How to simulate 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).
- 1Open the ready-made model
Open the "Refinery acid-gas treating: MDEA/PZ absorber-stripper" model in the MaximaLabs workspace — no install, no license. It loads live on the canvas, ready to edit and run.
- 2Confirm the thermodynamics
This process is modeled with the ENRTL-MDEA-PZ property package over methane, co2, h2s, water, mdea, pz — already selected, so the phase equilibrium and enthalpy are physically consistent from the first run.
- 3Review the flowsheet
The flowsheet chains 2× Strip, Richhx, Letdown. Every block is a real, solvable unit op you can reconfigure on the canvas.
- 4Run the simulation
Click Run. The deterministic solver converges the material and energy balances (recycles included) and fills the live stream table — the AI never invents a number.
- 5Read the results and iterate
Inspect the converged streams, tweak a spec, and re-run — or ask the AI copilot to explain a result or diagnose a failed solve in plain English.
- Thermodynamics
- ENRTL-MDEA-PZ
- Components
- methane, co2, h2s, water, mdea, pz
- Unit operations
- 2× StripRichhxLetdown
Opens live on the canvas — free, no install.
Explore the model & flowsheetModeling assumptions & limitations
What this model captures, and what it deliberately does not — from the engineers who built it.
- 1This is an EQUILIBRIUM capacity/selectivity model — NOT rate-based, so PZ's kinetic CO₂ promotion and MDEA's kinetic H₂S-over-CO₂ selectivity are not captured; the absorber/stripper are Kremser shortcut columns; the PZ carbamate constants and the H₂S path are screening-grade (see); and the lean-amine loop is left OPEN (the regenerated solvent is a product, not closed back onto the absorber — the same honest simplification the 'co2-from-natural-gas' example makes), with makeup steam as the reboiler surrogate. What it genuinely computes: deep sweetening of the gas, the rich CO₂/H₂S amine loadings, the concentrated acid-gas overhead, and a fully regenerated lean solvent.
Frequently asked questions
- What does the Refinery acid-gas treating: MDEA/PZ absorber-stripper model simulate?
- 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).
- Which thermodynamic method does it use?
- The ENRTL-MDEA-PZ property package, over methane, co2, h2s, water, mdea, pz — already selected. You can switch the method on the canvas before running.
- Which unit operations are in the flowsheet?
- It chains 2× Strip, Richhx, Letdown. Every block is a real, solvable unit operation you can reconfigure, add to, or remove.
- Do I need to install software or buy a license?
- No. Refinery acid-gas treating: MDEA/PZ absorber-stripper runs entirely in your browser on MaximaLabs — free, no install, no license. Open the model to load it live and run the deterministic solver.
More guides like this
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.
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.
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.
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.
Refinery sour water stripper (NH₃ + H₂S)
The standard refinery sour water stripper: sour water carrying ammonia and hydrogen sulfide is steam-stripped in a 10-stage column, sending both overhead as sour gas and returning stripped water fit for reuse. Runs on the new sour-water weak-electrolyte package, which is what makes the result meaningful — ammonia and H₂S suppress each other's volatility (ammonia raises pH and holds sulfide down as HS⁻; H₂S lowers pH and holds ammonia down as NH₄⁺), and heat reverses both, which is precisely why a stripper works. The two removals come out asymmetric for the real reason: H₂S strips essentially completely while ammonia, five orders of magnitude more soluble, is the duty that sets the steam rate.
CO2 removal from syngas (Rectisol-style physical solvent)
A CO₂-laden syngas stream from gasification/reforming (H₂/CO with 25% CO₂, the actual Rectisol duty — scrubbing raw syngas ahead of methanol/ammonia synthesis, not treating pipeline natural gas) is sweetened by a cold-methanol physical-solvent absorber (chosen because chemical amine reactions aren't modeled here) down toward synthesis-loop spec, then the rich solvent is regenerated by a pressure letdown into a second flash that flashes the bulk of the absorbed CO₂ back off — the same letdown-valve-plus-flash regeneration pattern used for HDA's and methanol synthesis's own dissolved-gas trains. No solvent recycle loop (an honest simplification: the regenerated solvent is reported as a product stream rather than closed back onto the absorber feed). From the ChemSep casebook (CO₂ removal from natural gas), adapted to Rectisol's real syngas duty.