

[0080] Figure 2A system 4 for managing the energy balance of a liquid gas contained in a tank of a floating structure is schematically shown. The energy balance of the liquid gas corresponds to data containing various characteristics of said gas, such as its temperature, saturation pressure, total mass of the liquid gas or specific heat capacity. The management system 4 comprises a control box 41 having in a memory a method 5 for estimating and regulating the energy balance of the liquid gas contained in a tank of a floating structure. The control box 41 is thus able to start the estimation and regulation method 5 in a conventional and automatic manner and / or following a manual control implemented, for example, by means of a control monitor 6. Data may also be manually entered by means of the control monitor 6, such as the characteristics of the liquid gas being conveyed, or any other information useful for the progress of the estimation and regulation method 5, as will be clarified later.

[0081] The management system 4 also comprises a fuel supply system 8 for the consumers of the floating structure. The supply system 8 has the function of condensing and / or cooling the liquid gas contained in the tanks and is able to regulate one or the other of these functions by activating or deactivating these functions. The regulation of the condensing and cooling functions of the supply system 8 depends on the result of the estimation and regulation method 5. Thus, when the latter is concluded, the control box 41 sends a signal to the supply system 8 indicating the regulation to be made by the supply system 8.

[0082] The management system 4 also comprises a computer 7. The function of the computer 7 is to estimate the amount of excess gaseous phase produced by the liquid gas during the journey of the floating structure. The gaseous phase produced by the liquid gas naturally appears in the tank of liquid gas, or can be forced. The estimated excess gaseous phase produced by the liquid gas is calculated using an estimate of the consumption of the engines of the floating structure and an image value of the heat input into the tank. The computer 7 and the control box 41 can be part of the same control unit, or independent of each other.

[0083] The consumption of the engine of the floating structure can be estimated by inputting the route plan into the control monitor 6, which transmits the information to the computer 7, or by calculating the average speed of the floating structure from the remaining distance between the position of the floating structure and the destination and the remaining time to reach the destination. The average speed of the floating structure can also be calculated by inputting data into the control monitor 6, which transmits the information to the computer 7.

[0084] The image value of the heat input to the tank may correspond to a design value of the heat input to the tank or may also correspond to an estimated value of the heat input to the tank. The design value of the heat input to the tank depends on the type of tank used for transportation and may be provided to the computer 7 via the control monitor 6. The estimated value of the heat input to the tank may also be communicated via a sensor included in the tank.

[0085] Once the computer 7 has estimated the excess gas phase produced by the liquid gas during the journey, it transmits the result to the control box 41. The excess gas phase produced from the liquid gas during the journey is data allowing estimation and regulation of the operation of the method 5, as described below.

[0086] Figure 3 is a schematic diagram of a method for estimating and regulating the energy balance of a liquid gas according to the invention. The figure shows the progression of the estimation and regulation method 5 when it is first started during a journey to a destination. The estimation and regulation method 5 can be started for the first time before or when leaving a floating structure. Figure 3 In the figure, solid arrows represent the progress of each step of the estimation and regulation method 5, and dashed arrows correspond to data transmission between two steps of the estimation and regulation method 5 or between an element of the system for managing the energy balance of liquid gas and a step of the estimation and regulation method 5.

[0087] When the estimation and regulation method 5 is first started, it starts with step A, which enables the calculation of the maximum permissible temperature of the liquid gas contained in the tank upon arrival at the destination. The calculation of step A depends on certain constant properties of the liquid gas, such as the total mass of the liquid gas and its specific heat capacity. Such properties depend on the type of liquid gas being transported and are known in one way or another to the personnel of the floating structure. Therefore, the total mass of the liquid gas and the specific heat capacity of the liquid gas can be input or preselected by the control monitor 6 and transmitted for the calculation of step A of the estimation and regulation method 5. The calculation of step A also depends on the maximum saturation pressure requirements of the liquid gas at the destination. Since these requirements vary from destination to destination, when the destination is known, the maximum saturation pressure value required for the liquid gas is also known. The saturation pressure requirements of the liquid gas can be input by the control monitor 6, or can be known, for example, by a database listing all destination locations authorized to receive and unload liquid gas.

[0088] Once the calculations of step A have been performed, the estimation and regulation method 5 can go directly to step B, or through an intermediate step A'. Step A' consists in determining a safety margin in order to determine that the energy balance of the liquid gas is lower than required to reach the destination. Therefore, step A' is not necessary for the smooth operation of the estimation and regulation method 5, which can perform all calculations and estimates without a safety margin, but still help to optimize the regulation of the energy balance of the liquid gas. The safety margin can be determined automatically based on route planning and / or weather conditions, or manually by the control monitor 6. The safety margin is used for the calculations during step E. Therefore, step A' can occur at any time before step E.

[0089] Step B of the estimation and regulation method 5 occurs after step A or step A'. Step B consists in establishing a 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 times of the journey the condensation function remains activated or inactivated, and at what times the condensation function is activated or deactivated. The establishment of the first operating plan depends on the amount of excess gas phase produced from the liquid gas during the journey. In fact, it is understood that, for example, if it is determined that no excess gas phase is produced from the liquid gas during the journey, the supply system has no gas phase produced from the liquid gas to be condensed, and therefore does not need to be activated during the journey. This excess may be caused by a situation where the consumers of the floating structure are turned off and the evaporation of the liquid gas continues to occur. The excess gas phase produced by the liquid gas is estimated by the computer 7, which therefore transmits information to the control box so that the estimation and regulation method 5 can perform step B.

[0090] Step C takes place in parallel or sequentially with step B. Step C is based on the same principle as step B, since it allows the establishment of a second operating plan for the cooling function of the supply system 8. Similar to step B, the second operating plan for the cooling function of the supply system 8 indicates, over time, at what times of the journey the cooling function remains activated or inactivated, and at what times the cooling function is activated or deactivated. The establishment of the second operating plan also depends on the amount of excess gas phase generated by the liquid gas during the journey, estimated by the computer 7. Therefore, for steps B and C, the estimate of the excess gas phase generated from the liquid gas is taken into account.

[0091] The estimation and regulation method 5 then continues with step D, which calculates the energy balance of the liquid gas at time t. Figure 3 The process of the estimation and regulation method 5 during its first start-up is shown, the time t here corresponding to the moment of departure or before the departure of the floating structure. In order to calculate the energy balance of the liquid gas at time t, the estimation and regulation method 5 requires the characteristics of the liquid gas, in particular the maximum permissible permissible temperature of the liquid gas contained in the tank on arrival used for calculating during step A, such as the total mass of liquid gas of the liquid gas, or the specific heat capacity of the liquid gas. These characteristics can be provided by the control monitor 6, just like step A. The calculation of the energy balance of the liquid gas at time t also requires the average temperature of the liquid gas contained in the tank at time t. The average temperature of the gas can be measured, for example, using a temperature sensor located in the tank. Therefore, the supply system 8 supplies the average temperature in the tank and transmits this average temperature to the control box so that the estimation and regulation method 5 can perform the calculation of step D.

[0092] Once step D has been completed, the estimation and regulation method 5 proceeds to step E, which comprises calculating the maximum energy balance. The maximum energy balance corresponds to a limit required by the destination, i.e. the energy balance of the liquid gas contained in the tank must not exceed it, otherwise the cargo will be rejected once the floating structure reaches the destination. However, the energy balance of the liquid gas may exceed this maximum energy balance limit during the journey without consequence, but must return below this maximum energy balance before the floating structure reaches the destination. It should be understood that the maximum energy balance is a target for regulating the energy balance of the liquid gas contained in the tank during the journey.

[0093] For the calculation of the maximum energy balance during step E, the estimation and regulation method 5 requires the properties of the liquid gas and the maximum permissible temperature of the liquid gas contained in the tank upon arrival calculated during step A. Thus, the data provided and the calculations completed during step A can be transmitted for the calculation of step E. If the estimation and regulation method 5 has already carried out step A', in other words, if a safety margin has been determined and selected, said safety margin is also transmitted in order to be taken into account in the calculation of the maximum energy balance. Thus, the maximum energy balance calculated during step E corresponds to the real maximum energy balance without the safety margin, or to a virtual maximum energy balance that is lower than the real maximum energy balance, because the safety margin was taken into account in the calculation.

[0094] The next step of the estimation and regulation method 5 is a step F which ensures the estimation of the energy balance of the liquid gas contained in the tank at the point of arrival of the journey. Step F makes it possible to determine the energy balance of the liquid gas contained in the tank at the point of arrival of the journey, while maintaining the operating plan of the condensation and cooling functions established during steps B and C. To carry out this estimation, a calculation is made based on the energy balance of the liquid gas at time t calculated during step D, and on the operating plan 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 regulation method 5 can then estimate the variation of the energy balance of the liquid gas during this step F, the condensation and cooling functions being able to vary said energy balance of the liquid gas according to whether they are active or inactive and when they are activated and deactivated. Thus, from these data it is possible to determine the energy balance of the liquid gas contained in the tank at the time of arrival.

[0095] The estimation and regulation method 5 then continues with a step G which ensures the regulation of the operating plans of the condensing and cooling functions of the supply system 8. These regulations are made based on a comparison between the maximum energy balance calculated in step E and the estimated energy balance of the liquid gas contained in the tank on arrival calculated in step F. As a reminder, the estimated energy balance of the liquid gas contained in the tank on arrival calculated during step F is based on the operating plans of the condensing and cooling functions drawn up during steps B and C. Step G therefore makes it possible to modify this estimated energy balance of the liquid gas contained in the tank on arrival by regulating the operating plans of the condensing and cooling functions.

[0096] When the estimated energy balance of the liquid gas contained in the tank upon arrival is greater than the maximum energy balance, this means that the cargo of liquid gas will be at a saturation pressure of liquid gas upon arrival that is excessive relative to the maximum requirement at the destination. Therefore, the operating schedule of the condensation and cooling functions must be adjusted to reduce the temperature of the liquid gas contained in the tank and, by analogy, the energy balance of the liquid gas.

[0097] When the estimated energy balance of the liquid gas contained in the tank upon arrival is lower than the maximum energy balance, which means that the cargo of liquid gas will comply with the requirements of the destination upon arrival, an adjustment may still be made to allow the temperature of the liquid gas contained in the tank to be increased if such an adjustment proves useful in terms of energy saving. Therefore, the operating schedule of the condensing and cooling functions must be adjusted to allow the temperature of the liquid gas contained in the tank to be increased and, by analogy, the energy balance of the liquid gas to be improved.

[0098] Therefore, step G determines the optimal adjustment of the operating plan of the condensing and cooling functions of the supply system 8 in order to optimally respond to the situation. An example of adjusting the operating plan will be described later.

[0099] The estimation and regulation method 5 finally ends with step H, which implements the operating plan regulated during step G. Step H marks the end of the estimation and regulation method 5 and sends the regulated operating plans of the condensing and cooling functions to the supply system 8 so that the latter executes them. The operating details of the supply system 8 will be given below.

[0100] Figure 4 is a schematic diagram of a method for estimating and regulating 5 the energy balance of a liquid gas by its iterations during repetition, that is, when the estimation and regulation method 5 is performed according to Figure 3 Most of the steps of the estimation and adjustment method 5 are similar to those described previously, so reference will be made to Figure 3 . Figure 3, solid arrows represent the progress of each step of the estimation and regulation method 5, and dashed arrows correspond to data transmission between two steps of the estimation and regulation method 5 or between an element of the system for managing the energy balance of liquid gas and a step of the estimation and regulation method 5.

[0101] When the estimation and regulation method 5 is repeated by iteration, the starting step A is no longer useful. In fact, the result of the calculation of step A, i.e. the maximum permissible temperature of the liquid gas contained in the tank on arrival, is invariant over time. However, the result of step A is used for the calculation of step E, said result having to be saved during the journey, for example by means of a memory of the control box.

[0102] Step A' consisting of selecting the safety margin is also not repeated. However, the safety margin can be made variable independently of the progress of the estimation and regulation method 5, because it is already configured to vary over time when the estimation and regulation method 5 is first started, or because it is changed manually by the control monitor 6. The variation of the safety margin is the reason why step E remains within the estimation and regulation method 5, because it is a factor that can vary over time for the calculation of step E.

[0103] When the estimation and regulation method 5 is repeated by iteration, it thus starts from step B. Steps B and C take place so that during the first start-up of the estimation and regulation method 5 , the amount of excess gas phase produced by the liquid gas is still calculated and provided by the computer 7 .

[0104] Step D is also performed in the same manner as described above. Instead, step D' is performed in parallel with step D, which also calculates the energy balance of the liquid gas at time t, but according to a calculation different from that of step D. The calculation of the energy balance of the liquid gas at time t of step D' is done according to the energy balance of the liquid gas at the previous time t (which was calculated during the previous iteration of the estimation and regulation method 5) and according to the execution of the condensation and cooling functions since the departure of the floating structure. For example, the energy balance of the liquid gas at the previous time t can be restored from the buffer memory of the control box. The execution of the condensation and cooling functions is the starting point of the heat transfer performed by the condensation function and the cold transfer towards the liquid gas cargo performed by the cooling function. Therefore, the execution of the condensation and cooling functions can be measured by sensors located at the elements of the supply system 8 to ensure the condensation and cooling of the liquid gas, which transmit this data to the control box to be applied during step D'.

[0105] After calculating the energy balance of the liquid gas at time t in steps D and D', only the energy balance of the liquid gas at time t with the highest value is retained. The latter is considered the most pessimistic value and is preferentially kept lower than the maximum energy balance calculated subsequently.

[0106] Then, the remainder of Method 5 is estimated and adjusted according to Figure 3 Once the estimation and regulation method 5 is completed, the adjustments for the operating plan for the condensing and cooling functions are transmitted to the supply system 8 and the estimation and regulation method 5 can be repeated again directly from step B according to the settings of the control box. Figure 4 The control box is configured to repeat the estimation and adjustment method 5 at regular intervals throughout the journey, for example once a day or every six hours.

[0107] Figure 5 is a general schematic diagram of a supply system 8 which ensures the functions of condensation and cooling of the liquid gas. Typically, the supply system 8 interacts with a tank 9 and a group of consumers.

[0108] The supply system 8 is capable of ensuring temperature management of the liquid gas of the tank 9. To this end, the supply system 8 comprises a liquid inlet 81 and a gas inlet 82. The liquid inlet 81 connects the supply system 8 to the tank 9 and is capable of sucking in the liquid gas 13, for example, by means of a gas pump 26 in liquid form. The gas inlet 82 extends from the tank top, which may comprise a certain amount of gas phase 14 produced from the liquid gas, to the supply system 8. The gas phase 14 produced from the liquid gas may be sucked in, for example, by a compressor 27, in order to be led to the supply system 8.

[0109] The supply system 8 also includes a gas outlet 83, which extends from the supply system 8 to a group of consumers. For example, the consumer can be a propulsion engine 16, a generator 17, a combustion chamber 18 or an exhaust pad 28. The propulsion engine 16 makes it possible to propel the floating structure during the journey, and can be supplied with the gas phase 14 produced by the liquid gas. The generator 17 supplies power to the floating structure, such as the lighting or onboard network of the floating structure, and more generally, any entity that needs a power source. Therefore, the gas phase 14 produced by the liquid gas is used as a fuel in one and / or another of these consumers. Therefore, for example, in the case where an excess of gas phase 14 is produced by the liquid gas, the supply system 8 can draw the gas phase 14 produced by the liquid gas in the gas inlet 82. The gas phase 14 produced by the liquid gas can then be processed by the supply system 8 and then leave the latter through the gas outlet 83, for example, in order to supply the propulsion engine 16 or the generator 17.

[0110] The gas phase 14 produced by the liquid gas that is not used to supply the propulsion engine 16 or the generator 17 represents the excess gas phase 14 produced by the liquid gas. The excess gas phase 14 produced by the liquid gas can be burned by the combustion chamber 18 or released into the atmosphere through the degassing pad 28.

[0111] The excess gas phase 14 produced by the liquid gas can also be returned to the supply system 8 via the bypass 84 in order to be condensed by the latter. Once completed, the condensed liquid gas returns to the tank 9 through the liquid outlet 85 of the supply system 8.

[0112] If the liquid gas 13 needs to be cooled, the latter is sucked in by the liquid gas pump 26 and circulates in the liquid inlet 81 until it reaches the supply system 8 where it is cooled. The cooled liquid gas 13 then returns to the tank 9 through the liquid outlet 85.

[0113] Figure 6 is a schematic diagram of a first embodiment of a supply system 8 which ensures the functions of condensation and cooling of the liquid gas.

[0114] Similar to Figure 5 , the supply system 8 manages the temperature of the tank 9. The tank 9 is at least partially filled with a certain amount of liquid gas 13. The tank top may also include a certain amount of gas phase 14 generated by the liquid gas. The tank 9 also includes at least a liquid gas pump 26. The tank 9 also includes a first temperature sensor 10. It is from this first temperature sensor 10 that the average temperature of the liquid gas 13 is measured and transmitted to the control box for the calculation of step D of the estimation and regulation method. For Figure 6 In the example of the tank 9, the first temperature sensor 10 records the temperature of the liquid gas surrounding it. If the floating structure comprises a plurality of tanks 9, each tank comprising a first temperature sensor 10, the temperatures are averaged and then sent to the control box.

[0115] As previously mentioned, the condensing function of the supply system 8 allows condensing the excess gaseous phase 14 produced by the liquid gas. To this end, the gaseous phase 14 produced by the liquid gas of the tank 9 is sucked in by a compressor 27 located outside the tank and constituting a gaseous phase circuit 15. The gaseous phase circuit 15 conveys the gaseous phase 14 produced from the liquid gas, which extends until it appears at the propulsion engines 16 and / or the generators 17, with the purpose of being used by them as fuel.

[0116] The gas phase 14 generated by the liquid gas and not used to supply the propulsion engine 16 or the generator 17 represents the excess gas phase 14 generated by the liquid gas, and circulates in the excess loop 19. The excess loop 19 allows the excess gas phase 14 generated by the liquid gas to circulate to the first heat exchanger 11. Due to the heat exchange between the first channel 111 and the second channel 112, the first heat exchanger 11 performs the function of condensing the excess gas phase 14 generated by the liquid gas. The excess gas phase 14 generated by the liquid gas passes through the first channel 111 and is then cooled by the second channel 112, so that the excess gas phase 14 generated by the liquid gas condenses and becomes liquid. Therefore, it can be understood that when the condensation function of the supply system 8 works, the excess gas phase 14 generated by the liquid gas is guided to the first heat exchanger 11 via the excess loop 19. If the condensation function of the supply system 8 does not work, the excess gas phase generated by the liquid gas is guided to the combustion chamber 18 for combustion, or is guided to the degassing pad 28 to be released into the atmosphere. In order to condense the excess gas phase 14 generated from the liquid gas, a fluid having a temperature lower than a state change temperature of the excess gas phase 14 generated from the liquid gas is circulated in the second channel 112 .

[0117] Once the excess gas phase 14 has been produced by condensing the liquid gas in the first heat exchanger 11 , the condensed gas circulates in a condensed gas circuit 20 until a return circuit 21 directing the condensed gas to the tank 9 .

[0118] Regarding 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 from the pump 26 circulates to the second heat exchanger 12. Due to the heat exchange between the third channel 121 and the fourth channel 122, the second heat exchanger 12 performs the function of cooling the liquid gas 13. The liquid gas 13 sucked in by the liquid gas pump 26 circulates in the second heat exchanger 12 through the fourth channel 122 and is cooled. In order to cool the liquid gas 13, which is already at a very low temperature, a fluid having a lower temperature than the liquid gas 13 circulates in the third channel 121. The third channel 121 may be part of a cooling circuit outside the supply system 8, Figure 6 The external cooling circuit can be part of a vacuum evaporator type system, for example.

[0119] Subsequently, after being cooled by the second heat exchanger 12, the cooled liquid gas 13 is returned to the tank 9 through the return loop 21. Thus, the cooled liquid gas 13 makes it possible to cool the tank 9 as a whole, the temperature of the cooled liquid gas 13 being lower than that of the liquid gas 13 remaining in the tank 9.

[0120] The heat exchange between the first heat exchanger 11 and the second heat exchanger 12 is measured by a plurality of temperature sensors. Therefore, 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 the temperature difference between the outlet and the inlet of each heat exchanger, it is possible to measure the heat input into the tank 9 due to the second temperature sensor 24 and the cold input into the tank 9 due to the third temperature sensor 25. The heat input and the cold input are data for calculating the execution of the condensation and cooling functions of the supply system 8, which are used to calculate the energy balance of the liquid gas at time t of step D' of the estimation and regulation method. Therefore, this data is sent by the supply system 8 to the control box.

[0121] At the end of the estimation and regulation method, the supply system 8 receives an regulated operating plan for the condensing and cooling functions. The supply system 8 then modifies its operation according to the regulated operating plan by being able to program the activation or deactivation of one and / or the other of the condensing and cooling functions.

[0122] Figure 7 A second embodiment of a supply system 8 is schematically shown. Figure 6 Compared to the first embodiment shown, only the implementation of the cooling function of the supply system 8 differs. Therefore, for any part of the supply system 8 common to both embodiments, reference will be made to Figure 6 Description.

[0123] In this second embodiment of the supply system 8, the latter implements its cooling function in conjunction with the function of supplying the consumers of the floating structure. In fact, when the gas phase 14 produced by the liquid gas is sucked into the gas phase circuit 15, it passes through the second exchanger 12, circulating in the third channel 121. The liquid gas 13 contained in the tank 9 is first sucked in by the liquid gas pump 26 and then circulates through the fourth channel 122 located in the second heat exchanger 12. The heat exchange that occurs between the third channel 121 and the fourth channel 122 makes it possible both to increase the temperature of the gas phase 14 produced by the liquid gas, so that it is sufficient to supply the propulsion engine 16 and / or the generator 17, and to supercool the liquid gas 13 sucked in by the liquid gas pump 26. Subsequently, after having been cooled by the second heat exchanger 12, the cooled liquid gas 13 circulates in the cooling gas circuit 23 until the return circuit 21, which guides the cooled liquid gas 13 to the tank 9.

[0124] Thus, the cooled liquid gas 13 , whose temperature is lower than that of the liquid gas 13 remaining in the tank 9 , returns to the tank 9 , and makes it possible to cool the tank 9 as a whole.

[0125] If the cooling function is activated, the liquid gas 13 is circulated in this way. Therefore, the supply system 8 allows the condensation and cooling functions to be active or inactive at the same time, as long as there is a gas phase 14 generated by the liquid gas for performing the cooling function and there is an excess gas phase 14 generated by the liquid gas for performing the condensation function.

[0126] Figures 8 to 11 shows the variation of the energy balance of the liquid gas 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 Figures 8 to 11 The upper part of each of the functions of the condensing and cooling functions is shown in the operating plan. Figure 8 and Fig. 9 They correspond to the estimation and adjustment, respectively, in the case where the estimated energy balance of the liquid gas on arrival is lower than the maximum energy balance. Fig.10 and 11 They correspond to the estimation and adjustment respectively in the case where the estimated energy balance of the liquid gas is higher than the maximum energy balance.

[0127] for Figures 8 to 11 In each of these, the initial situation presented is that of the floating structure starting the estimation and regulation method at time t during its journey between departure 50 and arrival 51 .

[0128] Figures 8 to 11 Each curve of the energy balance as a function of time comprises a real maximum energy balance 32 and a virtual maximum energy balance 33, that is to say the virtual maximum energy balance 33 takes into account a 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 serves only as an indication, since for each diagram the adjustment of the energy balance of the liquid gas 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 approaches the real maximum energy balance over time, but for the sake of clarity the virtual maximum energy balance 33 is shown in FIG. Figures 8 to 11 is also shown to be constant over time.

[0129] Figures 8 to 11 The curves of the first operation plan 36 of the condensation function and the second operation plan 37 of the cooling function over time are also shown. The ordinate of the operation plan curve has only two positions: position 0 and position 1. When the operation plan is in position 0, it means that the relevant function is inactive. When the operation plan is in position 1, it means that the relevant function is active, thereby allowing condensation and / or cooling of liquid gas through the supply system. For each case, it is assumed that the two operation plans are basically in position 1 throughout the journey, that is, the condensation and cooling functions are permitted throughout the journey.

[0130] therefore, Figure 8 A first situation during the journey of the floating structure is shown. Thus, at time t, the estimation and regulation method starts and, during step D or D' of the estimation and regulation method, an energy balance of the liquid gas at time t 38 is obtained, depending on the temperature of the liquid gas contained in the tank, or depending on the execution of the condensation and cooling functions since departure 50. It is possible to observe the variation of the energy balance of the liquid gas contained in the tank from departure 50 to time t, which corresponds to the measured energy balance 34. The measured energy balance 34 is shown in a solid line, since it has been measured in real time since departure 50, the first measurement corresponding to the starting energy balance 30 determined when the estimation and regulation method was first started. After time t, the variation of the energy balance of the liquid gas is shown in a dotted line and represents a predicted energy balance 35, which is therefore evaluated by the estimation and regulation method, more precisely during step F and according to the energy balance of the liquid gas at time t 38. Thus, if as Figure 8 The operation plan shown is maintained until the arrival point 51 , then when the floating structure reaches this arrival point 51 , the estimate of the energy balance 31 of the liquid gas contained in the tank at the arrival point 51 thus corresponds to the estimate of the energy balance value.

[0131] exist Figure 8 It is noted that, without adjusting the operating plan of the estimation and regulation method according to the invention, the estimated energy balance 31 of the liquid gas contained in the tank 51 at the point of arrival is less than the virtual maximum energy balance 33 calculated during step E of the estimation and regulation method. Therefore, the liquid gas in the tank meets the requirements of the destination. However, the operating plan can be adjusted to limit the energy consumption of the supply system.

[0132] Fig. 9 The graph shows the implementation of step G of the estimation and regulation method according to the invention, wherein the operation plan is relative to Figure 8 Those shown are adjusted. The estimation and adjustment method always takes place at time t and after observing that the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 is lower than the virtual maximum energy balance 33. Therefore, the estimation and adjustment method adjusts the operating plan to ensure energy saving. Therefore, although this is already the case in the example shown, the first operating plan 36 of the condensation function is adjusted to remain activated, that is, in position 1, until the arrival point 51 of the journey. Therefore, the excess gas phase generated by the liquid gas is completely condensed, which does not lead to cargo losses.

[0133] Furthermore, the cooling function can also be deactivated at an estimated time dt during the journey, since the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 is lower than the virtual maximum energy balance 33. To determine the estimated time dt, the estimation and regulation method performs one or more iterations, in which the regulation of the second operating plan 37 of the cooling function and the recalculation of the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 are continuously alternated. Here, the regulation of the second operating plan 37 of the cooling function consists in selecting the time at which the cooling function is deactivated by taking the arrival point 51 as a target. As long as the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 is lower than the virtual maximum energy balance 33, the iterations continue, the selected time for deactivating the cooling function being earlier and earlier with each new occurrence than the previous time, and the calculation of the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 is performed each time with a new regulation of the second operating plan 37 of the cooling function determined previously. These iterations therefore make it possible to determine the best estimated time dt so that the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 does not exceed the virtual maximum energy balance 33 , but at the same time the cooling function is deactivated as quickly as possible in order to save maximum energy.

[0134] Once the estimated time dt has been obtained, the estimation and regulation method regulates a second operating plan 37 for the cooling function and transmits it to the supply system. Fig. 9 , where it can be seen that the cooling function switches to position 0 after the adjustment, causing it to be deactivated at the estimated time dt. Therefore, between the estimated time dt and the arrival point 51, the cooling function remains deactivated. Knowing this, and assuming that the condensation function is always effective, the temperature of the liquid gas contained in the tank, and by analogy the energy balance of the liquid gas contained in the tank, presents a ratio of Figure 8 However, due to the iteration of the estimation and regulation method described above, the estimated time dt is calculated such that the estimated energy balance 31 of the liquid gas contained in the tank increases at the arrival point 51, but the latter does not exceed the virtual maximum energy balance 33 when arriving at the point 51 to the destination.

[0135] Thus, the liquid gas contained in the tank always meets the requirements of the destination, but energy savings are achieved between the estimated time dt and the arrival point 51, since the cooling function is deactivated during this period and therefore does not need to be supplied with energy. The estimation and regulation method thus makes it possible to limit energy waste while keeping the gas in liquid state according to the requirements of the destination.

[0136] Fig.10 The energy balance of the liquid gas contained in the tank is still shown over time, but this time relative to Figure 8 and 9 In fact, according to the estimation and regulation method, during the time t of the journey, the energy balance of the liquid gas at time t 38 is calculated, and then the estimation and regulation method calculates the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 from the energy balance of the liquid gas at time t38. Fig.10 As can be seen in the figure, although the cooling function is continuously activated throughout the journey, Fig.10 However, at the arrival point 51 the estimated energy balance 31 of the liquid gas contained in the tank is greater than the virtual maximum energy balance 33 and even greater than the actual maximum energy balance 32 .

[0137] In this case, upon arrival at point 51, if the operating plan of the condensation and cooling functions is not adjusted, the liquid gas contained in the tank will not meet the requirements of the destination, causing the latter to reject the cargo. To avoid this, the saturation pressure of the liquid gas contained in the tank must be reduced, causing the energy balance of the liquid gas also contained in the tank to decrease, so as to meet the requirements of the destination upon arrival at point 51. Given a time d't at Fig.10 , and corresponds to the time at which the predicted energy balance 35 exceeds the virtual maximum energy balance 33, ie from this time onwards the energy balance of the liquid gas contained in the tank no longer meets the requirements of the destination.

[0138] overcome Fig.10 The adjustments required for the situations mentioned are as follows Fig.11 Therefore, if this is not already the case, the estimation and regulation method regulates the second operating plan 37 of the cooling function so that the latter is active before the arrival point 51 of the journey.

[0139] As mentioned previously, the main factor causing the increase in the temperature of the liquid gas contained in the tank and in the energy balance of the latter is the condensation of the excess gaseous phase produced by the liquid gas. In fact, although the latter is condensed to enter liquid form, the temperature of the condensed gas is higher than that of the liquid gas contained in the tank. Therefore, in the long run, the return of the condensed gas to the tank causes an increase in the temperature of the liquid gas in the tank. Therefore, the best way to prevent this temperature increase is to execute the first regulation operation plan 36 for the condensing function so that the condensing function is deactivated.

[0140] Therefore, the estimation and regulation method regulates the first operating plan 36 of the condensing function. Therefore, the condensing function is programmed to be deactivated at a given time d't, that is to say, at the moment when the estimated energy balance 34 reaches the virtual maximum energy balance 33. Therefore, the estimation and regulation method makes it possible to keep the condensing function effective for as long as possible. When the given time d't is reached, the condensing function is deactivated. Due to the deactivation of the condensing function, and because the cooling function remains activated, the increase in the energy balance of the liquid gas contained in the tank then stops. Therefore, the estimated energy balance 31 of the liquid gas contained in the tank at the arrival point 51 remains at the level of the virtual maximum energy balance 33, which corresponds to the requirements of the destination. In this configuration, between the given time d't and the arrival time 51, the excess gas phase produced by the liquid gas is no longer condensed by the supply system.

[0141] Fig.12 A first example of a curve of the variation of the safety margin 60 as a function of time from the departure 50 to the arrival point 51 is shown. The first example shows that the safety margin 60 decreases over time. In other words, the closer the floating structure gets to its destination, the more the safety margin 60 decreases, and thus the closer the virtual maximum energy balance is to the real maximum energy balance, because the virtual maximum energy balance is recalculated in each step E by the iteration of the estimation and adjustment method using the safety margin 60, which decreases as the floating structure approaches its destination.

[0142] The value of the safety margin may also depend on the amount of information available to the personnel of the floating structure about the journey, such as weather conditions or sea conditions during the journey. Thus, if there is no information about the conditions of the journey, a higher safety margin 60 may be indicated.

[0143] Fig.13 A second example of the variation of the safety margin 60 over time is shown. At the starting point of the journey, the safety margin 60 decreases over time, as shown in the previous figure. However, an unforeseen event 61 may occur. The event 61 may be a natural phenomenon, for example a meteorological phenomenon such as a storm or fog, capable of slowing down the speed of the floating structure. The event 61 may also be a mechanical accident, such as a breakdown of the floating structure, susceptibly rendering the latter immobile for a non-negligible period of time. Such an event 61 therefore prolongs the travel time to the destination. In this case, the safety margin 60 that was programmed at the time of departure 50 is no longer appropriate for the journey. Therefore, the safety margin 60 can be reprogrammed so that it is adapted to the consequences of the event 61, that is to say, in the example given above, the slowing down or the stationaryness of the floating structure. In Fig.13In the example shown in FIG. 6 , when event 61 has occurred, the safety margin 60 rises and then falls again over time. This modification guarantees certainty about the virtual maximum energy balance and makes it possible to avoid errors that could lead to the rejection of liquid gas cargoes upon arrival at their destination.

[0144] Of course, the invention is not limited to the examples that have just been described, and many modifications may be made to these examples without departing from the scope of the invention.

[0145] As just described, the invention achieves the objectives it has set itself and makes it possible to propose a method for estimating and regulating the energy balance of a liquid gas contained in a tank of a floating structure, such that the energy balance of said liquid gas complies with the requirements of the destination of the liquid gas delivery, while optimally regulating the energy consumption of the supply system. Variants not described here may be implemented without departing from the invention, since according to the invention they comprise the estimation and regulation method according to the invention.

Claims

1. A method (5) for estimating and regulating the energy balance of a liquid gas (13) contained in at least one tank (9) of a floating structure (1), the floating structure being used to transport the liquid gas (13) to a given destination (2), the floating structure (1) comprising a supply system (8) for supplying fuel to consumers of the floating structure (1), the supply system being able to perform a condensation function of condensing a gas phase (14) produced by the liquid gas and / or a cooling function of cooling the liquid gas (13), characterized in that The estimation and adjustment method (5) comprises the following steps: Step A, calculating the maximum allowable temperature of the liquid gas contained in the tank upon arrival at the destination based on the maximum saturation pressure requirement of the liquid gas at the destination (2) and the characteristics of the liquid gas contained in the tank, step B, establishing a first operating plan (36) of the condensation function of the gas phase (14) produced from the liquid gas, performed by the supply system (8), until reaching the destination (2) at the arrival point (51), the first operating plan (36) being established based on an estimate of the excess gas phase (14) produced from the liquid gas in the tank (9) during the journey (3), step C, establishing a second operating plan (37) for the cooling function of the liquid gas (13) performed by the supply system (8) until reaching the destination (2) at the arrival point (51), the second operating plan (37) being established based on an estimate of the excess gas phase generated from the liquid gas during the journey (3), Step D, calculating the energy balance of the liquid gas at time t (38) based on the temperature of the liquid gas (13) contained in the tank (9) and the properties of the liquid gas (13) contained in the tank (9), step E, calculating a maximum energy balance (32, 33) based on said maximum permissible temperature of the liquid gas (13) calculated in step A and the characteristics of the liquid gas (13) contained in said tank (9), step F, estimating the energy balance (31) of the liquid gas contained in the tank at the arrival point (51) of the journey (3) according to the operation plans (36, 37) of the condensing function and the cooling function determined in steps B and C and according to the energy balance of the liquid gas at the time t (38) determined in step D, Step G, adjusting the first operation plan (36) and / or the second operation plan (37), Step H, implementing the supply system (8) according to the operation plan (36, 37) of the condensation function and the cooling function of the liquid gas (13) conditioned in step G.

2. The method (5) for estimating and regulating the energy balance according to claim 1, characterized in that Step G comprises activating the condensation function as long as the estimated energy balance (31) of the liquid gas contained in the tank (51) at the arrival point (3) of the journey calculated in step F is less than the maximum energy balance (32, 33) calculated in step E.

3. The method (5) for estimating and regulating the energy balance according to any one of the preceding claims, wherein: Step G consists in stopping the cooling function at an estimated time dt which ensures that the estimated energy balance (31) of the liquid gas contained in the tank at the arrival point (51) of the journey (3) calculated in step F is less than the maximum energy balance (32, 33) calculated in step E.

4. The method (5) for estimating and regulating the energy balance according to claim 1, characterized in that Step G consists in stopping the condensing function as long as the estimated energy balance (31) of the liquid gas contained in the tank at the arrival point (51) of the journey (3) calculated in step F is greater than the maximum energy balance (32, 33) calculated in step E.

5. The method (5) for estimating and regulating the energy balance according to claim 1 or 4, characterized in that Step G comprises activating the cooling function as long as the estimated energy balance (31) of the liquid gas contained in the tank at the arrival point (51) of the journey (3) calculated in step F is greater than the maximum energy balance (32, 33) calculated in step E.

6. The estimation and regulation method (5) according to claim 1 or 2, repeated by starting from step B and iterating during the journey (3) of the floating structure (1).

7. The estimation and regulation method (5) according to claim 6 comprises an additional step D', performed simultaneously with step D, of calculating the energy balance of the liquid gas at time t (38) according to the execution of the condensation function and the cooling function of the floating structure (1) from the departure (50) until time t, and according to the energy balance of the liquid gas at time t (38) calculated during an earlier iteration.

8. The estimation and regulation method (5) according to claim 7, wherein: The energy balance of the liquid gas at time t(38) saved for step F is the highest of the energy balance of the liquid gas at time t(38) calculated in step D and the energy balance of the liquid gas at time t(38) calculated in step D'.

9. The estimation and regulation method (5) according to claim 1 comprises an additional step A' of selecting a safety margin (60) for the maximum energy balance (32, 33) of the liquid gas (13) according to the characteristics of the journey (3) of the floating structure (1), and step E is performed taking into account the safety margin (60).

10. The estimation and regulation method (5) according to claim 9, wherein: During the journey (3) of the floating structure (1), the additional step A' is repeated by iteration.

11. The estimation and regulation method (5) according to claim 9 or 10, wherein: As the floating structure (1) approaches the destination (2), the safety margin (60) decreases.

12. The estimation and adjustment method (5) according to claim 1 or 2, characterized in that: The floating structure (1) is equipped with at least one engine (16) powered at least in part by a gas phase (14) produced by liquid gas, an estimate of the excess gas phase produced by the liquid gas during the journey (3) being established from an image value of the heat input into the tank (9) and an estimate of the consumption of the engine (16).

13. A management system (4) for managing the energy balance of liquid gas (13) contained in at least one tank (9) of a floating structure (1), the management system implementing the estimation and regulation method (5) according to any of the preceding claims, the management system (4) comprising at least one fuel supply system (8) for consumers of the floating structure (1) and at least one computer (7) having the function of estimating the amount of excess gas phase (14) produced by the liquid gas during the journey (3) of the floating structure (1) and transmitting the estimated amount of excess gas phase for establishing a first operating plan and a second operating plan.

14. A floating structure (1) for transporting liquid gas (13), comprising a management system (4) for managing the energy balance of said gas according to claim 13.

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