Sintering of the sinter is carried out by combustion of the fuel therein. The igniter heats the surface layer of the sinter material above the ignition point of the fuel (about 700 ° C), and then the exhaust process is performed by the exhaust fan, which is a purpose of ignition. Another function of the ignition is to replenish a certain amount of heat to the upper layer of the sintering material, which is beneficial for improving the quality of the sintered ore and strengthening the sintering process.
The ignition temperature affects not only the strength of the surface but also the strength of the lower sintered ore. The ignition temperature is too low, the amount of heat accumulated in the surface layer of the sintering material is too small, which is insufficient to create sufficient ignition conditions for the lower layer, and the material layer cannot reach the sintering temperature, and the ignition temperature is suitable. For example, if the temperature is raised to 1300 K, the maximum temperature of the material layer is along the material. The height of the layer rises until the sintering temperature is reached, see Figure 1. If the ignition temperature is too high (such as 1600K), although the drum strength will continue to increase, the surface sinter will be over-melted, and the FeO in the sinter will be too high and the reduction performance will deteriorate.
The ignition time is determined by the length of the igniter and the speed of the sintering machine. When the ignition temperature is constant, the ignition time is long, and the heat transferred from the igniter to the sinter is large, which can improve the strength of the surface sinter and improve the yield.
If the ignition time is insufficient, the ignition temperature must be increased to ensure that the surface mixture can store a certain amount of heat, as shown in Figure 2.
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At one time, great attention was paid to the strength of the surface layer. At home and abroad, the method of extending the igniter and adding the heat preservation section, that is, extending the ignition time and the holding time, was adopted to increase the strength of the surface sinter, but the gas burning rate was greatly increased. This method has its positive significance under the condition that the material layer is thin. At present, the height of the sintered layer has been greatly increased, and the specific gravity of the surface layer of the sintered layer in the entire sintered ore layer is reduced. At the same time, the sintering of the thick layer itself increases the strength of the sintered ore, so the length of the ignition is increased and the insulation is increased to improve the thickness. The method of surface sinter quality is less important.
The oxygen content in the exhaust gas (flue gas) has a great influence on the quality of the sintered ore. If the oxygen content in the exhaust gas is insufficient, the combustion of the solid fuel is delayed, and the strength of the sintered ore is affected. The oxygen content in the exhaust gas depends on the size and amount of the solid fuel ignition gas calorific value of coal, which is given in Figure 3.
For example, when the mass ratio of the mixture to the sinter is 1.8, the consumption of the solid fuel is 50 kg of dry coal per ton of sinter, and the oxygen content of the ignition exhaust gas is required to be 8.5%. When the ignition temperature is 1200 ° C, the ignition gas is required. The calorific value is above 8373 kJ/m3. It is often necessary to increase the amount of oxygen in the exhaust gas by increasing the excess air, but this is also difficult to use with a small amount of coke oven gas in the blast furnace gas, and preheating the air or enriching oxygen is a method. The preheated air can increase the combustion temperature, so that it is possible to infiltrate excessive air during combustion. Fig. 4 shows the relationship between the air preheating temperature and the oxygen content in the exhaust gas when various fuels are burned.
The uniformity of the flame is also important for the quality of the sinter. In order to ensure the uniformity of the flame, the configuration of each burner and the amount of gas and air should be adjusted.
The degree of vacuum of the ignition should be adjusted. Excessive vacuum will cause a large amount of cold air to infiltrate from the lower part of the igniter to lower the ignition temperature, and also cause uneven ignition of the material surface. On the other hand, the loose material is tightly laminated and the layer is lowered. Breathability. Too low a vacuum does not ensure that the combustion products of the igniter are all drawn into the layer, resulting in deterioration of heat utilization. In addition, in the case where the ignition temperature is the same, the increase in the ignition vacuum is always accompanied by an increase in gas consumption.
Infiltration of cold air from both sides of the trolley is one of the important factors affecting the ignition quality. The way to eliminate this effect is to strengthen the seal while controlling the furnace pressure. Many foreign sinter plant ignition furnaces are equipped with an automatic adjustment system for the pressure inside the furnace. Some operate under a slight positive pressure of 2 mm water column, and some control the pressure in the furnace - 5 mm water column, and a sealing device is arranged between the sides of the igniter and the side plates of the trolley.
To implement the above reasonable ignition process, a perfect igniter must be available.
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