ANS:A - pulverised fuel

The pulverized fuel combustion system is a widely adopted method for burning solid fuels, particularly coal, in thermal power plants. Here's a detailed explanation of this combustion system:

1. Coal Grinding: In this system, solid coal is first ground into fine particles, typically to a size of about 75 microns or less. This grinding process is usually performed in a pulverizer or a coal mill.
2. Fuel Injection: The pulverized coal is then injected into the combustion chamber of the boiler. This injection is typically achieved through a network of coal pipes that distribute the pulverized coal evenly throughout the furnace.
3. Primary Air Supply: Along with the pulverized coal, a stream of primary air is introduced into the combustion chamber. This primary air is responsible for carrying the pulverized coal into the furnace and ensuring its proper mixing with secondary air for combustion.
4. Secondary Air Supply: Additional air, known as secondary air, is supplied to the combustion chamber to support the combustion process. Secondary air is usually introduced through a separate set of air nozzles or ports located above the pulverized coal injection points.
5. Combustion Process: Once inside the combustion chamber, the finely ground coal particles are ignited and burned in the presence of oxygen from the primary and secondary air streams. This combustion process generates high temperatures, releasing thermal energy that is transferred to water circulating in the boiler's tubes.
6. Heat Transfer: The heat generated by the combustion of pulverized coal is transferred to water flowing through the boiler tubes. This heat transfer process converts the water into steam, which is then used to drive turbines connected to generators to produce electricity.
7. Ash Handling: After combustion, the remaining ash, which consists of non-combustible materials and unburned carbon, is collected at the bottom of the furnace or in ash hoppers. Depending on the type of boiler, the ash may be removed periodically through ash handling systems for disposal or recycling.

Advantages of Pulverized Fuel Combustion System:

• High Combustion Efficiency: The finely ground coal particles burn more efficiently, leading to higher thermal efficiency in power generation.
• Flexibility: This combustion system can accommodate a wide range of coal types and qualities, allowing power plants to use various coal sources.
• Low Emissions: Proper combustion control and efficient mixing of fuel and air can result in lower emissions of pollutants such as sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter.

Overall, the pulverized fuel combustion system is a well-established and widely used technology in thermal power plants due to its efficiency, flexibility, and relatively low environmental impact compared to other combustion methods.