Internal recirculation reactors

Key Features of an Internal Recirculation Reactor [After Shah, 1979]... 

Several reactors are presently used for studying gas-solid reactions. These reactors should, in principle, be useful for studying gas-liquid-solid catalytic reactions. The reactors are the ball-mill reactor (Fig. 5-10), a fluidized-bed reactor with an agitator (Fig. 5-11), a stirred reactor with catalyst impregnated on the reactor walls or placed in an annular basket (Fig. 5-12), a reactor with catalyst placed in a stationary cylindrical basket (Fig. 5-13), an internal recirculation reactor (Fig. 5-14), microreactors (Fig. 5-16), a single-pellet pulse reactor (Fig. 5-17), and a chromatographic-column pulse reactor (Fig. 5-18). The key features of these reactors are listed in Tables 5-3 through 5-9. The pertinent references for these reactors are listed at the end of the chapter. 

Figure 5-14 Internal recirculation reactors, (o) With catalyst at the wall.65 (b) with catalyst at the center.64...

Figure 8.4. Plot of / nhj versus //T(K ) at various water poisoning levels. The catalyst has been poisoned at 350 and ambient pressure in an internal recirculation reactor at H2O levels from 5.3 to 38.9 ppm. At steady state the temperature is quenched to 200 °C and the H2O supply is interrupted simultaneously. The rate is then measured at temperatures of 225-275 °C. Note that the lines are parallel, indicating an unchanged activation energy. Data from Brill et By permission of Verlag Chimie GmbH,...

Another version of a fluidized-bed reactor has been introduced by Vogelbusch (Austria). This reactor has an internal recirculation loop set up by means of a high flow impeller. The system utilises porous glass beads for immobilizing the cells. However, glass beads may not work with all types of cells. 

Exothermic processes, with cooling through heat transfer surfaces or cold shots. In use are sheU-and-tube reactors with smaU-diameter tubes, or towers with internal recirculation of gases, or multiple stages with intercoohng. Chlorination of methane and other hydrocarbons results in a mixture of products whose relative amounts... 

The older internal recycle reactors of Berty et al (1969), and Berty (1974) are shown on Figures 2.4.3 a, b. The reactor of Romer and Luft (1974) uses no mechanical moving parts. The recirculation is generated by the feed gas as it expands through a nozzle. A major disadvantage of using a jet is that feed rate and recirculation rate are not independent. Due to the low efficiency of jet pumps, recycle rates are quite low. 

One such laboratory flow reactor for a gas-phase reaction catalyzed by a solid (particles indicated) is shown schematically in Figure 1.2. In this device, the flowing gas mixture (inlet and outlet indicated) is well mixed by internal recirculation by the rotating impeller, so that, everywhere the gas contacting the exterior catalyst surface is at the same composition and temperature. In this way, a point rate of reaction is obtained. 

Fig. 7.18. CSTR with fixed bed and internal (Berty reactor) or external recirculation.

This concept was demonstrated at the Institute of Process Engineering and Cryogenics at ETH (Switzerland) during the last two years with the FilmCooled Hydrothermal Burner (FCHB). The FCHB operated at pressures of 25 MPa and temperatures up to 2000 K, cf. [1], Experiments and detailed analysis led to the basic design approach for SCWO reactors discussed herein which is based on wall boundary layer control and internal recirculation. 

Other reactor concepts show similar features (see [1] and [4]), which include boundary layer control and internal recirculation. Reference [5] proposes boundary layer control utilizing transpiration cooling. 

One unique feature of the monolith reactor is the possibility of having an internal recirculation of the gas flow without the use of a pump [5,8-10]. This self-recirculation is possible due to the very low net pressure drop across the monolith. In a monolith reactor with downflow operation in slug flow regime, the fluids are not driven through the channels by an external pressure, but pulled through by gravity. This corresponds to a total superficial velocity of about 0.45 m sec . When liquid is added to the channel at a lower rate, gas will be entrained to make the total velocity 0.45 m sec. ... 

The frictional pressure drop is always lower in the MR, by up to two orders of magnitude, for all relevant sizes of catalyst particles (shell catalysts of a greater size included). For an MR operating in downflow mode, it is possible to balance the frictional pressure drop with the hydrostatic pressure of the liquid inside the channels. The essentially zero net pressure drop provides an opportunity to operate the MR with internal recirculation of gas. Since the gas does not need to be recompressed, an open passageway from the bottom of the reactor to the top is all that is needed (Fig. 11). 

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