Solids Mass Flowmeters

less accurate methods (1-3% FS) of solids flow measurement include the impulse and the accelerator flowmeters. In the loss-in-weight-type measurement, the total weight of the supply tank is measured and that signal is differentiated by time. The rate at which the total weight is dropping is the mass flow from the tank. These systems do not provide high precision (1% AF over a 10 1 range), but are suited for the measurement of hard-to-handle process flows because they do not need physical contact with the process stream. 

Cross-correlation flowmeters in combination with concentration detectors are available for the measurement of the mass flow of solids in pneumatic conveying systems or for volumetric flow measurements. The cross-correlation flowmeter uses a microwave (or gamma ray, ultrasonic, or photometric detectors) as the densitometer and a measurement of the time it takes for particles to travel a known distance to determine velocity. 

Post-Oil Energy Technology After the Age of Fossil Fuels 

Belt-type gravimetric feeder with digital controls. 

Such noninvasive designs are suitable for the measurement of the flow of solids and two-phase flows, including heavy slurries, and very corrosive and difficult measurement applications. Their disadvantages include high cost, a 

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Density Gauges These are used to measure the density or suspended solids content of the feed and underflow streams. Gamma radiation devices are the most commonly used for automatic control, but ultrasonic devices are effective in the lower range of slurry density. Marcy pulp density scales are an effective manually operated device. A solids mass flow indication is usually obtained by combining a density gauge output with the output from a flowmeter. 

In industry, it is often more important to measure mass flow rate than to monitor volumetric flow rate. To determine the mass flow rate of a mixed-phase flow, one must measure the velocity and concentration of each phase. This becomes a very difficult task and none of the current techniques can accomplish it. In practice, most mass flowmeters measure the relative change of a physical parameter like capacitance. To relate this measurement to solids concentration, the flowmeters must be calibrated against other, direct, methods... 

To illustrate density measurement by capacitive methods, the performance of the ANL capacitive mass flowmeter is described. Instrument evaluation tests were conducted at the ANL Solid/Liquid Test Facility (SLTF), shown schematically in Fig. 6.19. The SLTF was designed as a specialized instrument-testing and calibration-loop facility for various liquid and liquid/solid media. The facility can provide volumetric flow rates that range from 0 to 10 L/s and flow speeds up to 6 m/s in 2-in. Schedule 40 pipe. It is equipped with an acoustic cross-correlation flowmeter, a PNA system to... 

In conclusion, the capacitive mass flowmeter can be a reliable instrument for measuring the flow of dilute suspended solids. For the flow of high concentrations of suspended solids, the velocity measurement becomes inaccurate. The inaccuracy may be caused by the velocity profile effect, but further study is required to confirm the observation. 

The principal advantages of this mass flowmeter in cryogenic service is that it requires no moving parts in the fluid stream, requires no flow straighteners, and can be used with two-phase flow. Its major disadvantage is that it is an inferential mass flow measurement with slow response time. Additionally, the screen and honeycomb open area may be insufiicient to allow free passage of solid particles. 

The usual measuring device for feed flow is a magnetic flowmeter, which is a volumetric device whose output F must be multiplied by density p to produce mass flowMo- For most aqueous solutions which are fed to evaporators, the product of density and the function of solid content appearing above is linear with density ... 

Shirato, Gotoh, Osasa, and Usami [J. Chem. Eng Japan, 1, 164-167 (January 1968)] present a method for determining the mass flow rate of suspended solids in a liquid stream wherein the liquid velocity is measured by an electromagnetic flowmeter and the flow of solids is calculated from the pressure drops across each of two vertical sections of pipe of different diameter through which the suspension flows in series. 

Solids flow measurement is more important in the control and optimization of coal-fired power plants than in alternative energy processes. The mass flow of solids can be detected by impact flowmeters, which are relatively low-accuracy devices (1-2% FS). Better accuracy and rangeability are provided by belt-type gravimetric feeders (0.5% AF over a 10 1 range), which measure both the speed and loading on the moving belt, as shown in Figure 3.89. 

Density is a frequently needed physical property of a process fluid. For example, engineers often know volumetric flow rates (F) of process streams from flowmeter readings but need to know mass flow rates m) or molar flow rates (h) for material balance calculations. The factor needed to calculate m or h from V is the density of the stream. This chapter illustrates the uses of both tabulated data and estimation formulas for calculating densities. Section 5.1 concerns solids and liquids Section 5.2 covers ideal gases, gases for which the ideal gas equation of state (PV - nRT) is a good approximation and Section 5.3 extends the discussion to nonideal gases. 

Electromagnetic flowmeters are mainly applied to single-phase conducting fluids, for example liquid metals, water-based industrial liquids, and blood. However, they are also being used to measure solid/liquid flows such as water-based slurries and sludge as long as conductivity of the liquid medium exceeds 50 microsiemens per centimeter (pS/cm). Output signals from an EM flowmeter are basically proportional to the volumetric flow rate, which is applicable to solid/liquid flows only if the solids particles are uniformly distributed in the liquid. Moreover, to obtain the mass flow rate of a solid/liquid flow, the EM flowmeter requires other means to measure solids concentration. 

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