In-situ checking of gas flow meters

For Dutch gas-transmission system operator Gasunie, we have developed a tracer method to perform in-situ checks on flow meters. This in-situ method has major advantages over traditional methods, such as preventing the need to detach flow meters and send them to a calibration facility, where they are checked and calibrated against high-pressure, natural gas-flow standards but do not always lead to the most reliable results, especially in cases where upstream conditions like swirl or pulsations influence meter readings. Moreover, these traditional methods are costly.

Project
Tracer methods are not new to the natural-gas-flow world, but issues surround the uncertainty of the method. Whereas early method attempts lead to results >~1%, current method target uncertainty is < 0.5%. Because of the high transport volumes of natural-gas grids, relatively small errors in flow measurements can have significant financial consequences.

This in-situ tracer technique involves injecting a tracer (Argon) into the main gas flow, upstream of the flow meter, and then checking and measuring its concentration downstream close to the flow meter. The injected Argon (mass flow) and its concentration in the gas flow are measured, which result in an accurate determination of gas flow through the flow meter. The instruments used for this tracer method were developed and have been tested at KEMA’s Groningen Flow Lab, the Netherlands over the past few years. The method will be tested in in Gasunie’s high-pressure natural-gas grid and will make any modifications necessary to prepare it for market introduction.

Objectives
The project’s objective is to make this tracer method available to gas transport companies for a wide range of applications (gas-pipe diameter, gas composition, gas flow velocity, configuration, and so forth).

Benefits
In custody-transfer applications, the accuracy of flow meters directly influence gas-trading companies’ incomes—ny measurement error has direct financial consequences. As a result, companies involved in gas trading need a reliable means of checking flow meters, since these meters contribute significantly to measurement uncertainty. Gas-trading companies could save a lot of time and money if they could check flow meters in-situ, instead of having to remove and send them to a calibration facility. In-situ checking has other benefits as well: it takes into account all process and piping conditions that influence proper flow measurement.
Project coordinator
> KEMA, the Netherlands

Project partners
> VSL (van Swinden Laboratory), the Netherlands

Project details
> Duration: 2006 – 2011