David W. Spitzer

We operated our reactor for about six months with its catalyst recirculation flowmeter installed backwards. This flowmeter measures the gas flow stream used to transport catalyst to the regenerator and is critical to proper reactor operation and preventing plugging in the recirculation piping. Before you conclude that we are “nuts,” let me explain how this occurred and why it made sense under the circumstances. Bear with me – this may take awhile.

Once upon a time, there was a shutdown. During this shutdown, changes were made to the raw material pipe upstream of the catalyst recirculation flowmeter. The Venturi flow element should not have been touched, and this was “confirmed.” During startup, the operator could not get sufficient recirculation flow – despite having the catalyst recirculation control valve wide open. The operator asked me to investigate because he knew that I had worked on the recirculation control valve.

Examination of the Venturi flow element quickly revealed that it was installed backwards (despite not being touched). In this installation, the Venturi flow element presented the flow stream with a different geometry that caused the pressure drop to be lower than expected at a given flowrate. Even opening the control valve completely could not generate enough differential pressure to obtain 20 percent flow, so the operator suspected a problem. In addition, the reactor system did not have the right “feel” under these conditions because the flow seemed to be approximately double its normal operating flow – even though the flowmeter measured only about 20 percent of flow.

At this stage in the startup, the decision was made to not shut down to reverse the Venturi flow element. To operate the plant, the flow measurement obtained with the control valve open in manual at its normal operating position was used as the setpoint for the flow controller. The reactor operated successfully for about six months with this setpoint.

More next month…

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.