(75e) Low Emissions Burner for Ethylene Furnaces

A new burner (patent pending), referred to as the Halo? burner, has been developed that incorporates the Coanda principle for controlling fluid flow, mixing, and stability. This aerodynamic effect is sometimes referred to as boundary layer attachment. The Halo? burner has some unique properties that give it enhanced performance compared to other burner technologies. It can entrain more furnace gases than previous designs, where furnace gas entrainment has been limited by the lower flammability limit for the mixture of the fuel, air, and inerts. Increased entrainment helps minimize NOx emissions. It has a significantly wider turndown range and more compact size compared to other ultra low NOx burners. The flame quality is improved because of the increased gas velocities that help minimize interactions between adjacent flames. The flames are less easily disturbed because of the increased momentum. The flames also tend to be significantly tighter in diameter than comparable low NOx burners due to the adhesion and flame forming properties of the Coanda affect. The tighter flame diameter, along with the increased momentum of unobstructed combustion air, minimizes flame issues typically associated with the longer flames needed in ethylene furnaces. The Coanda-formed combustion envelope greatly reduces the chance for flame roll over and the subsequent flame impingement on process tubes, known to shorten process tube life. This flame control also minimizes the chances for flame-to-flame interaction between adjacent burners. These interactions can significantly increase flame lengths, possibly even causing flames to coalesce into larger flames, which can lead to flame impingement and increased NOx emissions. The heat flux profile is also more uniform, which has many operational benefits. The combustion efficiency is high and the CO emissions are low from startup to shutdown. These are benefits for burners used in ethylene service. Noise levels are also lower than comparable low NOx burners. This paper will discuss testing of a wall-fired Halo? burner using a variety of fuels in a pilot-scale ethylene cracking furnace.