Centrifugal Compressor Surge Control Room: Greitzer Plenum, Compressor Map and Anti-Surge Valve (2D)

Presets

Events and faults

Speed1x

Alarms

Live readouts

Graphs

Numerical checks

running...

How to use

The big graph is the compressor map: head coefficient Psi against flow coefficient Phi. Curves are the speed lines, the red line is the surge line (peak of each curve), the yellow dashed line is the anti-surge control line, the blue parabola is the system curve set by the process valve, and the purple trail is where the machine really is.
Close the process valve (FCV-202) with the anti-surge system Disabled: the operating point slides left, crosses the surge line and starts a limit cycle that can reverse the flow. Three cycles in 30 s trip the machine.
Switch to Automatic: the recycle valve UV-201 opens as the point nears the control line and keeps flow through the compressor while the plant takes less. The valve stroke time, margin and PI gains decide whether it works.
The plenum volume sets the Greitzer parameter B: small B gives mild stall, large B gives deep surge with flow reversal. Gas temperature and molar mass change the speed of sound and therefore B.
In 3D the pipe beads reverse during deep surge, the casing shakes, the recycle line lights up when UV-201 opens, and the local panel shows the same map. Space pauses, R resets.

The science

Compressor, plenum and throttle are described by the lumped Greitzer (1976) model in Helmholtz time tau = omega_H t:

dPhi/dtau = B (Psi_c(Phi) - Psi)
dPsi/dtau = (Phi - Phi_out) / B , Phi_out = (g_thr + g_rec u) sqrt(Psi)
B = (U / 2a) sqrt(V_p / (A_c L_c)) , omega_H = a sqrt(A_c / (V_p L_c)) , a = sqrt(1.3 R T / M)

Compressor characteristic (cubic, Greitzer's shape) and affinity laws for speed ratio s:

Psi_c(Phi, s) = s^2 [ psi0 + H (1 + 1.5 (Phi/(W s) - 1) - 0.5 (Phi/(W s) - 1)^3) ] , surge flow Phi_s = W s

Linear stability about an operating point with slope c = dPsi_c/dPhi and throttle slope k = Phi/(2 Psi): trace = B c - k/B, determinant = 1 - c k. The point is stable when B < B_crit = sqrt(k/c) (for c > 0) and c k < 1. Dimensional values use Q = Phi U A_c, Delta p = Psi (1/2) rho U^2 and shaft power P = Q Delta p / eta.

Anti-surge control: the PI controller works on the distance between the measured flow and the surge control line Phi_s (1 + margin). The recycle valve has a stroke-time limit (it closes six times slower than it opens), and an optional fast open-on-surge-line rule fires when the point reaches the line while falling quickly. Surge cycles are counted when the flow drops below half the surge flow; three in 30 s trip the machine.

Numerical checks run in the page

The integrated steady state (RK4) equals the intersection of the compressor curve with the throttle parabola found independently by bisection.
The analytic critical B is verified in the time domain: a small perturbation decays at 0.9 B_crit and grows at 1.1 B_crit.
The damped oscillation period from the integrator equals 2 pi / Im(lambda) of the 2x2 Jacobian.

Honest simplifications

One-dimensional Greitzer model (no rotating stall, no hysteresis, no gas cooling in the recycle loop, constant gas properties); the cubic map and the geometry (U = 280 m/s, A_c = 0.12 m2, L_c = 40 m) are illustrative, not a specific machine; vibration and power are indicative. Educational process-engineering model, not for machine protection design.