HYSYS Reference

For hydrocarbon systems (oil and gas), use Peng-Robinson (PR) as the standard or SRK as an alternative. For polar/chemical systems, use NRTL for polar liquid mixtures, UNIQUAC for polymer systems, or Wilson for fully miscible liquids. For special cases: CPA handles hydrogen-bonding systems like MEG and methanol, Sour PR is designed for acid gas systems containing H2S and CO2, and ASME Steam provides accurate steam properties. Use PRSV when mixing polar and non-polar components.

A material stream requires C+2 specifications (degrees of freedom), where C is the number of components. You must specify temperature and pressure (or vapor fraction and pressure), flow rate (molar, mass, or volumetric), and composition (mole or mass fractions). Alternatively, you can specify T+P with individual component flows. HYSYS performs a flash calculation to determine the phase state, enthalpy, entropy, density, viscosity, and heat capacity of the stream.

Simple (End Point) mode specifies outlet temperature or UA value and calculates Q = UA * LMTD * Ft. Weighted mode divides the exchanger into sections to account for property variations, making it more accurate for phase-change scenarios. Steady State Rating mode accepts detailed TEMA geometry specifications and calculates the overall heat transfer coefficient and pressure drop. The Ft correction factor should be above 0.75 for practical designs.

Define the column type (Distillation with condenser and reboiler, Absorber without condenser/reboiler, or Reboiled Absorber). Specify the number of theoretical stages, feed stage location, and two column specifications such as reflux ratio and distillate rate, or component recovery and purity. HYSYS uses the Inside-Out convergence method by default. If the column does not converge, provide initial temperature and flow estimates, adjust the damping factor, or relax specifications and gradually tighten them.

Use the shortcut (Fenske-Underwood-Gilliland) method for preliminary design to quickly estimate minimum stages (Nmin), minimum reflux (Rmin), actual stages, and feed stage location. Specify light key and heavy key components with their distribution (e.g., 1% LK in bottoms, 1% HK in distillate), condenser/reboiler pressures, and R/Rmin ratio (typically 1.2-1.5). Switch to rigorous simulation for detailed design, optimization, and when side draws, pump-arounds, or multiple feeds are involved.

Define reactions in Simulation Basis > Reactions with four types: Conversion (specify conversion directly), Equilibrium (Keq or Gibbs free energy), Kinetic (r = A*exp(-Ea/RT)*C_A^a*C_B^b with pre-exponential factor A and activation energy Ea), and Heterogeneous Catalytic. Connect the Reaction Set to the Fluid Package. Use CSTR for perfectly mixed reactors (specify volume or residence time), PFR for plug flow with axial profiles, Gibbs Reactor for equilibrium without reaction equations, or Conversion Reactor for simple stoichiometric conversion.

Add a Recycle operation to the recycle stream. HYSYS compares the assumed (inlet) and calculated (outlet) stream values using the Wegstein method (default) or Direct Substitution. Set convergence tolerances: temperature 0.01 C, pressure 0.1 kPa, flow 0.01%, composition 0.001. Allow 50-100 maximum iterations. Adjust the Wegstein acceleration parameter between -5 and 0 if convergence is slow. For difficult cases, provide good initial estimates for the recycle stream.

Switch to dynamic mode via Simulation > Dynamic. You must specify additional information: equipment volumes/hold-up, control valve Cv values, and pressure-flow relationships. For PID controllers, define PV (measured variable), SP (set point), OP (output to control valve, 0-100%), and action (direct or reverse). Tune with Ziegler-Nichols, Cohen-Coon methods, or the built-in Auto-Tune. Set Kc (proportional gain), Ti (integral time in minutes), and Td (derivative time). Dynamic mode is essential for startup, shutdown, and upset scenario analysis.