General principles for electromagnetic flowmeter selection
(1) Whether the medium to be tested is a conductive liquid or slurry, thereby determining whether an electromagnetic flow meter is selected;
(2) The conductivity of the measured medium determines the type of electromagnetic flowmeter—whether it is high conductivity or low conductivity;
(3) The nominal diameter of the large, small and common flow process pipelines required by the process, determine whether the flow rate of the medium is at a more economical flow point, whether the pipeline needs to be reduced, and then determine the diameter of the flowmeter;
(4) Determine whether to use an integrated or split flowmeter, and the degree of protection of the flowmeter, etc., based on the layout of the process piping.
(5) Selecting the electrode type according to whether the measured medium is easy to crystallize or crusting;
(6) selecting an electrode material according to the corrosiveness of the measured medium;
(7) The corrosiveness, wear and temperature of the measured medium determine the lining material to be used;
(8) The high working pressure of the measured medium determines the nominal pressure of the flow meter;
(9) The insulation of the process piping determines the type of grounding ring.
Vortex flowmeter selection
(1) Selection of vortex flow transmitter
In the measurement of saturated steam, VA type piezoelectric vortex flow transmitter is adopted. Because of the wide range of vortex flowmeter, in practical applications, it is generally considered that the flow of measuring saturated steam should not be lower than that of vortex flowmeter. The lower limit, that is to say, the fluid flow rate must not be less than 5 m/s. According to the size of the steam, the vortex flow transmitters with different calibers are selected, and the caliber of the transmitter cannot be selected by the existing process pipe diameter.
(2) Selection of pressure compensation pressure transmitter
Since the saturated steam line is long and the pressure fluctuates greatly, pressure compensation must be adopted. Considering the corresponding relationship of pressure, temperature and density, only pressure compensation can be used in the measurement, because the saturated steam pressure of Mingtong Company is 0.3-0.7MPa. Range, the range of pressure transmitter can be selected 1MPa.
(3) Display instrument selection
Display instrument intelligent flow display instrument with voltage regulation compensation, instantaneous flow display and cumulative flow accumulation function.
The V-cone flowmeter is a new generation of differential pressure flow measuring instrument. In practical use, many factors have a great influence on the measurement accuracy of the differential pressure flowmeter, which increases the measurement error and reduces the accuracy.
The specific performance is as follows:
1) the design parameters are inconsistent with the working parameters;
2) there is no temperature compensation or compensation is incorrect;
3) the length of the upper and lower straight pipes is insufficient;
4) the cones and pipes are not concentric;
5) the pressure pipes Blockage, etc.
After on-site inspection, the shortage of straight pipe sections, disagreement, and blockage of the pressure guiding pipe can be ruled out.
The differential pressure transmitter is removed for verification, the transmitter is qualified, and the error is within the allowable range.
The technicians recalled the trend record of DCS preservation, and looked at the steam temperature and pressure recording curve. The temperature was between 120 °C and 150 °C, the pressure was between 0.3MPa and 0.6MPa, and the measured temperature and pressure deviated from the design value. The design parameter was temperature. 193 ° C, pressure 1.13 MPa). At the same time, the DCS configuration was viewed and it was found that there was no temperature and pressure compensation for the steam flow in the configuration.