The application of vortex flowmeter in steam metering. Overview:
The LS-LUG vortex flow sensor is the ideal alternative to the orifice flowmeter. The vortex flowmeter is a new type of flowmeter with international advanced level developed based on the principle of Karmen vortex street because it has other flowmeters. The advantages that cannot be possessed have been rapidly developed since the 1970s. According to relevant data, the proportion of vortex flowmeters in developed countries in Japan, Europe, and the United States has increased dramatically, and they have been widely used in various fields and will be used for future traffic. The leading position in the instrument. SDLUGB vortex flow sensor is suitable for measuring the mass flow and volumetric flow of superheated steam, saturated steam, compressed air and general gases, water and liquids.
2. The advantages of vortex street flow meters in steam metering:
1. The structure is simple and firm, no moving parts, high reliability, and long-term operation is very reliable.
2 • Easy to install and easy to maintain. Unlike differential pressure flowmeters, which are equipped with a guide tube and a fixed bracket, it saves installation costs, reduces failure points, and does not require insulation measures.
3. The detection sensor does not directly contact the measured medium, and has stable performance and long service life. (For built-in type)
4. The output is a pulse signal proportional to the flow rate, zero drift, high accuracy. It can also output 4-20MA signal as needed.
5. Wide measuring range, up to 1:10 ratio, up to 1:20. This is very useful for some steam metering of users who are very unbalanced with steam.
6. Less pressure loss, lower operating costs, more energy-saving significance. (relative to differential pressure flowmeters).
III. Working principle:
A vortex generating body (baffle) is provided in the fluid, and a regular vortex is alternately generated from both sides of the vortex generating body. This vortex is called a Karman vortex street, as shown in FIG. 1 . The vortex arrays are arranged asymmetrically downstream of the vortex generators. Let the vortex frequency be f, the average speed of the measured medium flow is U, the width of the vortex generator is d, and the diameter of the watch body is D. According to the principle of Karman vortex street, there is the following relationship f=SrU1/d =SrU/md(1)
In the formula U1--average velocity of the vortex generating body, m/s;
Sr-- Strouhal number;
M-- ratio of the arch area on both sides of the vortex generator to the cross-sectional area of ​​the pipe. The volume flow qv in the pipe is qv=πD2U/4=πD2mdf/4Sr(2)
K=f/qv=[Ï€D2md/4Sr]-1(3)
In the formula K--flowmeter meter coefficient, pulse number /m3(P/m3).
In addition to the geometric dimensions of the vortex generating body and the pipeline, K is also related to the Strouhal number. The Strouhal number is a dimensionless parameter, which is related to the shape of the vortex generator and the Reynolds number. Figure 2 shows the relationship between the Strouhal number of a cylindrical vortex generator and the Reynolds number of the pipeline. As can be seen from the figure, in the range of ReD=2×10 4 to 7×10 6 , Sr can be regarded as a constant, which is the normal operating range of the instrument. When measuring the gas flow rate, the vortex flowmeter's flow rate calculation formula is qVn, qV--in the standard state (0oC or 20oC, 101.325kPa) and the volumetric flow rate under working conditions, m3/h;
Pn, P - are the absolute pressures under standard conditions and conditions, respectively, Pa;
Tn, T - are the thermodynamic temperatures under standard conditions and conditions, respectively, K;
Zn, Z-- are the gas compression coefficients under standard conditions and conditions, respectively.
It can be seen from the above equation that the pulse frequency signal output by the vortex street flow meter is not affected by changes in the fluid properties and components, that is, the meter coefficient is only related to the shape and size of the vortex generating body and the pipe within a certain Reynolds number range. However, as the flowmeter needs to detect the mass flow in the material balance and energy metering, the output signal of the flowmeter should monitor the volume flow and the fluid density at the same time, and the fluid properties and components have a direct impact on the flowmeter.
four. Instrument selection:
The correct selection of the instrument is the key to the normal use of the instrument. In practical applications, too many faults are caused by the unreasonable selection of the instrument. Detailed understanding of the operating conditions and media parameters of the field application, selection of the appropriate pressure, temperature, Protection, explosion-proof grades and materials, structural methods, to ensure that the instrument can operate in the best condition. For vortex flow meters for steam metering, I think the main steps are as follows:
1. First understand the measured working medium, saturated steam or superheated steam.
2. Determine the scope of use of the flow: maximum flow and minimum flow.
3. Understand the maximum, common, minimum working pressure and working temperature of the medium; (for saturated steam, just know the pressure or temperature)
4. Check the table to get the density under working conditions.
5. According to the above data, for saturated steam, we can find the closest flow table from the table of saturated steam flow rates in the table of instructions. (Superheated steam can be checked from the saturated steam flow table according to the corresponding density. )
6. Finally, depending on the working environment of the site, whether the choice is to use integrated or separate. (eg medium temperature is high)
Fives. Limitations analysis:
1. The requirements for the straight section are relatively high. Generally, the minimum straight section is about 15D, and the straight section is about 5D.
2. Steam water hammer can easily damage the probe and vortex generator.
3. It is not suitable for installation in places where the vibration of pipelines is strong or where interference is strong.
4. The temperature of the measured medium can not be too high, the maximum can not be higher than 400 degrees.
5. The flowmeter with large diameter is now less stable (greater than DN250MM)
six. installation:
1. The vortex street flow meter is a flowmeter sensitive to the distortion of the flow velocity distribution of the pipeline, swirling flow, and moving flow. Therefore, attention should be paid to the installation conditions of the pipeline on site and it should be performed in accordance with the requirements of the manufacturer's instructions.
2. Reducing the effect of vibration on the vortex flowmeter should be of concern as a prominent issue in the field installation of vortex flowmeters. First try to avoid the vibration source when selecting the sensor installation site. Second, the use of elastic hoses connected in small diameters can be considered. Thirdly, the installation of pipeline supports is an effective method of vibration reduction.
3. Take a pressure measurement point at 2-10D upstream of the vortex flowmeter and take a temperature measurement point at the downstream 5-10D of the flowmeter. The temperature measuring element should be probed into the inside of the pipe and face the direction of the fluid.
4. The following rules must be followed when installing the instrument on the pipe:
(1). The inner diameter of the pipe should be consistent with the diameter of the sensor.
(2). When welding flanges, they should not be welded.
(3). When installing, pay attention to the flow direction of the sensor's flow direction to the medium.
In short, after several years of use, we have found that vortex flowmeters are very suitable for the steam metering of external heating users, and they have also been acknowledged by the majority of users. However, the vortex flowmeters we have made are not standardized yet. Standards, we look forward to, with the continuous development of technology, domestic vortex street flow meter can be more and more standardized, measurement accuracy is getting higher and higher, more convenient for our users.
The LS-LUG vortex flow sensor is the ideal alternative to the orifice flowmeter. The vortex flowmeter is a new type of flowmeter with international advanced level developed based on the principle of Karmen vortex street because it has other flowmeters. The advantages that cannot be possessed have been rapidly developed since the 1970s. According to relevant data, the proportion of vortex flowmeters in developed countries in Japan, Europe, and the United States has increased dramatically, and they have been widely used in various fields and will be used for future traffic. The leading position in the instrument. SDLUGB vortex flow sensor is suitable for measuring the mass flow and volumetric flow of superheated steam, saturated steam, compressed air and general gases, water and liquids.
2. The advantages of vortex street flow meters in steam metering:
1. The structure is simple and firm, no moving parts, high reliability, and long-term operation is very reliable.
2 • Easy to install and easy to maintain. Unlike differential pressure flowmeters, which are equipped with a guide tube and a fixed bracket, it saves installation costs, reduces failure points, and does not require insulation measures.
3. The detection sensor does not directly contact the measured medium, and has stable performance and long service life. (For built-in type)
4. The output is a pulse signal proportional to the flow rate, zero drift, high accuracy. It can also output 4-20MA signal as needed.
5. Wide measuring range, up to 1:10 ratio, up to 1:20. This is very useful for some steam metering of users who are very unbalanced with steam.
6. Less pressure loss, lower operating costs, more energy-saving significance. (relative to differential pressure flowmeters).
III. Working principle:
A vortex generating body (baffle) is provided in the fluid, and a regular vortex is alternately generated from both sides of the vortex generating body. This vortex is called a Karman vortex street, as shown in FIG. 1 . The vortex arrays are arranged asymmetrically downstream of the vortex generators. Let the vortex frequency be f, the average speed of the measured medium flow is U, the width of the vortex generator is d, and the diameter of the watch body is D. According to the principle of Karman vortex street, there is the following relationship f=SrU1/d =SrU/md(1)
In the formula U1--average velocity of the vortex generating body, m/s;
Sr-- Strouhal number;
M-- ratio of the arch area on both sides of the vortex generator to the cross-sectional area of ​​the pipe. The volume flow qv in the pipe is qv=πD2U/4=πD2mdf/4Sr(2)
K=f/qv=[Ï€D2md/4Sr]-1(3)
In the formula K--flowmeter meter coefficient, pulse number /m3(P/m3).
In addition to the geometric dimensions of the vortex generating body and the pipeline, K is also related to the Strouhal number. The Strouhal number is a dimensionless parameter, which is related to the shape of the vortex generator and the Reynolds number. Figure 2 shows the relationship between the Strouhal number of a cylindrical vortex generator and the Reynolds number of the pipeline. As can be seen from the figure, in the range of ReD=2×10 4 to 7×10 6 , Sr can be regarded as a constant, which is the normal operating range of the instrument. When measuring the gas flow rate, the vortex flowmeter's flow rate calculation formula is qVn, qV--in the standard state (0oC or 20oC, 101.325kPa) and the volumetric flow rate under working conditions, m3/h;
Pn, P - are the absolute pressures under standard conditions and conditions, respectively, Pa;
Tn, T - are the thermodynamic temperatures under standard conditions and conditions, respectively, K;
Zn, Z-- are the gas compression coefficients under standard conditions and conditions, respectively.
It can be seen from the above equation that the pulse frequency signal output by the vortex street flow meter is not affected by changes in the fluid properties and components, that is, the meter coefficient is only related to the shape and size of the vortex generating body and the pipe within a certain Reynolds number range. However, as the flowmeter needs to detect the mass flow in the material balance and energy metering, the output signal of the flowmeter should monitor the volume flow and the fluid density at the same time, and the fluid properties and components have a direct impact on the flowmeter.
four. Instrument selection:
The correct selection of the instrument is the key to the normal use of the instrument. In practical applications, too many faults are caused by the unreasonable selection of the instrument. Detailed understanding of the operating conditions and media parameters of the field application, selection of the appropriate pressure, temperature, Protection, explosion-proof grades and materials, structural methods, to ensure that the instrument can operate in the best condition. For vortex flow meters for steam metering, I think the main steps are as follows:
1. First understand the measured working medium, saturated steam or superheated steam.
2. Determine the scope of use of the flow: maximum flow and minimum flow.
3. Understand the maximum, common, minimum working pressure and working temperature of the medium; (for saturated steam, just know the pressure or temperature)
4. Check the table to get the density under working conditions.
5. According to the above data, for saturated steam, we can find the closest flow table from the table of saturated steam flow rates in the table of instructions. (Superheated steam can be checked from the saturated steam flow table according to the corresponding density. )
6. Finally, depending on the working environment of the site, whether the choice is to use integrated or separate. (eg medium temperature is high)
Fives. Limitations analysis:
1. The requirements for the straight section are relatively high. Generally, the minimum straight section is about 15D, and the straight section is about 5D.
2. Steam water hammer can easily damage the probe and vortex generator.
3. It is not suitable for installation in places where the vibration of pipelines is strong or where interference is strong.
4. The temperature of the measured medium can not be too high, the maximum can not be higher than 400 degrees.
5. The flowmeter with large diameter is now less stable (greater than DN250MM)
six. installation:
1. The vortex street flow meter is a flowmeter sensitive to the distortion of the flow velocity distribution of the pipeline, swirling flow, and moving flow. Therefore, attention should be paid to the installation conditions of the pipeline on site and it should be performed in accordance with the requirements of the manufacturer's instructions.
2. Reducing the effect of vibration on the vortex flowmeter should be of concern as a prominent issue in the field installation of vortex flowmeters. First try to avoid the vibration source when selecting the sensor installation site. Second, the use of elastic hoses connected in small diameters can be considered. Thirdly, the installation of pipeline supports is an effective method of vibration reduction.
3. Take a pressure measurement point at 2-10D upstream of the vortex flowmeter and take a temperature measurement point at the downstream 5-10D of the flowmeter. The temperature measuring element should be probed into the inside of the pipe and face the direction of the fluid.
4. The following rules must be followed when installing the instrument on the pipe:
(1). The inner diameter of the pipe should be consistent with the diameter of the sensor.
(2). When welding flanges, they should not be welded.
(3). When installing, pay attention to the flow direction of the sensor's flow direction to the medium.
In short, after several years of use, we have found that vortex flowmeters are very suitable for the steam metering of external heating users, and they have also been acknowledged by the majority of users. However, the vortex flowmeters we have made are not standardized yet. Standards, we look forward to, with the continuous development of technology, domestic vortex street flow meter can be more and more standardized, measurement accuracy is getting higher and higher, more convenient for our users.