Excess Air Requirement for Combustion of Pulverized Coal

Excess air refers to the additional amount of air supplied to the combustion process beyond what is required for complete combustion of the fuel. In the case of pulverized coal combustion, excess air is necessary to ensure efficient and complete combustion of the coal particles. The excess air requirement for combustion of pulverized coal is typically of the order of 15 to 40%.

1. What is pulverized coal?
- Pulverized coal is coal that has been ground into a fine powder, typically with a particle size of less than 75 micrometers.
- Pulverized coal is commonly used as a fuel in industrial boilers and power plants due to its ease of handling, high combustion efficiency, and low emissions.

2. Combustion process of pulverized coal
- Combustion of pulverized coal involves the rapid oxidation of coal particles in the presence of a sufficient amount of oxygen.
- The combustion process consists of three stages: drying and heating, pyrolysis, and combustion of volatile matter.
- During the combustion process, the coal particles are suspended in a stream of air, and the oxygen in the air reacts with the carbon in the coal to produce carbon dioxide (CO2) and heat.

3. Why is excess air required?
- Excess air is required to ensure complete combustion of the coal particles and to prevent the formation of pollutants such as carbon monoxide (CO) and unburned carbon.
- The excess air provides an adequate supply of oxygen to react with the carbon in the coal, ensuring that all the carbon is oxidized to CO2.
- Excess air also helps in maintaining the required temperature for efficient combustion and prevents the formation of clinkers (solid residues) that can hinder the combustion process.

4. Excess air requirement
- The excess air requirement for combustion of pulverized coal is typically of the order of 15 to 40%.
- This means that the amount of air supplied to the combustion process is 15% to 40% more than the stoichiometric air requirement, which is the theoretical minimum amount of air needed for complete combustion.
- The actual amount of excess air required depends on various factors such as the type and quality of coal, combustion equipment design, and operating conditions.
- The excess air requirement is determined by balancing the need for complete combustion and heat transfer efficiency with the need to minimize air pollutants and optimize energy efficiency.

In conclusion, the excess air requirement for combustion of pulverized coal is typically in the range of 15 to 40%. This additional air supply ensures efficient and complete combustion of the coal particles, preventing the formation of pollutants and maximizing energy conversion.