A sound approach
How to choose and use ultrasonic flowmeters

Fluid flow measurement using ultrasound has a whole string of advantages in theory. In practice, measurement company Krohne has played a big part in establishing this measurement principle in real industrial applications.

The UFM 3030 three-beam ultrasonic flowmeter from Krohne sets the standard in a wide range of applications. Wherever electromagnetic flowmeters reach their limits, the UFM 3030 with its three ultrasound beams, innovative electronics and digital signal processing provides stable and dependable results. The three measuring paths of the UFM 3030 generate a three-dimensional cross-section of the flow profile within the liquid, making measurements largely independent of the flow profile.

Krohne is a true pioneer in this field, with more than 25 years of experience in ultrasonic flow measurement and having played a decisive role in the standardization of applications in chemical plants, refineries and other industrial processes. The UFM 3030 offers all the advantages of process flow measurement using ultrasound, with measurements that are independent of conductivity, viscosity, temperature, density and pressure. The sensor has smooth surfaces inside and out, with no elements protruding into the flow, and there are no moving parts to wear out. As a result, pressure drop is low, periodic recalibration is unnecessary, and maintenance is minimal.
Calibration and accuracy
UFM 3030 flowmeters are available in sizes from DN 25 to DN 3000, with corresponding flowrates of 1–40,000 m3/h. Every flowmeter is wet-calibrated; in the case of DN 150 and larger flowmeters this is done on the world’s largest and most accurate production calibration rig, with a measurement uncertainty of less than ±0.03 percent of the measured value. Before delivery, all signal converters are also tested over several temperature cycles from –20 °C to +60 °C, powered up and with a simulated flow signal, and the results documented. This increases reliability in the field and helps ensure that the flowmeter will deliver its rated accuracy when installed out of doors, whatever the weather or the time of year.
The UFM 3030 is a universal device for in-line flow measurement of liquids with properties that can range from easy to difficult. For example, liquids with low or zero conductivity, such as demineralized water and hydrocarbons, are beyond the scope of electromagnetic flowmeters yet are ideal for ultrasonic measurement. In the energy sector, hot water is problematic for electromagnetic flowmeters because it causes magnetite to form in the pipelines. Because ultrasonic flowmeters are not affected by magnetite deposits, they are ideal for this application. The UFM 3030 is also used on liquids including sulfuric acid, sodium hydroxide solution, sulfur, chlorine, and organic substances from liquefied gases through to bitumen.
Difficult cases
Liquid sulfur is one of the most difficult products to measure. A crystalline substance at room temperature, it melts at 112 °C yet becomes highly viscous above 150 °C, and has low electrical conductivity. The tendency to freeze in pipelines, especially in dead spots, makes flow measurement difficult and can require frequent maintenance to remove solidified material. Dutch chemical company DSM used to use electromagnetic flowmeters for molten sulfur, but had trouble with pipe blockages and low conductivity. The high-temperature version of the Krohne UFM 3030 solved both problems, thanks to a heating jacket that allows operation at temperatures up to 220 °C. The system has worked reliably since start-up, and DSM is well pleased with its performance.
In the petrochemical industry, ultrasound is often the only way to measure the flow of products with low or zero conductivity, and it also works well for products that are considered difficult for reasons of viscosity or density. The Italian company Polimeri EU, a joint venture between EniChem and Union Carbide, needed to measure just such a difficult product at its factory in Ravenna. Polimeri EU produces polyethylene, olefins, aromatic hydrocarbons and elastomers.
This particular application was for a polymer-based flocculant that is suspended in water or toluene. The electrodes of the electromagnetic flowmeters previously used had to be cleaned every week to remove deposits that made it impossible to obtain accurate or reliable measurements. UFM 3030 ultrasonic flowmeters chosen to replace the electromagnetic flowmeters remained deposit-free, so measurements are now accurate and the only maintenance work needed is carried out during the routine annual plant shutdown.
Deionized water is used in many applications, yet it cannot be measured by electromagnetic flowmeters because of its virtually zero conductivity. Deltius, a utility company and provider of environmental services, produces demineralized water for various industrial customers on the former Hoechst site in Vlissingen/Netherlands. Production capacity is 90 m3/h, and the demineralized water is used for process applications and as boiler feedwater. Deltius previously used mechanical flowmeters to measure demineralized water flows, but wear had caused these to become inaccurate.
To replace the mechanical flowmeters Deltius chose a UFM 3030 in DN 125 size, which provides a standard accuracy of ±0.5 percent. This application is unusual because Deltius’s customers agreed to accept the readings of the UFM 3030 as the basis for billing, even though the flowmeter was not designed for this purpose. Krohne’s standard offering for custody transfer purposes would be the Altosonic III flowmeter.
Rapid payback
The rapid payback that ultrasonic flowmeters can provide was demonstrated at lubricants manufacturer RS Clare of Liverpool/UK. The company considered the issue of flow measurement as part of a more general project to increase efficiency and reduce costs. Previously, RS Clare used impeller-type flowmeters to measure the volumes of mineral oil and other substances added to batches of grease, but these devices were not sufficiently accurate and in any case were unsuitable for the high viscosities involved. This was a problem, because the quantities of additives are critical to the viscosity of the final product, which is a key parameter in quality control. To replace the impeller flowmeters RS Clare chose the UFM 3030, using the instrument’s new batching function to close the inlet valve as soon as the correct quantity of additive has been metered. The UFM 3030s have performed well, and the company has also installed Krohne’s Optimass Coriolis flowmeters.
Difficult applications like these have helped open up the market for ultrasonic flowmeters. With the UFM 3030, Krohne can now offer a standard solution for applications in the most varied industries: unaffected by corrosive and abrasive products; independent of conductivity, viscosity, temperature, density and pressure; no flow obstructions, for low pressure drop; suitable for difficult products and high flowrates; accurate, thanks to its three-beam design; reliable, maintenance-free and low-cost.