Reactor Geometries

Similar approaches are applicable in the chemical industry. For example, maleic anhydride is manufactured by partial oxidation of benzene in a fixed catalyst bed tubular reactor. There is a potential for extremely high temperatures due to thermal runaway if feed ratios are not maintained within safe limits. Catalyst geometry, heat capacity, and partial catalyst deactivation have been used to create a self-regulatory mechanism to prevent excessive temperature (Raghaven, 1992). 

Processes should be reviewed to identify the safest failure position for all electric or pneumatic valves. The designer should consider all failures 

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Modifications in reactor geometry, agitation and control (e.g. instrumentation, cooling, venting). 

Information on the composition and temperature changes is obtained from the rate equation, while the mixing patterns are related to the intensity of mixing and reactor geometry. Heat transfer is referred to as the exothermic or endothermic nature of the reactions and the mass transfer to the heterogeneous systems. 

Reactor geometry - flow pattern and manner of contacting the phases... 

Assume a reactor geometry as in Figure 3 with a vapor space and relief device located in the vapor space. 

Figure 3 shows a composite result from several simulations and considers the relationship between disk temperature and spin rate for a helium carrier in a fixed reactor geometry (fo/f[Pg.338]

Figure 3. Relationship of susceptor temperature to spin rate that is required to operate a particular reactor geometry in the one-dimensional regime.

In order to use Eqs. (3) and (4) or the data given in Fig. 1, for the calculation of maximum turbulent fluctuation velocity the maximum energy dissipation e , must be known. With fully developed turbulence and defined reactor geometry, this is a fixed value and directly proportional to the mean mass-related power input = P/pV, so that the ratio ,/ can be described as an exclusive function of reactor geometry. In the following, therefore details will be provided on the calculation of power P and where available the geometric function ,/ . 

Where the Reynolds stress formula (2) and the universal law of the theory of isotropic turbulence apply to the turbulent velocity fluctuations (4), the relationship (20) for the description of the maximum energy dissipation can be derived from the correlation of the particle diameter (see Fig. 9). It includes the geometrical function F and thus provides a detailed description of the stirrer geometry in the investigated range of impeller and reactor geometry 0.225derived from many turbulence measurements, correlation (9). 

On shrinking the size of micro-channel reactors by reducing the channel dimensions, a number of characteristic quantities such as pressure drop and the degree of chemical conversion are affected. In order to permit a meaningful comparison of the reactor geometry with a scaled geometry, it is important to keep one or a few... 

In chemical micro process technology with porous catalyst layers attached to the channel walls, convection through the porous medium can often be neglected. When the reactor geometry allows the flow to bypass the porous medium it will follow the path of smaller hydrodynamic resistance and will not penetrate the pore space. Thus, in micro reactors with channels coated with a catalyst medium, the flow velocity inside the medium is usually zero and heat and mass transfer occur by diffusion alone. 

It could be demonstrated that for any reaction with a reaction order higher than one, positive effects such as a conversion increase can be expected. Also, adaptation of the reactor geometry can improve the positive impact of periodic processing. 

Figure 5.18 Comparison of space-time yields of direct fluorination of toluene for the falling film micro reactor (FFMR), micro bubble column (MBC) and laboratory bubble column (LBC) referred to the reaction volume (a) and referred to an idealized reactor geometry (b) [38],...

The above-mentioned space-time yields were referred solely to the reaction volume, i.e. the micro channel volume. When defining this quantity via an idealized reactor geometry, taking into accoimt the construction material as well, natarally the difference in space-time yield of the micro reactors from the laboratory bubble column becomes smaller. Still, the performance of the micro reactors is more than one order of magnitude better [38], The space-time yields for the micro reactors defined in this way ranged from about 200 to 1100 mol monofluorinated product... 

In practice, nearly all reactors used for the manufacture of fine chemicals are neither isothermal nor adiabatic. The temperature-versus-time (location) profile is determined by the kinetic and physical characteristics of the reaction mixture as well as by the reactor geometry and hydrodynamics. The relationships governing this profile will be discussed in Section 5.4.2. 

The scale-up from a small to a large plasma reactor system requires only linear extrapolations of power and gas flow rates. However, in practice, the change in reactor geometry may result in effects on plasma chemistry or physics that were unexpected, due to a lack of precise knowledge of the process. Fine tuning, or even coarse readjustment, is needed, and is mostly done empirically. 

In contrast, Heintze and Zedlitz [236] also presented data on the plasma potential as function of frequency in silane plasmas the plasma potential varies from about 27 V at 35 MHz to about 20 V at 180 MHz. Moreover, Dutta et al. [284] used a symmetric capacitively coupled RF reactor and estimated the plasma potential in their system from the applied voltage at the powered electrode. A decrease of the plasma potential from 45 V at 13.56 MHz to only 15 V at 70 MHz is observed. This difference in behavior is thought to be solely due to the different reactor geometries. 

Optimization of reactor geometry in terms of charging and removal of materials... 

Reactor geometry and distributor design Growth rate... 

The CFD model described above has been used by Liu and Fox (2006) to simulate the experiments of Johnson and Prud homme (2003a) in a confined impinging-jets reactor. In these experiments, two coaxial impinging jets with equal flow rates are used to introduce the two reactant-streams. The jet Reynolds number Re, determines the fluid dynamics in the reactor. Typical CFD results are shown in Fig. 6 9 for a jet Reynolds number of Re, = 400 and a reaction time of tr — 4.8 msec. The latter is controlled by fixing the inlet concentrations of the reactants. Further, details on the reactor geometry and the CFD model can be found in Liu and Fox (2006). 

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