Reactors, factors affecting design

Many factors affect gas holdup in three-phase fluidized systems, including bead size and density, liquid physical properties, temperature, sparger type, and fluid superficial velocities (Bly and Worden, 1990). System parameters such as reactor and gas distributor design can have... 

We first present further examples of the types of reactions involved in two main classifications, and then a preliminary discussion of various types of reactors used. Following an examination of some factors affecting the choice of reactor, we develop design equations for some reactor types, and illustrate their use with examples. The chapter concludes with a brief introduction to trickle-bed reactors for three-phase gas-liquid-solid (catalyst) reactions. 

The factors affecting the design of mechanically agitated liquid-liquid reactors are the miscibility of the liquid phases, the interfacial tension, and the densities and viscosities of the liquid phases, as well as the density and viscosity differences between the two liquids. As shown in Fig. 21, a variety of stirrer configurations are available to carry out liquid-liquid reactions. 

The most important, factors affecting the design of a fluid-solid noncatalytic reactor are the flow patterns of solid and fluid in the vessel. As noted in Sec. 14-1, the simplest case is where the composition of the fluid phase is uniform. Then the conversiori-vs-time relationship for single particles, such as Eq. (14-19), can be employed, along with the residence-time and particle-size distributions of the solid phase, to evaluate the average conversion. This problem is considered in the next section. When the fluid phase does not have a uniform composition the design is more complex. However, quantitative treatment is possible when the flow patterns of both solid and fluid phases are well defined. These kinds of reactors are discussed in Sec. 14-6. 

The operation of a chemical reactor is affected by a multitude of diverse factors. In order to select, design, and operate a chemical reactor, it is necessary to identify the phenomena involved, to understand how they affect the reactor operation, and to express these effects mathematically. This section provides a brief review of the phenomena encountered in chemical reactor operations as weU as the fundamental and engineering concepts that are used to describe them. Figure 1.4 shows schematically how various fundamental and engineering concepts are combined in formulating the reactor design equations. 

Recently, the fluidized bed membrane reactor (FBMR) has also been examined from the scale-up and practical points of view. Key factors affecting the performance of a commercial FBMR were analysed and compared to corresponding factors in the PBMR. Challenges to the commercial viability of the FBMR were identified. A very important design parameter was determined to be the distribution of membrane area between the dense bed and the dilute phase. Key areas for commercial viability were mechanical stability of reactor internals, the durability of the membrane material, and the effect of gas withdrawal on fluidization. Thermal uniformity was identified as an advantageous property of the FBMR. 

Bergmann, C. A., Perock, J. D. Evaluation of factors affecting radiation field trends in Westinghouse-designed plants. Proc. 6. BNES Conf. Water Chemistry of Nuclear Reactor Systems. Bournemouth, UK, 1992, Vol. 2, p. 16—23 Bergmann, C. A., Roesmer, J., Perone, D. W. Primary side deposits on PWR steam generator tubes. Report EPRI NP-2968 (1983)... 

Immobilized enzyme reactors are increasingly popular due to their advantages over conventional catalysts. For efficient reactor design and performance prediction, quantitative knowledge of reaction kinetics and the factors affecting them is required. In this chapter, enzyme catalytic mechanisms are described and the kinetic models developed from these mechanisms are discussed. The chapter also discusses the kinetics of immobilized enzymes and their related mass transfer effects. Diffusion restrictions are described with a particular focus on packed bed reactors. The chapter concludes with a brief discussion of immobilized enzyme reactor design and scale-up. 

Many factors affect optimum fluidized bed reactor performance, including hydrodynamics, heat and mass transfer of interparticles and intraparticles, and complexities of reaction kinetics. The design of fluidized bed reactor processes follows the general approach for multiphase reactor processes. Krishna (1994) and Jazayeri (1995) outlined the general procedure for this process development. The design of the processes can be described by considering various factors as illustrated in Fig. 3. 

Although methods to analyse the instability mechanism have recently become available, small variations in the factors that cause power instabilities affect the predictable performance of any given reactor for a given flow. Those factors are primarily, void fraction, fuel time constant, power level, power shape, feedwater temperature and core flow. Additionally, the design of the fuel rod and bundle can affect the formation and propagation of the void density waves. These factors affect the power/flow region at which power oscillations are probable. 

NOTLEY M.J.P, and LANE A.D, Factors affecting the design of rodded UOp fuel bundles for high power outputs. IAEA Symposium on Heavy Water Reactors, Vienna, September 1967, Paper SM-99/35. 

When the transmission development plan is designed for the cable, the cable route will be studied further. One characteristic of cables, compared to overhead lines, is that the laying of the cables and soil conditions of the location affect planning studies in addition to the land availability. These factors affect the burial depth, soil thermal resistivity, and cable separation between phases, which may necessitate changes to the conductor size and the amount and locations of shunt reactors initially deter-mined in the planning studies. 

The many factors outlined above which affect reaction rates suggest that considerable caution is advisable when utilising laboratory data for the design of large-scale reactors. It is essential first to locate the reaction volume or volumes. This, in the case of the absorption of CO2 into aqueous ammonia liquid discussed above, the fast reaction between dissolved CO2 and dissolved ammonia occurs in a small volume of liquid close to the gas—liquid interface. The forward reaction rate is, therefore, proportional to the gas—liquid interfacial area. The conversion of the initially fomed NH2COONH4 to (NH4)2COa by hydrolysis is a much slower reaction and takes place throughout the whole volume of the liquid phase. Similarity would therefore dictate that the interfacial area per unit liquid volume should be the same in experimental and full-scale reactors. 

The quality of the TiOz pigment is influenced by vario us factors. Reaction temperature, excess oxygen, and flow conditions in the reactor affect particle size and size distribution. Therefore, optimum conditions must be established for every reactor design. Caking of the TiOz on the walls of the reactor leads to impairment of quality. 

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