Aspen Plus Process Simulation & Modeling

A: Option A matches first‑principles thinking: at 50 bar, methane and much of ethane stay vapor, propane is split, and C4+ largely liquid. A vapor fraction around two‑thirds is defensible without detailed K‑values. B sounds reasonable if you anchor on pressure alone, but ignores that methane’s critical pressure is only ~46 bar, so it's still gas‑like here. C mixes up normal boiling points with high‑pressure behavior; cubic EOS suppress vaporization hard at 50 bar. D is a classic mental shortcut that Aspen never uses — equilibrium doesn’t care about symmetry.

A: A fits because alkaline sour water drives SSC and hydrogen damage in carbon steel, and PWHT is the usual control when hardness is managed. B looks attractive due to stainless bias, but NH3/H2S service often causes ammonium bisulfide corrosion and under‑deposit attack that stainless doesn’t magically fix. C addresses chlorides, which aren’t the controlling species here. D is valid in hot dry sulfidation, not aqueous sour systems at 120 °C.

A: A holds under audit: contracts fix the technical baseline, and any shift needs a managed change. B feels safety‑driven, but regulators look for contractual clarity, not silent upgrades. C confuses software defaults with legal obligation — Aspen isn’t a code authority. D sounds pragmatic, yet mixing editions creates an untraceable basis that auditors tear apart.

A: A tracks the usual Fenske–Underwood–Gilliland logic: moving off total reflux typically doubles stages. B underplays the penalty of finite reflux. C exaggerates; that happens at very low relative volatility, not 2.5. D treats Gilliland as deterministic when it’s a band, not a point.