Ew. Jacobsen et S. Skogestad, MULTIPLE STEADY-STATES AND INSTABILITY IN DISTILLATION - IMPLICATIONSFOR OPERATION AND CONTROL, Industrial & engineering chemistry research, 34(12), 1995, pp. 4395-4405
The fact that distillation columns, even in the ideal binary case, may
display multiple steady states and unstable operating points has only
recently been recognized. This article addresses some implications of
these phenomena for the operation and control of distillation columns
. Under manual operation, the multiplicity and instability will result
in inability to reach separations corresponding to unstable operating
points and may furthermore cause abrupt changes and hysteresis in ope
rating conditions. It is shown that an unstable operating point may be
stabilized by feedback control of a single product composition or tra
y temperature (one-point control). The steady-state multiplicity does,
in this case, not represent any severe limitation in operation, but i
f the control is not sufficiently tight, the column may settle in sust
ained oscillations (stable limit cycle). Finally, the impact of open-l
oop instability on the achievable closed-loop performance with both pr
oduct compositions under feedback control is discussed.