This is a free, browser-based process flowsheet simulator for steady-state material and energy balances. It works like the drawing board of a commercial simulator: choose a property method, place unit operations, connect them with material streams, specify the feeds and the units, and run. The whole flowsheet — calculation order, recycle loops, design specs and sensitivity studies — is solved by the multicalci.com engine in one call.
Drag a unit from the palette on the left onto the canvas (or click it to drop it in the middle). Feed arrows and product arrows are created automatically on its ports. Red port circles are required inlets that still need a stream; blue ones are optional or outlets.
Click a feed arrow (blue label). Pick a typical stream (air, natural gas, steam…) or add components from the searchable dropdown, choose the basis (mole %, mass %, kmol/h, kg/h), then enter total flow, temperature and pressure in any unit — °C/K/°F, bar(a), bar(g), kg/cm²(g), psig, kPa, kmol/h, Nm³/h, t/h.
Click a unit and fill its specifications. The status lamp at the bottom turns green when everything needed is entered; the Issues tab lists anything missing. Press Run (or F5).
Click empty canvas to open the flowsheet panel and pick a property method for the whole flowsheet — Peng–Robinson or SRK for hydrocarbons, light gases and NH₃ / syngas at pressure; NRTL, UNIQUAC or Wilson (with ChemSep binary parameters built in) for polar liquids; UNIFAC or Dortmund UNIFAC when no binary data exist; or ideal. With a property method, mixers, heaters, flash drums, exchangers, pumps, compressors, turbines, valves and conversion reactors become rigorous: every outlet is flashed, so streams can leave two-phase, and enthalpies include heats of vaporisation and mixing. Review pure-component & binary data shows exactly which constants and binary pairs will be used; you can override kij and NRTL pairs. Set Valid phases to vapour–liquid–liquid for free water or partially miscible solvents. With an activity-coefficient method, carboxylic acids (acetic, propionic …) dimerise in the vapour (chemical theory) — vapour fugacities, densities and the liquid enthalpy of the acids then agree with measured data. Any rigorous unit can use its own method. Classic keeps the engine's per-unit models (the flash drum then offers Raoult, Peng–Robinson or NRTL individually).
The component list holds more than 400 components with ChemSep pure-component data; components marked “classic units only” (urea, carbamate, biuret …) can be used in the reformer and urea units only.
Two electrolyte (acid-gas) methods model chemical CO₂ absorption. Aqueous MEA solves the carbamate and bicarbonate equilibria of monoethanolamine (the published Akula et al. model used by IDAES): CO₂ dissolves by Henry's law on the free, unreacted CO₂, water and MEA follow Raoult's law on the true species. Hot potassium carbonate (Benfield-type solutions) uses the Pitzer electrolyte model with the USGS PHREEQC parameters for K⁺, CO₃²⁻, HCO₃⁻, CO₂, OH⁻ and the water activity. Enter the solvent as its apparent components — MEA or K₂CO₃, water and CO₂ (the CO₂ sets the lean loading or conversion); H₂, N₂, CH₄, CO, Ar and O₂ dissolve physically. Heats of absorption follow from the solubility model (about −84 kJ/mol CO₂ in MEA, −30 kJ/mol in hot carbonate). Liquid streams show the loading or conversion to KHCO₃, the equilibrium CO₂ pressure and, for carbonate, the water activity. H₂S, NH₃ and MDEA / activated MDEA are not modelled. The two CO₂-removal examples build an absorber + regenerator with each solvent.
The rigorous column solves the full stage-by-stage MESH equations (Naphtali–Sandholm Newton): choose stages, condenser (total, partial or none), reboiler (kettle or none), feed stages, top pressure and two specifications (reflux ratio, distillate or bottoms rate, duties, condenser temperature, a product purity or a recovery). Without condenser and reboiler it is an absorber or stripper. Trays can carry a Murphree vapour efficiency — one value for every tray, or per component (for example a low CO₂ efficiency in a chemical-solvent absorber while water stays at equilibrium); the condenser and reboiler are always equilibrium stages. Its panel shows temperature, composition and flow profiles. The Gibbs reactor finds chemical equilibrium by minimising Gibbs energy — list the species that may form, no reactions needed. The three-phase separator splits vapour, light liquid and heavy (aqueous) liquid.
The plug-flow and CSTR reactors take power-law or LHHW / Hougen–Watson kinetics: for each reaction give the stoichiometry, k0 and the activation energy (optionally about a reference temperature), optional orders (blank = elementary, negative orders allowed), a concentration or partial-pressure basis, and whether it is reversible — with a thermodynamically consistent driving force from the Gibbs-energy equilibrium constant of the databank or your own ln K correlation, or your own reverse Arrhenius rate. For catalytic kinetics add an adsorption term (Σ Kₜ Π aᵢ^eₜᵢ)^m — the Steam reformer example carries the full Xu–Froment model. Rates can be per m³ of reactor or per kg of catalyst (with the bed density). The plug-flow reactor is isothermal, adiabatic, fixed-duty or heated / cooled through the wall (U and coolant or furnace temperature) and shows axial temperature, pressure and composition profiles; fast, equilibrium-limited kinetics are integrated with a stiff (Rosenbrock) solver. Each reactor reports conversions, the heat of every reaction in the reacting phase and the residence time.
Select any stream and use Stream analysis: the phase envelope traces bubble and dew curves (with quality lines) and marks the critical point, cricondenbar and cricondentherm; the property table sweeps temperature or pressure and tabulates phase fraction, enthalpy, Cp, densities, viscosities and conductivities; the binary diagram draws T–x–y or P–x–y and y–x curves with azeotropes and the three-phase line of partially miscible pairs. All three use the flowsheet property method and can be copied into Excel.
In the flowsheet panel, a sensitivity study steps any feed or unit input over a range and tabulates up to eight stream or unit results (column duties, purities, flows, temperatures …). Results appear in the Sensitivity tab as a chart and a table you can copy into Excel.
Press Specs to make the simulator vary a feed or unit input until a result hits a target — for example process air until H₂/N₂ = 3, or a flash temperature for a given water content. Specs are solved on the server together with the whole flowsheet.
Loops are detected automatically. One stream in each loop is torn and iterated with Wegstein acceleration until the tear converges (relative tolerance 1e-5 by default). Torn streams are drawn dashed. You can give a torn stream an initial estimate from its properties panel.
The stream table shows T, P, flows, enthalpy and composition (mass or mole basis, flows or fractions) for every stream; copy it straight into Excel or download CSV. The Balance tab gives overall mass closure and heating / cooling utility totals. Turn on T·P·F tags to print results on the drawing, and use Report for a printable PDF.
F5 run · Del delete selection · Ctrl+Z / Ctrl+Y undo / redo · arrow keys nudge a block · Esc cancel / deselect · Ctrl+wheel or pinch to zoom, drag empty canvas to pan.
The property methods, the three-phase flash, the rigorous column and the phase envelope are checked against DWSIM and the open-source thermo library, the Gibbs reactor against NIST-JANAF, the kinetic reactors against exact solutions, the CO₂ packages against measured MEA vapour pressures, IDAES and USGS PHREEQC, the tray efficiencies against the exact Murphree–Kremser solution, and the energy balance and recycle / design-spec solver against independent references — see how the simulator is validated.
Results are for preliminary engineering. Property methods are only as good as their parameters (Peng–Robinson without fitted kij over-predicts water in hydrocarbon liquids; ChemSep activity parameters come from vapour–liquid data). The MEA model over-predicts the CO₂ pressure at high loadings (above about 0.35 mol/mol at regenerator temperatures, 0.5 at absorber temperatures), and the hot-carbonate Pitzer parameters are extrapolated above about 100 °C and are held at their stability limit in very strong, highly converted solutions (near KHCO₃ crystallisation); tray efficiencies stand in for mass-transfer rates. The McCabe–Thiele and Kremser columns are shortcut models and the urea units are tuned empirical correlations. Verify against plant data before using results for design.