Mass Measurement


Coriolis mass flowmeters with ­precision and robustness

June 2015 Mass Measurement

The exact dosing of raw materials and ingredients is crucial to the quality of many end products. In these cases, users attach great importance to the accuracy and repeatability of a Coriolis mass flowmeter. This was the case for the product developer at a testing facility for liquid laundry detergent.

Whether it is delicate wool clothing, football jerseys with grass stains, darks or whites, almost every type of material and stain has its own detergent. In Germany alone, the market for all-purpose detergents is over a billion Euros and climbing. In contrast to the slight decline in the sale of normal powder products and concentrates, liquid laundry detergents have seen double-digit growth. The process of developing a laundry detergent is long and costly and the focus is on testing the effects of different dosages. In the end, an excellent case must be presented to convince discerning consumers to use a new detergent. After all, consumers are set in their ways and that includes the brand of detergent they have always used. This is why all of the details are carefully recorded throughout the expensive testing and development of a new detergent. Especially when it comes to the dosing of reactants, product developers require flow-meters they can rely on absolutely.

The managers of a testing facility for a laundry detergent producer found themselves in just such a situation. For testing purposes, the facility manufactures liquid laundry detergent using different formulas in a liquid mixer with a capacity of one tonne. The proportions of the reactants must be strictly observed when manufacturing new types of detergent. In addition to demineralised water, alkaline lye and caustic lye, malonic acid and other acids and solvents are dosed into the mixer. Previously, the reactants have been added to the mixture sequentially and the level has been measured using a weighing cell. This method was very time-consuming and the mixing result was not always ideal. The developers were looking for a better solution to increase filling speed and accuracy. Because of the required accuracy and repeatability, Krohne recommended the use of Coriolis mass flowmeters to measure the added quantities.

Significant time savings

A total of 11 Optimass 7300 devices ranging in size from DN 15 to DN 40 were installed. The measuring devices feature a single straight measuring tube with no flow divider or internal intrusions. The highly viscous nature of some of the reactants thus posed no problem for the mass flow measurement. As some of the reactants required that the surfaces of the wetted parts feature increased chemical resistance, devices with titanium measuring tubes were used while the rest of the measuring points were equipped with stainless steel measuring tubes. In addition, the detergent producer was impressed with the high accuracy as reflected in the approval according to OIML R 117-1 for mass and volume flow measurement in accuracy class 0.3. A high safety factor with standard pressure rating and optimal PED-certified, explosion-proof housing up to 100 bar offers the operator enhanced safety. The operator of the testing facility provided precise information about the media beforehand so that the devices could be precisely sized and the accuracy could be guaranteed in practice. Remote converters were installed for improved display readability and to save space.

Using a mass flowmeter offers operators several advantages: The reactants can be extremely accurately added to the mixer simultaneously through the ring lines. This saves a lot of time compared to dosing using the weighing scales. The mixer can now be filled in half the time. This makes it available sooner for the next mixture which means that more tests can be conducted in the same period of time. On top of that, thanks to the simultaneous supply, the reactants are distributed even before the stirring device in the mixing tank starts, guaranteeing improved homogeneity of the end product. According to the operators, the relatively high initial investment for the mass flowmeters compared to the weighing cells pays for itself in just a few weeks due to the higher capacity of the mixer alone.

Accurate and sturdy

Meters using the Coriolis measuring principle impress with their extreme accuracy and sturdy design. The technology functions smoothly regardless of external disturbances or installation site. Even with difficult products like highly viscous or inhomogeneous mixtures, Coriolis mass flowmeters measure reliably. Air bubbles, slurries with abrasive solids or fibres and pipeline vibrations have no influence on the accuracy or quality of the measurement. The measuring system is also impervious to changes in the ambient temperature or temperature of the medium. This is thanks to standard calibration at three different temperatures. This process is also described as characterisation, as the behaviour of the devices during changing ambient and process conditions is tested and the coefficients for correction algorithms are determined and set. This process takes place at the fully automated, PC-controlled calibration facilities approved by the United Kingdom Accreditation Service (UKAS) as per EN ISO 17025. The company has three identical gravimetric calibration facilities at sites in England, China and the USA.

For users, extensive calibration translates into installation with practically no limitations: The devices are simply installed as part of the pipeline and can be directly supported on the sensor body. Installation is possible even when there are no straight inlet sections, and the flowmeters are also immune to cross-talk. In other words, two devices can be connected one after the other without influencing each other.

Low pressure loss, easy drainage and ease of cleaning are further arguments in favour of Coriolis straight tube measuring devices.

Optimal adaptation

It is not only in chemical plants that Coriolis mass flowmeters demonstrate their excellence. This type of measuring device is in demand precisely because of its wide range of applications. These devices measure low and high flow rates ranging from 9.5 to 560 000 kg/h. There are different designs available (eg single or twin tube, bent or straight) for selection depending on the measuring task and customer requirements (e.g. extremely high or low flow rates, minimum pressure loss, short installation length etc.). For example, due to the minimal pressure loss of the twin tube device, users can generally select a smaller nominal size of the standard Optimass 1300 device, allowing them to take advantage of the lower cost. There is also a suitable Coriolis measuring device for high-performance applications: The Optimass 7300 features a straight measuring tube in four materials including stainless steel, Hastelloy, Titanium or Tantalum. A Tantalum alloy with 10% Tungsten is used to increase the strength of the measuring tube. This material variant is used in plants where safety is the top priority and where the highest possible chemical resistance is desired for all components.

Another typical field of application for Coriolis mass flowmeters is the measurement of carbon dioxide and they can handle moist gases better than the commonly used thermal mass devices. The Optimass line performs impressively when used in the carbonation of juices, syrups and mixed drinks. This is the only type of device that offers high measuring accuracy regardless of pressure and temperature. This in turn ensures a consistent input of CO2 into the liquid.

In addition to batch and dosing processes, the devices are in demand for the measurement of continuous flows. This application showcases another advantage of this measuring system: In addition to the mass flow, the devices determine other measurements which provide the user with important information for the process including the density, volume flow or the concentration of the medium.

The Optimass 2300 is Krohne’s answer to especially large flow quantities up to 2300 t/h and pressures up to 150 bar. The device was especially designed for the safety and accuracy requirements of the oil and gas industry and is approved for custody transfer. Due to its high measuring accuracy and repeatability as well as its compact size compared to the U-tube devices, the twin straight tube device is also used in the chemical and petrochemical industry as well as in the food and beverage industry. In addition to petrol and oil, it can also be used to measure the mass flow of large quantities of syrup, molasses and other raw materials.

For more information contact John Alexander, Krohne SA, +27 (0)11 314 1391, j.alexander@krohne.com, www.krohne.com



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