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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.
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