(52b) Low NOx Burner Retrofit Experiences in Cracking Furnaces At Dow, Terneuzen

Low NOx Burner Retrofit Experiences in Cracking Furnaces at Dow, Terneuzen

D.J. Sinke                  Dow Benelux B.V.

M. Pitcher                  Technip Benelux B.V.

M. Martin                    UOP Callidus

Abstract

Dow has three ethylene plants in Terneuzen, the Netherlands. Technip has been requested to study options to reduce the cracking furnace NOx emissions. The results of this study combined with the experience elsewhere in Dow have been used to select the preferred solution: installation of new burners and modification of the firing arrangement.

Callidus has modeled the complete firebox using a Computational Fluid Dynamics (CFD) model and has recommended installing also burners above the horizontal coil outlet tubes. The addition of these four burners has improved the overall flue gas circulation pattern.

The first of sixteen furnaces has been retrofit late 2009. These burner retrofits are done during a major furnace overhaul to minimize production loss. Also the convection section tube bundles, radiant coils and radiant section refractory are replaced.

The furnace NOx emission has decreased by more than 50% and the guaranteed emission level has been achieved. The Low NOx burners have a relatively long heat release profile. An undesired side effect of this retrofit is a decrease in the radiant box efficiency.

Callidus has been requested to explore options to improve this radiant efficiency without sacrificing too much of the improvement in NOx emission. Many alternatives have been studied using CFD. The final conclusion is that the radiant efficiency can be improved by increasing the firing in the lower level burners. A small part of the realized reduction in NOx emission is unfortunately sacrificed.

Effective use of CFD modeling during several stages of the project and excellent team work between burner manufacturer, furnace designer and furnace owner have been keys to the success.