Fluid-bed processes

The fluidized-bed system uses finely sized coal particles and the bed exhibits liquid-like characteristics when a gas flows upward through the bed. Gas flowing through the coal produces turbulent lifting and separation of particles and the result is an expanded bed having greater coal surface area to promote the chemical reaction, but such systems have only a limited ability to handle caking coals. 

Slagging fixed-bed (Grand Forks Energy Research Center) 

Fluid bed reactors became important to the petroleum industry with the development of fluid catalytic cracking (FCC) early in the Second World War. Today FCC is still widely used. The following section surveys the various fluid bed processes and examines the benefits of fluidization. The basic theories of fluidization phenomena are also reviewed. 

Fluid cat cracking required identifying stable operating regimes for beds of fine catalyst at high gas flow rates. Highly efficient cyclone and electrostatic systems had to be developed for catalyst recovery. Finally, the principles of pressure 

While there are hydroformers still operating, reforming today is generally carried out in fixed bed units using platinum catalysts, because of their superior product yield and distribution. Fluid platinum catalyst processes are not feasible because catalyst losses would be too great. 

Fluid coking is very insensitive to poor gas-solids contacting, but has one problem not faced by cat cracking or hydroforming. If the heavy residual oil is fed too fast to the reactor, the coke particles will become wetted and stick together in large unfluidizable lumps. Correct control of feed rate is necessary to prevent this bogging. 

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Process Technology Evolution. Maleic anhydride was first commercially produced in the early 1930s by the vapor-phase oxidation of benzene [71-43-2]. The use of benzene as a feedstock for the production of maleic anhydride was dominant in the world market well into the 1980s. Several processes have been used for the production of maleic anhydride from benzene with the most common one from Scientific Design. Small amounts of maleic acid are produced as a by-product in production of phthaHc anhydride [85-44-9]. This can be converted to either maleic anhydride or fumaric acid. Benzene, although easily oxidized to maleic anhydride with high selectivity, is an inherently inefficient feedstock since two excess carbon atoms are present in the raw material. Various compounds have been evaluated as raw material substitutes for benzene in production of maleic anhydride. Fixed- and fluid-bed processes for production of maleic anhydride from the butenes present in mixed streams have been practiced commercially. None of these... 

Carbonyl sulfide can be either a starting or intermediate material (108—110), or it can be used as a fluidizing gas in a carbon fluid-bed process (111). Making carbon disulfide from boiler flue gas by catalyticaHy reducing SO2 with CO to COS, and then converting COS to CS2 over an alumina catalyst has been proposed (112). 

Activated alumina and phosphoric acid on a suitable support have become the choices for an iadustrial process. Ziac oxide with alumina has also been claimed to be a good catalyst. The actual mechanism of dehydration is not known. In iadustrial production, the ethylene yield is 94 to 99% of the theoretical value depending on the processiag scheme. Traces of aldehyde, acids, higher hydrocarbons, and carbon oxides, as well as water, have to be removed. Fixed-bed processes developed at the beginning of this century have been commercialized in many countries, and small-scale industries are still in operation in Brazil and India. New fluid-bed processes have been developed to reduce the plant investment and operating costs (102,103). Commercially available processes include the Lummus processes (fixed and fluidized-bed processes), Halcon/Scientific Design process, NIKK/JGC process, and the Petrobras process. In all these processes, typical ethylene yield is between 94 and 99%. 

Drawing on analogies with this work, the breakage rates by wear and fragmentation By for fluid-bed processing shoiild be of the forms ... 

Fluid bed processes have been subject to many problems and uncertainties in development and scale up from bench-scale reactors. The fluidization behavior of each process seems different and very often does not meet expectations based on experience with earlier plants. With hindsight fluid cat cracking seems to be an ideal system from the point of view of easy operation and straightforward scale up. 

Ullmanns Encykl. Tech. Chem., 4. Aull., Vol. 20, 300. fluid bed process ... 

Jones, D. M., Factors to Consider in Fluid-Bed Processing, Pharm. Tech., 9 50-62(1985)... 

Mehta, A. M., Scale-Up Considerations in the Fluid-Bed Process for Controlled Release Products, Pharm. Tech., 12 46-52(1988)... 

Olsen, K. W., Batch Fluid-Bed Processing Equipment - A Design Overview Parti f Pharm. Tech., 13(l) 34-46 (1989a)... 

Figure 4 Defluorinated phosphate rock fluid bed process (from Ref. 8).

The 100 BPD MTG project was extended recently to demonstrate a related fluid bed process for selective conversion of methanol to light olefins (MTO). The products of the MTO reaction make an excellent feed to the commercially available Mobil Olefins to Gasoline and Distillate process (MOGD) which selectively converts olefins to premium transportation fuels ( 1). A schematic of the combined processes is shown in Figure 1. Total liquid fuels production is typically greater than 90 wt% of hydrocarbon in the feed. Distillate/gasoline product ratios from the plant can be adjusted over a wide range to meet seasonal demands. 

Kam, A. Y. and Lee, W. Final Report "Fluid Bed Process Studies on Selective Conversion of Methanol to High Octane Gasoline",... 

The scale-up from the laboratory equipment to production size units is dependent on equipment design which may or may not have been scalable as far as its dimensional feature or components selection is concerned. The importance of scalability is well understood and accepted by the manufacturers of fluid-bed processors. Various sizes in their product line are logically designated and manufactured. Airflow in the fluid-bed process is a critical parameter. The design and selection of the processor is very important for the laboratory and production unit. Because airflow is one of the components of the drying capacity of a fluid-bed system, ratio of air volume per kg or liter of the product is very critical to achieve scale-up that is linear. 

Gore et al. (130) studied the factors affecting the fluid-bed process during scale-up. The authors found that processing factors that most affected granule characteristics were process air temperature, height of the spray nozzle from the bed, rate of binder addition and the degree of atomization of the binder liquid. 

Rambali et al. (134) scaled-up fluid-bed process based on the relative droplet size and the powder bed moisture content at the end of the spraying cycle. They scaled-up from 5 to 30 kg and then to 120 kg. with a geometric mean granule size of 400 pm. 

Figure 26 (A) and (B) Product discharge from the fluid-bed processing bowl using lift device. Source Courtesy of Niro Pharma Systems.

Scale-up is normally identified with an incremental increase in batch size until a desired level of production is obtained. The fluid-bed process, similar to other granulation techniques, requires an understanding of the importance of characterization of the raw materials, especially of an active... 

Parikh DM. Airflow in batch fluid-bed processing. Pharm Technol 1991 15(3) 100-110. 

Jones DM. Factors to consider in fluid-bed processing. Pharm Technol 1985 9(4) 50. 

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