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Flow metering gets more fluid

Jan. 9, 2006
There are more and more funcationalities being added to your most trusted instrumentation. These established technologies have expand their reach and performance.

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.”

Accuracy assured
Figure 2. Two Coriolis meters undergoing accreditation calibration on one of their maker’s test stands.
Source: Krohne 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.

However, not all Coriolis developments are at the heavy end of the measuring spectrum. Endress + Hauser recently supplied six of its Promass 83A units to Tyco Healthcare, Gosport, U.K., for an application that needed a flow meter capable of measuring acetone flow rates as low as 0.75 ml/min —  quite literally drop by drop, but well within the capability of an instrument that can measure as little as 100 g/h.

Even lower flow rates are featured in the Coriflow range of devices from Bronkhorst High-Tech, Ruurlo, the Netherlands, which this month launches its subsidiary Bronkhorst USA in Bethlehem, Pa. According to Andy Mangell, managing director of Bronkhorst UK, Cambridge, U.K., the company’s main area of interest is “very much low flow,” even down to 6 g/h. Flow rates aside, though, Bronkhorst differs from other Coriolis vendors in being concerned more with flow control than flow metering. “Our strength is in manufacturing mass flow controllers,” says Mangell, “rather than just flow meters. We integrate the meters with either our own or other manufacturers’ valves, and can control pumps directly from the controller with its own integral PID [proportional/integral/derivative] electronics, over most networking buses.”

An advantage of having flow control so tightly integrated with flow measurement, in Mangell’s view, is that you can get a very much faster step change when you want to alter the flow rate — around 15-20 ms, he says, compared with the few seconds that it might take via a conventional control loop through a distributed control system. Such speed of switching comes into its own in dosing applications in high value operations such as for some pharmaceuticals where a tight cut-off of the dosed additive can be very important. “You can lose a lot of valuable material in a few seconds,” he stresses.

In addition to the opening of its U.S. facility, Bronkhorst (whose products were previously licensed through Porter Instruments, Hatfield, Pa.) looks set for a busy year with six new products, including “a first for the Coriolis field,” claims Mangell, expected to be announced by June.

Sound progress
Clearly, Coriolis is on something of a roll, but longer established ultrasonic flow metering is not far behind in terms of expected growth. Again thanks to burgeoning interest from the oil and gas sector for custody transfer applications, ARC’s forecast for this market was for a compound annual growth rate of 7.9% through to 2008, ramping the business up to be worth near $600 million worldwide, compared with the $617 million forecast for Coriolis.

The custody transfer market has boomed largely on the back of the introduction in the 1990s of transit-time ultrasonic technology, which offers higher accuracies than achievable with the earlier pulse Doppler-based meters. While both have the same non-invasive attributes, there has in the past been something of a trade-off between the two techniques — the one offering high accuracy from multi-beam instruments (though at a relatively high cost), the other easier installation but less reliable measurements.

Last year, however, Fuji Electric, Saddle Brook, N.J., introduced what it describes as “the best of both worlds” in the form of the Duosonics ultrasonic flow meter. This clamp-on hybrid meter automatically switches between pulse Doppler and transit-time technologies depending on the fluid conditions in the pipe — and claims accuracies of ±1.0% for both on pipe sizes up to 1,000 mm. Toshihiro Yamamoto, Fuji’s senior manager for instrument R&D, explains: “Transit-time meters offer relatively high accuracy, but are not suitable for liquids containing a lot of bubbles and/or particles. Doppler meters, however, rely on bubbles and/or particles to act as reflectors of the ultrasonic pulses transmitted into the liquid — but they are only accurate to around ± 3 to 5%.” The Duosonic’s built-in algorithm automatically detects the optimum method for the prevailing flow velocity or the number of reflectors, switching from one to the other accordingly.

Bringing ultrasonics well and truly into the 21st century late last year was Sierra Instruments, Monterey, Calif., with the launch of its Innova-Sonic line, which includes a portable model that features a Bluetooth wireless PDA interface. All the Innova-Sonic units are transit-time instruments principally designed for clean liquid applications (though tolerant of the small amounts of bubbles or suspended solids found in most industrial applications, says product manager Scott Rouse).

Another clamp-on device making its mark recently is the Sonartrac VF-100 system from CiDRA, Wallingford, Conn. Although very much acoustic-based, the Sonartrac is not an ultrasonic meter in the conventional sense. Rather, it uses a patented sonar processing technology to listen to, and interpret, very low frequency acoustic fields generated by pipe flows — a passive approach which the company says enables the system to measure single and multiphase flows, as well as slurries, with the same level of accuracy (±0.5%) and performance.

Magnetic attraction
After Coriolis and ultrasonic, the other technology continuing to grow in popularity is the magnetic flow meter. Magmeters have been making inroads into the market for traditional technologies, such as DP, positive displacement and turbine meters, for some time now. According to industry analyst Jesse Yoder, president of Flow Research, Wakefield, Mass., sales are expected to grow at 5.1% per annum through to 2009, when they reach $910 million worldwide. Geographically, though, Europe remains the strongest market, at 41% of the total or nearly twice that of North America. Considering that three of the top suppliers of magmeters — Endress + Hauser, Krohne and ABB — are based in Europe, that is not too surprising, nor is the fact that many new developments are coming out of those companies’ R&D labs.

Krohne, for example, will be launching later this year (probably at either the Interkama or Achema shows in Germany) a new version of its Optiflux magmeter electronics that will feature “a virtual reference”, says Hans Windgassen, product business manager in Dordrecht, the Netherlands. “This option abolishes the need for grounding in most applications,” he explains, “and can save on installation costs.” And cutting installation and running costs even more will be a new battery-powered meter, with a battery life of up to six years, that should be of interest for remote installations, especially in water and wastewater pipelines.

In common with many other suppliers of flow meters— of all different types, not just magmeters —  Krohne has been concentrating much of its development work on the electronics side of the instruments. For example, Windgassen says the inclusion of a conductivity measurement circuit, now offered as a standard feature, has generated positive reactions from users. “Not so much that people wanted to measure conductivity itself,” he points out, “but more that they can now derive a lot of information on the product, or on the process conditions, or even on safety aspects such as whether or not a pipe has been adequately purged.”

Similarly, ABB Instrumentation, Rochester, N.Y., recently expanded its range of magmeters with the Parti-Mag II, which features improved sensor and microprocessor technology to give greater accuracy on partially full pipeline applications (Figure 3). The better signal quality eliminates the need for the instrument’s converter to be routinely reset to zero to ensure continued accuracy.
Although manufacturers have always looked to improve the performance and accuracy of their meters, Bret Shanahan, Chanhassen, Minn.-based marketing vice-president for vortex and magnetic meters at Emerson, sees the main growth coming from suppliers offering comprehensive solutions with their meters. An example of this, he says, is the temperature compensation now available with vortex meters to add multivariable capabilities.

More than a partial solution
Figure 3. The Parti-Mag II features improved sensor and microprocessor technology to provide greater accuracy on partially full pipelines.
Source: ABB More generally, he also cites the rapidly growing interest in on-line diagnostics and asset management solutions. “There’s almost a craving for more information from in-line meters,” he says. “In magmeters, for example, we’ve found that by having a grounding wiring diagnostic facility, we can accelerate users’ start-up times.” Another diagnostic feature recently added to the company’s magmeters is one for detecting high process noise — a condition that can upset meter readings but one that can be mitigated by changing coil drive frequency, if only the user knows about the problem in the first place.So, while the fundamentals of flow meters might not have changed much over the years, their functionality certainly has, adding value all the way down the line.

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