JP7614987B2 - Surface cleaning method and system - Google Patents

Description

Embodiments of the present invention relate to surface purification technology.

Metal surfaces can corrode due to interactions between the material and the environment. Usually, oxidation occurs due to a water film on the metal surface, moisture in the environment, or oxygen in the air. On the other hand, more significant corrosion occurs when corrosion-inducing components are present in the environment or material and contribute to the reaction. Corrosion involving corrosive components can cause the production of corrosion products or thinning of the material. For example, when metal materials are used as structural materials, the progression of corrosion can cause a decrease in strength. Also, in the case of parts such as the heat exchange fins of a heat exchanger, thinning can cause the loss of heat transfer medium or the adhesion of corrosion products, resulting in a decrease in thermal conductivity.

Therefore, in order to improve the functionality of parts where corrosion products have formed, it is necessary to remove these deposits, such as corrosion products or corrosion components of these metals. For small parts, the removal of these deposits can be done relatively easily by hand polishing or brushing. However, for large parts, parts with complex shapes with many irregularities, or items with a large number of parts lined up, it is difficult to remove all of the deposits by hand. Here, when removing deposits from the heat transfer tubes of a large heat exchanger, it is necessary to avoid situations where the heat exchange medium leaks during the removal work, or where the removed deposits are discharged into the environment as dust and affect the environment around the heat exchanger. Furthermore, even if the deposits are removed once, it is also necessary to avoid the creation of an environment that increases the risk of corrosion occurring thereafter.

Since heat transfer tubes are intended for heat exchange, they are almost always only a few millimeters thick. For this reason, it is necessary to avoid using removal methods that cause thinning of the tube, such as blasting or cleaning with chemicals, on heat transfer tubes that have been significantly thinned due to corrosion. Even if the removal method does not cause thinning of the tube, there is a possibility that the thinned parts will be damaged if removal methods that apply impact forces and vibrations, such as spraying compressed air, dry ice, or water jets, or using shock waves, are used on thin-walled heat transfer tubes.

In addition, among the deposits, there are components that are relatively easy to remove and components that have a strong adhesive force. For example, there are cases where the state of adhesion of rust is unstable. Furthermore, during the rust removal process, there may be a mixture of components that can be knocked off relatively easily with a wire brush and components that have stuck and cannot be easily removed. In such cases, if a removal method that involves thinning is used, it is possible to remove the strongly adhered components as well as thin the surface, but other removal methods are thought to have inferior removal capabilities. To address these issues, a technology is known that uses laser irradiation to remove deposits.

Patent No. 4012536 Patent No. 6893983 Patent No. 5574354

“Factors of fatigue strength degradation in hot-rolled steel plates corroded in salt water” Kazuyoshi Ogawa, Katsuji Saruki, Takashi Asano, Kenichi Suzuki, “Zeiryō” Vol. 34, No. 385, 1985, p. 1211-1216 "Basic study on the relationship between the rust properties of carbon steel substrate before painting and the durability of the coating film" Tatsuro Sakamoto, Shigenobu Kainuma, Junji Kobayashi "Materials and Environment" Vol. 64, No. 7, 2015, p. 307-310

In power generation systems that generate electricity by burning fossil fuels, materials to be removed accumulate on the surfaces of equipment that come into contact with the combustion gases over many years of use. There is a need to selectively and efficiently remove such materials without causing thinning of the equipment surfaces.

The embodiment of the present invention was made in consideration of these circumstances, and aims to provide a surface purification technology that can selectively and efficiently remove objects to be removed that are present on the surface of equipment that comes into contact with combustion gas.

A surface purification method according to an embodiment of the present invention is a method for removing a removal target that is present on a surface of equipment in a power plant that generates electricity by burning fossil fuels and that is made of a material containing at least iron as a main component, and that comes into contact with a combustion gas, using at least a laser, the method comprising: identifying a component of the removal target based on at least one of a component of the material, a component of the combustion gas, and a component of a sample of the removal target taken from the surface of the equipment that comes into contact with the combustion gas; referring to a database that is constructed according to the laser absorption characteristics of iron-based corrosion products and ammonium sulfate and that accumulates information indicating a relationship between components contained in a plurality of types of removal targets and the wavelength of the laser that is most easily absorbed by each component; identifying a wavelength of the laser that is most easily absorbed by the removal target based on the component of the removal target; and setting a wavelength of the laser to be irradiated to the surface of the equipment that comes into contact with the combustion gas based on the identified wavelength .

Embodiments of the present invention provide a surface purification technology that can selectively and efficiently remove objects to be removed that are present on the surface of equipment that comes into contact with combustion gas.

FIG. 1 is a block diagram showing a thermal power plant. FIG. FIG. FIG. 2 is a cross-sectional view showing the adhesion state of a metal surface in the presence of ammonium sulfate. A cross-sectional view showing the state in which a laser is irradiated onto a metal surface. FIG. 1 is a cross-sectional view showing a state in which ablation occurs on a metal surface. FIG. 1 is a block diagram showing a surface purification system. FIG. 2 is a block diagram showing an oscillator, a waveguide device, and an emission unit. FIG. 13 is a conceptual diagram showing a combination of an exit portion and a lens. A conceptual diagram showing the effect of lens movement. FIG. 11 is a conceptual diagram showing a change in the light collecting location by moving the reflecting device. FIG. 4 is a cross-sectional view showing a state in which light is irradiated onto the rear surface of a heat transfer tube using the reflecting device of the first example. FIG. 11 is a cross-sectional view showing a frame integrated with a reflection device of a second example. FIG. 11 is a cross-sectional view showing a frame integrated with a reflection device of a third example. FIG. 13 is a cross-sectional view showing an aspect in which a coating for fixing the waveguide device of the fourth example is provided. FIG. 13 is a cross-sectional view showing a circumferential illumination pattern using a reflecting device according to a fifth example. FIG. 13 is a side view showing a state of irradiation in the circumferential direction using the reflection device of the fifth example. A table showing wavelengths that are easily absorbed by iron-based corrosion products and ammonium sulfate. Graph showing absorption spectra of iron-based corrosion products and ammonium sulfate. 1 is a flow chart illustrating a method for cleaning a surface.

Below, embodiments of the surface purification method and surface purification system are described in detail with reference to the drawings.

Reference numeral 1 in FIG. 1 denotes a thermal power plant to which this embodiment is applied. A thermal power plant 1 is a facility that generates electricity by burning fossil fuels such as natural gas, oil, and coal. In this embodiment, a thermal power plant 1 that uses a combined cycle power generation method in which internal combustion power generation is performed using a gas turbine 2 and thermal power generation is performed using the exhaust heat from the gas turbine 2 is exemplified. Note that this embodiment may be applied to other types of power plants other than the combined cycle power generation method as long as they generate electricity by burning fossil fuels.

The combined cycle power generation thermal power plant 1 is provided with a gas turbine 2 as an internal combustion engine. The rotational force of the gas turbine 2 is transmitted to a first generator 3 to generate internal combustion power. The combustion gas G discharged from the gas turbine 2 is sent to a waste heat recovery boiler 5 via an exhaust duct 4. The waste heat recovery boiler 5 has a heat exchanger 6. The water W flowing through the heat exchanger 6 inside the waste heat recovery boiler 5 exchanges heat with the combustion gas G to generate steam. The combustion gas G that has passed through the waste heat recovery boiler 5 is sent to a denitrification device 7, which is provided as necessary, via the exhaust duct 4. The combustion gas G is denitrified by a catalyst in the denitrification device 7, and then sent to a chimney 8 via the exhaust duct 4, from which it is discharged into the atmosphere.

The water W (steam) evaporated in the heat exchanger 6 is sent to the steam turbine 10 via the water circulation line 9. The pressure of this steam rotates the steam turbine 10. The rotational force of the steam turbine 10 is then transmitted to the second generator 11 to generate steam power. The steam that passes through the steam turbine 10 is sent to the condenser 12. This steam is condensed in the condenser 12 and returned to water W. This returned water W is returned again to the waste heat recovery boiler 5 via the water circulation line 9.

As shown in Figures 2 and 3, the heat exchanger 6, which is the equipment of this embodiment, is provided with a number of heat transfer tubes 13. When the water W flowing through the water circulation line 9 passes through the heat transfer tubes 13, it exchanges heat with the surrounding combustion gas G and becomes steam.

In addition, heat exchange fins 14 are provided on the outer circumferential surface of the heat transfer tube 13 to increase the efficiency of heat exchange. The heat exchange fins 14 are wound around the outer circumferential surface of the heat transfer tube 13 and extend in a spiral shape. Note that multiple heat exchange fins 14 may be arranged along the length of the heat transfer tube 13. The spaces 15 between the heat transfer tubes 13 and the spaces 16 between the heat exchange fins 14 form the narrow portions of this embodiment.

The heat transfer tubes 13 and heat exchange fins 14 are made of a material that contains at least iron as a main component, such as carbon steel. The heat transfer tubes 13 and heat exchange fins 14 become corroded due to years of use and the adhesion of various substances that fly in due to the combustion gas G. As shown in FIG. 4, in order to continue using the heat transfer tubes 13 and heat exchange fins 14 whose surfaces 17 have deteriorated, the surfaces 17 of the heat transfer tubes 13 and heat exchange fins 14 may be painted. However, even if a paint is applied to the surface 17 of a metal that is corroded, peeling, swelling, and cracking may occur easily, and depending on the state of the corroding components, corrosion may progress between the surface 17 and the paint. Therefore, in this embodiment, a process is performed to purify the metal surface 17 before painting.

As shown in Figures 4 and 5, the surfaces 17 (metallic base material) of the heat transfer tubes 13 and heat exchange fins 14, i.e., the surfaces 17 that come into contact with the combustion gas G, contain corrosion products 18 of carbon steel, deposits 19 containing these corrosion products 18, or deposits 19 that have flown in with the combustion gas G and attached thereto. The deposits 19 include, for example, ammonium sulfate. In this embodiment, a purification process is performed to remove these substances using a laser L.

In the following description, the material to be removed by the laser L is referred to as the removal target 20. The removal target 20 includes at least one of the corrosion products 18 and the deposits 19 that have flown and adhered (accumulated). The corrosion products 18 also include deposits 19 that partially include the corrosion products 18 that have adhered to the surface of the equipment.

In this embodiment, the removal of the object 20 by irradiation with the laser L is achieved by the laser ablation effect (Figure 6), which is an interaction between light and matter. In this embodiment, the wavelength of the laser L is determined for the object 20 to be removed that has appeared on the surface 17 of the heat transfer tube 13 of the heat exchanger 6, based on the characteristic absorption wavelength of the object 20 to be removed, and the object 20 is removed selectively and efficiently.

As shown in FIG. 6, when a laser L having a certain energy density or more is irradiated onto an object to be removed 20 made of a specific material, the object to be removed 20 absorbs the light energy, is instantaneously heated, and turns into plasma and sublimes. Note that, although the manner in which this occurs varies depending on the subsequent recombination reaction, the object to be removed 20 that has been turned into plasma produces re-products 21, which are scattering metal elements or gasifying components.

Because the re-products 21 have been converted into plasma and ionized, their particle size will be much smaller than that of the object to be removed 20 that has simply been peeled off, and it is believed that they will be reduced to a size that is difficult for humans to detect. Also, if the re-products 21 are vaporized, the amount of solid components will be less than before ablation.

The method of purifying the metal surface 17 using a laser L is one of the dry surface cleaning methods. For the laser ablation effect to occur, at least one combination of the absorption characteristics for each wavelength of the compound (component) constituting the object to be removed 20, the density of the object to be removed 20, the thickness of the object to be removed 20, the oscillation wavelength of the laser L, or the density of the laser power must exceed the ablation threshold of the compound. Note that whether the laser L is a pulsed wave or a continuous wave, the principle is the same, although there are differences in parameters. As long as this combination does not exceed the threshold of the irradiated material, the material is simply heated and the effect ends.

Based on this principle, if one is only considering removing the object to be removed 20, this can be achieved by irradiating a high-intensity laser L. However, if the intensity is simply increased, not only the object to be removed 20 but also the healthy metal surface 17 to which the object to be removed 20 is attached will be ablated. Ablation of the healthy metal surface 17 by the laser L will have the same effect as the conventional removal method that causes metal loss, and there remains a concern that this may lead to damage to the heat transfer tube 13 and heat exchange fins 14.

In conventional technology, there is no appropriate wavelength control for the characteristic absorption wavelength of the object to be removed 20, and if the intensity of the irradiated laser L is lower than the ablation threshold of the object to be removed 20, removal is not possible. Furthermore, if the laser L is irradiated with an intensity higher than the ablation threshold, there is a risk of thinning of healthy metal parts. In addition, protective equipment to protect workers from the high-intensity laser L must be complex and heavy, which has the disadvantage of increasing costs and lengthening the construction period.

Therefore, in this embodiment, the absorption characteristics of the removal target 20 for each wavelength are grasped for the heat transfer tube 13 in the heat exchanger 6 to which the removal target 20 having a specific component is attached. Then, by providing a wavelength and light source of the laser L suitable for the wavelength with a strong absorption coefficient of the removal target 20, it is possible to selectively and efficiently remove not only the removal target 20 that is easy to remove, but also the removal target 20 that is stuck to the removal target 20.

Next, the system configuration of the surface purification system 30 of this embodiment will be described with reference to the block diagram shown in FIG. 7. This surface purification system 30 includes a laser purification device 31, a control unit 32, and a memory unit 33.

The control unit 32 includes a wavelength setting unit 34 as necessary. This is realized by the CPU executing a program stored in the memory or HDD. The wavelength setting unit 34 sets the wavelength of the laser L to be irradiated to the surface 17 of the heat exchanger 6. The setting of the wavelength of this laser L may be determined in advance depending on the material of the base material and the material of the precipitate.

The storage unit 33 further includes a database 35 and a construction record unit 36. These are collections of information stored in memory, a HDD, or the cloud and organized so that they can be searched or accumulated.

The control unit 32 of this embodiment is configured as a computer having hardware resources such as a CPU, ROM, RAM, and HDD, and in which software-based information processing is realized using the hardware resources as the CPU executes various programs. Furthermore, the surface purification method of this embodiment is realized by having the computer execute various programs.

The control unit 32 controls the laser purification device 31. Furthermore, the configuration of the control unit 32 does not necessarily have to be provided in a single computer. For example, a single control unit 32 may be realized using multiple computers connected to each other via a network.

The control unit 32 also performs a process of identifying the wavelength of the laser L that is most easily absorbed by the object to be removed 20 based on the components of the object to be removed 20. Furthermore, the control unit 32 performs a process of setting the wavelength of the laser L to be irradiated onto the surfaces 17 of the heat transfer tube 13 and the heat exchange fins 14 based on the identified wavelength.

The memory unit 33 stores various information required when performing the purification process using the laser purification device 31.

The database 35 stores information showing the relationship between components contained in multiple types of removal targets 20 and the wavelength of the laser L that is most easily absorbed by each component. In this way, the wavelength of the laser L that is most easily absorbed by the removal targets 20 can be set based on the information stored in the database 35. The database 35 may be provided in another computer that is connected to the surface purification system 30 (control unit 32) via a network.

As shown in FIG. 8, the laser purification device 31 includes an oscillator 37, a waveguide device 38, an emitter 39, and a robot arm 40.

The oscillator 37 is an output source (light source) of the laser L. The laser L output from the oscillator 37 is guided to the output section 39 via a waveguide device 38. An example of the waveguide device 38 is an optical fiber. The waveguide device 38 may also be configured with a plurality of reflecting mirrors or prisms (not shown).

The laser L guided by the waveguide device 38 is emitted from the emission section 39. In this embodiment, the waveguide device 38 is used to guide the laser L from the oscillator 37 to a surface 17 such as the heat transfer tube 13 of the heat exchanger 6 (equipment), and the emission section 39 from which the laser L in the waveguide device 38 is emitted is movable relative to the surface 17. In this way, the laser L can be guided to an appropriate position using the waveguide device 38.

The emission unit 39 can be moved to the treatment position by the robot arm 40. A potentiometer (not shown) or the like is provided at each joint of the robot arm 40. By recording the movable state of each joint of the robot arm 40, the location where the laser L is irradiated can be recorded. This treatment location is recorded in the treatment record unit 36 (Figure 7). For example, by mapping the locations where the laser L is irradiated on the heat transfer tube 13 and the heat exchange fins 14, the locations where the purification process was performed can be confirmed at a later date.

In this embodiment, the robot arm 40 fixes the emission unit 39 in a predetermined position for construction, but the worker may hold the emission unit 39 and fix it in a predetermined position for construction. In this case, the emission unit 39 is provided with a motion sensor (not shown) including an acceleration sensor and an angle sensor, and the movement of the emission unit 39 is recorded, thereby recording the location where the laser L is irradiated.

Due to its high coherence, when the laser L is emitted from the emission section 39, it propagates linearly without diffusing as compared to non-coherent light. Also, as shown in FIG. 9, the laser L emitted from the emission section 39 can be focused using a specified focusing lens 41 to increase the light intensity per unit area on the surface 17 of the target to be irradiated.

As shown in FIG. 10, if the focusing lens 41 is moved along the optical axis during irradiation, the laser L can be focused at any position according to the movable range of the focusing lens 41, even if the emission part 39 is fixed. In this way, for example, when the operator holds the emission part 39 in his/her hand, the surface 17 can be irradiated without precisely aiming at the irradiation position.

For example, as shown in Figures 2 and 3, the laser L can be irradiated to the heat exchange fins 14 of the heat transfer tube 13, or to the edge of the heat exchange fins 14 and the heat transfer tube 13 at the same time. In this way, the laser L can be irradiated even to narrow areas such as the spaces 15 between the heat transfer tubes 13 or the spaces 16 between the heat exchange fins 14. In other words, in this embodiment, the area where the laser L is irradiated to remove the object to be removed 20 includes the narrow area of the heat exchanger 6 (equipment). In this way, the object to be removed 20 can be removed even from narrow areas that are difficult to remove using other removal methods.

The narrow area may be at least one of the areas 15 between the heat transfer tubes 13 or the areas 16 between the heat exchange fins 14. In this way, the object to be removed 20 can be removed even in areas that are difficult for workers to reach.

Furthermore, as shown in FIG. 11, the optical path of the laser L can be easily adjusted by using a reflecting device 42 such as a reflector. For example, a reflecting device 42 whose reflection angle changes periodically, such as a galvanometer mirror, can be used. The laser L is then irradiated while periodically changing the reflection angle of the reflecting device 42. In this way, the laser L can be irradiated over a wide planar (two-dimensional) area, thereby improving the removal efficiency. The reflecting device 42 may also be a prism or a half mirror.

Figure 12 shows a first example of the construction mode. For example, the head 43 of the laser purification device 31 has an emission section 39 and a condenser lens 41 integrally provided. The laser L output from this head 43 is guided by a reflecting device 42 that combines multiple reflectors, and is irradiated to a predetermined irradiation location on the heat transfer tube 13 or heat exchange fin 14. In this way, the laser L can be irradiated even in a narrow area where it is difficult for the head 43 to enter. For example, the laser L can be irradiated deep inside a forest of heat transfer tubes 13, or to a position that is difficult for the worker to see.

For example, suppose there is a maintenance area (not shown) on the lower side of the paper in FIG. 12 where workers can move inside the waste heat recovery boiler 5. The worker visually checks the heat transfer tubes 13 from the lower side of the paper in FIG. 12 (see arrow 44 in FIG. 12). Here, the worker can see one side of the heat transfer tubes 13 (the side on the lower side of the paper) that stand in a row, but cannot see the other side of the heat transfer tubes 13 (the side on the upper side of the paper). The areas of these heat transfer tubes 13 that cannot be seen by the worker are invisible areas (invisible areas). The deep parts of the heat transfer tubes 13 that stand in a row are also included in the invisible area.

In this embodiment, a reflecting device 42 that reflects the laser L is installed inside the heat exchanger 6 (waste heat recovery boiler 5) in order to guide the laser L to the surface 17 of the heat transfer tube 13 or heat exchange fin 14 in the invisible area. In this way, the reflecting device 42 can be used to irradiate the laser L onto the surface 17 in the invisible area.

Figure 13 shows a second example of the installation mode. In this second example, a frame 45 is provided to integrate the reflecting device 42 with the emission section 39 and the focusing lens 41. A plurality of reflecting devices 42 are supported by the frame 45. In this way, the reflecting devices 42 can be easily provided between the heat transfer tubes 13.

In this second example, the laser L is irradiated using a waveguide device 38 that is an integral combination of a focusing lens 41 that focuses the laser L and a reflecting device 42 that reflects the laser L. In this way, it is possible to irradiate the laser L deep inside the forest of heat transfer tubes 13, which is a narrow area where it is difficult for the head 43 of the laser L or the worker's hand to enter, and to areas that are difficult for the worker to see.

Figure 14 shows a third example of the construction mode. In this third example, an objective lens 46 for adjusting the irradiation distance is provided at the end of the emission side of the frame 45 that supports the reflecting device 42. This objective lens 46 is periodically moved along the optical axis. In this way, even if the emission part 39 is fixed, the focus of the laser L can be moved by moving the objective lens 46 to any position, so that the laser L can be irradiated to any range.

Figure 15 shows a fourth example of the construction mode. In this fourth example, a waveguide device 47 is provided extending from the emission side of the emission section 39 (Figure 8). This waveguide device 47 is composed of an optical fiber or the like. This waveguide device 47 and the objective lens 46 are integrated with a bent support tube 48 that can be bent and supported as desired. The bent support tube 48 can be bent to match the arrangement of the heat transfer tubes 13 of the heat exchanger 6. The waveguide device 47 can be fixed in any shape. In this way, the waveguide device 47 can be used to irradiate the laser L onto the surface 17 of the invisible area (invisible area).

16 and 17 show a fifth example of the construction mode. This fifth example has a mechanism for irradiating the laser L in the circumferential direction around the emission axis 39A. For example, a rotation axis 49 is provided at a location that coincides with the emission axis 39A of the laser L in the emission section 39. A reflection device 42 is supported on this rotation axis 49. The reflection device 42 is rotated around the rotation axis 49 at an angle to the emission axis 39A. The emission section 39, the reflection device 42, and the rotation axis 49 are housed inside a cylindrical support tube 50. Furthermore, a window 51 through which the laser L can pass is provided along the outer circumferential surface of the support tube 50.

The emission unit 39 is arranged so that the direction in which the emission axis 39A extends is the same as the direction in which the heat transfer tube 13 extends. The laser L emitted from the emission unit 39 is reflected by the reflecting device 42. The reflecting device 42 rotates on the rotating shaft 49, so that the laser L can be irradiated in the circumferential direction around the emission axis 39A. In this way, the laser L can be irradiated to multiple surrounding heat transfer tubes 13, improving the removal efficiency.

If the support tube 50 is made of a material that does not transmit light, such as metal, the window 51 allows the laser L to pass through. The support tube 50 may have a shape other than a cylinder, such as a square or other shape.

The support tube 50 may also be a structure formed using a specified frame. However, in this case, the frame may become an obstacle to the irradiation of the laser L, so care must be taken when installing the frame during work.

In the first to fifth examples, the irradiation range of the laser L is generally on the order of several tens of μm, so irradiation of areas where removal of the object to be removed 20 is not required or where removal of the object to be removed 20 is not desired due to certain circumstances can be easily avoided.

In this way, if it becomes possible to remove the object to be removed 20 from the metal surface 17, it becomes possible to expose clean metal on the surface 17. In this way, it is possible to restore the heat exchange rate for equipment such as the heat exchanger 6, whose performance is affected by the surface condition. Also, depending on the degree of corrosion, random unevenness may occur on the metal surface 17, so by cleaning the surface 17, a surface condition suitable for pretreatment for painting can be obtained.

Next, the relationship between the components of the object to be removed 20 and the wavelength of the laser L will be explained with reference to Figures 18 and 19.

The components of the object to be removed 20 vary depending on the environment (atmospheric components, flying components, humidity, temperature) in which the metal material is placed, and the absorption characteristics of the laser L vary greatly depending on the compound. In particular, in the case of carbon steel, compounds such as iron oxide, iron hydroxide, and iron oxyhydroxide are generated. The absorption characteristics of iron oxide and iron oxyhydroxide at 25 μm to 200 μm have been confirmed. Furthermore, in the ultraviolet or visible light ranges, where absorption measurements are difficult, and in the near-infrared range of 600 nm to 1100 nm, diffuse reflection measurements are performed. The reflection and absorption characteristics can be obtained by taking the logarithm of the reflectance. Although there will be some differences in the values due to the influence of the measurement, it is possible to find characteristic absorption wavelengths.

The absorption characteristics of the actual object 20 to be removed are determined by the amount produced or the state of mixing. In particular, for iron-based corrosion products, there is an absorption region in the range of approximately 7 μm to 25 μm. For example, for iron oxide, there is an absorption region near 11.0 μm. For iron hydroxide, there is an absorption region near 12.0 μm. For iron oxyhydroxide, there are absorption regions near 2.5 μm to 3.0 μm, 15.0 μm, or 17.0 μm.

In the range from 600 nm to 2.5 μm, there is a region of high reflectance around 750 nm. From this peak, the reflectance decreases on the shorter wavelength side, meaning that absorption becomes stronger. On the other hand, on the longer wavelength side, there is a region of strong absorption around 900 nm for iron oxide, and around 920 nm for iron hydroxide and iron oxyhydroxide.

Furthermore, looking at the longer wavelength side, no absorption peaks are observed in iron oxide and iron hydroxide. Iron hydroxide also has an absorption region around 1,460 nm, but the coefficient is smaller than the absorption region at 750 nm.

In the ultraviolet to visible light range, for iron oxide, there is an absorption region around 580 nm. Here, the reflectance increases up to around 500 nm and tends to saturate. For iron oxyhydroxide, there is an absorption peak around 570 nm to 620 nm. Also, each metal material has the greatest absorption in the region below 500 nm.

By irradiating the object 20 with a laser L having these wavelengths or wavelengths close to these, it can be efficiently removed. Furthermore, since there is no need to increase the intensity of the laser L more than necessary, there is no damage to healthy metal base material where the object 20 is not present.

On the other hand, for example, the fuel burned in the gas turbine 2 may contain components that corrode metals. These corrosive components flow into the heat exchanger 6 and corrode parts such as the heat transfer tubes 13 of the heat exchanger 6, resulting in the production of compounds other than metal corrosion products.

In particular, a heat exchanger 6 containing ammonium sulfate has been identified, and the object to be removed 20 on the surface 17 of the heat transfer tube 13 and the heat exchange fins 14 contains ammonium sulfate in addition to iron-based corrosion products. When considering the removal conditions in this case, the wavelength of the laser L must be selected taking into account the absorption characteristics of ammonium sulfate in addition to the absorption characteristics of the iron-based corrosion products.

As shown in Figure 19, we focus on the reflection spectrum of ammonium sulfate in the near infrared region. We pay particular attention to the specified range R. Here, in the case of ammonium sulfate, slight absorption is observed near 850 nm and 950 nm, but the region of high reflectance generally continues from about 200 nm to 1000 nm. Absorption regions are observed near 1060 nm, 1390 nm, and 1590 nm, and an absorption peak is observed near 2.0 μm to 2.1 μm. In the infrared region, a wide absorption peak can be confirmed near 3.3 μm. Furthermore, steep absorption peaks can be confirmed near 6.6 μm and 10.0 μm.

Therefore, in this embodiment, for the object to be removed 20 in which ammonium sulfate and iron-based corrosion products are mixed in significant amounts, the condition is that the absorption peaks are in the same region. This wavelength region is the near-infrared region from 900 nm to 1390 nm and the infrared region from 9.0 μm to 18.0 μm.

The near-infrared region is particularly suitable because it has a narrower wavelength range than the infrared region and generally allows the selection of a high-intensity light source. In the ultraviolet region, the absorption of iron-based corrosion products is high, but the reflectance of ammonium sulfate is high, making it difficult to say that it is suitable.

For example, more efficient removal can be achieved by preparing multiple light sources, each matched to a different absorption wavelength for each compound constituting the object to be removed 20, and periodically changing the wavelength of the laser L irradiated onto the object to be removed 20. However, compared to using a single light source, using multiple light sources and wavelength conversion elements is inferior in terms of equipment cost and optical design cost.

In this embodiment, in the near-infrared region, the absorption region of ammonium sulfate overlaps with the absorption region of iron oxide and iron oxyhydroxide, and this region can efficiently remove the object to be removed 20.

Currently realized lasers can oscillate in the range of 9.0 μm to 18.0 μm, and the most common ones are quantum cascade lasers and _CO2 lasers. In addition, it can be realized by using optical parametric oscillation or difference frequency generation technology. Among these, _CO2 lasers used as processing lasers can obtain relatively high intensity.

In the near-infrared region, there are many options, and those capable of oscillating in the aforementioned wavelength region include fiber lasers, semiconductor lasers, YAG lasers, and disk lasers. In this wavelength region, it is possible to guide the light using optical fibers as the waveguide device 38, so the irradiation site can be easily changed.

Next, the surface purification method performed using the surface purification system 30 of this embodiment will be described with reference to the flowchart in FIG. 20. The aforementioned drawings will be referred to as appropriate.

First, in step S1, an operator performing the surface purification method executes a component identification process. Here, the operator identifies the components of the removal target 20 based on at least one of the components of the material that constitutes the heat exchanger 6 or the components of the combustion gas G. The information to be acquired may be, for example, information acquired in the past. It may also be based on design information for the heat exchanger 6.

Additionally or alternatively, the operator takes a sample of the material 20 to be removed from the surface 17 of the heat exchanger 6. The components of the material 20 to be removed are then identified based on the components of the sample.

In the next step S2, the operator performs a wavelength identification process using the surface purification system 30. Here, the control unit 32 of the surface purification system 30 refers to the information stored in the database 35 and identifies the wavelength of the laser L that is most easily absorbed by the object to be removed 20 based on the components of the object to be removed 20. Note that if the material of the base material and the material of the precipitate are known in advance, a laser purification device 31 that emits a laser L of a pre-specified wavelength may be used.

In the next step S3, the operator executes a laser setting process using the surface purification system 30. Here, the wavelength setting unit 34 of the control unit 32 sets the wavelength of the laser L to be irradiated onto the surface 17 of the heat exchanger 6 based on the identified wavelength.

The wavelength to be set may be the wavelength that is most easily absorbed by the object to be removed 20, or a wavelength that is close to this wavelength. If there are multiple wavelength candidates, any one of the candidates may be used.

In addition, in the laser setting process, not only is the wavelength of the laser L set, but other settings such as the intensity, irradiation time, and irradiation range of the laser L are also performed. Furthermore, the laser L is set according to the structure of the heat exchanger 6. For example, as shown in FIG. 1, the heat exchanger 6 has a high-temperature portion 6A that is first hit by the combustion gas G, a medium-temperature portion 6B that is at a medium temperature, and a low-temperature portion 6C that is last hit by the combustion gas G. The components or deposition state of the object to be removed 20 differ for each of these portions 6A to 6C. Various settings such as the wavelength of the laser L are performed taking into account the structure of the heat exchanger 6.

Returning to FIG. 20, in the next step S4, the control unit 32 controls the laser purification device 31 to execute a laser removal process for removing the object to be removed 20 on the surface 17 of the heat exchanger 6. The laser removal process is performed automatically by the control unit 32. The site where laser removal has been performed is recorded in the construction record unit 36.

In this embodiment, the control unit 32 automatically controls the laser purifying device 31, but other configurations are also possible. For example, the control unit 32 may receive input operations from an operator (user) and control the laser purifying device 31. In other words, the control unit 32 may be a remote control unit for controlling the laser purifying device 31 by manual operation by an operator.

By identifying the components of the object 20 to be removed in advance from the components of the material of the heat exchanger 6 or the components of the combustion gas G, or by taking a sample and identifying the components of the object 20 to be removed, it is possible to irradiate the object 20 with a laser L having a wavelength that is easily absorbed by the object 20 to efficiently remove the object 20.

In the next step S5, the worker performs a painting process to paint the surface 17 of the heat exchanger 6. In this embodiment, before painting the surface 17 of the heat exchanger 6, the laser L is irradiated onto the surface 17 to remove the object to be removed 20, so that the paint is less likely to peel off over a long period of time.

Then, the surface purification method is terminated. The above steps are at least a part of the processing included in the surface purification method, and other steps may be included in the surface purification method.

In the flowchart of this embodiment, an example is shown in which each step is executed in series, but the order of steps is not necessarily fixed, and the order of some steps may be interchanged. Also, some steps may be executed in parallel with other steps.

The surface purification system 30 of this embodiment includes a control device with a highly integrated processor such as a dedicated chip, FPGA (Field Programmable Gate Array), GPU (Graphics Processing Unit), or CPU (Central Processing Unit), a storage device such as ROM (Read Only Memory) or RAM (Random Access Memory), an external storage device such as HDD (Hard Disk Drive) or SSD (Solid State Drive), a display device such as a display, an input device such as a mouse or keyboard, and a communication interface. This surface purification system 30 can be realized with a hardware configuration using a normal computer.

The program executed by the surface purification system 30 of this embodiment is provided in advance in a ROM or the like. Alternatively, this program may be provided by being stored in an installable or executable file format on a non-transitory computer-readable storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD).

The programs executed by this surface purification system 30 may be stored on a computer connected to a network such as the Internet and provided by downloading via the network. This surface purification system 30 may also be configured by combining separate modules that independently perform the functions of the components and are interconnected via a network or dedicated lines.

In this embodiment, the object 20 to be removed is removed using a laser L, but other methods are also possible. For example, a cleaning method using blasting or a chemical solution may be used in combination with the removal using the laser L.

In this embodiment, the heat transfer tube 13 and the heat exchange fins 14 are formed from carbon steel, but other configurations are also possible. For example, the heat transfer tube 13 and the heat exchange fins 14 may be formed from stainless steel or the like.

In this embodiment, the surface 17 of the heat transfer tube 13 of the heat exchanger 6 inside the waste heat recovery boiler 5 of the thermal power plant 1 is purified, but other aspects are also possible. For example, the surface of a condensation tube through which cooling water flows to condense water vapor provided in a condenser installed in a nuclear power plant may be purified using this embodiment.

According to at least one of the embodiments described above, by using at least a laser to remove the object to be removed that is present on the surface of the equipment that is made of a material that contains at least iron as a main component and that comes into contact with the combustion gas, it is possible to selectively and efficiently remove the object to be removed that is present on the surface of the equipment that comes into contact with the combustion gas.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments or modifications thereof are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

1...thermal power plant, 2...gas turbine, 3...first generator, 4...exhaust duct, 5...waste heat recovery boiler, 6...heat exchanger, 6A...high temperature section, 6B...medium temperature section, 6C...low temperature section, 7...denitrification device, 8...chimney, 9...water circulation line, 10...steam turbine, 11...second generator, 12...condenser, 13...heat transfer tube, 14...heat exchange fin, 15...between heat transfer tubes, 16...between heat exchange fins, 17...surface, 18...corrosion products, 19...deposits, 20...object to be removed, 21...reproducts, 30...surface purification system, 31 ...Laser purification device, 32...Control unit, 33...Memory unit, 34...Wavelength setting unit, 35...Database, 36...Construction record unit, 37...Oscillator, 38...Waveguide device, 39...Emitting unit, 39A...Emitting axis, 40...Robot arm, 41...Condensing lens, 42...Reflecting device, 43...Head, 44...Arrow indicating viewing direction, 45...Frame, 46...Objective lens, 47...Waveguide device, 48...Bent support tube, 49...Rotating axis, 50...Support tube, 51...Window, G...Combustion gas, L...Laser, R...Predetermined range, W...Water.

Claims (12)

1. A method for removing a target object present on a surface of equipment in a power plant that generates electricity by burning fossil fuels, the equipment being made of a material containing at least iron as a main component and contacting combustion gas, the method comprising the steps of:
Identifying the components of the removal target based on at least one of the components of the material, the components of the combustion gas, and the components of a sample of the removal target taken from a surface of the device that comes into contact with the combustion gas;
referring to a database constructed according to the laser absorption characteristics of iron-based corrosion products and ammonium sulfate, which stores information indicating a relationship between components contained in a plurality of types of the objects to be removed and the wavelength of the laser most easily absorbed by each component, and identifying the wavelength of the laser most easily absorbed by the objects to be removed based on the components of the objects to be removed;
and setting a wavelength of the laser to be irradiated onto the surface of the device that is in contact with the combustion gas based on the identified wavelength.
Surface cleaning methods. The portion where the laser is irradiated to remove the removal target includes a narrow portion of the device.
The method for purifying a surface according to claim 1 . The narrow portion includes at least one of a space between heat transfer tubes of a heat exchanger as the equipment or a space between heat exchange fins provided on the heat transfer tubes.
The method for purifying a surface according to claim 2 . A waveguide device is used to guide the laser from an oscillator to a surface of the equipment in contact with the combustion gas, and an emission portion of the waveguide device from which the laser is emitted is movable or angle changeable with respect to the surface of the equipment in contact with the combustion gas.
The surface purification method according to any one of claims 1 to 3 . irradiating the laser using the waveguide device integrally combined with a lens for focusing the laser and a reflecting device for reflecting the laser;
The method for purifying a surface according to claim 4 . An objective lens is provided for adjusting the irradiation distance, and the objective lens is moved along the optical axis.
The surface purification method according to claim 4 or 5 . Fixing the waveguiding device in an arbitrary shape to guide the laser to a surface in a blind area that is not visible to an operator in the equipment;
The method for purifying a surface according to any one of claims 4 to 6 . irradiating the laser while periodically changing a reflection angle of a reflecting device that reflects the laser;
The method for purifying a surface according to any one of claims 1 to 7 . Rotating a reflecting device that reflects the laser, the laser is irradiated in a circumferential direction with respect to an emission axis of the laser.
The method for purifying a surface according to any one of claims 1 to 8 . a reflecting device is provided inside the equipment to reflect the laser so as to guide the laser to a surface in a non-visible area that is not visible to an operator of the equipment;
The method for purifying a surface according to any one of claims 1 to 9 . Before painting the surface of the device, the laser is irradiated onto the surface of the device to remove the object to be removed.
The method for purifying a surface according to any one of claims 1 to 10 . A surface purification system for use in a surface purification method that removes, by using at least a laser, a removal target that is present on a surface of equipment in a power plant that generates electricity by burning fossil fuels and that is made of a material containing at least iron as a main component and that comes into contact with combustion gas, comprising:
A database is provided which is constructed according to the laser absorption characteristics of iron-based corrosion products and ammonium sulfate, and which stores information indicating a relationship between components contained in a plurality of types of objects to be removed and the wavelength of the laser which is most easily absorbed by each of the components;
Identifying the components of the removal target based on at least one of the components of the material, the components of the combustion gas, and the components of a sample of the removal target taken from a surface of the device that comes into contact with the combustion gas;
referring to the database, and identifying the wavelength of the laser that is most easily absorbed by the object to be removed based on the components of the object to be removed;
and setting a wavelength of the laser to be irradiated onto the surface of the device that is in contact with the combustion gas based on the identified wavelength.
The surface purification method includes:
Surface purification systems.

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