Suspended particle reactor

In many important cases of reactions involving gas, hquid, and solid phases, the solid phase is a porous catalyst. It may be in a fixed bed or it may be suspended in the fluid mixture. In general, the reaction occurs either in the liquid phase or at the liquid/solid interface. In fixed-bed reactors the particles have diameters of about 3 mm (0.12 in) and occupy about 50 percent of the vessel volume. Diameters of suspended particles are hmited to O.I to 0.2 mm (0.004 to 0.008 in) minimum by requirements of filterability and occupy I to 10 percent of the volume in stirred vessels. 

An overly simplified model of fluidized-bed combustion treats the solid fuel as spherical particles freely suspended in upward-flowing gas. Suppose the particles react with zero-order kinetics and that there is no ash or oxide formation. It is desired that the particles be completely consumed by position z = L. This can be done in a column of constant diameter or in a column where the diameter increases or decreases with increasing height. Which approach is better with respect to minimizing the reactor volume Develop a model that predicts the position of the particle as a function of time spent in the reactor. Ignore particle-to-particle interactions. 

Aniline is to be hydrogenated to cyclohexylamine in a suspended-particle agitated-tank reactor at 403 K (130°C) at which temperature the value of k is 90 s 1. The diameter dp of the supported nickel catalyst particles will be 0.1 mm and the effective diffusivity De for hydrogen when the pores of the particle are filled with aniline is 1.9 x 10 9 m2/s. 

Special consideration shonld be given to the transformation of contaminants in sediments and gronndwater. Under saturated conditions, the solid phase may function as a sink, reservoir, and reactor for contaminants. Contaminant presence, persistence, and transformation in the water phase is controlled by the chemistry of the water body, the surface properties of the materials forming the solid phase (sediments or suspended particles), and environmental conditions (temperature and aerobic or anaerobic stams). 

The main difference is the particle size. In three-phase fluidized beds these are so large that a net upward liquid flow is necessary to keep the solids in suspension, whereas in slurry reactors the turbulence of the liquid is sufficient to keep the solids suspended particle sizes in slurry reactors are usually below 200 ftm. Particularly for fast reactions where intraparticlc dif-... 

Adsorption flotation involves the removal of dissolved pollutants by activated carbon in a bubble reactor, and subsequent removal of activated carbon as well as other suspended particles by flotation technique (71). This process was found efficient for removing both dissolved organics and suspended solids from an industrial effluent (72), and for removing the emulsifled oil from water (73). The mechanism of removal has been proposed by Wang (72,73). 

In principle, fluidized ion exchange beds are similar to stirred tank chemical reactors. The general equations of kinetics and mass transfer can be applied to the individual fluidized units in an identical manner to those for chemical reactors. The primary difference lies in accounting for the behavior of suspended particles in the turbulent fluid,... 

Seawater is pretreated before reaching the reactor and generally involves screening and filtration to remove suspended particles such as silts, sand, and marine creatures followed by decarbonation. Decarbonation is achieved by adding concentrated sulfuric acid to the seawater to lower the pH to 4 see reaction (3.9). The seawater is then passed over a wooden (creosote- and tar-treated) desorption tower where it is aerated to remove carbon dioxide. 

In an agitated reactor, the effect of mass transfer resistance can be reduced to a minimum by adjusting the stirring speed. The mass transfer coefficient is also a function of the size of suspended particles. From the point of view of reactor design, to maintain the uniformity of the desired product from batch to batch the particle size distribution of the solid reactant should be in a rather narrow range to render the mass transfer resistance unimportant. 

The work of Zaharov [34] describes the laws governing the granulometric composition of the suspended particles of calcium stearate under the changing conditions of the calcium stearate aqueous solution and calcium chloride reaction, in particular, for tubular turbulent reactors. 

When the diameter of the bubble (gas) has a value of the same order of magnitude as the diameter of the tube, the fluidized bed will operate in slugging regime, where the bubble occupies the entire cross section of the bed. Depending on the size of the bubble, we might have preferred paths in bed. These cases do not contribute to a good contact of the gas with the suspended particles in the bed, therefore, they should be avoided. The most suitable solution is the choice of a particular type of gas distributor in the inlet of the reactor. 

In the Cora code, the corrosion product layers outside the reactor core are rather arbitrarily subdivided into two layers, a transient one and a permanently deposited one. Supply to the transient layer occurs via deposition of suspended particles from the coolant, release from it includes erosion of particles back to the coolant as well as transport into the permanently deposited layer and partial conversion into dissolved species. In a comparable manner, the supply of nuclides to the permanent layer is assumed to result from transfer from the transient layer and the exchange equilibrium with the dissolved species present in the coolant. The deposition coefficients of suspended solids can be calculated on the basis of particle size and flow characteristics. The coefficients of relevance for the permanently deposited layer, including ionic transfer mechanisms between liquid and solid phases, can be derived from theoretical considerations as well as from laboratory studies of corrosion product solubilities. Finally, diffusion rates of nuclides at the interphase layers are needed, from the oxide layer to the coolant as well as in the reverse direction. These data can be obtained in part by theoretical considerations and by measurements at the plants. 

Knowledge about the mechanism of deposition of corrosion products onto the fuel rod surfaces is still limited. The dissimilar elemental concentrations for the brushed and scraped fractions in the filter/demineralizer plants are probably due to the fact that these two fractions were created by different mechanisms. The brushed fraction most likely results from the deposition of suspended particles from the reactor water, while the scraped fraction is assumed to be formed by precipitation of dissolved corrosion product species. The axial distributions of both fractions of the deposits on the fuel rod surfaces usually show differences which also suggest that they were generated by different mechanisms. The brushed fraction shows a characteristic profile, in which the corrosion products deposit preferentially near the bundle inlet and which can be correlated with the fluid shear at the heat transfer surface. This distribution is consistent with the assumption that particle deposition is the predominant mechanism for the buildup of the loosely-adherent deposits, since low fluid shear favors particle deposition. On the other hand, the axial profile of the tenacious fraction is quite different, being relatively constant over the middle region of the bundle and decreasing towards each end. 

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