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STEADY UNDER PRESSURE

Andrew W. Sloley

VECO USA, Inc. (current affiliation)
1313 Bay St
Bellingham, WA 98229 360-676-1500

Presented at the
University of Louisiana at Lafayette Graduate Seminar
Lafayette
19 April 2000

Abstract copyright Andrew W. Sloley
2000
All rights reserved

Most distillation control systems, either conventional or advanced, assume that the column operates at a constant pressure. Maintaining constant operation supports stable operation and unit profits. Pressure fluctuations make control more difficult and reduce unit performance. Pressure variations swing column vapor loads and temperature profiles. Using temperature control as a substitute for composition control requires using pressure compensation to maintain desired compositions. Varying pressure changes relative volatilities and affects fractionation performance. Vacuum columns are especially susceptible to this problem. Other, less commonly expected problems, can arise from pressure fluctuations. Pressure drops may also result in a normally single-phase feed to turn into a flashing feed. Having two-phase feed when expecting single phase feed can flood a column .

Effective pressure control prevents column flooding and minimizes compensation requirements for temperature substitution in composition control. Effective pressure control improves advanced control and unit optimization by making running close to the unit's maximum capacity more reliable. While important, few sources have thoroughly examined distillation pressure control systems. The paper major process factors involved in selecting pressure control schemes and examines the major types of column pressure control, their characteristics, and application.

36 pages.
Electronic version available in Adobe Acrobat PDF format file 085.PDF 281k.

Request paper 085.

This page updated 19 January 2005.
© 2005 Andrew W. Sloley. All rights reserved.