JP2023507467A - A method for estimating and adjusting the energy balance of a liquid gas contained in a tank - Google Patents

Abstract

The present invention is a method (5) for estimating and adjusting the energy balance of a liquid gas, wherein the liquid gas is located at a floating structure intended to convey said gas to a given destination. A consumer device for a floating structure (1) housed in at least one tank, the floating structure being able to carry out the functions of condensing the gas phase produced from the liquid gas and cooling the liquid gas. In a method (5) for estimating and adjusting an energy balance, the method (5) includes a system (8) for supplying fuel to a liquid gas, which The method (5) for estimating and adjusting the energy balance is characterized in that it comprises a plurality of steps leading to the adjustment of the operating schedule of the condensing and cooling functions to meet the local requirements.

Description

The present invention relates to the field of transportation of natural gas, and more particularly to the field of temperature control of said natural gas during such transportation.

In order to more easily transport and/or store liquid gas, such as liquid natural gas, over long distances, the gas is cryogenically cooled at atmospheric pressure to obtain liquefied natural gas, commonly known by the acronym "LNG". , for example, by cooling to -163°C. This liquefied natural gas is then loaded into dedicated storage tanks within the floating structure.

However, such tanks are never perfectly thermally insulated, so that the gas boils off unavoidably, a phenomenon referred to as BOG (an acronym for boil-off gas). Thus, the storage tank of the floating structure contains both liquid natural gas and gaseous natural gas, with the gaseous phase of the natural gas forming the upper portion of the tank.

As is known, at least a portion of the gaseous natural gas present in tanks is used to propel and/or mount floating structures, particularly in engines designed to meet the operational energy demands of floating structures. It can be supplied for power generation for equipment. For this purpose, it is particularly known to circulate natural gas in the gaseous state through at least one natural gas processing system so as to be able to heat and compress it, said systems both being upstream of the engine. including a heat exchanger used as a superheater and a compressor located in the

It is also known that natural gas processing systems are configured to allow a portion extracted from the gaseous natural gas to be condensed. Condensation of natural gas may be particularly required when the amount of natural gas boiled off in the tank is excessive compared to the operating energy needs of the floating structure; Allows any boil-off gas present to condense and return to the tank in a liquid state. Such a liquefaction system is particularly viable when the floating structure is shut down and the consumption of gaseous natural gas by its engine(s) is zero or near zero.

One of the essential data to consider for this type of transport is the condition of the liquid natural gas when the floating structure reaches its destination and unloads its cargo. In practice, stations receiving liquid natural gas have requirements regarding the properties of the transported liquid natural gas, such as the temperature or saturation pressure of said liquid natural gas. Therefore, a destination facility manager may refuse to unload a cargo of liquid natural gas if it does not meet the destination's requirements. Since temperature is a variable factor that changes significantly during transport, the main risk that can be considered during this type of transport is that the natural gas in its liquid state does not meet the standards expected by the facility manager at the destination, Thus, the cargo may arrive at its destination at saturation pressure and/or temperature, meaning potential rejection or downgrade.

Cargo thermal management poses two problems that are directly related to fuel supply systems for consuming equipment in floating structures. The first problem concerns the cooling function of the supply system. Reducing the temperature and/or saturation pressure of the liquid natural gas is futile if this leads to very large deviations from the destination requirements. In this situation, the cooling function of the supply system is overused, leading to unnecessary energy consumption.

A second problem relates to the condensation function of the supply system. When the condensation function is active, the excess gas phase produced from the liquid gas returns to the liquid phase and back to the transport tank. However, the condensed liquid gas may have a higher temperature than the liquid gas present in the tank. Returning the liquid condensed gas to the tank therefore leads to a general increase in the temperature of the liquid gas present in the tank, so that the cargo of liquid gas no longer meets the requirements of the destination and consequently transports may pose a risk of rejection. In contrast, if the condensing function of the supply system is inactive, the excess gas phase produced from the liquid gas is removed, for example by combustion or venting into the air, thus leading to waste of cargo.

A common problem, therefore, is to ensure that the cargo meets the requirements of its destination while at the same time removing the vapor phase produced from the liquid gas and/or energy due to excessive consumption in the cooling functions of the supply system. The goal is to find a balance between the condensing and cooling functions of the supply system so that consumption is limited. Therefore, the present invention is designed to ensure that the cargo, when transported, falls below the acceptance criteria of the destination, but does not deviate excessively from this criteria in order to avoid any overconsumption associated with the cooling function of the supply system. We propose to optimize the use of the liquefaction system.

Accordingly, the present invention is a method for estimating and adjusting the energy balance of a liquid gas, which is at least a floating structure intended to transport said gas to a given destination. Housed in one tank, the floating structure is capable of performing the function of condensing the vapor phase produced from the liquid gas and/or cooling the liquid gas. A method for estimating and adjusting an energy balance comprising a system for providing
- the maximum permitted liquid gas contained in tanks on arrival at the destination, based on the maximum saturation pressure requirements of the liquid gas at the destination and the characteristics of the liquid gas contained in the tank; a step A of calculating the temperature;
- a step B of establishing a first operating plan for the function of condensing the vapor phase produced from the liquid gas, carried out by the supply system until arrival at its destination, said first operating plan , established from an estimate of the excess gas phase produced from the liquid gas in the tank during the stroke, step B;
- Step C of establishing a second operating plan for the cooling function of the liquid gas, carried out by the supply system until its arrival at its destination, said second operating plan being in the liquid state during the journey; step C, established from an estimate of the excess gas phase produced from the gas;
a step D of calculating the energy balance of the liquefied gas at time t from the temperature of the liquefied gas contained in the tank and the properties of the liquefied gas contained in the tank;
- a step E of calculating the maximum energy balance from the maximum allowed temperature of the liquid gas calculated in step A and the properties of the liquid gas contained in the tank;
from the condensing and cooling function operating plans determined in steps B and C and the energy balance of the liquid gas at time t determined in step D, the a step F of estimating the energy balance of the liquid gas in
- a step G of adjusting the first driving plan and/or the second driving plan;
- a step H of performing the supply system according to the operation plan of the liquid gas condensation and cooling functions coordinated in step G;
A method for estimating and adjusting an energy balance, comprising:

The floating structure may, for example, be a transport vessel capable of storing and/or transporting liquid gas, such as liquid natural gas or LNG. The fuel supply system of the consuming device of the floating structure smartly utilizes the gas phase produced from the liquid gas produced in the tank to power one or several of the propulsion engines or generators of the floating structure. Feeding the consumer ensures control of the gas phase produced from the liquid gas produced in the tank. At the same time, the fuel supply system of the consuming device of the floating structure can manage the condition of the liquid gas contained in the tank due to its cooling function and its condensing function. The term "fuel supply system of the consumer of the floating structure" is hereinafter abbreviated as "supply system".

Estimation and adjustment methods are used to minimize the energy consumption required for temperature control while transporting the liquid gas cargo to its destination at the saturation pressure of the liquid gas according to the requirements of the destination. Control properties. The term "energy balance" 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 demanded by the cooling or condensing functions of the supply system. It is used to refer to numerical data obtained by simple calculations. The estimation and adjustment method can be initiated prior to the departure of the floating structure and/or during the journey from the origin of the floating structure, eg a gas liquefaction terminal, to the destination where the liquid gas cargo is to be carried. Tanks containing gas in liquid form are standardized tanks suitable for transporting such cargoes, which can be, for example, tanks having primary and secondary membranes, each of which is thermally insulated.

The estimation and adjustment method begins with step A, which generally determines the conditions for acceptance of cargoes of liquid gas by the destination and, in particular, the maximum permitted temperature upon arrival of the liquid gas contained in tanks. is performed as However, it is possible to determine the saturation pressure of the liquid gas or another value related to pressure and/or temperature. Calculation of such target values that should not be exceeded depends on the saturation pressure requirements of the liquid gas, the temperature of the liquid gas at the destination, and certain properties of the gas. It is therefore clear that the requirements for terminals accepting liquid gas are aimed at avoiding significant vaporization of natural gas during transit between the ship and the terminal by imposing conditions for the acceptance of cargo.

The maximum permissible temperature upon arrival of the liquid gas contained in the tank depends on the properties of the liquid gas to be transported, which is the total mass of the liquid gas and the specific heat capacity of the liquid gas. These two data are provided by any documentation relating to the cargo, for example a technical data sheet, and can be taken into account by the supply system, for example the control monitor.

The maximum permissible temperature upon arrival of the liquid gas contained in tanks, calculated by the estimation and adjustment method, is also dependent on the maximum saturation pressure requirements of the liquid gas as determined by the facility manager at the destination. . Such data may also be known through any source provided by the destination and recorded in the supply system in the same manner as described above.

Steps B and C are performed as setting up operational plans for each function of the supply system. A "drive plan" has to be understood as the course of action of each function in the journey, which makes it possible to reach the destination. Each of the functions, condensing and cooling, is either active or inactive and the supply system can switch from one mode to the other. Thus, the operational plan for each function determines the activation and inactivation sequence of each function during the journey, resulting in heating or cooling of the cargo depending on the situation.

When the condensing and cooling functions are considered active, this means that the supply system is allowed to perform its condensing and/or cooling functions. Conversely, when the condensing and cooling functions are considered inactive, this means that the supply system is not permitted to perform its condensing and/or cooling functions. When the cooling function is active, the supply system is allowed to cool the liquid gas provided there is a gas phase generated from the liquid gas. When the condensation function is active, the supply system can cool the liquid gas provided that there is also excess gas phase generated from the liquid gas.

When the condensation function is active, the temperature of the liquid gas contained within the tank may tend to rise. Cooling functions lead to a decrease in temperature when activated. When the two functions work simultaneously, the temperature will change differently, or may change naturally depending on the environmental conditions during the journey. However, it is understood that the major temperature changes that occur during the journey are dependent on the activation of the maneuver plan performed during steps B and C of the estimation and adjustment method.

Thus, the operating plan for the condensing or cooling function of the power supply system is a flow chart that determines at what time t of the stroke each of the functions should be activated or deactivated. It is also possible that the trip plan consists of keeping one or the other of the functions active or inactive during the entire journey.

Each of these operating plans is determined from an estimate of the excess gas phase produced from the liquid gas during the stroke. The vapor phase produced from the liquid gas escapes from the transport tank either spontaneously or in a forced manner. This gas phase can then be used to feed a floating structure, eg, an engine that enables propulsion of the floating structure, or a generator that supplies electricity to the floating structure. The gas phase produced from the liquid gas that is not used to feed the floating structure is the excess gas phase produced from the liquid gas. When the condensing and cooling functions work simultaneously, this means that there is an excess gas phase produced from the liquid gas circulating in the supply system.

The presence of excess gas phase produced from liquid gas can be detected by systems external to the management system of the invention or directly by the estimation and adjustment method of the invention.

Step D of the estimation and adjustment method is performed as calculating the energy balance of the liquid gas at time t, ie from the data measured at time t. Step D is independent of steps B and C, and thus can occur concurrently with or before steps B and C. The calculation of the energy balance during step D is based 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. depends on More specifically, the liquid gas energy balance is calculated from the following equation:
Be = mGas x Cp x T
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. is.

The temperature of the liquid gas can be measured by at least one temperature sensor arranged in the tank. In this case, said temperature is taken into account during the calculation of step D. The temperature can be treated in average form, for example if several temperature sensors are placed in the tanks or if the floating structure comprises several tanks each equipped with one or more temperature sensors. The liquid gas energy balance at time t, calculated during this step D, is used in the remaining estimation and adjustment methods.

Step E is performed as calculating an energy balance similar to the energy balance calculated in step D, but the energy balance of step E is the maximum energy income and expenditure. The calculation of the maximum energy balance calculated during step E does not depend on the liquid gas energy balance at time t, calculated in step D. Accordingly, steps D and E can be performed simultaneously or sequentially 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 allowable temperature of the liquid gas. The calculations performed in step E are therefore similar to those performed in step D, with the maximum allowable temperature of the liquid gas being used instead of the temperature measured in the tank of the floating structure.

During step F, the estimation and adjustment method calculates an estimated energy balance upon arrival of the liquid gas contained within the tank. In other words, the estimation and adjustment method makes it possible to predict the properties of the liquid gas contained in the tank, in particular its energy balance, when the floating structure reaches its destination. To estimate the energy balance of the liquid gas contained in the tank upon arrival from the journey, the estimation and adjustment method uses the energy balance of the liquid gas at time t calculated during step D, and the operating plans for the cooling and condensing functions of the feed 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 estimate by the saturation pressure of the liquid gas and the temperature of the liquid gas. The operating schedules for the cooling and condensing functions calculated in steps B and C are also part of the estimate, as they affect the temperature of the liquid gas contained in the tank as described above. . From these three data, the estimation and adjustment method determines the energy balance of the liquid gas when the floating structure arrives at its destination, taking into account the pre-established operational plans of the cooling and condensing functions. be able to. Since the energy balance of a liquid gas encompasses multiple properties, it can also be inferred by the saturation pressure, temperature, or amount of heat exchange of the liquid gas. By estimating the energy balance of the cargo at arrival in this manner, it is possible to adjust the operation plan so that the saturation pressure of the liquid gas at arrival will allow the cargo to be accepted.

Step G is then between the maximum energy balance calculated in step E and the estimated energy balance of the liquid gas contained in the tank on arrival from the journey calculated in step F. It is done as adjusting the operation plan based on the comparison of Depending on said comparison, the first operating plan of the condensing function and/or the second operating plan of the cooling function can be adjusted. Adjustment may consist of deactivating one and/or the other of the functions, deactivation optionally being immediate or programmed after a certain period of time. Also, one and/or the other of the functions can be executed or resumed immediately or scheduled. Accordingly, the first operating plan for the condensing function and/or the second operating plan for the cooling function are modified from the data calculated or estimated during steps E and F.

Step H is carried out as implementing the coordinated operation plan. In other words, the supply system no longer considers the operating plans established during steps B and C, which are replaced by the adjusted operating plans during step G. The adjusted drive plan is communicated to the delivery system after the estimation and adjustment method is completed. Accordingly, the supply system can perform cooling and/or condensation of the liquid gas according to the communicated respective coordinated operation plan, keep them active or deactivate them.

According to one aspect of the invention, the estimated energy balance of the liquid gas contained in the tank on arrival from the stroke calculated in step F is less than the maximum energy balance calculated in step E. is also small, step G is performed as activating the condensation function. When the estimated energy balance of the liquid gas contained in the tanks on arrival from the journey is less than the maximum energy balance, this means that, on arrival from the journey, a cargo of liquid gas may means that the liquid gas saturation pressure is lower than the requirement defined by If this situation occurs during the process, there is no disadvantage in adjusting the operating schedule for the functioning of the supply system to allow and control the temperature rise of the liquid gas contained in the tank. . Therefore, if this is not already the case, the first operating plan adjustment of the condensing function is to keep the condensing function active throughout the entire stroke. Excess gas phase produced from the liquid gas is therefore substantially condensed instead of being optionally removed. Therefore, there is no loss of the liquid gas contained in the tank, except for the gas phase produced from the liquid gas and used to supply the floating structure.

In this situation the condensation function is active. In other words, if there is an excess gas phase produced from the liquid gas, the feed system is allowed to condense the excess gas phase produced from the liquid gas. The effect of liquid gas condensation may vary based on the need to manage the excess gas phase produced from the liquid gas. Condensation of the liquid gas can be done in a more sustained manner, for example to reduce the pressure in the tank when excess gas phase is produced from the liquid gas in the tank.

According to one aspect of the invention, the estimated energy balance of the liquid gas contained in the tank on arrival from the stroke calculated in step F is less than the maximum energy balance calculated in step E. At an estimated time dt that ensures that is also small, step G is performed as turning off the cooling function. After the first operating plan adjustment for the condensing function has been made to maintain this throughout the journey, the estimated energy balance of the liquid gas on arrival should always be less than the destination requirement. is possible. Therefore, it is possible to adjust the second operating plan for the cooling function such that the cooling function is deactivated at the estimated time dt. Such regulation makes it possible to save the energy consumed by the cooling function during the period when the cooling function is deactivated. This leads to an increase in the temperature of the liquid gas contained in the tank, since the liquid gas is no longer cooled by the cooling function. This means that the estimated time dt to stop the cooling function is the time when the temperature of the liquefied gas contained in the tank rises and this rise occurs when the liquefied gas arrives at its destination from the journey of transportation. This is the reason why we establish not to exceed the requirements.

To do this, the estimation and adjustment method includes adjusting the second operating plan for the cooling function and step F, estimating the energy balance on arrival of the liquid gas contained in the tank. will be repeated successively. A second run plan adjustment for the cooling function is performed as determining an estimated time dt to target arrival at the destination. In this case, the estimated time dt is determined as a certain amount of time before arrival, eg days or hours before. The estimation and adjustment method then recalculates the estimated energy balance at the time of arrival of the liquid gas contained in the tank, at which time a new adjustment of the second operating plan for the cooling function; Thus, for example, consideration is given to turning off the cooling function days or hours before arrival at the destination. If the estimated energy balance at the time of arrival of the liquid gas contained in the tank is no longer less than the maximum energy balance calculated in step E, the estimation and adjustment method normally continues with step H. If the estimated energy balance on arrival of the liquefied gas contained in the tank is still less than the maximum balance, the estimation and adjustment method adjusts the estimated time dt to e.g. Repeat the adjustment of the second operating plan for the cooling function by predicting further forward. The estimated energy balance upon arrival of the liquid gas contained in the tank is then recalculated by taking into account the new adjustments. Therefore, the estimated time dt is delayed as long as the estimated energy balance at the time of arrival of the liquid gas contained in the tank is less than the maximum energy balance. This loop determines the estimated time dt closest to the current time t in order to save as much energy as possible, thus allowing the cooling function to be deactivated as soon as possible. Once the final estimated time dt has been determined, the estimation and adjustment method continues with step H.

According to one aspect of the invention, the estimated energy balance of the liquid gas contained in the tank on arrival from the stroke calculated in step F is less than the maximum energy balance calculated in step E. As long as is also large, step G is performed as turning off the condensation function. When the estimated energy balance of the liquefied gas contained in the tank on arrival from the journey is greater than the maximum energy balance, this indicates that the cargo of liquefied gas is at the destination on arrival of the floating structure. This means that the saturation pressure of the liquid gas is too high for the requirements. In order to avoid this situation, it is advisable to limit any actions that lead to an increase in the temperature of the liquid gas contained in the tank. Therefore, a first operating strategy for the condensing function, such that 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 of the supply system is shut down. is adjusted. The condensation function may optionally be reactivated if the estimated energy balance of the liquid gas contained in the tank on arrival from the journey is subsequently again less than the maximum energy balance.

According to one aspect of the invention, the estimated energy balance of the liquid gas contained in the tank on arrival from the stroke calculated in step F is less than the maximum energy balance calculated in step E. is also greater, step G is performed as activating the cooling function. In this situation it is essential to lower the temperature of the liquid gas contained in the tank. Therefore, the first operating schedule of the condensing function is adjusted such that the condensing function is deactivated at a given time d't while the saturated pressure of the liquid gas meets the requirements of the destination and A second operating schedule of the cooling function is also adjusted such that the cooling function is active until arrival of the floating structure at .

Therefore, in this situation the cooling function is active. In other words, the supply system is permitted to cool the liquid gas contained within the tank. The supply system cools the liquid gas according to the highest possible efficiency with respect to the configuration of said supply system.

According to one aspect of the invention, the estimation and adjustment method begins at step B and is repeated iteratively during the course of the floating structure. The journey time of a floating structure from its starting point to its destination is variable according to the transport, but the journey can last for days or even weeks. Estimates may be distorted in the medium to long term by environmental conditions such as weather or sea conditions for maritime transport. Therefore, the estimation and adjustment method must be repeated regularly during the journey to achieve the desired objectives. Thus, the estimation and adjustment method can be parameterized, for example, to be initiated at regular time intervals, for example, every 6 hours.

Step A is based on calculations that rely on fixed values. Therefore, there is no need to repeat this step after starting the estimation and adjustment method for the first time. The estimation and adjustment method is therefore repeatable iteratively, starting with the step of establishing a first operating plan for the condensing function of the supply system.

According to one aspect of the invention, the estimation and adjustment method consists of performing the condensation and cooling functions from the departure of the floating structure to time t and the liquid gas and an additional step D', performed concurrently with step D, of calculating the energy balance of the liquid gas at time t from the energy balance of . Although the calculation of the energy balance of the liquid gas at time t, which is performed in step D', no longer takes into account the temperature of the liquid gas contained in the tank at time t, recorded, for example, by a temperature sensor. , the energy balance of the liquid gas at a pre-calculated time t. In other words, step D' is performed only if the estimation and adjustment method has already been performed 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, ie from a previous iteration of the estimation and adjustment method, which is It may have been calculated during step D or D'.

The calculation of the liquid gas energy balance at time t during step D' also takes into account the performance of the condensation and cooling functions from the departure of the floating structure to time t. In the condensing function, this corresponds to the data on the heat transferred to the tank, which leads to a general increase in temperature, for example indicated by the temperature difference between the inlet and the outlet of the heat exchanger performing the condensing function. In the cooling function, this corresponds to data on low temperatures that are transferred to the tank and result in a general drop in temperature indicated by, for example, the temperature difference between the inlet and the outlet of the heat exchanger performing the cooling function.

According to one aspect of the invention, the energy balance of the liquid gas at time t saved for step F is the energy balance of the liquid gas at time t calculated in step D and the energy balance of the liquid gas at time t ', the energy balance of the liquid gas at time t. In other words, this means that when the estimation and adjustment method is followed by step F, estimating the energy balance of the liquid gas contained in the tank, estimated on arrival, the Energy balance of the liquid gas contained in the tank at time t having the largest value between the result obtained in step D and the result obtained in step D', used for estimation is. The liquid gas energy balance at time t, which has the largest value, is considered the most pessimistic result. Since the goal is not to exceed the maximum energy balance of the destination, as a safety measure it is good to keep the liquid gas energy balance at the longest time t.

According to one aspect of the invention, the estimation and adjustment method includes an additional step A' of selecting a safety margin for the maximum energy balance of the liquid gas as a function of the stroke characteristics of the floating structure; is implemented taking into account said safety margin. Consider a safety margin to substantially reduce the value of the maximum energy balance to ensure that floating structures do not arrive at their destination with a liquid gas cargo whose energy balance is greater than the requirements of said destination. It is possible to Therefore, during step E, the maximum energy balance is always calculated according to the maximum allowed liquid gas temperature calculated in step A, but also taking into account a safety margin. In this case, a safe maximum energy balance is obtained that has a smaller value than the actual maximum energy balance. In the remaining estimation and adjustment method, the first operating plan for the condensing function and the second operating plan for the cooling function are the liquid gas contained in the tank on arrival from the stroke. It is adjusted according to the comparison between the estimated energy balance and the hypothetical maximum energy balance, ie this takes into account the safety margin. The safety margin thus ensures certainty that the actual maximum energy balance remains below.

The safety margin can be chosen according to different parameters. For example, it is preferable to choose a higher margin of safety for longer trips. A high margin of safety is also recommended when in-process weather information is lacking. The safety margin can be manually entered via a control monitor, for example, or can be programmed to be variable over time.

Since the safety margin is used in the calculation of step E, step A' precedes step E in the estimation and adjustment method.

According to one feature of the invention, step A' is repeated in iterations during the course of the floating structure. The iteration of step A' may be independent of, or form part of, the iteration of the estimation and adjustment method. Step A' can also be triggered manually, for example after the appearance of an unforeseen weather phenomenon. In this case, it may be smart to manually increase the value of the safety margin to overcome the uncertainty introduced by said weather event.

According to one aspect of the invention, the safety margin is reduced as the floating structure approaches its destination. In other words, the closer the floating structure is to its destination, the lower the required margin of safety. Therefore, it is possible to program a safety margin that decreases over time.

According to one aspect of the invention, a floating structure comprises at least one engine driven at least in part by a gas phase produced from a liquid gas, and a gas phase produced from the liquid gas during stroke. An estimate of the excess gas phase is established from the predicted heat input to the tank and the estimated engine consumption. As previously mentioned, a floating structure may use or even generate a gaseous phase produced from a liquid gas, for example to drive its propulsion engine and/or its generator. be able to. The gas phase produced from the liquid gas that is not used for these various functions corresponds to excess gas phase produced from the liquid gas. The excess gas phase needs to be estimated in such an amount that steps B and C of the estimation and adjustment method, i. . Predicted values for the heat input into the tank may be available as a technical characteristic of the tank, for example as it may depend on the tank model used. The expected heat input to the tank can also be estimated using sensors.

Engine consumption can be estimated if the floating structure is equipped with a module that allows to define a path plan for the journey to the destination. If not, the engine consumption can be estimated from the average speed of the floating structure over the rest of the journey, which depends on the remaining distance to travel and the time remaining to reach the destination. .

The excess gas phase produced from the liquid gas can thus be estimated by a source external to the estimation and adjustment method, eg input by a control monitor to be taken into account in the estimation and adjustment method. In this case, this surplus can be quantified in tons/hour.

SUMMARY OF THE INVENTION The present invention is a system for managing the energy balance of a liquid gas contained within at least one tank of a floating structure, implementing the estimation and adjustment method as previously described, comprising: Also covers systems comprising at least one fuel supply system for the consumer of goods and at least one computer having the function of estimating the amount of excess gas phase produced from the liquid gas during the course of the floating structure do.

Such an energy balance management system includes a fuel supply system for the consumers of the floating structure, performing condensation and cooling functions, and allows the execution of estimation and regulation methods.

An estimation and adjustment method, in particular a first operating plan for the function of condensing the gas phase produced from the liquid gas and a second operating plan for the cooling function of the liquid gas, performed by the supply system, respectively. To ensure smooth execution of establishing steps B and C, the computer can communicate an estimate of the excess gas phase produced from the liquid gas that is essential for performing steps B and C. The energy budget management system may also include the control monitor described above.

The invention also covers floating structures for transporting liquid gas, including systems for managing the energy balance of liquid gas as described above.

Other features and advantages of the present invention will become apparent both from the following description and from some exemplary embodiments given by way of illustration and without limitation, with reference to the accompanying schematic drawings.

1 is a schematic view of a floating structure laden with gas in liquid form en route to its destination; FIG. 1 is a schematic diagram of one embodiment of a system for controlling the temperature of a liquid gas according to the invention; FIG. 1 is a schematic diagram of the initial start of a series of methods for estimating and adjusting the energy balance of a liquid gas according to the present invention; FIG. FIG. 2 is a schematic diagram of an iteratively initiated sequence of methods for estimating and adjusting the energy balance of a liquid gas according to the present invention; 1 is a schematic diagram illustrating a fuel delivery system for a floating structure consumer capable of executing multiple commands according to an estimation and adjustment method; FIG. 1 is a diagram of a delivery system according to a first specific embodiment; FIG. Fig. 4 is a diagram of a delivery system according to a second particular embodiment; FIG. 4 shows curves representing the change in the energy balance of the liquid gas as a function of time and the operating schedule for the condensation and cooling functions in a situation where the energy balance of the liquid gas is estimated to be underestimated on arrival; . Figure 9 shows curves representing the change in liquid gas energy balance as a function of time and an adjusted operating plan for the condensation and cooling functions to overcome the situation described in Figure 8; FIG. 4 shows curves representing changes in the energy balance of a liquid gas as a function of time and operating plans for the condensation and cooling functions in a situation where the energy balance of the liquid gas is estimated to be overestimated on arrival; . Figure 11 shows curves representing the change in liquid gas energy balance as a function of time and an adjusted operating plan for the condensing and cooling functions to overcome the situation described in Figure 10; FIG. 4 shows curves representing a first example of the variation of the value of the safety margin as a function of time; FIG. 5 shows curves representing a second example of the variation of the value of the safety margin as a function of time;

To visualize the context in which the present invention fits, FIG. 1 shows a floating structure 1 proceeding towards its destination 2 by following a journey 3. The floating structure 1 shown here is a transport vessel, for example an LNG carrier. A floating structure 1 transports a cargo of gaseous liquids intended to carry it to a destination 2 . In order to ensure such transport, the floating structure 1 contains at least one tank 9 .

Destination 2 is a terminal intended to receive liquid gas contained in tank 9 of floating structure 1 . When the floating structure 1 reaches its destination 2, the liquid gas is discharged, for example, into a reservoir 40. However, Destination 2 imposes requirements on the properties of the liquid gas. Destination 2 requirements may vary according to the operator of the facility to which the destination 2 is attached and relate primarily to the properties of the liquid gas, eg its saturation pressure and/or its temperature.

If the liquefied gas contained within the tanks 9 of the floating structure 1 does not meet these saturation pressure requirements for liquefied gas, the liquefied gas cargo could potentially be can be rejected.

To avoid this, liquid gas cargoes must be closely monitored throughout leg three. The journey 3 has a variable distance depending on the distance from the loading location to the destination 2 and the speed of the floating structure 1 and can last for days or even weeks.

FIG. 2 schematically shows a system 4 for managing the energy balance of a liquid gas contained within a tank of a floating structure. The energy balance of a liquid gas corresponds to data containing various properties of said gas, such as the liquid gas's temperature, saturation pressure, total mass, or specific heat capacity. The management system 4 includes a control box 41 having in memory a method 5 for estimating and adjusting the energy balance of the liquid gas contained in the tanks of the floating structure. The control box 41 can thus initiate the estimation and adjustment method 5 in a regular and automated manner and/or according to manual control provided by the control monitor 6 for example. This can be achieved by manually entering data via the control monitor 6, e.g. properties of the liquid gas to be transported, or any other information useful for the progress of the estimation and adjustment method 5, as will become apparent later. is also possible.

The management system 4 also includes a fuel supply system 8 for consumption equipment of the floating structure. The supply system 8 has the function of condensing and/or cooling the liquid gas contained in the tank, and activating or deactivating them regulates one or the other of these functions. can be done. Adjustment of the condensing and cooling functions of supply system 8 depends on the results of estimation and adjustment method 5 . Thus, when the estimation and adjustment method 5 ends, the control box 41 sends a signal to the delivery system 8 indicating the adjustments to be made by the delivery system 8 .

Management system 4 also includes computer 7 . The function of computer 7 is to estimate the amount of excess gas phase produced from liquid gas during the course of the floating structure. The gas phase generated from the liquid gas can be spontaneously generated or forced to form within the tank of liquid gas. The estimated excess gas phase produced from the liquid gas is calculated using the estimated engine consumption of the floating structure and the predicted heat input to the tank. Computer 7 and control box 41 may be part of the same control unit or independent of each other.

By inputting a path plan into the control monitor 6 which communicates information to the computer 7, or from the remaining distance between the position of the floating structure and the destination and the remaining time to reach the destination, the floating structure By calculating the average velocity, the engine consumption of the floating structure can be estimated. The average velocity of the floating structure can also be calculated by entering data into the control monitor 6 which transmits the information to the computer 7 .

The predicted heat input to the tank may correspond to the design heat input to the tank or to an estimated heat input to the tank. The design value of the heat input to the tank depends on the tank model used for transportation and can be provided to the computer 7 via the control monitor 6 . An estimate of the heat input to the tank may also be communicated by a sensor contained in said tank.

Once the computer 7 has estimated the excess gas phase produced from the liquid gas during the stroke, the computer 7 communicates the results to the control box 41 . As explained below, the excess gas phase produced from the liquid gas during the process is the data that allows the estimation and adjustment method 5 to be performed.

FIG. 3 is a schematic diagram of method 5 for estimating and adjusting the energy balance of a liquid gas according to the invention. This figure shows the progress when Estimation and Adjustment Method 5 is initiated for the first time during the journey to the destination. Estimation and adjustment method 5 can only be started before or at the time of departure of the floating structure. In FIG. 3 , the solid arrows represent the progress of each of the steps of Estimation and Adjustment Method 5, and the dotted arrows represent the data transfer between the two steps of Estimation and Adjustment Method 5, or the energy balance of the liquid gas. Corresponds to the transmission of data between one element of the system for managing and one step of the Estimation and Adjustment Method 5.

When the estimation and adjustment method 5 is started for the first time, it begins with step A, which makes it possible to calculate the maximum allowable temperature of the liquid gas contained in the tank on arrival at its destination. The calculation of step A depends on certain properties of the liquid gas, such as its total mass and specific heat capacity. Such properties depend on the type of liquid gas being transported and are in some way known to those involved in floating structures. Thus, the total mass of the liquid gas and the specific heat capacity of the liquid gas can be input or pre-selected through the control monitor 6 and transmitted for the calculation of step A of the estimation and adjustment method 5. . The step A calculation also depends on the destination liquid gas maximum saturation pressure requirement. Since these requirements vary according to destination, the required maximum saturation pressure value of the liquid gas is known if the destination is known. The liquefied gas saturation pressure requirement can be entered via the control monitor 6 or is known, for example, via a database listing all destination locations permitted to receive and offload liquefied gas. be able to.

Once the calculations of step A have been performed, the estimation and adjustment method 5 can proceed directly to step B or pass through an intermediate step A'. Step A' consists in determining a safety margin to ensure that the energy balance of the liquid gas is less than the requirements upon arrival at the destination. Therefore, step A' is not essential for the smooth execution of Estimation and Adjustment Method 5, and all calculations and estimations can be performed without a safety margin, but this is an adjustment of the liquid gas energy balance. Contribute to optimization. The safety margin can be determined automatically from route planning and/or weather conditions or manually via control monitor 6 . The safety margin is used in the calculations during step E. Therefore, step A' can be performed at any time before step E.

Step B of estimation and adjustment method 5 is performed after step A or step A'. Step B is performed as establishing a first operational plan for the condensing function of the supply system 8 . A first operating plan of the condensing function of the supply system 8 indicates, over time, when the condensing function remains active or inactive during the stroke and when the condensing function is activated or deactivated. . Establishment of the first operating plan depends on the amount of excess gas phase produced from the liquid gas during the stroke. In practice, for example, if it is determined that no excess gas phase produced from the liquid gas is produced during the process, the feed system will have no condensing gas phase produced from the liquid gas and therefore It is understood that it need not be active during the journey. Such a surplus can result if the consumer of the floating structure is shut down and boil-off of liquid gas continues to occur. The excess gas phase produced from the liquid gas is estimated by the computer 7, which therefore communicates information to the control box so that the estimation and adjustment method 5 can carry out step B.

Step C may be performed in parallel with or following step B. Step C is based on the same basic principle as step B, as it allows the establishment of a second operating plan for the cooling function of supply system 8 . As for step B, the second operational plan of the cooling function of the supply system 8 over time determines when the cooling function remains active or inactive during the stroke and when the cooling function is activated or activated. Indicates whether it is inactivated. Establishment of the second operation plan also depends on the amount of excess gas phase produced from the liquid gas during the stroke, as estimated by computer 7 . Therefore, an estimate of the excess gas phase produced from the liquid gas is taken into account in steps B and C.

Estimation and adjustment method 5 then continues with step D of calculating the energy balance of the liquid gas at time t. FIG. 3 shows the course of the estimation and adjustment method 5 at first start-up, where the time t corresponds to the moment of departure of the floating structure or before departure. In order to calculate the energy balance of the liquid gas at time t, the estimation and adjustment method 5 uses the total mass of the liquid gas, or the specific heat capacity of the liquid gas, especially of the liquid gas contained in the tank. We need the properties of the liquid gas used during step A to calculate the maximum allowable temperature upon arrival. These characteristics can be provided by the control monitor 6, just as for step A. Calculating 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 inside the tank. The supply system 8 therefore provides the average temperature in the tank so that the estimation and adjustment method 5 can perform the calculations of step D and communicates this to the control box.

Once step D is complete, estimation and adjustment method 5 continues with step E as calculating the maximum energy balance. The maximum energy balance corresponds to the limit of the requirements of the destination, which, when the floating structure arrives at its destination, must not exceed the energy balance of the liquid gas contained in the tanks and the cargo. is the limit under which the is rejected penalty. It should be noted that the liquid gas energy balance may exceed this maximum energy balance limit during the journey without incident, but must return below this maximum energy balance before the floating structure reaches its destination. not. It is understood that the maximum energy balance is the target for adjusting the energy balance of the liquid gas contained in the tank during the journey.

For this calculation of the maximum energy balance during step E, Estimation and Adjustment Method 5 uses the properties of the liquid gas and the maximum allowable upon arrival of the liquid gas contained in the tank calculated during step A. Requires temperature. Thus, the data provided and the calculations performed during step A can be passed on for the calculations of step E. If the estimation and adjustment method 5 has performed step A', in other words if a safety margin has been determined and selected, said safety margin is also communicated and taken into account for the calculation of the maximum energy balance. Therefore, the maximum energy balance calculated during step E is either the actual maximum energy balance in the absence of a safety margin, or a hypothetical maximum energy balance that is less than the actual maximum energy balance due to the safety margin considered in the calculation. corresponds to

The next step in Estimation and Adjustment Method 5 is Step F, which ensures an estimation of the energy balance of the liquid gas contained in the tank upon arrival from the stroke. Step F determines what the energy balance of the liquid gas contained in the tank will be on arrival from the stroke, while keeping the operating schedule for the condensing and cooling functions established during steps B and C. make it possible to To perform such an estimate, the calculations are made by combining the energy balance of the liquid gas at time t calculated during step D, and the operational plans for the condensation and cooling functions established during steps B and C. based on. Once the operation plan for the condensation and cooling functions is established for the entire stroke during steps B and C, then estimation and adjustment method 5 estimates the change in energy balance of the liquid gas during this step F. the condensing and cooling functions can vary the energy balance of the liquid gas depending on whether they are active or inactive and when they are activated or deactivated can be done. The energy balance on arrival of the liquid gas contained in the tank can thus be determined from these data.

Estimation and adjustment method 5 then continues with step G of ensuring adjustment of the operating plan for the condensing and cooling functions of supply system 8 . This adjustment is based on a comparison between the maximum energy balance calculated during step E and the estimated energy balance at the time of arrival of the liquid gas contained in the tank, calculated in step F. . The estimated energy balance upon arrival of the liquid gas contained in the tank, calculated during Step F, is based on the operating plans for the condensing and cooling functions established during Steps B and C. Please note. Step G thus makes it possible to change the estimated energy balance on arrival of the liquid gas contained in the tank by adjusting the operating schedules for the condensing and cooling functions.

When the estimated energy balance on arrival of the liquefied gas contained in the tank is greater than the maximum energy balance, this indicates that the cargo of liquefied gas is in excess of the maximum requirements of the destination on arrival. It means that it becomes the saturation pressure of the gas. Therefore, the operating schedules for the condensing and cooling functions must be adjusted in order to reduce the temperature of the liquid gas contained in the tank and correspondingly reduce the energy balance of the liquid gas.

When the estimated energy balance on arrival of the liquefied gas contained in the tank is less than the maximum energy balance, this means that the cargo of liquefied gas will meet the requirements of the destination on arrival, provided that adjustments are made to the energy balance. If it proves useful in terms of savings, it means that it is possible to make adjustments that allow an increase in the temperature of the liquid gas contained in the tank. Therefore, the operating schedule for the condensing and cooling functions must be adjusted to allow an increase in the temperature of the liquid gas contained in the tank and a corresponding increase in the energy balance of the liquid gas. not.

Step G therefore determines the optimal adjustment of the operating schedule for the condensing and cooling functions of the supply system 8 to best accommodate the situation. Examples of operation plan adjustments are presented later.

Estimation and Adjustment Method 5 finally concludes with Step H of implementing the maneuver plan adjusted during Step G. Step H marks the end of the Estimation and Adjustment Method 5 and sends these to the supply system 8 so that it implements a coordinated operating plan of the condensing and cooling functions. Details of the operation of the supply system 8 will be presented later.

FIG. 4 shows a method 5 for estimating and adjusting the energy balance of a liquid gas during iteration by iteration, i.e. when the estimation and adjustment method 5 is started in the process after it has been started for the first time according to FIG. 1 is a schematic diagram of FIG. Most of the steps of Estimation and Adjustment Method 5 are similar to those previously described, so please refer to the description of FIG. 3 for a description thereof. As for FIG. 3, the solid arrows represent the progress of each of the steps of Estimation and Adjustment Method 5, and the dotted arrows represent the transfer of data between the two steps of Estimation and Adjustment Method 5, or of the liquid gas. Corresponds to the transmission of data between one element of the system for managing the energy balance and one step of the Estimation and Adjustment Method 5.

If the estimation and adjustment method 5 is repeated with iterations, it is no longer useful to initiate step A. In fact, the result of the calculation of step A, i.e. the maximum allowable temperature of the liquid gas on arrival contained in the tank, remains unchanged over time. However, since the result of step A is used in the calculation of step E, said result must be retained during the process, for example by the memory of the control box.

Step A' as selecting a safety margin is also not repeated. However, because the safety margin was configured to change over time when Estimation and Adjustment Method 5 was first initiated, or because it was changed manually through Control Monitor 6, the progress of Estimation and Adjustment Method 5 It may be set to change independently. The change in safety margin is the reason that step E is maintained within Estimation and Adjustment Method 5, as this is a factor that can change over time for the calculation of step E. is.

Therefore, when the estimation and adjustment method 5 is repeated with iterations, it starts at step B. During the first start of the estimation and adjustment method 5, steps B and C are performed so that the amount of excess gas phase produced from the liquid gas is still calculated and supplied by the computer 7.

Step D is also performed exactly as described above. In contrast, step D' is performed in parallel with step D, where the energy balance of the liquid gas at time t is also calculated, but according to a different calculation than that of step D. The calculation of the energy balance of the liquid gas at time t in step D' is the energy balance of the liquid gas at the previous time t calculated in the previous iteration of Estimation and Adjustment Method 5, and the energy balance of the liquid gas at the previous time t. and performing the condensing and cooling functions of the The energy balance of the liquid gas at the previous time t can be retrieved, for example, from the buffer memory of the control box. The performance of the condensing and cooling functions begins with the heat transfer performed by the condensing function and the cold transfer performed by the cooling function towards the liquid gas cargo. The performance of the condensing and cooling functions can therefore be measured by sensors arranged in the elements of the supply system 8 that ensure the condensation and cooling of the liquid gas, the supply system 8 being the This data is communicated to the control box for

After calculating the liquid gas energy balance at time t in steps D and D', only the liquid gas energy balance at time t with the largest value is retained. The liquid gas energy balance at time t is considered to have the most pessimistic value and the priority is to remain below the subsequently calculated maximum energy balance.

The remaining estimation and adjustment method 5 is then performed according to the description of FIG. Upon completion of Estimation and Adjustment Method 5, the adjustment of the operating plan for the condensing and cooling functions is communicated to the supply system 8, and Estimation and Adjustment Method 5 repeats again directly from step B depending on the control box settings. be able to. Advantageously, the control box is arranged to repeat the estimation and adjustment method 5 at regular intervals throughout the journey, for example once a day or every 6 hours, according to the flow of FIG.

FIG. 5 is a schematic diagram of a supply system 8 that ensures the function of condensation and cooling of liquid gases. In general, the supply system 8 interacts with the tank 9 and also with the consumer set.

The supply system 8 can ensure temperature control of the liquid gas in the tank 9 . To do this, the supply system 8 includes a liquid inlet 81 and a gas inlet 82 . A liquid inlet 81 connects the supply system 8 to the tank 9 and allows the liquid gas 13 to be drawn in, for example by the liquid gas pump 26 . A gas inlet 82 extends from the tank head to the supply system 8 which may contain a quantity of gaseous phase 14 produced from liquid gas. The gas phase 14 produced from the liquid gas can be sucked off, for example by means of a compressor 27, for passage into the supply system 8.

The supply system 8 also includes a gas outlet 83 extending from the supply system 8 to the consumer set. By way of example, the consumer can be a propulsion engine 16, a generator 17, a combustion chamber 18 or a degassing mat 28. The propulsion engine 16 makes it possible to advance the floating structure during its stroke and may be supplied with a vapor phase 14 produced from liquid gas. The generator 17 provides electricity to floating structures, such as the lighting or on-board networks of floating structures, and more generally to any entity requiring power supply. The gaseous phase 14 produced from the liquid gas thus serves as fuel for one and/or the other of these consumers. Thus, the supply system 8 can draw into the gas inlet 82 the gas phase 14 produced from the liquid gas, for example, if excess gas phase 14 is generated from the liquid gas. The gas phase 14 produced from the liquid gas can then be processed by the supply system 8 and then exit the supply system 8 through the gas outlet 83, for example for supply to the propulsion engine 16 or the generator 17. .

Gas phase 14 produced from liquid gas but not used to supply propulsion engine 16 or generator 17 is referred to as excess gas phase 14 produced from liquid gas. This excess gas phase 14 produced from liquid gas can be burned in a combustion chamber 18 or discharged into the atmosphere by a degassing mat 28 .

Excess gas phase 14 produced from liquid gas may also be returned to supply system 8 via bypass 84 for condensing by supply system 8 . Once this is done, the condensed liquid gas returns to the tank 9 through the liquid outlet 85 of the supply system 8 .

When the liquid gas 13 needs to be cooled, it is drawn in by the liquid gas pump 26 and circulated in the liquid inlet 81 to the supply system 8 where it is cooled. The cooled liquid gas 13 then returns to tank 9 through liquid outlet 85 .

FIG. 6 is a schematic diagram of a first embodiment of a supply system 8 that ensures the condensation and cooling functions of the liquid gas.

As for FIG. 5, the supply system 8 controls the temperature of the tank 9 . The tank 9 is at least partially filled with a quantity of liquid gas 13 . The tank head may also contain a quantity of gaseous phase 14 produced from liquid gas. Tank 9 also includes at least a liquid gas pump 26 . Tank 9 also includes a first temperature sensor 10 . With this first temperature sensor 10 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 adjustment method. For the example of Figure 6, the first temperature sensor 10 of the tank 9 records the temperature of the liquid gas surrounding it. If the floating structure comprises multiple tanks 9 each containing a first temperature sensor 10, an average of the temperatures is formed and then sent to the control box.

As previously indicated, the condensation function of the supply system 8 allows condensation of the excess gas phase 14 produced from the liquid gas. To do this, the gas phase 14 produced from the liquid gas in the tank 9 is sucked by a compressor 27 arranged outside the tank and forming the gas phase circuit 15 . The gas phase circuit 15 transports the gas phase 14 produced from the liquid gas to be used by the propulsion engine 16 and/or the generator 17 as fuel. Extend until exit to 17.

The gas phase 14 produced from the liquid gas but not used to supply the propulsion engine 16 or the generator 17 is excess gas phase 14 produced from the liquid gas and circulates in the excess circuit 19 . The excess circuit 19 allows circulation of the excess gas phase 14 produced from the liquid gas to the first heat exchanger 11 . The first heat exchanger 11 performs the function of condensing the excess gas phase 14 produced from the liquid gas by heat exchange between the first flow path 111 and the second flow path 112 . The excess gas phase 14 generated from the liquid gas traverses the first flow path 111 and then the second flow path so that the excess gas phase 14 generated from the liquid gas condenses into a liquid state. 112 is cooled. It is thus understood that when the condensation function of the supply system 8 is active, the excess vapor phase 14 produced from the liquid gas is led to the first heat exchanger 11 via the excess circuit 19 . When the condensation function of the supply system 8 is inactive, the excess gas phase produced from the liquid gas is led to the combustion chamber 18 and burned or led to the degassing mat 28 and discharged into the atmosphere. be. A fluid having a temperature lower than the state change temperature of the excess gas phase 14 produced from the liquid gas is circulated in the second flow path 112 to condense the excess gas phase 14 produced from the liquid gas. do.

When the excess gas phase 14 is produced from the condensed liquid gas by the first heat exchanger 11 , the condensed gas travels through the condensed gas circuit 20 until it reaches the return circuit 21 which leads the condensed gas to the tank 9 . Circulate.

As regards the cooling function of the supply system 8 , the liquid gas 13 contained in the tank 9 is first aspirated by the liquid gas pump 26 . The liquid gas 13 sucked by the liquid gas pump 26 circulates to the second heat exchanger 12 . The second heat exchanger 12 performs the function of cooling the liquid gas 13 by heat exchange between the third channel 121 and the fourth channel 122 . The liquid gas 13 sucked by the liquid gas pump 26 circulates in the second heat exchanger 12 through the fourth flow path 122 and is cooled. A fluid having a lower temperature than the liquid gas 13 circulates in the third flow path 121 in order to cool the already cryogenic liquid gas 13 . The third flow path 121 can be part of a cooling circuit, not shown in FIG. 6, external to the supply system 8 . The external cooling circuit may for example be part of a vacuum evaporator type system.

Subsequently, after being cooled by the second heat exchanger 12 , the cooled liquid gas 13 returns to the tank 9 through the return circuit 21 . The cooled liquid gas 13 thus allows the overall cooling of the tank 9 and the temperature of the cooled liquid gas 13 is lower than the temperature of the liquid gas 13 remaining in the tank 9. lower.

Heat exchange of the first heat exchanger 11 and the second heat exchanger 12 is measured by a plurality of temperature sensors. The feed system 8 thus comprises two second temperature sensors 24 respectively located at the inlet and outlet of the first heat exchanger 11 and two second temperature sensors 24 respectively located at the inlet and outlet of the second heat exchanger 12 . 3 temperature sensors 25 . By calculating the temperature difference between the respective outlets and inlets of the heat exchanger, the heat input to the tank 9 can be measured by the second temperature sensor 24 and the tank 9 by the third temperature sensor 25. can be measured. Heat input and cooling input are the data used to calculate the performance of the condensing and cooling functions of the supply system 8, said performance of the liquid gas at time t in step D' of the estimation and adjustment method. Helps calculate energy balance. This data is therefore transmitted by the supply system 8 to the control box.

At the end of the estimation and adjustment method, the supply system 8 receives adjusted operating plans for the condensing and cooling functions. The supply system 8 is then programmable to activate or deactivate one and/or the other of the condensing and cooling functions, thereby changing its operation according to the coordinated operating plan.

FIG. 7 schematically represents a second embodiment of the supply system 8 . Compared to the first embodiment presented in FIG. 6, only the implementation of the cooling function of the supply system 8 differs. Therefore, reference is made to the description of FIG. 6 for any parts of the supply system 8 that are common to the two embodiments.

In this second embodiment of the supply system 8, the supply system 8 performs its cooling function in combination with the function of supplying the consumers of the floating structure. In practice, when the gas phase 14 produced from the liquid gas is sucked into the gas phase circuit 15 , it passes through the second heat exchanger 12 while circulating in the third flow path 121 . The liquid gas 13 contained within the tank 9 is first drawn by the liquid gas pump 26 and then circulated through the fourth flow path 122 located within the second heat exchanger 12 . The heat exchange that takes place between the third flow path 121 and the fourth flow path 122 is a vapor phase produced from liquid gas sufficient to supply the propulsion engine 16 and/or the generator 17 . 14, but also subcooling the liquid gas 13 drawn by the liquid gas pump 26. Subsequently, after being cooled by the second heat exchanger 12 , the cooled liquid gas 13 passes through the cooled gas until it reaches the return circuit 21 which leads the cooled liquid gas 13 into the tank 9 . It circulates in circuit 23 .

Thus, the cooled liquid gas 13 returns to the tank 9, allowing the tank 9 to be cooled overall, and the temperature of the cooled liquid gas 13 is adjusted to the temperature of the liquid gas 13 remaining in the tank 9. lower than the temperature of

The liquid gas 13 circulates in this way when the cooling function is active. Therefore, as long as the gas phase 14 produced from the liquid gas is present in the cooling function and the excess gas phase 14 produced from the liquid gas is present in the condensing function, the supply system 8 can perform the condensing function and the cooling function simultaneously. Make it active or inactive.

Figures 8-11 show the tank as a function of time, ie, during the course of the floating structure, as a function of the operating schedule for the condensing and cooling functions shown at the top of each of Figures 8-11. Fig. 3 shows a curve of change in energy balance of a liquid gas contained therein; Figures 8 and 9 correspond respectively to estimation and adjustment for the situation where the estimated energy balance at the time of arrival of the liquid gas is less than the maximum energy balance. Figures 10 and 11 correspond respectively to estimation and adjustment for the situation where the estimated energy balance of the liquid gas is greater than the maximum energy balance.

For each of FIGS. 8-11, the initial situation presented is the initiation of the estimation and adjustment method at time t during the journey of the floating structure from departure 50 to arrival 51. FIG.

Each of the curves of energy balance as a function of time in FIGS. 8-11 includes a real maximum energy balance 32 and a hypothetical maximum energy balance 33, ie taking into account a safety margin. The virtual maximum energy balance 33 is less than the actual maximum energy balance 32, the difference depending on the value of the safety margin. For each of the figures, the adjustment of the energy balance of the liquid gas contained in the tank is made according to the virtual maximum energy balance 33, so the actual maximum energy balance 32 is only indicative. The actual maximum energy balance 32 is constant over time. Advantageously, the virtual maximum energy balance 33 gradually approaches the actual maximum energy balance over time, but for clarity the virtual maximum energy balance 33 is also shown as constant over time in FIGS. It is

8-11 also show the curves of the first operating plan 36 of the condensing function and the second operating plan 37 of the cooling function, respectively, over time. The vertical axis of the curve of the trip plan has only two positions, position 0 and position 1 . When the maneuver is at position 0, this means that the associated function is inactive. When the operating plan is in position 1, this means that the relevant function is active, as a result of which condensation and/or cooling of the liquid gas via the supply system is permitted. For each of the situations, it is assumed that the two operating plans are basically at position 1 throughout the stroke, ie the condensing and cooling functions are allowed throughout the stroke.

FIG. 8 thus shows the initial situation during the flight of the floating structure. Thus, at time t, the estimation and adjustment method begins to determine the energy balance of the liquid gas at time t38 from the temperature of the liquid gas contained in the tank or from the condensing and cooling functions from start 50. From execution, it is obtained in step D or D' of the estimation and adjustment method. It is possible to observe the change in the energy balance of the liquid gas contained in the tank from departure 50 to time t, which change corresponds to the measured energy balance 34 . The measured energy balance 34 is shown as a solid line because it has already been measured in real time from departure 50, the first measurement corresponding to the starting energy balance 30 determined when the estimation and adjustment method was first started. do. The change in the energy balance of the liquid gas after time t is therefore indicated by the dashed line, and more precisely the predicted energy estimated in step F from the energy balance of the liquid gas at time t38 by the estimation and adjustment method. Balance 35 is represented. 8 is maintained until arrival 51, the estimated energy balance 31 at arrival 51 of the liquid gas contained in the tank is corresponds to an estimate of the value of the energy balance when arriving at .

In FIG. 8, without adjustment of the operation plan for the estimation and adjustment method according to the present invention, the estimated energy balance 31 at the time of arrival 51 of the liquid gas contained in the tank is equal to step E of the estimation and adjustment method. Note that it is smaller than the hypothetical maximum energy balance 33 calculated in . The liquid gas contained in the tank thus meets the requirements of the destination. However, it is still possible to adjust the operating schedule to limit the energy consumption of the supply system.

FIG. 9 shows a curve implementing step G of the estimation and adjustment method according to the invention, with the driving plan adjusted to the driving plan shown in FIG. The estimation and adjustment method always follows the observation that at time t the estimated energy balance 31 of the liquid gas contained in the tank at arrival 51 is less than the hypothetical maximum energy balance 33 . The estimation and adjustment method therefore adjusts the driving plan to ensure energy savings. Thus, as already in the example shown, the first operating plan 36 of the condensing function is adjusted to be active, ie to remain at position 1, until arrival 51 from the stroke. Excess gas phase generated from the liquid gas is thus sufficiently condensed and does not lead to cargo loss.

Furthermore, it is also possible to deactivate the cooling function at the estimated time dt during the journey, since the estimated energy balance 31 of the liquid gas contained in the tank at arrival 51 is less than the hypothetical maximum energy balance 33. be. To determine the estimated time dt, the estimation and adjustment method consists of adjusting the second operating plan 37 of the cooling function and recalculating the estimated energy balance 31 of the liquid gas contained in the tank at arrival 51. One or more iterations of successively alternating are performed. Here, the adjustment of the cooling function's second operating plan 37 is done by selecting the time at which the cooling function is deactivated, targeting arrival 51 . The iteration continues as long as the estimated energy balance 31 of the liquid gas contained in the tank at arrival 51 is less than the hypothetical maximum energy balance 33, and the selected time at which the cooling function is deactivated is Each new occurrence is progressively earlier than the previous one and the calculation of the estimated energy balance 31 of the liquid gas contained in the tank at the time of arrival 51 is based on a predetermined second operating plan 37 of the cooling function. is performed each time with a new adjustment of Therefore, the estimated energy balance 31 of the liquid gas contained in the tank at arrival 51 does not exceed the hypothetical maximum energy balance 33, while the cooling function is deactivated as soon as possible to save maximum energy. These iterations allow us to determine the optimal estimated time dt so that

Once the estimated time dt is obtained, the estimation and adjustment method adjusts the second operating plan 37 for the cooling function and communicates it to the supply system. A second adjusted operating plan 37 of the cooling function is visible in FIG. 9, where it can be seen that the cooling function switches to position 0 after adjustment and is deactivated at the estimated time dt. Therefore, between estimated time dt and arrival 51, the cooling function remains deactivated. Since this is known and the condensation function is always active, the temperature of the liquefied gas contained in the tank and correspondingly the energy balance of the liquefied gas contained in the tank can be estimated at the time Between dt and arrival 51 it shows a more significant increase than in the curve of FIG. However, the estimated time dt increases the estimated energy balance 31 of the liquid gas contained in the tank at the time of arrival 51 by repeating the estimation and adjustment method described above, but the estimated time dt is a hypothetical It is calculated so that the maximum energy balance 33 is not exceeded.

The liquid gas contained in the tank therefore always meets the requirements of the destination, but energy savings are achieved between estimated time dt and arrival 51, since the cooling function is deactivated during this time. and therefore no need for an energy supply. The estimation and adjustment method thus made it possible to limit the waste of energy while keeping the gas in liquid form according to the requirements of the destination.

FIG. 10 also shows the change curve of the energy balance of the liquid gas contained in the tank over time, but this time the situation is reversed with respect to FIGS. In practice, according to the estimation and adjustment method, during time t of the journey, the energy balance of the liquid gas at time t38 is calculated, and then the estimation and adjustment method calculates from the energy balance of the liquid gas at time t38 the arrival 51 Calculate the estimated energy balance 31 of the liquid gas contained in the tank at time. As can be seen from FIG. 10, in spite of the constant activation of the cooling function throughout the journey as shown in the second operating plan 37 for the cooling function seen in FIG. The estimated energy balance 31 at the time of arrival 51 of the liquefied gas is greater than the hypothetical maximum energy balance 33 and even the actual maximum energy balance 32 .

In this situation, if the operation schedule for the condensing and cooling functions at 51:00 arrival is not coordinated, the liquid gas contained in the tank will not meet the requirements of the destination and consequently Cargo will be refused. In order to avoid this, the saturation pressure of the liquefied gas contained in the tank is lowered and the energy balance of the liquefied gas contained in the tank is reduced in order to meet the 51 hour requirement of arrival at the destination. It is essential to lead to reduction. A given time d't is shown in FIG. 10, the time at which the predicted energy balance 35 exceeds the hypothetical maximum energy balance 33, i.e. the energy balance of the liquid gas contained in the tank is no longer at its destination. correspond to the time when the requirements of

The adjustments necessary to overcome the situation described in FIG. 10 are shown in FIG. Therefore, if this is not already the case, the estimation and adjustment method adjusts the cooling function's second operating plan 37 such that the cooling function is active until the arrival of the stroke 51 .

As previously mentioned, the main factor leading to an increase in the temperature of the liquid gas contained in the tank as well as an increase in its energy balance is due to the condensation of the excess gas phase produced from the liquid gas. In fact, although condensed to a liquid state, the temperature of the condensed gas is higher than the temperature of the liquid gas contained in the tank. Therefore, returning the condensed gas to the tank will eventually lead to an increase in the temperature of the liquid gas contained within the tank. Therefore, the best way to stop this increase in temperature is to implement an adjusted first operating plan 36 for the condensing function so that it is deactivated.

The estimation and adjustment method therefore adjusts the first operating plan 36 for the condensing function. The condensation function is therefore programmed to be deactivated at a given time d't, ie when the estimated energy balance 34 reaches the hypothetical maximum energy balance 33 . The estimation and adjustment method thus allows to keep the condensation function active for as long as possible. When a given time d't comes, the condensation function is deactivated. The increase in the energy balance of the liquid gas contained in the tank then ceases due to the deactivation of the condensation function and the cooling function being kept active. Therefore, the estimated energy balance 31 of the liquid gas contained in the tank at arrival 51 is kept at the level of the hypothetical maximum energy balance 33 corresponding to the requirements of the destination. In this arrangement, from the given time d't to arrival 51, excess gas phase produced from liquid gas is no longer condensed by the supply system.

FIG. 12 shows a first example of a curve of variation of safety margin 60 as a function of time from departure 50 to arrival 51. FIG. This first example shows a safety margin 60 that decreases over time. In other words, the safer margin 60 is reduced as the floating structure gets closer to its destination, and the hypothetical maximum energy balance is calculated by iterating the estimation and adjustment method with the safer margin 60 decreasing as the floating structure approaches its destination. , is recalculated at each step E, so that the virtual maximum energy balance approaches the actual maximum energy balance.

The value of the safety margin may also depend on the amount of information about the journey maintained by the parties involved in the floating structure, such as weather conditions or sea conditions during the journey. Therefore, a higher safety margin 60 may be indicated in the absence of information about the state of the journey.

FIG. 13 shows a second example of a change in safety margin 60 over time. The safety margin 60 at the beginning of this journey is reduced over time as in the previous figures. However, unforeseen events 61 can occur. Event 61 can be a natural phenomenon, such as a weather phenomenon such as a storm or fog, that can slow down the floating structure. Event 61 can be a mechanical event, such as a failure of the floating structure, that can immobilize the floating structure for a non-negligible period of time. Such an event 61 thus increases the travel time to the destination. In this situation, the safety margin 60 as programmed at departure 50 is no longer sufficient for the journey. It is therefore possible to reprogram the safety margin 60 in order to adapt it to the consequences of the event 61, ie deceleration or immobilization of the floating structure in the example above. In FIG. 13 the safety margin 60 is increased when an event 61 occurs and then reduced again over time. This modification ensures certainty regarding the hypothetical maximum energy balance and makes it possible to avoid errors that could potentially lead to rejection of liquid gas cargoes upon arrival at their destination.

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

The present invention, as has been described, achieves the goals set and optimizes the energy consumption of the supply system while meeting the requirements of the destinations to which the liquefied gas is intended to be delivered. It makes it possible to propose a method for estimating and adjusting said energy balance of the liquid gas contained in the tank of the floating structure so that the balance is met. According to the invention, variations not described herein are also included in the estimation and adjustment method according to the invention and can be implemented without departing from the context of the invention.

Claims (14)

A method (5) for estimating and adjusting the energy balance of a liquid gas (13), said liquid gas (13) intended to transport said gas to a given destination (2) in at least one tank (9) of a floating structure (1), said floating structure (1) having the function of condensing a gas phase (14) produced from said liquid gas and/or or a system (8) for fueling consumers of said floating structure (1) capable of performing a cooling function of said liquid gas (13), for estimating and regulating an energy balance. In method (5),
- based on the maximum saturation pressure requirements of the liquid gas of said destination (2) and the properties of said liquid gas contained in said tank, on arrival at said destination, contained in said tank a step A of calculating the maximum allowable temperature of said liquid gas in
- a first operational plan for the condensation function of said vapor phase (14) produced from said liquid gas, carried out by said supply system (8) until arrival (51) at said destination (2); step B of establishing (36), wherein said first operating plan (36) comprises excess vapor phase (14) produced from said liquid gas in said tank (9) during step (3); Step B, established from an estimate of
- establishing a second operational plan (37) for the cooling function of said liquid gas (13), carried out by said supply system (8) until arrival (51) at said destination (2); C, wherein said second operating plan (37) is established from said estimate of said excess gas phase produced from said liquid gas during said step (3);
- from the temperature of said liquid gas (13) contained in said tank (9) and the properties of said liquid gas (13) contained in said tank (9), a time t (38); a step D of calculating the energy balance of the liquid gas at
- from the maximum allowable temperature of the liquid gas (13) calculated in step A and the properties of the liquid gas (13) contained in the tank (9), the maximum energy balance (32, 33), a step E of calculating
- from the operating plan (36, 37) of the condensing and cooling functions determined in steps B and C and the energy balance of the liquid gas at time t (38) determined in step D; , a step F of estimating the energy balance (31) of said liquid gas contained in said tank upon arrival (51) from said step (3);
- a step G of adjusting said first driving plan (36) and/or said second driving plan (37);
- step H of implementing said supply system (8) according to said operating plan (36, 37) of said condensing function of said liquid gas (13) and said cooling function adjusted in step G;
A method (5) for estimating and adjusting an energy balance, characterized in that it comprises: The estimated energy balance (31) of the liquid gas contained in the tank on arrival (51) from the stroke (3) calculated in step F is the maximum A method (5) for estimating and adjusting an energy balance according to claim 1, wherein step G is performed as activating the condensation function as long as the energy balance (32, 33) is less than. The estimated energy balance (31) of the liquid gas contained in the tank on arrival (51) from the stroke (3) calculated in step F is the maximum Method for estimating and adjusting the energy balance according to claim 1 or 2, wherein at an estimated time dt ensuring that the energy balance (32, 33) is less than step G is performed as stopping the cooling function. Method (5). The estimated energy balance (31) of the liquid gas contained in the tank on arrival (51) from the stroke (3) calculated in step F is the maximum A method (5) for estimating and adjusting an energy balance according to claim 1, wherein step G is performed as stopping said condensation function as long as the energy balance (32, 33) is greater. The estimated energy balance (31) of the liquid gas contained in the tank on arrival (51) from the stroke (3) calculated in step F is the maximum Method (5) for estimating and adjusting the energy balance according to claim 1 or 4, wherein step G is performed as activating the cooling function as long as the energy balance (32, 33) is greater. Estimation and adjustment method (5) according to any one of claims 1 to 5, wherein the method starts from step B and is repeated by iteration during the travel (3) of the floating structure (1). The method includes performing the condensation function and the cooling function from the departure (50) of the floating structure (1) to time t, and calculating the liquid state at time t (38) during the previous iteration. 7. An estimation and adjustment method (5) according to claim 6, comprising an additional step D', performed simultaneously with step D, of calculating said energy balance of said liquid gas at time t(38) from the energy balance of said gas. ). The energy balance of the liquid gas at time t(38) saved for step F is combined with the energy balance of the liquid gas at time t(38) calculated in step D The estimation and adjustment method (5) of claim 7, wherein the energy balance of the liquid gas at time t(38) calculated at ' is the largest. wherein said method selects a safety margin (60) of said maximum energy balance (32, 33) of said liquid gas (13) as a function of stroke (3) characteristics of said floating structure (1). The estimation and adjustment method (5) according to any one of claims 1 to 5, comprising step A' and step E being performed taking into account said safety margin (60). 10. The estimation and adjustment method (5) according to claim 9, wherein step A' is repeated by iteration during the travel (3) of the floating structure (1). The estimation and adjustment method (5) according to claim 9 or 10, wherein the safety margin (60) is reduced as the floating structure (1) approaches the destination (2). said floating structure (1) comprising at least one engine (16) driven at least in part by said gas phase (14) produced from said liquid gas, during said stroke (3) 2. The estimate of the excess gas phase produced from the liquid gas is established from an estimate of the heat input into the tank (9) and an estimate of the consumption of the engine (16). 12. The estimation and adjustment method (5) according to any one of claims 1 to 11. A liquid gas (13) contained in at least one tank (9) of a floating structure (1) for implementing an estimation and adjustment method (5) according to any one of claims 1 to 12. comprising at least one fuel supply system (8) for consumers of said floating structure (1) and a stroke of said floating structure (1) ( 3) for managing the energy balance of the liquid gas (13), including at least one computer (7) having the function of estimating the amount of excess gas phase (14) produced from said liquid gas during system (4). A floating structure (1) for transporting a liquid gas (13) comprising a system (4) for managing the energy balance of a liquid gas according to claim 13.

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