Application of slurry electromagnetic flowmeter in coal slurry gasification

Case introduction

1. The necessity of slurry-type electromagnetic flowmeter to measure the flow rate of coal-water slurry. The main components of coal-water slurry are: Coal slurry particles and additives, and coal-water slurry is a non-Newtonian fluid. In view of the special physical properties of coal-water slurry, it is difficult to measure coal-water slurry flow. Currently, slurry-type electromagnetic flowmeters are widely used to measure coal-water slurry flow.

2. The importance of measuring the flow of coal-water slurry with a slurry-type electromagnetic flowmeter. Since coal-water slurry is the main reaction raw material of the four-nozzle gasifier, and each coal slurry pipeline is equipped with 3 units of coal The slurry electromagnetic flowmeter, at the same time, the coal slurry flow is implemented in the safety chain protection system of the four-nozzle gasifier according to the three-choose-two chain protection system. The amount of oxygen entering the four-nozzle gasifier is adjusted and controlled according to the oxygen-to-coal ratio, and the coal-water slurry flow is measured. It plays a very important role in the safe, stable and long-term operation of the four-nozzle gasifier device.

3. Factors affecting the measurement of slurry electromagnetic flowmeter and solutions

(1) The complex composition of coal-water slurry causes inaccurate measurement. The raw coal contains iron, copper and other metals. The weighing feeder transports the steel rods into the coal mill. During the process of squeezing and grinding the coal, some metal particles fall off. At the same time, the low-pressure coal slurry pump, coal slurry tank, high-pressure coal slurry pump, and coal slurry pipeline The friction, impact, wear, and damage of other equipment and devices during the coal-water slurry transportation process may mix metal particles into the coal-water slurry. By selecting a coal source with better coal quality, at the entrance of the coal mill and the low-pressure Adding a device for removing iron (easily adsorbed minerals) at the outlet of the coal slurry pump can alleviate the phenomenon of inaccurate measurement caused by the complex composition of coal-water slurry.

(2) The uniformity of coal slurry particles in coal-water slurry and the noise of solid-liquid two-phase slurry cause measurement instability. Coal-water slurry is a conductive liquid mixed with solid and liquid. If the coal slurry particles in coal-water slurry The size is uneven. During the long-term flow process, the friction damage caused by the coal slurry particles and bubbles in the coal-water slurry will increase, resulting in changes in the electrical structure and differences. In this way, the electromotive force induced by the electricity will appear in a shorter period of time. The phenomenon of high and low fluctuations within a time period produces sharp peak pulse noise. The electromotive force signal is converted and amplified by the converter to produce more serious instantaneous spike interference, which ultimately causes the measured coal slurry flow output signal to fluctuate frequently and greatly, making it unstable. . By controlling the uniformity of coal slurry particles and the concentration ratio of coal-water slurry, the influence of instability on coal slurry flow measurement can be reduced.

(3) Voltage causes measurement instability

The slurry type electromagnetic flowmeter conduit is lined with an improved polyurethane lining material, and the electricity is made of high-quality stainless steel coated tungsten carbide electricity. structure. Due to the long-term production process, measuring media such as coal-water slurry in the coal slurry pipeline may cause pollution to the measuring electricity, and the measuring electricity is made of two different metal materials, so chemicals will appear between the two electricity. Voltage, the voltage after electrical pollution will cause the coal slurry flow output signal to fluctuate greatly. By cleaning the inner tube wall of the sensor, the scale on the electrical surface will be removed.Materials and adsorbed metal minerals can avoid the influence of chemical voltage on coal slurry flow measurement.

(4) The impact of the pulsating flow of the high-pressure coal slurry pump on the measurement

It is inevitable that the high-pressure coal slurry pump will have pulsating flow during operation. The four nozzle gasifiers The process burner requires a high-pressure coal slurry pump to pressurize the coal-water slurry to about 8 MPa to achieve good atomization effect. The high-pressure coal slurry pump we use is a diaphragm pump. Due to its structure and working principle, even under 100% load working conditions, the pulsating flow of coal-water slurry pressurized by the high-pressure coal slurry pump will fluctuate greatly. This will cause the induced electromotive force signal measured by the electromagnetic flowmeter sensor to fluctuate greatly, eventually leading to large changes in the coal-water slurry flow rate. By increasing the flow rate of coal-water slurry and the rotation speed of the high-pressure coal slurry pump, and installing the electromagnetic flowmeter sensor farther away from the high-pressure coal slurry pump, the flow field can be made more stable and the impact of pulsating flow on the measurement can be reduced.

(5) The influence of coal slurry pipeline material on measurement

The four coal slurry pipelines of the four-nozzle gasifier are generally made of carbon steel. During shutdown and maintenance, the coal-water slurry If the coal slurry is no longer transported, the inner pipe wall of the coal slurry pipeline will be oxidized and rust will occur in a very short period of time. After the production operation, with the continuous flow, erosion and friction of coal water slurry, a lot of particles will fall off the inner pipe wall of the coal slurry pipeline. Small metal particles are magnetized in the electromagnetic field and then adsorbed near the electricity to generate a voltage, causing the induced electromotive force measured by the electricity to fluctuate, thereby increasing the fluctuation of the coal slurry flow rate, greatly reducing the measurement accuracy, and making the measurement unstable. By cutting off the power to the electromagnetic flowmeter, and at the same time, the wear protection work of the coal slurry circulation pipeline needs to be done in advance, and the iron filings, rust, etc. on the inner pipe wall of the coal slurry pipeline are removed by the flow of coal-water slurry. You can also choose stainless steel pipelines to solve this problem.

4. Chain design of coal-water slurry flow in production

Three electromagnetic flowmeters installed on the four coal slurry pipelines respectively adopt a two-out-of-three chain protection method. The rotation speed and current value of the high-pressure coal slurry pump adopt a two-choice chain protection method. The difference between the three coal slurry flow rates on the two opposing coal slurry pipelines adopts a three-choice chain protection method. That is: on each coal slurry pipeline, when the flow rates of two of the coal slurries are lower than the set chain value at the same time, or the speed and current value of the high-pressure coal slurry pump are lower than the set chain value at the same time, or the two opposing The two flow differences between the corresponding three coal slurry flow rates on the coal slurry pipeline (for example, the difference in coal slurry flow rate between coal slurry A pipeline and coal slurry B pipeline: FT1102A-FT1102B, FT1103A-FT1103B, FT1104A-FT1104B) are both low at the same time. At the set chain value, the four-nozzle gasifier will jump out of the chain to vent the oxygen to avoid gasifier explosion accidents.