Ultrasonic Flow Meters in Flaring Applications

The CFD approach allows us to model and analyse fluid flows, numerically solving the equations that govern the flow phenomena. This method is used in a wide range of industries and in the case of flow meters, it can either be employed in the initial design process to ensure the meter is installed in the most suitable location, or as a method of assessing errors related to installation effects.

This webinar, presented by Calum McLaughlin, discusses the impact of flaring and the operation of ultrasonic flow meters. Furthermore, it provides insights on how CFD can be used to correct ultrasonic flow meters in complex and non-ideal installations.

SPEAKER

Calum McLaughlin

CFD Engineer, TÜV SÜD

Calum is a Computational Fluid Dynamics (CFD) Engineer involved in engineering consultancy and research projects. He delivers innovative engineering solutions and offer customers technical advice on how to improve their products and services. Calum uses state-of-the-art software and hardware to help our customers reach their performance goals.

For oil and gas operations, the accurate measurement of flare gas emissions plays a crucial role in ensuring compliance with environmental regulations and maintaining operational efficiency. Flare gas meters are essential devices used to measure the flow of hydrocarbon gases that are safely burned off through flare stack. However, achieving precise and reliable measurements with traditional flow meters can be challenging due to the complex and dynamic nature of flow patterns in flare systems.

This is where Computational Fluid Dynamics (CFD) comes into play. Using its advanced capabilities, TÜV SÜD can simulate and analyse the complex flow dynamics within flare systems to predict flow behaviour and accurately predict correction factors. At TÜV SÜD, we specialise in using CFD to optimise the accuracy and performance of flow meters in flaring applications.

One of the key advantages of using CFD for flare gas metering is the ability to extract the flow profile at any point along the flare line. By creating virtual models of flare systems and analysing flow patterns, we can uncover insights into how factors such as bends, tee pieces, and disturbances impact the performance of these flow meters. This level of insight allows us to fine-tune meter calibration and correction strategies to ensure optimal accuracy in flare gas emissions.

Why is CFD modelling needed for flaring and venting systems?

Flare meter systems are designed and calibrated to work with perfect scenarios, Ie an ultrasonic flow meter with 20 diameters of undisturbed upstream flow and 5 to 10 diameters of undisturbed downstream flow. This flow profile is used to determine the correction factor, also known as the K factor or Velocity Distribution Factor (VDF). The K factor is the ratio of actual flow rate in the pipe over the measured flow rate by the meter. If the K factor is less than one, the meter is over-reading. If the K factor is greater than one, the meter is under-reading. As the flow rate in the pipe changes, the flow profile at the meter can also differ due to installation effect, swirl intensity and laminar or turbulent flow regimes. Therefore, by performing multiple simulations at different flow rates, a look-up table or curve fit of K-factors can be generated. In most cases, manufacturers of these meters are supplied with only a single K-factor (which is usually not from a physical calibration). These K-factors are usually based on ideal conditions, i.e. no disturbances upstream and downstream of the meter, something which is unusual in flaring applications. However, from our analysis using CFD modelling, we have found that the velocity profile of the installed meter is not the same as the ideal condition profile and is different between installations even for the same meter. Therefore, the supplied K-factor may no longer be sufficient and a look-up table should be supplied. This is why the use of CFD provides valuable insight into the operation of the meter in as-installed conditions.

Can we take the flare meter to a calibration laboratory?

Often, flare gas meters are installed in hard-to-reach locations and are therefore difficult to remove. These meters can also be up to 60 inches in diameter and be placed in flares that are 100s of meters in length, and the velocities can be as high as 150 meters per second, so finding a calibration facility that can operate with these conditions is unlikely and would be cost-prohibitive. Therefore, the most efficient option to support flare gas meter correction in situ is to use CFD.

How does a CFD model work?

A 3D model is constructed of the installation and the metering system using isometrics, general arrangement drawings, photographs and discussions with the operator to ensure an accurate representation of the installed. The CFD model incorporates pressure, velocity and any other physical property that needs to be calculated. The relevant turbulence model is applied along with other models to aid in the convergence of an accurate solution. This solution can then be used to extract the necessary data and act as a visualisation of flow behaviour.

With CFD, we can simulate different installation scenarios and evaluate the effects of varying flow conditions on meter readings. This modelling capability enables operators to make informed decisions about the placement and configuration of flow meters to minimise uncertainties and maximise measurement accuracy in safety critical systems such as flaring. By incorporating CFD into flare gas metering processes, operators can improve their compliance with emission regulations, avoid costly fines, and optimise operational efficiency. As the future of flare gas metering places greater emphasis on accuracy, compliance and transparency, the integration of CFD modelling will play a pivotal role in driving innovation and efficiency in the industry. At TÜV SÜD, we are committed to providing cutting-edge CFD modelling services tailored to the unique needs of our clients in the oil and gas sector. Our team of experts is dedicated to delivering comprehensive solutions that improve the performance and reliability of flare gas metering systems.

The incredible potential of CFD for optimising flare gas metering accuracy cannot be overstated. By partnering with our CFD experts, your business can benefit from CFD’s power to unlock new levels of precision, efficiency, and regulatory compliance in your flare gas measurement processes. Contact us today to learn more about how our flaring and venting services for the oil and gas industry can revolutionise your flare gas metering operations and help you avoid sanctions and fines.

Watch Calum Mclaughlin’s webinar on Ultrasonic Flow Meters in Flaring Applications and their Correction by Means of Computational Fluid Dynamics now. Complete the form to access the recording.