FUG Process Flowsheets & Simulations
Explore 2 validated, solved FUG simulation flowsheets in MaximaLabs — real components: methanol, water, propane, n_butane, n_pentane. Open any one directly in your browser.
Solved via: NRTL, PENG-ROBINSON.
Methanol column sized by design spec
A methanol-water column sized by design specification rather than by trial and error — Aspen's Design Spec / SimCentral's Adjust, and a capability that had no curated example despite being solver-native. The column is specified the way a shortcut (FUG) column is: light and heavy keys with their recoveries (98% of the methanol overhead, 2% of the water). What is not specified is the reflux ratio. Instead the flowsheet carries a design_specs entry — vary COL.reflux_ratio until the metric shortcut_n_stages equals 14 — and the solver root-finds it, re-solving the whole flowsheet each trial. Open the Design Spec panel to see it, or the solved result: reflux settles at 1.06 for exactly 14.00 stages. Why that is the interesting question. Reflux and stages trade off against each other, and against energy. Left at the initial 1.6, this separation needs only 10.8 stages but 4.35 MW of reboiler duty; pulled down to 1.06 it needs 14 stages and just 3.49 MW — a 20% energy saving bought with three more trays. A design spec lets you state the column you can afford to build and have the solver tell you how to run it, instead of guessing a reflux ratio and reading off whatever height falls out. The Sensitivity tab comes preloaded with that trade-off as a sweep (reflux ratio against reboiler duty) so the curve behind the single design-spec answer is one click away. **.
4 unit ops • NRTL
79 1
View & openShortcut column sizing (Fenske-Underwood-Gilliland)
Before anyone builds a rigorous column they size it in about a second, and this is that step — Aspen's DSTWU, the calculation every distillation design starts from. State the two keys and how well you want them separated, and the shortcut answers the four questions that set the capital cost. For a depropaniser feed (30% propane, 40% n-butane, 30% n-pentane) at 10 bar recovering 98% of the propane overhead and 98% of the n-butane in the bottoms: Fenske gives 8.34 minimum stages — the count at total reflux, where you spend infinite energy to buy the fewest trays. Underwood gives a minimum reflux of 1.54 — the reflux at infinite stages, the opposite corner. Neither is buildable; the real column lives between them, and Gilliland interpolates: at 1.3x the minimum reflux you need 17.7 theoretical stages, with Kirkbride putting the feed on stage 7.85. That is a little over twice the minimum stage count for 1.3 times the minimum reflux, which is the trade every column is designed on. The energy follows: 1.67 MW reboiler against a 1.35 MW condenser. Bounded, and this is the important part. These are screening numbers, not a design. The shortcut assumes constant relative volatility and constant molal overflow — it cannot see a pinch, a tangent, an azeotrope, or a temperature profile. Its job is to give a rigorous MESH column a starting point that converges, not to replace it. Run the distillation unit op on 18 stages with a feed at 8 to check it.
4 unit ops • PENG-ROBINSON
11 0
View & open