Flow Sensor Selection for Custody Transfer in Metering Systems

The world of liquid metering systems has been quietly undergoing a technological revolution. At the heart of this transformation is the application of Bernoulli’s principle to orifice flow measurements. The method connects the dots between the pressure drop across a sharp-edge orifice and the volumetric flow rate—a key determinant of accurate flow measurements in the crucial field of custody transfer.

Traditionally, the pressure drop is gauged at the flanges that secure the orifice plate. The collected data is then extrapolated to estimate the pressure drop at the vena contracta, a fluid dynamics term for the point in a fluid’s path where it reaches maximum speed. The location of the vena contracta shifts with the flow rate, and tracking its position is crucial for precision.

The unique characteristics of gas-liquid interfaces are pivotal in this process. They act as an essential metric for selecting the most accurate and reliable flow sensors, a key component in creating efficient liquid metering systems.

Surprisingly, despite their efficacy, orifice differential pressure (DP) flowmeters are not commonly used in liquid metering systems for custody transfer purposes. Yet, they are a staple in gas metering systems. This disparity begs the question: Why aren’t we leveraging this cost-effective, reliable tool in both realms?

To answer that question, we need to delve deeper into the world of hydrocarbon industries. Here, the primary goal is to curtail custody transfer costs. While accurate flow measurement is a critical part of this strategy, achieving optimal efficiency requires a more comprehensive approach.

Global per capita oil consumption currently rests at approximately five barrels per year. Known oil reserves can sustain this consumption rate for about 50 years. This is a sufficient window for the transition from fossil energy sources to a clean, inexhaustible solar-hydrogen-based energy economy—if the cost of conversion is provided.

However, the journey from now to then is fraught with economic challenges. Oil alone accounts for about 3% of the global GDP. If we consider the yearly consumption of nearly 40 billion barrels at $75 per barrel, we’re talking about $3 trillion. That’s an astronomical figure, equivalent to global military expenditures, a significant portion of which is spent on vying for control of the planet’s remaining fossil and mineral reserves.

In this high-stakes arena, oil losses in custody transfers—typically around 5-10%—can make a huge difference. By using the optimal flow and level detectors, coupled with superior monitoring practices, these losses can be halved.

The adoption of orifice flow measurements in liquid metering systems is more than a practical decision. It’s a strategic move towards a more sustainable hydrocarbon industry. By applying the principles of fluid dynamics, we can reduce losses, increase efficiency, and ultimately, make the transition to greener energy sources more feasible. This shift isn’t just a necessity; it’s an opportunity to revolutionize the industry from the ground up.