Consider the following statements:

1. Pulverized fuel gives high and controlled burning rate.
2. Insufficient air causes excessive smoking of exhaust.
3. Excess air is provided to control the flue gas temperature.
4. Effect of sulphur in fuel is to give high heat transfer rate.

Which of these statements are correct?

Explanation:

Statement 1: Pulverized fuel gives high and controlled burning rate.

• This statement is correct. Pulverized fuel refers to finely ground or powdered fuel, typically coal, which is used in many thermal power plants. The fine particles have a larger surface area per unit mass, allowing for better mixing with air and leading to a high and controlled burning rate. This results in efficient combustion and better control over the combustion process.

Statement 2: Insufficient air causes excessive smoking of exhaust.

• This statement is also correct. Combustion requires a proper air-fuel ratio to ensure complete burning of the fuel. If the amount of air supplied is insufficient, it leads to incomplete combustion, resulting in the formation of carbon particles and other unburned substances. These unburned particles cause excessive smoke in the exhaust gases.

Statement 3: Excess air is provided to control the flue gas temperature.

• This statement is incorrect. Excess air is provided primarily to ensure complete combustion of the fuel, especially when the air-fuel mixture is not perfectly balanced or when there are variations in fuel quality. While it can indirectly influence the flue gas temperature, its primary purpose is not to control the temperature but to achieve complete combustion and minimize the formation of carbon monoxide, soot, and other pollutants. In fact, excessive amounts of excess air can lead to heat loss and reduced efficiency.

Statement 4: Effect of sulfur in fuel is to give high heat transfer rate.

• This statement is incorrect. Sulfur in fuel does not enhance the heat transfer rate. Instead, sulfur can have detrimental effects, such as forming sulfur dioxide (SO₂) and sulfur trioxide (SO₃) during combustion. These compounds can combine with water vapor in the flue gases to form sulfuric acid, which can corrode equipment and reduce the efficiency of heat exchangers. Sulfur is generally considered an undesirable component in fuel due to these adverse effects.