It is known to drive motor vehicles, for example, by means of hydrogen or natural gas and to store this fuel as a condensed gas in a tank in the motor vehicle. For this liquefied storage, special compression-proof tanks are required which, because of the low storage temperatures, should have a very good insulation. In this case, it is known to use double-walled vacuum-insulated tanks for avoiding the entering of heat from the environment.
Thus, the storage of, for example, hydrogen in mobile vehicles frequently takes place in the form of low-temperature liquefied hydrogen, as condensed gas, since, in this condition, because of the high energy density (in contrast to a storage of warm compressed hydrogen gas) a high range can be achieved which is advantageous for vehicles.
The low-temperature liquid hydrogen supply is stored in the vehicle in the boiling condition in a thermally very well insulated compression-proof tank. The energy density of the boiling hydrogen becomes maximal by storage at a temperature slightly above the boiling temperature at an ambient pressure, approximately 20 K. In the currently technically implemented storage tanks, the hydrogen is typically present at temperatures of from approximately 21 K to approximately 27 K and the corresponding boiling pressures of approximately 2 bar (abs.) to approximately 5 bar (abs.).
In the lower part of the storage tank, the boiling hydrogen is present as a liquid phase with a denser mass (in the following also called LH2) and above the latter, as a gaseous phase (in the following also called GH2).
The direct delivery of the hydrogen (in the following also called H2) from the storage tank into a forward-flow pipe toward a conditioning or consuming device, in the simplest case, takes place by way of the static pressure difference existing between the tank interior and the environment or by means of a targeted pressurization of the storage tank. In principle, it is conceivable in this case to deliver predominantly LH2 or only GH2 as a result of the geometrical design of the forward-flow pipe starting in the tank interior.
From such a cryogenic tank, H2 stored in a boiling condition is generally removed from the gaseous phase as GH2. If H2 is removed from the liquid phase as LH2, in the case of a mobile application, the following conditioning devices, for example, pressure intensifiers, or the operating mode of a consuming device are nevertheless designed for the delivery of GH2. This is necessary because, as a result of possible deviations from the normal position of the mobile tank or as a result of dynamic accelerated conditions, the inflow opening of a removal pipe for LH2 may systematically be temporarily surrounded by flow also at high levels of the gaseous phase. In the course of the evacuation of the mobile tank, this may take place long before the point in time at which the gaseous phase in an identical immobile tank reaches the inflow opening of the LH2 removal pipe by pure removal. For this reason, H2 is predominantly removed from the gaseous phase in the case of mobile applications.
During the H2 removal, heat is supplied to the storage tank which leads to the evaporation of LH2 in the tank and thus to maintaining a tank pressure which is required for the delivery and which otherwise would fall so low as a result of the removal that a delivery would not longer be possible. This heating required for maintaining the pressure takes place by means of a separate heating device, which may be constructed, for example, as an electrically operated heating element, or, for example, directly by feeding heated gaseous H2, which was branched off in a targeted manner from a heated forward flow and is guided (back) into the interior tank.
According to the current state, mobile storage tanks have a removal device for the cryogenically stored fuel which consists at least of one removal pipe having a shut-off valve accommodated close to the tank. However, in most cases, the removal device has at least two removal pipes with at least one shut-off valve respectively,—a first removal pipe for the removal of condensed gas (LH2) and a second removal pipe for the removal of gas (GH2)—.
German Patent Document DE 37 41 145 C2 (U.S. Pat. No. 4,932,214 A1) describes a removal system for liquid nitrogen having a delivery unit arranged outside a storage tank, which delivery unit is connected with the storage tank by way of a suction pipe. On the input side of the delivery unit, a tank-side shut-off valve is provided in the suction pipe, and, on the output side of the delivery unit, an engine side shut-off valve is provided in the feed pipe to the internal-combustion engine. Both shut-off valves are controlled by way of a start-up control of the delivery pump and are illustrated in the drawing as electrically operated solenoid valves.
This has the disadvantage that, in the event of a leakage in the area of the delivery unit and of the shut-off valves, hydrogen may escape into the environment and, together with air, an explosible mixture may be created there, which requires a monitoring of the components carrying the hydrogen by means of sensors, in order to provide a ventilation in time. In this case, it is definitely not easy to avoid leakages in the cryogenic storage area in the case of electrically operated valves, because electromagnetic force is available only to a limited extent as a result of design limits when used in vehicles.
One object of certain embodiments of the present invention is to provide remedial measures for these and other disadvantages.
According to certain embodiments of the invention, a motor vehicle having a consuming device operable by means of cryogenically stored fuel, particularly an internal-combustion engine, and having a tank, particularly a cryogenic tank, for storing the fuel as condensed gas, the tank having a removal device for the cryogenically stored fuel, which removal device consists of at least one removal pipe having a shut-off valve, is characterized in that the shut-off valve is operated by means of compressed air.
This has the advantage that high valve contact pressure forces can be implemented which, for example, are higher than 1,000 Newton, in order to improve the tightness in the cryogenic area. The valve contact pressure forces are generated by stiff springs which can be released pneumatically. These high contact pressure forces at the valve face advantageously reduce also the susceptibility of the shut-off valve to dirt and particles which, in turn, has the result that no filters have to be installed for particles in the micrometer range. This reduces the pressure losses in the tank system, which decreases, for example, the fuelling times, increases the range, etc.
In a preferred embodiment of the invention, the removal device has at least two removal pipes, each having at least one shut-off valve—a first removal pipe for the removal of condensed gas and a second removal pipe for the removal of gas—. This has the advantage that the supply of the consuming device with gas is reliably ensured.
In another preferred embodiment of the invention, the removal device is also used as a filling device for cryogenically stored fuel. This has the advantage that a separately constructed filling device can be eliminated.
When compressed air for operating the shut-off valves is generated by means of a compressed-air system, sufficient compressed air is always available. In addition, the latter can also be used for other purposes, or a compressed-air system, which is present anyhow, is additionally used for operating the shut-off valves. This can advantageously be technically implemented in a cost-effective manner and without high expenditures.
Furthermore, in an advantageous embodiment, certain closed-off areas are constructed in the tank or close to the tank, particularly a secondary system capsule, which areas have a device for their sweeping with compressed air.
In this manner, areas or elements, such as shut-off valves, in which or on which leakages may form, as a result of a closed-off accommodation separate from the environment, can be swept with compressed air by way of a sweeping system when sensors detect an increased gas concentration in the closed-off area. The compressed air for sweeping the closed-off areas can then also be generated by means of the compressed-air system which is part of the motor vehicle. In addition, the outgoing air from the shut-off valve actuators, which occurs when the shut-off valves are closed, can also be used for the sweeping.
In another advantageous embodiment of the invention, the compressed-air system has a compressed-air supply control which, in an alternative manner, either sweeps the closed-off areas or operates the shut-off valves.
This has the advantage that both functions—the sweeping of the gas-enriched zones and the controlling of the shut-off valves—can be carried out by one system, which leads to a reduction of costs.