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Analysis and Countermeasures of Hot Air Pipeline Problems of Top-fired Hot Blast Stove





Top-burning hot blast stove technology has incomparable advantages over internal combustion and external combustion hot blast stoves. It was first successfully applied to Shougang No.2 blast furnace (1327m) in the late 1970 s, namely Shougang's big hat top-burning hot blast stove. In 2002, Karujin small hat top burning hot blast stove technology into China, the technology in the country has been vigorously promoted.
In recent years, the vast majority of new or renovation projects of 230m to 5500m blast furnaces in various iron and steel enterprises have adopted small hat top-fired hot blast stove technology. But with the test of practice, some defects in the structural design of the technology are gradually revealed. This paper only analyzes the causes of hot air pipeline damage and puts forward corresponding countermeasures.
Characteristics of Hot Air Pipeline of 1. Top-fired Hot Air Stove
Almost all of the small hat top-burning hot blast stoves are arranged in a row (Figure 1). The hot blast pipes are composed of hot blast branch pipes, hot blast main pipes (platform pipes), hot blast vertical pipes, reverse flow rest pipes, mixed air pipes, hot blast bridge pipes and hot blast enclosure pipes. The main damaged parts are mainly hot blast branch pipes, hot blast main pipes (platform pipes) and hot blast main pipes and branch pipes.
Hot air pipeline is the key device to realize high-temperature hot air transportation. Its medium temperature can reach above 1300 ℃ and the medium pressure is greater than 0.3MPa. For this, the refractory materials and steel shell of the pipeline inside the pipeline will be heated and expanded. The whole hot air pipeline will generate huge blind plate force, which is easy to blow in the weak parts with complex structure such as three forks and compensators or reserved expansion joints.

Figure 1

Analysis on Damage of 2. Hot Air Pipeline

1. Uneven longitudinal displacement at both ends of hot air branch pipe
The bottom of the hot blast stove and the hot blast vertical pipe of the top-fired hot blast stove are fixed. The hot blast stove body expands axially and radially when heated. The hot blast branch pipe and the hot blast stove are in a vertically connected state. After the hot blast stove heats up, with the alternating working state of the hot blast stove (air supply-combustion, combustion-air supply), the corrugated compensator set on the hot blast branch pipe needs to absorb the lateral displacement of the branch pipe and the longitudinal heat of the furnace. The internal refractory material of the hot air branch pipe cannot absorb the horizontal and longitudinal displacement of the ripple compensator, the structure of the refractory material of the working layer is unstable and the wind is channeled, burning the light insulation brick and the compound compensator of the hot air branch pipe, causing damage to the hot air branch pipe.
2. Influence of blind plate force of hot air pipeline
The main/branch pipe fork and the main/enclosing pipe fork of the hot air pipeline are the places where the pipeline connects. In the traditional masonry process, there is an annular through-seam and many triangular seams at the connection between the main pipe and the branch pipe (or enclosing pipe). During the operation of the pipeline, it is scoured by blind plate force, shearing force of hot air flow, shock flow, thermal expansion and cold shrinkage during air supply and wind rest, this causes rapid damage to the composite brick at the three forks, and then causes the steel shell to overheat and become red due to wind channeling.
3. The single brick design of hot air pipeline is unreasonable
The hot air pipeline is designed with ordinary "neat bricks", and the sealing and biting ability of the front and rear ring pipeline bricks are poor, resulting in wind channeling and brick falling.
4. It is unscientific to set the expansion joint of hot air pipeline
The expansion joint of the hot air pipeline does not accurately calculate the expansion coefficient of the refractory bricks of the hot air pipeline at a specific temperature. Generally, it is reserved according to experience. Refractory bricks are crushed and dropped when the expansion joint is small. When the expansion joint is large, hot air enters and burns the light insulation brick, causing the furnace shell to turn red.
5. Lack of large tie rod design
The design of hot blast stove usually takes into account the influence of thermal expansion of hot blast pipes. Bellows compensator is set up on hot blast pipes, but the influence of blind plate force of pipes is ignored. Hot blast branch pipes and main pipes are not equipped with tie rod devices.
3. Corresponding Countermeasures to Solve Hot Air Pipeline Damage
1. Adopt hot air branch pipe "joint pipe" technology
When the air supply and combustion of the hot blast stove are carried out alternately, the hot blast stove body and the hot air branch pipe are in different working conditions under pressure and temperature changes. The "joint tube" combined brick technology is adopted at the hot air branch pipe. Through the small angular displacement of the "joint tube" combined brick, the uneven longitudinal expansion at both ends of the hot air branch pipe is absorbed, and the damage of the refractory material inside the hot air branch pipe is reduced.
2. Change the layout of hot blast stove
The one-line arrangement of the hot blast stove is changed to rectangular or triangular symmetrical arrangement, and the hot blast branch pipe is directly connected to the hot blast outlet of the hot blast stove and the hot blast vertical pipe (Fig. 2).



ASchematic Diagram of Symmetrical Arrangement of Four Hot-blast Stoves BSchematic Diagram of Symmetrical Arrangement of Three Hot-blast Stoves

Figure 2
This arrangement can not only reduce the uneven longitudinal displacement at both ends of the hot air branch pipe, solve the problem of periodic expansion and contraction of the hot air pipe caused by the air supply of hot air stoves of different furnace numbers, but also reduce the adverse effects of the blind plate force of the arrangement of a row of hot air stoves. In addition, the arrangement cancels the hot air main pipe (platform pipe) and the hot air pipe frame structure, which not only improves the thermal efficiency of the hot air furnace system, but also reduces the investment. It is estimated that the investment of the symmetrical arrangement of the hot blast stove is more than 10% lower than that of the one-row arrangement of the hot blast stove system.
3. Hot air pipe refractory brick adopts "Z-shaped" structure design
The refractory bricks of hot air pipeline adopt "Z-shaped" design, which can play a good role in sealing air flow in the ring direction. The single brick turns are interlocked and mutually supported, and the structure is more stable.
4, hot air main pipe and branch pipe three fork using pouring combination brick technology
The lower half ring of the hot air pipe fork is built with composite bricks, and the upper half ring is cast with high-strength and wear-resistant castable. The material of the brick is synchronized with the material of the castable to ensure that the thermal stability and thermal conductivity of the brick and the castable are the same. This kind of structure has high strength at the joint of the pipeline and good overall stability of the structure, which can prevent the deformation, cracking and brick falling of the three forks, and at the same time avoid the problem of difficult construction.
5, hot air pipe refractory design and shell steel structure design complement each other
According to the working conditions of different parts of the hot air pipeline and the measured linear expansion coefficient of refractory bricks, the refractory materials shall be reasonably arranged and expansion joints shall be reserved according to the temperature gradient in the circumferential direction of the pipeline during the design of the brick lining, and the refractory structure design at the expansion joints, corrugated compensators, three forks and other places shall be subject to local special treatment, such as diversion bricks and labyrinth expansion joints, to ensure the sealing of the pipeline structure.
6. Eliminate the influence of blind plate force
The corrugated compensator is designed with a large tie rod, and the end corrugated pipe compensator and the corresponding tie rod device can eliminate the influence of the blind plate force on the pipeline system within the coverage of the tie rod.

To sum up,Zhengzhou Annike Industrial Co., Ltd.Through the design of the hot air pipe expansion and tension device based on stress and strain analysis, it is ensured that the hot air pipe system can not only bear great axial deformation, but also bear the radial deformation of the hot air pipe unique to the top-burning hot air stove, solve the problem of how to distribute, bear and eliminate the thermal stress and structural stress of the hot air pipe, and cooperate with the design of the three-fork composite brick and expansion joint to completely prevent the deformation and falling brick of the hot air pipe lining brick, provide reliable guarantee for high blast temperature and stable operation of blast furnace.