«

»

Oct
09

How Process Control Education Should be Changed in the Universities

Professor Tom Edgar of the University of Texas and Joseph Alford from Eli Lilly and Co. have been collecting data and opinions regarding the current syllabus of the typical undergraduate Chemical Engineering Process Control Course and its relevance to the skills and knowledge needed in today’s industrial process control environment. An upcoming issue of Intech magazine will have an article by Edgar on how process control education in the universities should be changed. There will be replies from a key group of professors and practitioners. My contribution is the first 250 words of the following:

Terry Tolliver and I have taught a course on dynamic modeling and control at Washington University (WU) in Saint Louis since 2002 that is a requirement for a degree in chemical engineering. The course uses an industrial virtual plant and the ISA book Advanced Control Unleashed. The students are very computer literate and pick up on the use of industrial software from just a few screen prints put into the laboratory exercises. The knowledge gained is generally applicable since the function blocks are based on Foundation Fieldbus used in millions of devices and by over a hundred manufacturers. The configuration environment is also consistent with the international standard IEC 61804. The students learn how to intelligently discuss and use an industrial process simulation, DCS, and data historian that form a virtual plant on their desk. There is companion course taught by Bob Heider where an actual hardware version of the same DCS is used to control the temperature, pressure, and level of vessels in a hardware lab. The three professors have a total of more than 100 years experience in industry.

Most of the chapters in Advanced Control Unleashed start with an introductory section on “Practice,” continues with sections on “Opportunity Assessment” and “Application” and concludes with “Theory”. The strategy is to provide the relevance and practical considerations before getting into the theory that offers a deeper understanding. For example, in Chapter 2 – “Setting the Foundation”, the student gets an overview and perspective, list of opportunities, examples, application detail, and rules of thumb before getting into the theory where the focus turns to the set up of the differential equations for the material and energy balances to enable the student to learn the source of process time constants and gains in terms of process parameters. The students are not asked to solve or integrate these equations. Instead, the students graphically create a dynamic simulation of processes for unit operations commonly encountered on the job. Blocks for filters, dead times, noise, periodic disturbances, and backlash and sticktion are added to make the challenge of process control more realistic. Additionally the students configure an actual control system that can be downloaded into a real DCS. The students apply industrial embedded tools for auto tuning, statistical analysis, and model predictive control (MPC). The course centers on time response because this is what they see on the trend charts in the control room but there is a session to show how to go from the time domain to the frequency domain.

When I recently went back to WU and gave a guest lecture on the use of PID and MPC for fed-batch control of a fermenter, a student asked “what is a batch?” I knew that students were taught to think in terms of a steady state and the material and energy balances on a Process Flow Diagram (PFD) for continuous operations but I didn’t fully realize the implications until the question.

I have had chemical engineers in industry ask, why do you need a PID or MPC when you can just set the flow shown on the PFD? In fact, the batch sequences defined by process engineers today often try to set a predetermined step sequence of flows instead of using feedback control to sort it out. I have also have had experienced instrument engineers ask why do you need a Coriolis density measurement when the composition is constant as shown on the PFD? I also see ads for pressure and temperature compensated differential pressure orifice meters that claim to offer an unqualified mass flow measurement. If only the composition in all the pipelines were constant. This would sure make life easy. Product quality would be a non issue. Obviously the importance of dynamics and disturbances for process measurement and control is often missing in action.

In a batch process, the product concentration follows a profile. In some case there is also a temperature profile and in almost every case where a PID or MPC is used, the transfer of variability for a constant set point means there is a profile in the controller output. This understanding is lacking when chemical engineers are taught to think steady state. The lessons from batch would also be useful for the automated startups and grade transitions in continuous operations.

To add a bit of levity, I offer the following Top Ten List:

Top Ten Reasons Why an ISA Book on Control is not a University Text

10. Costs less than $100

9. The authors spent too much time in industry

8. Contains top ten lists and cartoons

7. Shows flow sensors upstream instead of downstream of the control valve

6. Discusses stick-slip and backlash

5. Shows unmeasured load upsets as inputs to the process

4. Includes field implementation considerations

3. Estimates tuning settings to just two significant digits

2. Doesn’t use tensor analysis for flow loops

1. Depicts signal lines as electronic instead of the pneumatic