The gas branch pipe of the top-burning hot blast stove is located at the top of the burner. During the operation of the hot blast stove, due to the periodic changes of temperature and pressure under different working conditions and the influence of nitrogen purging, the refractory materials of the gas branch pipe often fall off and the composite brick at the gas inlet collapses, resulting in excessive temperature of the gas inlet shell, cracking and air leakage, which affects the safe operation of the hot blast stove and requires emergency repair treatment. The service life of the gas inlet of the top-fired hot blast stove burner has become the key to achieve high air temperature and long life of the top-fired hot blast stove.

1. Cause analysis of gas inlet damage

(1) Gas branch pipe lining refractory configuration is unreasonable

Part of the top-burning hot blast stove burner gas branch pipe is lined with only one layer of heavy refractory bricks, and the inner wall of the tube shell is not sprayed with paint; in addition, when the hot blast stove is running, the pipeline is in a state of alternating cold and heat, which is easy to cause refractory brick peeling, and there is no spraying insulation in the tube shell, resulting in too high temperature of the tube shell.

(2) Unreasonable setting of gas branch pipe

Because the gas branch pipe is located in the upper part of the hot blast stove, the spring support compensation of the gas branch pipe is insufficient, and the stress of the pipe shell intersecting the gas inlet and the burner is concentrated, resulting in deformation and peeling of the pipe lining resistant material.

The nitrogen purge system of the burner is not perfect.

The operating procedures for the top-fired hot blast stove require that nitrogen purging must be carried out after the hot blast stove is fired and the air supply is completed to ensure the safe operation of the hot blast stove system. Some top-burning hot blast stoves are not equipped with nitrogen tanks or gas collecting pipes, but only with a Φ φ100mm or Φ φ150mm nitrogen pipe. After the nitrogen valve is opened, the pressure of the pipe network will drop below 0.3Mpa within 3 seconds. This situation will not help to prolong the nitrogen purging time, but will affect the furnace change time. However, the high temperature or vibration at the gas inlet of the top-burning hot blast stove leads to the damage of refractory materials, because the residual gas is not purged clean during furnace change. During furnace burning or air supply, the residual gas/air and high-temperature air/gas periodically undergo secondary combustion in the gas ring and gas branch pipes, forming a combustion explosion effect in a narrow space to damage the inlet structure of the gas branch pipes. Therefore, the nitrogen purging system needs to be equipped with a nitrogen tank or gas collecting pipe with sufficient capacity, and the storage volume needs to be calculated according to the structural size of the burner to ensure that the nitrogen flow reaches the design value instantly after the nitrogen valve is opened, which not only achieves the purging effect, but also saves the furnace change time.

Improper operation procedure of hot blast stove

Part of the hot blast stove nitrogen purge valve control program is set incorrectly, even the gas combustion valve is closed, open the gas release valve for nitrogen purging, resulting in nitrogen is directly discharged, did not play a role in purging. In the computer PLC program, the pressure and flow peak of the nitrogen pipe network should be set up for safety interlock.

2. Emergency treatment measures for gas inlet

In order to ensure the safe operation of the hot blast stove, the gas inlet should be installed with patch temperature measurement to facilitate real-time monitoring. If the temperature of the gas inlet shell is more than 150 ℃, the inspection of this part should be strengthened, especially to detect whether the shell has leakage points. If the high temperature area is large or leakage points are found, the furnace must be stopped and emergency treatment measures must be taken.

⑴ Withdraw the furnace and take off the air

Determine the hot blast stove that needs to be overhauled, extend the nitrogen purging time after the end of combustion, ensure that the gas in the gas branch pipe and burner ring is purged clean, and close other valves outside the flue gas valve of the hot blast stove body that needs to be overhauled.

(2) Blind plate of gas branch pipe

When personnel are required to enter the branch pipe and the burner for maintenance and repair, the gas safety is involved, and the blind plate blocking operation shall be carried out on the gas branch pipe one day before the wind is closed. Install a blind plate on the side of the gas cut-off valve close to the flange of the hot blast stove to cut off the main gas of the gas. During the installation of the blind plate, the nitrogen purge valve and the flue gas valve shall be closed after the installation of the blind plate.

⑶ Burner gas loop and branch pipe cooling

Due to the high position of the gas branch pipe of the top-burning hot blast stove, once the tube shell is opened, the pumping force of the hot blast stove flue cannot meet the requirements, and the high-temperature gas in the furnace overflows through the manhole. In order to ensure the safety of maintenance personnel, Φ 900 holes are opened on the side of the pipeline between the gas branch combustion valve and the shut-off valve, and the manhole of the air branch pipe is opened and the guide pipe port is installed. Install a high-power fog gun fan at the Φ 900 hole on the side of the gas branch pipe to cool the gas branch pipe of the burner and the gas ring road. When the temperature in the gas branch pipe is lower than 30 ℃, the maintenance personnel can carry out the construction.

Refractoring of gas inlet

According to the damage of gas branch pipe and inlet refractory, pouring and spraying methods can be used to repair. Before removing the damaged refractory materials, block the gas nozzle hole with large asbestos felt, and arrange special personnel to monitor the thermocouple temperature at the top of the furnace and the operation status of the fan to prevent the fan from stopping. The gas inlet may be cast and the anchor welded. The gas branch spraying adopts the combination of anchor and hanging net.

In recent years, Annike has continuously improved the emergency treatment measures for the gas inlet. Under the condition of continuous blast of blast furnace, more than 10 gas inlets or branch pipes of hot blast furnaces in China have been repaired. The shortest maintenance time for a hot blast furnace is only 3 days, and the longest period after maintenance has been safe operation for 5 years. At the end of air supply, the surface temperature of the tube shell in the repair area of hot blast furnace is below 150 ℃, and the gas inlet has been repaired.