EP3642549B1 - Cleaning method for surfaces in the internal volume of aircraft components though which a medium flows - Google Patents

Description

The present invention relates to a method for cleaning surfaces in the interior volume of an aircraft component through which air flows.

Known rinsing methods are usually used to clean dirt from hard-to-reach surfaces, such as those present in aircraft components through which air flows, in particular in heat exchangers. Soiling with a low chemical potential, consisting of predominantly non-polar substances, can mainly only be removed mechanically. In many operational applications, aircraft components through which air flows are coated with carbon-containing lubricants, fuels or other carbon-containing substances. Likewise, under certain conditions, substances from the environment such as dust, sand, combustion products, oils, fuels or lubricants can be deposited. In the case of carbon-containing compounds, coking and partial oxidation, which occurs in certain temperature ranges, are particularly problematic. In the case of aircraft components through which air flows, such as heat exchangers, which usually have pronounced undercuts and large, crooked surfaces in their interior volume due to their design, it is often not possible to remove this contamination using conventional methods due to a lack of accessibility. The surfaces in the inner volume are therefore largely only accessible for rinsing processes or through-flow cleaning processes. However, for cleaning in the rinsing process, strong reactive acids, or other strong chemical cleaning agents are used.

If cleaning is not possible due to the inaccessibility or the mechanical or chemical resistance of the dirt, the aircraft components to be cleaned must even be replaced. Furthermore, with the known cleaning methods, long process times are to be expected in some cases. The use of highly reactive cleaning agents is also problematic with regard to occupational safety, environmental pollution or possible residues on the surfaces. In particular, this relates to heat exchangers through which air flows for air conditioning purposes during operation.

From the DE 10 2009 009 938 A1 a device for cleaning drinking water pipes or sewage pipes in vehicles is known, with which the pipe to be cleaned can be charged at intervals with gas blocks, which move in individual pulses intermittently as a result of liquid and gas flows through the pipe, filling the pipe.

It is therefore the object of the invention to provide a cleaning process that enables effective and gentle removal of mechanically and chemically resistant dirt on surfaces that are difficult to access in the interior volume of an aircraft component through which air flows.

The invention solves this problem with a cleaning method according to independent claim 1. Advantageous further developments and improvements of the method specified in the independent claim are possible through the measures listed in the dependent claims.

According to the basic idea of the invention, a method for cleaning surfaces in the interior volume of an aircraft component through which air flows is proposed, which comprises at least the following steps: connecting the interior volume to be cleaned to a steam generator, generating a cleaning steam with a predetermined steam pressure and temperature by the steam generator, applying the to be cleaned Surfaces in the interior volume of the aircraft component through which flow occurs with the cleaning vapor, maintaining the vapor pressure and the temperature within the interior volume for the duration of a predetermined condensation time, generating a pressure drop in the interior volume of the aircraft component through which flow occurs in order to evaporate the part of the cleaning vapor condensed during the condensation time and transporting the cleaning vapor away from the internal volume the through-flow aircraft component with the cleaning vapor, maintaining the vapor pressure and the temperature within the interior volume for the duration of a predetermined condensation time, generating a pressure drop in the interior volume of the through-flow aircraft component for evaporating the part of the cleaning vapor condensed during the condensation time and transporting the cleaning vapor away from the interior volume of the through-flow Aircraft component through an outlet device. This process allows dirt to be removed from hard-to-reach surfaces. Cleaning steam or its condensate serves as the cleaning medium. When the cleaning steam is applied to the surfaces, it condenses on the surfaces and in particular on the soiling with suitably selected parameters such as steam pressure, temperature, steam content or condensation time. The steam condensate can penetrate into cracks, cavities and porosity of the dirt and be deposited. The stored condensate is then evaporated again by generating a rapid drop in pressure in the interior volume of the aircraft component through which the air flows. The phase change of the cleaning medium from liquid back to a gaseous state is associated with a rapid increase in volume of the cleaning medium. The evaporation of the condensate deposited in and on the contamination generates locally high compressive forces in the contamination, which lead to the contamination flaking off and detaching. These loosened contaminants can then be transported away together with the cleaning vapor through an outlet device from the interior volume of the aircraft component through which flow has taken place. Compared to mechanical methods, the method according to the invention is gentle on the surfaces to be cleaned, since no material is removed from the base material and health effects can be reduced by avoiding or minimizing the use of chemical cleaning agents.

It is particularly preferred that the interior volume of the aircraft component through which flow occurs is flushed with water after the cleaning vapor has been transported away. As a result, the effect of the cleaning process can be increased and its successful completion can be achieved. One or more rinsing cycles of the interior volume with water following the cleaning steps removes further contamination, which was removed from the surfaces by evaporation but remained in the interior volume of the aircraft component through which flow occurred while the cleaning vapor was being removed.

Furthermore, it is preferred that the cleaning steps are repeated with a predetermined cycle time. Efficient cleaning can be achieved by repeating the cleaning steps, with the degree of soiling decreasing with each subsequent cleaning cycle. Particularly stubborn dirt can be removed layer by layer, since the steam condensate does not have to penetrate the entire dirt during a cleaning application, but detaches the top layers of dirt with each cleaning cycle. The times of the individual cleaning cycles can thus be reduced.

It is also preferred to use water vapor as the cleaning vapor. Since the removal of dirt is essentially achieved via mechanical forces that arise from the rapid increase in volume during evaporation, it is usually not necessary to provide special chemical cleaning agents such as strongly reactive acids. water vapor can be controlled precisely over a known and reproducible pressure and temperature range and is particularly well suited for cleaning surfaces in the interior volume of heat exchangers, also because of its health and ecological safety, especially in heat exchangers through which air flows for air conditioning purposes. Depending on the type of dirt and the area of application of the aircraft component through which the air flows, it can be advantageous to add chemical cleaning agents to the cleaning steam in order to improve the cleaning effect.

In order to achieve a good cleaning effect, it has been shown that cleaning steam should preferably be used with temperatures of at least 388 Kelvin, at most 646 Kelvin and ideally in the range of 433 Kelvin. It is further preferred that the vapor pressure of the cleaning vapor is at least 0.17 MPa, at most 22 MPa and particularly preferably 0.61 MPa. A cleaning steam with a steam content of 80%, but at least 10%, is advantageous for an optimal cleaning effect. The saturated steam thus provided enables sufficient condensation during cleaning. Allowing the condensate to act on the dirt in the range of a few minutes can increase the cleaning effect. Depending on the type of contamination, this cycle time can be just a few seconds or up to an hour. In order to ensure sufficiently rapid evaporation of the condensate after a pressure drop has been generated, the pressure gradient should preferably be at least 0.01 MPa/s and particularly preferably 0.1 MPa/s.

In a particularly advantageous embodiment, the method is carried out with a steam generator that can be regulated with regard to steam pressure and/or steam temperature. The cleaning effect depends essentially on the condensing ability of the cleaning steam. In the case of dry steam, i.e. superheated steam, the ability to condense is severely limited and the soiling can even burn in further. Since a temperature and a vapor pressure can always be assigned to a so-called saturated steam, a suitable condensing capacity can be set via these parameters. In particular, the method can be adjusted to different pressure and temperature resistances of the surfaces to be cleaned.

In a particularly preferred embodiment, a further method step is provided, in which the cleaning steam transported away is reused by being condensed and cleaned and fed to the steam generator for renewed generation of cleaning steam in a subsequent cycle. Carrying out the cleaning method according to the invention with recycling and recycling of the cleaning medium lowers the costs of the cleaning process, since a new, unused cleaning medium does not have to be provided for each cycle and reduces the amount of used cleaning medium to be disposed of per cleaning process.

In a further preferred embodiment of the method according to the invention, an additional method step is provided in which the cleaning steam transported away runs through an aircraft component through which it has flowed for energy recovery before it is fed back to the steam generator. Part of the thermal energy of the heated waste steam can thus be used to generate steam again in a subsequent cleaning cycle.

According to a particularly preferred embodiment of the cleaning method according to the invention, the pressure drop in the interior volume of the aircraft component to be cleaned is realized by opening an outlet device. Vapor pressure is maintained during the condensation period by a nearly closed outlet device that separates the internal volume from a lower pressure region. Slight opening of the outlet device while maintaining the pressure allows excess condensate to be discharged and prevents the undesirable accumulation of large amounts of water under pressure. A larger accumulation of water would reduce the achievable pressure gradient. When the outlet device is opened, the pressure in the interior volume is suddenly reduced, which means that the condensate evaporates quickly and the cleaning vapor is transported away. It is particularly preferred that the outlet device comprises a switching valve. For this purpose, the outlet device and the switching valve must have an adapted flow cross section in order to generate a sufficiently large pressure gradient. Ideally, there is no air in the system during the process to optimize heat transfer and cleaning efficiency. This can be achieved by initially leaving the outlet device slightly open at the beginning of the printing in order to allow the air to be displaced and blown out by the steam. Alternatively, the barrel can be sucked off (vacuum) before printing begins.

It is also preferred that the degree of contamination of the cleaning vapor transported away is measured. By analyzing the degree of contamination and the type of contamination, the cleaning effect of the rinsing cycle can be concluded and process parameters such as Condensation time and vapor pressure can be adjusted. Furthermore, it is preferred to repeat the cleaning cycle until the measured degree of contamination reaches a predetermined threshold value, so that the cleaning can be completed.

In a further embodiment, the pressure loss is measured during a cleaning process of a standardized comparison component (comparative value) and the cleaning cycle is repeated automatically until the measured pressure loss of the aircraft component to be cleaned essentially corresponds to the comparison value. A comparison component can ideally consist of a new or cleaned component that is structurally identical to the aircraft component to be cleaned. By integrating the comparison component into the cleaning setup, ideally in a parallel setup, both aircraft components are exposed to the same cleaning conditions. The analysis of the pressure loss during the cleaning thus offers a control of the cleaning result without having to carry out tests in advance to establish standard parameters of the different aircraft components. The exact achievement of the comparison value does not have to be achieved as the end point of the process. The comparison value can also be formed by a previously defined tolerance range, which allows us to expect a degree of cleaning that is sufficient for the functionality of the aircraft component through which the air flows. A time-limited end signal is also advantageous, so that the automated repetition of the cleaning cycles is aborted if the comparison value is not reached within a previously defined maximum time. This prevents time-consuming cleaning of heavily soiled components that can no longer be cleaned, which ultimately have to be replaced.

Fig. 1

eine schematische Darstellung des Aufbaus für ein erfindungsgemäßes Verfahren zur Reinigung von Oberflächen im Innenvolumen einer durchströmten Flugzeugkomponente;

Fig. 2

eine schematische Darstellung des Prozessablaufs eines erfindungsgemäßen Verfahrens zur Reinigung von Oberflächen im Innenvolumen einer durchströmten Flugzeugkomponente;

Fig. 3a-3d

eine schematische Darstellung des Wirkprinzips des erfindungsgemäßen Reinigungsverfahrens; und

Fig. 4

eine schematische Darstellung einer weiteren Ausführungsform eines erfindungsgemäßen Reinigungsverfahrens.

The invention is explained below on the basis of preferred embodiments with reference to the accompanying figures. It shows:

1

a schematic representation of the structure for a method according to the invention for cleaning surfaces in the interior volume of an aircraft component through which air flows;

2

a schematic representation of the process sequence of a method according to the invention for cleaning surfaces in the interior volume of an aircraft component through which air flows;

Figures 3a-3d

a schematic representation of the active principle of the cleaning method according to the invention; and

4

a schematic representation of a further embodiment of a cleaning method according to the invention.

1 and 2 show schematically and by way of example the structure and the process flow of a cleaning method according to the invention. In the following, it is assumed that the aircraft component 2 through which flow is to be cleaned is a heat exchanger 2 . This should not be understood as a limitation, rather the cleaning method according to the invention can be used on a large number of aircraft components 2 through which air flows, with surfaces to be cleaned in their interior volume. First, the surfaces to be cleaned are integrated into the cleaning structure 1 . When surfaces to be cleaned in the interior volume of a heat exchanger 2, the heat exchanger 2 is a suitable adaptation 3 to the Cleaning structure 1 connected. A steam generator 4 is provided in the cleaning structure 1 . It is necessary for the adaptation 3 to form a pressure-tight connection between the steam generator 4 and the internal volume of the heat exchanger 2 to be cleaned. A liquid cleaning medium, which as a rule consists largely of water, is prepared for the requirements of the surfaces to be cleaned in step 6 preceding the cleaning. The upstream processing 6 can consist, for example, in a demineralization of the liquid cleaning medium. The course of the cleaning process according to the invention is explained below using water as the cleaning medium; However, other suitable cleaning media, in particular chemical cleaning agents or aqueous solutions of chemical cleaning agents, are also expressly to be included in the disclosure content of this application.

The treated water is fed to the steam generator 4, which causes the water to form steam. For example, a cleaning steam 7 can be generated under overpressure by supplying heat and a pump. The generation of the cleaning vapor 7 is preferably controllable. In order to achieve a good cleaning effect, it has been shown that cleaning steam 7 with temperatures of at least 388 Kelvin, a steam pressure of at least 0.17 MPa and a steam content of at least 10% should be used. Ideally, the temperature should be around 433 Kelvin, the vapor pressure around 0.8 MPa and the vapor fraction around 80%. Such saturated steam is advantageous in order to ensure sufficient condensation during cleaning.

In principle, dry steam, i.e. superheated steam, can also be used, whereby it should be noted that the cleaning performance is much lower and the soiling 9 can burn in and solidify further. In the area of saturated steam, steam pressure and temperature are always clearly assigned, which means that control can be adjusted by regulating pressure and temperature.

The cleaning steam 7 generated in the steam generator 4 is then applied to the surfaces to be cleaned in the inner volume of the heat exchanger 2 . The loading of the inner volume of the heat exchanger 2 with the generated cleaning steam 7 and the heating of the heat exchanger 2 to a suitable temperature is followed by a sufficiently long condensation time, in which the cleaning steam 7 can act on the surfaces to be cleaned and on the surfaces a cleaning steam condensate 8 can form. In this case, the condensation also takes place on the dirt 9 .

In the next step, a strong pressure drop 10 is generated. This can be realized, for example, by opening a switching valve 11 in an outlet device. The pressure gradient essentially determines the cleaning effect, since the rapid evaporation and thus the speed of the volume expansion of the deposited condensate 8 during the phase change from liquid to solid is determined by the pressure gradient. The pressure gradient should be at least a rate of about 0.01 MPa/s, ideally about 0.1 MPa/s. The cleaning steam 7 is then transported away together with the loosened dirt 9 through the opened outlet device.

The cleaning steps are repeated with a predetermined cycle time. Depending on the type of dirt 9, this can last between about 20 seconds and up to an hour is ideally a few minutes. In order to monitor the cleaning process, the waste steam 13, ie the emitted cleaning steam, is condensed and analyzed. This allows the cleaning effect and the successful completion of the cleaning process to be determined. Subsequent to the cleaning steps, further rinsing processes 14 , for example with water, can be provided in order to transport away loosened contamination 9 , which was loosened by the cleaning steam 7 but still remained in the inner volume of the heat exchanger 2 . During the rinsing process 14 with water, the pressure loss across the heat exchanger 2 can also be measured in an analysis step 15 as a further indicator of the degree of cleaning. After the last rinsing process 14, the heat exchanger 2 is dried with steam 33, openly cooled 34 and dried 35 and is then available as a cleaned heat exchanger 2'.

Energy recovery is provided as an optional step 16 for the cleaning process, which can be implemented by using a heat exchanger which is arranged between the outlet device and the water inlet 18 of the heat exchanger 2 and which makes the heat obtained from the exhaust steam 13 available for the steam generation 4 . The polluted waste steam 13, or the polluted waste water 13, can then be disposed of 36. In addition, the waste steam 13 can also be reused by a steam cleaning cycle being followed by water recovery 19, for example by separating 20 the contaminants 9 from the waste water 13, filtration of the water and providing the water treated in this way at the inlet 18 of the steam generator 4 is realized.

The mode of action of the detachment of the surface contamination 9 is in the Figures 3a to 3d shown schematically. The cleaning method according to the invention makes use of the natural nature of the dirt 9 on the surfaces to be cleaned. The dirt 9 accumulates on the base material 21 of the surfaces to be cleaned and is generally porous and has cavities 22 and cracks 23 . During the cleaning process, the surfaces and the dirt 9 are subjected to overpressure and the cleaning steam 7 ( Figure 3b ). During the condensation time, the cleaning steam 7 begins to condense on all surfaces and thus also on the dirt 9. The cleaning steam condensate 8 covers the surfaces and, due to the porosity of the dirt 9, begins to penetrate cracks 23 and cavities 22 and deposit there ( 3c ). In the next step, a pressure drop 10 is generated, which causes sudden evaporation and thus an increase in volume of the cleaning steam condensate 8 embedded in the dirt 9 . The pressure forces generated in this way and acting locally in the contamination 9 then lead to the contamination 9 flaking off and detaching 24 . 3d ).

The cleaning according to the invention can be used not only for porous or solid soiling, but also for example liquid or viscous films can be removed. The previously referred to figure 3 The mechanism of action described may be different in the case of porous or solid soiling other than that shown.

In 4 a concrete manifestation of the cleaning procedure is explained. In this case, a heat exchanger 2 via a first adaptation 3 connected to a pressure and temperature controllable steam generator 4. This is supplied at its water inlet 18 via a demineralization device 6 with process water and treated water from a water circuit 28 . An outlet of the heat exchanger 2 to be cleaned is connected to a switching valve 11 via a second adapter 3'. Pressure is built up in the heat exchanger 2 by means of the steam generator 4 . In the process, condensate 8 initially collects on the surfaces which have a lower temperature than the cleaning steam 7 that is generated. After a predetermined vapor pressure and/or temperature level has been reached, this state is maintained for a defined condensation time. The condensation time can vary as required and is within the normal range of around half a minute to around an hour. The condensate 8 is stored in the dirt 9 depending on the structure and composition of the dirt 9 and the duration of the condensation time in which the vapor pressure in the internal volume of the heat exchanger 2 is maintained. After the condensation time has elapsed, the switching valve 11 provided in the outlet device is fully opened, so that a strong pressure drop 10 occurs in the internal volume of the heat exchanger 2 . Due to the sharp drop in pressure 10, the accumulations of steam condensate 8 evaporate with a large increase in volume. So that a sufficiently large pressure drop rate is established, the outlet device, the switching valve 11 and downstream pipelines are provided with a sufficiently large flow cross section. For example, DN12 flow pipe cross sections have proven to be sufficient for an internal volume of a heat exchanger 2 to be cleaned that is subjected to steam pressure and is to be cleaned. For larger pressurized volumes, correspondingly larger flow tube cross sections must be selected. The pressure loss across the heat exchanger 2 can be analyzed 15 become. The steam-condensate mixture 7, 8 exits via the outlet device. The outlet device is fluidly connected to a condenser 30 . The steam-condensate mixture 7, 8 is transported away 26 and fed to the condenser 30, in which a complete condensation of the exhaust steam 13 transported away is to take place. At this point, it is advantageous to take samples of the condensed mixture and examine them for contamination and their composition 31 in order to be able to draw conclusions about the cleaning effect. Based on the knowledge gained in this step 31, the process parameters of the following cleaning cycles can be effectively adjusted. The waste water 13 from a cleaning cycle is collected in a separating tank 20, whereby the dirt 9 can be separated depending on the type, so that the cleaned water is fed to the steam generator 4 via a water circuit 28 and a water treatment 32 with filtration and thus returns to the process .

In principle, the mechanical stresses caused by the pressure fluctuations and flow forces in the inner volume of the heat exchanger 2 to be cleaned must be taken into account. Heat exchangers 2 often have sensitive constructions with small material wall thicknesses that can be damaged. However, due to the significantly lower density of steam compared to liquids, the flow-mechanical loads in a steam cleaning process are lower than in a rinsing process.

Claims (15)

1. Method for cleaning surfaces in the internal volume of an aircraft component (2) through which a medium flows, said method comprising at least the following steps:

   - connecting the internal volume to be cleaned to a steam generator (4),

   - generating a cleaning steam (7) having a predetermined vapour pressure and temperature, by means of the steam generator (4),

   - applying the cleaning steam (7) to the surfaces to be cleaned in the internal volume of the aircraft component (2) through which a medium flows,

   - maintaining the vapour pressure and the temperature within the internal volume for the duration of a predetermined condensation time,

   - generating a pressure drop (10) in the internal volume of the aircraft component (2) through which a medium flows, in order to vaporise the portion (8) of the cleaning steam (7) that condensed during the condensation time,

   - removing (26) the cleaning steam (7, 13) from the internal volume of the aircraft component (2) through which a medium flows, via a discharge device.
2. Method according to claim 1, characterised in that the internal volume of the aircraft component (2) through which a medium flows is rinsed with water following removal (26) of the cleaning steam (7).
3. Method according to either claim 1 or claim 2, characterised in that the steps are repeated in a manner having a predetermined cycle time.
4. Method according to any of the preceding claims, characterised in that water vapour is used as the cleaning steam (7).
5. Method according to claim 4, characterised in that the vapour pressure of the cleaning steam (7) is between 0.17 mPa and 22 MPa.
6. Method according to claim 4, characterised in that the vapour temperature of the cleaning steam (7) is between 388 K and 646 K.
7. Method according to claim 4, characterised in that the pressure drop (10) in the internal volume of the aircraft component (2) through which a medium flows is at least 0.01 MPa/s, preferably 0.1 MPa/s.
8. Method according to any of the preceding claims, characterised in that the vapour pressure and/or vapour temperature of the steam generator (4) can be controlled.
9. Method according to claim 4, characterised in that the removed cleaning steam (13) is recycled, by means of being condensed (30) and cleaned (32), and supplied to the steam generator (4) for generating a cleaning steam (7) again, in a subsequent cycle.
10. Method according to claim 9, characterised in that the removed cleaning steam (13) passes through a heat exchanger for the purpose of energy recovery (16), before being supplied to the steam generator (4) again.
11. Method according to any of the preceding claims, characterised in that the pressure drop (10) in the internal volume of the aircraft component (2) through which a medium flows is achieved by opening a discharge device.
12. Method according to claim 11, wherein the discharge device comprises a switch valve (11).
13. Method according to any of the preceding claims, characterised in that the degree of contamination of the removed cleaning steam (13) is measured.
14. Method according to claim 13, characterised in that the cleaning cycle is repeated until the measured degree of contamination reaches a predetermined threshold value.
15. Method according to any of the preceding claims, characterised in that

    - the pressure loss during a cleaning process of a standardised comparison component (comparative value) is measured, and in that

    - the cleaning cycle is repeated in an automated manner, until the measured pressure loss of the aircraft component (2) to be cleaned substantially corresponds to the comparative value.

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