Spray fluidized bed processes

Significant improvements over the PPG process involve reaction of lime with concentrated HOCl (50%) and drying of the resultant slurry in a spray grainer or fluidized-bed spray dryer to produce hydrated product with av CI2 as high as 82% (126,127,129,210,211). 

Almost all PVC powder coatings are appHed by the fluidized-bed coating process. Although some electrostatic spray-grade formulations are available, they are very erratic in their appHcation characteristics. The resistivity of plasticized PVC powders is low compared to other powder coating materials and the appHed powder quickly loses its electrostatic charge. For the same reason, PVC powders show poor appHcation characteristics in an electrostatic fluidized bed and are seldom used in this process. 

One of the advanced concepts for capturing CO2 is an absorption process that utilizes dry regenerable sorbents. Pure sodium bicarbonate from Dongyang Chemical Company and spray-dried sorbents were used to examine the characteristics of CO2 reaction in a flue gas environment. The chemical characteristics were investigated in a fast fluidized reactor of 0.025 m i.d., and the effects of several variables on sorbent activity, including gas velocity (1.5 to 3.5 m/s), temperature (40 to 70 °C), and solid concentration (15 to 25 kg/m /s)], were examined in a fast fluidized-bed. Spray-dried Sorb NX30 showed fast kinetics in the fluidized reactor. 

Scale Up of Process. The scale up of fluidized bed coating processes has received little attention in the literature. Current practices in the pharmaceutical industry are reviewed by Mehta (1988). The basic approach described by Mehta (1988) is to scale the airflow and liquid spray rates based on the cross-sectional area for gas flow. This seems reasonable except for the fact that in the scaling of the equipment, the height of the bed increases with increasing batch size. For this reason, a time scale factor is also required. 

SCALE-UP OF THE CONVENTIONAL FLUIDIZED BED SPRAY GRANULATION PROCESS... 

Table 3 Major and Minor Process Variables to Be Considered in Fluidized Bed Spray Granulation...

Jones DM. Effect of process air dew point on a top-spray fluidized bed-coating process. Presented in Session 265 Coating in the pharmaceutical industry. Proceedings of AIChE Annual Meeting, 1998. 

Figure 12.17. Fluidized bed and spouted bed granulators, (a) A batch fluidized bed granulator used in the pharmaceutical industry performance data in Table 12.19(a). (b) Part of a fluidized bed incineration process for paper mill waste recovering sodium sulfate pellets performance data in Table 12.19(b). (c) A three-stage fluidized bed granulator for more complete control of process conditions and more nearly uniform size distribution, (d) Two modes of injection of spray to spouted beds, into the body on the left and at the top on the right performance data in Table 12.19(c).

Table 4.4 summarizes the main important parameters for the fluidized bed granulation process and their impact. Granule properties can be affected by several parameters. Granule size, for example, can be affected by starting material properties, atomization, spray liquid properties, and attrition. It is very important to take a comprehensive review of all the process parameters for process development. 

By use of this technique, it is possible to prepare fine spherical catalyst particles in the 10-100/rm diameter range, as arc required for typical fluidized-bed catalytic processes. In this technique used for large-scale catalyst manufacture, the feed is generally dilute hydrogel or sol that is sprayed from the top of a tower while hot air is blown in a cocurrcnt or countercurrent direction to dry the droplets before they reach the bottom of the tower. The fine droplets arc produced or atomized by pumping the hydrogel or sol under pressure cither... 

Panda, R.C. Zank, J. Martin, H. Modelling the droplet deposition behaviour on a single particle in fluidized bed spray granulation process. Powder Technol. 2001, 115, 51-57. 

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