On the effect of the mounting angle on single-path transit-time ultrasonic flow measurement of flare gas: a numerical analysis

Abstract

The oil and gas industry needs accurate flow measurement since it is required by law, and so, considered as a field of legal metrology. Nevertheless, curves and other commonly found obstacles may affect the quality of flow measurements, due to disturbances to the flow, such as swirl and asymmetries in the velocity profile. Single-path ultrasonic flow meters are often used to measure the flow rate in flare gas installations, even though they are sensitive to such disturbances. The present paper uses numerical tools to obtain disturbed flow fields downstream from single- and double-elbow pipe installations, aiming to investigate the effects of the mounting angle on disturbed ultrasonic flow measurements, taking into consideration the contributions of all velocity components. Several transducer mounting angles from 0° to 180° are assessed varying the Reynolds numbers (based on the pipe diameter D) from $$10^{4}$$ to $$2 \times 10^{6}$$ and axial positions up to 80D downstream from the curve. Results indicate that the correction factors for installation effects are mostly greater than in the guidelines and regulations, which suggests that, in real situations, the flow rate is being underestimated. Moreover, badly located measuring installations may be upgraded just by changing the mounting angle of the ultrasonic transducers.