Question 1

1. Gas Turbine Flowmeter

Accepted Answer

The gas turbine flowmeter is a frequently used instrument for measuring natural gas flow. Within a certain flow range, the turbine speed is proportional to the fluid flow rate. The fluid flow drives the turbine, and the turbine speed is converted into electrical pulses. The data is displayed on a secondary meter, reflecting the fluid flow rate.

Gas turbine flowmeters have low pressure loss and are suitable for gas metering in low-pressure transmission applications. Their excellent measurement repeatability makes them a preferred flowmeter for trade settlements.

Gas turbine flowmeters are suitable for measuring low-flow gases such as natural gas, air, and nitrogen. Currently, gas turbine flowmeters dominate the flowmeters used for gas measurement.

Question 2

2. Thermal Mass Flowmeter

Accepted Answer

A thermal mass flowmeter directly measures gas mass flow by detecting the heat exchange relationship between a fluid and a heat source. Its core principle is based on the cooling effect of a fluid flowing through a heating element. A mathematical relationship between the temperature difference and mass flow rate is established using the constant temperature difference method or the constant power method.

The pipeline type can cover pipes from DN10 to DN300. The insertion type can cover large-diameter pipes from DN65 to DN4000.

It features no moving parts, low pressure drop, and a wide range ratio (up to 100:1). It is widely used for measuring the flow of gases such as natural gas, coal gas, liquefied petroleum gas, flare gas, and hydrogen.

Question 3

3. Vortex Flowmeter

Accepted Answer

A vortex flowmeter can measure natural gas. It is a stress-type vortex flowmeter that measures flow based on the Karman vortex principle.

It offers advantages such as high measurement accuracy, a wide measuring range, low power consumption, easy installation, simple operation, and low pressure loss. It can measure operating volume flow or standard volume flow (with integrated intelligent temperature and pressure compensation).

It is widely used to measure the volume and mass flow of superheated steam, saturated steam, compressed air, and general gases and liquids.

Question 4

4. Roots Flowmeter

Accepted Answer

Roots flowmeters, also known as gas rotary flowmeters, can be used to measure not only dry gas but also wet gas.

When fluid passes through the flowmeter, the differential pressure between the flowmeter inlet and outlet causes the two rotary wheels to rotate in the positive direction. Liquid continuously flows in and out of the metering chamber. The fluid flow rate can be calculated simply by knowing the chamber volume and the number of rotary wheel rotations. Therefore, a gas rotary flowmeter is a positive displacement flowmeter, with high accuracy and low pressure drop as its main advantages.

In natural gas trade settlement, positive displacement flowmeters have inherent advantages. They do not require straight pipe sections and offer high accuracy and reliability, demonstrating long-term reliability in physical measurement.

Question 5

5. Swirl flowmeter

Accepted Answer

Swirl flowmeters are currently the preferred flowmeter for some small natural gas distribution stations.

Gas entering a swirl flowmeter first passes through a spiral vortex generator, where it is forced to rotate and accelerate, forming a vortex with the vortex core at its center. The accelerated vortex decelerates rapidly after entering the expansion section, causing pressure to rise and generating backflow. Driven by this backflow, the vortex core precesses spirally around the meter's axis. The vortex precession frequency f is measured using a sensitive element, and the flow rate Q can be derived.

Question 6

6. Orifice Flowmeter - Differential Pressure Flowmeter

Accepted Answer

The orifice flowmeter is currently the most widely used instrument for measuring natural gas flow.

When gas flows through a throttling device, the flow stream forms a localized constriction at the orifice plate. This increases the flow velocity and reduces the static pressure, creating a static pressure differential across the orifice plate. The greater the flow velocity, the greater the pressure differential across the orifice plate. Therefore, the natural gas flow rate can be measured by measuring the pressure differential across the orifice plate.

Orifice flowmeters offer the advantages of simple structure, easy installation, stable and reliable performance, and low price. Due to their long history of use, a comprehensive set of standards has been established for their manufacture and use, making them flexible in application.

Question 7

7. Ultrasonic Gas Flowmeter

Accepted Answer

Ultrasonic flowmeters estimate gas flow by measuring the propagation velocity of ultrasonic waves in a pipeline.

The flowmeter's measuring pipe section is equipped with one or more pairs of ultrasonic transducers. These transducers alternately transmit and receive ultrasonic waves. Using ultrasonic detection technology, the flowmeter calculates the gas flow rate and the gas flow rate under standard conditions by measuring the difference in the speed of sound as the ultrasonic waves propagate in the forward and reverse directions of the airflow, as well as the fluid pressure and temperature in the pipe section, including the gas's molar composition.

Gas ultrasonic flowmeters can be used to measure industrial gases such as natural gas, nitrogen, oxygen, air, hydrogen, argon, helium, ethylene, and propane.