Semi-fluidization

Separation characteristics of Phenoxyacetic Acids in Fixed and Semi-Fluidized Beds... 

Adsorption equilibrium of CPA and 2,4-D onto GAC could be represented by Sips equation. Adsorption equilibrium capacity increased with decreasing pH of the solution. The internal diffusion coefficients were determined by comparing the experimental concentration curves with those predicted from the surface diffusion model (SDM) and pore diffusion model (PDM). The breakthrough curve for packed bed is steeper than that for the fluidized bed and the breakthrough curves obtained from semi-fluidized beds lie between those obtained from the packed and fluidized beds. Desorption rate of 2,4-D was about 90 % using distilled water. 

Fig. 3 shows the breakthrough curves for the packed, semi-fluidized, and fluidized beds. It is seen that the breakthrough curve obtained from the semi-fluidized bed lies between those obtained from the packed and fluidized beds, since the semi-fluidized bed possesses the features of both the fluidized and packed beds. This figure also shows that the shape of the breakthrough curve for the packed bed is steeper than that for the fluidized bed. 

The shape of the breakthrough curve for a packed bed is steeper than that for the fluidized bed and the breakthrough curves obtained from semi-fluidized bed lies between those obtained from the packed and fluidized beds. 

The dynamics of such a mode of semi-fluidization is similar to that of jigging in ore dressing, which is a common operation in coal or ore dressing, though little used in the design of chemical reactors. Thus, at least on a periodic basis, jigging yields the same advantages as other modes of fluidization with no net fluid flow. 

Straightforward. We have therefore employed XAD-4 to combine biocatalytic synthesis with simultaneous product extraction. The system (Figure 15.8) comprises a continuously stirred tank reactor, a starting material feed pump, a product recovery loop with a (semi-) fluidized bed of XAD-4, and a pump to circulate the entire reaction mixture through the loop." ° Preliminary studies indicated that XAD-4 had no detrimental effects on E. coli JMlOl (pHBP461), hence, separation of biomass and reaction liquid prior to catechol extraction was not required. The biocatalytic reaction was carried out at very low concentrations of the toxic substrate and product. This was achieved by feeding the substrate at a rate lower than the potential bioconversion rate in the reactor. 

In a commercial fluidized bed, the presence of defluldized or semi-fluidized particles on the distributor in-between the gas inlet points is very undesirable since with "sticky" or "tacky" materials, these zones will grow and eventually plug the distributor. With exothermic catalytic reactions, these defluldized zones would lead to the formation of hot spots on the distributor. Fakhlml [60] developed a model which predicts the formation of defluldized zones and Zenz [22] suggested a distributor made of a honeycomb of nearly touching cones or hexagons to eliminate these stagnant zones. 

Knowledge of these types of reaetors is important beeause some industrial reaetors approaeh the idealized types or may be simulated by a number of ideal reaetors. In this ehapter, we will review the above reaetors and their applieations in the ehemieal proeess industries. Additionally, multiphase reaetors sueh as the fixed and fluidized beds are reviewed. In Chapter 5, the numerieal method of analysis will be used to model the eoneentration-time profiles of various reaetions in a bateh reaetor, and provide sizing of the bateh, semi-bateh, eontinuous flow stirred tank, and plug flow reaetors for both isothermal and adiabatie eonditions. 

The following semi-empirical equation relates the (hindered) settling velocity of a slurry of particles to the settling velocity of a single particle, known as the Richardson and Zaki (1954) (RZ) equation. The RZ equation is also used for liquid fluidization whereby particles are supported by an up-flow of fluid. 

On the other hand, there is a blizzard of empirical and semi-empirical correlations which exist in the fluidized bed literature to predict... 

The approach taken here is to employ standard materials characterization tests to measure the materials properties of the granulated product. With this information, the mechanism of attrition, i.e., breakage versus erosion, is determined. The rate of attrition can then be related, semi-empirically, to material properties of the formulation and the operating variables of the process, such as bed depth and fluidizing velocity. 

Thus, the three-dimensional voidage distribution in a fast fluidized bed can be determined, semi-empirically as our understanding stands at the present, from the physical properties of the solids and the gas and the operating variables. 

Fluidized bed granulation monitoring of a fertilizer product (urea) in a semi-industrial pilot plant (SIPP), illustrating the main features and benefits. 

The experiments were carried out on a semi-industrial fluidized bed reactor, illustrated in Figure 9.6, which shows four different sensor positions (A, B, C and D). Screw fittings were used to mount the sensors in order to secure optimal sensor pickup efficiency. Sensor location A is mounted onto an orifice plate on the main supply line of liquid urea to the reactor nozzles, following Esbensen et al. [5]. The sensors B, C and D are located on the wall of reactor chambers 1, 2 and 4, respectively. 

Based upon the work of Evans et al. (1983), Thorpe (1987) describes a semi-commercial scale continuous-flow fluidized bed disinfestor capable of handling up to 150 th of wheat. He gives a detailed description of the thermodynamic performance of the plant together with a mathematical model of the process which is validated by experimental results obtained from the plant. The plant consists of a single fluidized... 

Santos, J.C., Silva, S.S., Mussatto, S.I., Carvalho, W. and Cunha, M.A.A., Immobilized cells cultivated in semi-continuous mode in a fluidized bed reactor for xylitol production from sugarcane bagasse, World. Microbiol. Biotech., 21 (2005) 531-535. 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

Due to the fact that protein adsorption in fluidized beds is accomplished by binding of macromolecules to the internal surface of porous particles, the primary mass transport limitations found in packed beds of porous matrices remain valid. Protein transport takes place from the bulk fluid to the outer adsorbent surface commonly described by a film diffusion model, and within the pores to the internal surface known as pore diffusion. The diffusion coefficient D of proteins may be estimated by the semi-empirical correlation of Poison [65] from the absolute temperature T, the solution viscosity rj, and the molecular weight of the protein MA as denoted in Eq. (16). 

The measurements were carried out at a semi-industrial fluidized-bed plant DN 400. The scheme of the process is illustrated in Fig. 16.4, while the plant itself is illustrated in Fig. 16.5. 

Burovoi, I. A., Dracheva, T. V, and Ibraev, A. Kh., Semi-Industrial Testing of the Fluidized-Bed Acid Leaching of Zinc Calcine, Tsvet, Metal. 44(10), 16(1971) Chem. Abs. 76,36,301 (1972). Cankurt, N. T., and Yerushalmi, J., Gas Backmixing in High Velocity Fluidized Beds, Second Intern. Conf. Fluidization. Cambridge, pp. 387-393 (1978). 

Martin, G., Dolignier, J. C., Flament, P., and Nougier, L. The AUDE Boiler-Experience on A 10 MW Semi-industrial Unit and Modelling Results, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 124-130. Somerset, Pennsylvania (1993). 

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