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The single straight tube Coriolis flowmeter design offers considerableadvantages over mass flowmeters with curved or twin tube layouts. Curved-tube, ring-tube and twin-tube layouts with flow dividers have proved to be unreliable in many applications where Coriolis flowmeters arespecified.
In twin-tube instruments, viscous, non-Newton, shear sensitive media and fluids containing solids can cause high pressure losses. Abrasive media wear down flow dividers and pipe bends. Palmoil, cellulose and other materials containing fibre can accumulate inthe flow divider and cause blockages.
The principle advantagesof the straight tube design are: lower pressure losses; less abrasionwear; qualified for high flow volumes; wide measuring range; no blockage risk. Straight-tube meters are also easy to clean, self draining and suitable for measuring high-viscosity media. These are just some ofthe advantages of a short measuring tube with a large inner diameter.
Krohne's Optimass Coriolis mass flowmeter was the first of itskind to incorporate a single straight tube design. It incorporates a patented AST® (adaptive sensor technology) design, which ensures stableoperation under varying process conditions. The instrument is manufactured from materials that conform to Food and Drug Administration (FDA) guidelines and complies with EHEDG (European Hygienic Engineering &Design Group) and 3A standards. It is available with a wide range of industry standard hygienic process connectors which makes it ideally suited for use in food applications.
Making chocolate
Specialist chocolate manufacturer Classic Couverture Ltd in Liverpool has installed three Krohne Optimass Coriolis mass flowmeters to improve the measurement accuracy of ingredients during the production of its products.
The Optimass flowmeters measure precisely the amount of ingredients added during the manufacture of chocolate products produced for the confectionery industry. Accuracy is of paramount importance in maintaining the high level of quality control needed to produce chocolate to the highest standard. Three flowmeters have been installed to control critical ingredients, some of which have a high viscosity. EachOptimass is of hygienic design and incorporates a stainless steel hotwater jacket. This ensures that the ingredients being fed through theinstrument are maintained at the optimum temperature for manufacture.
The Optimass flowmeters replaced less accurate metering methods. The instruments are capable of measuring to an accuracy of ± 0.1 percent of actual measured flow rate. "We invested in Krohne's Optimassflowmeters to improve measurement accuracy of ingredients to give us better control in maintaining quality standards," said John Greenhalgh,consultant at Classic Couverture. Signals from the flowmeters are processed through a programmable controller as part of the automated plant control system.
"We found the Optimass particularly easy to install and commission," continued John. "Configuration is straight-forward and may be carried out with a magnet from the outside as an alternative to having to open the electronics housing to press buttons."
Fruit processing
The measurement range and low pressure differential of the Optimass has enabled a leading American fruit processorto almost halve the number of flowmeters it expected to install as part of an upgrade of its plant in California.
While planning theupgrade the fruit processor investigated the options available for accurately measuring the flow of bulk concentrates used in the manufacture of its products. Because the flow rate of the concentrate can vary substantially during production, the best solution presented from the company's previous supplier was to install two flowmeters for each production process; one to measure low and the other high flow rates.
As well as almost doubling the number of instruments needed—when compared to the original mechanical meters used—it was found that this solution also introduced production problems. Each instrument containedtwo 12mm tubes which introduced a significant pressure drop and restricted the flow of the concentrate. Krohne proposed using its Optimass7000 flowmeter for two reasons. First, because the straight-tube design does not impede the flow of substances passing through it. And secondly, the instrument has a broad measurement spectrum, which ranges from 0.3 to 560,000 kg/h. This meant that only one flowmeter was needed for each production process.
The fruit processor has already purchased 19 Optimass flowmeters and will be standardising on them throughout its plant. They are used to accurately measure the flow of bulk concentrates, including sucrose, corn syrups, and high fructose into mixing vessels.
A signal output from the Optimass is fed to a PLCwhich controls the flow of concentrate into the mixing process. Thisenables the fruit producer to manufacture bulk product to precisely the desired Brix. During a second phase the blended concentrate is diluted with water and placed into a container with fruit. During initial trials of the Optimass, engineers working for the fruit processor foundthat because the pressure differential was much less than the units that had previously been installed, they could use a smaller instrumentthan they had envisaged. This also enabled the company to further reduce costs.
Flow at high viscosities
A Swiss chemical companyuses the Optimass for batching various media into a fluid mixer. In the past the company dosed the reactants, one after the other, using aweighing cell in the mixer. Now it is possible to feed multiple reactants at the same time through ring pipelines to the mixer. The new process saves time and eliminates unnecessary measuring errors.
For the chemical company there are other advantages in using the Optimass flowmeter. The straight tube construction means that the instrumentis not influenced by the very high viscosity levels found in this particular application. The straight tube design also means that there areno pressure losses. The measurement accuracy of the flowmeter is considerably below one per cent.
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