Non-Intrusive Passive Acoustic Sensing for Accurate Gas Flow Measurement in Gas Pipelines

Gas flow rate measurement technologies in the oil and gas industry have evolved over the years with the use of sophisticated techniques of analysing signals to measure fluid flow in pipes. These techniques are accompanied by cost implications and accuracy dependence. This paper focused on the design and application of a cheap and accurate non-intrusive passive acoustic sensor (NIPAS) for accurate gas flow rate measurement in a horizontal pipe. The in-house built acoustic sensor was designed to consist of a stethoscope head and was linked to a designed electronic circuit that was designed to provide voltage sensor responses. The principle of operation of the NIPAS is that it receives acoustic energy from the flow of gas in the pipe which is proportional to the sound intensity a then hence voltage intensity. Calibration of the acoustic sensor setup was achieved using a horizontal flow loop of air which consists of a steel pipe test section of 2 inches diameter and 2 meters long. Gas flow rates varied between 0-20 l/min metered by a gas rotameter. Further statistical analysis was performed on the sensor responses based on time and frequency domains. Results from the calibration showed that there was a direct correlation between the gas flow rate measured from a gas rotameter based on the standard deviation and coefficient variance features derived NIPAS responses. Further validation of the observed trends was performed by testing the acoustic sensor with new gas flow rates. The results showed an error margin between +/-1.2% to +/- 5.12% based on the standard deviation model and +/-5.30% to +/- 6.12% based on the coefficient of variance model which indicates an acceptable proof of concept. Future applications of the passive non-intrusive acoustic sensor can be considered for liquid flow and multiphase flows in process engineering systems