The application of electromagnetic flowmeters in the water-coal slurry industry

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The special installation requirements for electromagnetic flowmeters must be strictly followed; ideally, three electromagnetic flowmeters should be installed at the top of the evaporator. Extending the straight pipe section ahead of the flow meter is the best way to address the pulsation in coal slurry booster pumps. For the special processing of electromagnetic flowmeters, specialized measuring tools are used to determine the dimensions of the flange connections of these flowmeters. Through calculation and design, erosion-resistant and wear-resistant sleeves for interface flanges are fabricated using special materials such as 316 manganese composite alloy. The surface of the chamber in electromagnetic flowmeters is coated with silicon carbide (which provides protection against electromagnetic interference) to prevent corrosion and wear. Tungsten carbide films are used as the sensing electrodes in electromagnetic flowmeters. Suggestions for using electromagnetic flowmeters: 1. It is strictly prohibited to supply power to the electromagnetic flowmeter during the individual unit testing phase. First of all, it is necessary to provide protection against wear in the coal slurry circulation pipes, and use water-coal slurry to remove rust from the inner walls of these pipes. Otherwise, rust will be attracted to the vicinity of the electrode by the magnetic field on the inner wall of the electromagnetic sensor, causing a polarization voltage disturbance at the electrode and leading to fluctuations in the flow meter. After the gasification furnace is shut down, the pipes should be cleaned after powering down the electromagnetic flowmeter, to prevent the magnetic field generated by the excitation in the flowmeter’s sensor from preventing the rust adhering to the electrodes from being properly removed. 2. During normal operation, if fluctuations or disturbances are suddenly observed in the electromagnetic flowmeter, the following possibilities exist: (1) The fluctuations may be caused by the pump; an abnormality may occur in one of the diaphragm chambers of the slurry pump. The change in flow rate might not be significant, but changes in the flow field can lead to pulsations, thereby increasing the magnitude of the fluctuations. Regularly check whether the pressure gauges in each diaphragm working chamber of the slurry pump show equal readings. (2) The fluctuations may be caused by slurry; an increase in the amount of metal particles in the slurry leads to their accumulation near the electrodes, which creates a polarizing voltage that interferes with the flow meter, resulting in fluctuations. It is necessary to stop the operation promptly for inspection or cleaning. (3) Sudden instantaneous sharp pulse interference appears in the output signal of the electromagnetic flowmeter. If instantaneous sharp pulse disturbances caused by the friction of large metal particles or bubbles in the coal slurry against the electrodes occur frequently, it is necessary to check the quality of the coal slurry. Due to temperature resistance limitations of the sensor lining in electromagnetic flowmeters, steam cannot be used to flush coal slurry pipelines. (4) Parameter tuning of electromagnetic flow meters: When the sensor of an electromagnetic flow meter cannot be installed under optimal conditions, it is possible to adjust the damping time of the flow meter itself. This adjustment compensates for fluctuations caused by pulsating flow at the expense of sensitivity. It is recommended that the damping time should not exceed 30 seconds; a value between 5 and 15 seconds is ideal. Especially after long-term use under high-pressure conditions, the structure of electromagnetic flowmeters undergoes certain changes due to severe erosion. To improve measurement accuracy, an angle grinder is used to shape the silicon carbide protective coating on the interior surface, particularly the tungsten carbide protective coating of the sensing electrodes. But it must be remembered that after shaping the protective film, the parameters of the electromagnetic flowmeter must be calibrated using measurement standards in order to operate it accurately; only then can its inherent advantages and strengths in measurement applications within the coal chemical and water-coal slurry industry be fully utilized.