JP3239678B2 - Composite tube for heat transfer of boiler using waste heat from waste incinerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite tube for heat transfer of a boiler utilizing waste heat of waste gas from a refuse incinerator.

[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. In addition, the outer surface of the heat transfer tube, which is a structural member of the waste heat boiler, is made of a highly corrosive HCl, SO ₂ gas, molten sulfate such as Na ₂ SO ₄ , and also corrosive molten chloride such as NaCl or KCl. Since it is exposed to a high-temperature exhaust gas containing a product and is placed in an environment where the above-mentioned sulfates and chlorides are deposited on the surface, a material having excellent high-temperature corrosion resistance is required for the production thereof. Therefore, carbon steel pipes have been used for heat transfer tubes in waste incinerator boilers.
SUS with higher corrosion resistance due to insufficient high temperature corrosion resistance
18-8 austenitic stainless steel such as 304 steel, 321, 347, 321, 316 steel, and SUS3
Use of heat-resistant and corrosion-resistant steel pipes such as 10 is under study. However, these conventional heat-resistant and corrosion-resistant steel pipes do not have a sufficient life as a heat transfer pipe for a boiler that uses exhaust gas from a refuse incineration facility. (JP-A-4-329
852, JP-A-4-221034, JP-A-5-70892, etc.). Since these newly developed alloy pipes with excellent heat and corrosion resistance are generally expensive, they are used as the outer layer of a composite pipe, and a composite pipe consisting of an inner layer made of steel for boilers and an outer layer made of a newly developed heat resistant corrosion resistant alloy is used. Fabrication and use of this composite tube as a heat transfer tube have also been attempted to reduce costs.

[0003]

On the other hand, due to the urgent energy situation in recent years, there is a tendency that the steam condition of the waste heat boiler is increased to a high temperature and a high pressure in order to make maximum use of the waste heat generated by the incineration of refuse. As a result, the wall temperature of the heat transfer tube further rises, and the corrosiveness of the exhaust gas tends to increase further due to the increase in the calories of the garbage and the increase of plastics. From such a viewpoint, the heat transfer tube material of the waste heat boiler is required to have even higher high-temperature corrosion resistance.However, in the newly developed various alloy tubes, sufficient corrosion resistance cannot be obtained in an exhaust gas atmosphere caused by the refuse incineration. Accordingly, even when a composite pipe having these newly developed various alloy pipes as the outer layer and a boiler steel pipe as the inner layer is used as a heat transfer pipe for a refuse incineration boiler, sufficient high-temperature corrosion resistance was not obtained.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above-mentioned viewpoint, as a result of conducting research to develop a heat transfer tube of a waste heat boiler utilizing waste gas incinerator exhaust gas having even higher high-temperature corrosion resistance, as a result, in terms of% by weight (hereinafter,% indicates% by weight), Cr: 20 to 25%, Mo: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C: 0.021% or less, Si: 0.1% or less, P: 0.03% or less, S: 0.03% or less, and if necessary, (a) W: 0.1 to 2%, (b) rare earth element: 0.001 to 0.1% , Y: 0.001 to 0.1%, Zr: 0.001 to 0.1%, Hf: 0.001 to 0.01%, B: 0.001 to 0.01%, Or a Ni-based alloy containing two or more, the above (a) and / or (b), and the balance having a composition consisting of Ni and other impurities When the pipe is used as a heat transfer pipe of a boiler utilizing waste heat from waste incineration exhaust gas, it shows even better corrosion resistance than before. The research results showed that the composite pipe exhibited better corrosion resistance in a severer high-temperature corrosive environment than the composite pipe.

The present invention has been made on the basis of the results of the above research. (1) Cr: 20 to 25%; Mo: 18 to 25%; Nb: 0.5 to 5%; 0.1 to 7%, C: 0.021% or less, Si: 0.1% or less, P: 0.03% or less, S: 0.03% or less, with the balance being Ni and other impurities A composite tube for heat transfer of a boiler utilizing waste heat of waste gas from a refuse incinerator, composed of an outer layer composed of a Ni-based alloy having a composition and an inner layer composed of boiler steel, (2) Cr: 20 to 25%, Mo: 18 -25%, Nb: 0.5-5%, Fe: 0.01-7%, C: 0.021% or less, Si: 0.1% or less, P: 0.03% or less, S: 0. And W: 0.1 to 2%, and the remainder is composed of Ni and other impurities. Composite tube for heat transfer of a boiler utilizing waste heat of waste gas from a refuse incinerator, composed of an outer layer composed of a Ni-based alloy having an internal composition and an inner layer composed of boiler steel, (3) Cr: 20 to 25%, Mo: 18-25%, Nb: 0.5-5%, Fe: 0.01-7%, C: 0.021% or less, Si: 0.1% or less, P: 0.03% or less, S: 0 0.03% or less, and Rare earth elements: 0.001 to 0.1%, Y: 0.001 to 0.1%, Zr: 0.001 to 0.1%, Hf: 0.001 -0.01%, B: 0.001-0.01%, and an outer layer composed of a Ni-based alloy having a composition of Ni and other impurities. (4) Combined tube for heat transfer of boiler utilizing waste heat of waste gas from refuse incinerator, which is composed of steel and inner layer made of steel for boiler r: 20 to 25%, Mo: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C: 0.021% or less, Si: 0.1% or less, P: 0.03% or less, S: 0.03% or less, W: 0.1 to 2%, Rare earth element: 0.001 to 0.1%, Y: 0.001 0.1%, Zr: 0.001 to 0.1%, Hf: 0.001 to 0.01%, B: 0.001 to 0.01%, A heat transfer composite pipe for a waste incinerator exhaust gas waste heat boiler, comprising an outer layer composed of a Ni-based alloy having a composition comprising Ni and other impurities and an inner layer composed of boiler steel. It has features.

When the composite tube for heat transfer of the present invention is used in a boiler or the like for utilizing waste heat from exhaust gas from a refuse incinerator, the Ni-based alloy in the outer layer of the composite tube for heat transfer ensures high-temperature corrosion resistance of the outer surface of the tube. The inner layer of the boiler steel acts to provide the composite tube with high temperature strength and steam oxidation resistance. Accordingly, the “steel for boiler” used for the inner layer of the heat transfer composite pipe of the boiler utilizing waste gas from waste gas incinerator of the present invention is specifically JIS G 3461-346.
Carbon steels and low alloy steels for boiler heat exchangers specified in Nos. 4 and 3467, ferritic stainless steels, austenitic stainless steels, etc., but the steel type can be appropriately selected depending on the conditions used, and is particularly limited. It is not something to be done.

Further, the composite pipe for heat transfer of the boiler utilizing waste heat of exhaust gas from a refuse incinerator according to the present invention can be manufactured by an ordinary method for manufacturing a composite pipe. It can also be manufactured by spraying or overlay welding the base alloy.

The reason why the composition of the Ni-based alloy used in the outer layer of the composite tube for heat transfer of the boiler utilizing waste heat of waste gas from the refuse incinerator according to the present invention will be described as follows.

(A) Cr and Mo These components have the effect of improving high-temperature corrosion resistance and high-temperature oxidation resistance against high-temperature waste incineration exhaust gas in the coexistence state, and improving high-temperature strength. If either of Cr and Mo is less than 20% of Cr and less than 18% of Mo, a desired effect cannot be obtained in the above-mentioned action, while the content of either Cr or Mo is 25% and If the Mo content exceeds 25%, the hot workability decreases. Therefore, the content of Cr is set to 20 to 25%, desirably 20 to 23%,
o: 18 to 25%, preferably 18 to 21%.

(B) Nb The Nb component has an effect of improving the corrosion resistance to sulfates, chlorides, and the like, which are corrosive products in high-temperature exhaust gas. The desired effect of improving the high-temperature corrosion resistance cannot be obtained. On the other hand, if the content exceeds 5%, the hot workability decreases, so that the content is 0.5 to 5%, preferably 0.1 to 0.5%. It was determined to be 5 to 2%.

(C) Fe The Fe component has an effect of improving hot workability, but if its content is less than 0.01%, the desired hot workability cannot be ensured. If the amount exceeds 7%, the toughness will decrease.
The content is determined to be 1 to 7%, preferably 0.5 to 5%.

(D) When the content of the C component as the C impurity exceeds 0.021%, the amount of carbides present at the grain boundaries increases, and particularly the molten chloride contained in the high-temperature exhaust gas. Therefore, the content is determined to be 0.021% or less.

(E) Si Since the Si component has a deoxidizing effect, it may be used for deoxidizing the molten metal. Even in this case, if the content exceeds 0.1%, the toughness is reduced. Therefore, the content was determined to be 0.1% or less.

(F) These components as P and S impurities each have P: 0.03%
And S: more than 0.03%, segregates at the grain boundaries, lowers hot workability, and also lowers high temperature corrosion resistance. Therefore, the content of P is set to 0.03%.
And S: 0.03% or less.

(G) W The W component has an effect of further improving the high-temperature corrosion resistance and is therefore contained as necessary.
If the content is less than 1%, a desired improvement effect cannot be obtained, and if the content exceeds 2%, the hot workability is reduced, so that the content is 0.1 to 2%. Desirably, it is set to 0.5 to 1.5%.

(H) Rare earth elements, Y, Zr, Hf, and B These components have an effect of improving hot workability, and are added as necessary. If the content of the component is less than 0.001%, the desired effect of improving hot workability cannot be obtained. On the other hand, the content of the rare earth element,
If the content exceeds 0.1% for Hr and B, and 0.01% for Hf and B, no further improvement effect can be obtained due to hot workability.
0.001-0.1%, Y: 0.001-0.1%, Z
r: 0.001 to 0.1%, Hf: 0.001 to 0.0
1% and B: 0.001 to 0.01%.

(I) Other impurities Mn, Ti, and Al may be contained as other impurities.
%, The hot workability is impaired, so that their contents must each be kept to 0.4% or less.

[0018]

EXAMPLE An alloy tube having the composition shown in Tables 1 to 3 and having an outer diameter of 66.0 mm and a wall thickness of 3.5 mm was prepared as an outer tube. Diameter: 57.1
A SUS304 steel pipe having a size of 7.0 mm and a thickness of 7.0 mm was prepared.

After descaling the outer tube and the inner tube, the inner tube is inserted into the outer tube, drawn out at a predetermined area reduction rate, and the outer tube is plastically deformed to convert the outer tube into the inner tube. A composite element tube in close contact was produced.

The composite tube thus obtained is placed in a heating furnace, kept at a temperature of 1200 ° C. for 1 hour, and further rolled by a helical roll mill, and the outer layer thickness: 3 mm, the inner layer thickness: 5 mm, the diameter: Composite pipes 1 to 26 of the present invention, comparative composite pipes 1 to 4 and conventional composite pipe 1 having a dimension of 50.8 mm
Was prepared.

The processing capacity of these various composite tubes is 150 tons.
/ Day Waste heat boiler installed in a refuse incinerator was installed as a heat transfer tube, the exhaust gas temperature was 680 ° C, the outer surface temperature of the composite pipe was 530 ° C, the operation time was 1500 hours, and the operation was completed after the operation. Remove the tube and remove the ash and scale attached to the surface, measure the thickness of the outer layer in the circumferential direction, determine the maximum thickness reduction, observe the cross-sectional microstructure of the outer layer surface, and determine the maximum intergranular corrosion length. Was measured, and the results are shown in Tables 4 and 5.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

According to the results shown in Tables 1 to 5, the composite pipes 1 to 26 of the present invention have smaller maximum wall loss and maximum intergranular corrosion length than the conventional composite pipe 1, It turns out that it shows excellent high-temperature corrosion resistance in a high-temperature refuse incineration exhaust gas atmosphere. However, as seen in the comparative composite tubes 1 to 4, Cr, Mo among the Ni-based alloys composing the composite tubes 1 to 4 were used.
It can also be seen that if the content of either Nb or Nb falls outside the range of the present invention, at least one of the maximum wall thickness reduction and the maximum intergranular corrosion length shows a bad value.

As described above, the heat transfer composite pipe of the present invention has much higher high-temperature corrosion resistance than the conventional heat transfer pipe, and therefore has an excellent effect as a heat transfer pipe of a boiler for utilizing waste heat generated by incineration of refuse. It is possible to reduce the wall thickness, thereby reducing the cost, and exhibit excellent industrial effects.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-2211034 (JP, A) JP-A-5-33092 (JP, A) JP-A-6-330226 (JP, A) JP-A-7-330 34166 (JP, A) JP-A-5-195125 (JP, A) JP-A-1-225753 (JP, A) JP-A-1-152246 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C22C 19/05 B32B 1/08 F23G 5/46 ZAB

Claims (4)

(57) [Claims] 1. In weight%, Cr: 20 to 25%, Mo: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C: 0.021% or less , Si : 0.1% or less, P: 0.03% or less, S: 0.03% or less, and an outer layer and a boiler steel composed of a Ni-based alloy having a composition composed of Ni and other impurities. Exhaust gas from a refuse incinerator characterized by comprising an inner layer consisting of
Composite tube for heat transfer of waste heat boiler . 2. In% by weight, Cr: 20 to 25%, Mo: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C: 0.021% or less , Si : 0.1% or less, P: 0.03% or less, S: 0.03% or less, and W: 0.1 to 2%, with the balance being Ni and other impurities. Exhaust gas from a refuse incinerator , comprising an outer layer made of a Ni-based alloy having the following composition and an inner layer made of boiler steel:
Composite tube for heat transfer of waste heat boiler . 3. In% by weight, Cr: 20 to 25%, Mo: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C: 0.021% or less , Si : 0.1% or less, P: 0.03% or less, S: 0.03% or less, Rare earth element: 0.001 to 0.1%, Y: 0.001 to 0.1 %, Zr: 0.001 to 0.1%, Hf: 0.001 to 0.01%, B: 0.001 to 0.01%. Exhaust gas from a refuse incinerator, characterized by comprising an outer layer made of a Ni-based alloy having a composition consisting of Ni and other impurities and an inner layer made of steel for boilers
Composite tube for heat transfer of waste heat boiler . 4. In% by weight, Cr: 20 to 25%, Mo: 18 to 25%, Nb: 0.5 to 5%, Fe: 0.01 to 7%, C: 0.021% or less , Si : 0.1% or less, P: 0.03% or less, S: 0.03% or less, W: 0.1 to 2%, Rare earth element: 0.001 to 0 0.1%, Y: 0.001 to 0.1%, Zr: 0.001 to 0.1%, Hf: 0.001 to 0.01%, B: 0.001 to 0.01% A refuse incinerator characterized by comprising an outer layer composed of a Ni-based alloy having a composition comprising Ni and other impurities, and an inner layer composed of steel for a boiler, wherein Exhaust gas
Composite tube for heat transfer of waste heat boiler .