August 3, 2019

Air Preheater

Air Preheater
Air Preheater
Credit: third-party image reference

Air Preheater


Air preheater pre-heats (increases the temperature) the air supply to the furnace with the help of hot gases.

Air Preheaters are heat exchangers to preheat or air heating of the combustion air using flue gas, steam, water, or thermal oil.


It is installed between the economizer and the chimney.


A tubular type air pre-heater consists of a large number of tubes. Flue gases pass through the tube. Air flows over the tubes. Baffles are provided to pass the air number of times over the tubes. A soot hopper is provided at the bottom to collect the soot.

Working of Air Preheaters:

Hot flue gases pass through the tubes of air pre-heater after leaving the boiler or economizer. Atmospheric air is allowed to pass over these tubes. Air and flue gases flow in opposite directions. Baffles are provided in the air pre-heater and the air passes several times over the tubes. Heat is absorbed by the air from the flue gases. This pre-heater air is supplied to the furnace for air combustion.

Advantages of Air Preheater:

  1. Increased efficiency of boilers
  2. Increased Evaporative rate
  3. Combustion is accelerated with less soot, smoke, and ash
  4. Low-grade and inferior-quality fuels can be used.