Topic

 

Process Control Concepts and Practice

The chemical process industries (CPI) convert natural resources into useful products.  The CPI sectors include pulp & paper, glass, petroleum refining, mineral refining, chemicals, polymers, food, paint, pharmaceuticals, water purification, fragrances, etc. 

Process control differs from many other application domains (such as mechatronics, aerospace, electronic, manufacturing, and distribution), because chemical processes are typically nonlinear, interactive, noisy, have delays, have constraints (associated with safety, loss prevention, and product specifications), and are managed by low cost (low computing power) devices and, typically, by folks at an associate degree level.  Fortunately, the slow dynamics of most processes, another differentiating characteristic, make control manageable.

A journey through the essential and fundamental concepts of automatic control of continuous process, which includes the in-batch control of batch processes, is aimed to provide:

  1. Practice-oriented context and conceptual support for a chemical engineering first course in process control, and
  2. Information for a practitioner needing to independently learn the essentials. 

Texts for college courses typically do an excellent job in deriving equations and exercising mathematical analysis.  But also, typically, texts that support the professor’s preferences of the content for upper-level Chemical Engineering courses, emphasize theory and mathematical analysis, necessarily in an idealized context.  The resources here provide the practicable complementary context and practices, and a hope is that instructors and textbook authors will use the material in this journey to complement their other learning resources.

Excellent sources of such supporting material can be found on web sites:

https://r3eda.com – Russ Rhinehart’s posting on materials and VBA simulators related to control, optimization, regression, steady state detection, and professional development.

https://controlguru.com – Doug Cooper‘s postings on materials and simulators for process control. Now managed by Dennis Nash, president of ControlStation.

https://www.opticontrols.com/ - Jacques Smuts’ postings on materials, book, and simulators for process control.

To come - various postings by Greg McMillan

https://www.aiche.org/community/sites/divisions-forums/computing-systems-technology-division-cast - AIChE’s Computer and Systems Technology Division which posts various newsletter articles and white papers.

https://github.com/A-make/awesome-control-theory - a diverse posting of materials and simulators.

This topic includes the following resources and journeys:

 

 

Tuning PID Controllers

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

Tuning controllers is the procedure for choosing the coefficient values for the P, I and D modes.  It must be simple to execute, fast, and non-disruptive to the operating process.  Heuristic...

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Orifice Calibration

R. Russell Rhinehart
15 min
Intermediate
Article / Blog
Application

The ISO method for orifice design and calibration is grounded in the ideal square-root relation between pressure drop and flow rate, specifies the in-pipe structure for an orifice, and...

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First-Order Filters

R. Russell Rhinehart
Beginner
Article / Blog
Application

Use data filters to temper noise - relation of options to lag and variance reduction

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Interpreting Lines on PFDs and P&IDs

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

Lines on a process flow diagram (PFD) indicate material flow.  In contrast, on a piping and instrument diagram (P&ID), the control overlay for the PFD, the lines represent information flow. ...

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Feedforward Control

Doug Cooper & Allen Houtz
Intermediate
Article / Blog
Application

When a Ratio Control strategy takes action too soon, use Feedforward to temper the dynamics.  When a disturbance can be measured, but would not be a ratio of the control output use...

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Override and Reset Feedback

R. Russell Rhinehart
15 min
Intermediate
Article / Blog
Application

Override (Select, Safety, Switch) control observes an auxiliary variable and takes over from the primary controller when a limit is exceeded.  Reset feedback is a method to prevent the non...

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