Q1: Which of the following relatively employs the highest heat transfer surface area in a high pressure boiler ?

ANS:A - Airpreheater

Among the options provided, the furnace water wall typically employs the highest heat transfer surface area in a high-pressure boiler. Explanation:

1. Furnace Water Wall:
   • The furnace water wall, also known as the water-cooled wall, is a crucial component of a boiler's combustion chamber.
   • It consists of tubes or panels that form the walls of the furnace or combustion chamber.
   • Water circulates through these tubes or panels, absorbing heat from the combustion process and preventing overheating of the furnace walls.
   • The extensive surface area of the furnace water wall allows for efficient heat transfer from the combustion gases to the circulating water.
2. Air Preheater:
   • An air preheater is a heat exchanger used to preheat combustion air before it enters the furnace.
   • While it plays an important role in increasing boiler efficiency by recovering waste heat from the flue gases, its surface area is typically smaller compared to the furnace water wall.
   • The primary function of the air preheater is to improve fuel combustion and reduce fuel consumption, rather than maximizing heat transfer surface area.
3. Economiser:
   • An economiser is another type of heat exchanger used in boilers to recover heat from the flue gases before they exit the boiler.
   • It preheats the feedwater using heat recovered from the flue gases, thereby reducing fuel consumption and improving boiler efficiency.
   • While the economiser provides additional heat transfer surface area, it generally has a smaller surface area compared to the furnace water wall.
4. Steam Superheater:
   • A steam superheater is a component of a boiler that further heats saturated steam to achieve higher temperatures and specific steam conditions.
   • It adds heat to the steam after it has been generated in the boiler's primary heating surfaces (such as the furnace water wall).
   • The surface area of the steam superheater is typically smaller compared to the furnace water wall since its primary function is to superheat steam rather than absorb heat from combustion gases.

In summary, while all components mentioned contribute to heat transfer in a boiler, the furnace water wall generally employs the highest heat transfer surface area due to its primary role in absorbing heat from the combustion process and preventing overheating of the furnace walls.