JPH09250897A - Heat transfer complex pipe for waste heat boiler utilizing dust combustion discharged gas with superior anti-particle corrosion characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer complex pipe of a waste heat boiler utilizing dust combustion discharged gas having a high temperature anti-corrosion characteristic, in particular a superior anti-particle corrosion characteristic. SOLUTION: This heat transfer complex pipe for a waste heat boiler utilizing dust combustion discharged gas with a superior high temperature anti-particle corrosion includes an outer layer composed of an Ni base alloy having a composition of Cr: 38 to 50wt.%, C: 0.001 to 0.05wt.%, Si: 0.1wt.% or less, Mg: 0.001 to 0.1wt.%, B: 0.001 to 0.1wt.%, P: 0.03wt.% or less, S: 0.03wt.% or less, one or two of Mo and W: 0.1 to 2wt.%, and further includes the following (a) and/or (b) as required, the balance is Ni and unavoidable impurities, and a normal steel for a boiler, where (a) one or two elements or more of rare earth elements: 0.001 to 0.1wt.%, Y: 0.001 to 0.1wt.%, Zr: 0.001 to 0.1wt.%, Hf: 0.001 to 0.5wt.% and (b) one or two elements or more of Mn: 0.01 to 1.0wt.%, Ca: 0.001 to 0.1wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite pipe for heat transfer of a waste heat boiler utilizing refuse incineration exhaust gas, which is excellent in high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance.

[0002]

2. Description of the Related Art Generally, a waste heat boiler is installed in a refuse incineration plant for the purpose of utilizing high-temperature latent heat of exhaust gas. Further, the composite tube for heat transfer, which is a structural member of the waste heat boiler, is made of highly corrosive HCl or SO ₂ gas, Na ₂ SO ₄
Exposed to high-temperature exhaust gas containing corrosive products such as molten sulfates such as molten chlorides such as NaCl and KCl, and placed in an environment where the sulfates and chlorides are deposited on the surface. Therefore, various materials having excellent high-temperature corrosion resistance are used for the production.

Conventionally, as various materials excellent in high temperature corrosion resistance, Cr: 38 to 50 by weight% (hereinafter,% means weight%) as seen in JP-A-1-132732.
%, C: 0.05% or less, N: 0.04% or less, one or two kinds of Mo and W: 0.1 to 2%, and the balance of Ni and unavoidable impurities. Have N
A material composed of an i-based alloy is known, and an idea of incorporating a heat transfer tube composed of this Ni-based alloy into a waste heat boiler is also known, and a heat transfer tube composed of these materials is also known. Since it is generally expensive, it is used as a heat transfer tube that covers the outside of ordinary boiler steel and a composite pipe consisting of an inner layer made of ordinary boiler steel and an outer layer made of newly developed Ni-based alloy. Attempts to use are also known.

[0004]

On the other hand, due to the recent urgent energy situation, there is a tendency to increase the steam condition of the waste heat boiler to high temperature and pressure in order to maximize the use of waste heat from waste incineration. As a result, the wall temperature of the heat transfer composite pipe further rises, and the corrosiveness of exhaust gas tends to become more violent due to high calorie content and increase in plastics. It is easy to occur. From this point, the heat transfer composite pipe of the waste heat boiler has
Further conventional intergranular corrosion resistance is required, and the above-mentioned various conventional materials provided to meet this requirement have considerably improved high-temperature corrosion resistance to exhaust gas, but they are still insufficient. The life of the composite tube for heat transfer consisting of was not fully satisfactory.

[0005]

Means for Solving the Problems Accordingly, the present inventors have
From the above viewpoints, as a result of conducting research to develop a heat transfer composite pipe for a waste heat exhaust gas utilization waste heat boiler, which has excellent high temperature corrosion resistance and further excellent intergranular corrosion resistance, and has a long life, ( a) Ni described in Japanese Patent Application Laid-Open No. 1-132732
Since the heat transfer tube made of a base alloy does not have sufficient resistance to high-temperature intergranular corrosion, it has strong corrosive properties such as HCl, SO ₂ gas, and Na.
Molten sulfate such as ₂ SO ₄ , K ₂ SO ₄ and NaC
When molten chlorides such as 1, KCl, PbCl ₂ , ZnCl ₂ and the like adhere to the surface and are exposed to high temperature exhaust gas at 300 to 1000 ° C., intergranular corrosion proceeds, resulting in sufficient high temperature corrosion resistance. Is not obtained, and therefore a sufficient life cannot be obtained. (B) When the composition of the Ni-based alloy described in the above-mentioned conventional Japanese Patent Laid-Open No. Hei 1-132732 is partially recombined and further added, in particular, when Mg: 0.001 to 0.1% is contained, the hot workability is A Ni-based alloy that is excellent and has improved high temperature intergranular corrosion resistance is obtained, and when a heat transfer composite pipe of a waste incineration exhaust gas utilization waste heat boiler having an outer layer composed of this Ni-based alloy is manufactured by plastic working, Mg from 0.001 to 01. %, The outer layer composed of the Ni-based alloy has excellent hot workability, so that a heat transfer composite tube with excellent adhesion to the inner layer made of ordinary steel for boilers can be obtained. From the excellent inter-field corrosion resistance, the research results showed that as a result, the high temperature corrosion resistance was further improved and the life of the heat transfer composite pipe was further extended.

The present invention has been made based on the above-mentioned research results. Cr: 38-50%, C: 0.001-0.05%, S
i: 0.1% or less, Mg: 0.001 to 0.1%, B:
0.001-0.1, P: 0.03% or less, S: 0.0
3%, Mo and W: 0.1 to 2%, and
(A) Rare earth element: 0.001 to 0.
1%, Y: 0.001-0.1%, Zr: 0.001-
0.1%, Hf: 0.001 to 0.5%, one or more kinds thereof, (b) Mn: 0.01 to 1.0%, C
a: One or two of 0.001 to 0.1%, the above (a) and / or (b) are contained, and the balance is composed of a Ni-based alloy having a composition of Ni and inevitable impurities. It is characterized by a heat transfer composite pipe of a waste incineration exhaust gas waste heat boiler which is excellent in high temperature corrosion resistance, particularly high temperature intergranular corrosion resistance, which is composed of an outer layer and an inner layer made of ordinary boiler steel.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The heat transfer composite pipe of the waste incinerator exhaust gas utilization waste heat boiler excellent in high temperature corrosion resistance of the present invention is prepared by using an ordinary high frequency melting furnace to prepare a Ni-based alloy molten metal having the above-described component composition and cast into an ingot. And then 10 for this ingot
Hot forging is performed at a predetermined temperature within the range of 0 to 1250 ° C. to obtain a round bar material, and then the round bar material is carved out to produce an outer tube having a predetermined diameter and wall thickness. As a normal boiler steel with a specified diameter and wall thickness, after descaling these outer and inner pipes, insert the inner pipe inside the outer pipe and pull it out at a predetermined surface reduction ratio. After processing, the outer tube was plastically deformed to bring the outer tube into close contact with the inner tube, thereby producing a composite shell. These composite shells are placed in a heating furnace, heat-treated at a predetermined temperature for a predetermined time, and then rolled by a helical roll mill.

Since the Ni-based alloy of the present invention contains Mg: 0.001 to 0.1% in addition to the main component of the conventional Ni-based alloy, it has excellent hot workability and high temperature grain boundary resistance. It becomes a Ni-base alloy with improved corrosiveness, and the outer layer composed of this Ni-base alloy has excellent hot workability. Therefore, it is a composite tube for heat transfer with excellent adhesion to the inner layer made of ordinary boiler steel. In addition, since the high temperature intergranular corrosion resistance is excellent, the high temperature corrosion resistance is further improved as a result, and highly corrosive HCl, SO ₂ gas, molten sulfate such as Na ₂ SO ₄ , K ₂ SO ₄ , Furthermore, NaCl, KCl, PbCl ₂ ,
Even in an environment where molten chloride such as ZnCl ₂ adheres to and deposits on the surface and is exposed to high temperature exhaust gas at 300 to 1000 ° C., a composite tube for heat transfer having a long life, which has not been seen in the past, can be obtained. Even under the above-mentioned energy circumstances, it is sufficiently satisfactory as a heat transfer composite pipe for an excellent waste incineration exhaust gas-use waste heat boiler capable of maximally utilizing waste heat from waste incineration. In this case, the outer layer composed of a Ni-based alloy has a function of ensuring high-temperature corrosion resistance, particularly high-temperature intergranular corrosion resistance, and the inner layer of ordinary boiler steel has a function of providing strength and steam oxidation resistance. Is.

The "normal boiler steel" used in the heat transfer composite pipe of the waste incineration exhaust gas utilization waste heat boiler excellent in high temperature corrosion resistance of the present invention is specifically JIS 3461 to 34.
Boiler heat exchangers specified in 64 and 3467 are carbon steel, low alloy steel, ferritic stainless steel, austenitic stainless steel, etc., but the steel type can be appropriately selected depending on the use conditions, and is not particularly limited. It is not something that will be done.

Further, the heat transfer composite pipe of the waste incineration exhaust gas utilization waste heat boiler excellent in high temperature corrosion resistance of the present invention, a normal boiler steel pipe is inserted into a pipe made of Ni-based alloy,
Although it is produced by a conventional plastic working method, the outer layer composed of the Ni-based alloy can also be produced by thermal spraying or overlay welding the new Ni-based alloy of the present invention.

Next, the reason why the composition of the Ni-base alloy forming the outer layer of the heat transfer composite tube of the present invention is limited as described above will be explained. (A) Cr The Cr component has a function of improving the high temperature corrosion resistance and the high temperature oxidation resistance to the high temperature waste incineration exhaust gas in the coexisting state, and also improving the high temperature strength, but when the content thereof is less than 38%. The desired effect is not obtained in the above action,
On the other hand, if its content exceeds 50%, it becomes brittle and cracks are likely to occur during the molding process.
50%, preferably 38-47%, more preferably 4
It was set to 3 to 47%.

(B) C C component has the effect of improving high temperature strength, but if its content is less than 0.001%, the desired high temperature strength cannot be ensured, while its content is less than 0.1%. If it exceeds 05%, the amount of carbides existing in the grain boundaries increases, and the progress of intergranular corrosion due to the molten chloride contained in the high-temperature exhaust gas is promoted. The amount was defined as 0.001-0.05%.

(C) Si Since the Si component has a deoxidizing action, it is used for deoxidizing the molten metal. In this case, if the content exceeds 0.1%, the toughness tends to decrease, The content was set to 0.1% or less.

(D) Mg The Mg component has the effect of improving grain boundary erosion resistance and hot workability, but its content is 0.001%.
When the content is less than the above, the desired effect cannot be obtained, while when the content exceeds 0.1%, a metal compound is formed at the grain boundary,
Since the hot workability and the corrosion resistance are reduced, the content thereof is set to 0.001 to 0.1%.

(E) BB The component B has the effect of improving hot workability, but if its content is less than 0.001%, the desired effect cannot be obtained, while its content is 0.1. %, A compound is formed at the grain boundaries, and the hot workability and high temperature intergranular corrosion resistance are deteriorated. Therefore, the content is 0.001 to 0.1.
%, Desirably 0.001 to 0.01%.

(F) P and S These components are P: 0.03% and S: 0.
If it exceeds 03%, segregation occurs in the grain boundaries, which deteriorates hot workability and also decreases high-temperature corrosion resistance. Therefore, its content is P: 0.03% or less and S:
It was determined to be 0.03% or less.

(G) Mo and W These components both dissolve in the base material and have the effect of further improving the corrosion resistance in the coexistence of Cr, Mo and W, but their contents are 0.1%. If the content is less than the above, the desired excellent corrosion resistance cannot be ensured, while if the content exceeds 2%, the moldability becomes remarkably reduced, so the content is preferably 0.1 to 2%. Is from 0.5
It was set at 1.5%.

(H) Rare earth element, Y, Zr, and Hf These components have an effect of improving hot workability, so they are contained as necessary. However, the content of any of the components is 0. If it is less than 0.001%, the desired hot workability-improving effect cannot be obtained. On the other hand, if the content is less than 0.1% for rare earth elements, Y and Zr, and more than 0.5% for Hf. Since the hot workability does not provide any further improvement effect, the content of the rare earth element: 0.001-
0.1%, Y: 0.001 to 0.1%, Zr: 0.00
1 to 0.1%, and Hf: 0.001 to 0.5%.

(I) Mn and Ca The Mn and Ca components have a deoxidizing effect and have an effect of improving the corrosion resistance, so they are contained if necessary, but the content is 0.01% of the Mn component. , Ca component 0.00
If it is less than 1%, the desired effect cannot be obtained. On the other hand, if its content exceeds 0.1% in the Mn component and 0.1% in the Ca component, precipitate phases thereof are formed and the hot workability and Since the corrosion resistance decreases, the content of Mn component is 0.0
1-1.0%, 0.001-0.1% with Ca component
It was decided.

(J) Inevitable Impurities Ti and Al may be contained as unavoidable impurities, but if the content of each of these components exceeds 0.4%, the hot workability will be impaired. The content of each must be kept to 0.4% or less.

[0021]

EXAMPLES Next, examples of the present invention will be specifically described. Using a normal high-frequency melting furnace, a Ni-base alloy melt having the composition shown in Tables 1 to 4 was prepared, cast into an ingot, and hot forged at a predetermined temperature within the range of 1150 ° C. in the ingot. A round bar material with a diameter of 55 mm is applied, and then the diameter of this round bar material is 50 mm x wall thickness: 6
Outer pipes having the component compositions shown in Tables 1 to 3 were produced by cutting into a size of mm. Further, as an inner tube, SUS having dimensions of outer diameter: 42 mm x wall thickness: 6.0 mm
A 304 stainless steel pipe was prepared. After descaling these outer and inner pipes, insert the inner pipe inside the outer pipe and perform drawing at a predetermined surface reduction ratio to plastically deform the outer pipe and bring it into close contact with the inner pipe. Thus, a composite tube was produced.
These composite raw tubes were put in a heating furnace and kept at 1180 ° C. for 1 hour, and then further rolled by a helical roll mill to obtain a composite tube for heat transfer 1 of the present invention having outer layer thickness: 3 mm, diameter: 38.1 mm. .About.35 and comparative heat transfer composite pipes 1 and 2, respectively. Further, as a conventional technique, using the alloy found in JP-A-1-132732,
A conventional heat transfer composite tube was manufactured by the same method as described above. In the comparative heat transfer composite pipes 1 and 2, among the constituent components of the Ni-based alloy constituting the outer layer, the content of Mg that affects the high temperature intergranular corrosion resistance is outside the scope of the present invention. .

Next, the various heat transfer composite pipes obtained as a result are incorporated into a waste heat boiler, and the waste heat boiler is installed in a refuse incineration facility with a processing capacity of 250 tons / day. Surface temperature: 550 ° C, exhaust gas temperature: 65
After operating for 2000 hours under the condition of 0 ° C., take out the heat transfer composite pipe after the operation, measure the wall thickness in the circumferential direction with the ash content and scale produced on the surface removed,
The maximum amount of wall thinning was determined, the cross-sectional microstructure of the surface was observed, and the maximum intergranular corrosion length was measured. Table 5 shows the results of these measurements.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

[0028]

From the results shown in Tables 1 to 5, the composite pipes 1 to 35 for heat transfer of the present invention show the maximum value when exposed to a high temperature refuse incineration exhaust gas atmosphere as compared with the conventional composite pipes for heat transfer. From the fact that the amount of thinning is small and the maximum intergranular corrosion length is short, it can be seen that excellent high temperature corrosion resistance is exhibited. However, as seen in the comparative heat transfer composite pipes 1-2, the Ni
It is clear that if the Mg content of the base alloy is out of the range of the present invention, the high-temperature corrosion resistance, particularly the high-temperature intergranular corrosion resistance, is inferior, and as a result, the high-temperature corrosion resistance is inferior. As described above, since the heat transfer composite pipe of the present invention has much higher high temperature corrosion resistance, it corresponds to the high temperature and high pressure steam conditions of the waste heat boiler for effectively utilizing the waste heat from waste incineration. It is possible to reduce the thickness of the outer layer made of an expensive Ni-based alloy, and to further extend the service life of the heat transfer composite pipe, thereby effectively utilizing the waste heat from waste incineration. It can greatly contribute to the improvement of boiler technology.

Claims (3)

[Claims] 1. Cr: 38-50% by weight, C:
0.001-0.05%, Si: 0.1% or less, Mg:
0.001-0.1%, B: 0.001-0.1, P:
Ni-based alloy containing 0.03% or less, S: 0.03% or less, one or two kinds of Mo and W: 0.1 to 2%, and the balance of Ni and unavoidable impurities. A composite pipe for heat transfer in a waste heat boiler using waste incineration flue gas, which has excellent intergranular corrosion resistance. 2. By weight%, Cr: 38-50%, C:
0.001-0.05%, Si: 0.1% or less, Mg:
0.001-0.1%, B: 0.001-0.1, P:
0.03% or less, S: 0.03% or less, Mo and W:
0.1 to 2%, and further rare earth element: 0.00
1 to 0.1%, Y: 0.001 to 0.1%, Zr: 0.
001 to 0.1%, Hf: 0.001 to 0.5%, and one or more of them, and the balance is composed of a Ni-based alloy having a composition of Ni and inevitable impurities. A composite pipe for heat transfer of a waste heat boiler using waste incineration exhaust gas, which has excellent intergranular corrosion resistance. 3. Mn: 0.01 to 1.0% by weight,
Ca: One or two of 0.01 to 0.1%,
A heat transfer composite pipe for a waste heat boiler using waste incineration exhaust gas, which further contains excellent intergranular corrosion resistance according to claim 1 or 2.