Coating film, furnace, combustion device, reaction device, alloy powder, and method for forming coating film

Abstract

This coating film is formed on a surface of a base material (11) of a furnace, and has a coating layer (12) that contains 10%-30% by mass of molybdenum, 0.5%-2.5% by mass of silicon, 0.1%-1.0% by mass of boron, 0.1% by mass or less of carbon, 5.5%-15% by mass of cobalt, and nickel which is an element accounting for the largest mass ratio among the metal elements and the metalloid elements, in terms of ratio with respect to the total of the metal elements and the metalloid elements.

Description

Coating, furnace, combustion device, reactor, alloy powder, and coating formation method

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to coatings, furnaces, combustion devices, reactors, alloy powders, and methods of forming coatings.

[0002] Ash is generated by combustion and gasification reactions in coal gasifiers, and by combustion in pulverized coal-fired boilers. Ash, which is incombustible, adheres to and accumulates on the surface of heat transfer tubes, increasing the thermal resistance of the entire tube and resulting in a decrease in heat transfer efficiency. If ash accumulates excessively, it can block the flow path and cause large ash blocks to fall, damaging the heat transfer tubes and causing the plant to shut down. For this reason, ash is periodically removed by blowing it away with a soot blower, or, in the case of pulverized coal-fired boilers, by using a thermal shock caused by temperature changes due to temporary load fluctuations.

[0003] Meanwhile, research has been conducted into methods for suppressing ash adhesion by forming a coating on heat transfer tubes. Specifically, a technology has been proposed in which a coating that controls the wettability of the heat transfer tube surface so as to be non-reactive with molten ash particles is formed by thermal spraying or the like, thereby suppressing the adhesion of ash particles. Patent Document 1 discloses a method for preventing ash adhesion by forming a coating layer on the surface of a steam pipe in a boiler by thermal spraying using a thermal spray material.

[0004] Japanese Patent Application Laid-Open No. 2005-146409

[0005] However, biomass fuels made from wood pellets, agricultural residues, and the like contain more alkaline components such as sodium, potassium, and calcium than coal, and are prone to ash adhesion due to a lower ash melting point, so the method of Patent Document 1 may not be sufficiently effective. Furthermore, for fuel types that are prone to ash adhesion and do not easily shed, additional measures to remove the ash, such as increasing the injection pressure of the soot blower, are required, which increases running costs. For these reasons, in order to accommodate the expansion of fuel types, it has been necessary to establish an ash adhesion suppression technology that improves ash detachment.

[0006] The present disclosure aims to provide a coating that can be applied to the surface of a base material to improve ash shedding, as well as a furnace, a combustion device, and a reactor on which the coating is formed. It also aims to provide an alloy powder for forming the coating and a method for forming the coating.

[0007] The coating according to the present disclosure is a coating formed on the surface of a base material of a furnace, and has a coating layer containing, in ratios relative to the total of metal elements and metalloid elements, 10 mass % to 30 mass % of molybdenum, 0.5 mass % to 2.5 mass % of silicon, 0.1 mass % to 1.0 mass % of boron, 0.1 mass % or less of carbon, 5.5 mass % to 15 mass % of cobalt, and nickel, which is the element that occupies the largest mass ratio among the metal elements and metalloid elements.

[0008] The coating layer may further contain chromium in a ratio of 0 mass % to 38 mass % based on the total of the metal elements and the metalloid elements.

[0009] In the coating layer, at least a portion of the molybdenum may be present in the form of molybdenum oxide.

[0010] The surface of the coating layer may further have a sliding material layer containing an oxide ceramic and a compound having a layered crystal structure.

[0011] The surface of the coating layer may further have a corrosion-resistant material layer containing at least one material selected from the group consisting of aluminum oxide, silicon dioxide, and chromium oxide.

[0012] A furnace according to the present disclosure may be provided with a coating according to the present disclosure.

[0013] The combustion device according to the present disclosure includes the furnace according to the present disclosure, and may be supplied with fuel containing at least one selected from the group consisting of coal, pulverized coal, biomass fuel, and ammonia.

[0014] The reactor according to the present disclosure includes the furnace according to the present disclosure, and at least one selected from the group consisting of coal, pulverized coal, biomass fuel, and ammonia may be supplied as a raw material.

[0015] The alloy powder according to the present disclosure is an alloy powder used for forming a coating layer of a film, and may be composed of an alloy containing, in ratios relative to the total of metal elements and metalloid elements, 10 mass % to 30 mass % of molybdenum, 0.5 mass % to 2.5 mass % of silicon, 0.1 mass % to 1.0 mass % of boron, 0.1 mass % or less of carbon, 5.5 mass % to 15 mass % of cobalt, and nickel, which is the element that occupies the largest mass ratio among the metal elements and metalloid elements.

[0016] The alloy may further contain chromium in a ratio of 0 to 38 mass % relative to the total of the metallic and semi-metallic elements.

[0017] The method for forming a film according to the present disclosure may be the method for forming a film described above, and may include a step of forming a coating layer from an alloy powder composed of an alloy containing, in ratios relative to the total of metal elements and metalloid elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass or less of carbon, 5.5% by mass to 15% by mass of cobalt, and nickel, the element that occupies the largest mass ratio among the metal elements and metalloid elements.

[0018] The alloy powder may further contain chromium in a ratio of 0 mass % to 38 mass % based on the total of the metal elements and the metalloid elements.

[0019] According to the present disclosure, it is possible to provide a coating that improves ash shedding when provided on the surface of a base material, as well as a furnace, a combustion device, and a reactor on which the coating is formed. It is also possible to provide an alloy powder for forming the coating and a method for forming the coating.

[0020] FIG. 1 is a cross-sectional view showing a schematic configuration of a coating according to some embodiments. FIG. 2 is a cross-sectional view showing a schematic configuration of a coating according to some embodiments. FIG. 3A is a cross-sectional view showing the configuration of a combustion furnace used in an ash adhesion test. FIG. 3B is a cutaway perspective view showing a portion of the combustion furnace shown in FIG. 3A. FIG. 4 is a graph showing the relationship between the distance from the probe surface and the porosity in an ash adhesion test. FIG. 5A is a photograph showing the results of SEM-EDS observation of the surface of the coating layer in an ash adhesion test. FIG. 5B is a photograph showing the results of SEM-EDS observation of the surface of the coating layer (elemental mapping of molybdenum) in an ash adhesion test. FIG. 6A is a photograph showing the state before air blowing in an ash adhesion test (exposure time: 1 hour). FIG. 6B is a photograph showing the state before air blowing in an ash adhesion test (exposure time: 3 hours). FIG. 7A is a photograph showing the state after air blowing in an ash adhesion test (exposure time: 1 hour). FIG. 7B is a photograph showing the state after air blowing in an ash adhesion test (exposure time: 3 hours). Fig. 8 is a graph showing the relationship between the exposure time in the ash adhesion test and the injection pressure of the air blow. Fig. 9 is a graph showing the relationship between the exposure time in the ash adhesion test and the heat flux after the air blow.

[0021] Hereinafter, several exemplary embodiments will be described with reference to the drawings. Note that the dimensional proportions of the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0022] 1 is a cross-sectional view showing the coating of this embodiment. The coating of this embodiment suppresses adhesion of ash to the furnace or facilitates the ash falling off.

[0023] As shown in Fig. 1, the film has a coating layer 12 formed on the surface of a base material 11. The base material 11 may be a steel or refractory material forming a wall surface of a furnace such as a coal gasifier or a pulverized coal-fired boiler, or a carbon steel or stainless steel material forming a heat transfer tube. Examples of refractory materials include high-alumina bricks and chrome-magnesia bricks.

[0024] The coating layer 12 contains molybdenum, silicon, boron, cobalt, and nickel and forms the outermost surface of the coating. The coating layer 12 is formed on the surface of the base material 11 to a predetermined thickness, and although not particularly limited, the thickness of the coating layer 12 is, for example, 100 μm to 1000 μm.

[0025] The molybdenum content of the coating layer 12 can suppress ash adhesion to the furnace or facilitate ash shedding. Molybdenum present near the surface of the coating layer 12 changes to molybdenum oxide in a high-temperature environment, and this volatilizes, creating gaps between the coating layer 12 and the ash and reducing the adhesion strength of the ash. That is, at least a portion of the molybdenum in the coating layer 12 may be present in the form of molybdenum oxide. The molybdenum content in the coating layer 12 is 10% by mass or more and 30% by mass or less, in terms of the ratio to the total of metal elements and metalloid elements. If the molybdenum content is less than 10% by mass, it is difficult to obtain the effect of improving ash shedding, and if it exceeds 30% by mass, oxidation resistance is likely to decrease.

[0026] The ratio of a metal element to the total of metal and metalloid elements refers to the content ratio of the target metal element or metalloid element when the total of the metal elements and metalloid elements contained in the coating layer 12 is taken as 100 mass %. The ratio of a metal element to the total of metal and metalloid elements can be measured by combustion-infrared absorption, volumetric, ICP, or gravimetric methods. Representative methods for measuring the major elements contained in the coating layer 12 include combustion-infrared absorption for carbon, volumetric for chromium, ICP for molybdenum, cobalt, boron, and nickel, and gravimetric for silicon. The combustion-infrared absorption method is a method in which a sample is burned and the amount of infrared absorption is measured. The volumetric method is a measurement method using redox titration. The ICP method is a method in which plasma energy is applied from an external source to excite atoms, and then the emission lines emitted when the atoms return to a lower energy level are measured. The gravimetric method is a method in which a sample is subjected to alkali fusion for measurement. Furthermore, in this specification, the term "metal element" includes alkali metals, alkaline earth metals, and transition metals. Metalloid elements include boron, silicon, germanium, arsenic, antimony and tellurium.

[0027] In order to improve the mechanical properties and corrosion resistance of the coating layer 12, the coating layer 12 further contains silicon, boron, cobalt, and nickel in addition to molybdenum. The coating layer 12 may further contain carbon or chromium.

[0028] Silicon dissolves in the matrix metal that constitutes the coating layer 12, contributing to improving the hardness and wear resistance of the coating. The silicon content in the coating layer 12 is 0.5% by mass or more and 2.5% by mass or less, expressed as a ratio to the total of metal elements and semi-metal elements. If the silicon content is less than 0.5% by mass, it is difficult to obtain the effect of improving the hardness and wear resistance of the coating, and if the silicon content exceeds 2.5% by mass, toughness decreases, making cracking and peeling more likely to occur.

[0029] Boron forms a complex boron with molybdenum and chromium, contributing to improving the hardness and wear resistance of the coating. The boron content in the coating layer 12 is 0.1% by mass or more and 1.0% by mass or less, expressed as a ratio of the total of metal elements and semi-metal elements. If the content is less than 0.1% by mass, it is difficult to obtain the effect of improving the hardness and wear resistance of the coating. If the content exceeds 1.0% by mass, toughness decreases, and cracking and peeling become more likely to occur.

[0030] Chromium forms complex borides with boron, contributing to improved hardness and wear resistance of the coating. Chromium also improves corrosion resistance in oxidizing acid environments by forming a passivation film. Furthermore, chromium is an effective element against oxidation or sulfidation in high-temperature environments. Chromium is not an essential element, and considering the environmental impact, it is preferable not to include chromium. On the other hand, from the viewpoint of further improving the hardness, wear resistance, and corrosion resistance of the coating, it is preferable that the coating layer 12 contains chromium. When the coating layer 12 contains chromium, specifically, it preferably contains 0.1% by mass or more of chromium relative to the total of metallic elements and semi-metallic elements, and more preferably contains 18% by mass or more of chromium. Furthermore, from the viewpoint of preventing a decrease in toughness and the occurrence of cracking and peeling, the chromium content in the coating layer 12 is preferably 38% by mass or less relative to the total of metallic elements and semi-metallic elements. Based on the above, the coating layer 12 may contain chromium in a ratio of 0% by mass to 38% by mass or less relative to the total of metallic elements and semi-metallic elements.

[0031] Cobalt dissolves in the matrix metal that constitutes the coating layer 12, contributing to improving the hardness and corrosion resistance of the coating. The cobalt content in the coating layer 12 is 5.5 mass % or more and 15 mass % or less, in terms of the ratio of the total of metal elements and semi-metal elements. If the cobalt content is less than 5.5 mass %, it is difficult to obtain the effect of improving the hardness and wear resistance of the coating, and if it exceeds 15 mass %, toughness decreases, and cracking and peeling are more likely to occur.

[0032] From the viewpoint of improving corrosion resistance, nickel is preferably used as the matrix metal constituting the coating layer 12. Therefore, the content of nickel in the coating layer 12 is the element that occupies the largest mass ratio among the metal elements and metalloid elements.

[0033] The coating layer 12 may contain carbon, but a low carbon content is preferable, and it is even more preferable that the coating layer 12 contains no carbon. Specifically, the carbon content in the coating layer 12 is 0.1 mass% or less, as determined by a method similar to the method for measuring the ratio of the carbon content to the total of the metal elements and metalloid elements described above. If the carbon content exceeds 0.1 mass%, the toughness decreases, and cracking and peeling become more likely to occur.

[0034] The coating layer 12 preferably contains, relative to the total of the metal elements and metalloid elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass to 0.1% by mass of carbon, 0% by mass to 38% by mass of chromium, 5.5% by mass to 15% by mass of cobalt, and nickel, the element with the largest mass ratio. Meanwhile, the remainder of the coating layer 12 may contain unavoidable impurities. "Avoidable impurities" refers to elements present in raw materials or unavoidably mixed in during the manufacturing process, such as elements other than silicon, molybdenum, chromium, cobalt, boron, and nickel. The content of the unavoidable impurities may be, for example, less than 0.1% by mass. The content of each element contained as an unavoidable impurity may be, for example, 0.05% by mass or less. Furthermore, by restricting the carbon content in the coating layer 12 to 0.1 mass % or less, and preferably by not containing carbon, peeling of the coating layer 12 from the base material 11 can be suppressed.

[0035] The method for forming the coating layer 12 is not particularly limited, and examples thereof include thermal spraying, laser cladding, and build-up welding.

[0036] 2, the film may further have a slidable material layer or a corrosion-resistant material layer 13 on the surface of the coating layer 12. In other words, the slidable material layer or the corrosion-resistant material layer 13 may form the outermost surface of the film.

[0037] The film has a sliding material layer 13 on the surface of the coating layer 12, which not only improves the ash shedding properties due to the molybdenum content of the coating layer 12, but also improves the sliding properties of the furnace surface, allowing colliding ash particles to slide on the furnace surface. This also improves the shedding properties of ash that adheres to the furnace surface and is cooled.

[0038] When the film has a slidable material layer 13 on the surface of the coating layer 12, the coating layer 12 plays the role of an anchor that enhances the fixation of the slidable material layer 13. By inserting the coating layer 12 between the base material 11 and the slidable material layer 13, the progression of corrosion of the base material 11 is prevented, and the slidable material layer 13 becomes less likely to peel off from the coating layer 12.

[0039] The slidable material layer 13 may be formed with a predetermined thickness on the surface of the coating layer 12. The thickness of the slidable material layer 13 is, for example, 10 to 90 μm. The slidable material layer 13 preferably contains an oxide ceramic and a compound having a layered crystal structure. Examples of oxide ceramics include oxides containing at least one of silicon, aluminum, chromium, manganese, and iron. A layered crystal structure is a crystal structure in which atoms or atomic groups are arranged in a plane to form a sheet structure, and the sheet structure is repeated in a direction perpendicular to this plane. Among these, those belonging to the hexagonal system are also called graphite-type crystal structures and are particularly highly symmetric. Examples of compounds that can form a graphite-type crystal structure include graphite, manganese sulfide, graphite fluoride, boron nitride, molybdenum disulfide, and tungsten disulfide. The slidable material layer 13 has a layered crystal structure that reduces surface friction resistance, allowing colliding ash particles to slip and improving the shedding of attached ash. Furthermore, the durability of the oxide ceramics inhibits the corrosion reaction between the ash and the coating layer 12 in a high-temperature environment.

[0040] The slidable material layer 13 may be formed by applying or spraying a slurry of the slidable material onto the surface of the coating layer 12. The slidable material can be made more coatable by including silicone in addition to the oxide ceramics and the compound having a layered crystal structure. Silicon is a polymer with a main chain formed by alternating bonds between silicon and oxygen atoms having organic groups, and examples include silicone resin, silicone rubber, silicone oil, and silicone grease. The proportion of the oxide ceramics contained in the slidable material is, for example, 1 to 30% by mass. The proportion of the compound having a layered crystal structure contained in the slidable material is, for example, 10 to 30% by mass. The proportion of the silicone contained in the slidable material is, for example, 10 to 50% by mass.

[0041] By providing the corrosion-resistant material layer 13 on the surface of the coating layer 12, it is possible to obtain the effect of improving the corrosion resistance of the surface of the furnace, in addition to the improvement in ash shedding due to the molybdenum contained in the coating layer 12. Specifically, by providing the corrosion-resistant material layer 13, it is possible to suppress the corrosion reaction between the adhered ash and the metal interface, thereby suppressing an increase in the adhesion strength of the ash. The corrosion-resistant material layer 13 preferably contains at least one material selected from the group consisting of aluminum oxide, silicon dioxide, and chromium oxide.

[0042] The coating according to this embodiment can be applied to furnaces such as coal gasifiers or pulverized coal-fired boilers.

[0043] The furnace on which the coating of this embodiment is formed may be applied to a combustion device to which a fuel containing at least one selected from the group consisting of coal, pulverized coal, biomass fuel, and ammonia is supplied. That is, the combustion device according to this embodiment includes a furnace on which the coating of this embodiment is formed and to which a fuel containing at least one selected from the group consisting of coal, pulverized coal, biomass fuel, and ammonia is supplied.

[0044] The furnace on which the coating of this embodiment is formed may be applied to a reactor to which at least one selected from the group consisting of coal, pulverized coal, biomass fuel, and ammonia is supplied as a raw material. That is, a reactor according to this embodiment includes a furnace on which the coating of this embodiment is formed, and to which at least one selected from the group consisting of coal, pulverized coal, biomass fuel, and ammonia is supplied as a raw material.

[0045] Pulverized coal is coal that has been crushed to a size of about several micrometers and is used as fuel for boilers.

[0046] Examples of biomass fuels include crushed materials produced by crushing woody biomass such as thinned wood, lumber scraps, and pruned branches using a crusher, sawdust, pellets produced from woody biomass, and agricultural residues.

[0047] Ammonia (NH ３ ) is a compound of hydrogen atoms (H) and nitrogen atoms (N), and does not contain carbon (C) as a constituent atom, so when it is burned, it does not produce CO ２ It is used as a fuel that does not emit CO ２ It can also be used in ammonia co-firing systems, in which ammonia and coal are mixed and burned to reduce emissions.

[0048] As described above, the coating according to this embodiment is a coating formed on the surface of the base metal 11 of a furnace, and includes a coating layer 12 containing molybdenum, silicon, boron, cobalt, and nickel. The molybdenum content of the coating layer 12 can suppress ash adhesion to the furnace or facilitate ash shedding in high-temperature environments. Furthermore, the inclusion of silicon, boron, cobalt, and nickel in the coating layer 12 in addition to molybdenum can improve mechanical properties and corrosion resistance. Therefore, by applying the coating layer 12 to the surface of the base metal, a coating with excellent mechanical properties, corrosion resistance, and ash shedding properties can be provided.

[0049] The alloy powder according to this embodiment is used to form the coating layer 12 of the film. The alloy powder is composed of an alloy containing, relative to the total of the metal elements and metalloid elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass to 0.1% by mass of carbon, 5.5% by mass to 15% by mass of cobalt, and nickel, which is the element with the largest mass ratio among the metal elements and metalloid elements. The alloy may further contain chromium, and the chromium content in the alloy is preferably 0% by mass to 38% by mass relative to the total of the metal elements and metalloid elements. That is, the alloy powder preferably contains, in ratios relative to the total of the metal elements and metalloid elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass or less of carbon, 0% by mass to 38% by mass of chromium, 5.5% by mass to 15% by mass of cobalt, and nickel, which is the element that occupies the largest mass ratio.

[0050] By forming the coating layer 12 using an alloy powder composed of an alloy containing molybdenum, it is possible to suppress ash adhesion to the furnace or facilitate ash shedding in a high-temperature environment. Furthermore, by adding silicon, boron, cobalt, and nickel to the alloy in addition to molybdenum, it is possible to improve mechanical properties and corrosion resistance. Therefore, by applying the coating layer 12 to the surface of the base material, it is possible to provide a film with excellent mechanical properties, corrosion resistance, and ash shedding properties.

[0051] Although the method for producing the alloy powder is not particularly limited, gas atomization is preferred. Gas atomization is a technique for finely pulverizing molten metal by spraying a high-pressure inert gas as a cooling medium onto the metal. Rapid cooling by the gas results in a finely and uniformly dispersed precipitate structure. Furthermore, since the produced powder has uniform composition for each particle, variations in the hardness and composition of the coating layer 12 are unlikely to occur, resulting in the formation of a homogeneous coating layer 12. Therefore, the ash adhesion suppression effect can be imparted uniformly to the entire coating layer 12, rather than locally.

[0052] The method for forming a film according to this embodiment includes a step of forming the coating layer 12 from the alloy powder described above. That is, the method for forming a film according to this embodiment includes a step of forming the coating layer 12 from an alloy powder including, in ratios relative to the total of metal elements and metalloid elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass or less of carbon, 5.5% by mass to 15% by mass of cobalt, and nickel, which is the element that occupies the largest mass ratio among the metal elements and metalloid elements. Furthermore, the coating formation method according to the present embodiment preferably includes a step of forming a coating layer 12 from an alloy powder composed of an alloy containing, in ratios relative to the total of metal elements and metalloid elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass to 0.1% by mass of carbon, 0% by mass to 38% by mass of chromium, 5.5% by mass to 15% by mass of cobalt, and nickel, the element with the largest mass ratio. The inclusion of molybdenum in the coating layer 12 can suppress ash adhesion to the furnace or facilitate ash removal in high-temperature environments. Molybdenum present near the surface of the coating layer 12 converts to molybdenum oxide in high-temperature environments, which volatilizes, creating gaps between the coating layer 12 and the ash, reducing the adhesion strength of the ash. Furthermore, the mechanical properties and corrosion resistance can be improved by including silicon, boron, chromium, cobalt, and nickel in addition to molybdenum in the coating layer 12. In this way, by including the step of applying the coating layer 12 to the surface of the base material 11, a method for forming a film that is excellent in mechanical properties, corrosion resistance, and ash shedding can be provided.

[0053] <Ash Adhesion Test> In order to evaluate the coating according to the present embodiment, an ash adhesion test was carried out using a horizontal combustion furnace as the furnace. In the ash adhesion test, the temperature inside the combustion furnace was simulated, and the state of ash adhering to the surface of a probe on which a coating was formed and exposed to the furnace was observed.

[0054] Fig. 3A is a cross-sectional view showing the structure of a combustion furnace used in the ash adhesion test. As shown in Fig. 3A, the combustion furnace 100 is configured horizontally, with the combustion chamber 101 extending approximately horizontally along a flow path from the inlet 102 to the outlet 103. The combustion chamber 101 has multiple segments detachably connected by flanges 105, and forms a preheating section 121, a combustion section 122, and an ash adhesion section 123 along the flow path.

[0055] In the preheating section 121, LPG and air are supplied from the inlet 102, and air and oxygen gas are further supplied along the flow path, causing the LPG to combust. A throat 104, where the flow path is narrowed, is formed at the transition point from the preheating section 121 to the combustion section 122. Pulverized coal stored in a tank 131 is supplied to the throat 104 by a coal supplier 133 through a supply path 135 together with air as a carrier gas. The calorific value of the supplied pulverized coal is 35 kW. In the combustion section 122, the pulverized coal supplied from the throat 104 is combusted. In the ash adhesion section 123, ash produced by the combustion of the pulverized coal adheres to the probe 111 and wall surfaces installed in the combustion chamber 101.

[0056] 3B is a cutaway perspective view showing the configuration of the segments 110 that make up the ash deposition portion 123 of the combustion chamber 101. The segments 110 are connected to each other by flanges 105, but the flanges 105 are omitted from this perspective view for simplicity. The cylindrical segment 110 is formed with a probe port 113 for introducing a probe 111 therein, an observation port 115, a sampling port 117, and a thermocouple port 119. The water-cooled probe 111 extends from the probe port 113 into the combustion chamber 101 and can be visually observed from the observation port 115. The diameter of the probe 111 is 31.8 mm. Samples of the combustion chamber 101 can be collected from the sampling port 117, and a thermocouple is inserted into the combustion chamber 101 from the thermocouple port 119.

[0057] 3A, symbols P1 to P6 indicate probes installed in the ash adhesion portion 123 of the combustion chamber 101. These probes P1 to P6 are located at 836, 1200, 1562, 1924, 2297, and 2794 mm, respectively, in the flow path direction with respect to the throat 104.

[0058] The ash adhesion test was carried out under slagging conditions. Slagging conditions are conditions in which molten ash adheres to the surface of the base material in an environment where the gas temperature is equal to or higher than the softening temperature of the ash. The slagging conditions were set to simulate the wall surfaces inside the furnace and at the furnace outlet, with an internal furnace temperature of 1,300°C and a probe surface temperature of 400°C. The time during which the probe was exposed to the above combustion atmosphere was defined as the exposure time.

[0059] Stainless steel (SUS304 steel) was used as the base material for the test samples used in the ash adhesion test. The coating layer had a matrix metal composed of nickel, and contained 30 mass% chromium, 15 mass% molybdenum, 10 mass% cobalt, 1.5 mass% silicon, and 0.5 mass% boron, relative to the total of the metal elements and metalloid elements. On the other hand, the carbon content of the coating layer was 0.05 mass% or less relative to the total of the metal elements and metalloid elements. The alloy powder used to form the coating layer was produced by gas atomization. The coating layer was then sprayed by atmospheric plasma spraying (using Ar-H as the plasma gas). ２ The coating layer contained molybdenum oxide formed when the molybdenum was atmospheric plasma sprayed, and the 15 mass % mentioned above also included the molybdenum present as molybdenum oxide.

[0060] The test sample having the base material and the coating layer prepared by the above method was designated as an example with coating, while the test sample having only the base material without the coating layer was designated as an uncoated comparative example.

[0061] Figure 4 is a graph comparing the porosity of the test samples after 3 hours of exposure, which were observed by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy) on the cross section of the coating surface. With the coating, the porosity was higher in the initial layer (the area closest to the probe surface) than without the coating.

[0062] Figures 5A and 5B show the results of SEM-EDS observations of the surface of the coating layer when a coating is applied, and Figure 5B is a photograph showing elemental mapping of molybdenum. When a coating is applied, molybdenum was confirmed on the surface of the coating layer and in the attached ash. Combined with the results of Figure 4, it appears that molybdenum oxide, formed in a high-temperature environment, is generated on the surface of the coating layer, reducing the adhesion strength of the ash.

[0063] 6A-6B and 7A-7B are photographs showing the state of a coated test sample in an ash adhesion test before and after air blowing. Each photograph shows an air nozzle 50 for spraying air during air blowing, and dry air was supplied to the air nozzle 50 from the outside via the sampling port 117 in FIG. 3B.

[0064] In the test sample after 1 hour of exposure, no ash was observed before air blowing, as shown in Figure 6A, but after air blowing, the center part turned black, confirming ash shedding, as shown in Figure 7A. On the other hand, in the test sample after 3 hours of exposure, no ash was observed before the air blowing test, as shown in Figure 6B, but after air blowing, ash shedding was confirmed, as shown in Figure 7B, similar to Figure 6B. Furthermore, comparing Figures 7A and 7B, it was confirmed that the amount of ash shedding was greater with an exposure time of 3 hours than with an exposure time of 1 hour. Therefore, it is believed that the ash that had adhered depending on the exposure time was able to be removed by air blowing.

[0065] Figure 8 shows the results of measuring the peak impact pressure (PIP*) (kPa) when ash is shed by air blowing, in order to quantitatively evaluate ash detachability. With the coating, the impact pressure PIP* was reduced by almost half compared to the uncoated case after an exposure time of 3 hours. Furthermore, with the coating, the impact pressure PIP* was lower than that of stainless steel (80 kPa) and carbon steel (8 kPa) after an exposure time of 1 hour. Therefore, it is believed that with the coating, ash detachability is improved compared to the uncoated case, stainless steel, and carbon steel.

[0066] Figure 9 shows the results of measuring the heat flux when ash adheres to the probe, and shows the heat flux when the maximum heat flux is normalized to 1. Heat flux (kW / m ２ ) is the amount of heat transferred per unit area when heat passes through the surface of an object or a cross section within it. The rate at which heat flux declines can be measured to determine the decline in heat transfer performance due to ash adhesion. In both the coated and uncoated cases, the heat flux initially declined sharply, followed by a gradual decline. In the coated case, the heat flux increased and recovered after one hour of exposure by blowing air. This is thought to be due to the ash falling off caused by the air blowing. In the uncoated case, however, no increase in heat flux was observed even after one hour of exposure, but the heat flux increased after three hours of exposure. Therefore, it appears that the ash shedding is improved in the coated case compared to the uncoated case.

[0067] From the above, it was confirmed that when a coating layer is formed on a base material, ash shedding is promoted compared to when no coating layer is formed. Therefore, the coating of this embodiment was found to have the effect of suppressing ash adhesion.

[0068] Although several embodiments have been described, the embodiments can be modified or varied based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined, unless they contradict each other.

[0069] This disclosure can contribute, for example, to Goal 7 of the United Nations-led Sustainable Development Goals (SDGs), "Ensure access to affordable, reliable, sustainable and modern energy for all" and Goal 13, "Take urgent action to combat climate change and its impacts."

[0070] The entire contents of Japanese Patent Application No. 2024-041189 (filing date: March 15, 2024) are incorporated herein by reference.

[0071] 11 Base material 12 Coating layer 13 Sliding material layer, corrosion-resistant material layer

Claims

1. A film formed on the surface of a furnace base material, having a coating layer containing, in ratios to the total of metallic elements and semi-metallic elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass to 0.1% by mass of carbon, 5.5% by mass to 15% by mass of cobalt, and nickel, which is the element with the largest mass ratio among the metallic elements and semi-metallic elements.

2. The film according to claim 1, wherein the coating layer further contains 0% by mass or more and 38% by mass or less of chromium relative to the total of metallic elements and semi-metallic elements.

3. The film according to claim 1 or 2, wherein at least a portion of the molybdenum in the coating layer is present in the form of molybdenum oxide.

4. The coating according to any one of claims 1 to 3, further comprising a sliding material layer on the surface of the coating layer, the sliding material layer comprising an oxide ceramic and a compound having a layered crystal structure.

5. The film according to any one of claims 1 to 4, further comprising a corrosion-resistant material layer on the surface of the coating layer, the corrosion-resistant material layer containing at least one material selected from the group consisting of aluminum oxide, silicon dioxide, and chromium oxide.

6. A furnace having the coating according to any one of claims 1 to 5 formed thereon.

7. A combustion device comprising the furnace according to claim 6, to which fuel containing at least one selected from the group consisting of coal, pulverized coal, biomass fuel and ammonia is supplied.

8. A reactor comprising the furnace according to claim 6, wherein at least one material selected from the group consisting of coal, pulverized coal, biomass fuel and ammonia is supplied as a raw material.

9. An alloy powder used to form the coating layer of the film according to any one of claims 1 to 5, the alloy powder being composed of an alloy containing, in ratios relative to the total of metallic elements and semi-metallic elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass to 0.1% by mass of carbon, 5.5% by mass to 15% by mass of cobalt, and nickel, the element which occupies the largest mass ratio among the metallic elements and semi-metallic elements.

10. The alloy powder according to claim 9, wherein the alloy further contains 0% by mass or more and 38% by mass or less of chromium relative to the total of the metallic elements and the semi-metallic elements.

11. A method for forming a film according to any one of claims 1 to 5, comprising the step of forming the coating layer from an alloy powder composed of an alloy containing, in proportions relative to the total of metallic elements and semi-metallic elements, 10% by mass to 30% by mass of molybdenum, 0.5% by mass to 2.5% by mass of silicon, 0.1% by mass to 1.0% by mass of boron, 0.1% by mass to 0.1% by mass of carbon, 5.5% by mass to 15% by mass of cobalt, and nickel, the element which occupies the largest mass ratio among the metallic elements and semi-metallic elements.

12. The method for forming a coating according to claim 11, wherein the alloy powder further contains chromium in a ratio of 0 mass % to 38 mass % relative to the total of metal elements and metalloid elements.

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