JPH09210260A - Anticorrosive steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously prevent oxygen corrosion of an inner surface generated by flowing of water (non-deairing) at an ambient temperature and sulfuric acid corrosion of an outer surface generated by adhesion of sulfuric acid to the outer surface due to dewing, in the case of attaining increase of a recovery heat from exhaust gas in an economizer of a boiler. SOLUTION: An economizer 10 is constituted of an anticorrosive steel pipe formed in a double pipe structure which comprises an inner surface side formed of a stainless steel pipe 1 and an outer surface side formed of a sulfuric acid dew point corrosive resistant steel pipe 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion resistant steel pipe, and is particularly effective when applied to an economizer for recovering heat from exhaust gas from boilers, diesel engines, gas turbines, incinerators, heating furnaces and the like.

[0002]

2. Description of the Related Art In a boiler or the like, an economizer is used which preheats water for supply to the boiler by the heat of exhaust gas discharged to the atmosphere to improve thermal efficiency. This economizer is usually formed by bending a carbon steel pipe into a meandering shape, and is arranged in an exhaust gas duct. By circulating degassed water inside, the heat of exhaust gas passing through the exhaust gas duct is reduced. The above water is preheated.

[0003]

In the economizer described above, in order to further save energy in the boiler,
Further improvement of exhaust heat recovery (exhaust gas temperature at atmospheric release: 50
-100 ° C) is required. Therefore, it is considered that the amount of heat recovered is increased by setting the temperature of the water flowing inside the economizer to about several tens of degrees from room temperature. However, if the amount of recovered heat is increased in this way, the following problems will occur.

In order to prevent corrosion of the inner surface of the economizer made of carbon steel pipe due to oxygen, the water is usually heated to 100 to 130 ° C. by a pressure deaerator to remove dissolved oxygen. However, as described above, when trying to circulate the water at room temperature to several tens of degrees inside the economizer, it is not possible to remove dissolved oxygen from the water, so the inner surface of the economizer made of carbon steel pipe is corroded. Will end up.

When the temperature of the water flowing inside the economizer is set to about several tens of degrees from room temperature, the temperature difference between the exhaust gas and the water becomes large, and dew point (dew point: about 140 ° C.) is generated on the outer surface of the economizer. I will end up. Therefore, sulfur oxides in the exhaust gas become sulfuric acid and adhere to the outer surface of the economizer, which corrodes the outer surface of the economizer made of carbon steel pipe.

Therefore, if an economizer consisting of a stainless steel pipe is used in order to solve the above-mentioned problems, a problem arises in the corrosion resistance to sulfuric acid under the above-mentioned environment, and in order to solve the above problems, the sulfuric acid resistance is If an economizer made of a dew-point corrosive steel pipe is used, a problem arises in the corrosion resistance to oxygen in the above environment, and the above problems cannot be solved at the same time.

[0007] Such a problem is not limited to the economizer applied under the above-mentioned environment, but can similarly occur in a steel pipe used so as to partition an oxygen-containing environment and a sulfuric acid-containing environment. Is. Therefore, it is an object of the present invention to provide a corrosion resistant steel pipe having oxygen corrosion resistance on one of the inner surface and the outer surface and sulfuric acid dew point corrosion resistance on the other.

[0008]

In order to solve the above-mentioned problems, a corrosion-resistant steel pipe according to the present invention is a double-walled pipe made of stainless steel, one of which is an inner surface or an outer surface, and the other of which is made of a sulfuric acid dew-point corrosion resistant steel. It is characterized by having a tubular structure.

[0009]

1 and 2 show an embodiment in which the corrosion resistant steel pipe according to the present invention is applied to an economizer of a boiler.
This will be described with reference to FIG. 1 is a schematic configuration diagram of the boiler, and FIG. 2 is a sectional view showing the configuration of the economizer.

As shown in FIG. 1, a water drum 12 is provided below the boiler body 11. Boiler body 11
A steam drum 13 is provided above. The water drum 12 and the steam / water drum 13 are connected by a plurality of water pipes 14 inside the boiler body 11. A burner 15 is provided on the side surface of the boiler body 11. An exhaust gas duct 16 is connected to a side surface of the main body 11 facing the burner 15. That is, when fuel such as C heavy oil is burned by the burner 15 to heat the inside of the boiler body 11, the water 21 in the water pipe 14 is heated to become steam, and the steam rises and flows into the steam drum 13. The exhaust gas 22 that has been sent to the outside while heating the water pipe 14 is exhausted from the boiler body 11 through the exhaust gas duct 16 to the atmosphere from the chimney 17.

Further, as shown in FIG. 1, inside the exhaust gas duct 16, an economizer 10 made of a meanderingly bent pipe is disposed. One end of the economizer 10 is connected to the water supply pump 18. The other end of the economizer 10 is connected to the steam drum 13. That is, the water 21 supplied from the water supply pump 18
Is supplied into the steam / water drum 13 through the economizer 10 and is used for the above-described generation of steam.

As shown in FIG. 2, the economizer 10 has a double pipe structure in which the inner surface side is made of a stainless steel pipe 1 and the outer surface side is made of a sulfuric acid dew point corrosion resistant steel pipe 2. Therefore, the economizer 10 has oxygen corrosion resistance on its inner surface and sulfuric acid dew point corrosion resistance on its outer surface. Examples of the material of the stainless steel pipe 1 include SUS316L (16Cr-12).
Ni-2Mo-extremely low C) and the like, and examples of the material of the sulfuric acid dew point corrosion-resistant steel pipe 2 include fire STBA-
10 (Si: 0.20 to 0.80%, Mn: 0.8% or less, P: 0.025% or less, S: 0.015 to 0.03
0%, Cu: 0.25 to 0.35%, Cr: 1.0 to
1.5%, C: 0.10% or less) and the like. The economizer 10 made of such a material can be manufactured by a contact double tube manufacturing method (composite tube manufacturing method) of the stainless steel tube 1 and the sulfuric acid dew point corrosion resistant steel tube 2.

Since the inner surface of the economizer 10 is resistant to oxygen corrosion, even if the water 21 supplied from the water supply pump 18 contains dissolved oxygen, the inner surface is corroded. Since it does not happen, there is no need to degas the water 21, that is, to heat it, and the water 21 can be fed to the economizer 10 at room temperature.

Further, when the water 21 at room temperature flows through the economizer 10, the exhaust gas 22 passing through the exhaust gas duct 16 is discharged.
Is contacted with the economizer 10, the heat of the exhaust gas 22 is recovered by the water 21 and the water 21 is preheated. At this time, since the temperature difference between the water 21 and the exhaust gas 22 is large, dew condensation occurs on the outer surface of the economizer 10, and the sulfur oxides and the like in the exhaust gas 22 become sulfuric acid and adhere to the outer surface of the economizer 10. Economizer 10
Since the outer surface of the has a sulfuric acid dew point corrosion resistance, the outer surface will not be corroded.

Therefore, according to the economizer 10 as described above, the undegassed room temperature water 21 is caused to flow inside,
Even if sulfuric acid adheres to the outer surface by collecting the heat of the exhaust gas 22,
Since it does not corrode the inner and outer surfaces,
The amount of heat recovered from the exhaust gas 22 can be further increased without any problem (exhaust gas temperature at the time of atmospheric release: 50 to 100).
℃), further energy saving of the boiler can be achieved. Further, since the pressure degassing device for degassing the water 21 is not necessary, the cost of equipment can be reduced.

In the present embodiment, the case where the present invention is applied to the economizer of the boiler has been described, but the present invention is not limited to this. For example, an economizer that recovers heat from exhaust gas from a diesel engine, a gas turbine, an incinerator, a heating furnace, or the like. The present invention can be applied to any steel pipe, of course, as long as it is a steel pipe that is used by separating an oxygen-containing environment and a sulfuric acid-containing environment. Further, in the present embodiment, the economizer 10 is composed of the stainless steel pipe 1 on the inner surface side and the sulfuric acid dew point corrosion resistant steel pipe 2 on the outer surface side. However, depending on the application environment, the inner surface side is composed of the sulfuric acid dew point corrosion resistant steel. It is also possible to have a double pipe structure in which the outer surface side is made of stainless steel.

[0017]

In the corrosion resistant steel pipe according to the present invention, for example,
When applied to the economizer of the boiler as a double pipe structure consisting of stainless steel on the inner surface and steel with sulfuric acid dew point corrosion resistance on the outer surface, by flowing undegassed normal temperature water inside,
The heat of exhaust gas is recovered, and even if sulfuric acid adheres to the outer surface, the inner surface and outer surface do not corrode, so the amount of heat recovered from the exhaust gas can be increased without any problems,
The amount of energy used can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a boiler in an embodiment in which a corrosion resistant steel pipe according to the present invention is applied to a boiler economizer.

FIG. 2 is a cross-sectional view showing the configuration of the economizer shown in FIG.

[Explanation of symbols]

 1 Stainless steel pipe 2 Sulfuric acid dew point corrosion resistant steel pipe 10 Economizer 21 Water 22 Exhaust gas

Claims (1)

[Claims] 1. A corrosion-resistant steel pipe having a double pipe structure in which one of an inner surface and an outer surface is made of stainless steel and the other is made of sulfuric acid dew-point corrosion resistant steel.