Mass market opens for CORIOLIS METERS

Drawing analogies with water running down plugholes, or spinning skipping ropes is all very well, but is the physics of the Coriolis effect really what interests the end-user of flowmeters based on the principle? More likely it is these meters' outstanding ability to give direct readings of mass flowrates for an increasingly wide range of products.

For custody transfer duties, such as in the oil industry or brewing and distilling, single measurements from highly accurate Coriolis meters are proving more cost-effective - and more preferable to the tax and customs and excise authorities - than derivative techniques based on temperature-compensated volume and density values. And in industries such as fine chemicals and pharmaceuticals, high value additives are increasingly being dispensed and dosed through metering systems reliant on Coriolis meters.

So where process economics dictate, Coriolis meters seem the obvious choice for accurate mass flow measurement. But they have not been without their drawbacks: some earlier models were too susceptible to external vibrations; the tubing of others was not robust enough for the intended duty - all factors that raised doubts about reliability.

However, many of these early problems have been successfully tackled by meter manufacturers in recent years. Endress+Hauser, for example, introduced its Promass range in 1995 with a twin-tube design that, by balancing the oscillations of the two tubes, decouples the instrument from external effects such as pipeline vibration and stress. According to E+H's business development manager John Salusbury: `the result is a meter that is mechanically stable and does not require regular re-zeroing, ensuring long-term accuracy and stability - simply, it's a "fit and forget" cost-effective installation.'

SINGLE, STRAIGHT, NO SUPPORT

The Promass meters need no special supports or brackets. As long as the pipework can take the meter's weight, installation is straightforward. E+H has now taken this approach a step further with the introduction of the Promass I. Available in the UK from September, Promass I is a single straight-tubed meter that also features a balancing system to make the meter immune from external vibrations. This patent-pending Torsion Mode Balance (TMB) system again ensures that the meter can be installed directly into the pipeline without any need for extra supports or brackets. The Promass I sensor tube is made of titanium in DN sizes from 8 to 50mm and, like all E+H Coriolis meters, is fitted with a 40bar secondary containment system for chemical and hazardous duties. With no manifolds or other restrictions to flow, the meter can be easily cleaned and drained down, and is even suitable for piggable pipeline systems.

Also new from E+H, available in the UK from July, is a new version of its `flagship' Promass 63 Coriolis meter. The Promass 64, as the new meter is known, features 90 degrees or 180 degrees phase-shifted dual pulse outputs, hazardous area Ex d options with IS outputs, and tamper-proof software and cases. More importantly, however, is its independent evaluation by the German PTB and the Dutch NMI - effectively certifying it for custody transfer duties. This means that a Promass 64 user can dynamically weigh product into containers, for sale by weight. Similar approval from the UK national weights and measures agency is expected later in the year.

The increasing acceptance of Coriolis metering is clear from the very wide ranges of flowmeters now available. Fisher-Rosemount Flow, for instance, has recently announced a new low-flow Micro Motion meter capable of measuring mass flow, and density, of gases and liquids down to flowrates of 100g/h over temperatures from -200 degrees to 204 degreesC.

Part of Micro Motion's Elite family, the new CMF010 operates in the low-flow market for rates up to 108kg/h, offering an accuracy of +/-0.1 per cent for liquids and +/-0.5 per cent for gases. This is also a single tube design, said to incorporate features making it immune to line vibrations.

Difficult chemical dosing applications at pressures of up to 900bar are within the capability of the new Rheonik Coriolis meter, according to UK agent Allison Engineering. Welded Grayloc hubs are used as part of a high pressure clamping system and the complete assembly is IS certified EEx ia IIC.

Also available to EEx ia IIC certification are the self-draining, single pipe Massflo Coriolis meters from Danfoss. Designed for corrosive, high pressure applications, the DN1.5-40 Massflo units can measure up to 52 000kg/h with an accuracy of +/-0.15 per cent.