"Sintering Activation Process: Essential Requirements for Ignition"

Understanding the Sintering Process: Key Factors and Considerations

The sintering process is a critical step in the production of sintered ore, involving the combustion of fuel within the sinter material. This process begins with an igniter that raises the temperature of the surface layer of the sinter to a point where combustion can occur, typically around 700 °C. Following this, an exhaust fan facilitates the removal of gases, which is essential for maintaining ignition. The igniter also plays a vital role in transferring heat back to the upper layer of the sintering material, which is crucial for enhancing the quality of the sintered ore and reinforcing the overall sintering process.

One of the most significant parameters in this process is the ignition temperature, which influences not only the surface strength but also the integrity of the lower sintered layers. If the ignition temperature is set too low, the heat accumulation in the surface layer may be inadequate, preventing the lower layers from reaching the necessary sintering temperature. Conversely, excessively high ignition temperatures can lead to over-melting of the surface sinter, increasing the FeO content and negatively impacting reduction performance.

The duration of ignition is determined by the length of the igniter and the operational speed of the sintering machine. A longer ignition time, at a constant temperature, allows for greater heat transfer from the igniter to the sinter, which can enhance the strength of the surface sinter and improve overall yield. However, insufficient ignition time necessitates an increase in ignition temperature to ensure adequate heat storage in the surface layer.

Historically, significant emphasis has been placed on the strength of the surface layer. Various strategies, such as extending the igniter length and incorporating heat retention sections, have been employed to increase surface sinter strength. These methods can be effective when dealing with thinner material layers. However, as the height of the sintered layer has increased, the surface layer's specific gravity has decreased, which complicates the relationship between ignition time and sinter quality.

The oxygen concentration in the exhaust gas is another critical factor affecting sintered ore quality. Insufficient oxygen can delay the combustion of solid fuel, adversely impacting the strength of the sintered product. The oxygen levels in exhaust gases are influenced by the size and amount of solid fuel used, as well as the calorific value of the fuel. For instance, if the mass ratio of the mixture to the sinter is 1.8, a solid fuel consumption of 50 kg dry coal per ton of sinter would require an oxygen content of 8.5% in the exhaust gas. Achieving the necessary oxygen levels may involve increasing excess air, although this can be challenging when using limited coke oven gas in blast furnace operations. Preheating the combustion air or enriching it with oxygen are potential solutions, as preheating can elevate combustion temperatures, allowing for better air infiltration during the process.

Moreover, the uniformity of the flame is critical for optimal sinter quality. Adjustments to the configuration of burners and the balance of gas and air supply are necessary to achieve this uniformity. The ignition vacuum also requires careful management; excessive vacuum can allow cold air to enter from below, lowering ignition temperatures and causing uneven ignition across the material surface. Conversely, insufficient vacuum may hinder the effective extraction of combustion products, leading to poor heat utilization.

Cold air infiltration from the sides of the trolley can significantly impact ignition quality. To mitigate this, enhancing seals and controlling furnace pressure are essential. Many modern sinter plants utilize automatic pressure adjustment systems within their ignition furnaces, maintaining a slight positive pressure to prevent cold air ingress.

In conclusion, to optimize the ignition process in sintering, it is essential to have a well-designed igniter and to carefully manage various operational parameters, including ignition temperature, time, oxygen levels, and vacuum conditions. These factors collectively influence the quality and strength of the resulting sintered ore, making them vital considerations in the sintering process.