Optimizing Coal Fired Kilns: Essential Fuel Quality Requirements

In industrial production, particularly for the cement industry, coal-fired kilns are the primary workhorse. The efficiency of these kilns and the quality of the final product are heavily influenced by the characteristics of the coal used as fuel. Here are some of the quality requirements for coal fuel in traditional kilns, and how to find the right rotary kilns for sale.

Ash Content

As a non-combustible component, ash directly impacts the chemical reactions and thermal efficiency within the kiln. High ash content can lead to a cascade of issues, including decreased heat generation capacity, which in turn affects the calcination reaction temperature and efficiency.

Elevated ash levels can also alter the composition of post-calcination products, potentially compromising the quality of the final cement. The increased presence of ash can lead to the formation of a more viscous liquid phase during firing, promoting the development of clinker rings. These rings can impede kiln ventilation and increase power consumption in exhaust fans.

Given these considerations, it’s generally recommended that coal powder ash content be maintained below 27% for optimal performance in ex-kiln calciners.

Calorific Value

Coal with a higher calorific value is preferred as it enhances heat generation capacity and allows for higher calcination temperatures. This promotes more effective calcination reactions within the kiln.

On the other hand, coal with a lower calorific value leads to increased unit heat consumption, negatively impacting the kiln’s thermal efficiency and output. To ensure optimal performance, it’s generally recommended that the lower heating value of coal should exceed 21,772 kJ/kg (equivalent to 5,200 kcal/kg).

Volatile Matter

This combustible component influences the ignition characteristics and overall combustion process within the kiln.

Insufficient volatile matter can hinder coal ignition and lead to unstable combustion zones. To maintain stable flames and ensure uniform calcination, the volatile matter content is typically kept between 22% to 32%.


The moisture content of coal fuel is a delicate balance that affects both the combustion rate and flame temperature. While high moisture content can slow down the combustion rate and reduce flame temperature, affecting calcination efficiency, a small amount of moisture can actually be beneficial. It can promote coal oxidation and enhance the radiative capacity of the flame.

For optimal performance, coal fuel moisture content should generally be controlled below 2.0%, with an ideal range between 0.5% to 1.0%. This balance ensures efficient combustion while maintaining the benefits of slight moisture presence.

Coal Powder Fineness

When using coal as kiln fuel, the fineness of the coal powder is a critical factor in achieving efficient and complete combustion. The particle size of the coal powder impacts both the integrity and uniformity of combustion.

To strike the right balance, coal powder fineness is best maintained around 88μm, with residual content below 15%. In cases where bituminous coal volatile matter is 15% or less, the coal powder fineness should be controlled to below 6.0% to ensure optimal combustion.

Contact Kiln Technology Company Company to Learn More About Our Rotary Kilns for Sale

If you’re interested in learning more about our state-of-the-art rotary kilns for sale or need expert advice on kiln fuel management, reach out to our team at Kiln Technology Company Company. Our experienced engineers are ready to assist you in achieving peak efficiency in your industrial processes with rotary kilns and coal-fired kilns.