Factors Affecting the Combustion Speed of Pulverized Coal in the Calciner

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Particle Size of Pulverized Coal
Finer pulverized coal particles have a larger specific surface area, enabling better contact with air. For instance, reducing the particle size from 150 μm to 70 μm significantly increases the specific surface area. In the calciner’s high-temperature environment, this allows oxygen to react more quickly with the carbon on the particle surface, accelerating combustion. Generally, a particle size range of 70 – 90 μm is ideal; larger particles (over 120 μm) lead to slow combustion and incomplete burning, resulting in unburned coke.

Volatile Matter Content
The volatile matter in pulverized coal, mainly hydrocarbons, greatly impacts combustion speed. Higher volatile content (25% – 30%) means rapid heat release in the initial stage of combustion, quickly raising the surrounding temperature. This creates favorable conditions for subsequent coke combustion, speeding up the overall process. Conversely, low volatile content (less than 15%) slows down combustion as less heat is initially available.

Oxygen Supply
Adequate oxygen is essential for rapid pulverized coal combustion. Theoretically, a certain amount of air is needed for complete combustion, and in practice, an appropriate excess air coefficient (1.05 – 1.15) is maintained. Insufficient oxygen restricts the combustion reaction, leading to slow burning and the production of incomplete combustion products like carbon monoxide. Excessive air, while ensuring complete combustion, reduces thermal efficiency by taking away too much heat.

Temperature Inside the Calciner
The calciner’s temperature significantly affects the combustion speed of pulverized coal. As a chemical reaction, combustion accelerates with increasing temperature. In the suitable range of 800 – 900 °C, a rise in temperature from 700 °C to 850 °C can increase the combustion speed by about 30% – 50%. However, overly high temperatures can cause problems such as slagging.

Mixing Degree of Pulverized Coal and Air
Good mixing of pulverized coal and air is crucial for combustion speed. In a calciner with a swirl burner, the swirl structure ensures even distribution of pulverized coal in the air, allowing each particle to access sufficient oxygen for timely combustion. Uneven mixing leads to slow burning as some particles lack oxygen and also causes local temperature imbalances, affecting the overall combustion process and raw meal decomposition efficiency.