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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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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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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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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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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No! Not Laplace Transforms

R. Russell Rhinehart
60 min
Intermediate
Course
Theory

In my 13-year industrial career, I never used Laplace transforms.  However, transfer functions and block diagram notation are efficient methods to describe dynamic behaviors, and are often...

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FOPDT Models from Skyline Inputs

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

The classic textbook method to generate FOPDT models is the reaction curve technique, a pre-computer era technique:  Start from a steady state, make a step and hold in the controller output...

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Understanding P, I, and D

R. Russell Rhinehart
30 min
Intermediate
Article / Blog
Theory

Understanding what the proportional, integral, and derivative terms do within the PID controller is essential to choose appropriate action, trouble shoot controllers, chose appropriate...

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Min IAE Tuning

Jacques Smuts
15 min
Intermediate
Article / Blog
Application

Procedure and Commentary on tuning for minimum Integral of the Absolute Error

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PID Explained

Jacques Smuts
20 min
Beginner
Article / Blog
Theory

A qualitative explanation of P, I, & D actions using graphs.

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Understanding Valve Flow Characteristics

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

The response of flow rate through a control valve depends on the friction losses in the piping in which it is installed as well as the controller signal.  The installed characteristic (a...

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Bumpless Transfer and Tuning

Jacques Smuts
15 min
Intermediate
Article / Blog
Application

Switching from MAN to AUTO mode or LOCAL to CASCADE or changing the controller integral time should not cause a change in the controller output, a bump.  But a primitive coding of the PID...

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PID Controller Variations

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

It is important to understand the variations on the PID algorithm when tuning and when choosing a version that is consistent within your use context.  Unfortunately, there are many names for...

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Cohen-Coon Tuning

Jacques Smuts
15 min
Intermediate
Article / Blog
Application

A procedure and commentary on this tuning approach that includes deadtime.

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