Why Natural Gas Meters Must Be Properly Matched to Customers
by Bob Shively, Enerdynamics President and Lead Facilitator
Gas meters are critical for ensuring accurate monetary settlements associated with gas receipts and deliveries. Metering is necessary whenever gas ownership changes hands. Meters are also used to monitor gas flows as part of gas system operations.
Selecting the correct meter for any given application requires a balance of accuracy and economics. Here are the five common types of meters used in natural gas delivery systems and where they are typically installed.
- Diaphragm meters are the most common type of meter. They are a type of volumetric meter, meaning they determine flow by measuring gas entering and leaving a space with known volume. The gas alternately fills and empties two compartments of fixed volume connected to a diaphragm. The meter counts the cycles of filling and purging to determine the volume. Diaphragm meters are relatively inexpensive, offering low-cost billing measurements for utility companies. They have a long life expectancy and are accurate to 1%. The main disadvantage of a diaphragm gas meter stems from the meter having moving parts. For this reason, they require periodic maintenance.
Diaphragm meter applications: Used on smaller pipes with low flow rates such as residences and small commercial applications.
- Like diaphragm meters, rotary meters work by measuring fixed volumes of gas. In this case, two figure-eight-shaped lobes spin in alignment. With each rotation, they displace a precise quantity of gas. By counting the number of rotations, the meter determines the volume of gas. Rotary meters are accurate to 1% and can handle higher pressures and volumes than diaphragm meters. Maintenance is required since they have moving parts.
Rotary meter applications: Used for medium-sized commercial and industrial customers.
- Turbine meters measure gas flow by measuring the rotational speed of a spinning turbine disk. Each revolution measures a specific volume of gas. Turbine meters are accurate to 0.5 to 1% when used for mid to high flow rates. They are inexpensive and can have an electronic output.
Turbine meter applications: Used for large commercial and industrial customers.
- Instead of measuring volumes in chambers or by rotations of a turbine, the orifice meter uses pressure differentials to calculate volume. This meter uses an orifice to cause a pressure drop over a short distance in the pipe. The pressure drop is correlated to the velocity of the gas, thus allowing volume flow to be calculated by measuring the pressure drop. They are inexpensive and straightforward. They have no moving parts and are mechanically stable. The accuracy is typically 2% within the specified flow range. On the downside, orifice meters have low accuracy at low flow conditions.
Orifice meters applications: Used for measurements at high pressures such as on transmission pipelines and on gas well production facilities.
- Ultrasonic meters use transducer and receiver pairs to bounce ultrasonic beams across the pipe interior. The speed of the beam as it travels from the transducer to the receiver is correlated to the velocity of the gas flow, which allows the volumetric flow rate to be calculated. The ultrasonic flow meter is extremely accurate with ranges of 0.2 to 0.5%. Since they have no moving parts, they require little maintenance and have long-term reliability. Disadvantages are that ultrasonic meters are expensive to install and can be disturbed by noise and dirt.
Ultrasonic meter applications: Used on large pipes where high accuracy is important due to the large volume of flow. Common applications are custody transfer points between pipelines and large customers such as power plants.
From this summary, you can see that various situations call for different metering solutions. Getting the right meter in the right place is critical to ensuring accurate measurement at a reasonable cost.
Do you need to educate your employees about the key components of the natural gas physical system and how a gas system is designed, built, maintained, and operated using these components? We recommend you check out our online courses Gas Systems Fundamentals and Gas Systems Fundamentals Condensed. Contact us at email@example.com or 866-765-5432 ext. 700.
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