Slurry flow meter

At present, the best method for measuring water-coal slurry is the electromagnetic flowmeter. As for some issues that arise during use, certain methods need to be employed to address them. The situation mentioned above occurs when the flow meter is installed on a horizontal pipeline; in such cases, when the flow rate of the material is low or it stops flowing, the solid particles in the slurry will adhere to the electrodes. This problem can be resolved by installing the flow meter on an upwardly inclined pipe or a vertical pipe. Additionally, if pressure and flow rates permit, an electromagnetic flowmeter with a ceramic lining and no electrodes can be used, thereby completely avoiding the problem of electrode contamination. You can consult me regarding the selection of such flowmeters, and I can also help you get in touch with the manufacturer. To be honest, other types of flowmeters are not really suitable for measuring water-coal slurry.

It is recommended that you install the gauge in a vertical pipeline, as this makes deposition less likely. If conditions permit, adding some backwash water should work.

One of the criteria for selecting an electromagnetic flowmeter is the flow velocity; if the flow velocity is not appropriate, there is clearly a problem with the selection of the flowmeter.

I’m asking about rectangular flow meters; they seem to be okay.

A rectangular flow meter is a throttling element that generates a differential pressure signal; based on fluid dynamics equations, and through the relationship between this differential pressure signal and flow rate, it is possible to accurately measure the flow rate of the fluid. The throttling element of a rectangular flow meter possesses some of the characteristics of the throttling wedge in wedge flow meters, as well as most of the characteristics of venturi flow meters; in simple terms, a rectangular flow meter is a combination of a wedge flow meter and a venturi flow meter. Rectangular flow meters use the standard formula for unidirectional fluid flow through a standard orifice plate; the flow calculation is given by the following formula. ???????? (1) ????? ???? Where: qV———volumetric flow rate ； C———Discharge coefficient ； ε———Coefficient of expansion ； m———throttle area ratio, flow arc area/pipeline cross-sectional area ； D———Inner diameter of the pipe, mm ； Δp———differential pressure, Pa ； ρ———medium density, kg/m3. Its structure is shown in Figure 1. ? Figure 1 Schematic diagram of the structure of the rectangular flow meter ????2 Performance analysis of the rectangular flow meter ????2.1 Wear resistance ????In the coal gasification process, the fluid involved is mainly a mixture of coal ash and water resulting from the reaction of coal, namely black water. The operating conditions for this fluid are typically a temperature of 200°C and a pressure level of 10.0 MPa, with 8%–10% coal particles present. Such conditions impose quite stringent requirements on flow meters, and ordinary flow meters find it difficult to meet these demands. To measure such high-viscosity, highly abrasive fluids, wedge flow meters are generally used. The structure of a wedge flow meter features a throttling edge with an angle of less than 90 degrees, as shown in Figure 2; this arrangement ensures the creation of a measurable throttling effect and a defined flow pattern downstream. However, when the fluid passes through the wedge flow meter, it experiences rapid flow reduction at the edges of the throttling element, followed by a quick restoration of pressure. This results in strong vortices forming at those edges. These vortices not only erode the back side of the wedge edges but also exert force against them, causing severe wear and thus reducing the accuracy of measurements. ? Figure 2: Schematic diagram of the structure of a wedge flow meter. ??? As can be seen from Figure 1, the throttling element of a rectangular flow meter has obtuse angles or curved edges; there are no sharp corners, and the flow moves smoothly from the converging section into the throat, which significantly reduces wear. At the same time, the rectangular flow meter features a streamlined throttling channel with a throat of appropriate length that serves to straighten the flow, effectively smoothing out fluid fluctuations. Together with the pressure recovery section at the rear, which extends this streamlined flow path, no vortices or vibrations occur inside the flow meter, thereby avoiding wear caused by vortices. A rectangular flow meter can be used continuously for 3 years with unchanged measurement accuracy, and its service life is more than 4 times that of a wedge flow meter. 2.2 Low permanent pressure loss and high differential pressure value: In engineering applications, the operating costs include the electrical energy consumed by pumps and compressors. By choosing flow meters with low pressure loss, it is possible to reduce the cost of transporting the medium. Moreover, the cost of transporting the medium represents a dynamic expense that, over the long term, far exceeds the one-time investment in the instruments. ????Typical throttling devices, such as wedge flow meters, generate a pressure difference by throttling through a throttling element in order to measure flow rate. Behind the throttling element, the pressure is restored naturally based on fluid dynamics principles. As a result, the head loss is usually quite high; moreover, the higher the measurement accuracy and the larger the range ratio, the greater the head loss. Generally, the head loss accounts for 30% to 60% of the measured pressure difference. As can be seen from Figure 1, the structure of the rectangular flow meter is similar to the pressure recovery section of a Venturi flow meter, allowing for maximum pressure recovery; the pressure loss is 15% to 25% of the measured pressure difference. ????Rectangular flow meters use pressure measurement at the center of the throat; since the flow velocity is highest at this point, the differential pressure resulting from Bernoulli’s equation is much greater than that of other types of flow meters. Therefore, they are widely used in applications involving low pressures and low pressure losses, such as measuring the air supply and exhaust in power plants as well as in heating furnaces. 2.3 High-precision measurement: Through extensive theoretical research, experimental data, and rigorous manufacturing inspection procedures, the accuracy of the rectangular flow meter has been achieved at over 0.25%. At the same time, due to the special structure of the rectangular flow meter, which ensures that the flow coefficient remains linear and stable over a wide range of Reynolds numbers, accurate measurements can be obtained regardless of whether high or low flow rates are involved. In the polysilicon industry, hydrogen is an industrial gas that is difficult to measure; the amount of hydrogen fed into the reduction furnace is controlled by adjusting the feed valve according to pre-set ratios. If the measured flow rate fluctuates significantly or is too low to be detected, this causes the control valve to operate frequently, thereby affecting the quality of the silicon rods and even leading to an emergency stop of the production process ； If the flow measurement is inaccurate, it can result in incomplete purging, posing a safety hazard. Normally, mass flow meters are used to measure hydrogen, but it is necessary to increase the flow rate by using a reduction in diameter, which results in significant pressure losses. Additionally, the high flow velocity at the outlet of the flow meter poses a risk, and a long straight pipe section is required behind the flow meter for the flow velocity to return to normal. Currently, using rectangular flow meters to measure hydrogen not only provides high precision but also stable performance, effectively solving this problem.