Question

----------- is the device which serves to recover some of the heat being carried by exhaust gases.

• A. Air pre-heater
• B. Economiser
• C. Fusible plug
• D. Steam super heater

Hint:

Installing an economiser typically increases the overall thermal efficiency of a boiler by \(1\%\) for every \(5^\circ\text{C}\) to \(6^\circ\text{C}\) rise in feed water temperature.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Industrial steam boilers generate flue/exhaust gases at very high temperatures.
To maximize thermal efficiency and save fuel, heat recovery devices are installed in the exhaust path to pre-heat inputs.

Step 2: Detailed Explanation:
- Economiser: A heat exchanger designed to recover the sensible heat from the boiler exhaust flue gases to preheat the boiler feed water before it enters the boiler drum. This reduces the fuel energy required to boil the water, improving overall efficiency.
- Air pre-heater: Also recovers exhaust gas heat, but specifically to heat the air used for fuel combustion.
- Fusible plug: A safety device that melts to release steam if the water level drops too low, preventing boiler explosions.
- Steam superheater: Heats saturated steam to superheated steam using heat from the combustion chamber.

Step 3: Final Answer:
The device used to recover exhaust heat to preheat feed water is the Economiser, which corresponds to option (B).