As an important cement kiln fuel, coal has been used in the cement industry for a long time. Every year there will be a large amount of coal requirement for cement plant. In the cement industry, the combustion of coal powder is a crucial process that influences both efficiency and environmental impact. We will explore the intricacies of coal powder combustion within coal fuel rotary kiln and preheater, focusing on optimizing combustion rates for enhanced efficiency and stability.
Understanding the Two-Stage Combustion Process
Coal powder combustion consists of two continuous stages: the volatilization of volatile matter and the combustion of residual coke. After heating, coal powder particles undergo volatilization at lower temperatures, rapidly igniting and mixing with surrounding air. Upon reaching its ignition point, coal burns completely in as little as 0.1 seconds, leaving behind loosely bonded coke particles. The combustion time of coke is closely related to its porosity, fineness, and temperature.
Factors Influencing Combustion in Coal Fired Kiln and Preheater
The combustion process in rotary kilns and preheaters is diffusion-controlled. Therefore, the volatile content of coal has a relatively minor impact on the combustion rate. However, in lower-temperature conditions within preheaters, combustion is influenced by chemical reaction rates, resulting in variations between coal powders with different volatile contents. As a result, the requirements for kilns, furnaces, burners, and combustion environments differ. Kiln combustion time is generally directly proportional to the square of coal powder particle size, while combustion time in preheaters is proportional only to particle size.
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Enhancing Combustion for Efficiency and Stability
Flame Length and Burner Thrust: Flame length is pivotal in determining the burner’s thrust, which affects combustion efficiency. The development of new multi-channel burners, especially for low-volatile coal powders, plays a significant role in controlling flame length and temperature.
Recent trends involve adopting new multi-channel burners in both kiln heads and preheaters to ensure rapid ignition and complete combustion, especially for low-volatile fuels like anthracite coal and petroleum coke.
Measures include optimizing the mixture of fuel and hot gas to raise the temperature, using new multi-channel burners, and increasing furnace volume to achieve complete combustion.
Innovative Approaches for Low-Volatile Fuels
Accelerated Ignition: For offline or semi-offline kilns, fuel can ignite in pure air upon entry, albeit with lower temperatures. For inline kilns, mixing high-temperature air with secondary air raises the ignition environment temperature significantly.
Elevated Charging Point: Raising the charging point of raw materials in the furnace provides more space for fuel ignition at higher temperatures, benefiting coke particle ignition due to their temperature sensitivity.
Optimizing coal powder combustion within rotary kilns and preheaters is a critical endeavor in the cement industry. By understanding the intricacies of combustion stages, adjusting burner designs, and adopting innovative approaches for low-volatile fuels, manufacturers can achieve enhanced combustion rates, improved efficiency, and reduced environmental impact. The synergy of advanced combustion technologies and operational adjustments contributes to a sustainable and efficient cement production process.