We are working on a new natural gas flow measurement; it is not a custody application but rather an energy measurement to regulate natural gas consumption. Natural gas flow applications are not overly complicated, but accurate flow measurement is important. Therefore, a natural gas flow meter should be simple to mount and provide consistently accurate measurements. The article discusses how to choose the best natural gas flow meter.
Coriolis natural gas flow meter: A Coriolis natural gas flow meter is our recommendation and the industry norm. The Coriolis is relatively simple to mount and offers a high degree of accuracy. Unfortunately, Coriolis is one of the most expensive flow meters. Though, in most situations, the benefits outweigh the drawbacks, in the long run, if the budget is a constraint, we may have to use a different measuring concept.
Thermal mass flow meter: Thermal mass flow meters use heat transfer from a heated element to calculate mass flow. There is no need for extra pressure or temperature adjustment since the calculation is in mass flow. They also have high accuracy and repeatability and are simple to mount.
Turbine: Turbine flow meters calculate volumetric flow bypassing fluid through a free-spinning rotor, with each revolution representing a particular volume of gas or liquid. The meters are highly accurate and have a high turndown. Unfortunately, due to the meter’s moving parts, it can only be used in clean, dry gases in gas applications, and pressure and temperature compensation are needed.
Ultrasonic: Ultrasonic flow meters calculate the difference in pulse transit time between a downstream transducer and an upstream sensor instead of the upstream transducer and the downstream transducer. This type of meter is extremely reliable, but it is also very expensive because it must measure pressure and temperature.
Vortex: A shedder bar (an obstruction) in the flow path of the vortex natural gas flow meter causes the fluid to flow around it, forming vortices on the backside of the bar. The frequency of vortex production is proportional to the velocity of the gas. The theory known as the Karman effect is used to calculate fluid velocity. Therefore, the frequency of vortex shedding is unaffected by fluid composition.
Positive displacement: Positive displacement meters enable fluid to mechanically displace components and monitor volumetric flow at the operating temperature and pressure. Although they have adequate precision, pressure and temperature compensation are needed to achieve mass flow, and since they have moving parts, the consumer must consider gas cleanliness. Therefore, a PD meter can also be referred to as a PD flow meter or a volumetric flow meter.
Orifice plate: The orifice plate is a type of differential pressure meter commonly used for natural gas measurement. It tests volumetric flow rather than mass flow. The drawbacks of this meter include reduced low flow sensitivity, restricted turndown, and a pressure drop, which affects operating costs. Furthermore, since it is a volumetric flow meter, temperature and pressure must be corrected to achieve mass flow.
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