Selection of flowmeter for large diameter gas pipeline

Selection of large-flow gas flowmeter, measurement of large-flow gas is of great significance to economic combustion, environmental protection and trade settlement.These gases are commonly found in urban gas, natural gas, air ducts, flue gas from boilers and various furnaces, and flare gas from oil refineries and petrochemical industries.

I. characteristics of gas mass flow measurement

1. Low static pressure, low flow rate, only a small loss of pressure is allowed.

2. With large caliber, straight pipe segment is often difficult to guarantee.

The fluid contains dust and sometimes a sticky substance such as tar.

4. The wide range of velocity variation requires the meter to have a larger range.

5. The composition of gas varies.

Some fluids are corrosive.

7. When the temperature of some flue gases decreases, the humidity increases, even with liquid.

8. High fluid temperature.

2. Meter selection of inserted vortex street flowmeter and differential pressure average tube flowmeter are also suitable for gas flow measurement in large diameter pipelines.However, due to different fluid properties, the problems in application are obviously different.

1. Differential pressure average velocity tube flowmeter.

This kind of flowmeter is widely used in the measurement of large-caliber gas flowmeter for the same reason as large-caliber water flow.The key to the success or failure of the differential pressure equal-speed tube flowmeter in the measurement of gas flowmeter is that the pressure tube should not be blocked by water droplets.Because the cut off valve of the finalized speed-equalizing tube product is mostly needle valve with small size, and the water vapor in the fluid turns into liquid drops after condensation, if the needle valve is not handled well or the slope of the pressure tube is not reasonable, this liquid drop will easily seal the path.

2. Inserted vortex street flowmeter.

The measuring head of the inserted vortex street flowmeter is generally DN50. For air under normal temperature and pressure, the lower limit of measured flow velocity is about 6m/s.There are many measurement objects, the flow rate is often less than 6m/s.Especially for water gas and some loose gas, due to the high hydrogen content and low fluid density, the thrust of the vortex sensor decreases correspondingly. At this time, the lower limit of flow velocity that can be measured reliably also increases, so the meter often fails to meet the requirements of the measurement object.

The volume flow indicated by vortex street flow will not be affected by density change due to fluid composition and temperature change. When the volume flow under pressure state is converted to standard state, compensation of fluid temperature, pressure and compressibility is required.

If there is a very thick viscous substance and dust attached to the inlet surface of the vortex generator, its shape will change, which will lead to the change of flow coefficient. Therefore, it is necessary to pull out the measuring head regularly to remove the attachment.