Question 1

1. Differential pressure flowmeter

Accepted Answer

Due to its simple structure and low price, this type of flowmeter is widely used in the domestic petrochemical industry. Among them, standard throttling elements, especially standard orifice plates, are most used because they do not require real-flow calibration.

Differential pressure flow meters also have the following weaknesses:

1) The range is relatively small, generally 3:1 to 5:1. The accuracy of the measurement cannot be guaranteed for working conditions where the flow measurement range changes.

2) The pressure pipeline between the orifice plate and the transmitter is easy to block, leak, and freeze, which affects the stability and accuracy of the measurement, and requires a large amount of work and cost for repairs and maintenance.

3) There are many uncertain factors in installation. For example, the front and rear straight pipe sections, the verticality and concentricity of the orifice plate during installation will affect the accuracy of the measurement, and these factors are difficult to strictly meet in the actual installation process.

4) Deviations caused by long-term operation.
During the operation of the orifice plate, the sharp angle becomes blunt or the orifice plate is deformed or blocked due to various reasons, which causes the measurement accuracy to decrease. Standard nozzles can be used instead of standard orifice plates. Compared with the orifice plates, the nozzle has a stable outflow coefficient. The outflow coefficient will not change due to the sharp edge angle becoming blunt. At the same flow rate and Lu value, the pressure loss is about 30% to 50% of the orifice plate.

Question 2

2. Vortex Flowmeter

Accepted Answer

Compared with the traditional differential pressure flowmeter, the vortex flowmeter has some obvious advantages: a wide range ratio, which can reach 20:1. It is easy to install and does not require pressure pipes and heat tracing. The pressure loss is smaller than that of an orifice plate. Accuracy It is higher than the differential pressure flowmeter.

Similarly, vortex flowmeters also have the following shortcomings:

1) The caliber is generally DN25～300. If the caliber is too large, the cost performance will be significantly reduced.
2) It is usually used in occasions where the medium temperature is below 200°C. When the medium temperature is 200-400°C, it is necessary to confirm the detection method (such as capacitive) and the applicable temperature range.
3) The Reynolds coefficient required by the measurement is twice as high as that of the orifice plate.
4) Poor vibration resistance, harsh requirements for vibration, unable to measure pulsating flow.

Question 3

3. Rotameter

Accepted Answer

Rotameter has a simple structure, and its installation method is mostly limited to vertical pipeline installation, and it is generally only suitable for measurement under small pipe diameters and low flow rates, so it is not widely used in petrochemical plants.

Question 4

4. Ultrasonic flowmeter

Accepted Answer

The main advantage of the ultrasonic flowmeter is that it can achieve non-contact measurement without additional pressure loss.

Ultrasonic flowmeter detection methods are mainly divided into propagation time method and Doppler method.

Among them, the propagation time method is mostly used for the measurement of clean, single-phase liquids and gases. The Doppler method can be applied to the measurement of liquids containing a certain number of bubbles or particles.

Although this type of instrument for measuring steam has been introduced in foreign markets, it is currently not widely used in China.

Question 5

5. Rotary vane steam flow meter

Accepted Answer

Mainly used for low pressure, small diameter direct reading steam flow and total measurement. The main features are simple structure, firmness, low price, moderate precision (± 2.5% R). But the wing wheel component bearing is vulnerable to damage Parts need to be replaced and repaired regularly. Due to the limited pressure, it is rarely used in petrochemical plants.