Procedures for cleaning aircraft fuel tanks

Abstract

The invention relates to a method for cleaning aircraft tanks (92), wherein the aircraft tank (92) is emptied, comprising the steps: a) Opening at least one access opening (93) to the interior of the aircraft fuel tank (92); b) Inserting a hand-held cleaning gun (20) connected via a hose (10) to a cleaning device (1) having a steam outlet nozzle (21) and a suction nozzle (22), wherein the steam outlet nozzle (21) is designed for the directed emission of steam provided by the cleaning device (1) and the suction nozzle (22) is designed for extraction by means of a negative pressure generated by the cleaning device (1), wherein the steam outlet and the extraction are coordinated such that a locally limited cleaning space (50) for the steam is formed in front of the cleaning gun (20); c) Guiding the cleaning gun (20) along the surfaces to be cleaned inside the aircraft tank (92) with the steam outlet and extraction activated, such that the cleaning gun (20) and the surface do not touch and at least parts of the surface are in the local cleaning space (50).

Description

[0001] The invention relates to a method for cleaning aircraft fuel tanks.

[0002] Fuel in aircraft tanks can become contaminated. Besides contaminants introduced through openings, for example during refueling or maintenance, bacteria, mold, and fungi can form in the tank, especially during extended periods of inactivity. These contaminants—at least if they are not firmly attached to the tank's inner surfaces—also lead to fuel contamination. However, once microbial contamination of the tank's inner walls is treated with suitable, known toxic biocides, the fuel becomes contaminated by biomass—in this case, in the form of killed microbes. Even excretions from living microbes can contribute to fuel contamination.

[0003] To prevent fuel contaminants from entering the aircraft's propulsion system, fuel filters are known that filter out solid particles above a predetermined size from the fuel during operation. A disadvantage of this prior art is that, particularly with heavy fuel contamination, the fuel filter can become clogged during operation, posing a safety risk.

[0004] If there is significant contamination of the tank or the fuel it contains, particularly by microbes, it is therefore standard practice – especially to avoid the risk of filter clogging – to clean the affected tank by opening it and conducting a so-called "tank inspection." Such tank inspections are complex and can therefore only be carried out by specially qualified and trained personnel. They typically take several days, also due to preliminary de-tanking and venting steps, during which time the aircraft with the tank being cleaned usually occupies a hangar space continuously.

[0005] To clean an aircraft fuel tank according to best practices, the tank must be emptied, opened, vented, and tested to ensure that no hazardous substances remain. A specialist then accesses the interior of the tank through one or more manholes and manually cleans the accessible surfaces with a solvent mixture using rags and brushes. This process is time-consuming and may not be thorough enough, as, for example, biofilm is often only partially smeared and not completely removed.

[0006] Furthermore, for aircraft with a sufficiently robust fuel tank, it is known to perform tank cleaning using a high-pressure cleaner spraying hot water. The resulting contaminated water then collects at the lowest point of the fuel tank and must be pumped out from there.

[0007] The object of the present invention is to provide a method for cleaning aircraft tanks which is improved compared to the known prior art.

[0008] This problem is solved by a method according to claim 1. Advantageous further developments are the subject of the dependent claims.

[0009] Accordingly, the invention relates to a method for cleaning aircraft tanks, wherein the aircraft tank is emptied, comprising the following steps: a) Opening at least one access opening to the interior of the aircraft fuel tank; b) Inserting a hand-held cleaning gun connected via a hose to a cleaning device, having a steam outlet nozzle and a suction nozzle, wherein the steam outlet nozzle is designed for the directed emission of steam provided by the cleaning device and the suction nozzle for extraction by means of a negative pressure generated by the cleaning device, wherein the steam outlet and the extraction are coordinated in such a way that a locally limited cleaning space for the steam is formed in front of the cleaning gun; c) Guiding the cleaning gun along the surfaces to be cleaned inside the aircraft tank with activated steam output and extraction, such that the cleaning gun and the surface do not touch and at least parts of the surface are in the local cleaning area.

[0010] Starting with an emptied aircraft fuel tank, from which all fuel has been removed using a method known from the prior art, e.g., by pumping or draining, the method according to the invention provides for cleaning the aircraft fuel tank with steam. In this process, steam is not only introduced through a steam nozzle to loosen the contamination, but is also immediately extracted. This extraction process removes not only the loosened contamination and any remaining fuel or other foreign matter, but also the steam itself. This prevents the interior of the tank from filling with steam or condensed water – although it cannot be ruled out that, for example, small amounts of the steam may be deflected by surfaces and components within the tank.cannot be completely vacuumed up again.

[0011] In principle, according to the invention, the steam is limited to an area in front of the cleaning gun by the configuration of the steam outlet nozzle and the extraction nozzle, as well as the operating parameters for steam outlet and extraction. The steam exiting the cleaning gun is therefore, after moving into the space in front of the cleaning gun, essentially extracted again by the cleaning gun itself. The area into which the steam exiting the cleaning gun spreads before being extracted again by the cleaning gun is referred to as the "locally limited cleaning area".

[0012] The steam loosens contaminants adhering to the tank, particularly biofilms. Thanks to the suction system, these loosened dirt particles are removed immediately, preventing splashing – as occurs, for example, when cleaning with a pressure washer. This eliminates the risk of re-soiling previously cleaned areas.

[0013] The actual implementation of the method according to the invention is easily possible for sufficiently trained personnel. As is known in the prior art for cleaning aircraft tanks, after the aircraft tank has been emptied, the access openings (so-called "manholes") regularly provided for cleaning are opened. Even if the aircraft tanks are generally not dimensioned in such a way that one can completely enter the tank, all internal surfaces of an aircraft tank can be reached for cleaning purposes through the – usually – multiple access openings of a tank.

[0014] In the inventive method, the cleaning gun, with steam output and suction activated, is guided along the surfaces to be cleaned in such a way that the surface in question, or successively different parts of the surface, are each located within the locally confined cleaning area. This allows them to be exposed to steam, which then draws away the loosened contaminants and other residues on the surface, such as any fuel residue. The cleaning gun is guided along the surface at such a distance that the cleaning gun and the surface do not touch, thus preventing potential damage from mechanical contact.

[0015] It is preferable for liquid and solid components to be separated and / or filtered out of the fluid extracted via the cleaning gun within the cleaning device. Separation allows larger contaminants and other substances, such as residual fuel, as well as water condensed from the extracted steam, to be removed from the fluid stream and ultimately disposed of. Naturally, further, usually downstream, material separation can be provided to separate, for example, biological contaminants from hazardous substances such as fuel and dispose of them properly. To prevent the uncontrolled release of residual substances into the environment that could not be removed from the fluid stream during separation, suitable filtration of the fluid stream can be provided after separation.It is also possible to rely solely on suitable filtration instead of separation, for which filter cascades are usually required.

[0016] It is preferred that the temperature of the surface to be cleaned, when the process is carried out correctly, does not exceed 80°C, preferably 70°C. Adherence to these temperature limits is advantageous to avoid potential damage to the aircraft fuel tank or the surface being cleaned. At the same time, it has been shown that excellent cleaning results can be achieved even at these higher temperatures.

[0017] As a helpful measure for adhering to the aforementioned temperature limit, in addition to appropriate training, where in particular the dwell time of the cleaning gun on a surface area must be taught as a parameter essential for the surface temperature, it is preferred that the temperature of the steam exiting the steam nozzle be between 80°C and 120°C, preferably 100°C. With corresponding steam exit temperatures, an increase in the surface temperature above 80°C is practically impossible, even if the process is carried out slightly differently than intended. At the same time, it has been shown that a good cleaning effect can be achieved with a corresponding steam exit temperature. To achieve a corresponding steam exit temperature, the steam can have a significantly higher temperature during generation (e.g., 180°C), since it is regularly generated at increased pressure (e.g.,at 10 bar) exits the steam outlet nozzle and thereby expands to ambient pressure (approx. 1 bar), during which time cooling also occurs.

[0018] The steam is preferably dry steam, i.e., steam containing no liquid components. If wet steam is used, its steam content is at least 90%, preferably at least 95%. The steam content is determined from the mass of the actual steam and the mass of the liquid components contained therein according to the formula... Steam content = mSteam, liquid components + mSteam.

[0019] The steam can, in principle, be generated from any type of water. However, it is preferable to generate the steam from softened or even demineralized water. By using appropriate water qualities, the maintenance and cleaning intervals of the cleaning device can be extended, as, for example, limescale deposits need to be removed less frequently. The cleaning device can also include a suitable softening or demineralization unit, with which the supplied water is first softened or demineralized before it is fed to the steam generator or a possible water tank for intermediate storage.

[0020] It is preferred to use a steam outlet nozzle suitable for generating a mechanical cleaning effect through the escaping steam. Although it may be sufficient to achieve a cleaning effect solely through the action of the steam in combination with the mechanical action of the suction, it has been shown that a kinetic action on the soiling achieved through suitably applied steam can significantly increase the cleaning effect.

[0021] The steam nozzle and / or the suction nozzle can generally be interchangeable on the cleaning gun. It is preferable, however, to select and attach the appropriate steam nozzle and / or suction nozzle to the cleaning gun for a specific cleaning task. For example, different steam nozzles and / or suction nozzles may be more advantageous in terms of cleaning results or efficiency for cleaning larger, smooth surfaces than those suitable for cleaning surfaces with riveted surfaces.

[0022] Preferably, the hose has a material-friendly outer surface and / or is conductive. Even if the cleaning gun is held at a distance from the surface to be cleaned, the hose connecting the cleaning gun to the cleaning device will come into contact with various edges and surfaces of the aircraft fuel tank. To prevent damage, the outer surface of the hose can be designed to be suitable for protecting the material. Conductivity of the hose is preferred to prevent the build-up of static charges.

[0023] The invention will now be described by way of example using an advantageous embodiment with reference to the accompanying drawing. It shows: Fig. 1: A schematic representation of the implementation of the method according to the invention.

[0024] In Fig.Figure 1 schematically shows the inventive method for cleaning a fuel tank 92 of an aircraft 90 using a cleaning device 1 designed for this purpose. The tank 92 is integrated into the wing 91 of the aircraft 90 and is empty. An access opening 93, shown by way of example, is already open.

[0025] The cleaning device 1 is connected via a hose 10 to a hand-held cleaning gun 20. The hose 10 has a material-friendly outer surface and is conductive.

[0026] The cleaning device 1 comprises a steam generator 2, which can generate dry steam at a temperature of 180°C and 10 bar from demineralized water. The steam thus generated travels via the hose 10 to the cleaning gun 20 and exits there through the replaceable steam nozzle 21, at which point the steam has a temperature of 100°C. Even if the steam is no longer completely dry in this state, the steam content is still 95% or more.

[0027] The cleaning gun 20 is further equipped with an interchangeable suction nozzle 22. For suction through this suction nozzle 22, the cleaning device 1 includes a suction pump 3. A separator 4 is provided on the suction side of the suction pump 3, and a filter 5 on the other side.

[0028] The steam generator 2 and the suction pump 3 are coordinated with each other, taking into account the steam outlet nozzle 21 and the suction nozzle 22, such that a locally limited cleaning space 50 is created in front of the cleaning gun 20: Steam exiting from the steam outlet nozzle 21 remains limited to this cleaning space 50 and is extracted from this cleaning space 50 by the suction nozzle 22.

[0029] The cleaning gun 20 is guided by suitably trained personnel, with steam output and suction activated, over the surfaces of the fuel tank 22 to be cleaned, such that a portion of the surface is always within the cleaning chamber 50, without the cleaning gun 20 and the surface in question touching. The steam exiting the steam nozzle 21 loosens contaminants adhering to the surface – depending on the design of the steam nozzle 21, also through mechanical cleaning action – which are then immediately extracted by the suction system. Other residues, such as residual fuel, are also removed by the suction system.

[0030] The fluid extracted by the suction pump 3 first enters the separator 4, where detached contaminants, fuel residues, etc., are separated from the fluid stream. The separator is designed to remove all solid and liquid components from the fluid stream. Any remaining residues are filtered out by the filter 5 to prevent environmental contamination.

[0031] Both the steam outlet nozzle 21 and the suction nozzle 22 are interchangeable on the cleaning gun. They can be selected to suit the specific cleaning task.

Claims

[1] A method for cleaning aircraft tanks (92), wherein the aircraft tank (92) is emptied, comprising the steps of: a) opening at least one access opening (93) to the interior of the aircraft tank (92); b) introducing a hand-held cleaning gun (20) connected to a cleaning device (1) via a hose (10) and having a steam outlet nozzle (21) and a suction nozzle (22), wherein the steam outlet nozzle (21) is designed for the directed discharge of steam provided by the cleaning device (1) and the suction nozzle (22) is designed for suction with the aid of a negative pressure generated by the cleaning device (1), wherein the steam outlet and the suction are coordinated with one another in such a way that a locally limited cleaning space (50) for the steam is formed in front of the cleaning gun (20); c) guiding the cleaning gun (20) along surfaces to be cleaned in the interior of the aircraft tank (92) with activated steam outlet and suction in such a way that the cleaning gun (20) and surface do not touch and at least parts of the surface are in the local cleaning space (50). [2] Method according to claim 1, characterized by that liquid and solid components are separated and / or filtered out from the extracted fluid in the cleaning device (1). [3] Method according to one of the preceding claims, characterized by that the temperature of the surface to be cleaned remains between 40°C and 80°C when the process is carried out correctly, preferably not exceeding 70°C. [4] Method according to one of the preceding claims, characterized by that the temperature of the steam when exiting the steam outlet nozzle (21) is between 80°C and 120°C, preferably 100°C. [5] Method according to one of the preceding claims, characterized by that the steam is dry steam or wet steam with a steam content of at least 90%, preferably at least 95%. [6] Method according to one of the preceding claims, characterized by that the steam is generated from softened or demineralized water. [7] Method according to one of the preceding claims, characterized by that a steam outlet nozzle (21) is used which is designed to produce a mechanical cleaning effect by means of the steam emerging therefrom. [8] Method according to one of the preceding claims, characterized by that the steam outlet nozzle (21) and / or the suction nozzle (22) is interchangeable and is suitably selected. [9] Method according to one of the preceding claims, characterized by that the hose (10) has a material-protecting outer surface and / or is conductive.

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