When measuring flue gas flow, thermal gas mass flowmeters, vortex flowmeters and differential pressure flowmeters are common choices. The following is a comprehensive analysis of the advantages and disadvantages of these three flowmeters in measuring flue gas:

Thermal Gas Mass Flowmeter

Working principle:

Based on the principle of thermal diffusion or heat balance, the mass flow rate of the gas is determined by measuring the temperature change or heat dissipation of the heating element.

Advantages:

  • Directly measure the mass flow of gas without compensating and correcting parameters such as temperature, pressure and humidity.
  • Wide measuring range, can be adapted to different flow and media types of measurement needs.
  • Fast response speed, can quickly reflect the flow changes.
  • The measurement results are not affected by the physical properties of the fluid (such as temperature, pressure, humidity, composition, etc.).

Cons:

  • The flow field is highly required, and the fluid should maintain a stable flow field when flowing in the measuring tube.
  • Due to the influence of ambient temperature, the sensor needs to be temperature compensated to eliminate the influence of ambient temperature on the measurement result.

Vortex Flowmeter

Working principle:

Based on the Karman vortex street principle, the fluid alternately separates and releases two columns of regular alternating vortex street on both sides of the vortex generating body. Within a certain flow range, the separation frequency of the vortex is proportional to the volume flow of the fluid flowing through the vortex street flow sensor.

Advantages:

  • Simple and firm structure, easy maintenance, less maintenance.
  • Suitable for a wide range of fluids, such as liquids, gases, vapors and partially miscible fluids.
  • The accuracy is high, generally ±1%R~±2%R.
  • The range is wide, up to 20:1~10:1.
  • The pressure loss is small, about 1/4 to 1/2 of the hole plate.
  • Output pulse frequency signal, suitable for total measurement and computer connection, no zero drift.

Cons:

  • It is not suitable for low Reynolds number measurements and is limited in the case of high viscosity, low flow rate and small aperture.
  • The stability of vortex separation is affected by the distortion of velocity distribution and rotating flow, which requires a long straight pipe section.
  • It is sensitive to mechanical vibration of pipeline and should not be used in strong vibration places.
  • The instrument coefficient is low (compared with the turbine flowmeter), the resolution is low, the diameter is lower, and it is generally used for DN300 or less.

Differential Pressure Flowmeter

Working principle:

Based on the Bernoulli equation and the fluid continuity equation, the flow rate is calculated by measuring the pressure difference generated when the fluid flows through a throttle, such as a standard orifice plate.

Advantages:

  • Simple structure, firm, stable and reliable performance, long service life.
  • A wide range of applications can be used to measure single-phase fluids (liquid, gas, steam) and partially miscible flows.
  • Detection parts, transmitters and display instruments can be produced by different manufacturers, which is convenient for economic production.
  • The standard throttle differential flowmeter can be used without real flow calibration.

Cons:

  • The measurement repeatability and accuracy are generally low.
  • The range is narrow, the general range is only 3:1~4:1.
  • Long straight pipe segments are required for high installation conditions on site.
  • The pressure loss is large, and the fluid flowing through the throttling part will produce a large pressure loss.

Sum up
When measuring the flue gas flow, it is necessary to choose the right flowmeter according to the characteristics of the flue gas and the measurement requirements. Differential pressure flowmeter has the advantages of simple structure and wide application range, but the measurement accuracy and range are relatively low. Vortex flowmeter has the advantages of simple structure, easy maintenance and many kinds of applicable fluids, but it is sensitive to pipeline mechanical vibration and has low instrument coefficient. The thermal gas mass flowmeter has the advantages of direct measurement of gas mass flow, wide measurement range, fast response speed, etc., but the flow field, ambient temperature and pipeline materials have requirements and high prices.

If you want to know more about the flow meter or flow meter selection, please consult the Aister flow meter manufacturer email: sales@aistermeter.com for help.