Evaluation of the Influence of the Composition of Natural Gas in the Ultrasonic Measurement of Flow in Flare-type Pressure Relief Systems

摘要

The objective of this work was to evaluate the influence of the composition of the natural gas on flow rate measurements in pressure relief flare systems, which is a legal requirement imposed by the Brazilian Regulator. The historical technical difficulties associated with collecting gas samples from flare systems, and the constant questions about the representativeness of the collected samples, are the main drivers motivating this study. The study indicated (i) a maximum error of 0.04% associated with ultrasonic measurement of gas flow rate when the actual gas composition was unknown; (ii) collected gas samples directly extracted from the flare systems do not necessarily represent the actual measured gas and (iii) the estimated maximum error associated with the totalization of the gas volume proved to be negligible when compared either to the total documented gas volume given by historical measurements or to the acceptable random errors that is inherent to this type of measurement system.