METHOD FOR THE OPERATION OF GAS STORAGE TANKS

Description

Field of invention

[0001] The invention relates to a method for operating gas storage tanks. In particular, the invention relates to a method for filling and withdrawing gas from gas storage tanks, especially for filling and withdrawing gas from gas storage tanks for use in a vehicle, wherein the gas serves as fuel for operating the vehicle. The invention further relates to a system of gas storage tanks for carrying out the method. Background of the invention

[0002] In recent years, interest in the use of alternative fuels in the automotive industry has increased dramatically. As a result, more and more vehicles powered by gaseous fuels such as natural gas, LPG (liquefied petroleum gas), or hydrogen are entering the market. This applies to all types of vehicles, including cars, especially passenger cars, but also commercial vehicles such as trucks or buses, as well as rail vehicles, watercraft, aircraft, and spacecraft. Furthermore, the increasing production of natural gas and fracked gas, particularly in countries without a suitable pipeline network, necessitates storage in pressurized containers.

[0003] Currently used cylindrical pressure vessels have a reinforcing layer made of fiber-reinforced composite material, consisting of fibers embedded in a matrix material. This outer layer is wound onto an inner vessel (the so-called liner) of the pressure vessel, which acts as the winding core, using a winding process. While the inner vessel guarantees, for example, the gas tightness of the pressure vessel, the fiber-reinforced composite reinforcing layer provides the necessary mechanical stability. Type 3 pressure vessels use a mechanical inner vessel (metallic liner), for example, made of aluminum or steel, while Type 4 pressure vessels use a plastic inner vessel (liner). However, pressure vessels consisting solely of one or more metallic materials are also known.

[0004] Pressure vessels are filled with filling gas. Since hydrogen filling stations, in particular, operate at very high pressures and low temperatures, and hydrogen is highly explosive when mixed with oxygen, these stations must meet stringent requirements. Furthermore, the safety of refueling vehicles and the sequential filling of various containers must be guaranteed at filling stations.

[0005] The SAE TIR J 2601 guideline describes the refueling procedure for hydrogen-powered vehicles. According to this guideline, the communication capability of the vehicle to be refueled, or rather its hydrogen tank, is first established. The hydrogen tank does not necessarily have to consist of a single container. On the contrary, it is common for the hydrogen tank to consist of a system of interconnected individual containers. The system typically includes a check valve, and it is equally common for each individual container in a system to have its own check valve. A distinction is made between vehicles that use an electronic interface to monitor various parameters, such as...The pressure and temperature of the hydrogen in the consumer's tank are communicated to the filling station. Vehicles that do not communicate electronically, but instead transmit the tank pressure to the filling station via a pressure sensor (applying pressure to the entire system), then deliver a pressure surge from the hydrogen filling station. This pressure surge opens all check valves, allowing pressure exchange between the vehicle and the filling station. This pressure surge corresponds to the pressure sensor for vehicles that do not communicate electronically. The pressure exchange establishes the starting pressure for refueling the respective vehicle. A leak test of the system is then performed to ensure safety. The filling procedure then begins, with parameters, particularly the filling pressure, being ramped up depending on the starting pressure.Nowadays, the average pressure rise rate method is usually used, which determines a pressure rise rate (max. approx. 60 g hydrogen / s) depending on the starting temperature and starting pressure, so that the filling time depends on the tank size.

[0006] The maximum operating pressure, particularly when filling a pressure vessel or pressure vessel system with hydrogen, can vary depending on the application, ranging from 200 to 1200 bar, typically between 350 and 875 bar. This pressure vessel or pressure vessel system can then supply a fuel cell or internal combustion engine with hydrogen. During filling, the gas flowing into the pressure vessel or pressure vessel system heats up due to compression. If a fuel cell or internal combustion engine is to be started after filling a pressure vessel or pressure vessel system, and hydrogen is to be drawn from this pressure vessel or pressure vessel system, the tank pressure must be reduced to the pressure required by the fuel cell or internal combustion engine. This pressure is typically between 8 and 12 bar for a fuel cell and approximately 30 bar for an internal combustion engine.Pressure reduction is typically achieved with a pressure regulator. Due to the throttling action and the associated Joule-Thomson effect at the pressure regulator, the temperature of, for example, hydrogen increases depending on the pressure difference between high and low pressure. This temperature increase can be up to 40 K. If the temperature after the pressure regulator exceeds the permissible limits of the valves or the fuel cell, operation must be interrupted until the gas has cooled sufficiently. The permissible upper temperature limit of a fuel cell, i.e., the maximum inlet temperature of the fuel gas, is typically around 85 °C. Although the fill gas cools down during withdrawal, for example, to feed it into a fuel cell.Especially when rapidly filling a pressure vessel or pressure vessel system with hydrogen, this cooling is insufficient, at least in the immediate aftermath, to reduce the filling gas temperature below the upper limit. Since the vehicle should be ready to drive immediately after filling, a waiting period for cooling is undesirable. Therefore, cooling devices are typically used to cool the filling gas to a temperature below the limit after filling.

[0007] On the other hand, at very cold ambient temperatures, for example, the fill gas can cool down too much during extraction. Fuel cells only operate efficiently within a specific temperature range, and they cease to function below a lower limit. Therefore, it is common practice to regulate the temperature of fuel cells during operation, i.e., to heat or cool them as needed. However, if a vehicle with a fuel cell is put into operation after a period of inactivity in a very cold environment, it is necessary to wait until the temperature control has heated the fuel cell above its lower limit and until the fill gas, which has cooled down to a very low temperature due to the inactivity, has also warmed sufficiently to prevent the fuel cell temperature from dropping below its lower limit again during operation.Therefore, a minimum gas inlet temperature is typically defined for the fuel cell, which the storage system must maintain. This is, for example, -40°C. If the inlet temperature becomes too low, the fuel cell must be switched off until the gas inlet temperature reaches the permissible range. In this case, too, undesirable waiting times occur.

[0008] Furthermore, it is of course desirable for the gas inlet temperature to be as close as possible to, or even above, the limit temperature in order to minimize the energy required by the fuel cell to temper the gas to operating temperature. Another disadvantage of tempering the fuel cell and / or the fill gas is that this tempering process itself is complex and consumes energy during operation.

[0009] German patent application DE 10 2021 103 105 A1 discloses a device for a pressure vessel system comprising a first pressure vessel with a first pressure vessel valve and a second pressure vessel with a second pressure vessel valve, each configured to direct fuel from the respective pressure vessel into a line supplying an energy converter. The device is configured to detect a pressure equalization situation in which, due to a temperature change in the first and / or the second pressure vessel, the internal pressures in the first and second pressure vessels differ. The device is further configured, in response to the detected pressure equalization situation, to cause the first pressure vessel valve and the second pressure vessel valve to open for a limited time in order to approximate the internal pressures in the first and second pressure vessels. Summary of the invention

[0010] The invention presented here is based on the objective of providing an improvement or an alternative to the prior art.

[0011] From a first perspective, the problem addresses a method for extracting fuel from a pressure vessel system comprising a first pressure vessel with a first volume and a second pressure vessel with a second volume, wherein the first volume is smaller than the second volume, and wherein either the fuel is first extracted at least partially from the first pressure vessel before being extracted exclusively from the second pressure vessel, provided that the fuel in the second pressure vessel has a temperature outside a previously defined permissible temperature window, or the fuel is first extracted at least partially from the second pressure vessel before being extracted exclusively from the first pressure vessel, provided that the fuel in the second pressure vessel has a temperature within a previously defined temperature window.The fuel withdrawal from the second pressure vessel is stopped and the system switches to the first pressure vessel as soon as the temperature of the fuel in the second pressure vessel leaves the previously defined temperature range. This also makes it possible for fuel to be initially withdrawn from both pressure vessels before being withdrawn exclusively from either the first or the second pressure vessel.

[0012] The following terminology should be clarified: It should be expressly noted that, within the context of this patent application, indefinite articles and indefinite numerical specifications such as "one...", "two...", etc., are generally to be understood as minimum specifications, i.e., "at least one...", "at least two...", etc., unless the context or the specific text of a particular passage indicates that only "exactly one...", "exactly two...", etc., is meant. Furthermore, all numerical specifications, as well as specifications relating to process parameters and / or device parameters, are to be understood in a technical sense, i.e., as being subject to the usual tolerances. Even the explicit inclusion of the limitation "at least" or "at least" or similar should not be interpreted as meaning "exactly one" when simply using "one," i.e., without the specification of "at least" or similar.

[0013] The terms "fuel," "filling gas," "gas," "propellant," etc., are used synonymously in this document. The invention can generally be used for the extraction of gaseous substances from a pressure vessel system. However, the invention is particularly advantageous when using hydrogen as fuel for operating a fuel cell or for combustion in a corresponding internal combustion engine to power a vehicle.

[0014] In this document, a "pressure vessel system" refers to a group of interconnected pressure vessels. For example, hydrogen-powered vehicles typically have pressure vessel systems, where the interconnected pressure vessels can have different volumes. Hydrogen pressure vessels must withstand high internal pressures of up to 1,200 bar and therefore usually have a spherical shape or a cylindrical central section, with the cylindrical central section sealed by end caps. For space reasons, several pressure vessels are usually combined into a pressure vessel system in vehicles, where the individual pressure vessels can have different volumes and are usually filled via a common filling line. The hydrogen is withdrawn via a withdrawal valve, with each pressure vessel typically having its own separate withdrawal valve.

[0015] In this document, the general term "vehicle" refers to any type of vehicle, such as a motor vehicle (in particular a passenger vehicle), a commercial vehicle (e.g., a truck, van, bus, or agricultural vehicle), a rail vehicle, a watercraft, an aircraft, or a spacecraft. Furthermore, it also includes appropriately powered work machines.

[0016] The filling process is also called "refueling", especially in the case of vehicles.

[0017] A "pressure reducer" is a pressure valve for installation in a hose or pipe system that ensures a specific outlet pressure is not exceeded, despite differing pressures on the inlet side. In this document, the pressure on the inlet side is also referred to as "high pressure," while the pressure on the outlet side is also referred to as "low pressure."

[0018] The Joule-Thomson effect describes the temperature change of a real, i.e., non-ideal, gas during an isenthalpic reduction in pressure. The direction and magnitude of the effect are determined by the strength of the attractive and repulsive forces between the gas molecules. Under normal conditions, the temperature of most gases and gas mixtures, such as air, decreases upon expansion. In contrast, the temperature of hydrogen, for example, increases.

[0019] A "temperature window" refers to a temperature range between a lower and an upper limit temperature.

[0020] When a pressure vessel is filled with a gas, the gas heats up due to the work done by compression. This work is proportional to the volume of the pressure vessel. The volume of a pressure vessel with a substantially cylindrical central section is directly proportional to its length and disproportionately proportional to its diameter, with the diameter having a squared effect on the volume.

[0021] Pressure vessel systems typically include a check valve, and it is also common practice for each individual pressure vessel in a system to have its own check valve. When a pressure vessel system is filled, the prevailing pressure within the system is first checked. This requires opening all check valves, for example, by applying a pressure surge to the entire system. To achieve this, all pressure vessels in the system are connected to a common filling line and are therefore usually filled simultaneously.

[0022] If a pressure vessel system comprises a first pressure vessel with a first volume and a second pressure vessel with a second volume, where the first volume is smaller than the second, less compression work is performed in the first pressure vessel than in the second. Consequently, the filling gas in the first pressure vessel heats up less than that in the second. Furthermore, the surface area to volume ratio of the first pressure vessel is greater than that of the second. In other words, the pressure vessel with the smaller volume has a larger surface area relative to its volume than the pressure vessel with the larger volume. However, heat is exchanged with the surroundings through this surface area.Since the filling gas typically heats up above the ambient temperature of the pressure vessel due to the compression work performed, more heat is dissipated from the filling gas to the environment in the first pressure vessel than in the second pressure vessel.

[0023] The permissible temperature range for the container must not be exceeded. Additionally, the temperature of the filling gas after the pressure regulator must not exceed the permissible range for the fuel cell. These two temperature ranges may differ.

[0024] If the fuel in the second pressure vessel has a temperature outside a previously defined permissible temperature range, particularly if the compression work performed causes it to exceed the upper limit temperature (which is typically 85 °C for conventional fuel cells), it can be advantageous to first withdraw at least some fuel from the first pressure vessel before also or exclusively withdrawing fuel from the second. This allows the fuel in the second pressure vessel time to cool below the upper limit temperature through heat exchange with the environment. At the very least, this allows any existing fuel cooling system to be smaller. Furthermore, the energy required for fuel cooling can be minimized. In certain cases, it may even be possible to completely eliminate the need for active fuel cooling.

[0025] Especially with trucks, long driving ranges on a single fill-up are required, leading to large fuel volumes. On the other hand, the available space for installing pressure vessel systems is limited, so every available space is utilized for the installation of a pressure vessel, with the pressure vessels having different volumes, primarily due to varying diameters. With the diameter ratios of pressure vessels commonly used in truck pressure vessel systems today, the effects described above result in temperature differences of 10 K to 25 K between the fuel in the largest and smallest pressure vessels.

[0026] Provided the fuel in the second pressure vessel has a temperature within a predefined temperature range, fuel can alternatively be drawn, at least partially, from the second pressure vessel before being drawn also or exclusively from the first pressure vessel. Fuel withdrawal from the second pressure vessel can be stopped and the process switched to the first pressure vessel as soon as the temperature of the fuel in the second pressure vessel leaves the predefined temperature range. This can be particularly advantageous when a vehicle is to be refueled at very low ambient temperatures, a pressure vessel system is installed in the vehicle, and the vehicle is to be put into operation shortly after refueling, for example, immediately after refueling.Such a scenario can occur, for example, in very cold regions of the world, such as Alaska. Ambient temperatures of -30°C are not uncommon there. While the compression work performed during filling warms the fuel, it also cools down rapidly again due to the effects described above, particularly in the first pressure vessel. By initially drawing fuel from the second pressure vessel, the vehicle can be operated while a temperature control device, if present, maintains the fuel temperature in the first pressure vessel within the previously defined temperature range. In this way, even under such extreme environmental conditions, safe vehicle operation can potentially be ensured immediately after refueling. These conditions can also be maintained, in some cases, by drawing fuel simultaneously from all containers.

[0027] Generally, the temperature of the filling gas in a large pressure vessel is higher than in a smaller one. To reduce the filling gas temperature in the larger vessel, the smaller vessel can be at least partially filled from the larger one after it has been filled. The withdrawal of gas from each vessel can be stopped once the respective temperature threshold is reached.

[0028] In an advantageous embodiment of the method according to the invention, the first pressure vessel is refilled with fuel from the second pressure vessel after at least partial emptying. The refilling of the first pressure vessel can be carried out without the temperature restrictions of the consumer, such as a fuel cell or an internal combustion engine. As described above, the temperatures in the first pressure vessel can adjust to the previously defined temperature range more quickly than in the second pressure vessel. This embodiment can be particularly advantageous when more than two pressure vessels with different volumes are present in the pressure vessel system, since a first pressure vessel with a smaller volume can always be filled from a second pressure vessel with a larger volume, while fuel can simultaneously be drawn from another first pressure vessel.

[0029] In a further advantageous embodiment of the method according to the invention, the withdrawal of fuel from the first pressure vessel or the second pressure vessel is controlled by a control unit, wherein the pressure vessels each have a withdrawal valve and the control unit actuates the withdrawal valves, the control unit receiving information about the temperature of the fuel in the first pressure vessel and in the second pressure vessel and comparing these temperatures with a previously defined temperature window. Optionally, the temperature information downstream of the pressure regulator can also be measured or calculated by the control unit using a model and included in the evaluation. The pressure vessels typically each have a withdrawal valve, wherein each withdrawal valve in the pressure vessel system can be actuated separately. In this way, the method according to the invention can be easily implemented.

[0030] According to a second aspect, the stated problem is solved by a device for carrying out the method according to the invention, wherein the device comprises a pressure vessel system with a first pressure vessel with a first volume and a second pressure vessel with a second volume, wherein the first volume is smaller than the second volume, wherein the first pressure vessel and the second pressure vessel each have a withdrawal valve, and the device includes a control unit, wherein the withdrawal valves can be controlled by the control unit, and wherein information about the temperature of the fuel in the first pressure vessel and in the second pressure vessel can be received by the control unit. For example, the pressure vessels can have temperature sensors that can transmit the temperature to the control unit. The control unit can be installed in the vehicle independently of the pressure vessel system in a space-saving manner.

[0031] In an advantageous embodiment of the device according to the invention, the first pressure vessel and the second pressure vessel each have a substantially cylindrical segment, wherein the substantially cylindrical segment of the first pressure vessel has a diameter that is smaller than the diameter of the substantially cylindrical segment of the second pressure vessel. Since the compression work performed is proportional to the volume of the pressure vessel, and the volume of a pressure vessel with a substantially cylindrical central section is in turn directly proportional to its length and disproportionately proportional to its diameter (with the diameter having a squared effect on the volume), a greater effect can be achieved by changing the diameter than by changing the length of the pressure vessel.Regarding the surface area of ​​the pressure vessel, the effect of changing the diameter is greater than that of varying its length.

[0032] In a further embodiment of the device according to the invention, the control unit comprises a data processing system, wherein the data processing system includes means for carrying out the method according to the invention. A data processing system can ensure the automated execution of the method at high speed.

[0033] The embodiments described above can be used individually or combined with each other as desired. Detailed description of the invention

[0034] The invention is explained in more detail below with reference to exemplary embodiments and the drawings. These show Fig. 1 a flowchart of the inventive method 100; Fig. 2 a pressure vessel system according to the invention 10.

[0035] Fig. 1 Figure 1 shows a flowchart of the method 100 according to the invention. The method 100 starts at process start 110 with the commissioning of a consumer (not shown) to be supplied with fuel from a pressure vessel system 10, for example, a vehicle with a fuel cell, wherein the fuel is hydrogen stored in the pressure vessel system 10. In the fuel cell, electricity is generated from the hydrogen, for example, for an electric motor to drive the vehicle. The pressure vessel system 10 has a first pressure vessel 11 and a second pressure vessel 12 (see also Figure 11). Fig. 2The fuel temperature in the second pressure vessel 12 is ϑ 2. The consumer, for example a fuel cell, requires the fuel at a temperature within a consumer-specific temperature window TB, where the temperature window TB is defined by a lower limit temperature ϑ g, u and an upper limit temperature ϑ g, o. For a fuel cell, these temperatures are approximately 70 °C for the lower limit temperature ϑ g, u and approximately 85 °C for the upper limit temperature ϑ g, o. In the method according to the invention, immediately after the start in step 120, it is checked whether the fuel temperature ϑ 2 in the second pressure vessel 12 is within the previously defined temperature window TB, i.e., whether the fuel temperature ϑ 2 in the second pressure vessel 12 is between the lower limit temperature ϑ g, u and the upper limit temperature ϑ g, o, whereby the temperatures at the outlet of the pressure reducer can be checked. ϑ g , u ≤ ϑ 2 ≤ ϑ g , o

[0036] If this is the case, the "Yes" output Y of the query is selected, and in step 300, fuel is extracted from the second pressure vessel 12. If the fuel temperature ϑ₂ in the second pressure vessel 12 is not between the lower limit temperature ϑ₀,u and the upper limit temperature ϑ₀, the "No" output N is selected in step 120, and in step 200, fuel is extracted from the first pressure vessel 11. In step 130, the system continuously queries whether the process should be stopped, i.e., whether power generation in the fuel cell should be stopped. If this query is answered with "Yes," the fuel extraction process is stopped after the "Yes" output Y in step 140. If, however, the question is answered with "No," the "No" output N is selected, and the process continues with step 120, i.e., the query to determine whether the fuel temperature ϑ₂ in the second pressure vessel 12 is within the previously defined temperature window TB.It is also possible to reduce the power output of the fuel cell if a predicted future temperature drop below the limit is likely, thereby preventing or at least postponing the shutdown.

[0037] Fig. 2Figure 1 shows a pressure vessel system 10 according to the invention. A first pressure vessel 11 and a second pressure vessel 12 are installed in a vehicle chassis 20. The vehicle chassis 20 is shaped such that the second pressure vessel 12 has a diameter D2 and the first pressure vessel 11 has a diameter D1, wherein the first diameter D1 is smaller than the second diameter D2. The first pressure vessel 11 has a first volume V1 and the second pressure vessel 12 has a second volume V2, wherein the first volume V1 is smaller than the second volume V2.If the fuel in the second pressure vessel 12 has a temperature ϑ₂ outside a permissible temperature window TB previously defined by a lower limit temperature ϑ₀,u and an upper limit temperature ϑ₀, in particular if the compression work performed during filling results in a higher temperature ϑ₂ than the upper limit temperature ϑ₀, fuel is first at least partially withdrawn from the first pressure vessel 11 before fuel is withdrawn from the second pressure vessel 12. This allows the fuel in the second pressure vessel 12 time to cool below the upper limit temperature ϑ₀ through heat exchange with the surroundings. At the very least, this allows any cooling device (not shown) for the fuel to be smaller. Furthermore, the energy required for cooling the fuel can be minimized. In certain cases, it may even be possible to completely forgo active fuel cooling.

[0038] The embodiments shown here are merely examples of the present invention and should therefore not be interpreted as limiting. Alternative embodiments considered by a person skilled in the art are likewise covered by the scope of protection of the present invention. List of reference symbols used

[0039] 10 Pressure vessel system 11 First pressure vessel 12 Second pressure vessel 13 Extraction valve 20 Vehicle chassis 100 Procedure 110 Process start 120 Check if the fuel temperature ϑ2 in the second pressure vessel 12 is within the previously defined temperature window TB (ϑg,u ≤ ϑ2 ≤ ϑg,o) 130 Check if the process should be stopped 140 Process stop 200 Fuel extraction from the first pressure vessel 11 300 Fuel extraction from the second pressure vessel 12 D1 First diameter D2 Second diameter V1 First volume V2 Second volume Y Yes output N No output ϑ1 Fuel temperature in the first pressure vessel ϑ2 Fuel temperature in the second pressure vessel ϑg,u Lower limit temperature

Claims

1. A method (100) for removing a fuel from a pressure container system (10) with a first pressure container (11) with a first volume (V1) and a second pressure container (12) with a second volume (V2), wherein the first volume (V1) is smaller than the second volume (V2), characterized in - that the fuel is initially at least partly removed from the first pressure container (11) before the fuel is removed exclusively from the second pressure container (12), provided that the fuel in the second pressure container (12) has a temperature (ϑ2) outside a previously defined permissible temperature window (TB), or - that the fuel is initially at least partly removed from the second pressure container (12) before the fuel is removed exclusively from the first pressure container (11), provided that the fuel in the second pressure container (12) has a temperature (ϑ2) within a previously defined temperature window (TB), wherein the fuel removal from the second pressure container (12) is stopped and switched to the first pressure container (11) as soon as the temperature (ϑ2) of the fuel from the second pressure container (12) leaves the previously defined temperature window (TB).

2. The method (100) according to claim 1, characterized in that after an at least partial emptying the first pressure container (11) is filled up with fuel from the second pressure container (12).

3. The method (100) according to any one of the preceding claims, characterized in that the removal of fuel from the first pressure container (11) or the second pressure container (12) is controlled via a control unit, wherein the pressure containers (11, 12) each have a removal valve and the control unit actuates the removal valves, wherein the control unit receives information about the temperature of the fuel in the first pressure container (11) and in the second pressure container (12) and compares these temperatures to a previously defined temperature window (TB).

4. A device for carrying out the method (100) according to any one of the preceding claims, characterized in that the device has a pressure container system (10) with a first pressure container (11) with a first volume (V1) and with a second pressure container (12) with a second volume (V2), wherein the first volume (V1) is smaller than the second volume (V2), wherein the first pressure container (11) and the second pressure container (12) each have a removal valve and the device has a control unit, wherein the control unit is configured for carrying out the method according to any one of the preceding claims and the removal valves can be actuated by the control unit, wherein information about the temperature of the fuel in the first pressure container (11) and in the second pressure container (12) can be received by the control unit.

5. The device according to claim 4, characterized in that the first pressure container (11) and the second pressure container (12) each have an essentially cylindrically shaped segment and the essentially cylindrically shaped segment of the first pressure container (11) has a diameter (D1), which is smaller than the diameter (D2) of the essentially cylindrically shaped segment of the second pressure container (12).

6. The device according to any one of claims 4 or 5, characterized in that the control unit has a system for data processing, wherein the system for data processing comprises means for carrying out the method according to any one of claims 1 to 3.