EP2270414A1 - Water spray in exhaust heat exchanger to reduce efficiency losses - Google Patents

Abstract

The method involves modifying the thermodynamic characteristics of the exhaust gas deposition layer, is done in a heat exchanger (11) by injection of water (14). The heat transition of the exhaust gases, is obtained in the heat exchanger. The water is injected in time intervals of 1 hour or 2 hours. Independent claims are also included for: (1) a controller for water injecting system; and (2) a device for reducing power loss in heat exchanger.

Description

The invention relates to a method and a device for reducing power losses in exhaust gas heat exchangers.

In the field of decentralized energy supply, combined heat and power plants are frequently used which generate electrical energy by means of a motor, turbine or other thermal conversion aggregates via a generator. A significant proportion of the resulting heat energy is located in the exhaust. Depending on the type, the exhaust gas temperature is between 350 and 600 ° C. However, most applications are in the range of 420 to 500 ° C. Similar exhaust gas flows can also be found in EGR coolers, thermal gasification plants, boiler plants or industrial processes.

In order to achieve a high overall efficiency, depending on the application, so-called exhaust gas heat exchangers (also waste heat boilers or steam generators) are switched into the exhaust gas flow, which cool the exhaust gases and couple the energy emitted into heating circuits or steam grids.

Furthermore, EGR coolers are often used to reduce exhaust emissions in engines, which are used for cooling and return of the exhaust gas flow to the suction side of the unit.

Depending on the exhaust gas source, the fuel used or the mode of operation, it can lead to contamination of the heat exchanger surfaces. This leads due to the impeded heat transfer to a reduction in performance of the exhaust gas heat exchanger, which is to prevent it.

It is known from the prior art that exhaust gas heat exchangers are manually cleaned with high-pressure water or a brush during an operating standstill. A disadvantage of this approach, apart from the additional workload that a cogeneration plant during this cleaning process can not be operated, or that the exhaust gas heat exchanger must be disconnected from the exhaust stream.

It is also known from the prior art that in large combustion plants, deposits are removed by means of water lance blower by direct irradiation. By the Direct impingement of the water causes a thermal and mechanical shock through which deposits are to be removed. However, this is accompanied by a high load on the material.

Furthermore, it is known from the prior art that exhaust gas heat exchangers can be cleaned during operation by means of water injection. In this approach, a disadvantage is that the water consumption is high. A further disadvantage is that, when water is injected into a hot exhaust gas heat exchanger, thermal shocks may occur which pollute the material (eg the exhaust gas heat exchanger).

The invention has for its object to reduce power losses in exhaust gas heat exchangers so that the operation of the exhaust gas heat exchanger does not need to be adjusted and that water consumption and thermal shocks are low.

This object is achieved with a method according to claim 1, a controller according to claim 9 and a device according to claim 10.

Preferred embodiments are disclosed in the dependent claims.

The method of reducing power losses in heat exchangers involves injecting water into a heat exchanger. The injection of water is carried out so that the thermodynamic properties of the deposition layer are changed in the heat exchanger so that there is an improvement in the heat transfer properties.

With the help of the above-mentioned method, apparatus and control, the power losses in heat exchangers are reduced by the fact that the soot in the injection of water no longer deposits as a smooth layer but is roasted or roughened. The thus structured surface leads to increased turbulence in the film layer at the transition of the exhaust gas flow to the tube wall of the heat exchanger and thus to an improvement of the heat transfer coefficient α on the exhaust side. This improved heat transfer coefficient α compensates for the additional heat transfer resistance, which results from the deposition layer on the pipe wall. Furthermore, there is a compaction of the soot layer, which leads to a higher thermal conductivity λ of the soot layer, whereby the heat transport through the layer is improved. In some cases, the roughening of the exhaust gas deposition layer still has the effect that the injection of water causes parts of the exhaust gas deposition layer be removed in the pipe wall. A cycle, which can consist of several individual steps, is typically repeated every 1 to 24 h, with each individual injection process lasting between 10 and 600 s. The maximum duration of the injection process can be determined by the exhaust gas temperature in front of the heat exchanger falling below a predefined limit value during an injection process and / or reaching an almost stable level and / or not falling any further.

The injected water in a preferred embodiment of this invention has a water pressure of at least 3 bar and meets certain purity requirements. For example, the water should be softened to a hardness of less than 0.1 ° dH, the conductivity of the water should be less than 1500 μS / cm, the chloride content should be less than 20 mg / L, and the pH of the water should be range from 9 to 10.5. Furthermore, a droplet size of water in the range of 100 to 900 μm is preferred.

The longer the distance in the cycles, the lower the resulting water consumption and the less thermal shocks occur. Thermal shocks occur when water strikes exhaust heated parts (such as the heat exchanger and / or pipes).

liegt in einem bevorzugten Bereich von 10 bis 300. Der Wert von ε kann dahingehend optimiert werden, dass nur so viel Wasser eingedüst wird, wie tatsächlich nötig ist, um einen hohen Wärmeübergang im Wärmetauscher zu gewährleisten.Therefore, it is advisable to choose the amount of injected water in relation to the amount of exhaust gas flowing through the heat exchanger. The relationship $$\mathrm{\epsilon }\mathrm{=}\mathrm{water\; flow}\left[\mathrm{G}\mathrm{/}\min \right]\mathrm{/}\mathrm{Exhaust\; gas\; mass\; flow}\left[\mathrm{kg}\mathrm{/}\min \right]$$

is in a preferred range of 10 to 300. The value of ε can be optimized so that only as much water is injected as is actually necessary to ensure a high heat transfer in the heat exchanger.

In other exemplary embodiments of the present invention, one or more additional ingredients are added to the injected water. For example, the injected water may be mixed with air to effectively inject a water-air mixture. Furthermore, there is the possibility that the water mixed with a water-soluble substance is mixed, such as acid, alkali or detergent. Hereby, an effect of the injection can be further optimized by better dusting of the injected mixture and / or by additional chemical and / or physically influencing the soot surface and / or neutralizing acidic combustion residues.

Furthermore, it is possible to replace the water entirely by an acid, alkali or detergent. In this way, a better dusting of the injected liquid and / or additional chemical / physical influence of the soot surface and / or neutralization of acid combustion residues can also be achieved.

In another possible embodiment of the present invention, there is the possibility that the injection process is started either abruptly or that the amount of water during the Eindüsungsvorgangs is continuously raised from zero to a maximum value during a period of at least 1 and at most 30 s. Furthermore, at the end of the injection process, it is possible to reduce the amount of water either abruptly or continuously in said time period from the maximum value to zero. This can be done by short successive injection cycles or by continuously increasing / decreasing the injected liquid. This serves to control and influence the possibly occurring thermal shocks.

For example, at the beginning of the injection of water, the amount of water is abruptly or continuously in a period of at least 1, 2, 4, 6, 8, 10 or 15 s and / or at most 2, 4, 6, 8, 10, 15, 20, 25 or 30 s from zero to a maximum value, and / or becomes the end of the injection of water, the amount of water abruptly or continuously in a period of at least 1, 2, 4, 6, 8, 10 or 15 s and / or at most 2 , 4, 6, 8, 10, 15, 20, 25 or 30 seconds from said maximum value to zero.

A water injection process is typically initiated by opening a water valve and terminated by closing the water valve. A water injection process may be preceded by one or more steps or followed by one or more steps.

One of the steps before the water injection process is to start a water injection cycle followed by the verification of one or more criteria, such as: B. that compressed air is present at a pressure of at least 1 and at most 12 bar or that the exhaust gas flow rate exceeds a minimum limit or that the exhaust gas inlet temperature in the heat exchanger is greater than a target temperature, thereby preventing a cycle is started, if a plant is being approached.

If all of the above-mentioned criteria are typically met, compressed air flushing of water-bearing components of a used water injection system can take place before the water is injected. This step is particularly useful for removing debris from the nozzles and for pre-cooling the nozzles.

After the subsequent water injection process, a further compressed air flushing of water-bearing components of a used water injection system can be carried out. This serves to remove residual water, as ingredients of the water can permanently lead to encrustation of the pipes, nozzles or other water-bearing components.

The operation of the compressed air purging is initiated by opening a compressed air valve and terminated after a period in the range of 5 to 120 s by closing the compressed air valve. The compressed air has a preferred pressure in the range of 1 to 12 bar. The compressed air purging can be used to optimize the exhaust gas deposition layer in the heat exchanger (in terms of heat transfer).

Subsequently, recorded during the Wassereindüsungsvorgangs measured data, in particular of depressed water quantity, water pressure during injection, exhaust gas inlet temperature in the heat exchanger and exhaust gas outlet temperature can be stored or documented from the heat exchanger. These measurement data can be used to re-design and optimize injection duration, injection volume, and time interval between water injection operations of future injection operations.

Furthermore, a controller for a water-jet system is used to automatically carry out the method. Said control can be part of a water injection system.

The device for reducing power losses in heat exchangers comprises the following components: a heat exchanger, a water injection system and one or more nozzles. Said components are provided for varying the thermodynamic properties of the exhaust gas deposition layer in the heat exchanger by injecting water by means of water injection system in the heat exchanger. As a result, a higher heat transfer of exhaust gases is achieved on the heat exchanger.

The device for reducing power losses in heat exchangers can, in addition to the heat exchanger of the water injection system and the nozzles, also comprise a cover, on which the nozzles are mounted, each nozzle being connected by pipeline to the water injection system. The said cover is located on the exhaust gas inlet side in front of the heat exchanger, so that the nozzles are aligned substantially parallel to the exhaust gas flow in the heat exchanger. Preferably, nozzles are mounted on the lid, flanged into which nozzle lances or screwed. In a preferred embodiment of the invention, the nozzles are mounted with the aid of the nozzle lances on the lid under an insulating layer, that only the tips of the nozzles are exposed to thermal stresses by hot exhaust gases and the pipes and water injection system are at least partially protected from thermal stress.

Furthermore, it is possible to install the nozzle / nozzles on a radially located at the heat exchanger inlet or before stored piping injector. This can be done both in the flow direction and against the flow direction of the exhaust gas.

Furthermore, it is recommended to avoid the contact of sensitive parts with water through a bulkhead plate and / or through the use of thin inserts of sheet metal, ceramic or other insulating and / or liquid-repellent materials called inlays. The partition plate prevents water accumulated in the area in front of the heat exchanger inlet side from coming into contact with sensitive components (eg the high-temperature seal of the cover).

Furthermore, it is possible to prevent thermal shock damage by having parts (eg wall parts of the chamber on the exhaust gas inlet side of the heat exchanger) having a different wall thickness or being made of a material that is less sensitive to thermal shocks or cooled by additional measures become.

The water injection system comprises in its preferred embodiment, a controller / control relay, piping, solenoid valves, a compressor or a connection for external compressed air supply. The water injection position can also include water filters, pressure switches, pressure monitors, check valves, data storage, additional pressure vessels to increase the pressure volume and a flow controller. The flow controller is used to record the amount of injected water so that an error message can occur if the set limit is undershot or exceeded. Likewise, an error message can occur if the flow controller displays a flow despite closed solenoid valves.

Preferably, the number of nozzles n is selected depending on the diameter d of the heat exchanger. For example, n = 1 for d <400 mm, n = 3 for 400 mm ≦ d <600 mm, n = 5 for 600 mm ≦ d <800 mm and n = 12 for 800 mm ≦ d <1500 mm.

The nozzles are preferably arranged so that injected water as evenly as possible covers the entire exhaust gas inlet side of the heat exchanger, so that the density variation of the injected water over the entire exhaust gas inlet side is a maximum in the range of 5% to 80%. In some embodiments of the present invention, the positioning of the nozzles is in response to the position of an exhaust gas entry port through which the exhaust gas enters the space in front of the heat exchanger.

The distance of the nozzles to the exhaust gas inlet side of the heat exchanger is selected as close as possible, provided that the abovementioned maximum density variation of the injected water is not exceeded.

Preferably, stainless steel nozzles are used with spray angles of either 15 °, 30 °, 45 ° or 90 °, which nozzles should be capable of producing water droplets having a droplet size in the range of 100 to 900 μm. In another embodiment of the present invention, 2-fluid nozzles are used, with which water can be injected by means of compressed air. Furthermore, it is possible to use nozzle heads with a plurality of nozzles, so that optionally or simultaneously in or against the direction of an exhaust gas flow can be injected. Furthermore, different types of nozzles can be combined with each other.

The above-mentioned device optionally comprises one or more nozzles which serve to discharge excess water or in which temperature sensors can be accommodated with which the exhaust gas inlet temperature into the heat exchanger or the exhaust gas outlet temperature from the heat exchanger can be measured.

In a further embodiment of the invention, the device comprises a plurality of heat exchangers, which are part of a multi-stage heat exchanger system, and several water injection systems, so that each heat exchanger is associated with a water injection system or only a part of the heat exchanger is associated with a water injection system, wherein each water injection system with at least one nozzle connected is.

Figur 1a

eine schematische Ansicht einer Vorrichtung zur Eindüsung von Wasser in einen Abgaswärmetauscher;

Figur 1b

eine schematische Ansicht der Abgaseintrittsseite eines Abgaswärmetau- schers, worin zusätzlich die möglichen Positionen von Düsen angedeutet sind;

Figur 2

eine schematische Detailansicht des Deckels mit Isolierschicht, Inlay, Rohr- leitungen, Verteiler, Düsenlanze und Düsen;

Figur 2b

eine schematische Detailansicht des Injectors mit Isolierschicht, Inlay, Rohrleitungen und Düsen;

Figur 3

eine schematische Ansicht einer Wassereindüsungsanlage;

Figur 4

den Ablauf eines Zyklus zur Wassereindüsung;

Figur 5

ein Diagramm mit der Abgasaustrittstemperatur aus einem Abgaswärme- tauscher als Funktion der Betriebszeit des Abgaswärmetauschers;

Figur 6a

eine schematische Ansicht von Abgasablagerungsschichten in einem Ab- gaswärmetauscher ohne Wassereindüsung; und

Figur 6b

eine schematische Ansicht von Abgasablagerungsschichten in einem Ab- gaswärmetauscher mit Wassereindüsung.

Other aspects of possible embodiments of the invention will be apparent from the FIGS. 1a, 1b . 2, 2b . 3 . 4 . 5 . 6a and 6b clear. Showing:

FIG. 1a

a schematic view of an apparatus for injecting water into an exhaust gas heat exchanger;

FIG. 1b

a schematic view of the exhaust gas inlet side of a Abgaswärmetau- shear, wherein additionally the possible positions of nozzles are indicated;

FIG. 2

a schematic detail view of the lid with insulating layer, inlay, piping, distributor, nozzle lance and nozzles;

FIG. 2b

a schematic detail view of the injector with insulating layer, inlay, piping and nozzles;

FIG. 3

a schematic view of a water injection system;

FIG. 4

the sequence of a cycle for water injection;

FIG. 5

a diagram with the exhaust gas outlet temperature from an exhaust gas heat exchanger as a function of the operating time of the exhaust gas heat exchanger;

FIG. 6a

a schematic view of exhaust gas deposition layers in an exhaust gas heat exchanger without water injection; and

FIG. 6b

a schematic view of exhaust gas deposition layers in a waste gas heat exchanger with water injection.

Although figures in the exhaust gas heat exchangers referred to below are mentioned in the figures below, it goes without saying that corresponding embodiments are also possible for heat exchangers in general, for example also for exhaust gas recirculation coolers.

A possible embodiment of the invention is in FIG. 1a which shows a device for injecting water 14 shows. Exhaust gas flows into the vestibule of the exhaust gas heat exchanger 11 and then flows through the exhaust gas heat exchanger 11, forming an exhaust gas deposition layer (not shown) in the exhaust gas heat exchanger 11. With the help of injected water 14, this deposit layer is changed in its properties, whereby a higher heat transfer α of exhaust gases to the exhaust gas heat exchanger 11 and a higher thermal conductivity λ in the deposition layer is achieved. The higher heat transfer α is due to the fact that the injection of an exhaust gas deposition layer is formed with a rough surface that swirls past exhaust fumes. The higher thermal conductivity λ is achieved by virtue of the fact that the exhaust gas deposition layer formed by injection has a greater density than an exhaust gas deposition layer which has been formed without injection. The injection of water 14 takes place with the aid of a water injection system 12, which is connected via pipes 16 with nozzles 13. The nozzles 13 are mounted on a lid 15, which closes the antechamber before the exhaust gas heat exchanger 11. Also shows FIG. 1a a bulkhead 17, which prevents injected water 14 comes into contact with thermal shock sensitive parts of the system. About the nozzle 18 excess water can be derived.

For further protection of thermal shock sensitive parts, an inlay or an insulating layer may be installed between them and the exhaust stream. This inlay or insulation prevents injected water from coming in contact with the thermal shock sensitive parts. A shock-like cooling is thus avoided. The insulating function also reduces the surface temperature of the parts sensitive to thermal shock, and thus also the sensitivity of the parts for spontaneous cooling.

More details will be in the Figures 1b . 2 and 3 shown or mentioned only in the text (such as additional nozzles for thermocouples). Multi-stage systems with multiple exhaust gas heat exchangers 11 or more water injection systems 12 and corresponding to other pipes 16 and nozzles 13 are not shown, but correspond to a series connection of the system of FIG. 1a with a plurality of the respective components 11 to 18.

In FIG. 1b Fig. 3 is a frontal view of an exhaust gas heat exchanger 11, wherein the exhaust gas flows into the image plane. Furthermore, the positions of five nozzles 13 in this case are indicated, with one nozzle 13 being centrally positioned and four further nozzles 13 being distributed at a constant distance from the central nozzle 13 and at a uniform angular distance (eg 90 ° each). Not shown, but possible, are configurations in which the nozzle pitches are different or the angular intervals are not regular. Furthermore, there is the possibility that, depending on the size of the exhaust gas heat exchanger 11, the number of nozzles is smaller (in the case of a smaller exhaust gas heat exchanger) or larger (in the case of a larger exhaust gas heat exchanger). Furthermore, different types of nozzles can be used.

In FIG. 2 Further details of a device for injecting water 27 are outlined. Water or air is first sent through pipes 23 through a manifold 24. The distributor 24 is in this case connected via pipes 23 and nozzle lances 25 with two nozzles 26. The nozzles 26 are mounted by means of nozzle lances 25 on a cover 21. Behind the lid 21 is in one possible embodiment of the invention, an insulating layer 22a, which reduces thermal stress on the underlying components. To protect thermal shock sensitive components, an inlay or insulative layer 22b may be installed between them and the exhaust stream.

In addition to individual nozzle lances can also as in FIG. 2b shown used an injector. This injector is installed radially in the exhaust pipe in front of the heat exchanger 21. The heat exchanger is provided with an insulation 22a which reduces the thermal load on underlying components. The injection of water 27 via a nozzle head 25 with one or more nozzles 26. The injection can be carried out here with or against the flow direction of the exhaust gas. To protect thermal shock sensitive components, an inlay or insulative layer 22b may be installed between them and the exhaust stream.

The schematic structure of a water injection system 12 is in FIG. 3 outlined. In the illustrated embodiment, compressed air is either generated by a compressor 31 or supplied externally and stored in pressure vessel 32. One or more additional external compressed air tanks are possible, which are not shown here. Check valves 37 prevent the built-up air pressure, z. B. after switching off the compressor 31 is maintained. If solenoid valve 36 is opened, the compressed air flows in the direction of one or more nozzles. If the solenoid valves 35 are opened, water flows in the direction of the nozzles.

The controller 33 of the water injection system 12 controls the opening and closing of the solenoid valves 35, 36 and the operation of the compressor 31. Further, measurement data from previous water injection operations may be used to configure the controller so that future water injection operations are optimized. The compressor 31 and the controller 33 are powered by a power supply 34 with electrical energy.

In FIG. 4 a typical course of an injection cycle is shown. Preferably at regular intervals, a new cycle is started. After cycle start 41, it is checked in step 42 whether compressed air is present at a pressure of at least typically 8 bar. Further, in step 43, it is checked whether the exhaust gas flow rate is a minimum value (eg 50%) of the maximum flow rate and whether the exhaust gas inlet temperature in the exhaust gas heat exchanger 11 is greater than a set temperature of z. B. 350 ° C is.

In step 44, steps 42 and 43 are used to check whether the cycle continues or whether the cycle is aborted 45. In the case of release, the first compressed air purge of the lines 46 is performed by first opening solenoid valve 36 and after a period of typically closed for 10 to 60 seconds. Subsequently, the Wassereindüsungsvorgang 47 by opening the solenoid valves 35 and optionally 36, which are closed again at the end of the Wassereindüsungsvorgangs 47. The water injection process 47 typically takes 60 to 180 seconds. Subsequently, a second compressed air flushing of the lines 48, which is normally performed as the first compressed air flush 46, wherein the duration of the second compressed air flushing, however, may be different from that of the first compressed air flushing. Thereafter, the cycle end 49 is reached.

In FIG. 5 a diagram is shown in which the exhaust gas outlet temperature from an exhaust gas heat exchanger [° C] is plotted as a function of the hours of operation of the same exhaust gas heat exchanger. When new (without exhaust gas deposits), the exhaust gas exit temperature from the exhaust gas heat exchanger is 120 ° C. This value increases to a value of approximately 170 ° C within approx. 1000 operating hours. After about 1000 and about 2300 operating hours, the exhaust gas heat exchanger was cleaned manually, which means that the exhaust gas outlet temperature drops more or less to the original temperature of 120 ° C again.

After about 2300 operating hours water was injected into the exhaust gas heat exchanger according to an embodiment of the invention, which causes the exhaust gas outlet temperature from the exhaust gas heat exchanger increases more slowly than in the two previous intervals without water injection (with manual cleaning) and that the exhaust gas outlet temperature from the exhaust gas heat exchanger even after more than 5,000 operating hours does not exceed 140 ° C. This fact indicates that the exhaust gas exit temperature has stabilized at a lower level.

Out FIG. 5 It is clear that the injection of water into an exhaust gas heat exchanger, a higher heat transfer of exhaust gases is achieved in the exhaust gas heat exchanger. This is achieved in that the exhaust gas deposition layer is roughened in the exhaust gas heat exchanger and does not build up further from a certain layer thickness. Complete removal of the exhaust gas deposition layer can be precluded because the exhaust gas exit temperature not to the original value of 120 ° C, as after a manual cleaning drops.

The effect of the injection of water is compared with the Figures 6a and 6b clear. While the exhaust deposition layers in FIG. 6a are typically smooth without water injection, the exhaust deposition layers are in FIG. 6b with water injection rough or irregular.

In the area of uniform deposition (eg, an area without flaking), there are irregular but widespread variations in the thickness of the exhaust gas deposition layer exceeding 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%. or more than 80% of the maximum thickness. Grain sizes of the deposit layer when viewed perpendicularly to a uniform deposit area are on average more than 10%, 20%, 30%, 40%, 50%, 75%, 100%, 150%, 200% or 300% and / or less as 20%, 30%, 40%, 50%, 75%, 100%, 150%, 200%, 300%, 400% or 500% of the average or maximum layer thickness in such a range. The addressed area can z. B. 1 cm ² or 10 cm ² .

Claims (15)

A method of reducing power losses in heat exchangers (11), such as exhaust gas heat exchangers or exhaust gas recirculation coolers, the method comprising: Injecting (47) water into a heat exchanger (11); characterized in that by the injection of water (14) a change in the thermodynamic properties of the exhaust gas deposition layer in the heat exchanger (11) is created, whereby a higher heat transfer of exhaust gases is achieved on the heat exchanger. The method of claim 1, wherein the thermodynamic properties are a heat transfer coefficient α and / or a thermal conductivity λ. The method of claim 1 or 2, wherein the injection of water (14) at intervals of at least 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20 hours and / or at most 2.3 , 4, 5, 6, 8, 10, 12, 14, 16, 20 or 24 hours; and / or wherein each injection process (47) over a period of at least 10, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160 or 180 s and / or at most 20, 30, 40, 50 , 60, 80, 100, 120, 140, 160, 180, 200, 250, 300 or 600 s; and or
wherein the injection operation (47) is terminated before a set time when the exhaust gas exit temperature from the heat exchanger (11) does not fall further during the injection operation. The process according to any one of claims 1 to 3, wherein the water is at a pressure of at least 1, 1.5, 2, 2.5, 3, 4, 5 or 6 bar and / or at most 2, 3, 4, 5, 6, 7, 8 or 9 bar is injected; and or
wherein the water meets purity requirements, wherein the purity requirements preferably a degree of hardness of less than 0.1 ° dH and / or a conductivity of less than 1500 μS / cm and / or a chloride content of less than 20 mg / l and / or a pH of between 9 and 10.5; and or
wherein the droplet size of the water is at least 100, 150, 200, 250, 300, 400, 500 or 600 μm and / or at most 150, 200, 300, 400, 500, 600, 700, 800 or 900 μm. The process of any one of claims 1 to 4, wherein the amount of injected water is chosen in relation to the amount of exhaust gas passing through the heat exchanger (11) and the ratio
ε = water flow [g / min] / exhaust gas mass flow [kg / min]
preferably in the range of at least 5, 10, 15, 20, 25, 30, 40, 50, 60, 70 or 80 and / or at most 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200 or 300 lies. The process of any one of claims 1 to 5, comprising at least one, two or three further of the following steps performed prior to injection (47) of water: Starting a water injection cycle (41); Check if one, two or all of the following criteria are met: • Compressed air (42) is available at a pressure of at least 1, 2, 3, 4, 5, 6, 7 or 8 bar and / or at most 2, 4, 6, 8, 10 or 12 bar; The exhaust gas inlet temperature (43) in the heat exchanger is greater than a target temperature of at least 100, 150, 200, 250, 300, 350, 400, 500 or 600 ° C and / or at most 200, 300, 400, 500, 600, 700 , 800 or 900 ° C, and • the exhaust gas mass flow (43) is at least 50, 60, 70, 80 or 90% of the
maximum mass flow through the heat exchanger; and Compressed air flushing (46) of water-bearing components of a used water injection system before the injection of water. The process of any one of claims 1 to 6, comprising at least one, two or three further of the following steps carried out after injection (47) of water: • purging air (48) of water-bearing components of a used water injection system after the injection of water, in particular to remove water residues from nozzles used; Documenting measurement data recorded during the water injection process, in particular of dewatered water quantity and / or water pressure during injection and / or exhaust gas inlet temperature in the heat exchanger (11) and / or exhaust gas exit temperature from the heat exchanger; and • Use the measurement data recorded during the water injection process to redetermine the duration of injection, the amount of injection, and the time interval between the water injection procedures of future injection operations. The method of claim 6 or 7, wherein the compressed air purging is at least 5, 10, 15, 20, 30, 40, 50, 60 or 80 seconds and / or at most 10, 15, 20, 30, 40, 50, 60, 80, 100 or 120 s lasts and / or with a pressure of at least 1, 2, 3, 4, 5, 6 or 7 bar and / or at most 2, 3, 4, 5, 6, 7, 8, 9, 10, 11th or 12 bar. A controller (33) for a water injection system (12) for automatically carrying out the method according to any one of claims 1 to 8, wherein the controller (33) is preferably part of a water injection system (12). A device for reducing power losses in heat exchangers (11), such as exhaust gas heat exchangers and exhaust gas recirculation coolers, the device comprising: a heat exchanger (11); a water injection system (12); and one or more nozzles (13); characterized in that said components for effecting a change in physical properties of an exhaust gas deposition layer in the heat exchanger (11) by injecting water (14) by means of water injection system (12) are provided in the heat exchanger, whereby a higher heat transfer of exhaust gases is achieved on the heat exchanger. The apparatus according to claim 10, wherein the nozzles (26) are mounted on a lid (21), each nozzle (26) is connected to the water injection unit (12) through a pipe (23), and the lid is located on the exhaust gas inlet side in front of the heat exchanger (11) is located so that the nozzles are aligned substantially parallel to the exhaust gas flow in the heat exchanger; or wherein the nozzles (26) are aligned by an injector located radially in the heat exchanger inlet or upstream pipes (23) in the flow direction or against the flow direction of the exhaust gas stream; in which the nozzles (26) are mounted on the cover (21) under an insulating layer (22) by means of nozzle lances (25) such that only the tips of the nozzles are subjected to thermal stresses by hot exhaust gases and the pipes (23) and the water injection system (12) are at least partially protected against thermal stress. The device according to any one of claims 10 or 11, wherein the contact of sensitive parts with water through a bulkhead plate (17) and / or through the use of thin inserts and / or insulating layers is avoided. The apparatus according to any one of claims 10 to 12, wherein the water injection system (12) comprises a PLC control (33) and / or piping (16) and / or solenoid valves (35, 36) and / or a compressor (31) and / or includes a connection for external compressed air supply; in which the water injection installation (12) comprises at least one, two, three or all further components from the following components: flow controller, water filter, pressure switch, pressure monitor, check valves (37), data storage, additional pressure vessel for increasing the pressure volume. The device according to one of claims 10 to 13, wherein the number of nozzles (13) is defined according to the diameter or maximum width of the height of a cross-sectional area d of the heat exchanger perpendicular to the exhaust gas flow, such as n = 1 for d <400 mm, n = 3 for 400 ≤ d <600 mm, n = 5 for 600 ≤ d <800 mm and n = 12 for 800 ≤ d <1500 mm; and or
wherein the nozzles (13) are arranged so that injected water as evenly as possible covers the entire exhaust gas inlet side of the heat exchanger (11), so that the density variation of the injected water over the entire exhaust gas inlet side a maximum of 5, 10, 20, 30, 40, 50, 60 or 80%; and or
wherein the distance of the nozzles (13) to the exhaust gas inlet side of the heat exchanger (11) is as close as possible, provided that the said maximum density variation of the injected water is not exceeded; and or
wherein the nozzles (13) used are preferably stainless steel nozzles with a spray angle of 0 ° - 20 ° and / or 20 ° - 40 ° and / or 40 ° - 60 ° and / or 60 ° - 90 ° and / or 90 ° - 120 ° are; and or
wherein the nozzles (13) are capable of having water droplets with a droplet size of at least 100, 150, 200, 250, 300, 400, 500 or 600 μm and / or at most 150, 200, 300, 400, 500, 600, 700, To produce 800 or 900 μm; and or
wherein the nozzles (13) used are 2-fluid nozzles, with which water can be injected by means of compressed air; and or
wherein a nozzle head with a plurality of nozzles (13) is used, so that optionally or simultaneously can be injected in and / or against the direction of an exhaust gas stream. The apparatus of any of claims 10 to 14, further comprising one or more of the following components: Connecting piece (18) for discharging excess water and / or for accommodating temperature sensors with which the exhaust gas inlet temperature into the heat exchanger (11) and / or the exhaust gas outlet temperature from the heat exchanger and / or the pressure loss via the heat exchanger can be measured; additional heat exchangers (11) forming, with said heat exchanger, a multi-stage heat exchanger system; and additional water injection systems (12), so that each heat exchanger is assigned a water injection system or only a part of the heat exchanger a water injection system is assigned, each water injection system is connected to at least one other nozzle (13).

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