Process Engineering Design Fundamentals

A: B lines up once you convert MMSCFD to actual volumetric flow at operating P and T, then apply v = K·√((ρL−ρG)/ρG). A is what you get if you forget to correct standard flow to operating conditions and treat MMSCFD as ACFD. C comes from using K = 0.5 ft/s, which shows up in vertical scrubber examples and looks tempting under time pressure. D drops Z entirely and quietly assumes ideal gas at pressure, which pushes density too high and area too low.

A: A matches how many EPCs flag thermal-only reliefs so reviewers don't assume blocked-outlet coverage. B sounds plausible if you’re thinking of car-sealed valves, but the symbol doesn't communicate valve position. C mixes up line type with responsibility breaks; that’s usually handled with tag numbering or notes. D is a real configuration in some systems, yet it’s drawn with a solid line plus restriction symbol, not a dashed inlet.

A: B fits mass balance: gas disengagement improves but liquid in still equals liquid out only if the valve moves. A feels right if you’re thinking separation efficiency, yet throttling worsens inventory buildup. C borrows logic from slug mitigation, but nothing changed upstream on liquid flow. D ignores that control valves don’t self-correct when one phase changes independently.

A: A explains why oscillation persists in manual — the valve is operating in the first few percent of travel where gain is extreme. B can cause erratic motion but usually shows deadband or step changes, not clean hunting. C would give abnormal Cv and noise, yet direction errors are usually obvious on FAT. D is a classic answer, but manual mode strips the controller out of the loop.