Cause analysis of temperature difference between two tapping fields of blast furnace

Recently, some netizens have put forward the problem that the temperature difference between the two casts of blast furnace is large. They hope to analyze and discuss the causes and countermeasures of the large temperature difference. For large and medium-sized blast furnaces with two or three taps, it is not a case in point that the temperature difference between the two taps is large. This phenomenon occurs from time to time in many double taps or exists in a long period of time. Moreover, the temperature difference between the two taps is also large or small. It is not enough to worry about the light one, and the temperature difference between the two taps can reach about 20-30 ℃. Although the temperature difference between the two events will not have a serious impact on the stable and smooth operation of the blast furnace in a short time, it is undoubtedly a heart disease for the ironmakers who have always been pursuing perfection.

In order to explore the reasons for the great difference between the two temperatures, we should first understand some factors that affect the temperature change of slag and iron. Whether it is large blast furnace or small blast furnace, the coke load is the most direct factor affecting the temperature of slag and iron; The second is the metallurgical properties of the charge, especially the soft melting characteristics and reducibility of the charge. Of course, the choice of slag making system is also included. Their influence on the slag iron temperature is mainly through the change of the position of the soft melting zone, which affects the preheating reduction time of the charge, the enthalpy of the slag iron dropping into the hearth, and the slag iron temperature; The last is the distribution form of gas flow. Gas is the carrier and transferor of heat. Different distribution forms of gas flow directly affect the distribution of temperature field in the furnace, thus affecting the temperature level of slag iron. The common distribution form of gas flow with the development of central gas flow is higher than that with the development of marginal gas flow. In addition, some colleagues believe that different levels of theoretical combustion temperature in front of tuyere will also affect the temperature that slag and iron can reach. Theoretically, it should be correct, but the theoretical combustion temperature of general blast furnace is controlled at about 2100-2300 ℃, while the slag and iron temperature is about 1350-1550 ℃, which is far lower than the theoretical combustion temperature, Therefore, no matter whether the theoretical combustion temperature is high or low, the slag iron will absorb heat and increase the temperature when it drips through the raceway.

For the same blast furnace, the temperature difference between the two fields is large, which obviously has little to do with the load, burden characteristics, slagging system and theoretical combustion temperature. No matter which direction of the taphole, the coke negative pressure, charge characteristics and slag basicity of the charge corresponding to the same direction in the furnace are basically the same as those of the other one, so there will be no obvious difference and no obvious temperature difference.
Therefore, the only reason for the big difference of slag and iron temperature between the two fields is the difference of gas flow distribution in the corresponding direction of the two fields. The uneven distribution of gas flow in the circumferential direction of the blast furnace leads to the difference of slag and iron temperature between the two fields. The reasons for the uneven distribution of gas flow in the circumferential direction of the blast furnace can be summarized as follows:

• 1. The air inlet state is not uniform, such as the area of the air outlet is not the same, or the pressure resistance loss of the far air inlet end and the near air inlet end of the enclosure is large, so that the air inlet gap in the two field directions is large.
• 2. The injection is uneven, and there is a big difference in the direction of two fields;
• 3. The results show that the material segregation and the uneven distribution in the circumferential direction caused by various reasons lead to the great difference in the air permeability of the material column above the two fields;
• 4. The center of the furnace throat is not in the same vertical line as the center of the chute distribution center and the center of the tuyere horizontal plane, that is, the three centers are not illuminated, which makes the distribution segregation larger;
• 5. The inclination of furnace body caused by various reasons also makes the difference between the center of furnace throat and the center of tuyere horizontal plane larger, resulting in the segregation of burden distribution and gas flow distribution;
• 6. The results show that there is a great difference in the degree of lining erosion between the two fields, which makes the distribution of gas and burden in the two fields different.

In fact, it is not only the temperature difference of slag and iron in two large and medium blast furnaces with more than two taps, but also the temperature difference in the early and late stage of tapping for the small blast furnace with single taphole due to the difference between the distribution of edge gas flow and central gas flow Theoretical combustion temperature and other factors have little relationship.

Of course, some colleagues think that the temperature difference between the two fields is caused by the inactivity of the hearth, but I think that unless the hearth is seriously accumulated, or partially accumulated, or the cooler in one field is seriously leaking, there may be a large temperature difference between the two fields. Otherwise, in most cases, the temperature difference between the two fields is large, and there is no obvious sign of hearth accumulation, The temperature difference between the two fields may also be caused by hearth accumulation, but not all the temperature differences between the two fields are caused by hearth accumulation. Of course, this is just a personal point of view. Whether it is correct or not, it also needs to be tested and verified by practice.
In fact, the best way is to find out the causes of uneven distribution of gas flow and try to overcome them. Of course, most of these factors are related to the design and construction of blast furnace body or production furnace type, which are difficult to overcome or basically impossible to overcome in a short time, and the measures that can be taken are relatively limited, mainly including:

• 1. Adjust the local air inlet area according to the actual situation. For example, we should increase the air inlet area of the side with high temperature or reduce the air inlet area of the side with low temperature.
• 2. Under the condition of smooth flow, the edge gas flow should be appropriately suppressed to develop the center gas flow, and the circumferential uneven distribution of edge gas flow is the main contradiction of uneven distribution of gas flow. The appropriate suppression of edge gas flow can effectively reduce the degree of circumferential uneven distribution of gas flow, and make the circumferential distribution of gas flow more uniform, so as to reduce the temperature difference between the two fields.
• 3. On the one hand, increasing the tapping times on the side with high temperature in the two games can improve the permeability of the material column on this side, increase the air intake, and increase the cutting speed on this side. On the other hand, it can reduce the slag iron retention on this side of the hearth, so that the slag iron dripping from above can quickly pass through the raceway, shorten the residence time in the raceway, and reduce the temperature.

Summary

• 1. The essence of causing the temperature difference between the two fields is the uneven distribution of gas flow in the direction of the two fields.
• 2. To ensure the circumferential uniformity of gas flow distribution is the basis to ensure the temperature uniformity of the two fields.
• 3. Adjusting the tuyere layout, developing the central air flow and adjusting the times of two tapping can improve the situation of large temperature difference between the two casting to a certain extent.

Source: China Flanges Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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