REVAMPING AIR PRE-HEAT DUCT WORK
XRG was selected to design and supply the new cold air bypass duct for the air preheater (APH) unit of a twin cell heater at a Texas refinery.
The Problem: The existing APH experienced frequent plugging, cold end corrosion, and leaks, therefore limiting production. The existing cold air bypass duct is an integral part of the APH itself, which is suspected to partially contribute to the current state of deterioration of the APH.
The Solution: XRG partnered with our customer to design a cold air bypass duct routed from the existing APH cold air inlet duct, splitting and reinjecting the cold air back into the existing hot combustion air duct that supplies hot air to 2 cells.
The project design included:
- A bypass air duct was designed which bleeds off cold air from the top of the FD fan outlet duct and splits into two secondary ducts to deliver the required amount of air into the mixing header at the air preheater outlet.
- A control damper at the main duct is used to vary the bypass air from 40,527 to 9,573 lb/h.
- Biasing dampers in the secondary ducts to allow for variation in firing rate between cells.
- A mixing vane designed to reduce temperature deviation of air at individual burners.
- Figure 3 shows the CFD simulation study that was used to optimize the design and location of the turning vane within the prescribed constraints of available pressure drop to minimize temperature variation to each burner while keeping the existing hot combustion air duct. This helped to minimize manufacturing and installation costs and lowered the turnaround time.
- Fabrication
- Logistics