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How To Obtain An Economical Measurement Method For Vortex Flow Meter

Dec 19, 2018

How to obtain an economical measurement method for vortex flowmeter

Our vortex flowmeters feature a unique sensor design that accurately identifies and eliminates noise, providing stable, accurate measurements and reduced maintenance costs without the need for start-up adjustments, giving you peace of mind. Today we will explore the use of vortex flowmeters to measure water vapour in order to obtain an economical measurement method. In the chemical production process, it is often necessary to measure the flow rate of water vapor. There are many factors affecting the measurement of steam flow. The water is heated and evaporated to become saturated steam, and there is a correspondence between the temperature and the pressure of the saturated steam. Reheating the saturated steam becomes superheated steam, and the temperature and pressure are no longer in a one-to-one correspondence. Because of its high temperature, it can meet the production needs, and it is not easy to change phase during transmission. Therefore, most of the products we measure in production are superheated steam.

How to obtain an economical measurement method for vortex flowmeter

    The mass flow rate of superheated steam is measured in units of kg/h or t/h. The mass flow of steam is related to the density of the steam, which in turn is affected by the pressure and temperature of the steam. The measurement of steam must track changes in pressure and temperature, otherwise it will cause large measurement errors. In order to accurately measure the steam flow, it is necessary to simultaneously measure the temperature and pressure of the steam, and then convert the density of the steam to obtain the flow rate of the steam. This is what we call warm pressure compensation. Temperature and pressure compensation is an indispensable part of measuring steam mass flow. 

1 Flow meter selection

    There are many types of instruments that measure steam flow. We must weigh the economics and applicability, both in terms of accuracy and cost and maintenance costs. The instruments for measuring steam flow mainly include standard orifice plates, constant velocity pipes, elbow pipes, float type flow meters, and thermal mass flow meters.

    At the earliest, people generally used standard orifice plates to measure steam flow. At the same time, temperature measurement points and pressure measurement points were installed to compensate for temperature and pressure. However, there are too many instruments required for the measurement process. People are too troublesome and often lack the temperature or pressure compensation. , causing a large measurement error. The orifice plate is used to measure steam, the pressure loss is large, and the running cost is high; the pressure guiding tube, the three groups of valves and the connecting head are easy to leak; and the pressure guiding tube needs to be insulated in winter, and the maintenance cost is high. Later, people used a thermal mass flow meter to measure steam flow, which has high measurement accuracy and low maintenance cost. However, the use of a thermal mass flow meter to measure steam flow is expensive, and it cannot be operated at high temperatures, and its use is limited.

    The vortex flowmeter has a simple structure and is directly installed on the pipeline. The pressure loss is small, the leakage problem in the pressure transmission is overcome, and the heat preservation measures are not needed; the installation and use are convenient, the measurement accuracy is high, the use cost is low, and the maintenance workload is Small, with many advantages unmatched by other flow measuring instruments, has been widely used.

2 vortex flowmeter measurement principle and its characteristics

    The vortex flowmeter is measured according to the Karman vortex principle. When the liquid flows through the vortex generator of the vortex flowmeter, two rows of vortices are generated. The frequency of the vortex is related to the flow velocity of the fluid, and the frequency of the vortex is measured. f can calculate the flow velocity v of the fluid, the flow rate q = vA, where A is the cross-sectional area of the flow through the vortex generator. Vortex flowmeters have been widely used due to the incomparable advantages of other flow measuring instruments. There is a trend to replace the differential pressure flow meter.

    Its characteristics are as follows:

    (1) The structure is simple and reliable;

    (2) No maintenance, low cost of use;

    (3) Overcoming the pipeline leakage phenomenon;

    (4) a wide range of applications;

    (5) The pressure loss is small;

How to obtain an economical measurement method for vortex flowmeter

3 Precautions for measuring steam flow with vortex flowmeter

    (1) Density compensation problem:

    Although the volumetric flow measured by the vortex flowmeter is not affected by the temperature and pressure, the actual flow of the medium steam is measured by mass, so the density of the steam must be obtained by temperature and pressure compensation. Some companies produce vortex flow meters, such as the LUGB intelligent vortex flowmeter, which can display temperature and pressure measurements. The smart meter has placed the density table corresponding to the temperature and pressure into the memory, and the density is checked by the smart meter CPU. After conversion, the mass flow rate is obtained. The use of the intelligent vortex flowmeter is simpler and more reliable than the differential pressure flowmeter, and the input cost and maintenance cost are low, and the superiority is obvious, which is a method that everyone is happy to adopt.

    If the vortex flowmeter used does not have the temperature and pressure compensation function, there are two treatment methods. One is to set the density of steam in the parameter setting item of the vortex flow meter, and the mass flow is obtained from the vortex flow meter, such as E+. H vortex flowmeter, set the density of steam in the parameter setting item, the flow meter gets the mass flow; the disadvantage is that the density is not the measured value, causing measurement error. If the working conditions are stable and the density under the working conditions is well known, the measurement requirements are not high, which is a simple and feasible method. Another method is to input the volume flow measured by the vortex flowmeter and the temperature and pressure measured on the same pipeline to the DCS (Distributed Control System) system, and the computer processes it to obtain the mass flow. What the process operator sees at the operator station is the mass flow of steam. If you choose a new instrument to use the vortex flowmeter with automatic temperature and pressure compensation function, if you use the existing vortex flowmeter to measure the mass flow of steam, the above two methods are not bad.

    (2) Vortex flowmeters also have requirements for straight pipe sections, generally the first 10D, the last 5D, and D is the pipe diameter.

    (3) The vortex flowmeter should be installed as far as possible from the vibration source and strong electromagnetic interference. If vibration cannot be avoided, the shock absorber must be used to reduce the influence of pipeline vibration on the vortex flowmeter.

    (4) The steam meter can not be installed in the low position of the whole casing road to prevent the accumulation of condensate and cause measurement error.

    (5) The problem of steam dryness. Measuring steam flow is often considered to be completely dry. However, the steam is not completely dry and always carries a certain amount of water. If the effect of steam dryness is not taken into account, the measured flow rate will be inaccurate. The vortex flowmeter should have the function of setting the steam dryness. However, it is also difficult to determine the dryness of steam in actual conditions. The method that can be adopted is to improve the steam quality at the inlet of the steam flow meter, and to take measures to ensure the superheat of the steam, the measurement accuracy of the vortex flowmeter can be improved.

    (6) Better to use a separate vortex flowmeter, the display part is installed in the protection box far from the steam pipeline, which not only protects the instrument, but also is easy to operate. For example, the vortex flowmeter produced by E+H Company used by our company measures the steam flow, and a separate structure is adopted.

    (7) Maintenance of the vortex flowmeter. Since the vortex flowmeter is impacted by high-temperature, high-pressure water vapor for a long time, it is easy to cause vortex-generating body wear and aging of electronic components, so frequent maintenance and regular maintenance are required.

4 vortex flowmeter inadequacies

    At the same time, the vortex flowmeter also has the following limitations, and we need to pay attention to it during use.

    (1) Vortex flowmeter measurement of steam flow is not suitable for large diameter pipes. It is recommended to use flow measuring instruments such as constant velocity pipes.

    (2) The vortex flowmeter is sensitive to vibration. When installing a vortex flowmeter in a pipe with large vibration, the pipeline must have certain damping measures. If it cannot effectively overcome the vibration, only other types of flowmeters can be selected. Such as orifice plate, elbow flowmeter, etc.

    (3) The flow rate of steam in the pipeline is generally large. Under normal conditions, the flow rate of steam in the pipeline is between 40 and 70 m/s. It is not uncommon for steam to flow at speeds of up to 100 m/s. High-speed steam creates an impact on the vortex generator of the vortex flowmeter, causing wear. Make a large error in the measurement results. This is a limitation of vortex flowmeters, which is related to its measurement principle. If the impact of steam is large, other types of flowmeters are required.

    In fact, the instruments used to measure the steam flow also have their own characteristics. Therefore, it is an important content to select the appropriate meter and measure the water vapor flow with an appropriate method. The above detailed understanding is to help us choose the most suitable according to the characteristics and nature of the product in the face of numerous flow meters.