Coriolis flow meters

Coriolis flow meters are characterised by their high accuracy and wide range of applications. They measure unaffected by temperature and process pressure or by changes in viscosity and density. In addition, they do not require straight inlet and outlet runs or an undisturbed flow profile. In contrast to the measuring methods of other flow technologies, which determine the volume flow rate via the flow velocity, mass flow meters measure the mass directly and also determine the density of a medium via the resonance frequency. Measuring devices for mass flow also have integrated temperature measurement. This makes them multivariable measuring devices for many standard applications and demanding areas of use.

Coriolis flow meters cover a wide range of process applications - from standard applications to highly demanding applications in many industries.

Typical areas of application are

• Chemical industry : Measurement of chemicals such as acids, alkalis, bleaching agents, dyes, chlorine and sulphur compounds

• Oil & gas : dosing, loading and unloading of hydrocarbons, measurement of cryogenic media such as LNG

• Marine: Bunkering, consumption and emission measurement of marine fuels such as diesel, marine gas oil and others

• Food & pharma : Hygienic applications for milk, chocolate, jam, ice cream; solvent extracts, ultrapure water, etc.

• Media containing solids and media with high viscosity : bitumen, fats, oils, sludge, dough, honey, syrup, molasses, pulp, spinach, minced meat, plant-based foods, pet food

• Gases : hydrogen, CO₂, supercritical gases

• Concentration measurements : alcohol in spirits production, fructose, sewage sludge, etc.

• Extreme conditions : high and low temperature ranges (-200...+400°C), liquids with gas entrainment of up to 100

• Safety & custody transfer applications : Safety Instrumented Systems (SIS), custody transfer (according to MID, OIML, AGA, etc.)

• High-accuracy dosing applications , measuring very small quantities or loading large quantities of several thousand tonnes per hour

• Other: Batching / filling systems, dispensing systems (e.g. for LPG)

The function of a mass flow meter is based on the Coriolis measurement principle. The mass flow rate of liquids and gases can be calculated from the deformation of the measuring tube caused by the mass inertia. The media density can also be derived from the resonance frequency of the oscillating tube. Two sensor coils are used to calculate the Coriolis effect. If there is no flow, both sensors record the same sinusoidal signal. Once a flow begins, the Coriolis force acts on the flowing mass particles of the medium and causes the measuring tube to deform, resulting in a phase shift between the sensor signals. The sensors measure the phase shift of the sinusoidal vibrations. This phase shift is directly proportional to the mass flow rate.

Coriolis mass flow meters can have different pipe designs and sizes. The customer's requirements determine the design of the measuring tube. With the OPTIMASS product series, KROHNE offers meters with twin bent-tube , twin straight tube, quadruple straight tube and single straight tube design. The measuring tube sizes range from 1 mm for very small flow rates from 0.3 kg/h up to 400 mm for a mass throughput of up to 4,600 tonnes/h.

KROHNE was the first manufacturer to develop and launch a Coriolis flow meter with a single straight measuring tube. It is very well suited for shear-sensitive, inhomogeneous liquids and aggressive chemicals. The single straight tube meter shows its particular strengths in applications with highly viscous liquids containing large amounts of fibres and solids, such as pulp, crude oil or sludge. Users benefit from significantly lower wear and maintenance requirements compared to Coriolis meters with a twin bent tube design.

As the measuring tube can also be drained and is easy to clean, it is also the preferred choice for increased hygienic requirements. Another advantage of the straight tube meter is the significantly lower pressure loss compared to standard mass flow meters with flow splitters. Today, KROHNE is still the only manufacturer to offer the single straight tube meter in four different materials: stainless steel, Alloy 22 (also known as Hastelloy® C22 ), titanium and tantalum.

The pressure loss of Coriolis meters depends on the pipe design. Coriolis devices with a single straight tube design, such as the OPTIMASS 7400 from KROHNE, can be regarded as part of the pipework and therefore have virtually no influence on the overall pressure loss in the system. They operate with virtually no pressure loss. Bent tube flow meters generate a higher pressure loss than straight tube designs for the same size or capacity.

The laws of physics dictate that the higher the number of bends and the tighter the bend angles, the greater the pressure drop created. In addition, where bent tube designs require elevated pipework there will, by definition, be an increase in pipeline length and the number of angled fittings required to achieve the installation. This in turn provides an additional contribution to the overall pressure drop calculation required for bent tube meters. The greater the total pressure loss of the installed flow meter, the higher the costs for investing in more powerful pumps and for energy consumption.

In order to keep the pressure loss in mass flow meters with a bent tube or a flow divider as low as possible, KROHNE's OPTIMASS flow meter series feature optimised flow splitter technology, which ensures that the pressure loss is as low as possible.

In addition to mass flow measurement and determining the volume flow rate, a mass flow meter can also determine the concentration of many liquids via the integrated density measurement, regardless of pressure and temperature fluctuations. Mass flow meters utilise this in many process applications. Parameters such as alcohol concentration, fructose content or sewage sludge concentration can be determined using Coriolis flowmeters. OPTIMASS mass flow meters from KROHNE have conversions for Brix, Baume, Plato, alcohol content and many other parameters stored in the devices as standard.

With the OPTIMASS 6400, KROHNE offers a mass flow meter for safety-related applications.The hardware and electronics of the device have been fully developed in accordance with the IEC 61508 standard and offer a comprehensive safety concept with a proven diagnostic coverage of >96% and an internal diagnostic test interval of less than one minute. It even allows the OPTIMASS 6400 to be used in SIL 3 applications in continuous demand mode, the highest specified level of operation.

For the OPTIMASS devices manufactured by KROHNE, a proof test and a partial proof test procedure have been developed in conjunction with TÜV Rheinland. The proof test coverage (PTC) is 82% without having to remove the device. This ensures the safe operation of any safety-relevant function in Coriolis flow measurement and helps to extend full proof test intervals.

The Coriolis force depends on the moving mass, which in turn is determined by the density and flow velocity of the medium. Too low a density at high flow velocity or too low a flow velocity at low pressure - for example in low-pressure applications - can push the measurement to its physical limits.

In addition, not all Coriolis mass flow meters are equally suitable for cryogenic, high-temperature or high-pressure applications. The decisive factors are the correct design, the appropriate device version and the suitable measuring tube material according to the fluid properties.

The difficulty in measuring a liquid with entrained gas increases with the fraction of gas. Without entrained gas, the measuring tubes in a Coriolis mass flowmeter have the desired regular oscillation. Gas entrained in the liquid dampens the regular oscillation of the measuring tubes, and as the gas content increases, the oscillation can come to a complete stop, causing the measurement to fail completely.

To solve this problem, KROHNE was the first manufacturer of Coriolis mass flow meters to develop and commercialise EGM TM (Entrained Gas Management) to solve these challenges. Today, all products in the OPTIMASS flow meter series using the MFC 400 signal converter are equipped with EGM. TM EGM TM utilises powerful control algorithms that allow a Coriolis flow meter to maintain operation over a wide range of gas fractions and complex flow conditions - even during a complete transition from a pure liquid phase to a gas phase and back. As a result, mass flow and density measurements remain stable, which the OPTIMASS devices have successfully demonstrated in many applications such as filling, loading, dosing or empty-full-empty applications

State-of -the-art mass flow meters offer extensive possibilities for self-monitoring, application diagnostics and on-site verification. For example, OPTIMASS Coriolis meters from KROHNE with OPTICHECK technology built-in have integrated diagnostic functions that continuously monitor all measurable parameters, electronic components such as CPUs, memory and internal bus connections as well as the flow sensor during operation. The meters comply with the NAMUR NE 107 industry standard for status processing.

In addition, the diagnostic software provides an insight into process and auxiliary values in order to ultimately confirm the condition of the process medium. OPTIMASS meters can even generate warning messages in the event of gas inclusions and when a certain proportion of gas bubbles or solids is exceeded, thus providing valuable information about the process. The Coriolis flow meters from KROHNE can also be checked via on-site verification in the field- including report generation - also wirelessly via Bluetooth® or via DTM. Redundant storage of all device configuration data allows the flow converter to be replaced at any time without the need for manual reconfiguration.

Mass flow meters are considered to be particularly long-term stable flow meters. Nevertheless, it is advisable to carry out a zero point adjustment at regular intervals. The flow in the Coriolis device must be brought to a standstill. Valves installed in front of and behind the meter are ideal for this. In the filled state, i.e. without movement in the measuring device, the zero flow rate is determined. This increases the measuring accuracy and improves the performance at low flow rates.

Recalibration of flow meters is often mandated by the regulations and standards of the respective industries. Typical intervals here are between one and two years. However, there is no generally applicable test interval. This depends on the application and the load on the mass flow meter. Particles in the medium can lead to increased wear of the measuring tube and thus to changes in the measuring accuracy. Deposits such as oxide or salt layers can also affect the balance of the measuring tubes. In these cases, recalibration in a certified calibration laboratory is recommended.

Our meters can be calibrated and certified according to various standards such as OIML or the European Measuring Instruments Directive (MI-002 and 005), and comply with API and AGA. The standards we use for calibration are ISO/IEC 17025 accredited and traceable to international or national standards. Regular inspections by national metrology institutes, round robin tests and alignments with national and international metrological standards guarantee the quality and comparability of our calibration rigs. Click here for an overview of KROHNE's calibration services.