Method and Device for Filling a Container with Liquid Gas from a Storage Tank

Abstract

A method and device for filling a container with liquid gas from a storage tank includes removing the liquefied gas from the storage tank and feeding it to a container via a liquid feed line through use of a delivery system. The gas is compressed in the container and is removed from the container in its gaseous state and is at least partially liquefied by cooling in a heat exchanger. The at least partially liquefied gas is fed into the liquid feed line at the suction end of the delivery device.

Description

Exemplary embodiments of the invention will be explained in more detail with reference to the drawings, in which, in schematic views:

FIG. 1 shows a first embodiment of a device according to the invention for filling a container with liquid gas, and

FIG. 2 shows another embodiment of a device according to the invention for filling a container with liquid gas.

FIG. 1 shows a container 1 which is intended for storing liquid gas, for example carbon dioxide. In the state of thermal equilibrium, the liquid gas is stored in the container 1, both in the liquid phase 2 and in a gas phase 3. The container 1 is also provided (in a way which is not of interest here and is therefore not shown) with connections for supplying actuators with gas in the liquid or gaseous state. For the purpose of filling, the container 1 is equipped with in each case one liquid connecting line 4 and with a gas return line 5.

The container 1 is supplied with fresh liquid gas from a storage tank 6. The storage tank 6 is part of a refueling system 10 which is mounted, for example, on a mobile tank unit, for example a tanker truck or a railroad tank car. However, the refueling system 10 can also be a fixed system which is installed, for example, in the vicinity of a production site for the liquid gas and is intended for filling a mobile container or refueling system which is mounted on a tanker truck or a railroad tank car; the container 1 can also be a storage tank for supplying liquid gas to other containers or customers' tanks, which container 1 is itself part of a refueling system of the type described here. Apart from the storage tank 6, the refueling system 10 has the devices described below. In order to fill a container, a liquid gas line 7 is arranged on the storage tank 6. As in the container 1, the liquid gas is also present in a liquid phase 8 and a gas phase 9 in the storage tank 6. The liquid gas line 7 opens into the storage tank 6 in a lower region, and therefore forms a flow connection to the liquid phase 8 of the liquid gas stored in the storage tank 6.

The liquid gas line 7 opens, at its end remote from the storage tank 7, into a connecting element 11 by means of which a detachable connection can be produced to a corresponding connecting element 12 on the liquid connecting line 4. Furthermore, a gas line 13, which can likewise be connected by means of a connecting element 14 to a connecting element 15 on the return line 5, is also provided in the refueling unit 10.

A pump 16, which is intended to deliver liquid gas (in the liquid state) from the storage tank 6 into the container 1, is arranged in the liquid gas line 7, downstream of the storage tank 6. A flow meter 20 is provided downstream of the pump 16 in order to measure the mass flow rate.

The gas line 13 opens, at its end opposite the connection 14, into a heat exchanger 19. The heat exchanger 19 brings about thermal contact between the gas flowing into the heat exchanger 19 from the gas line 13 and the liquid gas in the interior of the storage tank 6, and is arranged in the interior of the storage tank 6 in the exemplary embodiment, specifically in such a way that gas is fed into the heat exchanger 19 from above, that is to say through the gas phase 9, and the surfaces of the heat exchanger have good thermal contact with the liquid phase 8. From the heat exchanger 19, the gas which is now cooled and at least partially liquefied passes into a line 17 which is connected to the liquid line 7 at a connecting point 18 arranged at the suction end of the delivery device 16. In the liquid gas line 7, the gas which flows in from the line 17 is mixed with the liquid gas removed from the storage tank 6, and the said inflowing gas is then fed, together with this liquid gas, to the liquid phase 2 of the gas in the container 1.

When the device is being used appropriately, the connecting elements 11 and 12 are connected to one another in order to bring about a flow connection between the storage tank 6 and the container 1 to be filled. At the same time, the connecting elements 14 and 15 are connected to one another. By means of the pump 16, liquid gas in the liquid state is forced into the container 1, as a result of which the pressure in the container 1 is increased. Gas flows in the gaseous state out of the gas phase 3 of the liquid gas present in the container 1 via the gas lines 5 and 13 into the heat exchanger 19. As a result of the exchange of heat with the liquid phase 8 of the liquid gas in the storage tank 6, the gas is cooled to such an extent that it at least partially condenses and is transported on in the in the line 17 in the at least largely liquid state. The heat which is input into the storage tank 6 during this exchange of heat causes part of the liquid phase 8 to vaporize and contributes to maintaining or even increasing the pressure in the interior of the storage tank 6 despite the ongoing removal of liquid gas.

The greater the degree to which the pump 16 increases the pressure in the container 1, and thus in the heat exchanger 19, the more reliably is it ensured that the liquid gas is at least largely in liquid form in the region of the connecting point. Nevertheless, some of the gas can remain in the gaseous state. For example, it is assumed that the relaxing of the gas at the junction from the line 17 into the liquid phase 7 by 2 bar leads to a cavitation of 5% of the gas fed from the line 17. Since the proportion of liquefied gas from the line 17 is only approximately 5% of the total quantity of liquid gas delivered by the pump 16, only a total of 0.25% of the quantity of gas delivered by the pump is present as cavitation, that is to say in the gaseous state. However, such low cavitation can be accepted without difficulty by most commercially available pumps.

In order to avoid liquefied gas flowing back from the heat exchanger 19 into the storage tank 6 when disruption occurs in the operational sequence, for example when there is a sudden failure of the pump, a device for preventing backflow, for example a nonreturn valve 23, is installed in the liquid gas line 7 between the storage tank 6 and the connecting point 18 in terms of fluid dynamics. The same function is performed by using a multistage pump provided that the connecting point 18 is arranged between two pump stages.

In order to increase the efficiency of the device according to the invention it is appropriate, but not absolutely necessary, to provide a compressor 22 in the gas line 13 upstream of the heat exchanger 19, which compressor 22 promotes the feeding of liquefied gas into the liquid feed line 7.

The embodiment according to FIG. 2 differs from the previously described one merely in having one additional control device 21 in the line 17, arranged upstream of the connecting point 18 in terms of fluid dynamics. Furthermore, identical components to those in FIG. 1 are provided with the same reference symbols.

The control device 21 comprises a shutoff fitting, for example a valve, a butterfly valve or a throttle, by means of which the flow through the line 17 can be influenced. In addition, the control device 21 has a differencial pressure measuring device by means of which the pressure difference can be determined upstream and downstream of the shutoff fitting in terms of fluid dynamics, and which acts on the shutoff fitting as a function of the pressure difference, that is to say for example opens or closes the shutoff fitting at a specific value of the pressure difference. The control device 21 can in the simplest case be implemented, for example, by means of a pressure valve which is standardized or can be standardized and which opens, or else closes, the line 17 above a specific pressure difference. Furthermore, the pressure difference can also be measured by measuring the differential pressure between the lines 7 and 13 or the containers 1 and 6, or else indirectly by measuring the respective absolute pressures and calculating the difference therefrom. The control device 21 ensures that liquefied gas flows out of the line 17 into the liquid gas line 7 only above a specific pressure difference upstream and downstream of the control device 21, and the pressure upstream of the control device 21 is, for example, 1.5 to 2 bar higher than the pressure downstream of the control device 21 here. Cavitations in the liquid gas line 7, as a result of which the efficiency of the pump 16 can be decreased, are as a result reduced to such an extent that the delivery of the liquid gas by the pump 16 is not adversely affected. The control device can also be set to a relatively low pressure difference value or else can close the line 17 when a specific overpressure value is overshot, in order to prevent cross-contamination into the storage tank 6. The value for the minimum pressure difference depends on various parameters of the equipment used, in particular on the characteristic of the heat exchanger, the flow rate to be coped with by the pump, and the capacity of the pump to tolerate a certain proportion of gas in the delivered stream without a considerable reduction in the delivery capacity.

The device according to the invention feeds back the gas removed from the container 1 into the container 1 in a circuit. As a result, the container 1 can be filled without the risk of decontamination of the liquid gas in the storage tank 6. The device according to the invention is suitable for filling containers with any liquid gases or mixtures of gases.

List of Reference Numerals

1 Container

2 Liquid phase (in container 1)

3 Gas phase (in container 1)

4 Liquid connecting line

5 Gas return line

6 Storage tank

7 Liquid gas line

8 Liquid phase (in storage tank 6)

9 Gas phase (in storage tank 6)

10 Refueling system

11 Connecting element (on the liquid gas line 7)

12 Connecting element (on the liquid connecting line 4)

13 Gas line

14 Connecting element (on the gas line 13)

15 Connecting element (on the gas return line 5)

16 Pump

17 Line

18 Connecting point

19 Heat exchanger

20 Flow meter

21 Control device

22 Compressor

24 Nonreturn valve

Claims

1. A method for filling a container with liquid gas from a storage tank, in which liquefied gas is removed from the storage tank and is fed to the container via a liquid feed line by use of a delivery device, and the gas is compressed in the container to be filled, gas in the gaseous state is removed from the container to be filled and is at least partially liquefied by cooling in a heat exchanger, and the at least partially liquefied gas is fed into the liquid feed line at the suction end of the delivery device.

2. The method as claimed in claim 1, characterized in that the differential pressure between the pressure in the container and the pressure in the storage tank is measured directly or indirectly and the gas which is liquefied in the heat exchanger is fed to the liquid feed line only when a predefined, minimum differential pressure is present.

3. The method as claimed in claim 2, characterized in that the gas is liquefied in the heat exchanger by exchanging heat with the liquid gas in the storage tank.

4. The method as claimed in claim 3, characterized in that the gas from the container to be filled is compressed before being fed to the heat exchanger.

5. A device for filling a container with liquefied gas from a storage tank, having a liquid feed line which is connected to the storage tank, can be connected to the container and is equipped with a delivery device for delivering liquid gas into the container, and having a gas discharge line which can be connected to the container, passes through a heat exchanger and has a flow connection to the liquid feed line at a connecting point arranged at the suction end of the delivery device.

6. The device as claimed in claim 5, characterized in that the heat exchanger is embodied in such a way that it brings about thermal contact between gas removed from the container and gas in the storage tank.

7. The device as claimed in claim 6, characterized in that the heat exchanger is arranged inside the storage tank.

8. The device as claimed in claim 7, characterized by a control device which comprises a shutoff fitting which is arranged in the gas discharge line downstream of the heat exchanger, and a device for measuring the differential pressure upstream and downstream of the shutoff fitting.

9. The device as claimed in claim 8, characterized in that a valve which is standardized or can be standardized and which opens the gas discharge line when a predefined or adjustable differential pressure is reached is provided as the control device.

10. The device as claimed in claim 8, characterized in that an apparatus for compressing the gas, for example a compressor, is arranged in the gas discharge line.

11. The device as claimed in claim 8, characterized in that an apparatus for preventing backflow of liquid gas into the storage tank is provided in the liquid feed line between the storage tank (6) and the connecting point.

12. The device as claimed in claim 8, characterized in that a multistage pump is used as the delivery device, and the connecting point is arranged in the liquid feed line (7) between two pump stages.

13. The device as claimed in claim 8, characterized in that the storage tank and/or the container (1) are arranged in a tanker truck.

14. The device as claimed in claim 5, characterized by a control device which comprises a shutoff fitting which is arranged in the gas discharge line downstream of the heat exchanger, and a device for measuring the differential pressure upstream and downstream of the shutoff fitting.

15. The device as claimed 5, characterized in that an apparatus for compressing the gas, for example a compressor, is arranged in the gas discharge line.

16. The device as claimed in claim 5, characterized in that an apparatus for preventing backflow of liquid gas into the storage tank is provided in the liquid feed line between the storage tank and the connecting point.

17. The device as claimed in claim 5, characterized in that a multistage pump is used as the delivery device, and the connecting point is arranged in the liquid feed line between two pump stages.

18. The device as claimed in claim 5, characterized in that the storage tank and/or the container are arranged in a mobile supply unit.

19. The method as claimed in claim 1, characterized in that the gas is liquefied in the heat exchanger by exchanging heat with the liquid gas in the storage tank.

20. The method as claimed in claim 1, characterized in that the gas from the container to be filled is compressed before being fed to the heat exchanger.