In this paper, the types of commonly used gas flowmeters are analyzed in detail. If you think the answer is helpful to you, please give a compliment to the American Weidun VTON flowmeter!
Gases mainly include blast furnace gas flowmeter, coke oven gas mass flowmeter, gas, air, nitrogen, acetylene, phosgene, hydrogen, natural gas, nitrogen, liquefied petroleum gas, hydrogen peroxide, flue gas, methane, butane, chlorine, biogas, carbon dioxide, oxygen, compressed air, argon, toluene, benzene, xylene, hydrogen sulfide, sulfur dioxide and ammonia;
The commonly used gas flowmeters for measuring these gases mainly include vortex flowmeter, thermal gas mass flowmeter, turbine flowmeter, vortex precession flowmeter and metal tube float flowmeter; Their selection parameters and principles are as follows.
I. Gas Vortex Flowmeter
1. Category: vortex flowmeter
The imported gas vortex flowmeter adopts piezoelectric stress sensor, which has high reliability and can work in the working temperature range of -20℃ ~+250℃. With analog standard signal and digital pulse signal output, it is convenient to cooperate with digital systems such as computers. It is an advanced and ideal measuring instrument.
2. Specific parameters
Nominal caliber: DN 15 ~ DN 2000 can be inserted:
Measurable medium temperature: -40℃ ~ 280℃, -40℃ ~ 350℃
Nominal pressure ≦ 1.6Mpa ≦2.5Mpa ≦4Mpa.
Accuracy grade: liquid 0.5, gas and steam 1.0, plug-in 2.5.
Speed range: 0.6-6m/s for liquid, 5-60m/s for gas and 5-70m/s for steam.
On-site liquid crystal display: powered by 3.6V 1 lithium battery, the service life is more than 2 years.
Material: 304 stainless steel, other materials are ordered by agreement.
Range ratio: 10: 1
Reynolds number: normal 2× 103~7* 10 extension 1* 10~7* 10.
Explosion-proof grade: intrinsically safe type: EX (IA) Ⅱ CT2-T5 flameproof type: EXD Ⅱ BT2-T5.
Protection grade: IP65, IP68
Power supply: pulse type 12VDC ~+24VDC current type 12VDC ~+24VDC 4-20mA.
Battery powered 3.6V
Ambient temperature: -40℃~+55℃ (non-explosion-proof place) -25℃~+55℃ (explosion-proof place)
Relative humidity: ≤90%
Atmospheric pressure: 86 ~106 kpa
3. Main features
Simple and firm structure, no moving parts, high reliability and convenient maintenance.
The detection element is not in contact with the medium, with stable performance and long service life.
Simple mechanism, good universality and high stability.
Output pulse priority or analog-to-digital signal proportional to flow, no zero drift, high precision, easy to connect with computer.
The flow characteristics are not affected by fluid pressure, temperature, viscosity, density and composition.
4. Principles
The gas vortex flowmeter uses the Karman vortex principle to measure the flow. When a cylinder is inserted vertically in the measuring tube, the fluid passes through the two sides of the cylinder, naturally generating regular vortices alternately, which is called Carmen vortex street. When d/D=0.28 1, the released vortex is the most stable. (d is the pipe diameter. The release frequency of Carmen vortex street and the flow rate of fluid can be expressed by the following formula: F=st? In vertical/vertical type:
F F F———————— The release frequency of Carmen Vortex Street.
St ———————— coefficient
speed
D D d———————— Column width
Strouhal coefficient is an important coefficient of vortex flowmeter. In a certain Reynolds number range, Strouhal number is close to constant. As shown in the following figure, in the straight part of the curve St=0. 17, the vortex release frequency is directly proportional to the flow rate, and the flow rate v can be obtained by detecting the frequency f, and the volume flow rate can be obtained from v. ..
Second, the thermal gas mass flowmeter
1. Category: thermal gas mass flowmeter
The thermal gas mass flowmeter is designed based on the principle of thermal diffusion, and the instrument uses the constant temperature difference method to accurately measure gas. It has the advantages of small volume, high degree of digitization, convenient installation and accurate measurement.
2. Factors
Diameter range: DN80-DN6000mm (plug-in). DN 15-DN2000mm (segmented).
Speed range: 0 1. Nano/sec-100 nm/sec (standard temperature and pressure conditions: 20℃,10/0.33 kPa).
Accuracy: 1%.
Medium temperature: -40~200℃.
Working pressure: 2.5Mpa (plug-in type) and 4.0Mpa (pipe section type).
Power supply: integrated converter AC220V or DC24V 1A, split converter AC220V.
Corresponding speed: one second.
Signal output: 4-20mA RS-485.
Display contents: instantaneous flow, mass flow, standard temperature and pressure volume flow, cumulative flow and cumulative operation.
Time, Beijing time.
Protection grade: IP68.
Explosion-proof grade: ExdⅱCT4.
3. Characteristics
A real mass flowmeter is convenient and accurate for gas flow measurement without temperature and pressure compensation. The mass flow or standard volume flow of gas can be obtained.
Wide range ratio, which can measure gas with flow rate as high as 100Nm/s and as low as 0. 1Nm/s, and can be used for gas leakage detection.
Good seismic performance and long service life. The sensor has no moving parts and pressure sensing parts, so it is not affected by vibration on measurement accuracy.
Easy to install and maintain. If site conditions permit, installation and maintenance can be realized without stopping production. (Special customization is required)
Digital design. Overall digital circuit measurement, accurate measurement and convenient maintenance.
Using RS-485 communication or HART communication, factory automation and integration can be realized.
principle
Thermal gas mass flowmeter works according to the principle of large temperature difference. The sensor part consists of two reference platinum resistance temperature sensors. When the instrument is working, a sensor continuously measures the medium temperature T 1. The other sensor is self-heating, the temperature is higher than the medium temperature T2, and it is used to detect the fluid flow, which is called the speed sensor. Temperature δ t = T2-t 1, T2 >；; T 1, when the fluid flows, the temperature of T2 drops, because gas molecules collide with the sensor and take away the heat of T2. If Δ t is to be kept constant, the power supply current of T2 must be increased. The faster the gas flows, the more heat it takes away. There is a fixed functional relationship between gas flow and increased heat, which is the principle of constant temperature difference.
Third, the gas turbine flowmeter
1. Category: gas turbine flowmeter
Gas turbine flowmeter is a new generation of high-precision, high-reliability gas precision metering instrument, which integrates temperature, pressure and flow sensors and intelligent flow totalizer. It has excellent low-pressure and high-pressure metering performance, diverse signal output modes and low sensitivity to fluid disturbance, and is widely used in the metering of natural gas, coal-based gas, liquefied gas and light hydrocarbon gas.
2. Factors
Nominal diameter: pipe type: DN4~DN200, plug-in type: DN 100 ~ DN2000.
Accuracy grade: pipeline type: 0.5, 1.0, plug-in type: 1.5, 2.5.
Ambient temperature: -20℃ ~ 50℃
Medium temperature: measuring liquid: -20℃ ~ 120℃
Measuring gas: -20℃ ~ 80℃
Atmospheric pressure: 86 kPa ~ 106 kPa
Nominal pressure: 1.6 MPa, 2.5 MPa, 6.4 MPa, 25 MPa.
Explosion-proof grade: ExdIIBT4
Connection mode: threaded connection, flange clamping, flange connection, plug-in, etc.
Transmission distance: the distance from the sensor to the display can reach 500m m.
3. Characteristics
High-quality alloy turbine with higher flow stability and corrosion resistance;
Imported high-quality special bearings with long service life;
The metering room is isolated from the ventilation room to ensure the safety of the instrument;
It can detect the temperature, pressure and flow rate of the measured gas, automatically track and compensate the flow rate, and display it.
Gas volume accumulation in standard form (Pb = 10 1.325kpa, TB = 293.15k); Temperature and pressure values can be queried in real time;
Wide flow range (Qmax/Qmin≥20: 1), good repeatability, high accuracy (up to 1.0), small pressure loss and low initial flow rate, up to 0.6m3/h;
Multi-point nonlinear correction of intelligent instrument coefficients;
Built-in pressure and temperature sensors, high safety performance, compact structure and beautiful appearance;
The instrument has explosion-proof and protective functions. The explosion-proof marks are ExdⅱBT4 and ExiaⅱCT4, and the protection level is IP65.
The power consumption of the system is low, and a 3.2V 10AH lithium battery can be used continuously for more than 3 years.
The instrument coefficient and cumulative flow value will not be lost after ten years of power failure.
4. Principle of imported gas turbine flowmeter
When the fluid flows into the flowmeter, it is rectified and accelerated by a special integrated rectifier at the air inlet. Because the turbine blades form a certain angle with the flow direction of the fluid, the turbine generates a rotating torque at this time, and after overcoming the friction torque and the fluid resistance torque, the turbine begins to rotate. In a certain flow range, the angular velocity of turbine rotation is proportional to the fluid volume flow. According to the principle of electromagnetic induction, a magnetic sensor is used to induce a pulse signal proportional to the fluid volume flow from a coaxial rotating signal wheel. After amplification, filtering and shaping, the signal enters the microprocessor unit of intelligent flow totalizer together with the signals of temperature and pressure sensors for operation, and the volume flow and total amount of gas are directly displayed on the LCD screen.
Four, vortex precession flowmeter
1. Category: vortex precession flowmeter
Vortex precession flowmeter is used in petroleum, chemical industry, electric power, metallurgy, urban gas supply and other industries to measure various gas flows, and it is the first choice for oil field and urban natural gas transmission and distribution measurement and trade measurement.
2. Factors
Diameter: DN25-DN200
Flow range: 2.5m3/h
Ambient temperature: -30℃ ~+55℃
Relative humidity: 5% ~ 95%
Atmospheric pressure: 86 kPa ~ 106 kPa
Medium temperature range: -20℃ ~+70℃
Nominal pressure: 1.6, 2.5, 4.0 and 6.3MPa
Explosion-proof marks: explosion-proof type, and explosion-proof marks are ExdⅱBT4 and EXDⅱCT4 ~ T6 (excluding acetylene).
Outlet interface: M20× 1.5 internal thread.
3. Features:
No mechanical moving parts, corrosion resistance, stability and reliability, long service life, long-term operation without special maintenance;
Adopt 16 bit computer chip, with high integration, small size, good performance and strong function of the whole machine;
Intelligent flowmeter integrates flow probe, microprocessor, pressure and temperature sensors, and adopts
Built-in combination makes the structure more compact, which can directly measure the flow, pressure and temperature of fluid, and automatically track and compensate and correct the compression factor in real time;
Adopting double detection technology can effectively improve the detection signal strength and suppress the interference caused by pipeline vibration;
Adopt the leading intelligent seismic technology in China to effectively suppress the interference signals caused by vibration and pressure fluctuation;
Chinese character dot matrix display screen is adopted, which has many display digits, intuitive and convenient reading, and can directly display the volume flow in working state, the volume flow and total amount in standard state, and the parameters such as medium pressure and temperature.
Using EEPROM technology, the parameters are convenient to set and can be stored permanently, and the historical data can be stored for up to one year;
The converter can output frequency pulse, 4 ~ 20mA analog signal, and has RS485 interface, which can be directly connected with a microcomputer, and the transmission distance can reach1.2km.:
The power consumption of the whole machine is low, and it can be powered by internal battery or external power supply.
4. Principles
The flow curve of the flow sensor is similar to that of a venturi. A set of spiral guide vanes is placed on the inlet side. When the fluid enters the flow sensor, the guide vanes force the fluid to generate violent vortex. When the fluid enters the diffusion section, the vortex is affected by the backflow and starts to rotate for the second time, forming a gyro vortex precession phenomenon. The precession frequency is proportional to the flow velocity and is not affected by the physical properties and density of the fluid. The precession frequency of fluid secondary rotation measured by the detection element can obtain good linearity in a wide flow range. The signal is amplified, filtered and shaped by a preamplifier, and then converted into a pulse signal proportional to the flow rate, and then sent to a microprocessor for integration with detection signals such as temperature and pressure. Finally, the measurement results (instantaneous flow rate, cumulative flow rate and temperature and pressure data) are displayed on the LCD screen.
Five, metal tube float flowmeter
1. Category: metal tube float flowmeter
VNLZ series metal tube float flowmeter is a variable area flowmeter based on float position measurement. All-metal structure has the characteristics of small volume, small pressure loss, large range ratio (10 ~ 20: 1) and convenient installation and maintenance, and is widely used in flow measurement and process control of small flow, low flow rate and various harsh media conditions in complex and harsh environments in various industries.
2. Factors
The measuring range is water (20℃) 6 ~150000 liters/hour and air (0. 10 13 MPa 20℃) 0.05 ~ 4000 cubic meters/hour.
Range ratio 10: 1 (special type 20: 1)
Accuracy grade 2.5 1.5 (special type 1.0)
Working pressure dn 15 ~ dn50pn4.0mpa (special type 25mpa) dn80 ~ dn100pn1.6mpa (special type 16MPa).
Jacket pressure grade: 1.6MPa
Standard medium temperature -80℃ ~+220℃ High temperature type 300℃ PTFE lining type ≤85℃
The ambient temperature is -40℃ ~+ 120℃ (remote control type ≤65℃).
Medium viscosity dn 15: ≤ 5mpa.s, ≤30mPa.s, DN25: ≤250mPa.s, dn50 ~ dn150: ≤ 300mpa.s.
Liquid crystal display instantaneous flow display numerical range: 0 ~ 9999.99, cumulative flow display numerical range: 0 ~ 999999.90.
Output standard signal: 2-wire system 4 ~ 20ma.
Alarm signal: open collector, MAX 100Ma@30VDC internal impedance 100.
Standard power supply: 24 VDC 20%, AC type: 220 VAC (85 ~ 265 VAC), battery type: 3.6@5.2AH lithium battery.
Standard connection mode: HG20592 flange, special type: user-provided flange standard, threaded connection.
Connection: DIN 1 185 1 or user specified.
Electrical interfaces M20× 1.5, PG 1 1, 1/2 "NPT.
Total height standard: 250mm (except other installation methods)
Protection grade IP65
Intrinsically safe explosion-proof mark: EXAIICT 4
Flameproof type: ExdIIBT4
3. Characteristics
Large screen LCD display, which can display instantaneous flow and cumulative flow at the same time.
The upper row can be switched to display: instantaneous flow, loop current, cumulative small signal cut-off, current ambient temperature, pointer rotation angle and other information. At this time, the display of the cumulative quantity in the next line will not be affected.
The liquid crystal displays the instantaneous flow under the second working condition. When ordering, the cumulative quantity can be selected from the cumulative quantity under the first working condition or the cumulative quantity under the second working condition.
The power consumption of double-row liquid crystal is microampere, which meets the explosion-proof requirements of intrinsic safety.
Accuracy:
Perfect power-off protection function, which can save the cumulative current flow (cumulative sampling period is 0.3S) when power is cut off.
The transmitter can output: three-wire system, 0- 10mA signal, which has nothing to do with LCD display function.
Support battery power supply function, use the rechargeable battery of the specified model, and it can work normally for 3-4 months at a time according to the different environmental temperatures.
4. Principles
The measurement of flow rate is completed by the transmitter in the indicator through coupling magnetic steel to sense the change of float position, and the signal is transmitted to a far place. When the measured medium flows through the measuring tube from bottom to top, when the float is balanced by the vertical driving force of gravity, buoyancy and fluid flow rate, the float is relatively static at a certain position, which changes with the annular area of the float and conical tube and the fluid flow rate, and the position of the float corresponds to the flow rate of the measured medium.
According to the above principles and characteristics, users can choose VTON gas flowmeter with suitable working conditions.