Slurry Flow System

Figure 11-25 shows the nature of that disruption. The unsonicated crystals (top) are disrupted by sonication along cleavage planes (bottom), a mechanism which produces few fines to elutriate out of the seed bed. For this product, the sonicators were located in the column bottom (Fig. 11-26). Whether the sonicators are located internally, as shown, or in a slurry flow system, as shown in Fig. 11-28, the crystal population fed to the sonicators is always drawn from the bottom of the seed bed, where the largest particles are located.

The two procedures primarily used for continuous nitration are the semicontinuous method developed by Bofors-Nobel Chematur of Sweden and the continuous method of Hercules Powder Co. in the United States. The latter process, which uses a multiple cascade system for nitration and a continuous wringing operation, increases safety, reduces the personnel involved, provides a substantial reduction in pollutants, and increases the uniformity of the product. The cellulose is automatically and continuously fed into the first of a series of pots at a controlled rate. It falls into the slurry of acid and nitrocellulose and is submerged immediately by a turbine-type agitator. The acid is deflvered to the pots from tanks at a rate controlled by appropriate instmmentation based on the desired acid to cellulose ratio. The slurry flows successively by gravity from the first to the last of the nitration vessels through under- and overflow weirs to ensure adequate retention time during nitration. The overflow from the last pot is fully nitrated cellulose. 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Figure 2-49. Slurry flow regime (heterogeneous, homogeneous) is a function of solid s size and specific gravity. By permission, Der-annelaere, R. H. and Wasp, E. J., "Fluid Flow, Slurry Systems and Pipelines," Encyclopedia of Chemical Processing and Design, J. Mc-Ketta, Ed., M. Dekker, vol. 22,1985 [25].

The design of a cross-flow filter system employs an inertial filter principle that allows the permeate or filtrate to flow radially through the porous media at a relatively low face velocity compared to that of the mainstream slurry flow in the axial direction, as shown schematically in Figure 15.1.9 Particles entrained in the high-velocity axial flow field are prevented from entering the porous media by the ballistic effect of particle inertia. It has been suggested that submicron particles penetrate the filter medium and form a dynamic membrane or submicron layer, as shown in... 

To continuously separate FT wax products from ultrafine iron catalyst particles in an SBCR employed for FTS, a modified cross-flow filtration technique can be developed using the cross-flow filter element placed in a down-comer slurry recirculation line of the SBCR. Counter to the traditional cross-flow filtration technique described earlier, this system would use a bulk slurry flow rate below the critical velocity, thereby forcing a filter cake of solids to form between the filter media and the bulk slurry flow, as depicted in Figure 15.2b. In this mode, multiple layers of catalyst particles that deposit upon the filter medium would act as a prefilter layer.10 Both the inertial and filter cake mechanisms can be effective however, the latter can be unstable if the filter cake depth is allowed to grow indefinitely. In the context of the SBCR operation, the filter cake could potentially occlude the slurry recirculation flow path if allowed to grow uncontrollably. 

One goal of a bulk delivery system is to provide constant pressure to a CMP polisher, so that the peristaltic metering pump in the polisher can provide constant slurry flow to the polisher platen. While many schemes have been devised to minimize the fluctuations in pressure, there are many... 

Flow systems are developed mainly for liquid samples and their complexity can range from simple to very complex manifolds to deal with ultratrace amounts of the target analyte in complex matrices, which often require on-line separation/preconcentration steps. As a wide variety of chemical manipulations can be carried out in an FI manifold, the scope of the FI applications is enormous. Not only liquid samples, but also both gas and solid samples, can be also introduced into the liquid flow manifold if special adaptations are made. Gas samples simply require impermeable tubing. Solids can be either introduced into the system and leached with the help of auxiliary energy e.g. ultrasound) or introduced as slurries. 

The method just outlined and illustrated is route specific. It is very flexible and simple to use. It can also be easily computerized if the GP data can be fed in as numerical values. Here we have illustrated its use in the context of a cross-country pipeline, such as a crude oil, products, or perhaps slurry pipeline, which might be commonly encountered by chemical engineers. The method is completely adaptable to any hydraulic flow problem and could be used equally well for a short in-plant pumping system analysis. It can help the designer of flow systems to avoid sometimes subtle traps for slack flow and siphons that might not be immediately obvious if the mechanical energy equation is applied only once between the initial and final points of the flow system. 

The dissolving system was scheduled for maintenance while the rest of the unit continued at full production rates. The chemical process operator was concerned about the available room in the sump as the slurry accumulated during the two- to three-hour outage. The operator drastically increased the slurry flow-rate into the dissolving system for about an hour and a half period before the shutdown. However, he only increased the flow of acid into the system slightly during that time. The basic process is shown in Figure 4—3. 

Figure 5 shows typical H2 volumes generated by a flow system. Two important points are immediately evident from Figure 5. Firstly, H2 generation is extremely rapid, with an average rate of 42.3 milliliters/sec-gram catalyst for the first 90% of the available H2, with a maximum rate of 111 milliliters/sec-gram. Secondly, overall H2 yields based on stoichiometric amounts of NaBFL, is >95%. H2 generation rates decrease as the solution becomes more slurry-like and less water is available for reaction.

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