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
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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 + 2 H₂ → biphenyl + H₂S, the direct-desulfurization route; C₁₂H₈S + 2 H₂ balances, and the 3 H₂ this example once carried destroyed two hydrogen atoms per molecule) after a fired-heater preheat, at a treat-gas rate of ~3 mol H₂ per mol oil (~380 Nm3/m3) — the hydrogen excess that keeps the catalyst wet with H₂, not the 0.06 stoichiometric need. The effluent is cooled to 520 K (a real unit's feed/effluent exchange) before the hot high-pressure separator takes the gas off; a cold separator at 290 K condenses the carried-over oil; an amine wash (a fixed-recovery separator — the same simplification the carbon-capture example uses, not a full electrolyte amine model) scrubs H₂S from the recycle gas, and a compressor closes the loop with a 3% purge. The separator liquids are let down to 3 atm: a low-pressure separator flashes off the dissolved hydrogen and most of the H₂S as sour gas, and a six-stage steam stripper (Kremser, ~10 mol% stripping steam) finishes the desulfurized diesel. Every hydrogen atom is accounted for: makeup = reaction consumption + purge + sour gas + stripper overhead. History, because it changed the solver: this flowsheet used to run 6 mol/s of makeup on 50 mol/s of oil. All of that hydrogen dissolved in the hot liquid, both separators produced no gas, and the recycle the stream table showed was a stale tear iterate the loop had accepted as converged — the flowsheet now clears an edge its unit did not feed, so a loop can no longer converge onto a stream it fabricated. The refluxed stripper column that fed on it, asked to hold supercritical H₂S in a 600 K bottoms under a 239 K H₂S reflux, lost a fifth of its hydrogen and was gated unconverged for the same reason.
MEA post-combustion CO2 capture (electrolyte NRTL)
The reference amine process on the reference amine: flue gas (12% CO₂ at 1.1 bar, 313 K) scrubbed with 30 wt% aqueous monoethanolamine at a lean loading of 0.20 mol CO₂ per mol MEA, the rich solvent pumped and heated to 388 K, steam-stripped at 1.9 bar, and the overhead condensed at 313 K into a CO₂ product and a reflux-water stream. It runs on the enrtl package — carbamate/bicarbonate/protonation speciation with Davies activity, the CO₂ partial pressure a function of loading and temperature — which is what sets the rich loading of 0.53 mol/mol the absorber reaches and drives the stripper the other way at 390 K. What it computes: 24 mol/s of CO₂ into 695 mol/s of rich solvent, a 39 mol/s CO₂ product at 94 mol% after the condenser knocks out 109 mol/s of water, 3.9 MW of rich-solvent heating for 650 mol/s of circulation (the sensible-heat penalty the sensitivity sweep traces against solvent rate) and 6.8 MW of overhead condensing.
DEA natural-gas sweetening at 50 bar
A high-pressure gas-treating unit on diethanolamine, the canonical secondary amine: 100 mol/s of 5% CO₂ natural gas at 50 bar and 313 K against 200 mol/s of 25 wt% DEA (5.4 mol%), the rich amine let down to 1.8 bar, heated to 388 K and steam stripped, the overhead condensed. The enrtl-dea package carries DEA's cited protonation anchor (pKa 8.9) with a screening-grade carbamate constant. What it computes: a treated gas that is pure methane, a rich loading of 0.52 mol/mol — right at the carbamate ceiling of a secondary amine — a 5.1 mol/s CO₂ product at 89 mol% (the rest methane co-absorbed at 50 bar and water), 1.2 MW on the rich heater. Same model bounds as the MEA card: Kremser stages with the K at the entering liquid, open loop, regeneration to zero loading.