PIPE-WEIGHT-PIPE-WALL

Description

[0001] The invention relates to a tube-web-tube wall, particularly for use in a combustion plant, especially in a flue gas chamber, such as a combustion chamber of a boiler or other combustion plant, and to a method for the electroplating of such a tube-web-tube wall. The tube-web-tube wall comprises at least one wall section having several tubes running parallel to each other in a longitudinal direction and connecting webs arranged between adjacent tubes.

[0002] Electroplating, also known as electroplating or electrochemical plating, is an electrochemical process for producing a metallic coating on a workpiece, preferably made of steel, using electrolysis. In electroplating according to DIN EN ISO 1456, the objects to be nickel-plated are immersed in a nickel electrolyte, such as an electroplating bath, after suitable pretreatment. Applying an electrical voltage causes a nickel coating to be deposited on the surface of the workpiece. Particularly in the field of steam generators for waste, hazardous waste, or biomass incineration plants for the combustion or disposal of solid, liquid, and / or gaseous fuels, possibly containing pollutants, or in chemical reactors, the workpiece in question is typically a so-called tube-web-tube wall.In common usage, and also in the following, the term "pipe-rib-pipe wall" is sometimes used synonymously with the term "fin wall" (or membrane wall with finned tubes), which historically gave its name to the original casting process, without limiting it to this specific manufacturing method. Due to the extreme conditions prevailing there (including high temperatures and a chemically aggressive atmosphere), the pipe-rib-pipe wall must reliably meet the requirements of 24 / 7 continuous operation of the systems and be protected against corrosion for as long as possible.

[0003] More precisely, in technical circles, a pipe-web-pipe wall is understood to be a wall constructed from pipes with connecting webs between them, which can be soldered, bonded, welded, or cast together in one piece. It is used, for example, as the wall of a combustion chamber, a flue gas passage, or a dead flue, where a "passage" in a combustion system refers to a section of a flue gas path through which the flue gas flows without significant change in direction. The pipe-web-pipe wall consists of a multitude of parallel (steel) pipes, with a (steel) web (called a "fin" or "membrane" in the casting process) inserted between each pair of adjacent pipes, for example, by welding. This makes the wall flue gas-tight. The standard design stipulates that the webs lie in the same plane as the central axis of the pipes.The surface of such a tube-web-tube wall is therefore not flat, but follows the contours of the tubes and webs, resulting in a relief-like structure. Strictly speaking, it is not a flat wall, but rather a wall extending essentially in a plane with relief-like or profile-like structures. This is precisely where the greatest challenges lie in electroplating. The sharper or more uneven the surface to be electroplated, the more difficult it is to apply a preferably uniformly thin metal coating, such as nickel, to the surface using electroplating techniques. With an uneven, i.e.,Because the surface of the workpiece, in this case the pipe-web-pipe wall, is not uniformly spaced from the anode surface (an anode always used in electroplating), the formation of unevenly long field lines between the anode and the workpiece leads to varying rates of metal ion deposition on the workpiece (inhomogeneous with respect to hardness, microstructure, and thickness). Currently, this problem is addressed in a very time-consuming manner using so-called masks, which locally regulate or alter the amount of deposition on the workpiece.

[0004] The prior art documents WO 02 / 068863 A2 and XP001047236 address electroplating of fin walls in power plant systems. They do not disclose that the connecting webs between adjacent tubes extend in a web plane that is offset parallel to a central tube center plane defined by the adjacent tubes. WO 2020 / 032789 A2 discloses a boiler wall in which tubes are protected by a plate. This plate is offset from the tube center plane towards the combustion chamber. Furthermore, an arrangement is disclosed where webs between the tubes are offset towards the combustion chamber for the purpose of reducing fly ash accumulation. WO 2009 / 064415 A1 shows a fin tube wall provided with a nickel alloy for mechanical protection. The alloy is applied by arc spraying.

[0005] The invention is based on the objective of providing an improved tube-web-tube wall for use in a boiler area of ​​a combustion plant and an optimized method for the electroplating of such a tube-web-tube wall.

[0006] This problem is solved by a device according to claim 1 and a method according to claim 3.

[0007] In the pipe-web-pipe wall according to the invention, which, as mentioned at the outset, comprises at least one wall section having several pipes running side by side in a longitudinal direction and connecting webs arranged between adjacent pipes, the connecting webs extend in a web plane, i.e., in a common plane. As is usual, this is not an actually continuous, straight, flat plane, but merely a virtual plane that is alternately interrupted by the pipes located between them.

[0008] In this process, the web plane is shifted parallel to a centrally defined, imaginary pipe center plane (defined by the adjacent pipes) along the central axis of the pipes for electroplating of the pipe-web-pipe wall. "Parallel shift" here means that the web plane is displaced from the pipe center plane to the pipe vertices on one surface of the pipe-web-pipe wall. Thus, the connecting webs, which together form a web plane, are positioned off-center, i.e., decentered, between the opposite pipe vertices. The offset of the pipe center plane is directed towards the side of the pipe-web-pipe wall that is to be electroplated, as this side is typically exposed to thermal and / or chemical stresses in operation.

[0009] In its intended installed state, namely e.g. as a wall of a "flue gas chamber" of a combustion plant, the connecting webs (as the web plane) which are shifted parallel inwards towards the pipe crowns that come into contact with flue gas or are on the flue gas side, and the half-pipes or pipe crowns that protrude proportionally relative to the connecting webs, form a "flue gas side" of the pipe-web-pipe wall.

[0010] In the following, the term "flue gas room" refers only to spaces where high flue gas temperatures or even flames occur—as can typically arise during combustion processes—i.e., where thermal and / or chemical stress or strain usually occurs, at least on the inner surfaces of the flue gas room, i.e., on the flue gas side. Examples of such flue gas rooms include, for instance, the combustion chambers of a boiler, empty flues, or jet flues of a combustion plant. Such flue gas rooms are primarily used in combustion plants. However, they could also be used in other industrial plants, such as chemical reactors, coking plants (e.g., for dry coke cooling), steel mills (e.g., in converter cooling stacks and / or for secondary dust removal), and similar facilities, since protection against chemical attack is particularly necessary in these environments.

[0011] The flue gas side of a flue gas chamber is also referred to as the "fire side" in a combustion chamber, for example, because it may be in contact with flames or fire.

[0012] In other words, the flue gas side of the pipe-web-pipe wall is the side of the pipe-web-pipe wall facing away from the pipe's central plane, formed by the webs and (short) less protruding pipe crown.

[0013] In view of the high thermal and potentially corrosive stress to which the flue gas side of the pipe-web-pipe wall is permanently exposed during operation of the combustion plant or any other industrial plant, one surface, namely the flue gas side of the pipe-web-pipe wall - in particular the surface of the connecting webs and the pipe crowns projecting relative to the connecting webs - has, according to the invention, at least one nickel layer applied galvanically, in particular by means of an electroplating process in an electroplating bath.

[0014] An electroplating or electrolytic bath is a container in which metallic deposits are electrochemically deposited, i.e., coatings are applied to substrates (objects). The purpose is to coat, for example, a steel substrate with a metallic material to protect it from chemical attack such as corrosion.

[0015] When an electric current is passed through the electroplating bath, the metal ions (cations), in this case nickel, located at the anode (positive terminal or positively charged electrode), migrate through the electrolytic bath to the cathode (negative terminal or negatively charged electrode), i.e., the substrate to be coated, and are deposited there. In the context of the invention, the substrate is the tube-rib-tube wall. The electric current reduces dissolved metal ions to a metal, e.g., nickel, deposited on the tube-rib-tube wall. In addition to various properties of the bath, such as pH value or wettability, the exposure time (of the substrate in the electroplating bath) and the applied current also affect the growth of the metal layer on the object.Among other things, the applied current strength in turn influences the distance-dependent current density between the anode and cathode, and thus the layer thickness, the hardness and the grain size of the columnarly deposited substrate.

[0016] The electroplating bath comprises an anode extending essentially in a plane or surface as the opposite pole to the tube-web-tube wall, in order to arrange the tube-web-tube wall as a planar cathode also extending essentially in a plane at a defined cathode position at a distance from the anode in the electroplating bath and to coat it electroplating by means of a current source.

[0017] The current source or voltage source of the electroplating bath is connected to the anode at one pole as described above and can be connected to the tube-web-tube wall (cathode) at another pole in order to generate or induce a current flow from the anode to the cathode.

[0018] In a method according to the invention (specifically also to be referred to as a "coating" or "coating process", as will be explained below) for the electroplating of a tube-web-tube wall, this is introduced or immersed as a cathode (negative pole or negatively charged electrode) in an electroplating bath in which an anode is located at a distance from the tube-web-tube wall.

[0019] As already mentioned above, the pipe-web-pipe wall comprises at least one wall part which is formed from several pipes running side by side in a longitudinal direction with a common pipe center plane and connecting webs arranged in a web plane, offset between adjacent pipes parallel to the pipe center plane.

[0020] The cathode is positioned or immersed in the electroplating bath in such a way that the web plane is closer to the anode than the pipe center plane.

[0021] According to the invention, a surface of the wall portion of the tube-web-tube wall facing the anode is then electroplated with nickel. The surface in question is a surface offset from the central plane of the tube, i.e., the web plane itself as well as the portion of the tubes of the tube-web-tube wall located in front of the web plane, i.e., from the tube crown to the web plane.

[0022] The design according to the invention ensures that the pipe-web-pipe wall to be coated, or at least the relevant coated wall section, can be coated with a uniform thickness along its entire surface, at least on the flue gas side of the pipe-web-pipe wall facing away from the pipe's central plane. It also enables the application of a more uniform nickel layer to such a pipe-web-pipe wall in a shorter time by means of electroplating than is currently possible with conventional (non-electroplating) methods. Furthermore, the design according to the invention ensures a more uniform current density distribution, which in turn results in a more uniform layer thickness and surface hardness distribution. This allows for a reduction in both the specific amount of nickel required to achieve corrosion protection and the bath immersion or exposure time.It can be assumed that this also extends the service life of the tube-web-tube wall, since the tube-web-tube wall thus has no weak points that could lead to premature failure of the protective layer. Furthermore, the inventive method achieves that the normally necessary rework of the tube-web-tube wall, e.g., at the blunter inner corners between tubes and webs, is reduced to a minimum after the inventive coating process. The process is also simpler than currently known methods, as it can be carried out without masks, covers, or auxiliary anodes. The structural parallel displacement of the web plane from the tube's central plane also ensures that the anode wall for electroplating with nickel can be designed with less pronounced profiling.

[0023] Further, particularly advantageous embodiments and developments of the invention result from the dependent claims and the following description, wherein the independent claims of a claim category may also be further developed analogously to the dependent claims and embodiments of another claim category, and in particular individual features of different embodiments or variants may be combined to form new embodiments or variants.

[0024] Preferably, the pipe-web-pipe wall can be made of steel. Then, for example, steel webs or steel connecting webs can form the virtual web plane, whereby the steel webs can be welded between steel pipes of the pipe-web-pipe wall.

[0025] Preferably, the web plane can be offset or arranged parallel to the pipe center plane by at least 10%, preferably at least 20%, particularly preferably at least 40%, further preferably at least 60%, and most preferably at least 80%.

[0026] To support uniform nickel deposition along the tube-web-tube wall, the anode can preferably also be adapted, at least in some areas, to the shape of the profile-like surface of the tube-web-tube wall facing the anode, i.e. e.g. plateau-shaped or forming spaced-apart plateaus, on a surface facing the tube-web-tube wall.

[0027] Preferably, the profiling or profile depth of the anode surface can be reduced by at least 20%, preferably at least 40%, particularly preferably at least 60%, and most preferably at least 80%, relative to the profile depth of the wall portion of the tube-web-tube wall. Profiling or profile depth here refers to the distance between the web plane of the connecting webs and the central plane of the projecting tube crowns.

[0028] The anode can therefore have a significantly weakened, i.e., less deep or increased, relief compared to the tube-web-tube wall, namely a reduced (tube-web) profile depth, if the weakened profile depth is sufficient to allow the tube-web-tube wall to be electroplated with nickel sufficiently uniformly using connecting webs that are shifted parallel from the tube's central plane.

[0029] The distances between the anode and the cathode can preferably be made more uniform or adjusted to achieve the most consistent possible current density distribution, as this is essentially the decisive factor for a uniform electroplating process. This can be achieved either by approximating the distance to the anode with respect to the webs of the tube-web-tube wall, for example, by welding them off-center to the tube's central plane, and / or by adapting or matching the contour of the anode to the profiled shape of the tube-web-tube wall, i.e., by profiling the anode accordingly.

[0030] According to a further particularly preferred embodiment of the invention, the surface of the anode can be designed such that, at least in the area of ​​the wall portion, it has a substantially constant, i.e., consistently uniform, distance to the wall portion. This embodiment is explained in more detail below with reference to a drawing.

[0031] Preferably, the tube-rib-tube wall according to the invention can be detachably coupled to the anode by means of a mounting device. Particularly preferably, the mounting device can be mechanically, but electrically, insulated from the tube-rib-tube wall to be electroplated. To remove gases, such as hydrogen, which are typically produced during electroplating, a forced flow can be generated in the electroplating bath. The mounting device can preferably be designed such that vibration of the anode during flow through the bath does not impair the electroplating process.

[0032] Preferably, the mounting device can have at least one coupling element for coupling to the pipe-web-pipe wall. The coupling element can particularly preferably comprise a plug which can be inserted into one end of a tube of the pipe-web-pipe wall and clamped or secured there. This plug can particularly preferably also seal the tube tightly at this end, so that at least at this end of the tube, as little liquid as possible can enter the tube, and thus no material can accumulate on the inside of the tube.

[0033] Preferably, the mounting device can comprise at least two coupling elements, each with at least one plug or pipe plug. In intended use, two of the plugs (also known in practice as sealing discs or pipe closures) can be arranged relative to each other such that they can be inserted into opposite ends of the same pipe.

[0034] Preferably, at least one pipe, more preferably at least two, more preferably three, and most preferably four pipes (without a direct connection to the support device) can be located between two further pipes, where the pipe-web-pipe wall is connected at the pipe end to the plugs of the support device. The number of pipes in question, located between the two lateral pipes held at the top and bottom of the support device, can each be provided with a tightly sealing, preferably conically tapered, blanking plug, particularly without a connection to the support device. This ensures that the two ends of the number of pipes in question are sealed as required, so that as little material as possible enters the interior of the pipes and accumulates there or coats the interior of the pipes.

[0035] This also ensures that the deposition of metal ions on the pipe-strut-pipe wall is more uniform, i.e., especially in the area of ​​the inner corners at the transition between the pipes and the connecting struts.

[0036] For the construction and repair of steam generators, in particular membrane walls for steam generators, the invention, i.e., in particular the mounting device and / or the anode wall, can preferably be designed or dimensioned such that at least the following usual dimensions of such membrane walls can be electroplated: Preferably, the invention can be designed such that the pipe diameter or the wall thickness of a pipe can be 60.3 x 5.0 or 5.6 mm, particularly preferably 57.0 x 5.0 or 5.6 mm.

[0037] Preferably, the invention can be further designed such that the wall thickness of the connecting webs can measure 5 mm, particularly preferably 6 mm.

[0038] Preferably, the invention can also be designed such that the division, i.e. the average distance between the pipe centers or central axes, of two pipes can be between 70 and 100 mm.

[0039] Delivery sizes for membrane walls with regard to longitudinal and transverse dimensions are currently determined, at least in Germany, by practical transport dimensions for road traffic. Accordingly, such membrane walls for new installations—provided they are transported by road as usual—can preferably be manufactured in sections of no more than 12 m in length and 3.6 to 5 m in width, and particularly preferably in sections of no more than 6 m in length and 0.9 m in width. The invention can also be preferably dimensioned to suit this purpose. For the repair or replacement of damaged wall sections of membrane walls, the membrane walls can typically be manufactured, limited by the transport dimensions in the respective system, preferably in sections of no more than 6 m in length and 1.5 m in width.

[0040] However, the invention is not limited to the electroplating of workpieces with the aforementioned dimensions. Such membrane walls can also have special dimensions at the customer's request, which can in particular be larger than the dimensions mentioned. The invention can also be suitably dimensioned for such special dimensions.

[0041] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. In the various figures, identical components are designated with identical reference numerals. The figures are generally not to scale and should be understood as schematic representations only. They show: Figure 1 A schematic representation of the course of the electric field lines between a section of an anode wall and a tube-web-tube wall during electroplating according to the state of the art, in top view. Figure 2 a schematic representation of the course of the electric field lines in a first embodiment of a tube-web-tube wall according to the invention during electroplating in an electroplating bath between the anode wall and a wall part of the tube-web-tube wall, in top view, Figure 3 a representation of the pipe-web-pipe-wall according to Figure 2 , with an exemplary embodiment of an anode wall roughly adapted to the tube-web-tube wall, in top view, Figure 4 another representation of the pipe-web-pipe wall according to Figure 2 and 3 , with a preferred variant of the embodiment according to Figure 3 with a surface of the anode wall spaced at a constant distance from the tube-web-tube wall, in top view.

[0042] Figure 1Figure 1 shows a rough schematic top view of a prior art construction, illustrating how, until now, a wall section FW' opposite an anode wall 20 of a tube-rib-tube wall FW (as cathode FW) was typically electroplated in an electroplating bath B. A tube-rib-tube wall FW is sometimes also referred to commercially as a fin wall, although this does not exclusively refer to the historically original manufacturing method. For the sake of simplicity, the wall section FW' consists, without limiting the invention to this (as also in the following(Figures) representatively only a first pipe R 1, which is connected or welded to a second pipe R 2 via a first connecting web S 1 extending in a web plane XS. The pipes R 1 , R 2 are arranged side by side and together define a pipe median plane XR extending in the transverse direction QR of the pipe-web-pipe wall FW. The web plane XS and the pipe median plane XR lie in a plane of symmetry XR , XS of the pipe-web-pipe wall FW.

[0043] In the depicted operating situation (as in the other figures), a current flows, as is usual during electroplating, between the anode wall 20 and the wall section FW' of the tube-web-tube wall FW through the liquid (not shown here). The electric field E forms the electric field lines E between the anode 20 and the cathode FW, which are schematically indicated here. These lines symbolize the (particle or) ion flow or current flow from the anode wall 20 (anode 20) to the wall section FW' (cathode FW), essentially perpendicular to the transverse direction QR of the connecting webs S 1. This ion flow causes the wall section FW' of the tube-web-tube wall FW, or more precisely a surface O of the wall section FW', to be coated, as the particles are deposited there. Since the particles are nickel particles, a corrosion-protective, electroplated nickel layer is formed on the pipe-web-pipe wall FW.

[0044] Since the surface O of the wall part FW' of the tube-web-tube wall FW, which points towards the anode wall 20, in particular of the first tube R 1, the connecting web S 1 between them and the second tube R 2, does not run exactly parallel to the anode wall 20 at a consistently constant distance, the path length and thus the density of the electric field lines E increases progressively from the two tube vertices (i.e. the points that protrude furthest towards the anode wall 20 in the top view) of the tubes R 1 , R 2 towards the center to the connecting web S 1 .

[0045] This results, firstly, in different material deposits and hardnesses (deposition or deposition of metal ions) on the wall section FW' of the tube-web-tube wall FW due to the different current density of the electric field lines E for the same exposure duration, and thus in different layer thicknesses in the area of ​​the tubes R1, R2 and the connecting web S1. Secondly, the electric field lines E, which originate from the anode wall 20 at the level of the connecting web S1, run in a slightly curved path towards the respective tube R1, R2, since the electric field E is shaped by the almost semicircularThe protruding pipe profiles of pipes R1 and R2 are affected or deflected accordingly. Thus, more metal ions are deposited or precipitated on pipes R1 and R2 than on the connecting web S1 located between them. As has been shown by tests and practical experience, this difference in layer thickness also affects the hardness distribution, thermal conductivity, and service life of the pipe-web-pipe wall FW during operation.

[0046] Figure 2 Figure 1 shows a wall section FW' of a tube-web-tube wall FW according to the invention, which, due to the surface structure of the anode wall 20, is arranged in an electroplating bath B at a distance from the anode wall 20 that is at least partially identical and only slightly varying. The wall section FW' also consists of two tubes R1, R2, which are connected by means of a connecting web S1.

[0047] In contrast to the design according to Figure 1is the middle web S 1 between the two tubes R 1 , R 2 in Figure 2 However, it is not arranged exactly in the center of the tube's central plane XR. It is positioned off-center, parallel to the anode wall 20, in order to generate more nickel deposition on the web and thus achieve a more uniform layer thickness distribution overall. Consequently, the tubes R1 and R2 protrude significantly less arcuately from the web plane XS of web S1 relative to the adjacent and surrounding webs, as is the case in the prior art according to Figure 1This is the case. The web plane XS of the web S 1 is thus closer to the anode wall 20 than the tube center plane XR, but further away than the two tube vertices of tubes R 1, R 2, and therefore still set back relative to the tube vertices. It is located in between, here approximately two-thirds of the way between the tube center plane XR and the tube vertices of tubes R 1, R 2. For the subsequent intended use of the tube-web-tube wall FW, this positioning of the web S 1 is advantageous in two respects. During manufacturing, more nickel is deposited on the web compared to symmetrical membrane walls or fin walls, so that the layer thickness distribution of the tube-web-tube wall FW is very even or uniform overall.Furthermore, in operation, the heat transfer from the boiler or flue gas in the boiler to the liquid in the tubes is significantly less impaired or worsened by this web plane, which is not completely shifted towards the tube crowns, i.e., towards the later hot side – as is the case, for example, with so-called Ω-shaped membrane walls – since a substantial part of the tubes still extends into a flue gas chamber, such as the combustion chamber of the boiler. Kessels, It protrudes and thus absorbs heat directly. Furthermore, Ω-shaped membrane walls are significantly heavier than the construction described here, which only resembles Ω-shaped membrane walls. This is because Ω-shaped membrane walls typically consist of a metal plate with welded-on metal tubes. The metal plate further impairs heat transfer to the fluid in the tube behind the metal plate.

[0048] The two levels XS and XR therefore do not extend into a common level XS and XR, but are separate from each other (as also in the further Figures 3 and 4 ) arranged at a distance a RS. Thus, the construction of the pipe-web-pipe wall FW is no longer symmetrical with respect to the pipe center plane XR. However, this only affects one installation direction of the pipe-web-pipe wall FW, whose subsequent flue gas side in a flue gas chamber is thereby determined.

[0049] Figure 3 Figure 1 shows a further preferred embodiment of the invention to make the coating application in electroplating nickel-plated even more uniform. In this embodiment, the same tube-web-tube wall FW (made of) is used in the electroplating nickel-plated process. Figure 2 ) positioned in an electroplating bath B, but this time with an anode wall 20 roughly adapted to the surface O' (i.e. later the "flue gas side") of the tube-web-tube wall FW at a distance from the tube-web-tube wall FW.

[0050] Following the design of the tube-web-tube wall FW, the anode wall 20 is also structured or relief-like, but in a smoother or less pronounced version compared to the tube-web-tube wall FW. The heights (tube crowns) and depths (webs S 1) of the tube-web-tube wall FW are indicated here with a slight slope on the anode wall 20 to simplify its manufacture, i.e., to create an almost flat surface. Thus, the relief-like surface 20f consists of obliquely angled (triangular) recesses that are set back from the tube-web-tube wall FW into the anode wall 20, creating a negative projection compared to the rest of the flat surface. The recesses are therefore centered so that their deepest point is centrally opposite the tube crown of tubes R1 and R2, i.e., a distance between tube-web-tube-wall FW and anode wall 20 there (relative to Figure 2) is enlarged.

[0051] To a first approximation, the surface 20f of the anode wall 20 is thus already slightly adapted to the tube-web-tube wall FW, so that a more uniform deposition or deposition of the metal ions on the wall part FW' of the tube-web- Pipe-wall FW, especially increasingly on the S1 bridge, occurs because the opposing surfaces run parallel to each other, at least to a first approximation.

[0052] Figure 4 Figure 1 shows the same wall section FW' of the pipe-web-pipe wall FW again. According to a particularly preferred embodiment from Figure 3 Here, the anode wall 20 is even further adapted to the tube-web-tube wall, namely it is formed almost exactly as a mirror image of the tube-web-tube wall FW. This allows the layer thickness distribution to be optimized even further, i.e., made even more uniform.

[0053] The surface 20f' of the anode wall 20, viewed relative to the opposite surface O' of the tube-web-tube wall FW, is thus, so to speak, a phase-shifted image or mirror image of it. The surface 20f' of the anode wall 20 is also straight relative to the web S 1 of the wall section FW' of the tube-web-tube wall FW. Opposite the tube crown, the surface 20f' of the anode wall 20 is recessed, leaving a kind of "rounded arc". Thus, the surface 20f' of the anode wall 20 facing the wall section FW' of the tube-web-tube wall FW essentially corresponds to the surface O' of the wall section FW' facing the anode wall 20, in particular of the tube R 1, the connecting web S 1, and the further tube R 2 of the tube-web-tube wall FW.

[0054] This results in a nearly constant distance between the surface 20f' of the anode wall 20 and the tube-web-tube wall FW, i.e., in the transverse direction QR along the wall section FW'. In other words, the surface 20f' (i.e., the negative relief) of the anode wall 20 could be positively inserted or slid into the surface O' (i.e., the positive relief) of the wall section FW' of the tube-web-tube wall FW if the two walls 20 and FW were pushed together.

[0055] This results in a uniform current density distribution of the electric field lines, which in turn leads to a particularly uniform deposition of nickel particles on the surface O' of the wall section FW' of the tube-web-tube wall FW during the electroplating nickel plating process. Accordingly, the layer thickness of the surface O' of the wall section FW' in the area of ​​the web S1 is the same as in the area of ​​the tubes R1, R2.

[0056] By combining the displacement of the web S 1 of the tube-web-tube wall FW with the alignment of the anode wall 20 with the tube-web-tube wall FW, it may also be sufficient to design the anode wall 20 with a profile depth that is proportionally reduced compared to the profile depth of the tube-web-tube wall FW, in order to minimize the effort required for the manufacture of the anode wall 20. Therefore, the recesses in the anode wall 20 can also be proportionally smaller than the corresponding depth or the distance between the tube crowns and the web S 1 in the tube-web-tube wall FW.

[0057] The wall section FW' of the pipe-web-pipe wall FW, shown schematically only from the end face in the figures (e.g., from above in plan view), or the pipe-web-pipe wall FW itself, can extend almost arbitrarily into the picture plane or drawing plane. The wall section FW' can, for example, continue straight into the drawing plane. However, it could also be bent or angled as needed – possibly even subsequently, after electroplating with nickel – to accommodate a certain shape of a flue gas chamber, e.g., a combustion chamber, a flue passage, or a boiler's empty passage, such as a flue passage that narrows pyramidally upwards from a certain height, etc.

[0058] Finally, it should be noted once again that the devices described in detail above are merely exemplary embodiments which can be modified in various ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Reference symbol list

[0059] 20Anode / Anode wall 20fSurface of the anode wall, roughly adapted to tube-web-tube wall 20f'Surface of the anode wall, with constant distance to the tube-web-tube wall a RS Distance tube center plane - web plane BElectroplating bath EElectric field / electric field lines FWRub-web-tube wall / Cathode FW'Wall section of the tube-web-tube wall OSurface of the tube-web-tube wall according to the state of the art O'Surface of the tube-web-tube wall with web offset parallel to the anode QRTransverse direction / transverse extension direction R1, R2 Tubes S1 Connecting web XR Tube center plane XS Web plane

Claims

1. A tube-web-tube wall (FW), in particular for use in a combustion plant, in particular in a flue gas chamber, such as a combustion chamber of a boiler, of a combustion plant, with at least one wall part (FW') which has several tubes (R1, R2) running adjacently in a longitudinal direction (LR) and connecting webs (S1) arranged between adjacent tubes (R1, R2), which connecting webs (S1) extend in a web plane (XS) that is offset from and parallel to a tube centre plane (XR) defined centrally by the adjacently running tubes (R1, R2) for nickel electroplating of the tube-web-tube wall (FW), wherein at least one surface (O') of the tube-web-tube wall (FW), in particular of the connecting webs (S1), facing away from the tube centre plane (XR) and of tube crests of the tubes (R1, R2) projecting relative to the connecting webs (S1), has at least one nickel plating applied by electroplating.

2. The tube-web-tube wall according to claim 1, wherein the web plane (XS) is parallel to and offset by at least 10%, preferably at least 20%, particularly preferably at least 40%, further preferably at least 60% and very particularly preferably at least 80% from the tube centre plane (XR) in the direction of the tube crests of the tubes (R1, R2).

3. A method for nickel electroplating a tube-web-tube wall (FW), in particular according to any one of the preceding claims, which tube-web-tube wall has at least one wall part (FW') formed of several tubes (R1, R2) running adjacently in a longitudinal direction (LR) with a common tube centre plane (XR) and connecting webs (S1) arranged parallel to but offset from the tube centre plane (XR), between adjacent tubes (R1, R2), in a web plane (XS), in which the tube-web-tube wall (FW) is introduced as a cathode (FW) into a galvanic bath (1) in which an anode (20) is located at a distance from the tube-web-tube wall (FW), wherein the tube-web-tube wall (FW) is arranged such that the web plane (XS) is closer to the anode (20) than the tube centre plane (XR), and then a surface (O') of the wall part (FW') of the tube-web-tube wall (FW) facing the anode (20) is nickel plated by electroplating.

4. The method according to claim 3, wherein the anode (20) is adapted in a profile-like manner at least in some regions on a surface (20f) facing the tube-web-tube wall (FW) to the shape of the surface (O') of the tube-web-tube wall (FW) facing the anode (20).

5. The method according to claim 3 or 4, wherein a profile depth of the surface (20f) of the anode (20) is reduced by at least 20%, preferably at least 40%, particularly preferably at least 60%, very preferably by at least 80% in relation to a profile depth of the surface (O') of the wall part (FW') of the tube-web-tube wall (FW).

6. The method according to claim 3 or 4, wherein the surface (20f) of the anode (20) is designed such that, at least in the region of the wall part (FW'), it has a substantially constant distance from the wall part (FW').