(1) Combustion reaction and its thermodynamic analysis The fixed carbon content of the fuel for sintering is generally 68-80%, and it can be burned when the temperature rises above 700 °C. When sintering is ignited, the ignition temperature should be between 1100 and 1200 ° C because the surface has a certain heating strength and a certain low melting point liquid phase is formed. As the exhaust sintering continues to supply oxygen, the oxygen in the air reacts with the carbon in the fuel as follows: Drawing the above equation in Figure 1, you can see: The actual analysis of the exhaust gas composition demonstrates the above thermodynamic analysis. In addition, the relationship between the combustion ratio and the thickness of the layer is: when the thickness of the layer is 250 to 300 mm, the combustion ratio reaches a maximum. When the amount of returning minerals increases and the amount of fuel does not change, the combustion ratio drops to a minimum and then changes toward the return equilibrium value. As shown in Figure 4. The particle size of the fuel is finer, the amount of fuel is increased, and the sintering temperature is increased to deteriorate the combustion ratio. This is because the combustion reaction tends to result in a shell-wave reaction, and the thickening of the layer and the decrease in the returning of the ore cause the increase in CO due to the fuel. The results of increased distribution density, extended sintering time, and increased sintering temperature. Increasing the negative pressure causes an increase in CO. Fracture: at high temperature, >1600°C C x O y 3→nCO+mCO 2 (n=2m)
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C+O 2 =CO 2 +33411kJ/kgC ΔZ=-94200-0.2T (1)
2C+O 2 =2CO+9797kJ/kgC ΔZ=-53400-41.9T (2)
CO 2 +C=2CO+13816kJ/kgC ΔZ=-13500+41.5T(2CO=CO 2 +C) (3)
2CO+O 2 =2CO 2 +23616kJ/kgC ΔZ=-40800+41.7T (4)
How the above four reactions develop during the sintering process depends on the change in the isostatic pressure ΔZ of the reaction. When ΔZ < 0, the reaction can proceed; when ΔZ = 0, the reaction reaches equilibrium; when ΔZ > 0, the reaction does not proceed, or facilitates the reverse reaction. 
The reaction (1) does not substantially change with the change of temperature, and since the negative value of ΔZ is large, it is advantageous for the progress of the reaction. In the reaction (2) formula, when the temperature is higher, the ΔZ negative value is larger, so the reaction is easy to proceed. When the reaction formula (3) is T>954K, the positive value of ΔZ increases, so the reaction is not easy to proceed, but it is favorable for the reverse reaction. This formula is also called a shell-wave reaction, which is also called a carbon loss reaction. When the temperature rises, the positive value of ΔZ increases, which is not conducive to the progress of the reaction, and is favorable for the reverse reaction.
It can be seen from the above reaction that in addition to the reaction (1), high temperature is favorable for CO generation, and low temperature is favorable for CO 2 formation.
The reaction (1) is easy to occur during the actual sintering process, and the reaction (2) is favored in the high temperature zone. Since the combustion zone is narrow and the exhaust gas passes through the preheating drying zone, the temperature is rapidly lowered, so the reaction (2) is limited. The reverse reaction of the reaction (3) can be carried out during the sintering process, but the reaction is limited. The reaction (4) is easy to carry out in the low temperature region of the sintering process. Therefore, the sinter exhaust gas is mainly CO 2 , only a small amount of CO, and some free oxygen. [next]
Fig. 2 is a graph showing the change of the exhaust gas composition of the self-fluxing sintered ore of the smelting refinery concentrate.
The combustion ratio (CO/CO + CO 2 ) is usually used to measure the chemical energy utilization of carbon during sintering, and the composition of the exhaust gas is used to measure the atmosphere of the sintering process. When the combustion ratio is large, the carbon utilization is poor, and the atmosphere is more reductive. On the contrary, the carbon utilization is good and the oxidation atmosphere is strong.
Factors affecting the combustion ratio are the particle size of the fuel, the fuel content of the mixture, and the magnitude of the negative pressure. Figure 3 shows the relationship between them. [next]
(2) Kinetic analysis of combustion reaction
The fuel combustion reaction is a gas-solid phase reaction that obeys the following five steps:
1) oxygen molecules in the gas diffuse to the surface of the solid fuel;
2) oxygen molecules are adsorbed by the surface of the solid fuel;
3) the adsorbed oxygen molecules react with carbon to form an intermediate product;
4) The intermediate product is broken to form a reaction product, a gas, which is adsorbed on the surface of the carbon particle;
5) The reaction product is desorbed, and the gas diffuses away from the surface of the carbon to the gas phase.
The mechanism equation is:
At low temperatures, <1300 ° C, impact fracture by oxygen C x O y + O 2 = nCO + mCO 2 (n = m)
At medium temperature, both reactions are possible, n: m = 1/2 CO / CO 2 = 1/2
Therefore, the overall combustion reaction rate depends on the chemical reaction rate of combustion and the diffusion reaction rate.