David W. Spitzer

Sound engineering practice and judgment can yield significant operational improvements. I started my career in the mid-1970s in the central engineering department of a major steel company where nothing was “too big.” After about a year of on-the-job training, I was assigned to work on a $400 million expansion. This same expansion would cost well over $1 billion today. Later in my career, when working as the only electrical, instrumentation and utility engineer at an operating chemical company, I could suggest and make changes subject to questioning for reasonableness and achievable benefits. The details of implementation were left for me to decide.

The chemical plant had an extractor, which was a horizontal tank where relatively clean solvent entered at one end of the extractor and an aqueous solution containing the raw product entered at the opposite end. The center section of the extractor contained a rotating mixer that caused the solvent to scavenge the product from the water. Solvent with product and “clean” water exited at opposite end of the extractor.

I was upgrading the instrumentation on this unit when I noticed the existing extractor was controlled using a local pneumatic level controller. Interestingly, the outlet flow of clean water at one end of the extractor was controlled using the interface level on the opposite end of the extractor. This did not seem logical because there was a significant distance between the interface level measurement and the control valve that would cause a relatively long response time.

What would you do if confronted with this application? How would you control the extractor? Remember the existing extractor is installed and operating, but the plant is planning to install an identical refurbished extractor in parallel as part of the upgrade to improve extraction efficiency. The existing extractor will similarly be refurbished afterwards. Send your suggestion/comments/etc. to FlowControl@GrandViewMedia.com.

David W. Spitzer is a regular contributor to Flow Control with more than 35 years of experience in specifying, building, installing, startup, troubleshooting, and teaching process control instrumentation. Mr. Spitzer has written over 10 books and 150 technical articles about instrumentation and process control, including the popular “Consumer Guide” series that compares flowmeters by supplier. Mr. Spitzer is a principal in Spitzer and Boyes LLC, offering engineering, expert witness, development, marketing, and distribution consulting for manufacturing and automation companies. He can be reached at 845 623-1830.