Classification and selection of common steam flow meters

1, differential pressure flowmeter

In the measurement of steam flow, the differential pressure flowmeter still ranks first. It is based on authoritative standards and has easy detection of the detection parts. The structure is simple, firm, reliable, and has a long service life. The temperature and pressure range that can be used Wide; low price, no need for real-current calibration. The differential pressure flowmeter complete set of instruments is composed of standard throttle devices, differential pressure transmitters and flow totalizers from different manufacturers, so it is flexible and convenient to use. Differential pressure flow meters are especially suitable for measuring high temperature, high pressure saturated steam and superheated steam. However, there are also some shortcomings, such as: the installation is more complicated, easy to leak, the labor intensity of maintenance and disassembly is large; the range ratio is only 3:1, the pressure loss is large; the process parameters deviate from the design value due to the change of measurement conditions during use. Both will produce large measurement errors.

2, vortex flowmeter

The vortex flowmeter has a simple structure and does not require a pressure guiding tube; the measuring range is large, the range ratio can reach 10:1; the pressure loss is small, and the proportion in the saturated steam flow measurement is increasing. The ease of installation is similar to that of the orifice plate, and there are certain requirements for the straight pipe section. However, there are also deficiencies, such as: regular verification of the general user can not do, need to remove the inspection; its stability is affected by the flow rate, the stress vortex flowmeter is sensitive to vibration, easy to be affected by the vibration of the pipeline or equipment Measurement error, which is also limited by temperature, usually cannot exceed 300 °C (Vortex flowmeter is suitable for saturated steam flow measurement and cannot be used for superheated steam flow measurement). It is also not possible to measure multiphase flow, such as saturated steam with high humidity.

3, rotary vane steam flowmeter

The rotary vane steam flow meter has a wide range of applications in the measurement of saturated steam in small and medium-sized enterprises. It is a purely mechanical measuring instrument. The utility model has the advantages of simple structure, firmness and small maintenance; the adjustment range only needs to replace the inner orifice plate, and has the manual adjustment pressure compensation function, and does not need the power source and the like. However, there are also some shortcomings, such as: there are certain requirements for the straight pipe section: the adaptability of the pipe diameter is limited, and it can only be installed in a horizontal position; the accuracy is not high, and only the manual manual meter reading is not convenient for measurement management.

4, linear orifice differential pressure flowmeter

Linear orifice differential pressure flowmeters have been used in the enterprise. It is also known as an elastically loaded variable area variable indenter orifice with a linear relationship between flow and differential pressure. The measuring range is up to 100:1, which is very suitable for measuring occasions with large flow changes; high measurement accuracy, low requirements for straight pipe sections and good anti-vibration performance. However, there are also deficiencies, such as the need to calibrate the temperature of each instrument to change the temperature of the fluid, which will lead to changes in fluid density, as well as changes in the inner diameter of the pipe, the diameter of the orifice and the geometry of the piston, resulting in measurement errors. Due to the movable parts, the maintenance is more complicated, the gap between the orifice plate and the piston is small, and a filter is installed upstream of the meter to prevent the impurities in the pipeline from jamming the piston.

5, V cone flowmeter

The measuring principle of the V-cone flowmeter is the same as that of the differential pressure flowmeter, and is also a throttle type differential pressure flowmeter. It adopts the gradual contraction and throttling of the side wall, that is, "the variable fluid shrinks at the center of the pipe to shrink the side wall". It requires extremely low installation of straight pipe sections and requires almost no straight pipe sections; the range ratio is up to 10:1; the pressure loss is only 1/3 of the orifice plate. Not afraid of vibration, high temperature and high pressure, it can measure saturated steam and superheated steam. The geometry of the throttle can be kept unchanged for a long time, and it can work stably for a long time without calibration. When measuring the steam flow, the special three-valve group is connected between the transmitter and the flow meter, so there is no need to use the pressure guiding tube. However, there are also deficiencies. For example, there is still a problem of pressure loss. When measuring high temperature superheated steam, it is still necessary to install a condenser, or to lengthen the conduit to protect the meter. When measuring the steam flow, temperature and pressure compensation are still needed.

6, curved pipe flowmeter

The elbow flowmeter is an elbow with a fixed geometry and a fixed shape. The structure is simple, without any additional parts and throttles, so there is essentially no pressure loss. The range ratio can reach 10:1, the precision is high, the measuring device is maintenance-free, the service life is long, high temperature resistance, high pressure resistance and vibration resistance. However, there are also deficiencies. For example, the differential pressure generated by the measurement is relatively low, generally around 3000 Pa. Therefore, the selection of the differential pressure transmitter is relatively high. When measuring the steam flow rate, temperature and pressure compensation are still required.

7, flute-shaped constant velocity tube flowmeter

Flute-shaped constant velocity tube flowmeter is based on the principle of pitot tube velocity measurement. It outputs differential pressure signal, which is used together with differential pressure transmitter for measuring differential pressure. It can measure the flow of steam, liquid and gas. Its structure is simple and pressure. The loss is small, the length of the upstream and downstream straight pipe sections is short, the installation is convenient, the turndown ratio can reach 10:1, high temperature and high pressure resistance, no abrasion and no leakage. However, there are also deficiencies, such as high requirements for on-site installation conditions, which produce a small differential pressure, some only 20-30Pa, must be equipped with high-precision differential pressure transmitters, due to structural reasons, each pressure port The flow rate is different, there is a certain pressure difference between the pressure tapping holes, and there is a medium flow between the pressure tapping holes. If there is a medium, there may be a blockage and a measurement error occurs. The measured fluid flows in the round pipe due to fluid separation. Different points cause different pressure distributions caused by the circular tube when facing the fluid, which causes the flow coefficient to be unstable and the flow rate to be unstable.