Low-Nox Burner retrofit Experiences in Cracking Furnaces at Dow, Terneuzen

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Abstract: Dow Benelux B.V. (Dow) operates three ethylene plants from the Netherlands, all based within its Terneuzen facility. In 2009, Technip Stone & Webster Process Technology (Technip) studied options to reduce the NOx emissions from the cracking furnaces of cracker 1. The results of this study, combined with the experience elsewhere within the Dow Chemical Company, have been used to select the preferred solution: installation of new burners and modification of the firing arrangement.

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

The first of sixteen furnaces was retrofit in late 2010. Burner retrofits are performed during a major furnace overhaul to minimize production loss. At the same time the convection section tube bundles, radiant coils and radiant section refractory are replaced.

The furnace NOx emission decreased by 50% and the guaranteed emission level was achieved. The Low-NOx burners exhibited a flatter heat flux profile, with an undesired side effect: a decrease in the radiant box efficiency.

UOP Callidus explored options to improve the radiant efficiency without substantial sacrifice of the improvement in NOx emission. Many alternatives were studied using CFD. The final conclusion was that radiant efficiency could be improved by increasing the fraction of firing at the hearth burners, without exceeding the guaranteed NOx emission level. Effective use of CFD modeling during several stages of the project and excellent team work between burner manufacturer, furnace designer and furnace owner were keys to the success of this project.

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