Staged fluid beds

The HF is fed into the bottom stage of a three-stage fluid bed reactor and Al(OH)2 is fed to the top stage where it is converted to activated alurnina at 300—400°C. In the middle stage, rising HF gas contacts downcorning alurnina and forms A1F. 

Fig. 15. A two-stage fluid bed dryer (a) gas and material temperature profiles (b) bed arrangements.

Tampella Corporation is commercializing the U-GAS process, which was developed by the Institute of Gas Technology. Tampella has constructed a 10-MW, integrated U-GAS-combined cycle power plant in Finland that uses coal, peat, and wood wastes as feedstocks. U-GAS incorporates a single-stage, fluid-bed gasifier in which coal reacts with steam and air at 950 to 1090°C at pressures... 

Several investigations have been made on the flow characteristics in multistaged fluid beds. Nishinaka et al. (N6, N8, N9) have measured the average bubble holdup, the lateral distribution of bubble holdup, and the longitudinal dispersion of solid particles in four- and eight-stage fluid beds installed with various horizontal baffles. As shown in Fig. 25 the average bubble holdup (except for beds baffled with tube plates) is correlated by the equation of Nishinaka et al., (N8) ... 

Work on pretreatment by other investigators was discussed in an earlier report (2). One big advantage of the two-stage fluid bed system is that all the products from the pretreatment are sent to the gasifier, and none is wasted. In other methods the coal was pretreated separately with air or other gases, and the loss in coal may be as much as 20% essentially volatile matter. 

Unless a burn-up cell or second stage fluidized bed is provided, complete conversion can not be achieved in one stage fluid bed. 

Fig. 24. Elements of a bubbleless turbulent fluid-bed reactor design where the internals create four stages. A represents the shrouded grid B, the first feed ...

A urea melt is suppHed to a one-stage reactor containing a fluid-bed catalyst. The reactor is heated internally by circulating molten salt. Upon entering the reactor, the urea is converted to melamine by the hot catalyst. 

Fig. 21. Iadirect-heat, two-stage, back mixed, and plug flow fluid-bed dryer.

Figure 28. Operating stages of a dense-phase fluid bed.

Fluid Iron Ore Reduction (FIOR) is a process for reducing ore to iron with a reducing gas in a fluid bed. For thermodynamic efficiency, iron ore reduction requires counter current flow of ore and reducing gas. This is achieved in FIOR in a multiple bed reactor. Precautions are necessary to prevent significant back mixing of solids between beds, since this would destroy counter current staging. 

A slurry bed reactor is in a pilot stage investigation. This type is characterized by having the catalyst in the form of a slurry. The feed gas mixture is bubbled through the catalyst suspension. Temperature control is easier than the other two reactor types. An added advantage to slurry-bed reactor is that it can accept a synthesis gas with a lower H2/CO ratio than either the fixed-bed or the fluid-bed reactors. 

Since it was known that theophylline monohydrate can be thermally dehydrated to form either the stable Form I or the metastable Form I, the effect of different drying methods on the phase composition was studied [89], Using either a multichamber microscale fluid bed dryer or the hot stage of a variable-temperature XRPD diffractometer, Form I was produced when the drying was conducted at 40-50°C. Drying at 60°C in the VT-XRPD unit yielded only Form I, while mixtures of products were produced in the microscale fluid bed dryer even at temperatures as high as 90 °C. 

See also Fluidized-bed entries Fluid-bed direct oxidation process, 10 656 Fluid-bed dryers, 9 122-123, 130-131 two-stage, 9 125 Fluid-bed roasters, 16 141 Fluid catalytic cracking (FCC), 11 678-699, 700-734 18 651, 653 20 777 24 257, 271. See also FCC entries Fluidized-bed catalytic cracking (FCC) clean fuels production and, 11 686-689 defined, 11 700... 

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