Commercial fluid bed

Figure 2.2.1 shows the simplified sketch of the reactor used for the microactivity test. As can be seen, a fluid-bed catalyst is tested in a fixed bed reactor in the laboratory to predict its performance in a commercial fluid bed reactor. This can be done only because enormous empirical experience exists that has accumulated throughout several decades in several hundreds of reactors both in production and in laboratories. The standard states ... 

Economic considerations dictate that a commercial fluid bed operates at as high a gas velocity as practicable. A frequent limiting factor is entrainment from the bed which is a very strong ftmction of gas velocity. A well defined fluid bed can be maintained even at gas velocities well in excess of the free fall velocity of the biggest particles... 

Engineers at Mobil Oil Corporation are satisfied that a one-dimensional analysis is suitable for treating reaction kinetics in these beds, simply using an appropriate Peclet number to represent the effective axial gas diffusivity (Avidan, 1982 Krambeck et al, 1987). Inputs for Mobil s analysis are two (1) the Peclet number expected for a commercial fluid bed in question—they estimate this to be 7 for beds they contemplate for carrying out Mobil s methanol-to-gasoline or methanol-to-olefin reactions—and (2) kinetic data from a pilot fluid bed, which can be expected to reflect, reasonably well, whatever top-to-bottom mixing of powder will occur in the commercial bed. 

Molybdate-Based Catalysts. The first catalyst commercialized by SOHIO for the propylene ammoxidation process was bismuth phosphomolybdate, Bi9PMoi2052, supported on silica (9). The catalytically active and selective component of the catalyst is bismuth molybdate. In commercial fluid-bed operation, the bismuth molybdate catalyst is supported on silica to provide hardness and attrition resistance in the fluidizing environment. Bismuth molybdate catalysts can be prepared by a coprecipitation procedure using aqueous solutions of bismuth nitrate and ammonium molybdate (10). The catal3ret is produced by drying the precipitate and heat treating the dried particles to crystallize the bismuth molybdate phase. Heat treatment temperature for bismuth molybdate catalysts is generally arovmd 500°C. 

Now let us turn to the point mentioned imder item 2 above the interpretation of cyclone pressure drop measurements. Interpreting the measured pressure in the inlet of cyclones is not a problem the static pressure is fairly uniform over the cross section, and can be measured with a pressure tapping in the wall. In fact, in many commercial fluid-bed cyclone installations, the inlet static pressure is, for all practical purposes, simply that existing in the relatively low-velocity, dilute-phase region of the vessel containing the cyclone(s). Interpreting the pressure measured in the outlet of cyclones, however, is made difficult by any swirl still present at the point of the pressure tapping ... 

Funk furthermore reported that the tight turn inward and downward might also contribute to separation (i.e., improve separation performance). On the other hand, the writers are aware of at least two separate commercial fluid bed primary cyclone installations that have experienced serious erosive wear at the location of the white dots shown in Fig. 12.1.4 and which have exhibited rather poor separation performance. In both cases the height of the vortex finder below the roof line, i.e., its penetration, was substantially less than the height of the inlet chute, allowing particles that were deflected inwards to short-circuit the cyclone. Obviously, this is an area deserving of further investigation. 

More recently, Sasol commercialized a new type of fluidized-bed reactor and was also operating a higher pressure commercial fixed-bed reactor (38). In 1989, a commercial scale fixed fluid-bed reactor was commissioned having a capacity similar to existing commercial reactors at Sasol One (39). This effort is aimed at expanded production of higher value chemicals, in particular waxes (qv) and linear olefins. 

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... 

The catalyst is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process used commercially and employs a static bed of catalyst in several reactors, which allows a continuous flow of feedstock to be maintained. The cycle of operations consists of (/) the flow of feedstock through the catalyst bed (2) the discontinuance of feedstock flow and removal of coke from the catalyst by burning and (J) the insertion of the reactor back on-stream. The moving-bed process uses a reaction vessel, in which cracking takes place, and a kiln, in which the spent catalyst is regenerated and catalyst movement between the vessels is provided by various means. 

Hot air, steam, and hot water vulcanisation is widely used in the latex industry, and fluid-bed heat transfer and electronic microwave curing has also been used. Cross-linking by electron radiation has been experimentally used, but has not yet been developed commercially. 

Polyethers such as monensin, lasalocid, salinomycin, and narasin are sold in many countries in crystalline or highly purified forms for incorporation into feeds or sustained-release bolus devices (see Controlled-RELEASE technology). There are also mycelial or biomass products, especially in the United States. The mycelial products are generally prepared by separation of the mycelium and then drying by azeotropic evaporation, fluid-bed driers, continuous tray driers, flash driers, and other types of commercial driers (163). In countries allowing biomass products, crystalline polyethers may be added to increase the potency of the product. 

Although a number of low temperature processes have been studied, only a few have been used commercially. These have been limited in the types of coal that are acceptable, and the by-products are less valuable than those obtained from high temperature processing. The Disco process is used in the United States to supply a limited amount of fuel to meet requirements of smoke ordinances. The British CoaUte and Rexco processes produced substantial amounts of domestic smokeless fuel. Development of fluid-bed methods of carbonizing finer coal at ca 400°C has been studied in the United Kingdom. A reactive char is briquetted without a binder to produce a premium open-fire smokeless fuel. 

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%. 

Several important applications of fluid beds exist outside the petroleum industry. Fluid bed roasting of pyritic ores is widely used in the metallurgical industry. Calcination of lime is a commercial process. There are also fluidization processes for various nuclear processing steps. 

Physical models of commercial fluidized bed equipment provide an important source of design information for process development. A physical model of a commercial fluidized bed processor provides a small-scale simulation of the fluid dynamics of a commercial process. While commercial processes will typically operate at conditions making direct observation of bed fluid dynamics difficult (high temperature, high pressure, corrosive... 

It is likely that future commercialization of Methanol-to-Olefins (MTO) will take place in a fluid-bed reactor for many of the same reasons which encouraged fluid-bed MTG development, including better temperature control and constant product composition. The olefins produced by this process can be readily converted to gasoline, distillate and/or aviation fuels by commercially available technologies such as Mobil s MOGD process. 

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