JPS61201760A - Structural member of boiler for black liquor recovering treatment - Google Patents

Abstract

PURPOSE:To improve high temp. corrosion resistance of boiler and to prolong its service life, by manufacturing boiler for treating black liquor generated at manufacturing soda pulp, sulfate pulp with austenitic stainless steel having a specified compsn. CONSTITUTION:At manufacturing soda pulp or sulfate pulp, a boiler used for recovering Na2CO3 from black liquor generated as waste liquid after vaporization and decomposition is manufactured with austenitic stainless steel contg. <0.1% C, <2% Si, 1-15% Mn, <0.03% P, <0.03% S, 15-35% Cr, 10-20% Ni, 0.3-5% Mo, 0.001-0.2% B, 0.05-0.4% N or further one or >=2 kinds among Ti, Nb, V, W, Mg, Ca, rare earth element. Boiler having superior high temp. corrosion resistance in combustion circumstance of black liquor and long service life can be manufactured.

Description

Detailed Description of the Invention (Industrial Application Field) This invention provides a boiler used to recover cooking chemicals from black liquor produced as cooking waste liquid when manufacturing soda valves, sulfate valves, etc. This invention relates to a structural member with excellent high-temperature corrosion resistance that can be used for a long period of time.

[Conventional technology]

Conventionally, for example, a water tube boiler was used to combust the above-mentioned black liquor in the form of a spray, and the resulting combustion heat heated the water flowing through the tubes and turned it into steam, which was used for power generation. The combustion ash produced produces NazS as a cooking agent and Na as a raw material for producing NaOH.
2 CO3, etc. are being recovered, and 5U is used to manufacture the structural components of these boilers, such as pipe materials.
Austenitic stainless steels such as S321H and 5US316H are used.

(Problems to be Solved by the Invention) In this way, the structural members of the boiler for black liquor recovery, such as the pipe materials, are constantly exposed to high-temperature combustion gas, and combustion ash becomes attached to them. However, the combustion gas is a highly corrosive substance whose main component is N2-CO2-02-302, and the combustion ash is also mainly composed of Na2-CO2-02-302.
Since it is a highly corrosive material consisting of 804- and 2804-Na CL, the conventional austenitic stainless steel pipe material mentioned above cannot withstand such a severe high-temperature corrosive environment and thins in an extremely short period of time. This caused the product to reach the end of its service life.

[Means for solving problems]

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to develop materials suitable for structural members of boilers for black liquor recovery processing, and as a result, found that C: 0.1% or less.

Si: 2% or less.

Mn: 1-15%.

P: 0.03% or less.

3: 0.03% or less.

Cr: 15-35%.

Ni: 10-20%.

Mo: 0.3-5%.

B: o, ooi ~ 0.2%.

N: 0.05-0.4%.

and, if necessary, one or more of Ti, Nb, V, W, Mg, Ca, and rare earth elements: o, oos ~ 0
．． When the structural members of a boiler for black liquor recovery treatment are constructed of austenitic stainless steel having a composition (the above weight %, the below % indicates weight %), containing 5% Fe and other unavoidable impurities, Since this austenitic stainless steel exhibits excellent high-temperature corrosion resistance, particularly in a black liquor combustion environment, it has been found that the service life of the boiler can be significantly extended.

This invention has been made based on the above findings, and the reason why the composition of the austenitic stainless steel is limited as described above will be explained below.

(a) C, Si, P, and S These components are all components contained as unavoidable impurities, and their contents are C: 0.1%, 3i: 2%, P:
If the content exceeds 0.03% and S: 0.03%, high temperature corrosion resistance in a black liquor combustion environment will deteriorate, so the content should be reduced to C: 0.1% or less,
Si: 2% or less, P: 0.03% or less, S: 0.03%
It was determined as follows.

(b) Mn The Mn component has the effect of improving high-temperature corrosion resistance in a black liquor combustion environment, but if its content is less than 1%, the desired effect of improving the above effect cannot be obtained; on the other hand, if it exceeds 15%. If it is included, the structure stability after long-term heating will deteriorate, so the content was set at 1 to 15%.

(c) Cr The Cr component has the effect of improving the heat resistance of the member, but if the content is less than 15%, the desired excellent heat resistance cannot be secured; on the other hand, if the content exceeds 35%, Even if the N1 content is increased, not only the effect of further improving heat resistance cannot be obtained, but also the high-temperature strength required for the component decreases, and it becomes necessary to increase the N1 content from the viewpoint of structural stability, which causes high costs. Therefore, the content was determined to be 15 to 35%.

(d) Ni The Ni component is contained for the purpose of ensuring the stability of the austenite structure, but if the content is less than 10%, sufficient austenite stabilization cannot be achieved.
On the other hand, if the content exceeds 20%, the high temperature corrosion resistance will deteriorate, so the content a was set at 10 to 20%.

(e) MO Generally, in the case of coal-fired boilers, Mo
If this Mo component is contained, it acts as a component harmful to high-temperature corrosion resistance, so it is usually not included as an alloy component.

However, the Mo component has excellent high-temperature corrosion resistance due to the combustion environment of the boiler for black liquor recovery, especially the content of Na Cl, which is extremely high in combustion ash compared to coal-fired boilers. From this point of view, the structural member of the present invention contains Mo as an alloy component, but if the Mo content is less than 0.3%, it will not work as desired in a high-temperature corrosive environment such as a black liquor combustion environment. On the other hand, even if the content exceeds 5%, not only will it not be possible to further improve the high temperature corrosion resistance, but the stability of the austenite structure will decrease. , and the N component, which has the effect of improving high-temperature corrosion resistance, promotes the precipitation of C as a nitride, and
Since the effect of improving high-temperature corrosion resistance by the component is significantly impaired, its content is set at 0.3 to 5%.

U) N The N component has the effect of improving high-temperature corrosion resistance when coexisting with the Mo component, but if its content is less than 0.05%, the desired effect cannot be obtained; If the content exceeds 4%, weldability deteriorates, so the content was determined to be O,OS~0.4%.

((1) The B component, in coexistence with the N component, significantly refines the crystal grains, thereby significantly reducing the selective corrosion of grain boundaries, which is a characteristic of high-temperature corrosion, in the high-temperature corrosive environment of the boiler for black liquor recovery processing. The content is 0.001%.
If it is less than 0.2, the desired effect cannot be obtained;
Since weldability will be impaired if the content exceeds 0.001% to 0.2%.

(h) Ti, Nb, V, W, M, Ca, and rare earth elements These components have the effect of further improving high temperature corrosion resistance, so even higher temperature corrosion resistance is required. It may be included if necessary, but if the content is
If the content is less than 0.00%, the desired effect of improving high-temperature corrosion resistance cannot be obtained, while if the content exceeds 0.5%, the workability will deteriorate.
It was set at 5% to 0.5%.

Note that these components will be collectively referred to as the high-temperature corrosion resistance improvement effect hereinafter.

[Example] - Next, the structural member of the present invention will be specifically explained with reference to an example.

Ingots having the compositions shown in Table 1 are produced using the usual melting and casting method, and then hot forged and hot rolled under the same normal conditions to obtain a width of 100a*.
Invention plates 1 to 36 and conventional plate 1 as structural members of a boiler for black liquor recovery treatment having dimensions of X thickness: 5 mm
．． 2 was returned to g4i, respectively.

In addition, conventional plate material 1 is 5LJS321H, conventional plate material 2 is 5LJS321H, and conventional plate material 2 is 5LJS321H.
They each have a composition corresponding to US316H.

Next, the resulting plates 1 to 36 of the present invention and conventional plate 1.2 were held at a temperature of 1150°C for 5 minutes and then subjected to water-cooling finish annealing to obtain a diameter of 15 mφ x thickness:
A test piece having a size of 3#l1m was cut out, the surface of which was polished with No. 320 emery paper, degreased, and washed before being subjected to a high-temperature corrosion test.

The high-temperature corrosion test was conducted under conditions equivalent to the high-temperature corrosion environment to which the structural members of the boiler for black liquor recovery treatment are exposed.
2804: 60%.

Black liquor combustion ash containing 30% K2804 and 10% NaCff was applied at a rate of 30I1g/cd and placed in a heating furnace, and the atmosphere gas was SOz: 0.25, which also corresponds to black liquor combustion gas. %, 02:1%.

It shall have a gas composition (volume %) consisting of CO2: 15% and N2: the balance, and the test will be carried out under conditions of holding at 600°C for 100 hours. Descaling was performed using an alkali descaling method, and the corrosion weight loss was measured. These measurement results are also shown in Table 1.

〔Effect of the invention〕

As is clear from the results shown in Table 1, all of the plates 1 to 36 of the present invention were as good as the conventional plates in the black liquor combustion environment.
．． It shows superior hot corrosion resistance compared to 2.
Therefore, the boiler for black liquor recovery processing constructed with structural members made of austenitic stainless steel according to the present invention can significantly extend its service life.

Claims (2)

[Claims] (1) C: 0.1% or less, Si: 2% or less, Mn: 1 to 15%, P: 0.03% or less, S: 0.03% or less, Cr: 15 to 35%, Ni: 10 ~20%, Mo: 0.3~5%, B: 0.001~0.2%, N: 0.05~0.4%, with the remainder consisting of Fe and other inevitable impurities. A structural member of a boiler for black liquor recovery processing, characterized in that it is made of austenitic stainless steel with excellent high-temperature corrosion resistance and having a high temperature corrosion resistance (weight% or more). (2) C: 0.1% or less, Si: 2% or less, Mn: 1 to 15%, P: 0.03% or less, S: 0.03% or less, Cr: 15 to 35%, Ni: 10 ~20%, Mo: 0.3~5%, B: 0.001~0.2%, N: 0.05~0.4%, and further contains Ti, Nb, V, W, Mg, One or more of Ca and rare earth elements: 0.005~
0.5%, with the remainder consisting of Fe and other unavoidable impurities (weight %). Structural components of boilers.