JPH10272317A - Porous material with high corrosion resistance at high temperature, and filter for high temperature exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous material with a high corrosion resistance at a high temperature, and useful as a filter for removing corrosion substances such as fly ash from an exhaust gas from a refuse incinerator. SOLUTION: This porous material has a porous sintered metal body as a base, and the surface and the inner faces of the opened voids in the base inside are coated with a ceramic coating. The base is produced by hydroisostatic pressure sintering at a low temperature under a low pressure, and the ceramic coating is formed by chemical evaporation. As the material of the ceramic coating, for example, oxides such as Al2 O3 , carbides such as SiC, nitrides such as Si3 N4 , borides such as TiB, and silicides such as MoSi are preferable and the thickness of the coating is several μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature resistant material useful as a filter for filtering out corrosive substances such as fly ash from high-temperature corrosive exhaust gas such as exhaust gas generated from an incinerator of waste such as refuse. It relates to a porous material excellent in corrosiveness.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of promoting effective use and diversification of energy, development of waste power generation technology and the like utilizing residual heat from incineration of waste such as refuse has been promoted. A waste heat recovery system for recovering thermal energy from high-temperature exhaust gas from a waste incinerator comprises a waste heat boiler, a super heater, a dust collector, a gas treatment tower, and the like. In the waste heat boiler, saturated steam is generated by heat exchange between the exhaust gas and water in the water pipe, and the saturated steam is sent to the super heater, and further heat-exchanged with the exhaust gas to be converted into high-temperature, high-pressure superheated steam. The superheated steam is supplied to a steam turbine and used for power generation. Exhaust gas that has passed through the waste heat boiler and super heater is dedusted by the dust collector,
After removal of hydrogen chloride, nitrogen oxides, sulfur oxides, etc. in the gas treatment tower, it is released into the atmosphere.

[0003]

The high-temperature exhaust gas generated from a refuse incinerator contains a high concentration of chlorine (about 500 to 2000 ppm), and fly ash in the exhaust gas contains bases such as sodium, potassium and calcium. Salt (NaCl, KCl, Na
₂ SO ₄ ). For this reason, it becomes a strong corrosive environment at high temperature, and there is a problem that the components of the waste heat recovery system are corroded and damaged. In order to increase the power generation efficiency of the waste heat recovery system, it is necessary to raise the temperature of the superheated steam in the super heater. However, in order to prevent corrosion of the heat exchange pipe, the temperature of the pipe wall must be relatively low (about (About 320 ° C), and the steam temperature in the pipe is at most 30.
It stays around 0 ° C.

In order to suppress and prevent corrosion of the members of the waste heat recovery system, corrosive substances in the gas may be removed on the upstream side of the exhaust gas passage, but the exhaust gas generated from the refuse incinerator has a remarkably high temperature ( (Eg, 800-950 ° C)
A bag filter made of glass fiber filter cloth, metal fiber, or the like, which has been conventionally used for high-temperature dust collection, has insufficient heat resistance and cannot be used. As a heat resistant filter that can withstand the high temperature of the exhaust gas, a ceramics filter,
It is conceivable to use a porous sintered material of heat-resistant metal, but ceramic filters can be broken by thermal shock, mechanical shock, thermal stress, etc., and it is difficult to guarantee stable use.
On the other hand, a porous material made of a heat-resistant metal has no brittleness problem,
It is difficult to ensure sufficient corrosion resistance to salts and the like contained in fly ash. The present invention provides a porous material having high-temperature corrosion resistance and toughness, which is useful as a filter for removing fly ash from exhaust gas from waste incinerators such as refuse.

[0005]

The porous body of the present invention is obtained by subjecting a porous sintered body made of a refractory metal to a chemical vapor deposition treatment.
It is characterized in that its surface and the inner surface of the open pores are covered with a ceramic film.

In general, ceramics have excellent high-temperature strength, low wettability with salts, and exhibit excellent high-temperature corrosion resistance. Although the metal has toughness, it has good wettability with salts, and even if it is a heat-resistant and corrosion-resistant alloy, it cannot avoid the adhesion of salts and significant corrosion in a high-temperature environment. The porous body of the present invention has a porous metal sintered body as a base,
High toughness against corrosive substances such as salts in high-temperature exhaust gas due to having the toughness required as a component of exhaust gas filters and the like and the surface and the inner surface of open pores (through pores) are coated with a ceramic film. Has resistance.

FIG. 1 schematically shows a cross section of the porous body of the present invention. (1) is a heat-resistant metal particle constituting a porous metal sintered body as a substrate, and (2) is a ceramic film formed by chemical vapor deposition. Ceramic coating (2)
Covers the outer surface of the substrate and the surface of the open pores (3) penetrating the inside thereof, and shields the substrate from high-temperature corrosion by blocking contact between the high-temperature corrosive exhaust gas and the substrate. In addition, the low wettability of the ceramic film with salts prevents the adhesion of fly ash and the like in exhaust gas filter applications,
Facilitates filter regeneration by backwashing.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The type of heat-resistant metal constituting a substrate (porous metal sintered body) is appropriately selected according to the specific use and environmental conditions of the porous material. Exhaust gas filters for refuse incinerators include, for example, carbon steels and alloy steels for boilers, stainless steels, heat-resistant steels, Ni-based / Co-based heat-resistant alloys (Inconel, Hastelloy, Stellite, etc.). And the like are also suitable. The porosity and pore diameter of the substrate are arbitrarily controlled by the metal particle diameter and the sintering conditions. In an exhaust gas filter of a refuse incinerator, for example, the average pore diameter is about 30 to 70 μm, and the porosity is about 15 to 40%.

The ceramics covering the outer surface of the porous substrate and the surface of the open pores penetrating the inside thereof can be selected from a wide range such as oxides, carbides, nitrides, borides and silicides. In particular, as a ceramic film of a high-temperature gas filter in which chlorine gas is present, such as exhaust gas from a refuse incinerator, and in which fly ash containing basic salts such as Na, K, and Ca is mixed, alumina (as an oxide) Al ₂ O ₃ ), sialon (SiAlNO), silicon carbide (SiC) as a carbide, silicon nitride (Si ₃ N ₄ ) as a nitride, titanium boride (TiB ₂ ) as a boride, and molybdenum silicide (MoSi) as a silicide. Are preferred. The thickness of these ceramic films may be several μm (about 1 to 5 μm).

[0010] The porous body of the present invention is manufactured by sintering a metal powder as a sintering raw material to form a porous metal sintered body as a base, and forming a ceramic film by chemical vapor deposition. [Production of Porous Metal Sintered Body] For the sintering of metal powder, it is preferable to apply hot isostatic pressing sintering (HIP). According to the HIP treatment, a homogeneous porous sintered body can be obtained regardless of the shape and size. HIP
The treatment is suitably achieved by the following Method A or Method B. Method A: Encapsulate metal powder in a capsule and use H at low temperature and low pressure.
Perform IP processing. Method B: A metal powder is molded under pressure, and HIP treatment is performed without encapsulating the compact.

First, the method A (low-temperature low-pressure HIP processing) will be described.
Unlike ordinary HIP processing for producing high-density sintered products, the sintered body is made into a porous body (for example, porosity: about 15 to 40%, pore diameter: about 30 to 70 μm) necessary for a filter or the like. To do that. The encapsulation of the metal powder is also replaced with the vacuum (reduced pressure) encapsulation in the normal HIP process.
N2 _, Ar, etc.).
The HIP treatment is preferably performed at a temperature of 0.35 to 0.85 mpK.
[However, mpK is the melting point of metal powder (absolute temperature)], pressure:
It is adjusted to 5 to 150 MPa. The porous sintered body obtained by the low-temperature low-pressure HIP treatment is subjected to a heat treatment (strengthening heat treatment) for strengthening the interparticle bonding, if desired. The processing temperature is suitably in the range of about 0.6 to 0.95 mpK, whereby the mechanical strength of the sintered body can be increased without impairing the porosity of the sintered body. The heat treatment can be performed in the HIP device in a state where the pressurizing action of the hydrostatic medium is released.

On the other hand, the method B (compacted capsule-free HI
The green compact in the case of (P treatment) is formed by uniaxial press molding, extrusion molding, cold isostatic pressing (CIP molding), or the like, but is preferably formed by CIP molding from the viewpoint of homogeneity. The relative density of the green compact required to make the sintered body porous is about 95% or less (about 30 to 95%), and the molding pressure is, for example, 50 to 250 MPa.

The HIP treatment of the green compact is performed in a state where a pressure medium (an inert gas such as Ar or N ₂ ) is in contact with the green compact. The processing temperature is adjusted to about 0.7 to 0.95 mpK (mpK is as defined above), and the pressure is adjusted to about 5 to 150 MPa. This processing condition is almost the same as the normal HIP processing for the purpose of high-density sintered body. However, unlike the normal HIP processing, when the pressure action of the hydrostatic medium acts on the surface of the green compact. At the same time, it acts on the interior through the open pores. For this reason, the particles can be sintered together without impairing the porosity of the green compact, and can be baked into a sintered body having high mechanical strength and toughness. Therefore, in this case, the strengthening heat treatment after the HIP treatment in the above method A is not particularly required.

[Formation of Ceramic Coating by Chemical Vapor Deposition] The porous metal sintered body formed as a HIP sintered body has a surface and an open contaminant (oil, scale, moisture) as a pretreatment for chemical vapor deposition. Etc.). The treatment can be performed by various methods known as cleaning treatment of metal materials (such as pickling, electrolytic pickling, alkali degreasing, solvent degreasing, electrolytic degreasing, ultrasonic cleaning, etc.), and the metal material type and adhered contaminants of the sintered body. Appropriate purification processing is applied according to the type and the like.
After the cleaning treatment, the surface and the inside of the open pores are sufficiently dried and then subjected to a chemical vapor deposition treatment.

In chemical vapor deposition, a film composition is formed on an object to be processed by a thermochemical reaction of a regulated gas or a gas mixture containing a halide, sulfide, hydride or the like as a raw material gas. The resulting film has high adhesion and is dense. By flowing the raw material gas into the open pores of the workpiece (porous metal sintered body), the inner surface of the open pores can also be covered with the dense ceramic film.
The vapor deposition process can be performed using a normal chemical vapor deposition apparatus, and it is sufficient that the raw material gas has sufficient time to flow into the open pores, and is suitable for the inlet side and the outlet side of the open pores of the object to be processed. By applying an appropriate pressure difference and promoting the flow of the raw material gas into the open pores, the processing can be efficiently achieved.

FIG. 2 schematically shows an example of the above-mentioned vapor deposition processing apparatus. (10) is a reaction vessel, (11) is a heater, (12) is a source gas supply pipe, and (W) is an object to be treated charged in the reaction vessel. The object to be treated (porous metal sintered body) in this example is a hollow cylindrical body, which is placed upright on a table (13) in a reaction vessel (10), and a top end face is covered with a lid member (14). An exhaust pipe (15) communicating with the inner space of the hollow cylindrical body is connected to the lid (14). The inside of the reaction vessel (10) is filled with a source gas supplied from a source gas supply pipe (12), and the workpiece (W) is heated and maintained at a predetermined temperature by a heater (11). The raw material gas in the reaction vessel (10) permeates through the open pores of the workpiece (W) and flows into the inner space. Thereby, the object to be processed (W)
In the method, the raw material gas comes into contact with the outer and inner surfaces and the entire inner surface of the open pores to form a film by chemical vapor deposition.

The composition of the raw material gas and the temperature of the vapor deposition treatment are adjusted according to the type of the ceramic film to be formed. For example, chemical vapor deposition of an alumina film (Al ₂ O ₃ ) is performed using aluminum chloride (AlCl ₃ ), carbon dioxide (CO ₂ )
And a mixed gas consisting of hydrogen and hydrogen (H ₂ ) as a source gas,
The treatment is performed at a processing temperature of about 1000 ° C. Silicon nitride film (Si
₃ N ₄ ) is composed of silicon tetrachloride (SiCl ₄ ) and ammonia (N
H ₃ ) can be used to form a film at a processing temperature of about 1200 ° C. The silicon carbide film (SiC)
Using a mixed gas of ₄ and propane (C ₃ H ₈ ), a film is formed at a processing temperature of about 1200 ° C. Also, titanium boride coating
(TiB ₂ ) is titanium tetrachloride (TiCl ₄ ) and boron trichloride (BC
l ₃ ) can be used to form a film at a processing temperature of about 1150 ° C. In addition, a ceramic film can be formed by a reaction between an alloy element of an object to be processed (porous metal sintered body) and a raw material gas.
In the case of a sintered body made of an Mo-containing alloy (nickel-chromium molybdenum alloy or the like), by using SiCl ₄ as a raw material gas and treating at about 1000 ° C., molybdenum silicide (M
oSi) ceramic film can be formed.

Since metals and ceramics generally have different coefficients of thermal expansion, the difference in the coefficient of thermal expansion ensures that the adhesive strength at the interface between the substrate (porous metal sintered body) and the ceramic film is sufficiently ensured. In such a case, the ceramic film may have a laminated structure including a plurality of layers of different material types, and have a gradient of the coefficient of thermal expansion in the film thickness direction. For example, when a porous sintered body of stainless steel or the like is to be processed and an Al ₂ O ₃ film is formed thereon, for example, a TiC film is formed as a first layer and a TiN film is laminated as an intermediate layer. By laminating an Al ₂ O ₃ film thereon, the gradient of the thermal expansion coefficient is reduced, and the adhesion strength of the film to the substrate is increased. This laminated structure can be used to switch the source gas during chemical vapor deposition,
It can be easily formed by adjusting the processing temperature.

[0019]

【Example】

[1] Production of substrate (porous metal sintered body) (1) Sintering raw material: atomized powder (average particle size: 200 μm) (2) HIP treatment and heat treatment Treatment temperature: 0.56 mpK (mpK is the melting point of metal powder) (Absolute temperature) Pressure: 100 MPa, Processing time: 3 Hr After the HIP processing, the pressurizing action of the pressure medium is released and the strengthening heat treatment is performed in the HIP apparatus. Treatment temperature: 0.85 mpK, treatment time: 10 Hr After the heat treatment, the capsule is removed by machining to obtain a porous metal sintered body. The sintered body is a hollow cylindrical body (outer diameter: 100, wall thickness: 2, length: 300, mm), and all have a porosity:
About 28%, average pore size: about 70 μm.

[2] Formation of Ceramic Coating (1) A ceramic deposited film is formed on a substrate by a chemical vapor deposition apparatus shown in FIG. 2 to obtain a porous material. The treatment time was adjusted so that the film thickness in the open pores was about 1 to 3 μm (total layer thickness in the case of a multilayer film). Alumina (Al ₂ O ₃ ) film: AlCl ₃ -CO ₂ -H ₂ gas, processing temperature 1000 ℃ Silicon carbide (SiC) film: SiCl ₄ -C ₃ H ₈ gas, processing temperature 1
000 ℃ Silicon nitride (Si ₃ N ₄ ) film: SiCl ₄ -NH ₃ gas, processing temperature
1200 ° C Titanium boride (Ti B ₂ ) film: TiCl ₄ -BCl ₃ gas _, processing temperature
1150 ℃ Molybdenum silicide (MoSi) film: SiCl ₄ gas, processing temperature 1000
℃ Titanium carbide (TiC) film: TiCl ₄ -CH ₄ -H ₂ gas _, processing temperature 1200 ℃ Titanium nitride (TiN) film: TiCl ₄ -N ₂ -H ₂ gas _, processing temperature 9
00 ℃

[3] Properties of the test porous body (1) Bending strength measurement A three-point bending test specified in JIS B1601 (span distance: 30 mm, test temperature: normal temperature).

(2) Filtration test The following mixed gas (actual furnace gas standard composition) and ash (actual
Crushed powder, particle size 10 μm or less)
Permeate the porous material (hollow cylinder) from outside to inside space
You. Fly ash capture from weight change of porous material before and after filtration test
Find the quantity. Mixed gas: NO 100ppm, SO_Two50ppm, HCl 1000ppm, CO 1
00ppm, CO_Two10ppm, O _Two10%, H_TwoO 20%, N_TwoBal. Ash composition: Al 3.8, Si 5.07, Fe 1.72, Na 6.43, K 7.7
7, Ca 14.2, Mg 1.56, Pb 0.78, Zn 1.95, Total S 13.4
5, Total Cl 2.06, H_TwoO 0.43 (mass%). Ash concentration in gas: 5 gr / Nm^Three Gas flow: 500 cm^Three / min Test temperature: 700 ° C Test time: 96 Hr

(3) Backwashing test Fly ash trapped in the test porous material is backwashed and removed, and the difficulty of backwashing is evaluated based on the change in weight of the porous material before and after backwashing. The backwashing process was repeated 5 times using pressurized air (5 kgf / mm ² , room temperature) and opening and closing the solenoid valve (opening time 0.1 sec).

In Table 1, "A" and "B" (A:
The production conditions and the porosity (porosity, average pore diameter, etc.) of the substrate of the comparative example having no ceramic film and B: the invention example in which the ceramic film was formed by vapor deposition) were substantially the same. The numerical value in the column of “Filter / Backwash Test” indicates the fly ash weight of the test porous material as a ratio of “1” to the fly ash capture weight in the filtration test of the porous material A (without a ceramic film). ing. In the column "Amount of fly ash trapped", the larger the value, the higher the efficiency of fly ash filtration. In the column "Remaining amount of fly ash after backwashing", the smaller the value, the easier the filter regeneration by backwashing Is shown.

As shown in Table 1, a comparison between the porous material A having no ceramic film (Comparative Example) and the porous material B having the same (Inventive Example) shows that both of the mechanical members required as a filtering member were used. While having strength, the filtration efficiency of fly ash in the exhaust gas filtration is almost the same, but there is a great difference in the difficulty of backwashing / regeneration after the filtration. That is, in the porous material, even if the backwashing treatment is performed, most of the captured fly ash remains as it is, whereas the porous material B is
Almost all of them have been washed away by backwashing, and have been restored to a clean state before use. The difference is that in the porous material A, the fly ash reacts and adheres to the surface (metal surface) of the porous body, while the porous material B reacts and adheres to the fly ash by the ceramic film. It is because suppression is prevented. Fly ash deposits cause filter clogging. The porous material B of the invention example is different from the porous material A due to the effect of the ceramic film, in which the corrosive action of fly ash and the accompanying deposition of fly ash are prevented, and regeneration by backwashing is easy, A good filtration function can be stably maintained.

[0026]

[Table 1]

[0027]

Since the porous material of the present invention has both the toughness of the metal constituting the substrate and the high-temperature corrosion resistance of the ceramic film covering the metal surface of the substrate, it is generated from, for example, a refuse incinerator. Useful as a filter for filtering high-temperature exhaust gas containing corrosive substances such as fly ash.Corrosion damage of components such as waste heat boilers and super heaters in waste heat recovery systems of refuse incinerators by filtering fly ash from exhaust gas. This is effective in stabilizing the operation of the waste heat recovery system. Also, high-temperature operation becomes possible, and power generation efficiency can be greatly increased by increasing the temperature and pressure of the superheated steam. In addition, the porous material of the present invention is useful as a constituent member of various devices requiring high-temperature corrosion resistance, such as an air preheater used in a refuse incinerator.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a porous material of the present invention.

FIG. 2 is a schematic illustration of a chemical vapor deposition process of a ceramic film on a substrate (porous metal sintered body).

[Explanation of symbols]

 1: Metal particles of a substrate (porous metal sintered body) 2: Ceramic film 3: Open pores 10: Reaction vessel: 11: Heater 12: Source gas supply pipe 13: Table 14: Lid 15: Exhaust pipe W: Substrate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takahiro Kitagawa 1-1-1, Nakamiya Oike, Hirakata City, Osaka Prefecture Inside Kubota Hirakata Plant Co., Ltd. (72) Akira Kosaka 1-1, Nakamiya Oike, Hirakata City, Osaka Prefecture No. 1 Inside Kubota Hirakata Manufacturing Co., Ltd. (72) Inventor Hideo Fujita 1-1-1 Nakamiya Oike, Hirakata City, Osaka Prefecture Inside Co., Ltd. Kubota Hirakata Manufacturing Co., Ltd. No. 1 in the Kubota Hirakata Plant

Claims (4)

[Claims] 1. A porous material excellent in high-temperature corrosion resistance, characterized in that a porous sintered body made of a heat-resistant metal is subjected to a chemical vapor deposition treatment, and its surface and inner surfaces of open pores are coated with a ceramic film. . 2. The porous material excellent in high-temperature corrosion resistance according to claim 1, wherein the ceramic is made of an oxide, carbide, nitride, boride or silicide. 3. The method according to claim 1, wherein the oxide is alumina or sialon,
3. The porous material having excellent high-temperature corrosion resistance according to claim 2, wherein the carbide is silicon carbide, the nitride is silicon nitride, the boride is titanium boride, and the silicide is molybdenum silicide. 4. A high temperature exhaust gas filter comprising the porous material according to claim 1. Description: