Air Preheat System Upgrade on Coker Heaters

One of the refineries in the gulf coast region had two coker heaters that were designed to operate on balanced draft. The heaters had separate air preheater (APH) systems with FD and ID fans. The heaters were connected to a common grade mounted stack. The client was limited on the charge rate when operating the air preheaters. The existing APHs were leaking, and as a result both the FD and ID fans were limiting. The client was by-passing approximately 50% of the hot flue gas directly to the stack. The heaters were also facing O₂ limitations. The client was getting more capacity on natural draft but losing a lot of energy to the stack. FIS conducted a study and identified the deficiencies in the air preheater system.

New APHs were designed for higher heat transfer duty than the existing APHs, and new FD and ID fans were redesigned for higher capacities than the existing fans. A new steam preheat coil was installed at the inlet of the main APH. The steam preheat coils and combustion air by-pass ducts were designed to minimize the acid dew point corrosion in the APH cold blocks. The new combustion air by-pass ducts were sized for 100% by-pass of combustion air. This would help run the heater on forced draft when the APHs get corroded. The existing convection section had two future row provisions. Two rows of process coils were installed to maximize the heater efficiency. The heaters have been commissioned successfully and have been operating for the past six months.