NOx Reduction in 4H-102 and 5H-205 Heaters
In 2009, FIS was employed by a Texan Refinery to develop a NOx reduction study for Depentanizer Reboilers (H-102 and H-205). Client wanted to reduce the NOx emissions of the heaters by installing Ultra Low NOx Burners. The targeted NOx emissions were 0.035 lb/MMBtu (HHV basis).
The heaters were originally designed in 1972 as vertical cylindrical type, natural draft heaters with a horizontal convection section and a top mounted stack. Both the heaters were designed for all process heat duty of 46.2 MMBtu/hr (4H-102) and 33.7 MMBtu/hr (5H-205) respectively.
Client also wanted to revise the current heater permit level to 76.2 MMBtu/hr (HHV). The conventional vertical firing would result in flame impingement. FIS installed Ultra Low NOx Burners with FIS patented Inclined Firing Technology to address the flame impingement issues. In Inclined Firing Technology, the burners are inclined to point the flames away from tubes. Angle of inclination is determined using CFD analysis. Optimum angle ensures uniform heating & no flame to flame interaction. The technology is very useful for installing Ultra Low NOx burners in very tight radiant chambers.
The following are the benefits of Inclined Firing System Technology:
Improved flame pattern
Uniform heating of tubes
Uniform tube metal temperature
Uniform heat flux distribution
Elimination of hot spots
Longer tube life
Increased heater run length
Lower coking rate of internal tube surface
Salient features of the revamped design are as follows:
Absorbed duty of both the heaters increased by 10%
Improved thermal efficiency of the heaters
Flue gas temperature leaving convection section is alleviated by 30 °F in 4H-102 heater and 60 °F in 5H-102 heater as compared to the original design.
The heaters were successfully commissioned in 2011.