Rate-based reactive amine absorber (packed, MDEA/PZ) — a ENRTL-MDEA-PZ process flowsheet
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.
Modeling assumptions & limitations
- 1(see): 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.
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- Rigorous ENRTL-MDEA-PZ thermodynamics, solved by the same engine every simulation runs on.
- 1 unit operations modeled: ABS.
- Focus areas: Rate-based, Packed column, Amine treating, Onda, MDEA, Piperazine.
- Thermodynamics
- ENRTL-MDEA-PZ
- Components
- methane, co2, h2s, water, mdea, pz
- Unit operations
- ABS
Opens in a new tab, loaded straight into the app — no setup.
Read the step-by-step guideReproduce this exact result from Python — the real client.get_example() → run_and_wait() path, not a mockup.
from flowsim.sdk import FlowSimClient
client = FlowSimClient()
example = client.get_example("rate-based-amine-absorber")
sim = client.create_simulation(example["title"], example["flowsheet"])
result = client.run_and_wait(sim["id"])
print(result["status"]) # "converged"
streams = client.streams(sim["id"])Related models
High-CO2 LNG with amine capture and CO2 reinjection
One 5.3 Mtpa LNG train on a reservoir whose gas is 14 mol% CO₂, where the CO₂ is not vented but compressed to dense phase and injected — 2.8 Mtpa of it, at 200 bar, which is the scale that makes this a storage project rather than a gesture. Two things make this different from every other LNG example here. First, the acid-gas removal is real chemistry, in the same flowsheet as the cryogenics: per-node thermo_overrides run the absorber, the rich/lean loop and the stripper on the 'enrtl-mdea-pz' electrolyte package (MDEA protonation + piperazine carbamate/dicarbamate speciation) while the gas train and the cold end run Peng-Robinson — the amine unit and the MCHE are not two models bolted together, they are one solve. Second, the CO₂ goes somewhere: the stripper overhead is knocked back, two-stage compressed with interstage cooling and drying, and pumped to 200 bar as a ~96 mol% dense-phase stream ready for a reinjection well, rather than leaving as a vent. The sweet gas is water-washed, dried and liquefied in the C3MR cold end to LNG at ~116 K.
Refinery acid-gas treating: MDEA/PZ absorber-stripper
Simultaneous CO₂ AND H₂S removal from a sour natural-gas / refinery off-gas stream by a piperazine-promoted MDEA solvent — the mixed-amine chemistry legacy tools reach for heavy rate-based/OLI add-ons to model. A high-pressure absorber contacts the sour gas with lean MDEA/PZ solvent (both acid gases absorb into the amine); the rich amine is heated and let down to a low-pressure steam stripper that drives the acid gases back off as a concentrated acid-gas stream and regenerates the lean solvent. Runs on the new 'enrtl-mdea-pz' electrolyte package: a generalized speciation (MDEA protonation + piperazine carbamate/dicarbamate + CO₂/HCO₃-/CO₃-- + H₂S/HS- + water) with Davies activity — it correctly reproduces piperazine's promotion (the blend holds more CO₂ at a given partial pressure than MDEA alone).
aMDEA closed solvent loop (activated-MDEA acid-gas removal)
The activated-MDEA (aMDEA) acid-gas removal process BASF developed at Ludwigshafen — methyldiethanolamine promoted with piperazine — run as a genuinely CLOSED solvent loop: the regenerated lean amine is cooled, pumped back to absorber pressure and returned to the absorber, with a small side bleed and a demin-water/amine makeup. The companion 'mixed-amine-acid-gas-treating' showcase deliberately leaves that loop open (the regenerated solvent is a product); closing it is what this example adds, and it changes what the model can tell you. Sour gas at 50 bar (5% CO₂, 3% H₂S in methane) is contacted with lean solvent; the rich amine is heated, let down to 1.8 bar and stripped; the lean solvent returns through a cooler and a pump; a 3% bleed purges degradation products; makeup replaces what leaves. One Wegstein tear on the lean stream closes it. The headline result is one no open-loop model can produce: the lean-solvent composition is not specified anywhere in the flowsheet — it is the fixed point of the loop's own water and amine balance — and it converges to 87.7 mol% water / 10.2% MDEA / 2.0% piperazine, which is 41 wt% MDEA and 5.9 wt% PZ (about 3.6 and 0.7 mol/L at a typical 1.04 g/cm3 solvent density), inside the concentration window BASF's own aMDEA patents claim. Also computed: 114 mol/s of circulating solvent for 100 mol/s of sour gas, a rich loading of 0.36 mol CO₂ + 0.21 mol H₂S per mole of amine, treated gas that is pure methane, a 39 mol/s acid-gas overhead, and 0.23% hydrocarbon slip into it. Sweeping the stripping steam traces the loop's water balance: more steam carries more water overhead, so the circulating inventory shrinks from 225 to 53 mol/s across the sweep — a closed-loop coupling that simply does not exist in an open-loop model. Balance closure is the precondition for an acceptance test under VDI 2048 (control and quality improvement of process data by correction calculation, for operation and acceptance tests in energy technology and the chemical industry); the same variance-weighted least-squares correction that standard is built on is available on solved results through the data-reconciliation tool.
Diesel hydrotreater with closed H2 recycle + amine wash
Diesel (an n-hexadecane carrier with a dibenzothiophene sulfur slice) and hydrogen react over a trickle-bed-equivalent reactor (dibenzothiophene + 3H2 → biphenyl + H₂S, the real HDS desulfurization route) after a fired-heater preheat. Hot and cold high-pressure separators knock the light gas off the treated oil; an amine wash (a fixed-recovery separator — the same simplification the existing carbon-capture example uses, not a full electrolyte amine model) scrubs H₂S from the recycle gas before a compressor closes the loop back to the reactor feed, with a small purge controlling buildup. A pressure-letdown valve + stripper finish the treated oil, removing dissolved light ends before the desulfurized diesel leaves the bottoms.
Rate-based distillation (Maxwell-Stefan, ChemSep-style)
A depentanizer split (n-pentane overhead from an n-pentane/n-hexane/n-heptane feed) solved with a rigorous rate-based (nonequilibrium) stage model rather than the usual equilibrium-stage assumption. Every stage carries separate bulk vapor and liquid compositions with a vapor-liquid interface in equilibrium and finite Maxwell-Stefan mass-transfer fluxes across each film, and the per-stage transfer coefficients come from the real Chan-Fair (1984) tray-efficiency correlations off estimated tray geometry — the exact physics ChemSep and Aspen RateSep are built on. The result: real trays lag equilibrium, so the finite-transfer distillate is measurably less pure (~98.7% C₅) than an equilibrium-stage model predicts (~99.8%) on the identical column — roughly 5x more hexane slips overhead. Open the equivalent equilibrium column ('ethanol-water-distillation' or any 'distillation' node) to see the gap the equilibrium-stage assumption hides. As the mass-transfer coefficients grow the model collapses back onto the equilibrium column (the built-in validation limit).
Blue hydrogen with rigorous amine capture (multi-thermo)
The blue-hydrogen train done properly: steam-methane reforming and water-gas-shift run on a cubic gas EoS (Peng-Robinson), while the CO₂ capture runs on the rigorous electrolyte amine package (MDEA/piperazine 'enrtl-mdea-pz') — two thermo methods in one flowsheet, via per-node thermo_overrides. This is what legacy tools do with a property-method 'section' and what the plain 'blue-hydrogen-smr-ccs' showcase couldn't (one package per flowsheet forced a component-separator stand-in for the capture). Here the shifted syngas is contacted with a lean MDEA/PZ solvent in an absorber that removes the CO₂ by real reactive equilibrium (H₂/CO/CH₄ pass through as insoluble gases), delivering ~94% H₂ with the CO₂ driven to trace and a rich amine at a realistic ~0.7 mol CO₂/mol amine loading.