Recently, Zhengzhou Annike Industrial Co., Ltd. contracted a 3200m steel company in Tianjin.³Blast furnace hot blast stove system maintenance and renovation project.

The blast furnace was completed and put into operation in 2006, equipped with 4 small hat top-burning hot blast stoves, which is the first foreign top-burning hot blast furnace technology introduced on a large blast furnace in China. Over the past 14 years, the average air supply temperature of the hot blast stove has gradually decreased from 1230 ℃ to 1170 ℃, and the local temperature on the surface of the furnace shell has increased from about 100 ℃ to more than 200 ℃. The fuel ratio of blast furnace and the cost of ironmaking have increased significantly, and the current situation of hot blast furnace has been difficult to meet the second generation of blast furnace service, nor does it meet the requirements of modern blast furnace ironmaking efficiency, longevity, energy saving and environmental protection.

Taking advantage of this blast furnace overhaul opportunity, Annike and the owner conducted a comprehensive assessment and analysis of the current situation and damage of the hot blast stove. After the inspection of the hot blast stove, it was found that the large wall of the regenerator of the hot blast stove was basically intact, the lattice brick had no slag sinking phenomenon, and the hot air outlet, combustion chamber, mixing chamber and hot air pipeline were seriously damaged. With the goal of reducing investment, ensuring construction period and meeting the service of the second generation furnace for more than 15 years, Annike has formulated a feasible implementation plan.

1,Main Damage of Hot Blast Stove System

(1) Dislocation of burner (mixing chamber) nozzle and brick falling

Fig. 1 Gas Nozzle Inside the Burner Fig. 2 Gas Nozzle Outside the Burner

(2) The arch (combustion chamber) bricks are staggered and peeled off.

Fig. 3 Upper part of manhole Fig. 4 Deformed wrong platform

(3) Deformation and collapse of hot air outlet

Fig. 5 Inside of Hot Air Outlet Fig. 6 Outside of Hot Air Outlet

(4) Collapse and brick falling of hot air pipeline

Fig. 7 Main pipe fork Fig. 8 Hot air main pipe

2,damage cause analysis

(1) Dislocation of burner (mixing chamber) nozzle and brick falling

1) Structural design reasons

The design of the nozzle position of the gas ring of the burner is unreasonable, which is not conducive to nitrogen purging. The residual gas in the gas ring will cause deflagration after contacting with hot air, resulting in nozzle damage.

The brick buckle of the gas nozzle cannot lock the nozzle structure, and has poor resistance to deflagration impact, and loosens and shifts after impact.

2) Process setting reason

When the hot blast stove is changed, due to incomplete nitrogen purging, there is residual gas or high-temperature air in the gas ring channel and gas nozzle, and the two meet to cause deflagration and cause nozzle damage.

(2) Vault (combustion chamber) damage

1) Structural design reasons

The vault is designed as an oblique masonry structure, and the single brick type is designed with sub-female buckles on the upper and lower sides only. The expansion joint is not reasonably set according to the temperature and diameter change of the vault. The upper temperature is relatively low, and the expansion of the silica brick cannot be completely released. The construction does not hang the center line, and the masonry close to the furnace shell causes the wrong platform of the working layer to lose round, the force is uneven, the single brick loosens and slips downward, resulting in the collapse of the arch roof.

(3) Deformation and collapse of hot air outlet

1) Structural design reasons

The hot air outlet opening is located at the junction of the straight section of the vault and the cone section. The steel structure at the opening is affected by axial and longitudinal stresses during the operation of the hot air furnace. The stress is most concentrated at the center of the upper part of the intersecting line between the hot air branch pipe and the hot air furnace body shell, and the deformation of the steel shell is the largest. The hot air outlet combination brick is designed with a single inner ring pipe brick petal brick structure. The force situation changes periodically during the combustion and air supply of the hot air furnace. The deformation of the upper half of the hot air outlet is intensified, resulting in the deformation and collapse of the hot air outlet combination brick and the cracking of the furnace shell.

The inner ring channel of the hot air outlet is connected with the hot air branch pipe, the design of the brick expansion joint of the working layer of the hot air branch pipe is unreasonable, and the thermal expansion stress cannot be effectively released, resulting in the inner ring of the hot air outlet inclining to the furnace and damaging the hot air outlet.

2) Material design reasons

Top-fired hot blast stove vault (combustion chamber) working layer refractory material using silica brick, hot air outlet using high alumina brick. The thermal expansion rate of silica brick and high alumina brick is quite different under the same working condition, and the brick seam at the junction of the two materials becomes larger, which is easy to blow the wind, resulting in high temperature of the furnace shell around the hot air outlet.

(4) Brick dropping from hot air pipeline

1) Structural design reasons

The opening of the three-way fork of the hot air pipe is asymmetrical, and the force distribution of the blind plate is uneven. The bite ability at the intersecting line of the composite brick is poor, and the periodic expansion and contraction of the hot air main brick causes the composite brick at the three forks to collapse and fall off the brick.

The hot air pipeline adopts the ordinary "flush brick" design, and the sealing and biting ability of the front and rear ring pipeline bricks are poor, causing the pipeline to blow and drop bricks.

3,Solutions to the above problems

(1) Dislocation of burner (mixing chamber) nozzle and brick falling

1) Changing the distance between the gas nozzle and the lower part of the gas ring is more conducive to the purging of residual gas in the ring. The structure of "burner non-displacement anti-micro-explosion nozzle" and special low-temperature sintering mud for burner are adopted to improve the stability of nozzle structure.

2) When changing the hot blast stove, ensure sufficient nitrogen purging time and amount to avoid deflagration caused by incomplete nitrogen purging.

(2) Vault (combustion chamber) damage

1) The structure of "interlocking vault flat masonry" is adopted, and the single brick adopts the design of four-sided double-row sub-female buckle. During construction, the vault brick does not slide downward, the sealing performance does not flow through the wind, and the stability does not fall off the brick.

2) The vault adopts "slab" masonry structure, and the expansion joints shall be set reasonably according to the temperature and diameter changes of the vault, so as to avoid the extrusion damage of the vault bricks caused by wind channeling or small expansion joints.

(3) Deformation and collapse of hot air outlet

1) The hot air outlet opening is designed in the straight section of the vault (combustion chamber) to reduce the influence of axial and longitudinal stress of the hot air furnace. The design of rigid hoop type tensioning device is added to reduce the deformation of refractory material and furnace shell structure at the hot air outlet during the operation of the hot blast furnace.

2) The hot air outlet combination brick adopts the structure of "multi-ring interlocking anti-channeling hot air outlet" to improve the upper load capacity of the hot air outlet. The upper part of the composite brick adopts a "stress-free orifice" structure to disperse the upper load of the hot air outlet and absorb the expansion of the vault refractory.

3) The hot air branch pipe adopts the structure of "joint pipe combined brick", which absorbs the axial expansion and longitudinal expansion of the refractory material of the hot air furnace body during the operation of the hot air furnace, and prevents the inner ring brick of the hot air outlet from tilting into the hot air furnace.

4) The working layer of the combined brick at the hot air outlet and the large wall of the straight section of the vault are all made of silica bricks to avoid non-synchronous expansion and deformation caused by different material designs under the same working conditions. The local use of red pillar stone brick to improve the hot air outlet pressure bearing capacity, but also to avoid the hot air valve leakage damage to the hot air outlet combination brick.

(4) Brick dropping from hot air pipeline

1) The lower half ring of the three forks of the main branch pipe adopts combined bricks, and the upper half ring adopts prefabricated block or integral casting technology, which has good stability and avoids the collapse of the three forks.

2) The pipe brick adopts the "Z-shaped" design, which can seal the air flow, and the ring is interlocked, and the structure is more stable.

The 3200m³The blast furnace hot blast stove system mainly carries out local maintenance on the burner (mixing chamber), vault (combustion chamber), hot air outlet and hot air pipeline, and more than 20 items of Annike patents and proprietary technologies are applied. Through this overhaul, after the hot blast stove system is put into production again, it can fully meet the expected target of air supply temperature ≥ 1230 ℃ and service life of more than 30 years.

Through continuous independent innovation and improvement, Zhengzhou Annike Industrial Co., Ltd. has completely solved the problems of nozzle dislocation of small hat top-burning hot blast stove burner (mixing chamber), damage of vault (combustion chamber), deformation and collapse of hot air outlet, brick falling of hot air pipeline, slag sinking of lattice brick heat storage body, and wind running at the bottom of the furnace. Since 2010, more than 1000 new and renovated hot blast stoves have adopted Annike's technology and products, and none of the above problems have occurred since they were put into production.