(3b) Flameless Combustion Technology for Reduced NOx Emissions in Ethylene Furnaces

As environmental regulations are tightening, flameless burner technology is implemented as a viable solution for many petrochemical and refining furnaces that require lower NOx emissions.  Ethylene furnaces have proved to be some of the most difficult targets for NOx emissions reduction due to elevated furnace temperatures and high heat densities.  These necessary conditions also cause high NOx emissions in conventional burners.  This has motivated the development of flameless combustion technologies.

Flameless combustion utilizes the free jet mixing theory to maximize the amount inert internal products of combustion (flue gas) mixed with the fuel gas within the combustion chamber to produce a reconditioned fuel mixture of gas and flue gas.  The resulting mixture then oxidizes in the combustion process at much lower flame temperatures and produces inherently lower NOx emissions.  This conditioned fuel/flue gas mixture burns cleanly with very little visible radiation, i.e. flameless.

These concepts have been used for over 10 years in many process furnaces, but there are special challenges to adopting these concepts successfully in ethylene furnaces.  Special burner designs are required to provide the NOx reduction required in ethylene furnaces without sacrificing burner performance with respect to flame length, turndown, and stability.  It is also desired to avoid designs that require special advanced controls with different start-up or operation modes.

This paper will discuss the development of flameless combustion technology, with the specific focus on ethylene furnaces, both in new and retrofit applications.