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Distillation 559
of the control valve. The flow controller is used to open SEE ALSO THE FOLLOWING ARTICLES
or close the control valve in response to differences be-
tween the measured flow rate and the target flow rate (the CHEMICAL THERMODYNAMICS • FLUID DYNAMICS,
flow controller’s set point). The rate of steam flow to the CHEMICAL ENGINEERING • FLUID MIXING • MEM-
reboiler is regulated by measuring the temperature (usu- BRANES,SYNTHETIC • PETROLEUM REFINING
ally with a thermocouple) at a point in the column and
comparing this temperature to the set point of the tem-
perature controller (TC). The rate of flow of the bottoms BIBLIOGRAPHY
product is regulated by measuring the level of liquid in
Billet, R. (1995). “Packed Towers,” VCH, Weinheim.
the column sump and opening or closing a control valve
Kister, H. Z. (1990). “Distillation Operation,” McGraw–Hill, New York.
using a level controller (LC) to keep the level steady and at Kister, H. Z. (1992). “Distillation Design,” McGraw–Hill, New York.
its set point. Similarly, the liquid level in the reflux drum Lockett, M. J. (1986). “Distillation Tray Fundamentals,” Cambridge Uni-
is controlled by regulating the flow of reflux back to the versity Press, Cambridge, U.K.
column. Column pressure is controlled via a pressure con- Luyben, W. L. (1992). “Practical Distillation Control,” Van Nostrand–
Reinhold, New York.
troller (PC) acting on the condenser inlet valve, and the
Seader, J. D., and Henley, E. J. (1998). “Separation Process Principles,”
reflux drum pressure is controlled by a valve in the bypass Wiley, New York.
line around the condenser. Shinskey, F. G. (1984). “Distillation Control for Productivity and Energy
The control scheme described is just one of a wide va- Conservation,” McGraw–Hill, New York.
riety. In the past few years, the art and science of column Stichlmair, J. G., and Fair, J. R. (1998). “Distillation,” Wiley, New York.
Strigle, R. F. (1994). “Packed Tower Design and Applications,” Gulf
control have developed rapidly, and now control system
Pub., Houston, TX.
design tends to be the prerogative of the specialist control Taylor, R., and Krishna, R. (1993). “Multicomponent Mass Transfer,”
engineer. Wiley, New York.