JPH0726178B2 - High Ti high Mn austenitic stainless steel for coal gasification - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a stainless steel having excellent corrosion resistance and high temperature strength in a coal gasification environment, and in particular, for an exhaust heat recovery device of a coal gasification combined cycle power plant. The present invention relates to an austenitic stainless steel suitable as a material.

[Background of the Invention]

Today, with the diversification of energy, coal is expected to play an important role as an alternative energy source for oil along with nuclear power. Above all, coal gasification technology that gasifies coal and uses it as clean energy is
It is attracting attention as a new coal utilization technology. In addition, the integrated coal gasification combined cycle power generation system that combines this coal gasification furnace, gas turbine, and steam turbine attracts attention as a new power generation system with high efficiency and low pollution.
Development is in progress. However, many problems still remain for its practical application. In particular, the gasification reaction system and the exhaust heat recovery system become a reducing atmosphere containing H ₂ S under high temperature and high pressure, and the corrosion of the materials used is a serious problem. Moreover, because of this, it is difficult to construct a highly efficient power plant.

In order to improve the thermal efficiency of the integrated coal gasification combined cycle power generation plant, how to efficiently recover the exhaust heat generated by the gasification reaction becomes a problem, and in order to recover the exhaust heat efficiently, it is necessary to obtain it from the exhaust heat. It is necessary to increase the temperature and pressure of steam generated by the amount of heat generated.

R. A. RA Perkins is the Corrosion Resistant Materials for Focal Coal Convergence System, Applied Science Publications
Coal Conversion Systems, Appl.Sci.Pab.) (1983) p21
As mentioned in 9-p258, it is known that in order to prevent the corrosion of metallic materials by coal gasification gas, the working temperature of the materials must be lowered. For example,
25Cr austenitic stainless steel is below 500 ℃, 18C
r-8Ni stainless steel is 400 ° C or less, and low alloy steel is 300
It is said to be below ℃. Considering that temperatures commonly used in steam power plants are 550 ° C or lower for 12Cr-based ferrite heat-resistant steel and 600 ° C or higher for 18Cr-8Ni-based steel, the importance of the problem of material corrosion can be seen.

For this reason, Earl D'Abrieu
adshow) et al., Corrosion / Erosion of Corrosion / Erosion of Call Convergion System Materials Proceedings
Coal Conversion System Materials Proceedings.NAC
E) (1979) p872, which is the existing 25Cr austenitic stainless steel. 2-3 for SUS310 stainless steel
% Ti is added to enhance its corrosion resistance and it is being used as a material for coal gasification. However, a large amount of Ti in the steel
Is not preferable because it produces a large amount of ferrite phase. If the amount of Ni in the steel is increased in order to suppress this ferrite phase, the corrosion resistance deteriorates, the effect of adding Ti decreases, and the steel price rises.

Therefore, at present, as a heat exchanger material for coal gasification, SUS309S (21Cr-13Ni) is used as the maximum operating temperature of 400 ° C.
Steel), SUS 310S (25Cr-20Ni steel), and Incoloy 80
0 (21Cr-32Ni-Ti, Al steel) is being studied. this is,
To obtain good corrosion resistance over a long period of time, at least
Due to the need for a Cr content of 20-50%. Although these materials cannot be said to have sufficient corrosion resistance in a coal gasification environment, they are attracting attention because of their excellent manufacturability and processability. Therefore, the development of a material that has corrosion resistance equal to or higher than that of SUS309S, SUS310S, Incoloy 800, etc. and has excellent manufacturability and processability is an essential condition for constructing highly efficient coal gasification equipment. ing.

[Object of the Invention]

The purpose of the present invention is excellent in corrosion resistance in a coal gasification atmosphere,
Another object of the present invention is to provide an austenitic stainless steel for coal gasification which has excellent high temperature strength.

[Outline of Invention]

The present invention, by weight C0.15% or less, Si1.0% or less, Ni6-20
%, Cr 13 to 20%, Mn 2 to 30%, and Ti 2 to 5%, and the balance is iron, which is a high Ti high Mn austenitic stainless steel for coal gasification.

Iron exists naturally in the form of oxides and sulfides. This is because iron is originally more stable in nature than oxides and sulfides. Therefore, if left alone, it will return to the form of an oxidized or sulfurized compound. This is the corrosion phenomenon.
To slow down the rate at which steel oxidizes and sulfides,
An alloying element is added to steel to form a strong protective film on the steel surface. An example of this is stainless steel. Stainless steel generally protects the inside of the steel by forming a dense protective film of Cr ₂ O ₃ on the steel surface.
Whether the film formed on the surface can protect the steel is determined by the environment in which the material is used. In an environment with a high oxygen potential, such as in the atmosphere, Cr ₂ O ₃ is the main constituent and sufficient protection can be provided by a film. However, under a condition where oxygen potential is low and sulfur potential is high, such as a coal gasification environment, Cr added to form a film is also sulphurized, so that a film with high protective properties is difficult to form. That is, the protective film mainly containing Cr is not always sufficient under the coal gasification environment. The elements added to protect steel and the amount added should be determined according to the environment of use.

Al and Ti are additional elements that form a highly protective film in a coal gasification environment. It is thermodynamically inferred that these have a stronger oxygen affinity than Cr and form a sufficiently protective film mainly composed of Al ₂ O ₃ and TiO ₂ even in a coal gasification environment. However, how much of these elements should be added to steel in a coal gasification environment,
It was unclear whether sufficient protection could be obtained. To determine the amount to be added, in a coal gasification environment, or
It is an indispensable condition to evaluate the corrosion resistance by performing a corrosion test under conditions sufficiently simulating it.

There have been examples of adding Ti to steel in order to improve the sulfidation corrosion resistance of stainless steel. However, the addition of Ti to austenitic steel causes the formation of a large amount of ferrite in the structure, embrittles the steel, and lowers the high-temperature strength of the steel, especially the creep strength, so it is preferable as a high-temperature material. Absent. On the other hand, in order to reduce the amount of ferrite in the steel, it is necessary to increase the austenite-forming element in the steel, for example, Ni, but increasing the amount of Ni reduces the sulfidation corrosion resistance. Therefore, in order to obtain a material that has both high corrosion resistance and high strength in a coal gasification environment, the minimum required Ti and Cr contents in the coal gasification atmosphere are determined, and the corrosion resistance is adversely affected. It is necessary to increase the high temperature strength of the steel by suppressing the amount of ferrite in the alloy structure by a method that does not apply.

However, no conventional existing material has satisfactory corrosion resistance and strength as such a coal gasification material.

Therefore, the present inventor (24% H ₂ , 18% CO, 12% CO ₂ , 6% C in the atmosphere recognized by the US MPC as a simulated coal gasification atmosphere)
H ₄ , 0.5 to 1% H ₂ S Residual H ₂ O, 300 ℃ to 900 ℃) We conduct research on high temperature gas corrosion of various materials and evaluate various mechanical properties. Steel containing 2 to 5% of Ti and 6 to 20% of Ni and 2 to 30% of Mn as austenite-forming elements shows extremely excellent corrosion resistance in a coal gasification environment, and its high temperature It was found that the strength is equivalent to that of ordinary austenitic stainless steel.
It has been found that this steel type can further improve its corrosion resistance and hot workability by adding a small amount of one or more rare earth elements and Ca. In addition, when the main components of this steel grade are expressed as wt%, Cr (%) + 2.2 x Ti (%) + 1.5 x Si (%)-Ni (%) -30 x C (%) -0.5 x Mn It has been found that it is preferable to set the ratio within the range of (%) ≦ 10 in order to have both corrosion resistance and strength.

The reasons for limiting the alloy composition in the present invention will be described below. In addition,% described below is% by weight.

C: C is an austenite-forming element and at the same time is an important element for obtaining high-temperature strength, but if added in a large amount, the toughness and weldability are significantly reduced, so its upper limit is 0.
15% Preferably it is 0.05 to 0.09%.

Si: Si is an important deoxidizing component in manufacturing. However, if added in a large amount, the toughness, ductility and weldability are adversely affected, so the upper limit is made 1.0%. The preferred component range is 0.2
~ 0.8%.

Ni: This is the most important element for forming an austenite structure, but its upper limit is 20% because it forms a sulfide with a low melting point in a coal gasification atmosphere to promote corrosion. In order to maintain sufficient corrosion resistance, it is preferable to adjust the components so as to satisfy the relationship of Ni (%) ≦ 5 × Ti (%). Further, by adding 6% or more of Ni, it is possible to suppress heat embrittlement of a high manganese steel such as the present steel type at high temperatures, so the lower limit is 6%. From the viewpoint of corrosion resistance and prevention of embrittlement, the Ni content is preferably in the range of 8 to 14%.

Cr: This is the most basic element for maintaining corrosion resistance at high temperatures, but in this steel type, it plays a role of promoting the formation of a protective film mainly composed of Ti. Since the lower limit of the effect is 13%, the lower limit of the Cr content is 13%. However, if it is added in a large amount, δ-ferrite or σ phase is generated to cause adverse effects such as embrittlement during high temperature use, so the upper limit is made 20%. A preferred component range is 15% to 19%.

Mn: In general stainless steel, Mn slightly lowers the oxidation resistance, so it is suppressed to 2% or less, but this is not a concern because the coal gasification environment has a low oxygen potential. According to the knowledge of the inventors, Mn positively uses Mn as an austenite-forming element together with Ni in this steel grade because Mn improves corrosion resistance in a coal gasification atmosphere. The preferable addition amount is determined by the amount of alloy components contained,
If added excessively, the hot workability of steel will be deteriorated, so its upper limit is made 30%. A preferable component range is 4% to 18%. More preferably, it is 4% to 12%.

Ti: This is an essential element that improves the corrosion resistance of this steel grade in a coal gas environment. In order to improve the corrosion resistance, it is necessary to add at least 2%, but if it is added excessively, δ-ferrite will be formed and embrittlement will occur during high temperature use, so the upper limit is made 5%.
A preferable component range is 2 to 4%.

Rare earth elements such as rare earth elements (REM), Ca: Y, La, Ce and
If one or more of Ca is contained in an amount of 0.001% or more, it is effective in preventing hot cracking of steel and can improve corrosion resistance. However, if 0.1% or more is contained, the cleanliness of the material deteriorates due to the precipitation of inclusions. Therefore, 0.1
% Is the upper limit. A preferable component range is 0.01 to 0.7%.

In addition to these, it contains elements that are unavoidably mixed in during manufacturing.

It is basically preferable that the steel of the present invention has an austenitic structure, but it does not prevent inclusion of 10% or less of a ferrite phase, which does not significantly increase the adverse effects of the ferritic / austenitic dual phase steel. Preferably wt% of each component element
Is Cr (%) + 2.2 × Ti (%) + 1.5 × Si (%) − Ni (%) − 30 × C (%) − 0.5 × Mn (%) ≦ 10, preferably 0 to 5, It is desirable to adjust the composition so as to satisfy the above condition, to appropriately suppress the formation of the ferrite phase, and to suppress the embrittlement of the ferrite phase which causes the reduction of the ductility of the steel.

Example of Invention

Table 1 shows the chemical composition (wt%) of the high Ti, high Mn austenast stainless steel for coal gasification according to the present invention (hereinafter referred to as "invention steel") and the comparative steel. The balance is substantially Fe, and contains P, S, etc. as unavoidable impurities.

The invention steels No. 1 to No. 9 and the comparative steels No. 10 to No. 23 are obtained by vacuum melting and forging, followed by heating and water cooling at 1100 ° C. for 1 hour.
Corrosion test pieces and creep test pieces were prepared from this forged material.

Table 2 shows the composition of simulated coal gas H ₂ : 24%, CO: 18%, CO ₂ : 12
_{%, CH 4: 6%,} H 2 S: 0.5%, showing the amount of corrosion in an atmosphere of residual between H ₂ O 100 hours corrosion test was the invention steels and comparative steels. The test temperature is 850 ° C and the pressure is 30 atm. The amount of corrosion was represented by the sum of the cross-sectional thickness reduction thickness and the internal erosion depth (grain boundary erosion).

As is clear from Table 2, the steel of the present invention is comparative steel No. 11 (S
US304), Comparative Steel No.12 (SUS316), Comparative Steel No.13 (SUS32)
1), Comparative Steel No.14 (SUS347), Comparative Steel No.15 (SUS Compared with 631), its high temperature gas corrosion resistance is greatly improved. Comparative steel No. 16 (SUS31 with high Cr content that improves corrosion resistance)
0S) and comparative steel No. 17 (SUS347), the high Ti, high Mn steel of the present invention has excellent corrosion resistance. Corrosion resistance is Ti
Although it largely depends on the amount, if the Ti amount is the same, the Mn amount is large, and the smaller the Ni amount is, the better the poor corrosion resistance is.

Fig. 1 shows the invention steels No. 1, No. 2, No. 3, No. 4 with high Ti and high Mn and the comparative steels No. 18, No. 19, No. 20, No. 3 with high Al and high Mn. This is a comparison of the amounts of corrosion of 21. As is clear from the figure, the corrosion resistance of the steel of the present invention is almost comparable to that of Al-containing stainless steel in a coal gasification environment.

FIG. 2 shows the relationship between the ratio of the Ni content to the Ti content of the steel of the present invention and the corrosion amount. As is clear from the figure, it is preferable to decrease the amount of Ni and increase the amount of Ti in order to enhance the sulfidation corrosion resistance, and particularly good corrosion resistance can be obtained when Ni (%) / Ti (%) ≤5. .

FIG. 3 shows the results of creep rupture tests of the invention steel No. 5 and comparative steel 11 (SUS304). As is clear from the figure, the creep rupture strength of the steel of the present invention is comparable to that of ordinary austenitic stainless steel, and it is clear that it has sufficient performance as a material for high temperature equipment.

FIG. 4 shows an example of a system diagram of an integrated coal gasification combined cycle power plant according to the present invention, FIG. 5 is a schematic vertical sectional view of a spouted bed gasification furnace, and FIG. 6 is a water-cooling structure in the upper part of the gasification furnace. FIG. 3 is a cross-sectional view taken along the line III-III in FIG.

The coal 1 is introduced into the gasification furnace 4 from the burner 3 using air or oxygen as the gasifying agent 2, and is gasified in the gasification section 5.
In this case, the gas temperature is as high as 1600 ° C. or higher, so that the gasification section 5 has a refractory structure 6. The high-temperature gas is sent to the heat recovery section composed of the steel of the present invention of the water-cooled structure 17 and cooled to 900 ° C. or less in the vicinity of the outlet of the gasification furnace 4, and then the crude product gas 10 is discharged from the outlet of the gasification furnace 4. Then, it is sent to the steam generator 11 using the steel of the present invention and further cooled.

The sensible heat of this crude product gas 10 is recovered as steam 12.
The crude product gas 13 at the outlet of the steam generator 11 is heat-exchanged with the refined gas 15 by the gas / gas heat exchanger 14 using the steel of the present invention, cooled to a temperature required for the gas refinement and refined. The purified gas 15 is heat-exchanged in the gas / gas heat exchanger 14 and heated up, and then burned as a fuel gas 18 in the gas turbine combustor 19 and then generated as high temperature gas to generate electrical energy in the gas turbine generator. Let

As a heat recovery system, the gas turbine exhaust gas 20 generates sensible heat in the gas turbine exhaust heat recovery boiler 22, and at the same time, the crude product gas 10 at the outlet of the gasification furnace 4 is a steam generator 11
The sensible heat is recovered to generate steam, which are combined and mixed with the steam generated in the gas turbine exhaust heat recovery boiler 22, superheated by the superheater, and sent to the steam turbine 23 as superheated steam. The generated steam works in the steam turbine 23 to generate electric energy by steam turbine power generation.

The steam that has passed through the steam turbine 23 is cooled by the condenser 24 and becomes condensed water, which is supplied to the exhaust heat recovery boiler by the water supply pump.

〔The invention's effect〕

As described above, the present invention steel is the conventional steel SUS304, SUS316, SU
S321, SUS347, SUS631 Furthermore, SU, which is said to be corrosion resistant steel
Compared with S310S and Incoloy 800, it has excellent high-temperature gas corrosion resistance, and has the same workability and high-temperature strength as those of austenitic stainless steels with a high penetration angle. Therefore, in a coal gasification plant, when it is used as a material for an exhaust heat recovery device such as a coal gasification comparison cold wall or a commercial gas cooler, the temperature and pressure of generated steam can be increased. Therefore, it has a remarkable effect of increasing the power generation efficiency of the integrated coal gasification combined cycle power plant.

[Brief description of drawings]

Fig. 1 is a diagram showing the relationship between the amount of Ti and Al contained in the alloy and the amount of corrosion, Fig. 2 is a diagram showing the relationship between the ratio of the amount of Ni and the amount of Ti, and corrosion corrosion, and Fig. 3 is the creep. Diagram showing breaking strength, No. 4
FIG. 5 is a schematic view of an integrated coal gasification combined cycle power plant according to the present invention, FIG. 5 is a schematic vertical cross-sectional view of a spouted bed gasification furnace, and FIG. 6 is a III- of FIG. 2 showing a heat recovery part in the upper part of the gasification furnace. FIG. 3 is a transverse sectional view taken along the arrow III. 4 ... Coal gasifier, 17 ... Heat recovery part, 11 ... Steam generator, 14 ... Gas / gas heat exchanger.

Front Page Continuation (72) Inventor Seinobu Kirihara 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Inc.

Claims (4)

[Claims] 1. C0.15% or less, Si1.0% or less, Ni6 by weight
-20%, Cr13-20%, Mn2-30%, Ti2-5%,
High Ti high Mn for coal gasification characterized by the balance Fe
Austenitic stainless steel. 2. The alloy according to claim 1, wherein Cr (%) + 2.2 × Ti (%) + 1.5 × Si (%)-Ni (%)-30 × C (%)- High Ti high Mn austenitic stainless steel for coal gasification with a relationship of 0.5 x Mn (%) ≤ 10. 3. By weight, C0.15% or less, Si1.0% or less, Ni6
~ 20%, Cr13 ~ 20%, Mn2 ~ 30%, Ti2 ~ 5% and 0.001 ~ 0.1% of one or more kinds of rare earth elements and Ca, and the balance Fe Fe High Ti
High Mn austenitic stainless steel. 4. The alloy according to claim 3, wherein Cr (%) + 2.2 × Ti (%) + 1.5 × Si (%)-Ni (%)-30 × C (%)- High Ti high Mn austenitic stainless steel for coal gasification with a relationship of 0.5 x Mn (%) ≤ 10.