Solids flux

In Eqs. (18-103) and (18-104), under hindered setthng and 1 g, the solids flux is assumed to be a hnear function of p, decreasing at a rate of Vg. Also, the sohds flux is taken to be zero at the maximiim solids concentration (b max- As G/g 1, this solids flux behavior based on 1 g is assumed to be ratioed By G/g. 

Evaluates the performance of each unit of a wastewater treatment plant based on hydraulic loadings, solid flux loadings, food/microorganism ratios, sludge age, settleability, and related parameters. 

A new process for the partial oxidation of n-butane to maleic anhydride was developed by DuPont. The important feature of this process is the use of a circulating fluidized bed-reactor. Solids flux in the rizer-reactor is high and the superficial gas velocities are also high, which encounters short residence times usually in seconds. The developed catalyst for this process is based on vanadium phosphorous oxides... 

At many plants, fluxes are added to the metal to reduce hydrogen contamination, remove oxides, and eliminate undesirable trace elements. Solid fluxes such as hexachloroethane, aluminum chloride, and anhydrous magnesium chloride may be used, but it is more common to bubble gases such as chlorine, nitrogen, argon, helium, and mixtures of chlorine and inert gases through the molten metal. 

The solids flux depends on the local concentration of solids, the settling velocity of the solids at this concentration relative to the liquid, and the net velocity of the liquid. Thus the local solids flux will vary within the thickener because the concentration of solids increases with depth and the amount of liquid that is displaced (upward) by the solids decreases as the solids concentration increases, thus affecting the upward drag on the particles. As these two effects act in opposite directions, there will be some point in the thickener at which the actual solids flux is a minimum. This point determines the conditions for stable steady-state operation, as explained below. 

Because the batch flux data are obtained in a closed system with no outflow, the net solids flux is zero in the batch system and Eq. (14-40) reduces to FL = —(pV%/ 1 — cp). Note that FL and Vs are of opposite sign, because the displaced liquid moves upward as the solids settle. The relative velocity between the solids and liquid is Vr = Vs — VL which, from Eq. (14-20), is Vr = Fs/(1 — relative velocity that controls the dynamics in the thickener. If the underflow draw-off rate from the thickener is gu, the additional solids flux in the thickener due to superimposition of this underflow is qu = Qu/A = Vu. Thus, the total solids flux at any point in the thickener (qs) is equal to the settling flux relative to the suspension (i.e., the batch flux qsb) at that point, plus the bulk flux due... 

Once the operating line is set, the equations that govern the thickener operation are determined from a solids mass balance as follows. At steady state (stable) operating conditions, the net solids flux is... 

You must determine the maximum feed rate that a thickener can handle to concentrate a waste suspension from 5% solids by volume to 40% solids by volume. The thickener has a diameter of 40 ft. A batch flux test in the laboratory for the settled height versus time was analyzed to give the data below for the solids flux versus solids volume fraction. Determine ... 

The thickness of the downflowing layers at the wall of the CFB is typically defined as the distance from the wall to the position of zero vertical solid flux. Measurements of the layer thickness were made on a 12 MW and 165 MW CFB boiler by Zhang, Johnsson and Leckner (1995). They found that the thickness increased for the larger bed. They related data from many different beds (Fig. 19), with the equivalent bed diameter, taken as the hydraulic diameter, using the following form... 

The thickness, 8, was found to be insensitive to particle concentration, gas velocity and height within the furnace. That suggests that the thickness results from a balance of solids internal circulation which is generally much higher than netthroughflow. If the local solids flux profile,... 

Ishii and Murakami (1991) evaluated the CFB scaling relationships of Horio et al. (1989) using two cold CFB models. Solids flux, pressure drop, and optical probe measurements were used to measure a large number of hydrodynamic parameters to serve as the basis for the comparison. Fair to good similarity was obtained between the beds. Dependent hydrodynamic parameters such as the pressure drop and pressure fluctuation characteristics, cluster length and voidage, and the core diameter were compared between the two beds. The gas-to-solid density ratio was not varied between the beds. As seen in Table 7, the dimensionless solids flux decreased as the superficial velocity was increased because the solids flux was held constant. 

Figure 18. Parametric effects of solid flux and particle diameter on heat transfer in fast fluidized beds. (From Furchi et al, 1988).

Figure 19. Interactive effects of solid flux and axial location on heat transfer in fast fluidized bed. (From Dou, Herb, Tuzla and Chen, 1991.)...

Total reflection X-ray fluorescence spectrometry, 26 435-437 Total sideband suppression (TOSS) technique, 23 741 Total site pinch analysis, 20 751 Total solids flux, in thickener design and scale-up, 22 58... 

Figure 5.7. Solids flux per unit area as a function of volumetric concentration...

Thus, by drawing the tangent at a series of points on the curve BDC and measuring the corresponding slope — uc and intercept OT, it is possible to establish the solids flux f for any concentration ( ((, < C < Cmax). 

In a continuous thickener, the area required for thickening must be such that the total solids flux (volumetric flowrate per unit area) at any level does not exceed the rate at which the solids can be transmitted downwards. If this condition is not met, solids will build up and steady-state operation will not be possible. If no solids escape in the overflow, this flux must be constant at all depths below the feed point. In the design of a thickener, it is therefore necessary to establish the concentration at which the total flux is a minimum in order to calculate the required area. 

Figure 5.13. Solids fluxes as functions of concentration and Yoshioka construction ...

Using the Kynch theory, tabulate the sedimentation velocity and solids flux due to sedimentation as a function of concentration. What area of tank will be required to give an underflow concentration of 1200 kg/m3 for a feed rate of 2 m3/min of slurry ... 

Thus, for each height, the corresponding concentration may be calculated and the slope of the tangent measured to give the sedimentation velocity. The solids flux in kg/m1 2s is then ... 

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