(4) Temperature distribution in the sinter layer and factors affecting temperature The characteristics of the temperature distribution in the layer are:
1) A typical temperature profile from low to high temperature and then rapidly falling from high to low, with the highest point in combustion. This curve only changes position as the sintering progresses in a wave-like manner along the direction of the gas flow, while the highest temperature point rises. This feature has nothing to do with the height of the layer, the properties of the material, and many other factors. Only when a new sintering method is used, such as preheating of the sinter layer or heat treatment of the sinter is different.
2) The heat exchange in the lower part of the combustion zone is completed in a very narrow heating and drying zone. Its height rarely exceeds 50 mm. Although the distance is very short, the gas can be cooled from 1400 to 1500 ° C to 50 to 60 ° C. Mainly It is the airflow speed, the temperature difference is large, and the convection heat transfer amount is large. On the other hand, since the pellets have a large specific surface area and are in close contact with each other, conduction heat transfer is also rapidly progressing.
3) The maximum temperature of the combustion zone increases with the progress of the sintering process, which is mainly due to the above-mentioned heat storage, see Figure 3.
Based on the heat exchange law of the fixed layer, the heat balance of the combustion zone and the combustion dynamics formula, the approximate method of calculating the sintering temperature along the height of the layer is proposed. The calculation results and the measured data are used to sinter the inert material. Relatively close, but for real ore sintering, there is still a distance between the two. [next]
The particle size and fuel consumption of the material as well as the air consumption have an effect on the temperature distribution within the layer.
(1) The influence of the particle size of the material on the temperature field distribution. Figure 4 shows the effect of material size on the maximum temperature of the layer.
The larger the particle size, the lower the temperature at the same level. In a layer of the same size level, the temperature of the material layer containing no carbon at the same level is significantly lower than that of carbon. The size of the particle size directly affects the heat exchange, and the material having a coarse particle size has a relatively small surface area per unit volume, and receives less heat from the gas stream than the fine particle portion. Since the airflow preserves its own heat in a longer passage, this results in a larger "heat wave" movement speed and a smaller material temperature in the coarse pellets. It is generally considered that the coarse-grained sintering mixture has a large sintering speed due to the large gas permeability. But in fact, the average speed of heat waves is closely related to the particle size. That is, the size of the heat exchange area has an important influence on the speed of the sintering process.
(2) The effect of fuel consumption on the maximum temperature of the layer (Figure 5).
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1) When the heat wave passes through the layer containing no fuel (0% C), the temperature decreases as the heat wave moves downwards, because part of the heat is left in each unit layer and the rest is The gas is taken away. If there is no other heat supplement (solid fuel) in the material layer, the downward heat wave will continue to decrease gradually;
2) As the carbon content of the material increases (0.5% to 1.5% C), the curve changes. At the lower level, the temperature is increased due to the heat accumulated by the combustion of the solid fuel, and the maximum temperature at the same level increases as the amount of fuel increases. When C = 2.5%, a concave curve appears. The tendency to fall in the upper portion of the bed is due to the reduced temperature during heat exchange and cannot be compensated for by the heat generated by the solid fuel. In the lower part of the layer, the temperature of the air entering the combustion zone is also higher due to better heat storage conditions. Therefore, the highest temperature in the layer begins to rise. If the fuel exceeds a certain value, the maximum temperature in the lower part of the layer may even increase gradually.
Figure 6 is the use of quartz sand in the sintering cup of the central laboratory of Baotou Steel Co., Ltd. with the addition of 3.0%, 3.6%, 4.2%, and 8.2% carbon powder. The height of the layer is 200 mm and the negative pressure is 1100 mm. ×9.08665 Pa), a change in temperature of a certain layer at a fixed point during sintering.
As the carbon content increases, the sintering temperature increases, and the time to maintain the same temperature is extended, that is, the curve is expanded. However, when the carbon content is increased to 4.2% or more, the rise in the maximum temperature is not obvious. [next]
F. Cappel and EU Wendeborn determined the temperature distribution of the mixed layer based on heat transfer calculations. He adds enough fuel to the inert material; the temperature of the second horizontal layer of the layer rises from 1000 ° C to 1500 ° C (1000 ° C is the ignition temperature), and the material temperature of each of the following horizontal layers can be calculated to be above 1500 ° C. , as shown in Figure 7. However, due to the presence of the melt, the temperature cannot rise further. The shaded portion of the curve indicates the effective heat of fusion within each layer.
(3) The impact of air consumption. As the amount of air passing through the layer increases, the maximum temperature value decreases. The increase in air flow rate causes an increase in the heat transfer coefficient, while the amount of material passing through the gaseous heat carrier of each unit per unit time also increases. If the heat transfer coefficient increases in proportion to the air flow rate, the heat entering the layer also increases, so that the maximum temperature may remain unchanged. However, in fact, when the air velocity is increased, the temperature of the material layer is lowered, which indicates that the favorable influence of the increase in the heat transfer coefficient is smaller than the adverse effect of the growth of the heat carrier. That is, the heat storage in the previous layer is consumed by the heating of a large amount of air material, so that the maximum temperature in the layer is lowered, as shown in Fig. 8.
In addition, the exothermic and endothermic reactions of the sintered mixture during the sintering process, the temperature at which the solid material is preheated, the heat added during ignition, the volume specific heat of the sinter layer, and the maximum temperature in the sinter layer are certain. influences.
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