Method for heating a tank, heated tank and tank system

Abstract

The invention relates to a method for heating a tank (1), in particular a hydrogen tank, with a metallic wall (2) and / or lining (3), in which an excitation coil (4) surrounding the tank (1) is supplied with an alternating current, so that eddy currents are generated in the metallic wall (2) and / or lining (3), which heat the metallic wall (2) and / or lining (3). The invention further relates to a heated tank (1) and a tank system with at least one heated tank (1).

Description

[0001] The invention relates to a method for heating a tank, in particular a hydrogen tank. Furthermore, the invention relates to a heatable tank, in particular a heatable hydrogen tank, and a tank system comprising at least one tank according to the invention.

[0002] The preferred application area of ​​the invention is tanks and tank systems for storing hydrogen, in particular mobile tanks and tank systems, for example for fuel cell vehicles. State of the art

[0003] Hydrogen tank systems typically consist of several hydrogen tanks, each equipped with a tank valve and connected to each other via pipes. The hydrogen tank itself usually comprises a gas cylinder with a steel or fiber-reinforced plastic casing. If the latter is used, the inside of the gas cylinder is lined with a metal liner to ensure a tight seal. This metal liner can have a significantly thinner wall than a pure metal casing because the fiber-reinforced plastic absorbs tensile stresses. As a result, the tank is lighter than one made entirely of steel.

[0004] The pressure in a hydrogen tank is nominally up to 350 bar or up to 700 bar, depending on the design and fill level. When heated, for example during refueling or by sunlight, the pressure in the tank can increase by up to 25%. When hydrogen is drawn from the tank, the remaining hydrogen expands and cools down. If this cooling occurs at a low initial temperature, for example due to low ambient temperatures and / or during the start-up of a hydrogen-powered vehicle, the pressure can increase significantly.

[0005] In fuel cell systems, very low gas temperatures can occur. For example, the tank or tank system may be designed for ambient temperatures down to -40°C. When gas is drawn off, it can then cool down to as low as -60°C. At certain points in the tank valve, gas temperatures of -100°C or even below can be reached locally. This can impair the valve's function.

[0006] To avoid such low temperatures, heated gas cylinders have already been proposed. Pickling can be carried out, for example, using an electrically operated heating element. This can be inserted and secured into the bottom of the gas cylinder so that the heating element protrudes into the high-pressure gas volume. However, this requires that the heating element and its electrical connections be sealed against pressures up to 700 bar (plus a 25% safety margin). This solution is therefore very complex and prone to failure.

[0007] The present invention addresses the problem of providing a less complex solution for heating a tank, in particular a hydrogen tank. To achieve this problem, the method with the features of claim 1 and the tank with the features of claim 3 are proposed. Advantageous embodiments of the invention are described in the respective dependent claims. Furthermore, a tank system with at least one tank according to the invention is described. Disclosure of the invention

[0008] A method for heating a tank, in particular a hydrogen tank, with a metallic wall and / or lining is proposed. In this method, an excitation coil surrounding the tank is subjected to an alternating current, generating eddy currents in the metallic wall and / or lining, which heat the metallic wall and / or lining.

[0009] The proposed method has the advantage that the excitation coil, which serves as a heating device, can be positioned externally, thus eliminating the need for additional openings and therefore sealing points on the tank. Consequently, neither the stability nor the tightness of the tank is affected by the heating device. Furthermore, the excitation coil, positioned externally on the tank, can be electrically connected very easily.

[0010] A further advantage arises from the fact that the length of the excitation coil can be adapted to the length of the tank. In this way, the tank can be heated along its entire length. Heating via the excitation coil thus enables a uniform heat distribution within the tank, which distinguishes it from point heat sources, such as a heating cartridge. This significantly reduces the risk of local hot spots forming within the tank.

[0011] Furthermore, it is proposed that the excitation coil be supplied with alternating current, preferably a high-frequency alternating current, by a power electronic output stage. Suitable power electronics are generally present – ​​at least in a fuel cell system – so that the excitation coil can be supplied with the required electrical energy via this system. If necessary, an energy converter must be interposed to convert direct current into alternating current.

[0012] Furthermore, a heated tank, in particular a hydrogen tank, with a metallic wall and / or lining is proposed. The tank is surrounded by an excitation coil for generating eddy currents in the metallic wall and / or lining.

[0013] The proposed tank is particularly suitable for carrying out the previously described method according to the invention, so that the same advantages can be achieved. In particular, the tank can be effectively heated via the externally arranged excitation coil without impairing the stability or tightness of the tank. This is because no opening needs to be provided in the tank wall to insert a heating device into the tank. Consequently, additional sealing points, which – in the case of a hydrogen tank – would have to be sealed against high pressure, are also eliminated.

[0014] According to a preferred embodiment of the invention, the tank is at least partially cylindrical, and the excitation coil is arranged within a cylindrical section. For example, the tank can be a cylindrical gas cylinder. The cylindrical shape facilitates the mounting of the excitation coil, as it can simply be slid onto the tank from below or from above like a sleeve.

[0015] Preferably, the excitation coil is attached to the outside of the tank, for example, using tension straps and / or an adhesive bond. This attachment prevents the excitation coil from sliding back and forth on the outside of the tank. This is particularly advantageous if the tank is a mobile tank subject to dynamic stress. If a detachable attachment method is chosen, the excitation coil can be reused.

[0016] Furthermore, the excitation coil preferably has a plastic overmolding. The overmolding protects the excitation coil from external influences, such as moisture. It also reduces the risk of mechanical damage, which is inherent due to the excitation coil's external mounting on the tank.

[0017] In a further development of the invention, it is proposed that the excitation coil has sections that differ with respect to the number of winding layers and / or the pitch of the windings. In this way, individual sections or areas of the tank can be heated more or less intensely in order to distribute the heat in a targeted, inhomogeneous manner. Depending on the specific circumstances, this can also be advantageous.

[0018] According to a particularly advantageous embodiment of the invention, the tank is made of a fiber-reinforced plastic and has a metallic lining. For heating, eddy currents are generated in the metallic lining by means of the excitation coil, causing it to heat up and transfer the heat to the medium stored in the tank. Since the metallic lining is surrounded by a shell made of fiber-reinforced plastic, the heat is essentially only transferred inwards, thus enabling even more effective and efficient heating. At the same time, such a tank has a low weight, especially compared to a pure steel tank, which is particularly advantageous for mobile applications.

[0019] Furthermore, a tank system for a fuel cell system with at least one heated tank according to the invention is proposed. In this case, the tank serves to store hydrogen. Preferably, the tank system comprises several identical tanks connected to each other via tank valves and lines connected thereto. The identical design of the tanks does not preclude the possibility that the multiple tanks may have different storage volumes. drawing

[0020] The invention and its advantages are explained below with reference to the accompanying drawing or figure. This shows a schematic longitudinal section through a preferred embodiment of a tank according to the invention. Detailed description of the drawing

[0021] The accompanying figure shows a tank 1, for example for storing hydrogen. The tank 1 is essentially cylindrical. At its upper end, it has a tank valve 6 to which a line 7 is connected. The tank 1 can be connected to other, identical tanks 1 via the line 7, so that together they form a tank system.

[0022] Tank 1 has a wall 2 and a lining 3, with at least the lining 3 being made of a metallic material. The wall 2, on the other hand, can be made of a fiber-reinforced plastic to save weight. Tank 1 is surrounded by an excitation coil 4, which is overmolded with plastic. The overmolding 5 protects the excitation coil 4 from external influences. At its lower end, the excitation coil 4 is connected via electrical leads 9 to an AC / DC converter 8, through which the excitation coil 4 can be supplied with a high-frequency alternating current. This current generates eddy currents in the metallic lining 3 of tank 1, causing the lining 3 to heat up. The lining 3 then transfers this heat to the medium stored in tank 1, for example, hydrogen.

[0023] The excitation coil 4, located on the outside of tank 1, does not require contact with the metallic lining 3 of tank 1 to heat it. This means that the excitation coil 4 forms a non-contact heating device. Consequently, no opening needs to be provided in tank 1 to insert the heating device. This also eliminates the need for additional sealing points. The proposed heating device can therefore be implemented very easily, and heating tank 1 requires minimal effort.

Claims

[1] Method for heating a tank (1), in particular a hydrogen tank, with a metallic wall (2) and / or lining (3), in which an excitation coil (4) surrounding the tank (1) is supplied with an alternating current, so that eddy currents are generated in the metallic wall (2) and / or lining (3), which heat the metallic wall (2) and / or lining (3). [2] Method according to claim 1, characterized by , that the excitation coil (4) is supplied with an alternating current, preferably a high-frequency alternating current, by a power electronic output stage. [3] Heatable tank (1), in particular hydrogen tank, with a metallic wall (2) and / or lining (3), wherein the tank (1) is surrounded by an excitation coil (4) for generating eddy currents in the metallic wall (2) and / or lining (3). [4] Heated tank (1) according to claim 3, characterized by, that the tank (1) is at least partially cylindrical and the excitation coil (4) is arranged in the area of ​​a cylindrical section. [5] Heated tank (1) according to claim 3 or 4, characterized by , that the excitation coil (4) is attached to the outside of the tank (1), for example by means of tension straps and / or an adhesive connection. [6] Heated tank (1) according to any one of claims 3 to 5, characterized by , that the excitation coil (4) has a plastic overmolding (5). [7] Heated tank (1) according to any one of claims 3 to 6, characterized by , that the excitation coil (4) has sections which differ in the number of winding layers and / or in the pitch of the windings. [8] Heated tank (1) according to any one of claims 3 to 7, characterized by , that the tank (1) is made of a fiber-reinforced plastic and has a metallic lining (3). [9] Tank system for a fuel cell system with at least one heated tank (1) according to any one of claims 3 to 8.

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