Electromagnetic flowmeters Many acetic acid devices use orifice, vortex, turbine, and oval gear flow metering devices. These flowmeters have many shortcomings: easy to wear, leaking after being corroded by medium, short life span, large maintenance workload, it is difficult to meet production requirements [1]. With the technological transformation of the device, a new type of electromagnetic flowmeter is used instead of the designed flowmeter. This change not only satisfies the acetic acid production process requirements but also greatly reduces investment and reduces maintenance strength. In the actual production has achieved very good results.
1 Types of Electromagnetic Flowmeters Electromagnetic flowmeters can be classified in many ways, classified by excitation method, classified according to the composition of sensors and transducers, classified by connection method, and classified by sensor and pipeline connection method. They can also be classified by application. Introduce the classification by excitation method.
1) DC excitation type. This kind of electromagnetic flow meter has a very small quantity and is only used to measure the flow of liquid metal, such as mercury at room temperature and liquid sodium and potassium at high temperatures.
2) AC power frequency excitation type. The earlier electromagnetic flowmeters were excited with 50Hz power frequency and were gradually replaced by low frequency rectangular excitations because of their vulnerability to electromagnetic interference and zero drift. However, in the measurement of liquid-solid two-phase flow such as mud and slurry, the low-frequency rectangular wave excitation method cannot overcome the spike noise generated on the surface of the solid wiper electrode, while the instrument of the power frequency AC excitation does not have this disadvantage. Some electromagnetic flowmeters still use AC excitation.
3) Low frequency rectangular wave excitation type. The low-frequency rectangular wave excitation method has low power consumption and stable zero point, and is currently the main excitation method of the electromagnetic flowmeter. Its waveform has two kinds of "positive-negative" and "positive-zero-negative-zero" three values. Some electromagnetic flowmeter excitation frequency can be set by the user. Generally, the small-diameter instrument uses a higher frequency and the large-caliber instrument uses a lower frequency.
4) Dual-frequency excitation type. The waveform of excitation current is to superimpose a high-frequency rectangular wave on a low-frequency rectangular wave, which is mainly to overcome the presence of the slurry noise and flow noise of the square-wave excitation, and to improve the stability and response characteristics of the instrument.
2 Characteristics of electromagnetic flowmeter Electromagnetic flowmeter is a kind of flow measuring instrument made according to Faraday's electromagnetic induction law, used for measuring the volumetric flow of conductive liquid in the pipeline. Since the parts of the electromagnetic flowmeter have no rotating parts and no parts that impede the flow of fluid, there is almost no pressure loss; the liquid to be measured only contacts the pipe liners and electrodes of the electromagnetic flowmeter, so as long as the electrodes and lining materials are selected properly, Has good corrosion resistance, wear resistance [2]; easy to install the level, vertical, tilt can be installed; high measurement accuracy, can reach 0.5%; large range ratio, generally 1:20.
Electromagnetic Flowmeter
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The fluorinated mica crystals have very good
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properties, and can work for a long time at a high temperature of 1100°C.
No reaction occurs
with strong acids and alkalis; complete light transmittance (pure and
transparent). The natural mica plates traditionally used in the observation
window of high-pressure boiler water level gauge are all brown, and the light
transmittance is not good, and the temperature resistance is in the range of
200-700°C, especially the corrosion resistance is poor. The boiler steam drum
water in thermal power plants contains alkali. After reacting with natural mica
and alkali, it is washed with hot air and hot water, and it is prone to
fluffing, scaling, and being broken. In the short term (about 1-2 months), the
water level is not clearly understood. After being broken, it can easily cause
leakage. The fluorite mica does not react with the acid-base solution, and does
not react with water in the hydration reaction, so that it does not form a
layer, does not scale, and does not break. In the long-term (2 to 3 years)
scouring of high-temperature and high-pressure water (including acid and
alkali), the original clarity and transparency can still be maintained. In
China, it has been widely applied to the observation window of steam boiler
water level gauge in high-pressure boilers of thermal power plants. It has also
been selected by Japanese BBK company and NDK (Colin) company for the
observation window of high pressure boiler drum level gauge.
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