Perry's Chemical Engineers' Platinum Edition

Perry's Chemical Engineers' Platinum Edition

Other Format(7TH BK&CDR)

$225.00

Product Details

ISBN-13: 9780071355407
Publisher: McGraw-Hill Companies, The
Publication date: 07/26/1999
Edition description: 7TH BK&CDR
Pages: 3000
Product dimensions: 8.30(w) x 10.70(h) x 5.08(d)

About the Author

Robert H. Perry (deceased) and Donald W. Green, University of Kansas.

Read an Excerpt

Section 8: Process Control

Benefits of Advanced Control

...The economics of most processes are determined by the steady-state operating conditions. Excursions from these steady-state conditions generally average out and have an insignificant effect on the economics of the process, except when the excursions lead to off-specification products. In order to enhance the economic performance of a process, the steady-state operating conditions must be altered in a manner that leads to more efficient process operation.

The following hierarchy is used for process control:

Level 0: Measurement devices and actuators
Level 1: Regulatory control
Level 2: Supervisory control
Level 3: Production control
Level 4: Information technology
Levels 2, 3, and 4 clearly affect the process economics, as a three levels are directed to optimizing the process in some manner. However, level 0 (measurement devices and actuators) and level 1 (regulatory control) would appear to have no effect on process economics. Their direct effect is indeed minimal, but indirectly, they have a major effect. Basically, these levels provide the foundation for all higher levels. A process cannot be optimized until it can be operate consistently at the prescribed targets. Thus, a high degree of regulatory control must be the first goal of any automation effort. In turn, the measurements and actuators provide the process interface for regulatory control.

For most processes, the optimum operating point is determined by a constraint. The constraint might be a product specification (a product stream can contain no more than 2 percent ethane); violation of this constraint causesoff-specification product. The constraint might be an equipment limit (vessel pressure rating is 300 psig); violation of this constraint causes the equipment protection mechanism (pressure relief device) to activate. As: the penalties are serious, violation of such constraints must be very infrequent.

If the regulatory control system were perfect, the target could be set exactly equal to the constraint (that is, the target for the pressure controller could be set at the vessel relief pressure). However, no regulatory control system is perfect. Therefore, the value specified for the target must be on the safe side of the constraint, thus giving the control system some "elbow room." How much depends on the following:

  1. The performance of the control system (i.e., how effectively it responds to disturbances). The faster the control system reacts to a disturbance, the closer the process can be operated to the constraint.
  2. The magnitude of the disturbances to which the control system must respond. If the magnitude of the major disturbances can be reduced, the process can be operated closer to the constraint.
One measure of the performance of a control system is the variance of the controlled variable from the target. Both improving the control system and reducing the disturbances will lead to a lower variance in the controlled variable.

In a flew applications, improving the control system leads to a reduction in off-specification product and thus improved process economics. However, in most situations, the process is operated sufficiently far from the constraint that very little, if any, off-specification product results from control system deficiencies. Management often places considerable emphasis on avoiding off-specification production, so consequently the target is actually set far more conservatively than it should be.

In most applications, simply improving the control system does not directly lea to improved process economics. Instead, the control system improvement must be accompanied by shifting the target closer to the constraint. There is always a cost of operating a process in a conservative manner. The cost may be a lower production rate, a lower process efficiency, a product giveaway, or otherwise. When management places extreme emphasis on avoiding off-spec production, the natural reaction is to operate very conservatively, thus incurring other costs.

The immediate objective of an advanced control effort is to reduce the variance in an important controlled variable. However, this effort must be coupled with a commitment to adjust the target for this controlled variable so that the process is operated closer to the constraint. In large throughput (commodity) processes, very small shifts in operating targets can lead to large economic returns. ...

Table of Contents

Conversion Factors and Mathematical Symbols.

Physical and Chemical Data.

Mathematics.

Thermodynamics.

Heat and Mass Transfer.

Fluid and Particle Dynamics.

Reaction Kinetics.

Process Control.

Process Economics.

Transport and Storage of Fluids.

Heat Transfer Equipment.

Psychometry, Evaporative Cooing, and Solids Drying.

Distallation.

Gas Absorption and Gas-Liquid System Design.

Liquid-Liquid Extraction Operations and Equipment.

Adsorption and Ion Exchange.

Gas-Solid Operations and Equipment.

Liquid-Solid Operations and Equipment.

Solid-Solid Operations and Equipment.

Size Reduction and Size Enlargement.

Handling of Bulk Solids and Packaging of Solids and Liquids.

Alternative Separation Processes.

Chemical Reactors.

Biochemical Engineering.

Waste Management.

Process Safety.

Energy Resources, Conversion and Utilization.

Materials of Construction.

Process Machinery Devices.

Analysis of Plant Performance.

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Perry's Chemical Engineers' Platinum Edition 4 out of 5 based on 0 ratings. 1 reviews.
Guest More than 1 year ago
For virtually the same price, the Platinum Edition (1999) contains the same printed book plus a CD-rom with everything in it. I would not recommend to buy the CD-alone, you'll get tired of looking a the screen, but having both for the price of the printed copy is a better deal.