Fluidized bed reactions

Fluidized-bed reaction systems are not normally shut down for changing catalyst. Fresh catalyst is periodically added to manage catalyst activity and particle size distribution. The ALMA process includes faciUties for adding back both catalyst fines and fresh catalyst to the reactor. 

The previous example was a rather unique application and not a typical case for fluidization. Although some fluidized bed reactions are executed at elevated pressure, like the naphtha reforming, most are used at atmospheric or at low pressures. The proceeding conceptual sketch. Figure 8.2.4, gives the most important features of a fluid-bed, cataljdic reactor. 

The fluidized bed reactions were carried out in a glass reactor (fig. 1) 2.5 cm diameter and 50 cm long. The reactor was heated in an oven in which the temperature could be controlled within 0.2 C. 

Reacting in the rotating flask under vacuum gave a progress of reaction similar to the synthesis in the fluidized bed. Reactions under vacuum also gave coloured products. 

A. Adris, J. Grace, C. Lim, S. Elnashaie, Fluidized Bed Reaction System for Steam/ Hydrocarbon Gas Reforming to Produce Hydrogen, US Patent 5,326,550, Date June 5, 1994... 

The principal reactors used are fluidized bed reactors, called Synthol reactors, in which the feed gas entrains an iron catalyst powder in a circulating flow. The suspension enters the bottom of the fluidized bed reaction section, where the Fischer-Tropsch and the gas shift reactions proceed at a temperature of from 315 to 330°C. These reactions are highly exothermic, as described previously, and the large quantity of heat released must be removed. The products in gaseous form together with the catalyst are taken off from the top of the reactor. By decreasing the gas velocity in another section, the catalyst settles out and is returned for reuse. The product gases are then condensed to the liquid products. 

Squires, A. M. Role of solid mixing in fluidized-bed reaction kinetics, AlChE Symp. Ser. 69(127), 8-10 (1973). 

Kullavinajaya, P., "Statistical Study of the Benzene Oxidation Process in a Fluidized Bed Reaction", Ph.D. thesis, Ohio State University, Columbus, 1966. 

Owens, N. J. P. (1986). Estuarine nitrification — A namrally-occurring fluidized-bed reaction. Estuarine Coastal and Shelf Science 22, 31—44. 

Descriptive Behavior of the Kurui-Levenspiel Bubbling Bed Model Mass Transfer in Fluidized Beds Reaction in a Fluidized Bed... 

A.M. Adris, J.R. Grace, C.J. Lim and S.S.E.H. Elnashaie, Fluidized bed reaction system for steam/hydrocarbon gas reforming to produce hydrogen. U.S. Patent Appl. 07965011, Canad. Patent Appl. 2081170 (1992). 

Most chromium catalysts are used at lower temperatures in slurry- or fluidized-bed reactions. In these processes there is no lower bound on temperature, other than those imposed by the polymer MW, the catalyst activity, and the economics of heat removal. The upper temperature bound is set by the melting point of the polymer, or, more accurately, the softening point. 

FIGURE 236 Traces of 02 are sometimes added to a fluidized-bed reaction as a means of controlling the polymer melt index. 

The main drawback of kinetic models, based only on steady-state data, is associated with the fact, that start-up and transient regimes cannot be reliably modeled. Kinetic models for nonstationary conditions should be applied also for the processes in fluidized beds, reactions in riser (reactor) - regenerator units with catalyst circulation, as well as for various environmental applications of heterogeneous catalysis, when the composition of the treated gas changes continuously. 

Figure 25 Fluidized bed reaction without regeneration in pilot-scale experiments. Reaction conditions T—460-470 °C, catalyst inventory=1 kg, WHSV=2h water MeOH = 20 80, and superficial gas velocity=25 cm/s.

General Procedure for the Development of Fluidized Bed Reaction Processes... 

Reaction rate in the bubble phase in a fluidized bed Reaction rate in the cloud phase in a fluidized bed Reaction rate in the emulsion phase in a fluidized bed Rate of reaction ... 

The catalyst mixture is supported on alumina or silica and is either packed into a tubular reactor or used in a fluidized bed. Reaction conditions are 200-350°C and 0.2-1 MPa (2-10 atmospheres) and high yields of ethylene dichloride are obtained. The ethylene dichloride is then pyrolysed as described previously (and the hydrogen chloride produced is recycled). 

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