Phosphoric acid concentration: steam evaporator baseline (29 → 54% P2O5)

The conventional wet-process step, at the scale of one Jorf Lasfar concentration line: 138 t/h of 29% P2O5 acid, heated by 3.5 bar LP steam in a graphite exchanger and flashed under vacuum (0.12 bar) to 54% P2O5, evaporating 64.0 t/h of water. The steam feed is tuned so the concentrate lands on 54.0 wt% P2O5 (the user variable p2o5_wt_product), which takes 73.6 t/h of steam — 1.84 t steam per tonne of P2O5, 44.5 MW of condensing duty. That is the single-effect ideal; the published plant benchmark of ~2.8 t/t carries exchanger approach, losses and off-design operation on top. The point of the number here is what it costs the site: at Jorf Lasfar this steam is a co-product of the exothermic sulfuric-acid plants, which is the fact any electric alternative has to beat. Compare the two sibling examples, phosphoric-acid-concentration-microwave and -hybrid. Model scope, stated up front. The acid runs on the brine package, which carries phosphoric acid as a non-volatile molecular solute with its CRC liquid heat capacity (145 J/mol/K) — the streams show the real H3PO4/water compositions and the acid's sensible heat is in the balance — and a water activity fitted to measured data: binary boiling points (Li 2017, NIST TRC ThermoML Archive) and 20 °C vapour pressures up to 85 wt% (Kirk-Othmer), with a held-out error of 2% in water activity. The boiling-point elevation is therefore the fitted one, 23.5 K at 54% P2O5 and 0.12 bar (the ideal, Raoult's-law activity this replaced gave 9 K). Checked against a boiling point the fit never saw, it puts 85 wt% acid at 164 °C at atmospheric pressure against a measured 158 °C. Above 18 mol% acid the temperature dependence rests on one coefficient and that single check, so read the concentrate temperature to within a few kelvin. No heat of dilution is carried (about 1.5% of the latent duty at 54% P2O5). The 320 K feed stands in for a hotter plant feed. The acid heated at 1 atm here partly boils in the exchanger (the model's fitted boiling point at 1 atm); the real acid is kept liquid under static head and flashes in the chamber.