Although the electromagnetic flowmeter can be used to measure media with complex composition such as coal water slurry or mud, the special conditions of the medium composition will still have a certain impact on the measurement of the electromagnetic flowmeter. Here are some major difficulties. point:

 

 1. The complex composition of coal water slurry leads to easy damage to measurement related equipment, which makes measurement difficult

Because coal contains iron wire, copper wire and other metals in the mining process, it is conveyed to the rod mill or ball mill through the belt and ground with additives such as papermaking waste liquid and methanol wastewater. The generated content is 60%~70% and the operating density is 1250. ~1286kg/m3, a coal-water slurry with a dynamic viscosity of 700~3000cp. Rod mills or ball mills will further fall off some metal particles when grinding coal. The subsequent equipment cannot completely filter and remove the metal particles contained in the coal water slurry. Impact and wear during the metering process will easily cause the main and auxiliary pumps and electromagnetic flowmeters. The equipment is easily damaged.

 

 2. Difficulty in measurement caused by the characteristics of coal water slurry medium

When measuring the flow of liquid and solid two-phase mixed conductive media such as coal water slurry and mud, when solid particles or fiber media rub the surface of the electrode, the contact electrochemical potential of the electrical level surface suddenly changes, causing the output from the electromagnetic flowmeter sensor The electrode detection signal appears sharp pulse slurry (interference) noise, which will cause display and signal output fluctuations. The amount of fluctuation is related to the frequency 1/f spectrum characteristics of the sensor's excitation current. The friction of metal particles will produce more serious instantaneous spike interference, which will eventually cause serious interference to the electromagnetic flowmeter signal and lead to unstable measurement.

 

 Third, the measurement difficulties caused by the pressure pump

It is inevitable that there is a pulsating flow when the pressure pump is working. The "screw pump" is basically used in the pressurization of coal water slurry manufacturing and ordinary boiler combustion. Because of its structure and working mode, the fluctuation of the pulsating flow at different speeds is small (the fluctuation is generally 0.5%~5%) , Under normal circumstances does not affect the measurement and control applications. Due to the process requirements of the gasifier, the coal-water slurry nozzle needs a pressure pump to pressurize the coal-water slurry to 6~9.6Mpa to achieve the best atomization effect. In the future, it will even be higher. "Diaphragm pump", because of its working principle and structure, the pulsating flow of the pressurized liquid is very large even when working at full load (the fluctuation is generally 6%~15%). If the coal slurry pump works for a long time, if A problem in a working chamber will further increase its pulsation, and the working state of each working chamber cannot be monitored in the central control room, but can only be reflected in the instantaneous display and signal output fluctuations of the electromagnetic flowmeter.

 

4. Measurement difficulties caused by coal slurry transportation pipeline factors

The conveying pipeline of the coal water slurry in the gasifier unit is generally made of No. 20 carbon steel. When the coal slurry is stopped, the inner wall of the pipeline will oxidize to produce a large amount of oxidized iron rust. The friction of the coal water slurry on the inner wall of the pipeline will peel off the fine carbon steel particles and be contained in the coal slurry. When the electromagnetic flowmeter is working, the magnetic field generated in the measuring cavity of the sensor will magnetize the metal particles, which causes the metal particles in the coal slurry to be adsorbed near the measuring electrode, forming a polarization voltage to the electrode, which will increase the measurement accuracy of the electromagnetic flowmeter itself. And further increase the amount of fluctuation, while the stainless steel pipeline basically does not have this problem.