Fluidized-bed design

Fluidized-bed design procedures requite an understanding of particle properties. The most important properties for fluidization are particle size distribution, particle density, and sphericity. 

The optimum conditions needed to achieve the desired sulfur capture efficiency (90 percent) is dependent on sorbent type, coal type, and fluidized bed design. Representative conditions are a bed temperature of 1116 K, a sorbent particle of 1 mm, and a Ca/S ratio of about 3. The bed temperature selection is based on the admittedly shaky evidence that this is where the maximum sulfation peaks. The particle size selection is a compromise between a desire to use high gas velocities and the observed decrease in sulfation with increasing size (Figure 2). The Ca/S ratio corresponds to a maximum sulfation of about 0.3. For these conditions the mass feed rate of a limestone sorbent is 0.345 that of the coal feed and the flow rate of the partially sulfated spent sorbent is 0.285 the coal feed rate. 

An important alternative type of crystallizer is the fluidized bed. One fluidized bed design is shown in Fig. 6-6. As shown, the supersaturated solution enters at the bottom of the crystallizer and the clear, partly or fully depleted solution exits at the top of the crystallizer. The slurry is suspended in the crystallizer by the upward liquid flow, which usually lies in the... 

Fluidized bed designs have a number of advantages, including the capability for fines removal from the main crystallizer by elutriation (carrying out with the fluidizing hquid) and low shear mixing by fluidization without the need for mechanical agitation. 

Fluidized beds Fluidization of the bed can result in enhanced heat and mass transfer performance. Unfortunately, many fluidized bed designs tend to be voluminous, which reduces overall storage efficiency. 

Knowlton, T. M. (1997) Standpipes and non-mechanical valves, notes for the continuing education course Gas Fluidized Beds Design and Operation, Department of Chemical Engineering, Monash University. 

An even greater problem is the quantitative application of the population balance in the coarse grain crystallizers of DTB and fluidized bed design, which due to the cyclical behavior described above are almost impossible to describe with the MSCPR (mixed suspension classified product removal) and CSCPR (classified suspension classified product removal) approaches. 

In reality, particles spend vastly different amounts of time in the bed, depending very much on the locations of feed and withdrawal nozzles, on flow and mixing patterns in the bed, and on many other factors. The particles residence time is an even more important consideration in fluidized bed design. 

Methane is undesirable in most synthesis gas applications. The HTW demonstration plant was also designed specifically for reactive brown coal. Therefore, carbon conversion was not a problem, and the gasifier was a bubbling fluidized-bed design. 

Physical deactivation Demanding reaction, 20 Design of reactor. See Fixed-bed Fluidized-bed design Multiphase reactors Differential reactor, 72 Diffusion... 

Chen JC, Grace JR, Golriz MR Heat transfer in fluidized beds design methods. Powder Technol 150 123-132, 2005. 

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