SE541662C2

SE541662C2 - Arrangement, system and method for treating a closed container

Info

Publication number: SE541662C2
Application number: SE1750739A
Authority: SE
Inventors: Jonas Holmström
Original assignee: Scania Cv Ab
Priority date: 2017-06-12
Filing date: 2017-06-12
Publication date: 2019-11-19
Also published as: SE1750739A1; DE102018004050A1

Abstract

The disclosure relates to an arrangement (30) for treating a closed container (2), the closed container (2) containing liquefied fuel gas. The arrangement (30) comprises a first fluid line (20) with an inlet connectable to a source (22) of inert fluid and an outlet connectable to an inlet of the closed container (2) for transport of vaporized inert fluid to the closed container (2). The arrangement (30) further comprises a heating control device (24) arranged for heating the inert fluid comprised in the first fluid line (20) and a second fluid line (21) comprising an inlet connectable to an outlet of the closed container (2), the second fluid line (21) being arranged to transport drained fluid from the closed container (2). The arrangement (30) also comprises a first sensor (28) arranged to measure a property of the drained fluid, thereby enabling determining that the liquefied fuel gas in the closed container (2) is evaporated based on the monitored property fulfilling a predetermined criterion. The disclosure also relates to a method, and a system (40).

Description

Arrangement, system and method for treating a closed container Technical field The present disclosure relates to an arrangement, a system and a method for treating a closed container, e.g. for storage of liquefied natural gas. The disclosure also relates to a computer program and to a computer-readable medium.

Background Natural gas is an alternative fuel for heavy vehicles. Generally, natural gas comprises methane, with some mixture of ethane. Compressed natural gas or Liquefied Natural Gas, LNG, is a cleaner alternative to other fossil fuels.

LNG is stored in cryogenic tanks, i.e. LNG tanks, under pressure. The temperature inside the actual gas container must be low enough for a main portion of the fuel to be in liquid form. To achieve this LNG tanks generally comprise a closed container comprising an inner tank and an outer shell. In between there is insulation material. Typically, a vacuum is also drawn from this space to create a super insulating tank. LNG tanks also comprise several components installed outside the closed container, to for example ensure safety and correctly vaporized fuel.

If there is a problem with some of these components service or repair is needed. Some components are positioned after manual shut-off valves, which enables servicing of these without emptying the closed container. However, some components are positioned before the manual shut-off valves and cannot be isolated. Hence, in order to service these components, the LNG tank needs to be emptied and flushed from fuel in order to secure a safe environment for the mechanics.

To empty the tank the liquefied fuel gas first must be drained. This is done by creating a pressure head and then pressing the fuel out of the container using the pressure head. When the container has been drained, some liquid will remain. The remaining liquid is then vaporized and flushed out with e.g. nitrogen gas.

This is a process that is difficult to control and therefore the duration of the process varies from case to case and is hard to estimate. Consequently, maintenance may take much more time than it should. In some cases, it might take weeks to change a component such as a coupling or meter, which is not desirable as during this time the tank cannot be used.

From WO2016048162A1 a method and apparatus for treatment of pressure vessels is known. Here, nitrogen in liquid form is heated in order to convert the nitrogen to gaseous form before it is introduced into the ship’s LNG tank with a temperature that is gradually controlled up to the ambient temperature. The ship’s tank is flushed by allowing the gas to pass through the tank and out from the tank’s ventilation pipe.

Summary The above mentioned patent document WO2016048162A1, which only exemplifies rather simple LNG tanks i.e. for vessels, discloses to heat the nitrogen before it is introduced into the LNG tank in order to reduce time spent on flushing the LNG tank. However, it does not explain how to optimize flushing in order to save on flushing medium. As a consequence, large amounts of flushing medium is needed for emptying an LNG tank, e.g. as it is difficult to determine when the liquefied fuel gas is evaporated. However, in general it is desired to also keep the amount as low as possible in order to lower costs.

It is thus an object of the disclosure to alleviate at least some of the drawbacks with the prior art. It is a further object to achieve an apparatus and a method for reducing the amount of flushing medium used for emptying a closed container containing liquefied fuel gas, such as LNG. It is a still further object to reduce the time needed for emptying the closed container.

These object and others are at least partly achieved by the apparatus and method device according to the independent claims, and by the embodiments according to the dependent claims.

According to a first aspect, the disclosure relates to an arrangement for treating a closed container. The closed container contains liquefied fuel gas. The arrangement comprises a first fluid line with an inlet connectable to a source of inert fluid and an outlet connectable to an inlet of the closed container for transport of vaporized inert fluid into the closed container. The arrangement also comprises a heating control device arranged for heating the inert fluid comprised in the first fluid line. The arrangement further comprises a second fluid line, comprising an inlet connectable to an outlet of the closed container, the second fluid line being arranged to transport drained fluid from the closed container. The arrangement further comprises a first sensor arranged to measure a property of the drained fluid, thereby enabling determining that the liquefied fuel gas in the closed container is evaporated based on the monitored property fulfilling a predetermined criterion.

By monitoring a property of the drained fluid, it is possible to accurately determine when all liquefied fuel gas in the closed container has become vaporized, and with accurate timing when it happens. Thus, the present arrangement reduces the time required for emptying a closed container and increase the safety for emptying the same. Also, as the vaporization time point of the liquefied fluid gas can be accurately determined, the amount of inert fluid used for treating the closed container can be reduced.

Further, the first sensor comprises a temperature sensor, and wherein the predetermined criterion comprises that the temperature of the drained fluid is equal to or greater than a first temperature limit. Thus, the vaporization status of the mixed fluid in the closed container can be determined based on the temperature of the drained fluid, thus the mixed fluid.

According to some embodiments, the arrangement comprises a temperature sensor arranged to measure the temperature of the inert fluid downstream the heating control device, thereby enabling control of the heating control device based on the measured temperature, in order to keep a temperature of the inert fluid downstream the heating control device within a predetermined temperature interval. Thereby, a fast and steady vaporization of the liquefied natural gas in the closed container can be achieved, that does not go beyond what the closed container can take.

According to some embodiments, the arrangement comprises a pressure sensor arranged to measure the pressure of the inert fluid from the inert fluid source upstream the heating control device, and a pressure regulator arranged to regulate the pressure in the first fluid line upstream the heating control device, enabling regulation of the pressure in the first fluid line based on the measured pressure such that the pressure in the first fluid line is below a first pressure limit. Alternatively, the arrangement comprises a flow regulator arranged to control the flow rate of the inert fluid in the first fluid line. The flow regulator may be regulated based on the measured temperature of the inert fluid, and/or a measured flow rate of the inert fluid and/or the measured pressure of the inert fluid. The arrangement may thus also comprise a flow sensor arranged to measure the flow rate in the first fluid line. By the embodiments, a fast and steady heating of the fluid in the closed container may be achieved, that does not go beyond what the closed container can stand.

According to some embodiments, the arrangement comprises a control arrangement configured to obtain the measured property of the drained fluid, and upon the measured property fulfils the predetermined criterion, the control arrangement is configured to determine that the liquefied fuel gas in the closed container has evaporated. Thereby, it can be automatically determined that the liquefied fuel gas in the closed container has evaporated.

According to some embodiments, the control arrangement is configured to obtain an indication of the pressure in the closed container, and upon the temperature of the drained fluid is equal to or greater than a first temperature limit while the pressure in the closed container is within an interval of the pressure of the drained fluid, the control arrangement is further configured to determine that the liquefied fuel gas in the closed container has evaporated. Thereby, it can be automatically determined that the liquefied fuel gas in the closed container has evaporated, with a greater accuracy.

According to some embodiments, the control arrangement is configured to initiate a dilution and flushing procedure upon determining that the liquefied fuel gas in the closed container has evaporated. Thereby, the closed container can be automatically emptied.

According to some embodiments, the first sensor is arranged to measure the property of the drained fluid in the second fluid line. Thus, the measurement can be made simply, without having to make changes to the closed container itself.

According to a second aspect, the disclosure relates to a system comprising a source of inert fluid and an arrangement according to any of the embodiments disclosed herein, wherein the source of inert fluid is connected to the inlet of the first fluid line.

According to some embodiments, the system comprises a closed container and a pressure sensor for measuring a pressure of the fluid in the closed container, and wherein the outlet of the first fluid line is connected to the inlet of the closed container, and the inlet of the second fluid line is connected to the outlet of the closed container.

According to some embodiments, closed container is arranged to a vehicle.

According to a third aspect, the disclosure relates to a method for treating a closed container, the closed container containing liquefied fuel gas. The method comprises controlling inert fluid to pass, from a source of inert fluid, to the closed contained and controlling heating of the inert fluid being passed to the closed container. The method further comprises draining a fluid from the closed container while monitoring a property of the drained fluid and determining that the liquefied fuel gas in the closed container has evaporated upon the monitored property fulfils a predetermined criterion.

According to some embodiments, the monitored property is a temperature of the drained fluid, and wherein the method further comprises monitoring a pressure of the fluid in the closed container, and determining that the liquefied fuel gas in the closed container has evaporated, upon the temperature of the drained fluid is equal to or greater than a first temperature limit, while the pressure in the closed container is within an interval of the pressure of the drained fluid. The pressure of the drained fluid in the second fluid line might also need to be monitored, if not known by other means.

According to some embodiments, the method comprises controlling a dilution and draining procedure for flushing the closed container, upon determining that the liquefied fuel gas in the closed container has evaporated.

According to a fourth aspect, the disclosure relates to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the steps of the method as disclosed herein.

According to a fifth aspect, the disclosure relates to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out any of the steps of the method as disclosed herein.

Brief description of the drawings Fig. 1 illustrates a vehicle to which the proposed arrangement and method may be used.

Fig. 2 illustrates an arrangement connected to a closed container containing liquefied fuel gas.

Fig. 3 illustrates a flow chart of a method for treating a closed container containing liquefied fuel gas.

Fig. 4 illustrates an LNG system in more detail.

Detailed description Liquefied fuel gas, such as LNG, is a quite pure fuel, consisting of mainly methane. In addition, the LNG typically also comprises small amounts of heavier gases, such as hydrocarbons. If a gas fuelled vehicle is not used in approximately five days, the pressure in the cryonic tank builds up sufficiently for safety devices to activate. The safety devices thereby ventilate vaporised fuel gas, which mainly consists of the more readily vaporised methane, into the atmosphere. This process can lead to that the heavier gases, such as heavier hydrocarbons, are enriching in the cryonic tank over time, as they are less likely to vaporise and be ventilated. Ventilating these heavier gases by pressurizing the cryonic tank with nitrogen gas and then emptying the mixed gas to the atmosphere is cumbersome and at least three days are generally required for ventilating the closed container to below LFL, Lower Flammability Limit, of LNG. In some situations, the emptying and ventilating may take up to two weeks.

The method and arrangement proposed herein propose to heat the inert fluid before it is introduced into the closed container, and monitor when the liquid inside the closed container has evaporated. This heating and monitoring enables determining when all liquid in the container has been transformed in gaseous phase, such that is easily can be flushed and drained from the container. The invention relies on the insight that a property of the drained fluid from the closed container, gives insight of the state of the fluid in the closed container. Controlled heating of the inert fluid before it is introduced into the closed container, reduces the time needed for emptying the closed container as the liquid in the closed container evaporates faster when exposed to heated inert fluid than if the inert fluid was not heated, as the heated inert fluid adds more energy to the liquid residing in the closed container. Furthermore, by adding heated inert fluid into the closed container, the vaporized liquid at the same time becomes diluted. In an example embodiment, the heated inert gas, e.g. heated vaporized nitrogen, is introduced into the closed container, whereby the liquefied natural gas inside becomes vaporized into natural gas and diluted with the heated vaporized nitrogen. The arrangement further enables immediate determination of when the operation has been completed, i.e. when all the liquid natural gas has become vaporized, by sensing a property of the drained fluid. The arrangement thus reduces the time for flushing by far, compared to previously used methods and equipment. The arrangement also enables optimization of the amount treating medium to be used, that is, the inert fluid. Thereby the amount of treating medium for emptying a closed container may be reduced, compared to previous known methods.

In the following an arrangement and a method for treating a closed container containing liquefied fuel gas will be explained, with reference to Figs.1 to Fig 3.

Fig. 1 schematically illustrates a vehicle 1, here a truck. The vehicle 1 comprises a cryonic tank 7 comprising a closed container 2 configured for storage of liquefied fuel gas. The proposed arrangement and method system are usable for such a closed container 2. The closed container 2 is for example arranged to provide fuel gas, such as LNG, for use by a gas fueled engine 3 in the vehicle 1. The cryonic tank 7 may also comprise several components (not shown) installed outside the closed container 2. A closed container 2 configured for storing LNG and the components in the cryonic tank 7 are sometimes referred to as an LNG system.

In Fig. 2 the proposed arrangement 30 for treating the closed container 2 comprising liquefied fuel gas is schematically illustrated. The arrangement 30 comprises a first fluid line 20, a heating control device 24, a second fluid line 21 and a first sensor 28. The closed container 2 is arranged with a first pressure sensor 31 for measuring a pressure of the fluid in the closed container 2. An outlet 32c of the closed container 2 is arranged to pass vaporized fuel to the engine 3 of the vehicle 1. Note that even if the closed container 2 in this example is comprised in the cryonic tank 7 of the vehicle 1, the closed container 2 may according to some embodiments be arranged in a stand-alone cryonic tank or it may be a closed container arranged in another way. Further details of the cryonic tank 7 of Fig. 1 are described in relation to Fig. 4 below.

The first fluid line 20 comprises an inlet connected to a source 22 of inert fluid and an outlet connected to an inlet 32a of the closed container 2 for transport of vaporized inert fluid to the closed container 2. The inert fluid has a boiling point that is lower than the liquefied fuel gas residing in the closed container 2. The source 22 of inert fluid may comprise inert fluid in a liquid state or in a gaseous state. The inert fluid is for example liquefied or vaporized nitrogen. The inert fluid may be referred to as a “flushing medium” or “treating medium”. The heating control device 24 is arranged for heating the inert fluid comprised in the first fluid line 20.

The heating control device 24 is arranged to heat the inert fluid such that is reaches a preset temperature. The preset temperature is for example set to a high temperature, but below the temperature limit for the closed container 2 itself. The heating control device 24 comprises e.g. a heating element or a heat exchanger. The second fluid line 21 comprises an inlet connected to an outlet 32b of the closed container 2. The second fluid line 21 is arranged to transport drained fluid from the closed container 2, e.g. to a reservoir 23, such that the drained fluid can be collected and taken care of. The second fluid 21 is in one embodiment arranged to conduct fluid from the closed container 2 from a lower part from the closed container 2. This is exemplified in connection with Fig. 4. Thereby the drained fluid should contain fluid from the lower part of the closed container 2, and thus be a reliable sample of the state of the fluid in the closed container 2. The first sensor 28 is arranged to measure a property of the drained fluid, thereby enabling determining that the liquefied fuel gas in the closed container 2 is evaporated based on the monitored property fulfilling a predetermined criterion. If the liquefied fuel gas is evaporated, it can be transported out of the closed container 2 by further dilution and flushing. The apparatus 30 thus enables determining at what time the flushing can be started, and thereby decreases the time for emptying the closed container 2. In prior art, an excessive amount of inert fluid had to be used to ensure that all liquefied fuel gas had become vaporized. Also, by controlling heating of the inert fluid, the vaporization of the liquefied fuel gas can be made rapidly.

According to some embodiments, the first sensor 28 comprises a temperature sensor. In these embodiments, the predetermined criterion comprises that the temperature of the drained fluid is equal to or greater that a first temperature limit. Alternatively, the first sensor 28 comprises a chemical property sensor. In this alternative, the predetermined criterion comprises that the chemical property content of the drained fluid is equal to or smaller than a property content limit. The chemical property is for example methane, and the chemical property sensor is then a methane sensor. The first sensor 28 measures the property of the drained fluid, and is thus arranged to the second fluid line 21. Alternatively, the property may be measured in the reservoir 23.

In some embodiments, the arrangement 30 comprises an inert fluid pressure sensor 26 arranged to measure the pressure of the inert fluid from the inert fluid source 22 upstream the heating control device 24. A pressure regulator 25 is arranged to regulate the pressure in the first fluid line 20 upstream the heating control device 24. The pressure regulator 25 enables regulation of the pressure in the first fluid line 20 based on the measured pressure by the inert fluid pressure sensor 26 such that the pressure in the first fluid line 20 is below a first pressure limit. The first pressure limit is for example a tolerance limit of the closed container 2. Alternatively, the inert fluid pressure sensor 26 is exchanged for a flow sensor, arranged to measure a flow of the inert fluid in the first fluid line 20. Further, the pressure regulator 25 is exchanged for a flow regulator, thereby enabling regulation of the flow in the first fluid line 20 based on the measured flow.

The temperature of the inert fluid is for example measured by a temperature sensor 27. The temperature sensor 27 is arranged to measure the temperature of the inert fluid downstream the heating control device 24. Thereby, control of the heating control device 24 is enabled based on the measured temperature, in order to keep a temperature of the inert fluid downstream the heating control device 24 within a predetermined temperature interval. The predetermined temperature interval is for example limited by an upper temperature limit being the maximum allowed temperature of the closed container 2, and a lower temperature limit being the lowest temperature the inert fluid should have to make sure that the inert fluid has evaporated, if it was liquefied before heating. For example, the temperature limit is between 150°C and 200 °C. However, in most cases it is desired to reach a temperature of the inert fluid as high as possible, thus close to the upper temperature limit, in order to have a fast process. The inert fluid is heated to a temperature as high as possible without damaging the vacuum isolation of the closed container 2. By measuring the temperature of the heated inert fluid before it is introduced into the closed container 2, i.e. the inlet temperature of the heated inert fluid, the flow of the inert fluid in the first fluid line 20 may be optimized such that the inlet temperature is steady at maximal temperature. Alternatively, a user of the arrangement 30 may manually control the heating control device 24 with feedback of the obtained temperature from the temperature sensor 27.

For using the arrangement 30, the first fluid line 20 is connected to the source 22 of inert fluid at the inlet of the first fluid line 20, and connected to the closed container 2 at the outlet of the first fluid line 20. The pressure regulator 25 is regulated to let inert fluid into the fluid line 20. The inert fluid will be transported because of the pressure differences between the source 22 of inert fluid and the closed container 2. The inert fluid is heated by the heating control device 24.

During the transport, the heating control device 24 heats the inert fluid to a certain temperature. By monitoring the temperature, the power to the heating control device 24 may be regulated such that the desired temperature of the inert fluid can be obtained. The heating control device 20 heats the inert fluid to a high temperature, e.g. 180°C. The heating evaporates any inert liquid from the closed container 2, such that only evaporated inert fluid is introduced into the closed container 2. The heated evaporated inert fluid, i.e. the heated inert gas, heats the residuals of the liquefied natural gas in the closed container 2, whereby the liquefied natural gas evaporates into natural gas. The heated inert gas and the natural gas are mixed, such that the natural gas is diluted. When the mix of heated inert gas and the natural gas, hereafter referred to as “the mixed gas”, obtains a certain temperature correlated with the pressure of the mixed gas, then all liquefied natural gas has become vaporized and is ready for being further diluted and the closed container 2 thereafter flushed. Optionally, the arrangement 30 comprises a second pressure sensor 10 arranged to measure the pressure of the drained fluid in the second fluid line 32, if the pressure of the drained fluid cannot be obtained with other means. Upon the temperature of the drained fluid is equal to or greater than a first temperature limit while the pressure in the closed container 2 is within an interval of the pressure of the drained fluid, it can be determined, thus established, that the liquefied fuel gas in the closed container 2 has evaporated. The pressure of the drained fluid should thus be the same, or essentially the same, as the pressure of the mixed fluid in the closed container 2. Thus, the service technician may by manually monitoring the different sensors, precisely determine when the liquefied fuel gas in the closed container 2 has evaporated.

Thus, if the pressure of the drained fluid is essentially the same as the pressure of the mixed fluid in the closed container 2, then the temperature of the drained fluid can be relied upon. Otherwise a pressure drop from the closed container 2 to the second fluid line 21 may compromise the temperature measurement, such that the temperature measured of the drained fluid does not indicate the true temperature of the mixed fluid in the closed container 2.

Alternatively, when the mixed gas contains a chemical property content that is equal to or smaller than a property content limit correlated with the flow of the mixed gas, then all liquefied natural gas has become vaporized and is ready for being further diluted and the closed container 2 thereafter flushed. The temperature or flow rate of the mixed gas is measured when flowing in the second fluid line 21. Thus, the measurements are made on the drained fluid flowing in the second fluid line 21. The above described arrangement 30 is in some embodiments manually actuated.

Alternatively, the arrangement 30 comprises a control arrangement 29 for controlling one or several functions of the arrangement 30. The control arrangement 29 is for example in one embodiment configured to obtain the measured property of the drained fluid, and upon the measured property fulfils the predetermined criterion, the control arrangement 29 is configured to determine that the liquefied fuel gas in the closed container 2 has evaporated.

The control arrangement 29 is in some embodiments arranged to control the heating of the inert fluid, by means of the heating control device 24. The control arrangement 29 is then arranged to obtain the temperature of the heated inert fluid, measured by the temperature sensor 27, and to control the heating control device 24 based on the measured temperature such that the desired temperature of the heated inert fluid is obtained. The control arrangement 29 is in some embodiments arranged to control the pressure of the inert fluid, by means of the pressure control device 25. The control arrangement 29 is then arranged to obtain the pressure of the inert fluid, measured by the inert fluid pressure sensor 26, and to control the pressure control device 25 based on the measured pressure such that the desired pressure of the inert fluid is obtained.

According to some embodiments, the control arrangement 29 is configured to obtain an indication of the pressure in the closed container 2, e.g. from the first pressure sensor 31 in the closed container 2. Upon the temperature of the drained fluid is equal to or greater than a first temperature limit while the pressure in the closed container 2 is within an interval of the pressure of the drained fluid, the control arrangement 29 is further configured to determine that the liquefied fuel gas in the closed container 2 has evaporated. Thus, automatic evaporation detection of liquefied natural gas in a closed container 2 is enabled.

According to some embodiments, the control arrangement 29 is configured to initiate a dilution and flushing procedure upon determining that the liquefied fuel gas in the closed container 2 has evaporated. The dilution comprises for example to continue passing inert fluid from the source of inert gas to the closed container 2.

The control arrangement 29 for example comprises a processing unit 29a and a memory unit 29b. The processing unit 29a may be made up of one or more Central Processing Units, CPU. The memory unit 29b may be made up of one or more memory units. A memory unit 29a may comprise a volatile and/or a nonvolatile memory, such as a flash memory or Random Access Memory, RAM. The control arrangement 29 can provide control data and/or receive measured data to or from the different components of the arrangement 30 in different ways, e.g. via a bus, via dedicated lines or via wireless interfaces. The memory unit 29b comprises a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the steps of the method as disclosed herein. The computer program may reside on a computer-readable medium. The computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out any of the steps of the method as disclosed herein. The control arrangement 29 may be arranged to communicate with the described sensors 10, 26, 27, 28, 30, 31, the heating control device 24 and the pressure regulator 25 via wireless communication or by wire, as illustrated with the hatched lines in Fig. 2. The control arrangement 29 may also be arranged to communicate with other sensors, devices etc, and to control other devices, such as valves etc., of the cryonic tank 7 that will be explained in the following.

The disclosure also relates to a system 40 comprising the source 22 of inert fluid and the arrangement 30 according to any of the herein disclosed embodiments, wherein the source 22 of inert fluid is connected to the inlet of the first fluid line 21.

The system 40 optionally comprises the closed container 2 and the first pressure sensor 31 for measuring a pressure of the fluid in the closed container 2. The outlet of the first fluid line 20 is connected to the inlet of the closed container 2, and the inlet of the second fluid line 21 is connected to the outlet of the closed container 2. The closed container 2 is for example arranged to the vehicle 1.

The disclosure also relates to a method for treating the closed container 2 containing liquefied fuel gas. The method will be explained with reference to the flow chart in Fig. 3. The method starts with connecting A1 the first fluid line 20 to the source of inert fluid 20. The method further comprises controlling A2 inert fluid to pass, from the source of inert fluid, to the closed container 2. Thereafter, the method comprises controlling heating A3 of the inert fluid being passed to the closed container 2. The method thereafter comprises draining A4 a fluid from the closed container 2 while monitoring a property of the drained fluid. The drained fluid is the mix obtained in the closed container 2. The monitored property is for example the temperature of the drained fluid. The method further comprises determining A6 that the liquefied fuel gas in the closed container 2 has evaporated upon the monitored property fulfils a predetermined criterion.

In one exemplary embodiment, the predetermined criterion comprises that temperature of the drained fluid has to be equal to or greater that a first temperature limit, while the pressure in the closed container 2 is within an interval of the pressure of the drained fluid. The method then comprises monitoring A5 a pressure of the fluid in the closed container 2, and determining A6 that the liquefied fuel gas in the closed container 2 has evaporated, upon the temperature of the drained fluid is equal to or greater that a first temperature limit, while the pressure in the closed container 2 is within an interval of the pressure of the drained fluid. In response to determining that all liquefied fuel gas has evaporated A61, the method comprises controlling A7 a dilution and draining procedure for flushing the closed container 2. If the criterion is not fulfilled, that is upon the temperature of the drained fluid is not equal to or greater that a first temperature limit, while the pressure in the closed container 2 is within an interval of the pressure of the drained fluid, the method returns to step A2.

The dilution and draining procedure is for example simply a continuation of the previous introduction of inert fluid into the closed container 2. When the closed container 2 has become filled with inert fluid, it is emptied again by creating a pressure head in the closed container 2. By knowing how much liquid natural gas it was in the closed container 2 when the process started, it is possible to calculate how many times the closed container 2 has to be flushed by the inert fluid, and at what pressure, before the amount of natural gas is low enough to guarantee a safe working environment. By monitoring the property in the second line 21, it is possible to determine and/or verify when the closed container 2 is emptied in a simple and safe way. The dilution and flushing procedure may thus be made with heated inert gas.

For better understanding of the proposed technique and underlying technology, Fig. 4 illustrates the closed container 2 and the components in the cryonic tank 7 in further detail according to one example implementation. As mentioned above, the closed container 2 typically comprises an inner tank 2b and an outer shell 2a. The inner tank 2b is surrounded by a vacuum positioned inside an insulating layer.

As mentioned above, the closed container 2 has a fuel inlet 32A, a liquid fuel outlet 32B arranged to let out liquid from a lower part 12 of the closed container 2, a fuel gas outlet 32C arranged to let out gas from an upper part 11 of the closed container 2 and a vent (short for ventilation) outlet 32D. The closed container 2 may of course have further inlet and outlets if desirable.

In the closed container 2, inner lines (not shown) may be arranged to the inlets and outlets 32A, 32B, 32C, 32D for guiding liquefied fuel gas or fuel gas in to and out from the closed container 2.

Note that, to achieve good isolation, the inner tank 2b of the closed container 2 is generally only connected to the outer shell 2a on one side of the cryonic tank 7.

This may be the only connection to the outside from the inner tank 2b and therefore the inner lines all goes via this connection. In other words, the different ports for letting gas and liquid in to and out from the closed container 2 may be implemented by fitting the respective lines in one shared connection (or opening) from the inner tank 2b to the outside. However, in Fig. 5 the ports and lines are illustrated separately for ease of understanding and for better visibility.

The different ports, lines and the components arranged in connection with the ports and lines will now be described in more detail.

A fueling line 211 connected to the inlet 32A allows liquefied fuel gas to be introduced into the closed container 2, e.g. when fueling the vehicle 1. When the arrangement 30 according to the invention is used, this fueling line 211 is removed, and exchanged with the first fluid line 20.

An inner liquid pick-up line 222 inside the closed container 2 and connected to the fluid outlet 32B allows liquefied fuel gas (i.e. liquid fuel) to be removed from the lower part of the closed container 2, e.g. when providing fuel to a gas fueled engine 3 of the vehicle 1 during operation or when emptying the closed container 2.

An outer liquid pick-up line 221 extends outside the closed container 2 from the fluid outlet 32B. The liquid flow through the outer liquid pick-up line 222 may be manually regulated by a liquid fuel outlet valve 240b. When the arrangement 30 is in use, the outer liquid pick-up line 221 is exchanged for the second fluid line 21, or the second fluid line 21 is arranged in connection to the outer liquid pick-up line 221, e.g. connected to an emptying connection 36 of the outer pick-up line 221. However, also the liquid fuel outlet valves 240a, 240b also need to be open during emptying of the closed container 2. The manual liquid fuel outlet valve 240b is mainly used to allow isolation of the closed container 2 for servicing.

The liquid pick-up line 221 is connected to a gas fueled engine 3 of the vehicle 1 through via a fuel line that herein is referred to as an engine line 381. In Fig. 5 this is illustrated by the connecting line 34. However, the connection may of course be implemented in different ways. The engine line 381 is an extension of the outer liquid pick-up line 221 that connects the outer liquid pick-up line 221 to an engine connection 38. The outer part of the liquid pick-up line 221, i.e. the part outside the closed container 2, and the engine line 381 together define a liquid flow path between the liquid fuel outlet 32B and the engine connection 38.

A heat exchanger 37 is arranged in the engine line 381 to vaporize and heat liquefied fuel gas, or to heat fuel gas, before it is provided to the gas fueled engine 3. The heat exchanger 37 does not change the fuel pressure. Instead, the heat for this process is obtained from the gas fueled engine cooling system, which is connected to one side of the cryonic tank 7. In addition, a solenoid valve (not shown) is located downstream from the heat exchanger 37. The solenoid valve is closed when the tank 7 is not being powered and opens when the gas fueled engine 3 is running and thereby fuel is provided to the gas fueled engine 3. The solenoid is typically also closed when emptying the closed container 2.

The liquid pick-up line 221 is also connected to an emptying line 361. The emptying line 361 is used when emptying the closed container 2 e.g. before servicing. The outer part of the liquid pick-up line 221 and the emptying line 361 together define a liquid flow path between the liquid fuel outlet 22 and the abovementioned emptying connection 36. The emptying connection 36 may be designed in different ways. For example, it may be configured to be attached to the storage 4. The flow through the emptying connection 36 may be closed by the above-mentioned emptying shut-off valve 35, which is arranged in the emptying line 361. When the emptying shut-off valve 35 is opened, emptying of the closed container 2 is started if there is a pressure head in the closed container 2. A prerequisite is of course that any other valve in the liquid flow path is open.

A gas pick-up line 231 allows fuel gas to be guided from the closed container 2, out through the fuel gas outlet 32c and further to the engine line 381. This is e.g. desirable when the pressure in the container is above a pre-determined limit, as it is desirable to keep the pressure in the closed container 2 at about 10 Bar when providing fuel to the gas fueled engine 3. Hence, like the liquid pick-up line 221, the gas pick-up line 231 is also connected to the engine line 381.

The gas flow from the closed container 2 through the gas pick-up line 231 may be adjusted by one or more fuel gas outlet valves 260a, 260b. A manual fuel gas outlet valve 260b is positioned right after the fuel gas outlet 32c in the downstream direction.

An automatic fuel gas outlet valve 260a is positioned right after the manual fuel gas outlet valve 260b. The automatic fuel gas outlet valve 260a is a so-called economizer pressure regulator. The economizer pressure regulator 260a reduces the closed container 2 pressure by venting gas to the fuel line when the gas fueled engine 3 is running. Thus, depending on the pressure in the closed container 2, it determines whether fuel should be used from the top of the closed container 2 (in a gaseous state) or from the bottom 14 of the closed container 2 (in a liquid state). The economizer function is e.g. set at 10 bar. This means that when the pressure reaches 10 bar fuel is taken from the top of the closed container 2 to reduce the pressure. In other words, the automated fuel gas outlet valve 260a is configured such that when the automated fuel gas outlet valve 260a is open, i.e. in normal operation, gas flows out from the closed container 2 through the fuel gas outlet 32c if the pressure in the closed container 2 is above a predefined threshold provided that liquid flow through the liquid pick-up line 221 is closed e.g. by the automatic liquid fuel outlet valve 240a. When the liquid flow through the liquid pick-up line 221 is open, the economizer will not work properly as there is the more pressure drop over the liquid pick-up line 221 than over the gas pick-up line 231 and the flow would then choose the easier route through the liquid fuel outlet 32c.

A boil-of line 201 allows fuel gas to be removed from the closed container 2, when the pressure is too high. The boil-of line 201 comprises a first pressure relief valve 300 and a second pressure relief valve 310. By having two valves, security can still be maintained is one valve breaks down. The first pressure relief valve 300 is connected to a vent line 33 that vents out fuel gas though a pipe behind the vehicle 1. The second pressure relief valve 310 may have a seal to show when gas has been vented and thereby indicate that something is wrong with the system 10. For example, the first pressure relief valve 300 is set at 16 bar and the second pressure relief valve 310 is set at 24 bar.

Furthermore, a shut-off valve 290 is arranged at the vent line 201. The shut-off valve 290 is arranged right after the second pressure relief valve 31, in the gas flow direction. The shut-off valve 290 is arranged to open and close gas flow through the vent line 201, e.g. to isolate components during servicing.

The vent line 201 also comprises components for measuring the pressure in the tank. A manometer 280a is arranged right after the shut-off valve 290, in the gas flow direction. The manometer 280a is an analogue instrument that is arranged to be manually read. The pressure sensor 280b is arranged right after the manometer 280a, in the gas flow direction.

The present disclosure is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the disclosure, which is defined by the appending claims.

Claims

1. An arrangement (30) for treating a closed container (2), the closed container (2) containing liquefied fuel gas, the arrangement (30) comprising - a first fluid line (20) with an inlet connectable to a source (22) of inert fluid and an outlet connectable to an inlet of the closed container (2) for transport of vaporized inert fluid into the closed container (2); the arrangement (30) further comprising - a heating control device (24) arranged for heating the inert fluid comprised in the first fluid line (20); - a second fluid line (21), comprising an inlet connectable to an outlet of the closed container (2), the second fluid line (21) being arranged to transport drained fluid from the closed container (2); characterized in that - a first sensor (28) is arranged to measure a property of the drained fluid, thereby enabling determining that the liquefied fuel gas in the closed container (2) is evaporated based on the monitored property fulfilling a predetermined criterion, wherein the first sensor (28) comprises a temperature sensor, and wherein the predetermined criterion comprises that the temperature of the drained fluid is equal to or greater that a first temperature limit.

2. The arrangement (30) according to claim 1, comprising: - a temperature sensor (27) arranged to measure the temperature of the inert fluid downstream the heating control device (24), thereby enabling control of the heating control device (24) based on the measured temperature, in order to keep a temperature of the inert fluid downstream the heating control device (24) within a predetermined temperature interval.

3. The arrangement (30) according to any one of the preceding claims, comprising - a pressure sensor (26) arranged to measure the pressure of the inert fluid from the source (22) of inert fluid upstream the heating control device (24), and - a pressure regulator (25) arranged to regulate the pressure in the first fluid line (20) upstream the heating control device (24), enabling regulation of the pressure in the first fluid line (20) based on the measured pressure such that the pressure in the first fluid line (20) is below a first pressure limit.

4. The arrangement (30) according to any of the preceding claims, comprising - a control arrangement (29) configured to obtain the measured property of the drained fluid, and upon the measured property fulfils the predetermined criterion, the control arrangement (29) is configured to determine that the liquefied fuel gas in the closed container (2) has evaporated.

5. The arrangement (30) according to claim 4, wherein the control arrangement (29) is configured to obtain an indication of the pressure in the closed container (2), and upon the temperature of the drained fluid is equal to or greater than a first temperature limit while the pressure in the closed container (2) is within an interval of the pressure of the drained fluid, the control arrangement (29) is further configured to determine that the liquefied fuel gas in the closed container (2) has evaporated.

6. The arrangement (30) according to claim 4 or 5, wherein the control arrangement (29) is configured to initiate a dilution and flushing procedure upon determining that the liquefied fuel gas in the closed container (2) has evaporated.

7. The arrangement (30) according to any one of the preceding claims, wherein the first sensor (28) is arranged to measure the property of the drained fluid in the second fluid line (21).

8. A system (40) comprising: - a source (22) of inert fluid and - an arrangement (30) according to any of the preceding claims, wherein the source (22) of inert fluid is connected to the inlet of the first fluid line (20).

9. The system (40) according to claim 8, comprising - a closed container (2); - a pressure sensor (31) for measuring a pressure of the fluid in the closed container (2); and wherein the outlet of the first fluid line (20) is connected to the inlet of the closed container (2), and the inlet of the second fluid line (21) is connected to the outlet of the closed container (2).

10. The system (40) according to claim 9, wherein the closed container (2) is arranged to a vehicle (1).

11. A method for treating a closed container, the closed container containing liquefied fuel gas, the method comprising - controlling (A2) inert fluid to pass, from a source of inert fluid, to the closed contained; - controlling heating (A3) of the inert fluid being passed to the closed container; - draining (A4) a fluid from the closed container while monitoring a property of the drained fluid; - determining (A6) that the liquefied fuel gas in the closed container has evaporated upon the monitored property fulfils a predetermined criterion, wherein the monitored property is a temperature of the drained fluid, and wherein the method further comprises - monitoring (A5) a pressure of the fluid in the closed container, and - determining (A6) that the liquefied fuel gas in the closed container has evaporated, upon the temperature of the drained fluid is equal to or greater that a first temperature limit, while the pressure in the closed container is within an interval of the pressure of the drained fluid.

12. The method according to claim 11, comprising - controlling (A7) a dilution and draining procedure for flushing the closed container, upon determining that the liquefied fuel gas in the closed container has evaporated.

13. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the steps of the method according to any one of the claims 11 to 12.

14. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out any of the steps (A2) to (A6) of the method according to any one of the claims 11 to 12.