Annular lamp reactor

Even though this chapter is devoted mostly to solar photocatalytic reactors, we would like to discuss the modeling of an annular lamp reactor, as a different example of the application of the PI approximation. This problem was studied (Cuevas et al., 2007) with reference to a particular reactor known as photo CREC-water II (Salaices et al., 2001, 2002). Equation (38) is again written in cylindrical coordinates. Nevertheless in this case the... 

If the size of the production unit requires higher radiant power than can be provided, for technical reasons, by one lamp, clusters of light sources may be installed, which, consequently will alter the diameter or the height of the inner core of, for example, an annular photochemical reactor. However, following the check list of concepts (vide supra), optimal reaction conditions will in most cases limit the size of the photochemical reactor, and the planned rate of production may require several reactor units installed in a parallel mode (batch process) or in series (continuous process). 

Deposits at the lamp jacket can also be prevented in bubble photochemical reactors, where small rising gas bubbles of nearly uniform size and distribution create strong turbulences [2, 3, 18, 68]. This reactor is usually conceived as an annular photochemical reactor of relative small thickness (/R, Eq. 36). In principle, its use with reactive gas is rather limited, as the turbulence provoked by the bubbles must be maintained over the entire height of the reactor [69, 70]. Bubble characteristics may also change as a function of the flux of the substrate solution. 

Annular flow reactors are characterized by a cylindrical lamp surroimded by two concentric tubes such that the polluted air flows in the annulus between the inner and the outer tubes. That way, all emitted photons can be utilized without the use of expensive reflectors. In certain cases (Doucet et al., 2006), an optical (occasionally liquid) filter is introduced between the lamp and the flowing zone to control the wavelength and the power of the impinging light, as well as the temperature within the reactor. 

A two-flux radiation field model for an annular packed bed photocatalytic oxidation reactor was presented by Raupp et al. (1997). Similar to other annular flow reactors, the UV source was located at the center of the cylindrical reactor. Yet, the photocatalyst was not introduced in the form of a thin film but rather as spherules filling the annular space between the lamp and the housing. The principal assumptions made in this model included a steady state, isothermal operation, cylindrical symmetry. 

Tsekov, R., Smirniotis, P.G., 1997, Radiation filed in a continuous annular photocatalytic reactors role of the lamp of fitrite size, Chem. Eng. Sci. 52 1667-1671. 

Figure 14. Cross section along the plane perpendicular to the axis of an annular reactor with a cylindrical excimer lamp mounted in its axis [12, 58, 59],...

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

The larger reactor operates under a steady state, continuous flow conditions and was made of two 1 m cylindrical reactors of annular shape in order to use conventional Germicidal lamps (Figure 14). The system of tanks shown in the flow sheet was used to (i) feed the reactor with a constant flow rate and (ii) wash the system after each experimental run. The actual operating length (Zi) of each lamp (1.2 m long) was Im. Operation could be made with just one reactor or the two in series. 

The commercial reactor consists of 13 reactor tubes in the recycle section and five tubes in the cleanup section. Each reactor tube consists of a concentric arrangement of a 2-in. Pyrex tube into which are inserted two 40-watt fluorescent lamps, a 4-in. Karbate tube enclosing the reactor section, and an 8-in. steel pipe enclosing the cooling section. Chilled water at 60 F circulates in the annular section enclosed by the steel pipe and removes the heat of reaction, which is estimated and checked calorimetrically to be around 190,000 Btu per lb mole BHC. A reaction velocity constant... 

Eigure. 4.3 illustrates the net radiative flux distribution, qo,y,t, in an empty annular reactor, as predicted by the validated ESSDE model. Several independent qe,z.t single measurements were taken at 1.47 cm from the lamp axis (0.2 cm from the lamp surface) and 22.2 cm axial position. 

Limits of integration for the 3D emission models. When a lamp with superficial emission is used, according to equation 6.38, a constant value must be incorporated as a boundary condition. Conversely, when lamps with voluminal emission are used, according to equation 6.51, the boundary condition infioduces a function of x, 0, and . The limits of integration for the annular reactor with the tubular lamp were derived by Irazoqui etal. (1973) and systematically described by Cassano etal. (1995). They are... 

A pilot plant scale, tubular (annular configuration) photoreactor for the direct photolysis of 2,4-D was modeled (Martin etal, 1997). A tubular germicidal lamp was placed at the reactor centerline. This reactor can be used to test, with a very different reactor geometry, the kinetic expression previously developed in the cylindrical, batch laboratory reactor irradiated from its bottom and to validate the annular reactor modeling for the 2,4-D photolysis. Note that the radiation distribution and consequently the field of reaction rates in one and the other system are very different. 

Reactor model. The reactor model was constructed according to the following sequence (i) the annular reactor, radiation distribution model of Romero etal. (1983) was adapted for this particular set-up (ii) the tubular lamp with voluminal and isotropic radiation emission model was applied to this system (iii) a mass balance for an actinometric reaction carried out in a tubular reactor inside the loop of a recycling system was adapted from Martin etal. (1996) and (iv) the verification of the radiation model, actinometer experiments were performed in the reactor to compare theoretical predictions... 

Figure 26.1 Examples of basic photochemical reactors (some adapted from Cassano et al., 1995). (a) tubular photoreactor inside a cylindrical reflector of elliptical cross section (b) annular photoreactor (c) film-type photoreactor (d) single-lamp multitube continuous photoreactor (e) perfectly-mixed semibatch cylindrical photoreactor irradiated from the bottom by a tubular source and a parabolic reflector...

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