Control Process Flowsheets & Simulations
Explore 2 validated, solved Control simulation flowsheets in MaximaLabs — real components: water, methane, ethane. Open any one directly in your browser.
Solved via: STEAM, PENG-ROBINSON.
Pressure-controlled cooling-water header
A distribution header held at pressure by a control valve, rather than a valve with a pressure typed into it. A pressure transmitter reads the header downstream of the distribution line, a controller compares it with the 4.5 bar setpoint, and its output is written back into the valve — the flowsheet is re-converged until the manipulated variable and the measurement agree. What makes it a real loop rather than a tautology is the line between them. The transmitter sits 180 m downstream, so the valve cannot simply be set to the setpoint: it has to sit above it by exactly whatever the line is losing, and the controller has to find that. Solved here, it lands at 462.1 kPa at the valve for 450.0 kPa at the header — a 12.1 kPa line loss it was never told about — in 5 control passes. The controller runs in integral mode, so the steady-state offset a proportional-only controller would leave is driven to zero: the header sits at the setpoint to the last significant figure, not near it. One detail worth copying if you build your own: the pipeline carries an explicit molar_mass. Darcy-Weisbach needs mass density and ThermoPkg.density returns mol/m³, so a line without it inflates its pressure drop by roughly 1/M — about 55x for water. It warns, but the warning is easy to miss, and 12 kPa became 587 kPa while this example was being built. Bounded: steady state, so this finds the operating point a controller settles at, not the transient getting there — no overshoot, no settling time, no derivative action. Those live in the dynamic engine. The consumer splits are fixed fractions, so this demonstrates pressure control, not flow redistribution when a user throttles.
14 unit ops • STEAM
19 0
View & openInstrumentation: transmitters and controllers on the canvas
Field instruments are first-class wireable nodes here, not annotations. A flow transmitter and a pressure transmitter sit in the line, pass their stream through completely unchanged, and report their reading on a signal wire — a distinct edge kind that carries information rather than material — to a controller. In this let-down station the FT reads the 200 mol/s flowing through it and the PT reads the 20 bar downstream of the control valve. Each controller compares its reading against a setpoint and reports the measurement, the setpoint and its output. These two controllers are report-only, deliberately. Neither has an OUTPUT wire, so nothing is written back and the flowsheet solves once — this is the instrumentation and measurement layer on its own. Give a controller an output wire plus an output_param and the same machinery becomes a genuine closed loop: the output is written into the manipulated variable and the flowsheet re-converged through a Wegstein outer loop. Bounded: a signal edge never carries material, so it can never affect a mass or energy balance — which is exactly why a transmitter is safe to insert anywhere in a working flowsheet. The steady-state controller is proportional by default and therefore keeps a genuine offset (it converges the self-consistent operating point, not the setpoint); integral removes that offset. Derivative action needs a time history a single steady-state solve does not have.
7 unit ops • PENG-ROBINSON
10 0
View & open