In the world of process control, when Cecil Smith speaks people listen. He is president of Cecil L. Smith, Inc., Houston, a firm specializing in automation technology that he founded after leaving the faculty of Louisiana State University. Cited as one of the 50 most influential people in the field by the International Society of Automation’s Intech magazine, he teaches courses on control topics and has authored or co-authored 14 books, including "Digital Control of Industrial Processes,” and more than 100 articles. Among his contributions to CP is a four-part series on level control: “Neglect Level Control at Your Peril,” “Be Levelheaded about Surge-Tank Control,” “Avoid Vessel Level Trips,” and “Control Level with a Cascade.” Additionally, he is one of our experts in our Ask the Experts forum.
[pullquote]
And when Cecil Smith says he’d like to create a video series to help Chemical Processing readers master off-gas processes, you should jump at the chance to scoop up that valuable content (you can view the videos at ChemicalProcessing.com/cp-videos). In all, there are 21 short videos narrated by Smith, starting with an introduction to the off-gas process. The simplicity and generic nature of the off-gas process make it an excellent example of a multivariable process control application, he stresses.
“The videos describe proceeding from a non-performing single-loop configuration to one that not only delivers the required performance, but addresses the various issues required for the control configuration to be usable in practice,” says Smith.
[javascriptSnippet ]
He also notes that the videos explain the deficiencies of a proposed single-loop configuration. An understanding of these deficiencies from the process perspective provides the basis for modifying and enhancing the control configuration to obtain one that delivers the required performance. “But stopping here is premature,” Smith adds. “Additional issues must be addressed to obtain a configuration that is usable in practice. The option for manual control is an absolute must. Provision must be made for an operator to assume manual control of any final control element, preferably without seriously degrading the control logic for the remaining final control elements. The videos present a comprehensive treatment of developing the control configuration for the off-gas process.”
Smith made the videos as part of his ongoing campaign to promote two observations. First, in the practice of process control, the overriding principle is that you have to understand the process. “Process types, and specifically chemical engineers, do this far better than anyone else,” says Smith. The second pertains to the “s” variable and LaPlace transforms. “I started with the view that those in process control ‘just had to know this stuff.’ I then evolved to ‘just understand the notation,’ the basis being that LaPlace expressions appear in manuals on process control systems. I have now concluded that LaPlace has absolutely no role in the practice of process control.”
Here is a list of videos in the series (chemicalprocessing.com/cp-videos):
• Introduction Of Off-Gas Process
• Single-Loop Control Configuration for Off-Gas Process
• Tuning the Hot Air Loops
• Tuning the Bag House Inlet Temperature Loop
• Tuning the Scrubber Duct Inlet Temperature Loop
• Understanding the Behavior of the Off-Gas Process
• Interaction in the Single-Loop Configuration
• Alternate Control Configuration for Off-Gas Process
• Ratioing Fresh Air and Fuel Flow to Furnace
• Characterization Function for Implementing Ratio Control
• Configuration Issues for PID Blocks in Alternate Control Configuration
• Commissioning the Ratio Controls for Fresh Air and Fuel Flow
• Controls for Hot Air Dampers in Alternate Control Configuration
• Commissioning the Alternate Control Configuration
• Analysis of Performance of Alternate Control Configuration
• Providing Capability for Manual Control
• Using Output Tracking for Bumpless Transfer from Manual to Automatic
• Output Tracking for the Hot Air Temperature Controller
• Output Tracking for the Hot Air Dampers
• Integral Tracking for the Hot Air Temperature Controller
• Integral Tracking for the Hot Air Dampers
