Combustion Air Preheating of Furnaces / Heaters


The overall thermal efficiency of a furnace is improved if the air that enters the radiant section around the burners is  preheated. Economic studies are performed early in a project to determine the feasibility of such a system.

The two most common preheating systems are re-generative system and recuperative systems.

A typical regenerative system

  1. Hot flue gas exiting the convection section is diverted through a duct to a heat exchanger called an air preheater.
  2. Incoming fresh air is heated and sent by the forced draft fan to the burner plenum, where it enters the burner through the air register for combustion.
  3. An induced draft fan draws the flue gas through the preheater and sends the cooled gas back into the atmosphere through the stack.

Conventional Recuperative (Closed Loop) System

  1. Oil is circulated through the convection section tubes, heated and sent through the inlet air duct, where it releases its heat.
  2. The hot air then enters the burner for combustion and the hot oil is recirculated to a storage tank for recycling.
  3. From a layout standpoint, the hot oil system with a storage tank and pump is far less complex than the regenerative system.


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