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Direct Fired Heaters & Their Design

In the process plant industry, heat is one of the essentials. Equipment that produces and supplies in heat requirement to process plant is called a furnace. A direct fired heater is a style of heater in which a burner provides hot gases that transfer their heat energy to a process liquid or gas flowing directly through coils installed inside the heater vessel. It can utilise radiant and/or convection heat transfer sections, and can be configured in many different ways depending on the customers’ specific requirements.

The choice of furnace style and design is crucial for the best performance of furnace. The factors affecting the performance are influenced by the maximum heat that is being absorbed, the capacity of burners, process requirements, economics and safety. For a fire heater to work well, the design requirements must be properly addressed.

To achieve the lowest possible utility cost, a furnace ought to operate at maximum efficiency. Only when a furnace is operated properly, it can be operated longer with minimal repairs required.

There are several design considerations to ensure the efficiency of a direct fired heater. For instance[1]: –

  • Heaters should be designed for uniform heat distribution
  • The maximum allowable inside film temperature for any process service shall not be exceeded in the radiant, shield, or convection sections.
  • Heaters should be designed such that a negative pressure of at least 0.10 inches of water is maintained in the radiant and convection sections at maximum heat release with design excess air.
  • The radiant-section heat duty of a well-designed heater should represent more than 60%-70% of the total heat duty
  • The range of the bridge wall temperature should be between 800 degree Celsius to 1,000 degree Celsius
  • And many more…

Direct-Fired Heaters: Their Design & Operation is a 3-day course crafted to allow plant engineers better understand the function of direct-fired heaters. On top of that, trainer will also go in-depth into improving heater designs to increase efficiency, that will benefit the plant. For more information, please visit us at or contact us at

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[1] Taken from KLM Technology Group

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