Brent Blend CDU (characterized from a real assay)

An atmospheric crude unit fed by a named, cited crude rather than invented pseudocomponents: Brent Blend (NOAA ADIOS oil EX00009, API 40.1, SG 0.8246, 0.35 wt% sulfur; the underlying assay is ExxonMobil's published Brent distillation curve). The bundled assay library (561 crudes, flowsim.backend.crude_assays) supplies the true-boiling-point curve; assay_to_pseudocomponents cuts it into 8 equal-volume pseudocomponents and characterizes each by Riazi-Daubert (Tc/Pc/MW from NBP+SG) and Edmister (acentric factor) — the eight cut_N entries below are that output verbatim, not hand-tuned numbers. The train is preflash drum → fired heater (660 K) → 20-stage atmospheric column with two side draws, yielding a light-naphtha overhead, heavy-naphtha and light-kerosene side cuts, and atmospheric residue — named for what the D86 says they are (side-draw D86 50% about 131 °C and 182 °C, the lower one at SG 0.78), not for the naphtha / kerosene / diesel slate a crude unit is usually drawn with: a diesel is D86 50% 260–300 °C and SG 0.82–0.86, and this column, for the reason in point 4, does not reach one (moving the lower draw down to stage 16-17 lifts it only to ~245 °C). Four things worth knowing: (1) an assay reports one whole-crude gravity, but density rises steeply with boiling point, so the cuts are characterized at constant Watson K — Kw is fitted by requiring the cuts' volume-average SG to return the measured bulk 0.8246, giving Kw = 11.95 (the published paraffinic band is 11.4–12.1, which the fit was not tuned to hit) and per-cut gravities running 0.689 for the light naphtha to 0.971 for the 595 °C residue; (2) mole fractions follow from that — equal volume means mass ∝ SG, so each cut's mole fraction is proportional to SG/MW; (3) the column runs with rigorous_draws — real MESH liquid withdrawals — because the default carve mode (side products sliced out of a converged 2-product profile) returns two near-identical draws here and does not fractionate; (4) the column carries no pumparound, so its energy balance has nowhere to put the heat the 660 K furnace outlet brings in except the bottom: the reboiler duty comes out at about -7.7 MW (the column asking to be cooled), and the CDU says so in a warning. A real crude unit takes that heat out in pumparounds — the companion 'crude-unit-pumparounds' showcase is exactly that comparison. Bounded: constant Kw is itself an idealization (a real crude's Kw drifts a few tenths across the barrel, and aromatic/naphthenic crudes differ), but it is the standard characterization and is strictly better than one gravity for every cut.