Feed Product Circuits

Chapter from the Piping Design Guide.

FEED & PRODUCT CIRCUIT DESIGN

Feed Circuit Hydraulics

Feed circuits from storage to process units:

1. Storage Tank → Feed Pump → Preheat Train → Unit Feed Control Valve → Reactor/Column

2. Pump suction: static head from tank level minus friction losses
• Use minimum tank level for worst-case NPSH
• Include strainer ΔP at 50% plugged
• If tank is blanketed: add blanket gas pressure to suction head

3. Pump discharge: size for max expected flow × 1.1 margin
• ΔP budget: CV (30-50%) + piping friction + heat exchanger ΔP + elevation + operating pressure
• Include future fouling ΔP for heat exchangers (add 50-100% of clean ΔP)

4. Control valve location: as close to final destination as practical
• Minimizes high-pressure piping length
• Exception: if downstream piping is two-phase, CV may need to be upstream

5. Check for flashing across CV:
• If P downstream of CV < bubble point → two-phase downstream
• Size downstream piping for two-phase flow
• Consider anti-cavitation trim on CV

Product Circuit Considerations

Product rundown to storage:

1. Typically pressure-driven (no pump if adequate elevation/pressure)
• Check: pressure at column/drum - friction losses - static head > tank design P
• If deficit → product pump required

2. Product cooler sizing:
• Cool to max storage temperature (typically 150°F for atmospheric tanks)
• Air cooler + trim cooler combination common
• Control scheme: temperature controller on trim cooler bypass

3. Tank connection:
• Submerged inlet (below liquid level) to prevent static charge generation
• For atmospheric tanks: max 6 ft/s in inlet nozzle to prevent splashing
• Consider thermal expansion of liquid in blocked-in piping (thermal relief)

Source: Piping_Design_Guide_v1.xlsx · sheet “Feed Product Circuits”

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