Green urea synthesis — a PENG-ROBINSON process flowsheet
Green ammonia and captured CO₂ react over a single-pass stoichiometric reactor (2NH₃ + CO₂ ⇌ CO(NH₂)₂ + H₂O) at synthesis-loop conditions — the fertilizer step downstream of green ammonia. Screening fidelity: a real plant recycles the unconverted carbamate/excess ammonia to push per-pass yield well above this single-pass conversion; that recycle isn't modeled here.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 1 unit operations modeled: RX.
- Focus areas: Urea, Fertilizer, Green ammonia downstream, Stoichiometric reactor.
- Thermodynamics
- PENG-ROBINSON
- Components
- ammonia, co2, urea, water
- Unit operations
- RX
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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("green-urea-synthesis")
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
Wet-process phosphoric acid: electrochemical removal of copper and cadmium
Wet-process phosphoric acid (about 42 wt% H₃PO₄, 10 kg/s) carries the metals its phosphate rock brought in: iron, zinc, nickel, copper and the cadmium that limits how the acid may be used in fertilizer. Two flow-through electrochemical cells remove the two noble enough to plate from strong acid. The first holds its cathode at -0.05 V vs SHE: copper's Nernst potential sits far above that, so copper plates at its mass-transfer limit (plug-flow law, 99% removed) while zinc, nickel, iron and cadmium, whose potentials lie below the cathode, stay dissolved. The second cell runs at -0.55 V and is told that only cadmium plates: mass transfer alone would take 99.4% of it, but at that potential and 323 K the Nernst floor holds about 2.6e-5 mol/L in solution, so the solver reports the equilibrium-limited 91% instead. Each cell's current comes from the metal's partial current and the current efficiency you give it; the copper and cadmium currents regenerate phosphoric acid (one proton per dihydrogen-phosphate counter-ion), and the rest of the charge evolves hydrogen beside the anode's oxygen, which the cell gas reports, with a flammability warning.
Wet-process phosphoric acid: dihydrate reactor-filter, 1500 t/d P2O5
A dihydrate (DH) phosphoric acid line at the scale of one large Moroccan train: 4,830 t/d of a 33% P₂O₅ phosphate rock (78 wt% fluorapatite, 13% calcite, 9% silica) attacked at 75 C with 98 wt% sulfuric acid at 2.5% sulfate excess, the gypsum filtered off and washed in three countercurrent stages. The phosphoric_acid_reactor block makes 1,500 t/d of P₂O₅ as a 28.4 wt% P₂O₅ filter acid at 94.2% recovery; the three losses close it exactly: 1.0% unattacked rock, 3.0% co-crystallized in the gypsum lattice, 1.9% water-soluble P₂O₅ left in the washed cake by the countercurrent washing equation. It throws 4.79 t of dry gypsum and uses 2.80 t of sulfuric acid per t P₂O₅. Gypsum is the stable hydrate here, and that is computed, not assumed: the acid's water activity (0.838, from the H₃PO₄/water model fitted to measured data) sits above the gypsum/bassanite transition activity (0.565, from LLNL log K(T)). The attack releases 50.0 MW on formation enthalpies (-464 kJ per mol of apatite) plus the acids' heats of solution: the 98 wt% acid enters already partly diluted and takes 1.1 MW back, while the phosphoric acid made dissolves at its own strength and adds 3.5 MW (NBS 1982). The flash cooler removes 25.6 MW by evaporating 11.0 kg/s of water, which leaves through the off-gas with the CO₂ and SiF₄. At the 6 h digestion residence EPA's 1976 phosphoric acid report cites, the attack system holds about 4,060 t of slurry (48 wt% solids). Fluorine is split 7% to the gas, 43% to the cake as CaF₂ and 50% dissolved in the acid, the typical dihydrate distribution in the EFMA BAT booklet on phosphoric acid (most of the dissolved share leaves later, in the concentrator). The tilting-pan gypsum filter is sized by Ruth's constant-pressure law: 230 m2 at 6.5 t P₂O₅/m2/day, limited by cake formation (the cake forms in 18 s of its 18 s sector; the three-stage wash needs 20 s of its 81 s). The vacuum (14.5 inHg), the 3 min cycle and the 18 s formation time are within the ranges in Pillai et al., US 5,185,135; the filtrate viscosity, 3.95 mPa s, is the middle of the 3.3-4.6 mPa s Anouar et al. (Heliyon 2024) measured on wet-process acid, at a temperature they do not state; the wash liquor's is the pure-acid fit at the first wash filtrate's strength. The cake's specific resistance, 1.44e8 m/kg, is back-calculated to the middle of the 5.5-7.8 t P₂O₅/m2/day Anouar et al. measured on dihydrate slurries. The cloth resistance (1e9 1/m) and the wash/dry sector split are representative, not sourced; at 1e10 1/m no cake reaches 5.5. Scope, stated rather than implied: (1) one block for the attack tanks, flash cooler and filter, so there is no tank-by-tank residence time or crystal size, and the filter's cake resistance is an input, not a prediction from crystal size; (2) the attack efficiency, co-crystallized fraction, fluorine split and cake liquor are plant inputs, not predictions (the 4% insoluble loss, mostly co-crystallized, follows the EFMA booklet's 4-6% DH losses "most of them co-crystallised"); (3) the heats of solution are 298.15 K values, one strength per liquid stream; (4) the water activity reads the P₂O₅ strength only, not the sulfate, fluoride or impurities that also lower it; and (5) anhydrite, the truly stable phase above about 42 C, is not considered, as in the real process, where gypsum forms metastably.
DAP granulation loop: pre-neutralizer, ammoniating granulator, scrubbers
Diammonium phosphate at the scale of one Jorf Lasfar (JESA) granulation train: 40.2 kg/s (145 t/h) of wet-process phosphoric acid is neutralised by ammonia in two steps and granulated in a loop that recycles four times its own product. The acid carries the composition Handley (IFA, 1984) gives for a commercial merchant-grade acid, per 100 g: 54.82 g H₃PO₄ (39.7% P₂O₅), 3.90 g H₂SO₄, 5.68 g of metal and fluoride impurities (carried as one inert lump) and 35.60 g water. It is pumped first through the tail-gas scrubber and the pre-scrubber, which take back the ammonia the reactors do not absorb, then into the pre-neutralizer, which holds a mole ratio NH₃:H₃PO₄ of 1.44 at 114 °C (near the ratio of highest ammonium phosphate solubility, so the least water keeps the slurry fluid) and boils off water with its own reaction heat. The slurry is sprayed onto the rolling bed of the ammoniating granulator, where sparged ammonia lifts the ratio to 1.845. New solid layers onto the recycled granules (an equal-thickness growth law on the full size distribution), the bed is dried to 3% moisture, a double-deck screen splits it at 3.35 and 1.70 mm, the oversize is crushed, and fines, crushed oversize and 73% of the on-size go back to the granulator. The rest is cooled and sold. The 73% is the split that puts the loop at the recycle ratio Handley reports, 4: a plant sets its recycle to absorb the slurry's water, so here it is an input, not a prediction. Solved: 33.7 kg/s of product (121 t/h), 18.7% N and 47.6% P₂O₅ on a dry basis, above the 18-46-0 commercial grade, which is set by the acid's sulfate and impurities rather than by the 21.2-53.8 of pure DAP. Consumption per tonne of product is 0.227 t NH₃ and 0.474 t P₂O₅. An 18-46-0 product carries 0.219 t of NH₃ as nitrogen and 0.46 t of P₂O₅ per tonne by its grade alone; the difference is this product's richer grade and the ammonia lost at the stack. The recycle ratio is 4.0, and the loop converges on its own tear machinery (six tears, Wegstein). The pre-neutralizer releases 19.1 MW of reaction heat and evaporates 7.3 kg/s of water; the granulator releases 6.9 MW and evaporates 5.2 kg/s; the dryer takes 1.7 kg/s more for 7.1 MW. 0.029 kg/s of ammonia leaves the stack, 0.4% of what is fed, which is what two scrubbers at 90% recovery each give.
CO₂ methanation (e-fuels / power-to-gas)
The Sabatier reaction (CO₂ + 4H₂ ⇌ CH₄ + 2H₂O) converts captured CO₂ and green H₂ into synthetic natural gas at a 97% single-pass-equivalent conversion (real plants stage several adiabatic beds with intercooling to reach this; lumped into one reactor here), then a cooler and knockout drum condense the reaction water from the SNG — the e-fuels loop that closes the loop on captured carbon instead of just storing it.
LOHC hydrogen release (methylcyclohexane dehydrogenation)
A liquid organic hydrogen carrier (LOHC) power train: methylcyclohexane (MCH) is preheated and catalytically dehydrogenated (MCH → toluene + 3H2, endothermic, equilibrium-limited to ~90% single-pass conversion) to release hydrogen for downstream power generation. A flash drum separates the H₂-rich gas from the liquid; a distillation column then recovers the unreacted MCH overhead and recycles it to the reactor feed, closing a real tight liquid recycle loop, while spent toluene leaves the bottoms (to be re-hydrogenated back to MCH off-site, closing the supply-chain loop — out of scope for this dehydrogenation-side flowsheet). Screening-fidelity note: MCH and toluene are genuinely close-boiling (relative volatility ~1.4 under this thermo package at column conditions), so the recycle carries real toluene along with the recovered MCH rather than a sharp cut — a production column would use more stages to purify it further; this shows the recycle topology and its convergence, not an optimized column design.
On-site oxygen: multi-bed vacuum pressure swing adsorption (VPSA)
Medical- / green-steel-grade oxygen generated on site from air by a 4-bed vacuum pressure swing adsorption unit over an N₂-selective zeolite (LiX/13X). This uses the native VPSA unit op — the proven 2-bed Skarstrom engine generalized to N beds with pressure-equalization steps and sub-atmospheric evacuation: nitrogen is adsorbed while oxygen passes as the light product, then each bed is pulled to a vacuum to desorb the nitrogen tail gas. The solver runs the real cyclic transient (tanks-in-series bed discretization + linear-driving-force kinetics + inter-bed equalization) to a periodic steady state — the transient dynamic equilibrium legacy steady-state simulators cannot capture without a separate dynamic license.