Source: China Metallurgical News - China Iron and Steel News Network

I. Causes of air outlet burning

1. The furnace condition is unstable, and the cylinders are piled up.

Such a situation is often encountered in production. The blast furnace condition has been fluctuating greatly, the stability is very poor, and the wind addition and reduction are frequent, and the long-term stability of the blast furnace has not been achieved. Due to the frequent air reduction operation of the blast furnace and the long-term unplanned suspension of the external influence, the furnace cylinder is inactive and accumulated. The generated slag iron cannot penetrate into the furnace cylinder in time, and the iron circulation at the accumulation site is not smooth, resulting in the accumulation of slag iron in front of the air outlet, which is easy to cause damage to the air outlet.

2. Influence of the decrease of liquid permeability in dead coke reactor

After the liquid permeability of the cylinder dead coke reactor decreases, the slag iron falling from the drip zone cannot quickly penetrate into the bottom of the cylinder through the dead coke reactor. The slag iron is easy to accumulate at the front end of the air outlet. The molten iron touches the front end of the air outlet, burns the air outlet, and the air outlet burns in the lower part. One of the main reasons is the poor metallurgy performance of coke, which makes the coke particle size of the dead coke reactor in the furnace small, resulting in a decrease in the liquid permeability of the dead coke reactor.

3. The wind is overturned.

Another serious burn of the blast furnace outlet is due to the upturned sleeve in the air outlet. Alkali metal and zinc in blast furnace materials can cause the strength of carbon bricks to deterioate, volume expansion and plastic expansion, resulting in the upturning of the middle sleeve. Due to the upturning sleeve in the air outlet, it has a great impact on the distribution of the initial gas flow. The initial gas flow goes up from the air outlet, not down, resulting in the accumulation of the cylinder, especially the edge of the cylinder, which is prone to dead angles, resulting in the burning of the air outlet.

4. Wear of the air outlet

The front end of the air outlet extends into the cylinder, causing wear under the friction of pulverized coal injection and the erosion of high-speed moving materials in the air outlet rotary area. The wear part is generally on the left and right sides of the horizontal centerline plane of the small air outlet.

5. The impact of the wind

When the blast furnace is produced normally, it will perform normally. When the blast furnace is closed or the air is reopened after braised furnace, a large number of burn-damaged air outlets occur, which delays the blast furnace rewinding process. For this phenomenon, it often leads us into the misunderstanding of serious accumulation of the cylinder, thinking that it is caused by the heavy accumulation of the cylinder. After all, the accumulation of the cylinder is an important cause of the burning air outlet. It is also believed that the air outlet opened too fast, and the originally blocked air outlet area was not fully active, so that the slag iron generated after being opened could not smoothly penetrate into the cylinder and burn the air outlet.

6. The loading system is too marginal.

The amount of suspended air material under the blast furnace, considering the long time of the closed air of the blast furnace, the loading system has been adjusted accordingly. After the resumption of air, the production practice proves that the loading system has developed the edge of excessively, resulting in a decrease in the gas utilization rate and an increase in the direct reduction of the blast furnace, which affects the flow of slag and iron and smelting performance; and the loading on the edge of excessive development. The system is a factor in the subsequent air outlet burning.

II. Countermeasures for blast furnace air outlet burning

According to the analysis of the form of blast furnace air outlet damage, a targeted blast furnace operation management system and technical measures to prevent air outlet leakage are formulated to improve the service life of the air outlet, reduce the wind break rate, improve economic benefits, and achieve safe and efficient blast furnace production. The work mainly focuses on the following:

(1) Precision technology to improve and stabilize the quality of raw fuel and reduce harmful elements entering the furnace. According to the logistics situation incoming the factory, coking, sintering and pellet ingredients are optimized, the comprehensive grade of the furnace is improved, and the amount of slag is reduced. Improving the quality of coke, especially the thermal performance of coke, ensuring the skeleton of coke in the furnace, and good slag permeability in the cylinder are important factors to ensure the stability of airflow and reduce air outlet wear.

Strengthen the screening of raw fuel and carry out the whole process of screening monitoring and assessment of high furnace inlet materials. Strictly formulate and implement the cleaning of the bottom of the screening under the tank. Especially in the rainy season, avoid a large amount of powder furnace material into the furnace as much as possible. Reduce the resulting raw material conditions for poor breathability of the furnace material, high pressure difference in the furnace, and the development of edge airflow.

(2) Control technology of harmful elements. Study the impact of harmful element enrichment on air outlet deformation, track the changes of harmful elements, establish an early warning system for harmful elements and a regular alkali discharge system; study the mechanism of the influence of harmful elements on air outlet deformation, study the control range of harmful elements, and study how to reduce the harm of harmful elements to the blast furnace through blast furnace operation. Track changes in harmful elements and establish an early warning system for harmful elements and a regular alkali discharge system. The zinc load in the blast furnace is less than 300g/t-p, and the alkali load is less than 4kg/t-p, effectively reducing the effect of harmful elements on wind deformation caused by enrichment.

Control the amount of alkali metal entering the furnace and take an appropriate way to reduce the alkalinity of the slag to discharge the alkali. The sulfur content of molten iron can be broadened from the current 0.01-0.02% to 0.03-0.45%. However, this operation requires that the components of the furnace ore (especially the sintering alkalinity) must be relatively stable.

(3) Improve the stability of blast furnace conditions.

Change the fabric thinking and resolutely control the marginal airflow. Develop the central airflow, control the marginal airflow, and improve the gas utilization rate. This is an important cloth means to reduce costs and be stable. Penetrate the center, control the edge, stabilize the slag skin, and strictly implement the 'edge pressing' operation, so that the blast furnace will travel smoothly. Of course, the specific means and range depend on the specific situation of each furnace.

According to the peripheral changes, the lower system, the thermal system, and reasonable furnace parameters are controlled. Through production practice, the blast furnace control parameters and furnace shape parameters are reasonably corrected to further promote the improvement of the flushing degree of the furnace condition. With the extension of the flush time of the furnace condition, some furnace parameters are corrected again, according to the furnace entry. The change of titanium load adjusts the thermal system, especially the control of furnace temperature and alkalinity. Such a benign cycle can achieve long-term stable and smoothness. In production, according to the changes of furnace lining temperature, temperature difference and gas flow, we make full use of the adjustment means such as mine batch, material line, air outlet area, air outlet layout, cloth angle, etc. to adjust the upper and lower parts, stabilize the furnace lining temperature and gas flow within a reasonable range, maintain a reasonable operating furnace shape, and prevent the sudden The aftertachment causes damage to the air outlet.

(4) Improve the material of the coal spray gun, and correctly install and adjust the position and angle of the spray gun. Establish the inspection of the daily spray gun work in the air outlet, adjust the angle of the spray gun at any time to prevent coal painting the air outlet from leakage; carry out detailed statistics on the use cycle of the spray gun, regularly take it out, check and replace it, and study the economical and reasonable spray gun material to maximize the service life of the spray gun.

Stable oxygen-rich coal injection operation maintains a reasonable theoretical combustion temperature before the air outlet according to the level of the coal injection ratio. Avoid the influence of too little gas in front of the air outlet caused by excessive oxygen enrichment, the large amount of SiO and other factors on the breathability of the furnace material. At the same time, the production speed of excessive slag iron can be controlled, which can penetrate into the cylinder in time in the furnace material, so as to avoid burning the air outlet caused by a large amount of accumulation before the wind. Especially in the continuous furnace conditions, premature oxygen-rich coal injection is due to insufficient heat reserves in the furnace, which makes it difficult for the slag iron in the furnace to penetrate the cylinder, resulting in air outlet burning.

(5) Blast furnace iron outage management. Determine the reasonable iron outlet angle and depth, determine the reasonable number of iron outlets, the flow rate of iron, and the slag see time, and reduce the abnormal erosion of the furnace by the slag iron circulation. Determine the iron outlet depth, the iron discharge speed and the slag-to-iron time ratio of 1.2 to 1.5 times the thickness of the brick lining in the iron mouth area, which effectively avoids the local accumulation caused by uneven operation of the furnace cylinder, resulting in the erosion of the air outlet by the slag iron in front of the air outlet.

(6) In the early stage of cylinder accumulation, it is treated by means of operation, and a cylinder pretreatment system is established to improve cylinder activity. Through the means of cylinder temperature detection, the trend of local accumulation or activity decline of the cylinder is judged early. In the early stage of cylinder accumulation, it is treated through operational means to establish a cylinder pretreatment system. The use of furnace detergent should be eliminated at the end of the furnace service.

(7) Water quality management. According to the water quality test, drug and algae are added in time to reduce Ca2+, Mg2+ and Cl-1 ions in the water, control PH at 7.0, prevent the cooling equipment from scaling and reduce the cooling effect. The wind should be treated in time after the air outlet leaks.

(8) Stable wind temperature operation. According to the specific situation of each hot air furnace, the converted average wind temperature value should be adopted to use mixed air control. Instead, it should not be the mechanical operation of the full-level air mixing valve. Avoid the change of temperature field in the furnace caused by large fluctuations in wind temperature before and after furnace change.

(9) The air outlets that are continuously burned in the same air outlet area shall be blocked accordingly, and the working condition of the cooling wall in this direction shall be checked at the same time. Open the air outlet in time under the condition of good heat in the furnace cylinder and the flow of slag iron around the air outlet, so as to avoid a vicious cycle caused by continuous burning damage and frequent wind suspension.