JP3477342B2 - Air inlet nozzle of recovery boiler - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air nozzle of a recovery boiler having high corrosion resistance. 2. Description of the Related Art A recovery boiler is used in a paper making process or the like, and the role of the recovery boiler in a paper making process is to generate smelt from black liquor which is waste liquid generated in the paper making process. From the smelt discharged through the smelt pout provided at the lower part of the recovery boiler, Na required in the papermaking process is recovered. [0003] The smelt generated by the recovery boiler is a very corrosive substance containing a large amount of Na ₂ S. Therefore, the recovery boiler is always exposed to a severe corrosive environment. [0004] Carbon steel has been used as the material for the air port nozzle provided on the side wall of the conventional recovery boiler. However, in recent years, the corrosive environment has further progressed with the rise in furnace temperature. SUS430, which is a 17Cr-based material having more excellent corrosion resistance, is increasingly used. [0005] In the conventional air port nozzle of a recovery boiler, carbon steel is generally used as the material as described above. Accordingly, the use of SUS430 having more excellent corrosion resistance tends to increase. However, recently, the furnace temperature has been further increased due to a change in fuel composition and the like.
Corrosion troubles began to be seen also in the air port nozzle using No. 0. As a countermeasure, 25Cr-20, which is generally considered to be superior in corrosion resistance to SUS430, is used.
An attempt was made to use SUS310, a Ni-based material,
It has been found that the material is more easily corroded than SUS430, and it has been desired to develop a material having excellent corrosion resistance that can be used for the air port nozzle instead. The present invention seeks to solve the above problems. [0008] According to the first aspect of the present invention, the air port nozzle of the recovery boiler according to the first aspect of the present invention has a weight percentage of C;
08-0.15%, Si; 0.2-0.5%, Cr; 2
2 to 27%, Nb; 0.8 to 1.5%, with the balance being formed of a material comprising Fe and unavoidable impurities. In the present invention, as a result of various studies, C,
Si, Cr, Nb, and Fe are used as main material components, and the reason why they are used as main material components will be described below. [0010] Corrosion of the air port nozzle of the recovery boiler basically proceeds by a sulfidation reaction. As a factor, H ₂ S has been mainly used in the past. As a result, some corrosion due to the molten smelt began to occur. Corrosion due to the molten smelt does not always occur but occurs intermittently, but the progress of the corrosion is remarkable, and there is a great difference in the amount of corrosion from the corrosion due to H ₂ S. [0011] Corrosion due to the molten smelt having such properties is more prominent in the case of an air port nozzle that does not actively cool, as the thermal conductivity of the material is lower.
This has been a cause of increased corrosion when SUS310 containing Ni is used. Further, the corrosiveness to H ₂ S increases with an increase in the amount of Cr, but the corrosiveness to molten smelt increases with an increase in the amount of Cr, but deteriorates with an increase in the amount of Ni. SUS430 is SU
The result showed that the corrosion resistance was superior to S310. As a result of conducting various studies on conventional materials, the above findings were obtained. Therefore, in the present invention, a material that contains Cr but does not contain Ni, which leads to an improvement in corrosion resistance, is used. Further, when the content of the above-mentioned Cr is made high, the crystal grain growth of the heat-affected zone is liable to occur at the time of welding, and the toughness is lowered, so that the weldability is deteriorated. Therefore, in the present invention, Si is reduced and Nb is added to secure the toughness of the heat affected zone. For the above C, Si, Cr and Nb,
Each component range is limited, and the reason for this limitation will be described below. C exhibits a pinning effect by reacting with Nb to form fine carbides, thereby preventing coarsening of crystal grains in the heat-affected zone and improving weldability.
If it is less than 0.08, no pinning effect can be obtained, and 0.15%
With the above, although the pinning effect can be obtained, the toughness of the base material is reduced. Therefore, it is set to 0.08 to 0.15%. Although the toughness is improved by reducing the content of Si, a remarkable effect is not seen at 0.5% or more. This Si is used for the purpose of deoxidation on steel making, but if it is made 0.2% or less, special steel making must be performed, resulting in high cost. Therefore, it is set to 0.2 to 0.5%. Cr improves the corrosion resistance, but when it is 22% or less, a sufficient effect cannot be obtained, and when it is 27% or more, the toughness is deteriorated. Therefore, it is set to 22 to 27%. Nb is C
To form fine carbides to prevent coarsening of crystal grains in the heat-affected zone and enhance weldability.
The effect is not obtained below, and when it is 1.5% or more, the toughness is reduced. Therefore, it is set to 0.8 to 1.5%. DESCRIPTION OF THE PREFERRED EMBODIMENTS An air nozzle of a recovery boiler according to one embodiment of the present invention will be described. The air port nozzle according to the present embodiment has a material component of 0.08 to 0.08% by weight.
0.15% C, 0.2-0.5% Si, 22-27
% Of Cr, 0.8 to 1.5% of Nb, and the balance made of a material containing Fe and impurities inevitable in steelmaking. In the present embodiment, a corrosion test and an on-bead test are performed to evaluate the characteristics of the material forming the air port nozzle. Each test content and result will be described below. In the corrosion test, a smelt sampled from an actual machine was pulverized to # 200 or less, 10 g of the smelt was placed in a crucible, and a test specimen of 14 mm × 14 mm × 3 mm was buried in the crucible. The environment was 800 ° C., in the air, and the test time was 1 h × 2. After the test, corrosion products were removed by washing with water and pickling, and the difference in sheet thickness before and after the test was measured to determine the amount of corrosion. The on-bead test was performed at 300 mm × 20 mm.
The test was performed by melting a part of the surface of the test material of 0 mm × 6 mm with a TIG welding machine. After the test, changes in crystal grains were examined by microscopic observation of the cross section of the heat affected zone and the general zone. In the above-mentioned corrosion test and on-bead test, test materials having 14 types of compositions indicated by test material numbers 1 to 14 in Table 1 were used. It is indicated by the amount and the presence or absence of a change in crystal grain. The amount of corrosion is also shown by the graph of FIG. [Table 1] From the results of the corrosion tests shown in Table 1 and FIG. 1, it can be seen that the corrosion resistance is improved by an increase in Cr, and the corrosion resistance is degraded by an increase in Ni. Also, from the results of the on-bead test shown in Table 1, it can be seen that the crystal grain coarsening can be prevented by optimizing Nb and C. The air port nozzle of the recovery boiler of the present invention is
0.08 to 0.15% by weight of C, 0.2
0.5% Si, 22-27% Cr, 0.8-1.
By using 5% Nb and the balance being made of a material consisting of Fe and impurities inevitable in steelmaking, it is possible to suppress the amount of corrosion of the air port nozzle, which has increased with an increase in furnace temperature. Becomes

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a corrosion test result of an air port nozzle according to an embodiment of the present invention.

Continuation of the front page (72) Inventor Yuichi Doi 5-717-1, Fukahori-cho, Nagasaki-shi Inside Nagaishi Engineering Co., Ltd. (56) References JP-A-10-1531312 (JP, A) JP-A-5-70892 (JP, A) JP-A-61-201760 (JP, A) JP-A-5-70891 (JP, A) JP-A-57-148102 (JP, A) JP-A-62-160300 (JP, U) Kaihei 1-87198 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21C 11/00-11/14 C22C 38/26 F22B 37/04 F-term (4L055)

Claims (1)

(57) [Claims 1] By weight%, C: 0.08 to 0.15%,
Si; 0.2 to 0.5%, Cr; 22 to 27%, Nb;
An air port nozzle for a recovery boiler, wherein the air port nozzle is formed of a material containing 0.8 to 1.5%, the balance being Fe and unavoidable impurities.