Flow metering gets more fluid

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

By Mike Spear, editor at large

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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 <plus/minus symbol>±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 <plus/minus symbol>± 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.

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