Coal properties and their effect on combustion in utility boiler

Coal properties play a critical role in the combustion process in utility boilers when fired in pulverized condition. The following are some of the essential coal properties that can affect combustion:

1. Heating Value: The heating value of coal, measured in Btu/lb, is an essential parameter that determines the energy content of coal. Higher heating values are generally preferred for efficient combustion as they provide more energy per unit mass of coal. Low heating values require more coal to be burned to produce the same amount of heat, which can lead to higher emissions and lower efficiency.
2. Moisture Content: Moisture in coal can significantly affect the combustion process as it reduces the heating value and increases the required amount of air for combustion. Moisture also lowers the flame temperature, which can lead to incomplete combustion and higher emissions. Therefore, low moisture content is preferred for efficient combustion.
3. Volatile Matter: Volatile matter in coal is the percentage of the coal that is released as gas during combustion. Higher volatile matter leads to more rapid combustion, higher flame temperatures, and a shorter burnout time. Lower volatile matter can lead to incomplete combustion and higher emissions.
4. Ash Content: Ash content in coal refers to the inorganic materials that remain after combustion. High ash content can lead to the formation of slag, fouling, and corrosion, which can reduce the efficiency of the boiler. Therefore, low ash content is preferred.
5. Sulfur Content: Sulfur in coal can lead to the formation of sulfur dioxide (SO2) during combustion, which is a major contributor to acid rain. Therefore, low sulfur content is preferred, and sulfur removal technologies are often used in utility boilers to reduce emissions.
6. Particle Size: The particle size of coal can affect combustion efficiency and emissions. Smaller particles have a higher surface area to volume ratio, which leads to faster combustion and higher flame temperatures. However, small particles can also lead to increased emissions of particulate matter and fly ash.