In terms of the characteristics of the heating system, the soaking pit furnace belongs to the type of chamber furnace, that is, the furnace temperature changes at any time. The soaking pit furnace determines the heating system of the furnace according to the material, size, charging temperature, discharging temperature, etc. of the steel ingot.
Charging
Soaking pit accounts for a large proportion of the energy consumption in blooming process. The greatest potential of soaking pit energy saving is to make full use of the physical heat of hot ingots and reduce the sedation time and transfer time of ingots after pouring. The old process is to demould the ingot after it is completely solidified, and then send it to the soaking pit. At this time, a large part of the physical heat has been lost. After charging, the ingot temperature has dropped to 500-600 ℃. Therefore, the development trend of modern soaking pit thermal operation is to adopt liquid core ingot soaking and micro energy heating.
Thermal operation of steelmaking soaking pit and use of refractory materials
Practice has proved that, except that the killed steel needs to be completely solidified before demoulding, the rimmed steel and semi killed steel can be demoulded into the furnace without waiting for the ingot to be fully solidified, that is, when the liquid core rate in the center of the ingot is about 30%, the quality and safe transportation of the ingot can be ensured. For example, the motor car can be started after the boiling steel is poured for 10min, the mold can be demoulded when the solidification rate of the boiling steel and semi killed steel is 60%-70%, and the furnace can be loaded when the solidification rate is 70%-80%. At this time, the surface temperature of the ingot can reach about 1000 degrees. In this way, the ingot brings a large amount of solidification latent heat, which greatly reduces the heat consumption of the furnace and significantly improves the productivity. Moreover, the heating cycle of liquid core ingot is short, and the burning loss rate is also hot, which greatly reduces the heat consumption of the furnace and significantly improves the productivity. Moreover, the heating cycle of liquid core steel ingot is short, and the burning loss rate can also be reduced. In addition, since it is not necessary to burn steel at high temperature, the service life of the furnace can be extended, so the modern soaking pit furnace strives to improve the hot ingot rate.
To improve the liquid core ratio of hot ingots, a series of problems need to be solved. Firstly, it is the ratio of unit and external surface area of steel ingots. If the single weight of steel ingots is too small and the external surface area is relatively large, the heat dissipation area is large. Under certain conditions of transmission and storage time, the liquid core rate is also low. Most ingots in China are small ingots, so the liquid core rate is relatively low. Secondly, it is necessary to minimize the transmission and storage time, strictly control each link of the transmission and storage process, and scientifically prepare the transmission and storage schedule. Steel making and local rolling shall be well coordinated. After hot ingot demoulding, it is better to send it to the blooming mill with insulation cover type insulation car, or demould it in the soaking workshop. The delivery time and route shall be shortened as much as possible. If the ingot cannot be loaded into the furnace immediately after demoulding, it should be installed in the insulation box cover or insulation pit, so as to control the charging time of the ingot according to the best transmission interval. It may even be that the ingot does not have to enter the soaking pit and is rolled directly after insulation. Because of adopting the technology of demoulding, transferring and heating the liquid ingot, the accurate prediction of the change of solidification field with time in the ingot temperature field becomes the key to the realization of the process. Therefore, it is necessary to study the mathematical model of ingot thermal process, compile the corresponding transmission schedule, and realize the online control of heating process with the help of computer, so as to achieve the purpose of optimizing the thermal process of soaking pit furnace.
During charging, the steel ingot shall have proper clearance in the furnace. The clearance is too small. Although there are many loads, the heating condition of the steel ingot is poor, which prolongs the heating time. If the clearance is too large, the furnace output will be reduced. Generally, the coverage of the furnace bottom during charging is 35%-45%. The high-temperature area can be arranged slightly densely, while the low-temperature area is sparse, because the heat loss of the furnace pit during uncovering is very large.