Convection Section. In a process heater or boiler, which operates at lower
temperatures, the convection section will be located directly above the radiant section,
but the convection section in an olefins furnace must be shielded from high firebox
temperatures. The olefins convection section is offset with respect to the firebox so that
there is no direct radiation to the bottom rows of tubes (shock tubes), as shown in
Figure 9.2. Direct radiation could lead to localized overheating, reduced heat transfer,
and premature failure of tubes, all of which lead to reduced efficiency.