Vertical cylindrical fired heater as used in crude oil atmospheric distillation unit is simulated numerically to analyse the distribution of thermal loading on the tubes. The model describes flow, gas combustion and radiative heat transfer inside the radiation section of the fired heater. Attention is focused on the tube-wall distance and the effect it has on circumferential distribution of heat flux on tube walls. It is shown that assumptions invoked in ID design calculations of fired heaters are significantly underestimating heat flux variability.
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