Rate-based reactive amine absorber (packed, MDEA/PZ)

A packed acid-gas absorber sized the way ChemSep / Aspen RateSep size one -- by real mass-transfer rate over a PACKED HEIGHT, not an assumed stage count. Sour gas (CO2 + H2S in methane) contacts a piperazine-promoted MDEA solvent in a structured-packed column, and the recovery of each acid gas is set by three coupled pieces of physics: the Onda-Takeuchi-Okumoto (1968) gas/liquid film coefficients and wetted area over the packed height (the rate), a reaction-enhancement factor on the liquid film from the Hatta number (the reaction speeding up liquid-side transfer), and the reactive vapor-liquid equilibrium from the electrolyte 'enrtl-mdea-pz' package (the capacity). The result is a genuine design curve: CO2 recovery climbs from ~85% at 0.3 m of packing to pipeline spec by ~1.5 m (5 ppm CO2, 3 ppm H2S) -- run the built-in packed-height sweep to see it. A revealing rate-based insight the equilibrium-stage shortcut can't give: the fast amine reaction makes the liquid resistance negligible, so this absorber is gas-film-controlled -- recovery barely moves with solvent rate but scales directly with packed height. Honesty notes (see flowsim/solver/unitops/rate_based_absorber.py): dilute-absorption HTU-NTU with a lean-solvent Colburn form, mean-property diffusivity, a pseudo-first-order (Ha/tanh Ha) enhancement with no instantaneous-reaction cap, and screening-grade reaction rate constants -- it captures the real rate-based behaviour (recovery vs. height, gas-film control) without claiming RateSep-grade rigor. The companion 'mixed-amine-acid-gas-treating' showcase runs the full absorber-stripper loop with the equilibrium-stage (Kremser) absorber for contrast.