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Natural Gas Flow Meter
Jan 10, 2019


Natural gas flow meter


Natural gas is a multi-component mixed gaseous fossil fuel, and its measurement as a high-quality energy and chemical raw material is increasingly being valued and utilized. Countries such as Europe and the United States started the research on natural gas metering technology earlier, especially the natural gas metering for trade settlement. With the construction of China's West-East Gas Pipeline Project, natural gas coverage is becoming more and more extensive, so the selection of natural gas flowmeters is an important part of all natural gas metering sites.

Flowmeters for measuring natural gas include a swirling vortex flowmeter, a gas Roots flowmeter, a gas turbine flowmeter, and a vortex flowmeter (relatively used, for reasons explained below). These flowmeters have their own strengths. Or how should the factory choose the right flow meter under different working conditions?

First of all, we must look at the working conditions of the customer's on-site pipeline, with or without interference or vibration.

1. When there is interference and vibration at the site, the gas Roots flowmeter can be selected because the flowmeter adopts the mechanical measurement principle and is free from vibration interference.

2. There is no interference and no vibration at the scene, then we can choose fluid oscillating flowmeter (screw vortex flowmeter).

3. If the on-site flow is relatively large and there is vibration and interference, then the gas turbine flow meter can be selected for the customer.

4. Why is the vortex flowmeter used less? The current vortex flowmeter with temperature and pressure compensation can directly display the standard and flow, but the defect is that compared with the other three flowmeters, it has very high requirements for straight pipe sections, and many natural gas pipelines have long transport distances, in order to resist thermal expansion and cooling. Shrinking, there will be many arched pipes, so it is difficult to find a suitable mounting point. Moreover, the natural gas transmission pipeline is long and there is no guarantee of interference vibration around. The following three detailed flow meters are described in detail.

Natural gas flow meter

Rotary vortex flowmeter:

I. Overview: 


The precession vortex flowmeter is a kind of precision flow measuring instrument. It can be used to measure the flow and total amount of gas with the corresponding flow accumulating instrument and field display instrument. It is widely used in petroleum, chemical, metallurgy, scientific research and other fields. The metering and control system, especially for the measurement of natural gas, dry gas, compressed air, etc., the gas turbine flowmeter is a kind of low-reproducibility and high precision. It is a precision instrument suitable for trade settlement. It is One is suitable as one of the corporate trade settlements.

Rotary vortex flowmeter

Ⅱ.The working principle:


When the vortex flowmeter is used to measure gas, firstly, according to the pipeline gas delivery volume and the temperature and pressure range that the medium can reach, the zui high and zui low volume flow rate under working conditions are estimated, and the flowmeter specifications are correctly selected; The caliber can cover the flow range. When the pressure range allows, it is recommended to select a smaller flow meter. In order to facilitate maintenance, it does not affect the fluid transportation. It is recommended to install a bypass pipe and ensure the length of the straight pipe segment specified. If the gas contains large particles or fibers, a filter should be installed upstream.


Ⅲ.The characteristics:


1, no mechanical moving parts, not easy to corrode, stable and reliable, long life, long-term operation without special maintenance;


2, using 16-bit computer chip, high integration, small size, good performance, the machine features strong;


3. Intelligent flowmeter integrates flow probe, microprocessor, pressure and temperature sensor. It adopts built-in combination to make the structure more compact. It can directly measure the flow, pressure and temperature of the fluid, and automatically track the compensation and compression factor in real time. Amend


4. Double detection technology can effectively improve the detection signal strength and suppress the interference caused by pipeline vibration;


5. Adopting the intelligent anti-seismic technology of domestic ling first, effectively suppressing the interference signals caused by vibration and pressure fluctuations;


6, using Chinese character dot matrix display, display more digits, the reading is intuitive and convenient, can directly display the volume flow under working conditions, the volume flow under standard conditions, the total amount, as well as the medium pressure, temperature and other parameters;


7, using EEPROM technology, parameter setting is convenient, can be stored for a long time, and can save the historical data of zui for one year;


8, the converter can output frequency pulse, 4 ~ 20mA analog signal, and has RS485 interface, can be directly connected with the microcomputer, the transmission distance can reach 1.2km;


9. Multi-physical parameter alarm output, which can be selected by the user;


10, the flow meter head can be rotated 360 degrees, easy to install and use;


11. With the company's FM data collector, remote data transmission via the Internet or network


12, pressure, temperature signal is the sensor input mode, strong interchangeability;


13. The power consumption of the whole machine is low, and it can be powered by the internal battery or external power supply.


Ⅳ.How to ensure the accuracy of the measurement of the spiral vortex flowmeter:


1, The correct selection


In the case where the type of flow meter has been selected, it is a crucial step in the selection of the flowmeter specifications and the matching originals. Because only the selection is correct, the customer can use it well. However, there are two basic principles to be adhered to in the selection: one must ensure the accuracy of use, and the other must ensure production safety. To achieve these two points, we must implement three selection parameters, 1. The size of the near and long term 2. The commonly used instantaneous flow rate 3. The design pressure and working pressure of the measured medium.


2. Standard school before use

Firstly, it is considered that there are still some difficulties in the field calibration of such flowmeters. Secondly, if the purchase is used, this flowmeter is used for important measurement occasions, such as the measurement points of large-flow trade measurement or measurement disputes, and The use site does not have the conditions for the flow site calibration. In this case, it is easy to judge that all the performance of the flowmeter is qualified by the certificate provided by the manufacturer at the time of purchase. It is. Therefore, in order to ensure the reliability and accuracy of the measurement results of the flowmeter in the future, it is necessary to send the flowmeter to an authoritative and qualified inspection department for a system verification within the full flow range before the official site installation.


3, Gigorous process installation

Although this type of flowmeter does not have too many special requirements for the process installation and use environment, any type of flowmeter has such a commonality, that is, to avoid vibration and high temperature environment as much as possible, and to keep the inner wall of the straight pipe section before and after the flowmeter smooth and flat. Straight, to ensure that the measured medium is a clean one-way fluid.


4. Strengthen post management

Although the flowmeter has many automatic disposal functions and micro-power consumption characteristics, it still needs to be strengthened after it is put into operation. For example, in order to ensure the stability and accuracy of long-term operation of the flowmeter, the system should be regularly calibrated and transcribed. Header data, change media parameters and check battery conditions from time to time, check flow meter coefficients and seals.


5, Pay attention to internal maintenance

If it is necessary to inspect or clean the measuring chamber of the flowmeter and its components due to impurities in the gaseous medium or other reasons, special attention should be paid to the following points: for the same type of flowmeter of the same specification, the core of the body, the fluid guiding body, etc. The components are not interchangeable. Otherwise, the metering factor of the meter needs to be recalibrated and the temperature and pressure sensors associated with it are coefficient corrected.


Gas turbine flow meter:


I. Overview:


The gas turbine flow meter is a precision flow meter that can be used to measure the flow and total amount of liquid in conjunction with the corresponding flow meter. Gas turbine flowmeters are widely used in metrology and control systems in petroleum, chemical, metallurgical, scientific research and other fields. Gas turbine flow meters equipped with sanitary fittings can be used in the pharmaceutical industry.


The integrated gas turbine flowmeter is an explosion-proof design that displays total flow, instantaneous flow and flow full percentage. The battery uses a long-lasting lithium battery. The battery life of the single-function integrated meter can reach more than 5 years, and the battery life of the multi-function display meter can reach more than 12 months.


The integrated meter can display a large number of flow units, including cubic meters, gallons, liters, standard cubic meters, standard liters, etc., which can set fixed pressure and temperature parameters to compensate for gas, and occasions where pressure and temperature parameters change little. The instrument can be used for fixed compensation integration.

Gas turbine flow meter

Ⅱ.The working principle:


 Gas turbine flow meters are measured using an impeller probe. It first converts the flow rate to the speed of the turbine and then converts the speed into an electrical signal proportional to the flow. This flow meter is used to detect instantaneous flow and total accumulated flow, and its output signal is frequency, which is easy to digitize. In the figure, the induction coil and the magnet are fixed together on the casing. When the ferromagnetic turbine blade passes the magnet, the magnetic resistance of the magnetic circuit changes to generate an induced signal. The signal is amplified and shaped by an amplifier and sent to a counter or frequency meter to display the total integrated flow. At the same time, the pulse frequency is frequency-voltage converted to indicate the instantaneous flow rate. The speed of the impeller is proportional to the flow rate, and the number of revolutions of the impeller is proportional to the total amount flowing. The output of the turbine flowmeter is a frequency modulated signal that not only improves the immunity of the detection circuit, but also simplifies the flow detection system. It has a turndown ratio of 10:1 and an accuracy of ±0.2%. Turbine flowmeters with small inertia and small size have a time constant of 0.01 seconds.



Ⅲ.The characteristics:


1. Gas turbine flowmeter has high precision, low pressure loss, low initial flow, automatic tracking and compensation for temperature and pressure, battery power supply, can output a variety of signals, use imported bearings, long life and easy installation. The intelligent speed flow meter integrates flow, temperature and pressure detection functions, and can perform temperature and pressure compensation. It has the advantages of high accuracy, good repeatability, wide measuring range and convenient installation and use.


2, the use of new microprocessors and high-performance integrated chips, high computing precision, powerful machine features, superior performance.


3, using micro-power high-tech, the overall power consumption is low. It can be operated with long-term power supply with built-in 3.6V battery, and can be powered by 24V external power supply.


4. Adopting new type of sensor, it has good anti-vibration and anti-pulsation flow performance, is not easy to corrode, has good reliability and long service life.


5. According to the flow frequency signal, the meter coefficient can be automatically corrected linearly in eight segments, and the calculation accuracy of the instrument can be improved according to the needs of the user.


6, using EEPROM data storage technology, with historical data storage and query functions, three historical data recording methods for users to choose.


7. The meter head can be rotated by 180°, which is easy to install and use.


8, high-precision measurement, generally up to ± 1.5%, ± 1.0%.


9. Repeatability is good, and the short-term repeatability can reach 0.05%~0.2%. It is because of good repeatability that it is the preferred flow meter in trade settlement.


10, can detect the temperature, pressure and flow of the detected gas, can automatically track the flow compensation, and display the standard state (

  Gas flow rate of Pn=101.325KPa, Tn=293.15K): The temperature, pressure, time, date and other data can be queried in real time.


Ⅳ.How to improve the accuracy of gas turbine flowmeter use:

1. As long as the flowmeter's operating conditions (including fluid flow characteristics, medium characteristics, operating process and flow range) are consistent with the timing, the accuracy of the same accuracy as the flowmeter calibration accuracy will be obtained. This requires that the flowmeter be used in the same way as the flow characteristics of the calibrated fluid (the velocity distribution at the flowmeter inlet); the physical properties (density, etc.) of the fluid are the same; the verification process is the same, and the meter is used within the flowmeter's calibrated flow range. Constant, then after the medium density pressure correction, its accuracy is equivalent to its verification accuracy.

2. If the flowmeter's use and verification conditions meet the above-mentioned principle of identity, and the flowmeter is used at a fixed point within the verification flow range (using the average of the meter coefficients under its verification flow), the accuracy of the flowmeter will be greatly improved. Better than its verification accuracy.

3. If the flowmeter is actually used in the verification of the range, the characteristic equation can be used, that is, according to the corresponding relationship between the average meter coefficient and the flow rate Q under each flow obtained in the verification, by the principle of least squares, the straight line fitting obtains Kl= Aq+b, replacing the meter constant k with the fitted K1, can also improve the accuracy of the flowmeter.


Gas Roots Flowmeter:

I. Overview:


Gas Roots Flowmeters are primarily used for high-precision meters that continuously or intermittently measure the flow of gases or liquids in a pipeline. The utility model has the advantages of high precision, good reliability, light weight, long service life, low running noise, convenient installation and use, etc. The waist wheel flow meter can indicate cumulative flow, instantaneous flow, single quantity, etc., and can also output pulse signals, 4- 20mA or 1-5V analog signal, 485 communication, 4-20mA+HART, MODBUS protocol, etc. The waist wheel flow meter is composed of a measuring chamber, a metering rotor, a metering component assembly (ie, an internal measuring component), and a counting indicating component. There is a measuring chamber in the housing of the waist flow meter. There are one or two pairs of waist wheels that can be rotated tangentially in the measuring chamber (in fact, the gear with modulus 2). In the place of replacement, it can be equipped with intelligent volume conversion equipment. In order to realize the volume conversion of the total volume of gas under working conditions to standard state or other agreed state, as well as auxiliary functions such as data storage and data transmission.

Gas Roots Flowmeter

Ⅱ.The working principle:


 The rotational speed of the gas Roots flowmeter is detected by a sensing coil mounted outside the casing. When the Roots flowmeter blade cuts the magnetic lines of force generated by the magnetic steel inside the casing, it causes a change in the magnetic flux in the sensing coil. The sensing coil sends the detected magnetic flux cycle change signal to the preamplifier, amplifies and shapes the signal, generates a pulse signal proportional to the flow rate, and sends it to the unit conversion and flow total calculation circuit to obtain and display the cumulative flow value; At the same time, the pulse signal is also sent to the frequency current conversion circuit, and the pulse signal is converted into an analog current amount, thereby indicating the instantaneous flow value.


Ⅲ.The characteristics:


1. Advanced machining and surface treatment processes, wear-free rotation, contactless sealing, self-cleaning and good lubrication of the bearings ensure high accuracy and long-term normal operation of the flowmeter.


2. Wide range: wide range of applications


3. Strong interchangeability: The flowmeter replacement work is simple and fast, no need to re-pipe. The dial can be equipped with a threaded looper and a looper flange. The height of the looper is 75mm.


4. High precision and long service life


The measurement accuracy is 1.5 (special requirements of the standard table 1.0); after 15 years of use under the clean gas conditions, the metering accuracy basically maintains the original factory accuracy.


5. The starting flow rate and the stop flow rate are extremely low: generally 0.05 to 1.15 m3/h.


6. The pressure loss is small: generally less than 0.5 kPa, and the Zui is as small as 0.08 kPa.


7. A variety of display instrument matching options:


8. Configure the performance characteristics of the DTCM intelligent flow totalizer


9. Configuring the performance characteristics of the MCQ pulse counter


Ⅳ.Several factors affecting the accuracy of the gas lumbar flowmeter:


It is not difficult to see from the principle that the key components affecting the metering accuracy of the flowmeter are mainly the measuring chamber and the rotor. The machining accuracy of these two components directly affects the metering accuracy of the flowmeter after assembly. In the past, our factory used a profile milling cutter to machine the rotor. The result was not good. The symmetry of the machined rotor surface was poor. Therefore, the measurement accuracy was always maintained at 1.5, which is difficult to improve. Later, all machining centers were used to ensure the symmetry of the rotor and the measuring chamber. In addition, the dynamic balance of the rotor is also a key factor. After each rotor is processed, there is more or less unbalance, and these unbalances generally affect the flow rate of the flowmeter.

Synchronous gear machining accuracy affects the metering accuracy of the flowmeter and the noise during operation. The function of the synchronous gear is to ensure that the two conjugate rotors maintain a certain gap regardless of the angle. The gap between the two rotors varies according to the diameter of the flowmeter. Generally, the small-diameter flowmeter is maintained at about 0.1 mm, and the large-diameter is maintained at about 0.4 mm. The size of the gap directly affects the accuracy of the measurement: the gap is large, and the gas is relatively lost through the gap, which causes the measurement accuracy of the flow meter to decrease. However, the relatively large particle impurities in the gas can also pass through the gap without affecting the measurement. On the contrary, the gap is small, the amount of gas lost through the gap is small, the flow metering accuracy is increased, and large particle impurities are not easily passed through the gap, thereby causing the flow meter card table to make the flow meter unable to work normally.


The selection of standard parts can also affect the measurement accuracy of the flow meter. The most important part of the standard parts is the bearing. Our factory mainly chooses SKF, NSK imported bearings. In order to reduce the flow rate of the flowmeter, the dust cover at one end of the bearing is picked up, and the grease inside the bearing is washed out because the grease will be damped during the rotation of the bearing. In the process of using the flowmeter, the bearing is lubricated by means of splash lubrication, so that the bearing can dissipate heat in time and prolong the service life of the bearing.

Natural gas flow meter

The above analysis is the impact of the flowmeter's own components on the accuracy of the flowmeter measurement. There are also many other situations that affect the metering of the flowmeter during actual use. There are mainly the following aspects:


1. High pressure metering and low pressure gas. That is, the measuring chamber is installed on the high-pressure pipeline, and then the pressure is regulated by the pressure regulator, and the gas is used by the gas household on the low-pressure pipeline. When the gas consumption of the low-pressure pipeline is small, according to the gas state equation, the temperature is similar. When the low flow rate of the low pressure pipeline is calculated, the flow rate of the high pressure pipeline will be smaller, and even this flow rate does not reach the flow rate of the flowmeter. The flow meter does not count. Therefore, it will cause a large measurement error.


2. Unreasonable piping design may cause large measurement errors. Two parallel pipes, when the main network uses gas, the sub-network manual valve is closed. The flow meter is normally measured. When the pipe network is also used, the manual valve is opened. Since the gas of the main pipe is diverted from the sub-pipe, the air pressure in the main pipe will drop, so that the pressure in front of the flow meter is less than the pressure behind the table. The meter reverses and the flow meter also accumulates flow, resulting in double metering. To avoid this, a check valve must be installed in front of the flow meter.


Correct installation of the pipe installation diagram helps to improve the metering accuracy and extend the service life of the flowmeter. When the flowmeter is installed on the pipeline, the threaded hole on the meter body and the screw hole of the pipe flange should be aligned to ensure the parallelism of the flange, and the flowmeter should be protected from other external forces to prevent the deformation of the body. The flow meter is stuck. When opening the flowmeter, first open the front valve, then slowly open the rear valve to make the flowmeter pressure start, to avoid the gas impact of the flowmeter rotor due to the air hammer effect, causing the flowmeter to be stuck.


Huaheng Instrument specializes in supplying electromagnetic flowmeter, vortex flowmeter, gas turbine flowmeter, spiral vortex flowmeter, orifice flowmeter, liquid turbine flowmeter, natural gas flowmeter, steam flowmeter, dual rotor flowmeter, target type Flowmeter, thermal gas flowmeter, elliptical gear flowmeter, ultrasonic flowmeter, magnetic flap level gauge, ultrasonic level gauge, radar level gauge, diaphragm pressure gauge, digital pressure gauge, diaphragm pressure gauge, stainless steel Series of flowmeters such as pressure gauges, bimetal thermometers, thermocouples, pressure calibrators, bench pressures, etc. It is widely used in electric power, petroleum, chemical, machinery, metallurgy, cement, glass, coking and other industries in various countries.