Slurry velocity

Each person should find the remaining parameters and physical property data for this material required to solve the three models [Eqs. (8.14), (8.19), and (8.20)] for the erosive wear of a coal slurry that is, each person will have three calculations to do and three erosion rates as a result. Assume that the test temperamre is 343°C, the slurry velocity is 100 m/s, and the angle of attack is 50°. 

If the operations run in the semibatch mode and the linear superficial slurry velocity wsL is zero, the above equation would become the mean bubble rise velocity in the swarm (Shah et al, 1982). 

Effect of Slurry Velocity on Solid Concentration Profiles. 

Figures 2a and 2b show axial solid concentration profiles for the iron oxide system in hatch and continuous mode, respectively. Figures 3a and 3h show the same information for the silicon oxide system. For "both systems, concentration profiles were much more uniform in continuous mode than in hatch mode. This is to he expected from equation 6, because of the dependence shown on the difference between the solids settling velocity and the upward slurry velocity.

Ruid layer thickness as a hincdon of slurry velocity. (From Ref. (7)). 

FIGURE 5-21 Slurry velocities obtained from cross-correlation peaks vs. velocities measured by flow diversion for coal/oil slurries. 

FIGURE 5-22 Uncorrected slurry velocities by acoustic sensing vs. corresponding velocities obtained by flow diversion. 

Figure 5-21 shows the coal/oil slurry velocity derived from the peak of the correlation function plotted against the velocity measured by flow diversion. The flow diversion gives basically the mass flow rate divided by density to give the volumetric flow rate and then the flow velocity. The data can be fitted by two linear relationships with slopes of 1.16 and 1.55, corresponding to meter factors of 0.86 and 0.64. The meter factor may be directly related to the flow profile effect (Sheen et al., 1985). 

Table 5-1 Coal/water slurry velocity data for 0-15 wt. % coal.

Coal Concentration, wt.% Slurry Velocity by Diversion, m/s Ultrasonic Parallel, m/s Cross-correl. Crossed, m/s Meter Factor Parallel Crossed Geometry Geometry ... 

FIGURE 5-25 Relative attenuation vs. slurry velocity for various coal concentrations. 

FIGURE 5-26 Relative attenuation vs. coal concentration for two slurry velocities. 

The density measurements for coal concentrations that ranged from 0 to 60 wt.% are presented in Fig. 6.21. A linear relationship was measured with an accuracy < 5%. The relationship was independent of slurry velocity and particle size. Because of the large contrast between the coal and oil dielectric... 

FIGURE 6-23 Typical cross-correlation function obtained by ANL capacitive flowmeter for two slurry velocities (0.26 and 0.4 m/s) and two electrode spacings (1.52 and 15.2 cm). Coal concentration was 60 wt.%. 

The slurry velocity at which a particle bed forms is defined as critical deposition velocity, VD, and represents the lower pump rate limit for minimum particle settling. A further decrease in slurry velocity leads to increased friction loss, as indicated by a characteristic hook upward of curve A, and may also lead to pipe plugging. After shutdown, if flow rate over the settled solids is gradually increased, a response similar to curve A of Figure 16 is once again obtained. With increasing nominal shear rate, wall shear stress decreases until a minimum is reached and then increases rapidly thereafter. The fluid velocity that corresponds to this minimum stress value is the critical resuspension velocity, Vs. 

A 13% (by volume) phosphate slurry (m = 3.7Pa-s", n = 0.18, density 1230 kg/m ) is to be pumped through a 50 nun diameter horizontal pipe at mean slurry velocities ranging from 0.2 to 2 m/s. It is proposed to pump this slurry in the form of a two-phase air-slurry mixture. The following data have been obtained ... 

At the cocurrent upflow of the gas and the slurry the accumulation of solids is decelerated by the slurry velocity which acts against the settling. This is shown in Fig. 7 where the calculated average values of the catalyst concentrations are plotted as functions of Dp at different liquid velocities. According to the increasing solid dispersion the accumulation of the catalyst within the reactor is reduced with increasing the reactor diameter. 

Descriptions of typical slurry reactors used in the three processes considered here are available in the literature (4,5, 11,12). The operating conditions employed in these reactors are briefly outlined in Table 1. Some similarities in the operation of the three reactors can be noted. The reactors for both DCL and CCC processes are operated in a similar manner. In the FTS process, the liquid-solid (catalyst) slurry phase is usually stagnant. While the solid particle size in catalytic proQesses (FTS and catalytic DCL) can be large, in most practical situations, the solids are very fine and the slurry is considered to be pseudo-homogeneous. Slurry velocities for all the three processes are either small or none. In general, the gas velocities are in the same range however, FTS uses somewhat smaller gas velocities as compared to DCL and CCC processes. 

There are two basic (and interrelated) useful parameters for an open-channel slurry system design the minimum slope (to maintain slurry suspension) of straight lengths of launder, Smin (usually expressed as a percentage), and the velocity head corresponding to the minimum slurry velocity, K (expressed in metres), is often quoted as part of process technology, and may be arrived at directly by practical experience, whereas K is usually derived. The parameters have an approximate theoretical relationship, and the minimum slurry velocity Kmin is essentially the same as the minimum velocity to avoid settlement in full-flow pipes of comparable diameter, in terms of wetted perimeter. 

Vg is the average slurry velocity, and is the density ratio of the solids to that of the carrier liquid. Cp is the single particle drag coefficient and is given for spherical particles by [56]... 

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