Basic Application of Electromagnetic Flowmeter in Water Treatment Industry

Electromagnetic flowmeter has been applied for more than 50 years and has been widely used in the world. The field involves water/sewage, chemical, pharmaceutical, papermaking, food and other industries. Large-caliber instruments are mostly used in water supply and drainage projects. Small and medium calibers are often used for solids, liquids, or difficult fluids or high demand locations. Small calibers and micro calibers are often used in places where there are health requirements, such as the pharmaceutical industry, food industry, and bioengineering.

With the acceleration of China's industrialization process, the problem of environmental pollution has become more and more serious. The voice of society for sustainable development has also been increasing. The concept of the harmonious coexistence between man and nature has been accepted by people and the governance of all kinds of pollution has become more urgent. Shaoxing Water Treatment Development Co., Ltd. is an integrated urban wastewater treatment enterprise mainly for the printing and dyeing industry. The completed Phase I and Phase II projects have reached 700,000 tons/day of sewage treatment capacity. Because in the sewage treatment process, the discharge water, additives, sludge, etc. need to be measured and controlled, so the flow measurement is very important.

1. Measuring principle

The working principle of electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. When the conductive metal rod moves perpendicular to the direction of the magnetic force line at a certain speed, an induced voltage is generated.

In the electromagnetic flowmeter, the conductive medium in the measuring tube is equivalent to the conductive metal rod in the Faraday test, and two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When there is a conductive medium flowing, an induced voltage is generated. Two electrodes inside the pipe measure the induced voltage generated. The measuring pipe is electromagnetically isolated from the fluid and the measuring electrode by a non-conducting inner lining (rubber, Teflon, etc.).

Assume that the magnetic field strength B of the electromagnetic induction coil is constant, the induced voltage Ue is proportional to the fluid velocity v, and the sectional area A of the pipeline is known, then the volume flow rate Qv can be calculated by the following formula:

Electromagnetic flowmeter consists of flow sensor and transmitter. The sensor measuring tube is equipped with excitation coils above and below, and the magnetic field generated through the excitation current passes through the measuring tube. A pair of electrodes are installed on the inner wall of the measuring tube to contact with the liquid to draw out the induced potential and send it to the transmitter. Excitation current is provided by the transmitter. According to the converter and sensor assembly methods, there are two kinds of separation and integration. In the wastewater treatment process, large diameter flowmeters are mostly split type, with one part installed underground and the other part on the ground. Small caliber is more of a one-piece type.

The functions of electromagnetic flowmeters on the market are also very different. The simple one is to measure one-way flow, only to output the analog signal to drive the rear instrument; multi-function instrument has to measure bidirectional flow, range switching, upper and lower limit flow alarm, air pipe and power supply Cut off the alarm, small signal removal, flow display and total calculation, automatic check and fault self-diagnosis, communication with the host computer and motion configuration. The serial digital communication function of some models of instruments can choose multiple communication interfaces and dedicated chip (ASIC) to connect HART protocol system, PROFTBUS, Modbus, FF field bus and so on.

The scope of the electromagnetic flowmeter is wider than that of other types of flowmeters. E+H offers W, P, and H types of sensors for the water and sewage industries (W type), chemical and food industries (P type), respectively. Food, pharmaceutical industry (H type), caliber range from 2 mm to 2 meters. The transmitter can provide 10, 50, 23, 53 kinds of options, 10 for the economic development of the water industry, 50 for the general type, 53 for the enhanced type, 23 for the two-wire system. Accuracy can be 0.5%, 0.2% two options. Measurable positive and negative bi-directional flow, can also measure pulsating flow.

The prerequisite for using an electromagnetic flowmeter is that the fluid to be measured must be electrically conductive and must not fall below the threshold (ie, the lower limit value). Conductivity lower than the threshold will produce measurement error until it can not be used, even if the change in the threshold value can be measured, the indication error does not change much, general-purpose electromagnetic flowmeter threshold is 10-4 ~ (5 × 10-6) S / cm Between, depending on the model. When used, it also depends on the length of the flow signal line between the sensor and the converter and its distributed capacitance. The manufacturer's instruction manual usually specifies the length of the signal line corresponding to the conductivity.

The conductivity of industrial water and its aqueous solution is greater than 10-4S/cm, the conductivity of acid, alkali, and salt solution is between 10-4 and 10-1S/cm. There is no problem in use, and the low distilled water is 10-5S/. There is no problem with cm. Electromagnetic flowmeters cannot measure liquids with very low electrical conductivity, such as petroleum products and organic solvents. Can not measure gas, steam and liquids containing more large bubbles. From the data, it was found that some pure liquids or aqueous solutions had low conductivity, and they were considered unusable. However, in actual work, there were instances where they could be used due to the presence of impurities. Such impurities are beneficial for increasing the conductivity. For aqueous solutions, the conductivity in the data is measured in the laboratory using the pure water ratio. The actual aqueous solution may be formulated with industrial water, the conductivity will be higher than that found, and it is also favorable for flow measurement.

2. Electromagnetic flowmeter features

The electromagnetic flowmeter is not influenced by external factors such as temperature, pressure, viscosity, etc., and there is no pressure loss due to shrinkage or projection inside the measuring tube. In addition, the initial signal detected by the flow element is an accurate linear relationship with the average flow velocity of the fluid. The varying voltage, which has nothing to do with the other properties of the fluid, has great advantages. According to the sewage has the characteristics of large flow variation, impurities, low corrosion, certain conductivity, etc., to measure the flow of sewage, electromagnetic flowmeter is a good choice. It is compact and small in size. Easy to install, operate and maintain, the measurement system adopts intelligent design, and the overall seal is strengthened, so it can work normally in harsh environments. For vortex flowmeters due to technical reasons, it is difficult for the caliber to be large and the quality and quality of ultrasonic flowmeters in pipelines are inferior to those of electromagnets. Therefore, in the water and sewage industries, electromagnetic flowmeters, especially large-diameter electromagnetic flowmeters, have a great advantage and have been used very commonly.

E+HPROMAG electromagnetic flowmeter is powerful and easy to operate. The specific features are as follows:

1) There are no obstructed flow components in the measuring pipe, no pressure loss, and the straight pipe section requires bottom.

2) Measurements are not affected by variations in fluid density, viscosity, pressure, temperature, conductivity.

3) Lining is available in hard rubber, polyurethane, PTFE, PFA and many other materials.

4) Transmitter DC power supply / AC power supply, four-wire / two-wire, explosion-proof / non-explosion-proof, economic / standard and other subdivision to meet your different needs.

5) Photosensitive key, can avoid opening the cover operation; Chinese menu display, more convenient for domestic users.

6) The quick setting menu guides the completion of parameter setting, which is convenient and quick.

7) High measurement reliability, good repeatability, and long-term maintenance-free. Up to 1000:1 ratio

8) Provide current, frequency, pulse, Hart, Profibus-PA, Profibus-DP, FF and other output modes for selection.

3. Installation requirements

PROMAG series electromagnetic flow meter provides protection class IP67 (dust-proof and anti-immersion water level) or IP68 (dust-proof diving level). Large-diameter flowmeter sensors are mostly installed underground in wastewater treatment plants, so it is recommended to use IP68 (dust-proof submersible). Usually electromagnetic flow has all the following requirements for the installation site:

1) When measuring the mixed phase fluid, select the place that will not cause phase separation; when measuring the two-component liquid, avoid installing in the downstream where the mixing is not uniform; when measuring the chemical reaction pipeline, install it in the downstream of the reaction fully completed segment; Meet the straight pipe before and after the paragraph is not less than 5D and 2D;

2) Avoid as much as possible negative pressure in the measuring tube;

3) Choose a place with little vibration, especially for integrated type instruments;

4) Avoid large electric motors, large transformers, etc. nearby to avoid electromagnetic interference;

5) It is easy to realize the place where the sensor is grounded separately;

6) Avoid high concentrations of corrosive gases in the surrounding environment as much as possible;

7) Avoid direct sunlight as much as possible

4. Application and effect

The wastewater treatment process mainly aims to achieve the purpose of purifying the wastewater through biological oxidation, flocculation, and sedimentation processes. At each stage, a certain amount of meter is required for measurement. In the sewage industry, E+H mainly supplies 10W, 50/53W, 23W, 50/53P and other products.

In the sewage treatment process, according to the process requirements, configure the corresponding detection instrument to form a reliable control system. Shaoxing Sewage Treatment Plant is equipped with a flow meter in the following process inspection process: 1 inlet pipe; 2 primary sedimentation tank to mud storage tank mud detection; 3 sludge pumping house surplus, sludge flow detection; 4 sludge pumping house returning pollution Mud flow detection; 5 Second settling tank with water wells outflow detection; 6 Digestion tank into the mud detection; 7 Digestion pond out of the mud detection; 8 flocculant pool into the amount of detection and so on.

Cylindrical roller bearings

    Cylindrical roller bearings are separable, easy to mount and dismount especially more outstanding when they are used on bearings requiring interference fit between inner and outer rings with the shaft and housing. Cylindrical Roller Bearing is contacted with the fair line between the rollers and the raceway, which is of elimination of edge stress. Comparing with the ball bearings, with same boundary dimensions, cylindrical roller bearings have larger radial carrying capacity. Comparing with structure, this type of bearing is more suitable for high speed rotation.

Structures

1.  N0000 type cylindrical roller bearings without rib on outer ring and NU0000 type cylindrical roller bearings without rib on inner ring

These type of bearings can carry large radial load, rotate at a high speed, there is no limit to axial displacement on shaft or housing, but cannot withstand axial load.

2.  NJ0000 and NF0000 types Cylindrical roller bearings with ribs on both of inner rings and outer rings

    NJ0000 and NF0000 types of bearings can allow axial displacement on the shaft or housing and carry little single-direction axial load; NU0000+HJ0000 types and NUP0000 type bearings can allow two-direction displacement within axial clearance range on the shaft and housing and carry little double-direction axial load.

3.  RNU0000 Type Cylindrical roller bearings without inner rings.

RNU0000 types of bearing are applicable to the parts with limitation on radial size. The shaft surface can be directly used as raceway surface, the hardness, processing precision and surface roughness should be similar to those of ring raceway.

 4.NAL0000 type and NNAL0000 type of long cylindrical roller bearings with double ribs on outer rings are applicable to petroleum machinery.

5.Four-row cylindrical roller bearings FC,FCD and FCDP types are mainly applicable to heavy-duty machines, such as rolling mills. These bearing designations are different from general rule.

Cage material

    When the outer diameter is less than (inclusive)400mm, solid brass cage or steel sheet are adopted for Single Row Cylindrical Roller Bearing. When the outer diameter is more than400mm, brass cage and pin-type cage are adopted for four row cylindrical roller bearing.

Permissible tilt angle

    Generally the Cylindrical Roller Bearing shaft is not allowed to be tilted relative to the housing; while for single-row cylindrical roller bearings, when under light load, a relative2`tilt angle is allowed between the inner ring axial line and outer axial line. If the load is larger, the allowable error can be a little more, but should not exceed4`.

Tolerance and clearance

In accordance with requirement, Single row cylindrical roller bearings can be different tolerance classes. The tolerance value can be finding in the section Rolling Bearing Tolerance. For four row cylindrical roller bearings, the tolerance is normally P0, P6 and P5.

The Radial clearance of cylindrical roller bearing is as attached table 1.

Load-carrying capacity

    The load-carrying capacity of cylindrical roller bearings with ribs on inner rings and outer rings are related to the magnitude of the radial load and lubrication methods. The maximum allowable axial load is as following:

            Oil lubrication

               Grease lubrication

     Fap<0.4F_r

Fap-(N);Maximum allowable axial load

K-Factors related to bearing size series

2.3  series       K=0.2;

22.23  series       K=0.16.

C_0r-(N);Basic static load rating

ng-F_r>0.1C_r,

(r/min);For the limit rotational speed of a bearing carrying       a purely radial load, when F_r>0.1C_r, use the speed reduction factor to compensate the limit rotational speed.

n-(r/min).Actual operating rotation speed

As the axial load given by the above formula and under the following conditions, bearing with tolerance class 0 (except improved and enhanced types) can function normally:

The temperature of oil lubricate is55℃and grease lubricate is40℃, the highest is90℃. (The viscosity of lubricate oil is ν50=30mm²/s, and the dropping point of lubricate grease is170℃.)

If the axial load is acted internally, the allowable axial load can be doubled; when acted temporally, the allowable load can be increased by 2 times.

Dynamic equivalent radial load

          P_r=F_r

For the cylindrical roller bearing with axial load

2.3

To 2 and 3 series

          P_r=F_r+0.3F_a         (0≤F_a/F_r≤0.12)

          P_r=0.94F_r+0.8F_a     (0.12≤F_a/F_r≤0.3)

22.23

To 22,23 series

          P_r=F_r+0.2F_a         (0≤F_a/F_r≤0.18)

          P_r=0.94F_r+0.53F_a    (0.18≤F_a/F_r≤0.3)

Static equivalent radial load

               P_0r=F_r

Table 1  Radial clearance of cylindrical roller bearing with cylindrical bore

                                                  Î¼m

Cylindrical Roller Bearing

Single Row Cylindrical Roller Bearing,Double Row Cylindrical Roller Bearing,Three Row Cylindrical Roller Bearing,Four Row Cylindrical Roller Bearing

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