Sometimes plants go through a revamp and things just don’t work right. Loops that used to run fine in automatic mode now run in manual mode and require constant attention. I caught up last week with Emerson’s James Beall, a principal process control consultant, whom you may recall from earlier posts.
James shared a great story with me about a recent visit he had to a refinery. Many months ago, they had gone through a crude unit revamp. They were struggling with the operations and it required quite a lot of operator intervention to keep things running. Many of the key crude unit loops were being run in manual because automatic mode was too unstable.
James described it to me as a back-to-basics visit. Working with the operations and plant engineering staff, they discovered quite a number of instrument and tuning problems. One example was a level transmitter that had been improperly configured. James used some of the control performance tools to gather and assess the process dynamics around the level loop.
While performing a bump test on the level loop, the team noticed the level signal responding in the wrong direction. A quick check revealed that the level transmitter calibration had set the transmitter to have reverse action, which prevented the level controller from working. It’s no wonder the operators wisely had put the loop into manual mode to prevent this from happening.
Using a methodical one-by-one process through the critical loops, James helped the team properly tune each loop and discover problems with the surrounding control valves and instruments. All the tuning skills in the world can’t help get a loop to behave properly if the valve is sticking or the transmitter is not performing well. The maintenance staff fixed what they could with their available spare parts and put a plan together for fixing the other problem assets.
Over the course of five days, the team resolved the major issues and smoothed out the operations of the crude unit. James shared with me that this approach helped the operations team regain confidence in the tuning and return the loops into automatic mode. His time spent with the team also was used to share his expertise to help them be able to work through future issues as they arise. In that sense, it was also in-the-field training on process control performance.
I like the quote he shared from one of the operators after the first two days on-site:
My goodness, you fixed more of these problems in two days than has been fixed in the past several months.
James noted that these results were really the result of a great teamwork effort with the plant personnel. Thanks for sharing this great story, James!
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