(248w) Selection of the Optimal Operating Conditions in Fired Heaters Based on Two Phase CFD Simulations

Fired heaters are widely used in the chemical industry. Helical coils configuration is preferred over others due to the high heat transfer area that can be accommodated in a relative small volume.

The effective gas temperature is usually calculated assuming complete flue gas mixing (Lobo-Evans, 1939) in the firebox. In other words, they ignored the existence of a longitudinal and transverse temperature gradient effects. A numerical method is usually used in order to determine the amount of heat in the radiant section and the effective gas temperature (Chapra Steven, 2005). For those cases where this assumption is not valid (e.g. high temperature heaters with tall narrow fireboxes), the radiant section is divided into zones for the energy balance calculations.

One of the most typical issues faced in this type of equipment is the short lifetime if the operating conditions are not adequate for the two-phase flow developed inside coils. In this work, a CFD study is carried out in order to provide the best configuration of the combustion chamber, specially closed to the location where the nucleate boiling point occurs. For this evaluation, different diameters of piping in the radiation zone will be studied. In addition, different insulating materials, usually placed in the inner wall of the vessel, will be used in order to minimize the radiation over the typical affected zones.

Chapra Steven C, Applied Numerical Methods with MATLAB for Engineers and Scientists, McGraw-Hill Companies, Inc, 2005. 1st edition.

W.E. Lobo, J.E. Evans, "Heat transfer in the radiant section of petroleum heaters", Trans AIChE , 743â??778. 1939