Numerical Analysis of Heat Transfer in Radiant Section of Fired Heater with Realistic Imperfect Geometry of Tube Coil

Complex numerical computations are performed for vertical cylindrical fired heater operated in crude oil atmospheric distillation unit to analyse the distribution of heat flux on the tubes of radiant section. The numerical model describes flow, gas combustion and radiative heat transfer inside the radiation section of the fired heater. Analysis of variations of heat flux on circumferential and longitudinal distribution on individual tube walls is executed comparing case of ideal (originally designed) tube coil geometry and tube coil containing typical real geometry imperfections (developed during years of operation). Results of heat transfer analysis confirm and quantify the significant effects of non-uniform heat flux distribution on individual radiant tubes negatively sharpened by geometry imperfections of tube coil. It is recognized, that fired heater design standards recommendations invoked in 1D design calculations of fired heaters are significantly underestimating real heat flux variability.