Turbine flow meter principle

Turbine flowmeters are a common type of flow that can measure various gases and liquids. It adopts a new intelligent design, which can maintain high-precision measurements when used. Turbine flowmeter has superior performance and long service life when used, and it has strong anti-interference ability. When it is used, turbine flowmeter may encounter various electromagnetic interferences if the flowmeter resists interference. The capacity is not good enough, which may affect the measurement accuracy of the flow meter when it is used.

Turbine flowmeters use less power and are constructed of stainless steel, which ensures strong corrosion resistance during use, is not susceptible to corrosion, and turbine flow for some corrosive media. The meter can also measure well and will not be limited. This type of turbine flow meter is very small in size. If there is a malfunction during use, the flow meter can be easily disassembled to facilitate the user to perform repairs in time, and after daily use, when the flow meter needs to be cleaned, it is easy to disassemble. Makes the user more convenient cleaning.

As China's energy conservation and emission reduction policies continue to change the energy structure, domestic companies are using more natural gas and other types of gas as industrial energy. Currently, there are many types of metering instruments widely used for gas metering. Commonly there are gas turbine flow meter, precession flow meter, gas waist wheel flow meter, membrane gas meter and so on. These instruments are widely used in the handover measurement of gate stations, industrial users, commercial users, residential users, and pressure regulating stations at all levels and process metering, and their usage varies. Due to the need to face a large number of different users, it is particularly important to select an appropriate flow meter. To select the appropriate flow meter, you must first understand the characteristics of each meter.

Second, gas flow metering instrument introduction

The following elaborates the principle, characteristics and main technical parameters of these flow metering instruments.

(a) gas turbine flowmeter

The working principle of the gas turbine flow meter: When the air flow enters the flow meter, it first passes through the special structure rectifier and accelerates. Under the action of the fluid, the turbine overcomes the resistance moment and the friction moment and starts to rotate. The rotation of the turbine changes the magnetic resistance of the magnetoelectric converter periodically, and the magnetic flux in the detection coil periodically changes, generating a periodic electrical pulse signal. When the torque reaches equilibrium, the rotation speed is stable, and the rotation speed of the turbine and the gas flow rate become Proportional, and through the mechanical transmission and magnetic coupling connected to the word wheel counter, directly measuring the total volume of gas working conditions, and through the configuration of the flow compensation instrument, measuring gas temperature, pressure, standard volume flow and total volume.

1. Accuracy

The use of gas turbine flowmeters is mainly based on its high precision. At present, gas turbine flowmeters are: ±0.5%R and ±1.0%R in the international market, and ±1%R and ±1.5%R in the domestic market mean the range of 6:1 or 10:1. If the range is reduced, the accuracy can be improved. If it is used at a fixed point, the accuracy can be greatly improved under real-flow calibration conditions. For custody transfer metering, an on-line calibration device is often provided for regular verification.

2. The requirements of the fluid

Gas turbine flowmeters require clean (or substantially clean), single-phase, and low-viscosity fluids without large particles, fibers, and other impurities.

3. Installation conditions

Gas turbine flowmeters are sensitive to the distribution of flow velocity distortions in the pipeline and to the rotation flow. Into the sensor stress to fully develop the flow, it is necessary to have the necessary straight sections or rectifiers based on the upstream blockage of the sensor. If the upstream blockage is unclear, it is generally recommended that the length of the upstream straight pipe section should be no less than 2D, and the length of the downstream straight pipe section should not be less than 1D. If the installation space does not meet the above requirements, a flow control valve can be installed between the blocker and the sensor.

4. Economical

The use of gas turbine flowmeters for high-precision applications has many economic considerations. The purchase cost of the instrument is only part of the cost. The following expenses should also be considered: auxiliary equipment costs; calibration fees; frequent verification must be done to maintain high accuracy; even an on-line calibration device must be installed on site; the cost is considerable; Cost, replacement of consumables for gas turbine flowmeters, which is necessary to maintain high performance.

(B) Gas Swirl Flowmeter

The working principle of the gas swirling flowmeter: When the fluid flowing in the axial direction enters the inlet of the flow sensor, the swirling body forced the fluid to rotate, and then the swirling flow generates a vortex flow in the center of the swirl generating body. The swirling flow swirls in the Venturi tube. The sudden throttling to the contraction section accelerates the vortex flow. When the vortex flow enters the diffusion section, it is forced by the recirculation action to perform the precession-type secondary rotation. The rotational frequency of the vortex flow at this time is proportional to the flow velocity of the fluid flowing through the precession vortex sensor, and is linear. Two piezoelectric sensors detect the weak charge signal. After the preamplifier differentially amplifies, filters, and reshapes, it becomes two pulse signals whose frequency is proportional to the flow velocity. Simultaneously, the processing circuit compares and discriminates the two-phase pulse signals. The interference signal is removed and the normal flow signal is counted.

1. The main technical parameters are:

Flow range: 1.2-3600m3/h

Instrument accuracy (±1.0%~±1.5%)R

Instrument diameter: DN20~200mm

Working pressure: generally ≤1~1.6Mpa

2. Fluid requirements

Applicable to high medium pressure (5kPa-30kPa, different specifications can be used with different minimum pressure), the required flow range is less than 15:1, and no special requirements for the initial flow, there is no strong vibration, there is no strong pressure Volatility occasions.

3. The meter is affected by the pulsating flow in the pipe and a long straight pipe section is required. It is generally recommended that the length of the upstream straight section be not less than 5D, and the length of the downstream straight section should not be less than 1D. If the installation space does not meet the above requirements, a flow control valve may be installed between the flow block and the sensor.

4. Large pressure loss, not suitable for use in low pressure media. The flow rate range is 15:1, but the initial flow rate is relatively high and it is not suitable for applications requiring low initial traffic, such as residential areas.

(III) Gas Waist Wheel Flowmeter (also called Gas Roots Flowmeter)

The operating principle of the gas roots flowmeter: The gas roots flowmeter is a volumetric flowmeter. It consists of two eight-shaped rotors and a tight flow detection chamber. With the passage of gas, the difference between the inlet and the outlet of the instrument is generated. The pressure acts on a pair of lumbar wheels that are linked together by a high-precision synchronous wheel, thereby driving the lumbar wheel to rotate in rotation. During this period, the metering chamber formed by the waist wheel and the inner wall of the housing is periodically inflated and vented, and the number of rotations of the waist wheel is proportional to the volume of gas passing through the meter. The rotation of the lumbar wheel is decelerated via a multi-stage gear train and then magnetically coupled to the counter, accumulating the total amount of gas flowing through.

1. The main technical parameters are:

Flow range: 2.5-3500m3/h

Instrument accuracy (±0.5% to ±1.5%)R

Instrument diameter: DN50 ~ 400mm

Working pressure: generally ≤1~1.6Mpa

2. The accuracy of the instrument is high. PDF is the highest accuracy in all flow meters; the range is wide (30:1 to 100:1).

3. The instrument is not affected by the distortion of the flow field in the pipeline and does not require a long straight pipe section. Particularly suitable for installation in skid mounted units.

4. Roots flowmeters rely on the fluid energy to push the measuring element, thus bringing relatively high pressure loss. The pressure loss at low pressure is 200-500 kPa.

5. It is sensitive to media contamination and requires upstream filters.

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