Axial distribution of reactivity inside a fluid‐bed contactor

Abstract

The axial distribution of reactivity inside a fluid-bed contactor is studied for the hydrogenation of ethylene. The reactivity is large near the surface of the dense phase. The significant effect of the dilute phase, or the free board region, is verified experimentally, and the contact efficiency in the transition zone and in the dilute phase is obtained. The contact efficiency was approximated by T~ = 1 -0.75(c,/~,d~)O.~. The temperature rise in the dilute phase is measured in the small reactor. The transition zone between the dense and dilute phases is almost isothermal, but it is found that temperature increases in the dilute phase. Toei et al., 1972). Some of the models originate from basic studies on the behavior of bubbles inside the bed, and these are referred to as physical bubble models by Rowe (1972) who compared them with arbitrary two-phase models. A comparison of these models shows that the main differences between these models are related to whether or not some fraction of the catalyst is in direct contact with the bubble gas, the extent of axial mixing in each phase, and the axial change in bubble size. SHINTARO FURUSAKI TATSUJIRecently, Miyauchi (1974 a, b) proposed the concept of successive contact, taking account of catalyst particles suspended above the dense bed. This effect is important because of the good contact in the suspending zone (called the dilute phase). According to this theory, the reaction proceeds first in the dense phase in poor contact with the catalyst, then in the dilute phase in good contact. According to the theory, Miyauchi and Furusaki (1974) calculated conversions using the HHU or the contact efficiency. Experimental data previously obtained (Lewis et al., 1959;Van Swaay and Zuiderweg, 1972) were compared successfully with the calculation. The importance of the catalyst suspended in the dilute phase in controlling the selectivity was also discussed. This paper presents experimental verification of the successive contact by the hydrogenation of ethylene on MS-Ni catalyst. This proof is essential in pursuing the analysis of fluid-bed contactors and is examined in detail. If the efficiency in the dilute phase is much higher than that in the dense phase as shown above, control of the reactivity in the dilute phase by the use of fines is considered useful in determining the optimal operation of fluid-bed contactors. This seems one of the reasons of utilizing fine particles in a fluid bed. This point is briefly discussed. CONCLUSIONS AND SIGNIFICANCEIn studying the operation of a fluid-bed reactor by the concept of the successive contact, it is important to study the axial distribution of reactivity inside the bed. This is done by moving the axial position of the nozzle, through which one of the reactants, CzH4, is introduced into the fluid bed. By this method, the reactivity in the dilute phase is proved large, especially for the case of large reaction rates. The transition zone between the dense and dilute phases is found to be quite effective. The effective reactivity in t...

Mass transfer coefficients and amounts of direct‐contact‐catalyst in fluidized catalyst beds

“…The LGG plot gives the value of kebab and the fraction of directcontact-catalyst. The effect of the bed diameter on these parameters is discussed and compared with previous experimental results (Lewis et al, 1959;van Swaaij and Zuiderweg, 1972;Furusaki et al, 1976;Miyauchi et al, 1980;Nozaki et al, 1984).…”

“…Miyauchi (1974a) has noticed that the effect of the catalyst particles in the freeboard is significant in comparison with the overall reactivity of the bed. Furusaki et al (1976) and Miyauchi et al (1980) gave experimental results on the change of reactivity in the longitudinal direction including the effect of the freeboard. By examining their results it was found that besides the mass transfer coefficient the fraction of direct-contact-catalyst was important in controlling the reaction in fluid beds.…”

Modeling of the chemical-looping combustion of methane using a Cu-based oxygen-carrier

“…This phenomenon was taken into account by the use of a contact efficiency parameter,  g-s , between gas and solids in the freeboard, calculated by the equation proposed by Furusaki [19] 0.4…”

The influence of the freeboard region in a fluidized bed catalytic cracking regenerator

“…Recent experimental work (Chavarie and Grace 1975, Furusaki et al 1976, Ford et al 1977, Pereira and Beer 1978 shows the need to consider regions other than the bubbling bed in modeling fluidized bed reactors. Behie and Kehoe (1973) modeled the grid jet entry region at the bottom of fluidized beds.…”