Along with temperature and pressure, flow is fundamental to the operation of any chemical plant. And, as with temperature and pressure, the underlying technologies for measuring this basic parameter are pretty well established. The orifice plate and differential pressure (DP) cell configuration, for instance, has a history almost as old as the chemical industry itself, while even today’s fastest growing technology — Coriolis flow metering — first appeared on the scene some 20 years ago. Most other types of meter routinely used today go back decades: electromagnetic flow meters (magmeters), for example, were introduced in the 1950s, followed around 20 years later by the first ultrasonic devices and vortex shedding meters.
In their own ways, all of these technologies have established themselves in specific applications best suited to their particular measuring principle. But now, with decades of development behind them, the various technologies are being touted to ever widening markets by instrument vendors intent on adding more and more functionality to the fundamental flow meter.
Coriolis bubbles up
Nowhere is this more apparent than in Coriolis flow meters, which should have an annual growth rate of nearly 9% over the next five years according to the ARC Advisory Group, Dedham, Mass. The market leader is Boulder, Colo.-based Micro Motion Division of Emerson Process Management, whose product line business manager, Marc Buttler, points to some recent developments that help explain why Coriolis is in such increasing demand, “We’re currently releasing a new version of our flagship product, the Elite, that has dramatically improved performance on two-phase flow and entrained vapor flow,” he says. (For more about entrainment issues with Coriolis meters, see CP, Nov., p. 42. or visit www.chemicalprocessing.com/articles/2005/583.html) “We’ve done this by making many changes both to the sensor as well as the electronics and software, so by working together they establish a more stable drive under varying entrained air conditions and also filter out undesirable noise resulting from the entrained air condition”
The Elite meters were validated last year by the Gas Research Institute (part of the Gas Technology Institute, Des Plaines, Ill.) for use in natural-gas custody transfer applications, for which Coriolis meters have a distinct advantage due to their ability to measure mass flow directly, notes Paula Haywood, ARC’s field systems analyst. “Supplier efforts to make Coriolis technology more stable and user-friendly are very apparent in the current generation of flow meters,” she says. “Improved digital signal processing techniques have improved performance even in applications with entrained air.”
Eddie Bridges, international product group manager for the Optimass range of Coriolis meters (Figure 2) from Krohne, Peabody, Mass., describes two-phase and multiphase measurement technology as “the hot topic” at the moment in Coriolis. “Most major manufacturers are investing heavily to solve this issue, but up to now the solution has eluded most,” he says. He acknowledges that Foxboro, a part of Invensys Process Systems, Foxboro, Mass., has “achieved some measure of success” with its CFT50 Coriolis transmitter introduced in 2002, while noting that system is not perfect. He does believe, however, the problem will be solved in the near future “as the research in this area is progressing rapidly.”
|Figure 2. Two Coriolis meters undergoing accreditation calibration on one of their maker’s test stands.
The Foxboro solution is essentially one of improved signal processing, rather than any changes to the fundamentals of the measuring tube itself. Joseph Downey, Foxboro’s director of marketing, cites two patents here — one for the high-speed digital signal processing of the CFT50 unit that responds to changing flow conditions much faster than other Coriolis meters, and the other for the two-phase flow detection and compensation itself.
Sizing up opportunities
Multiphase measurement aside, one of the other trends noted by both Bridges and Buttler is the growing demand for ever larger Coriolis meters. Although Krohne only has units up to 3-in. diameter in its range of single straight tube meters, Bridges says the trend to larger sizes is likely to continue as the oil and gas sector switches to Coriolis for custody transfer. Micro Motion’s Buttler agrees: “Our customers in the oil and gas industry have sent a clear message that they would value even larger Coriolis meters, even to the extent of one of them buying four of our largest meters and running them in parallel, rather than buying a single ultrasonic flow meter [of larger diameter] for the same duty.”
Introduced last October at the ISA Show in Chicago, the CM Series Coriolis meters from Fluid Components International (FCI), San Marcos, Calif., typify this trend. While the CMB general purpose models range from 1/8-in. to 3-in. line sizes with maximum flows to 60 metric tons/h, the largest mass-flow and density meters, the CMU units, have brought Coriolis measurement to pipe sizes of 12-in. diameter and flow rates of 2,200 metric tons/h — but still with accuracies of 0.1% to 0.15% for liquids and 0.5% for gas flows. FCI product line manager Sam Kresch says that, because of improvements in tube construction and electronics, the 12-in. model operates at around the same power efficiency as smaller units.
Endress + Hauser, Greenwood, Ind., is another manufacturer extending Coriolis meter sizes. Last year, it launched the Promass F 10-in. (DN250) sensor. Also capable of handling mass flow rates to 2,200 metric tons/h, this instrument offers total mass flow, density and temperature as primary measured variables. By using even its basic electronics, says Andy Capper, flow product manager in Manchester, U.K., you can calculate derived values such as totalized mass, volume flow or standardized volume flow. And the extended electronics functionality offers the possibility of more-complex calculations such as concentration measurement — for example, determining the percentage of solids in a slurry.