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766 Chemical Process Design, Simulation, Optimization, and Operation

(level 3; e.g., the catalytic reforming unit) in the refinery. SEE ALSO THE FOLLOWING ARTICLES
Setpoints for the unit operations (level 4; e.g., distillation)
are determined at this point. The unit operations level de- CERAMICS,CHEMICALPROCESSING OF•HEATEXCHANG-
termines the process flowrates, such as the distillate or re- ERS • MINERAL PROCESSING • PETROLEUM REFINING •
flux flowrates (level 5). These controllers then determine, PHARMACEUTICALS • PLASTICS ENGINEERING • POLY-
for example, the pressure to the control valves to regulate MER PROCESSING • PROCESS CONTROL SYSTEMS • PULP
various flowrates. AND PAPER • TEXTILE ENGINEERING

B. Real-Time Optimization
It should be noted that the optimization problems solved BIBLIOGRAPHY
forlevels2and3begintomergeastheplantwideoptimiza-
tion begins to set targets for the unit operations in many Bequette, B. W. (1998). “Process Dynamics: Modeling, Analysis and
process units. This large-scale, frequent optimization of Simulation,” Prentice Hall, Upper Saddle River, NJ.
Biegler, L. T. (1989). “Chemical process simulation,” Chemical Engi-
operating conditions is known as real-time optimization
neering Progress October, 50–61.
(RTO). RTOs are run approximately every 30 minutes to Biegler, L. T., Grossmann, I. E., and Westerberg, A. W. (1997).
1 hour, with the resulting optimal setpoints downloaded “Systematic Methods of Chemical Process Design,” Prentice Hall,
to model predictive controllers (MPC). Upper Saddle River, NJ.
Douglas, J. M., and Stephanopolous, G. (1995). “Hierarchical ap-
C. Data Reconciliation proaches in conceptual process design: framework and computer-
aided implementation,” In “Foundations of Computer-Aided Process
Another important optimization problem that is solved Design” (L. T. Biegler and M. F. Doherty, eds.), pp. 183–197, AIChE
frequently is data reconciliation. All measurements have Symposium Series, 91(304), New York.
some degree of uncertainty, and the measurements need Edgar, T. F. (2000). “Process information: achieving a unified view,”
Chemical Engineering Progress 96(1), 51–57.
to be reconciled so that the entire set of measurements is
Edgar, T. F., Himmelblau, D. M., and Lasdon, L. S. (2001). “Optimiza-
consistent with plant material and energy balances. This tion of Chemical Processes,” McGraw-Hill, New York.
is particularly useful for monitoring inventories and for Fletcher, R. (2000). “Practical Methods of Optimization,” 2nd ed., Wiley,
improving model predictions used in MPC. Chichester.
Malone, M. F., Trainham, J. A., and Carnahan, B., eds. (2000). “Founda-
D. Vertical Integration of Software tions of Computer-Aided Process Design,” AIChE Symposium Series,
96(323), New York.
and Consulting Firms
Morari, M., and Perkins, J. (1995). “Design for operations,” In “Foun-
Until relatively recently the wide range of process dations of Computer-Aided Process Design” (L. T. Biegler and M. F.
Doherty, eds.), pp. 105–114, AIChE Symposium Series, 91(304), New
systems-related activities was performed by a wide va-
York.
riety of independent design and consulting services firms. Seider, W. D., Brengel, D. D., and Widagdo, S. (1991). “Nonlinear anal-
Simulationsoftwarewasprovidedbyanumberofsoftware ysis in process design,” American Institute of Chemical Engineers
companies, and there were many different software pack- Journal 37(1), 1–38.
ages for particular simulations. Process designs were often Seider, W. D., Seader, J. D., and Lewin, D. R. (1999). “Process Design
Principles,” Wiley, New York.
performed by companies working in specific process areas
Siirola, J. J. (1995). “An industrial perspective on process synthesis,”
(catalytic reforming, etc.). Project engineering firms pro- In “Foundations of Computer-Aided Process Design” (L. T. Biegler
vided more detailed and integrated plant design layout, de- and M. F. Doherty, eds.), pp. 222–233, AIChE Symposium Series,
veloped the overall piping and instrumentation diagrams, 91(304), New York.
and contracted the equipment fabrication, while construc- Westerberg, A. W., Hutchison, H. P., Motard, R. L., and Winter,
P. (1979). “Process Flowsheeting,” Cambridge University Press,
tion companies supervised the construction project. Con-
Cambridge, U.K.
trol and automation consulting firms provided software Wright, S. (1997). “Primal–Dual Interior-Point Methods,” Society for
for control and assisted with process startup. Industrial and Applied Mathematics Philadelphia, PA.
In recent years, however, there has been a vertical in-
tegration of process systems-related engineering services. The following are widely used numerical packages:
Computer software firms have purchased or merged with
control and automation companies and process control ASPEN PLUS—process simulation
consulting firms. It is now becoming feasible to use the AUTO—bifurcation analysis
same software, or have relatively transparent links that al- FLUENT—fluid-flow simulation
low a smooth transition between simulation models for HEXTRAN—heat-exchanger network synthesis
design, data reconciliation, and parameter estimation, on- HYSYS—process simulation
line optimization, and control. PRO/II—process simulation