Reactors Real gases, chemical

The gas motion near a disk spinning in an unconfined space in the absence of buoyancy, can be described in terms of a similar solution. Of course, the disk in a real reactor is confined, and since the disk is heated buoyancy can play a large role. However, it is possible to operate the reactor in ways that minimize the effects of buoyancy and confinement. In these regimes the species and temperature gradients normal to the surface are the same everywhere on the disk. From a physical point of view, this property leads to uniform deposition - an important objective in CVD reactors. From a mathematical point of view, this property leads to the similarity transformation that reduces a complex three-dimensional swirling flow to a relatively simple two-point boundary value problem. Once in boundary-value problem form, the computational models can readily incorporate complex chemical kinetics and molecular transport models. 

Internal reflection spectroscopy is widely applied for on-line process control. In this type of application, the chemical reactor is equipped with an internal reflection probe or an IRE. The goal of this type of application is the quantification of reactant and/or product concentrations to provide real-time information about the conversion within the reactor. In comparison with other analytical methods such as gas chromatography, high-pressure liquid chromatography, mass spectrometry, and NMR spectroscopy, ATR spectroscopy is considerably faster and does not require withdrawal of sample, which can be detrimental for monitoring of labile compounds and for some other applications. 

The two extreme hypotheses on mixing produce lumped models for the fluid dynamic behavior, whereas real reactors show complex mixing patterns and thus gradients of composition and temperature. It is worthwhile to stress that the fluid dynamic behavior of real reactors strongly depends on their physical dimensions. Moreover, in ideal reactors the chemical reactions are supposed to occur in a single phase (gaseous or liquid), whereas real reactors are often multiphase systems. Two simple examples are the gas-liquid reactors, used to oxidize a reactant dissolved in a liquid solvent and the fermenters, where reactions take place within a solid biomass dispersed in a liquid phase. Real batch reactors are briefly discussed in Chap. 7, in the context of suggestions for future research work. 

E will be different from 1 only if R4 is small relative to / 2, resulting in a bulk concentration of c — 0 and in a real parallel mechanism of the enhancement. The advantage of the concept of the enhancement factor as defined by eq 33 is the separation of the influence of hydrodynamic effects on gas-liquid mass transfer (incorporated in Al) and of the effects induced by the presence of a solid surface (incorporated in E ), indeed in a similar way as is common in mass transfer with homogeneous reactions. The above analysis shows that an adequate description of mass transfer with chemical reaction in slurry reactors needs reliable data on ... 

In the framework of this description an attempt to model an effect of spatial non-uniformity of real catalytic systems was made (Bychkov et al., 1997). It was assumed that reaction proceeds in a heterogeneous system represented by two active infinite plane surfaces and in the gas gap between them. Surface chemistry was treated as for the Li/MgO catalyst (see Table III). Because of substantial complexity of the kinetic scheme consisting of several hundred elementary steps, the mass-transfer was described in this case as follows. The whole gas gap was divided into several (up to 10) layers of the same thickness, and each of them was treated as a well-stirred reactor. The rate of particle exchange between two layers was described in terms of the first-order chemical reaction with a rate constant ... 

The time-averaged velocities and gas holdups in the compartments, as well as the fluid interactions between the zones, are first calculated by computational fluid dynamics (CFD). Then, balance equations for heat and mass transfer and for chemical reactions are evaluated and solved using appropriate software. First results from a simulation of a cumene oxidation reactor on an industrial scale were impressive, as they matched real temperature and concentration fields. 

In this chapter, a brief description of the main bio-SNG facilities and projects in Europe is presented as well as the main process units (gasification, gas cleaning and methana-tion) integrated for bio-SNG production. Therefore, a case study for bio-SNG production is modeled by using the CHEMCAD 6.3.1.4168 software. Two process technologies, a fixed (adiabatic case) or fluidized (isothermal) bed methanation reactors are considered, while three different product gas compositions from real biomass gasification data are fed as input syngas for the modeled system. Einally, CH4 yield and chemical efficiency of the different cases are compared and discussed. 

It is important to stress the difference between a pure plasma and a real plasma. Essentially all of the published VUV emission data in the literature, for low pressure discharges, is from spectroscopic smdies in which extreme care was taken to ensure pure gases. However, plasma reactors, by definition, are used to process materials and the plasma gas will be contaminated with the by-products of that processing. Therefore, a real plasma gas will never be pure. It will be shown later that there can be 10% to 20% contaminants in the gas. In the case of the oxidation of polymers or photoresist, these will be C, H, O species, all of which can interact, both chemically and energetically. 

Dispersion of bubbles in a molten metal bath and the induced flow strongly influence the performance of gas-agitated steelmaking processes. Unfortunately, measurements of the bubble and molten metal flow characteristics are quite difficult in real steelmaking processes. Hence water model experiments have been extensively employed for such investigations, as discussed in detail in Chap. 1 [17,18]. The vessels used for such model experiments are usually fully wetted by water, whereas in the actual steelmaking processes, the wettability of the reactor wall is generally poor. When the wall material, i.e., refl actory, is wetted by the molten metal, some chemical reactions may occur between them, and consequently, the molten metal may be contaminated by the refractory. As mentioned earlier, the wettability is evaluated in terms of 0a [19]. 

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