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Study on reducing coke ratio of blast furnace
Based on the analysis of the actual situation of the current national iron and steel industry, the development of non blast furnace ironmaking technology in China is slow (such as rotary hearth furnace), high energy consumption and environmental protection are not up to standard. There is still a long way to go in the future. Therefore, blast furnace ironmaking is still the mainstream of ironmaking process. Reducing pig iron cost can improve the production profits of iron and steel enterprises and promote the competitiveness of enterprises, which is one of the important symbols of the development of ironmaking technology. In order to reduce the cost of pig iron, it is necessary to take measures to optimize the structure of raw materials and fuels, reduce the charging coke ratio of blast furnace, realize process optimization and ensure the smooth operation of each production process.
1. Main functions of coke
Coke is an important basic raw material in blast furnace ironmaking at present, and its influence on blast furnace ironmaking is more than 30%, which has an important influence on blast furnace ironmaking and refining technology. Therefore, the role of coke in blast furnace ironmaking is analyzed from the following points:
(1) Provide the heat required for ironmaking. The amount of heat required for blast furnace ironmaking is very large, and the use of coke is gradually reduced with the increase of coal injection ratio. However, the coke consumption will exceed the coal injection. From the theoretical point of view, the minimum coke ratio is 250kg/t, and the coke burns off 55%~65% at the tuyere.
(2) Reductant. Coke reduction is the reduction of iron ore in the form of C and Co. The coke dissolution reaction from furnace charge to tuyere is 25%~35%.
(3) Dissolved carbon of pig iron. During the blast furnace ironmaking operation, the carbon in the coke gradually seeps into the pig iron. Generally, the carbon content of cast pig iron is 3.9%, that of steel-making pig iron is 4.3%, and the coke consumption for pig iron carburization is about 7%~10%.
Comprehensively analyzing the specific role of coke, it is the most critical to provide the dominance of heat source, which determines the minimum value of theoretical coke ratio. If it is lower than this value, blast furnace ironmaking will not continue. Under various application conditions, the reduction and carburizing functions of blast furnace ironmaking remain basically unchanged. Under the influence of high coal injection ratio, the skeleton effect of Coke will be more obvious, and the quality of Coke will be gradually improved. Otherwise, the requirements of high coal injection ratio will not be met, and blast furnace ironmaking will not be effective. The average particle size of coke from the feed line to the tuyere is reduced by about 20%~40%. Low quality coke and poor thermal reactivity will result in high pulverization rate.
2. Influence of different coke on blast furnace ironmaking
The coke quality shall be controlled from the aspects of strength, ash content, sulfur content, etc. if the coke quality is unqualified, it will easily lead to the deterioration of the blast furnace smelting process and affect the effect of the whole process. In blast furnace ironmaking, the coke quality shall meet the following requirements: the ash content shall not exceed 12.5%; The coke strength meets the specified technical standards; Coke particle size is qualified; If there is a problem of wet coke or yard coke, the quality cannot be effectively controlled. In the composition of coke ash, the main harmful substance is alkali metal, which will lead to the increase of burden pulverization rate, the effect of blast furnace gas and liquid permeability can not meet the requirements, and the mechanical strength of coke decreases, which is not conducive to the permeability of the whole charge column structure. Coke quality, on the one hand, needs to ensure the stability of blast furnace ironmaking, and the upper air permeability is qualified; On the other hand, the coke quality should also ensure the normal operation of the hearth and the permeability of the material column. Therefore, coke quality has a direct impact on the whole blast furnace ironmaking process.
3. Analysis of influencing factors of coke charging ratio
(1) The screening quality of small ore is poor, and the silicon content in pig iron is relatively high; It is found from the analysis of the test results under the trough that the proportion of the powder less than 5mm into the furnace should be controlled below 5%, otherwise it will have a great impact on the smooth operation of the blast furnace. The increase of silicon content in pig iron and the increase of coke feeding ratio need to be strictly controlled.
(2) When the alkalinity is low, the position of slag forming zone will move, the change of furnace row will lead to the fluctuation of silicon content in pig iron, the heat loss is very serious, and the coke feeding ratio will also increase. It can be improved by changing the ore batch, which can produce a certain effect.
(3) Poor gas utilization. At present, the applied focal angle difference is 1.5 °, which can meet the requirements of forward travel. If the angle difference is expanded, it can appropriately promote the improvement of gas utilization.
(4) Oxygen enrichment capacity limitation. Through test and analysis, it is found that the oxygen enrichment rate parameter needs to be increased in order to ensure the improvement of coal ratio because of insufficient oxygen enrichment capacity or poor stability.
4. Methods of reducing coke ratio of blast furnace
4.1 selection of raw materials
In order to ensure that the powder content of raw materials into the furnace meets the requirements, the sinter and coke screening treatment shall be strengthened before entering the furnace. Regularly clean the sinter screen and coke screen to ensure that the screening quality is qualified, and ensure that all powders with particle size less than 5.0mm are cleaned, so as to meet the requirements of stable furnace operation and provide basic conditions for coke ratio reduction. Make corresponding adjustment to the change of coke moisture to ensure that the furnace temperature remains normal. The furnace charge structure should also be adjusted accordingly to improve the clinker rate and furnace grade, reduce the slag amount, ensure that the soft melt zone meets the specified requirements, and promote the improvement of gas utilization rate.
4.2 air blowing
It is very important to select the appropriate air supply mode to form a good utilization of gas. A large circulation area shall be ensured in front of the tuyere to allow the gas to gradually extend to the center, avoid dead material column in the center, ensure the air permeability and liquid permeability of the hearth, and achieve structural stability. The air supply system shall select appropriate wind speed to ensure the blast kinetic energy and fuel temperature, ensure that the gas flow meets the requirements, the hearth can operate normally, the heat can meet the requirements, and the operation is stable. If the tuyere area is relatively large, the air flow in the surrounding area will be enhanced. Adjust it when the wind is off, lengthen the tuyere appropriately, and control the edge air flow to form a reasonable distribution and control of gas flow.
4.3 increase coal injection ratio
Controlling the coal injection ratio as required can reduce the project operation cost and promote the overall benefit. Increase the coal injection ratio, test and analyze the fuel ratio parameters, and realize the optimal setting of coal injection ratio. By increasing the coal injection ratio, the combustion effect can be improved. The increase of coal ratio can achieve the effect of coke reduction. During production, in the process of determining the coal injection ratio, the amount of pulverized coal should be strictly controlled in combination with the actual production situation of the enterprise, and the metallurgical treatment link should be optimized to reduce the operation cost. Increasing the coal ratio can reduce the use of coke and achieve the purpose of cost control, so as to solve the problem of coke resource shortage in China and help the long-term development of iron and steel enterprises.
4.4 improve oxygen enrichment rate
After the treatment of this measure, the theoretical combustion temperature in front of the tuyere increases, which promotes the improvement of pulverized coal combustion efficiency, ensures that the pulverized coal injection volume meets the requirements, and then reduces the coke feeding ratio.
4.5 control silicon content of pig iron
Ensure that the proportion of silicon is about 0.3%, the heat of slag iron is relatively high, the output will also increase, and the coke feeding ratio will decrease.
4.6 strengthen maintenance
In order to better promote the stability and safety of blast furnace production and reduce energy consumption, equipment maintenance and management should be done well to ensure that the equipment can work normally. To reflect the role of equipment, scientific and reasonable maintenance and management is very important, such as determining spot inspectors and doing a good job in daily equipment spot inspection management. Each system of the blast furnace shall be managed by a full-time point inspector, who shall be responsible for daily maintenance and management. In case of equipment failure, which leads to slow wind, wind shutdown and other problems, full-time personnel shall be organized to check to ensure that the operation performance of the equipment is qualified and there will be no failure again. The spot inspectors strictly implement the management system and standards, maintain high work enthusiasm, and finally enable the equipment maintenance and management to be carried out orderly to ensure that the equipment is under high operation performance.
4.7 fabric system progress
In the production process of blast furnace, the determination of distribution system is the basis to ensure the smooth operation of blast furnace. The upper adjustment relationship will have a great impact on the burden distribution, as well as the gas flow distribution and gas utilization. Under the long-term analysis and research, the advanced central coke distribution mode is gradually selected and applied to ensure that the central loose edge air flow can be carried out effectively, and the distribution start angle and angle difference can be reduced. In the work, combined with the situation of raw fuel, the above part system is fine adjusted to ensure that the edge gas flow is loose, so that the gas in the furnace can reach a stable state, which can also effectively improve the utilization rate of gas, avoid excessive use of fuel, and improve the economy of the blast furnace.
4.8 strengthening management
The quality of slag and iron emission has a vital impact on the production of blast furnace. At present, blast furnace has begun to develop in the direction of short and fat. The requirements for slag iron discharge shall be gradually increased to prevent adverse effects on production, and the problems of suspended and collapsed materials shall be prohibited. In combination with specific conditions, the following treatment measures are formulated:
First, it is necessary to strictly inspect the taphole to ensure that the tapping meets the requirements of uniformity, and do a good job in the detection and analysis of various parameters to ensure that the operation in front of the furnace is more uniform. Standardized management method shall be adopted to ensure smooth shift handover, so as to prevent mud emission and running due to problems in iron port plugging.
Second, inspect the quality of the gunshot mud to ensure that the pressure on the top of the furnace meets the requirements, and that it is about 400kPa, so that the gunshot mud can be stabilized by sufficient supporting force. Summarize the actual experience, select the best type of blasting mud, select the best blasting mud supplier through bidding, do a good job in the quality control of blasting mud, meet the production requirements and improve the process level.
5. Conclusion
To sum up, the article takes measures to adjust the charging coke ratio, determine the appropriate management system and work standards, control various production processes in the production process, improve the technical level, ensure that the raw fuel effect is qualified, and the quality of iron tapping can meet the standard requirements, so as to achieve the purpose of reducing the charging coke ratio.
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