|By David W. Spitzer, P.E.|
When Coriolis mass flowmeters were first introduced, piping vibration was a prominent issue. To capitalize on the ability of this flowmeter technology to measure mass flow, users would install Coriolis systems on rigid supports. One rule-of-thumb was to mount them on metal plates that corresponded to the size of the piping. For flowmeters over one inch in size, installing them on a concrete foundation was more practical, assuming that the flowmeter was located near grade.
Over the years, design enhancements have relaxed the mounting requirements for many Coriolis mass flowmeters. Some such flowmeters can be mounted in piping using “good piping practices,” including the proper alignment of the mating flanges.
On the process side, enhancements have allowed Coriolis mass flowmeters to expand from their “liquid only” measurement roots to include the measurement of liquid density and, subsequently, gas flow measurement. It was commonly accepted that as long as the flowing stream was homogeneous and did not stall the tubes, the Coriolis mass flowmeter would measure accurately.
Some manufacturers of Coriolis mass flowmeters have taken this technology one step farther to include flow and density measurements of two-phase liquid/gas streams. By sensing the two-phase condition, this Coriolis mass flowmeter controls tube vibration to prevent the tubes from stalling. Proprietary signal processing algorithms are used to measure the mass flow rate and density of the two-phase fluid. Therefore, this enhancement is a result of improved electronics connected to a flowmeter with the same hydraulic design.
The extension of Coriolis mass flow technology to include the mass flow and density of two-phase flow streams is of interest, but perhaps more interesting is how many of these applications may already be installed and operating “satisfactorily.”
The next time you are at a technical exhibition, make a point to visit booths that have flowing liquid streams as part of the exhibit. The point of the flowing stream could be to show the operation of a flowmeter, a level control, a pH probe, a pump, or perhaps a valve. The point of the exhibit really does not matter, but the piping will often be constructed of clear plastic or contain sections of clear plastic. Careful observation of the flowing liquid will often reveal flowing gas bubbles in the liquid, even though the equipment is installed in a manner in which it would seem that they should not be present. This would imply that many existing liquid Coriolis mass flowmeter installations may operate with some gas, and hence contain two phases.
A panel discussion about difficult Coriolis mass flowmeter applications was held at the ISA Show in Houston. Represented on the panel were two users of Coriolis mass flowmeters, two Coriolis mass flowmeter manufacturers, and the manufacturer of an instrument that can measure two-phase flow. Interestingly, much of the audience consisted of interested parties from various other Coriolis mass flowmeter manufacturers.
Implied in the discussions was that Coriolis mass flowmeters operating with gas in the liquid stream are not accurate. Implicit lines were drawn between the manufacturer who could measure two-phase flow and those that could not. The users on the panel generally favored the Coriolis mass flowmeter that could measure two-phase flow, especially when two-phase flow was desired or when an existing installation did not work because of an unanticipated two-phase flow condition.
The point of the discussion was that users are now able to purchase a Coriolis mass flowmeter that now has fewer restrictions on its installation orientation (many existing designs already better meet this criteria), and has fewer restrictions on the states of the fluid flowing through the flowmeter. In addition, many existing installations can be “fixed” by installing new electronics.
Test data was notably absent from the discussions. Claims and counter-claims resonated back and forth during the panel discussion and in subsequent discussions. Both sides have made seemingly contradictory claims, but to my knowledge, neither has published test data. What is the user to do?
About the Author
David W. Spitzer, P.E., is a regular contributor to Flow Control. He has more than 25 years of experience in specifying, building, installing, start-up, and troubleshooting process control instrumentation. He has developed and taught seminars for almost 20 years and is a member of ISA and belongs to ASME MFC and ISO TC30 committees. Mr. Spitzer has published a number of books concerning the application and use of fluid handling technology, including the popular The Consumer Guide to… series, which compares flowmeters by supplier. Mr. Spitzer is currently a principal in Spitzer and Boyes LLC, offering engineering, product development, marketing, and distribution consulting for manufacturing and automation companies. He can be reached ar 845 623-1830.
For More Information: www.spitzerandboyes.com