Dinâmica dos fluidos computacional para implementação de um novo modelo para estimativa de overreading em placas de orifício

Abstract

The amount of money involved in differential pressure flow measurement is enormous, within the UK it is estimated that most natural gas is measured at least once using an orifice plate: every year around £25 billion of natural gas is measured with an uncertainty of around £250million. The accuracy of orifice plates has been demanded by regulatory bodies and the industry due to so-called legal measurement. Liquid hydrocarbon flow measurement systems must have a maximum permissible error of ±0.3% and, for natural gas systems, a measurement uncertainty less than or equal to 5%. For flow measurement involving only one fluid, the orifice plate is consolidated equipment, however, in the oil industry, the condition of a single fluid flowing through the pipe is hardly verified, and it may contain impurities or other fluids. In case fluids are passing through the meter, the problem of gas humidity arises; this effect causes a positive error in the flow measurement due to the presence of liquid in the gas flow called overreading. Many works were carried out by empirical methods, to understand the overreading in orifice plates. However, the experimental infrastructure for testing meters is expensive and robust. To reduce the costs of semi-industrial or industrial infrastructure, they propose to replace these tests supported by numerical experimentation via computational fluid dynamics. With CFD it is possible to analyze systems involving fluid flow, heat exchange, and associated phenomena, such as chemical reactions and phase change, common in oil flow. In the context of this work, it is proposed to use a numerical method that estimates the overreading using a new mechanistic model developed for an orifice plate, in which the input parameters are obtained by computational fluid dynamics (CFD) simulation.