Utility agglomerates from

All the discussion so far is on the particle separation in a gas fluidized bed based on velocities very close to the minimum fluidization velocity of the jetsam. Particle separation can also be accomplished by employing velocities close to that of the terminal velocity of the particles. The U-Gas coal gasification process developed by the Institute of Gas Technology utilized the principle of terminal velocity for separating ash agglomerates from char in the coal gasifier. A comprehensive study on this subject using a fluidized bed similar to that of the U-Gas process has been published by Leppin and Sahay (1980). Some experiments were also carried out by Chen and Keairns (1978). 

Figure 9.4 Agglomerates from the Utility-Gas (U-Gas) test facility in Des Plaines, Illinois (a) small grains, (b) large grains.

Spray Drying and Agglomeration. Most instant coffee products are spray-dried. Stainless steel towers with a concurrent flow of hot ak and atomized extract droplets are utilized for this purpose. Atomization, through pressure nozzles, is controUed based on selection of the nozzles, properties of the extract, pressures used, bulk density, and capacity requkements. Low inlet ak temperatures (200—280°C) are preferred for best flavor quaHty. The spray towers must be provided with adequate dust coUection systems such as cyclones or bag filters. The dried particles are coUected from the conical bottom of the spray drier through a rotary valve and conveyed to bulk storage bins or packaging lines. Processors may screen the dry product to... 

For a zeohtic catalyst where Pt, Pd or other transition metal might be present to provide metal activity, STEM can be used to determine whether the metal is agglomerated and to what extent, whether the metal is in the zeolite or present on the geometric exterior or whether the metal is associated with the zeolite or binder. As an example of the utility of the technique. Figure 4.15 shows the growth of Pt clusters for fresh and spent faujasite zeolite catalyst. After time under reaction conditions, the Pt clusters have grown from Inm to 2nm. The clusters have remained in the channels of the faujasite. Pt agglomeration can be concluded as the deactivation mechanism. 

More complicated expressions than those above can be used in the 0-D models, but these usually stem from a more complicated analysis. For example, the equation used by Ticianelli and co-workers comes from analysis of the catalyst layer as a flooded agglomerate. In the same fashion, eq 21 can be embedded and used to describe the polarization behavior within a much more complicated model. For example, the models of Springer et al. " and Weber and Newman " use a similar expression to eq 21, but they use a complicated 1-D model to determine the parameters such as ium and R. Another example is the model of Newman,who uses eq 22 and takes into account reactant-gas depletion down the gas channels by, in essence, having a limiting current density that depends on the hydrogen utilization. All of these types of models, which use a single equation to describe the polarization behavior within a more complicated model, are discussed in the context of the more complicated model. 

According to the different exchange current densities, i0, for hydrogen oxidation and hydrogen evolution on Ni and Pt, the catalytic activity of platinum is by a factor of several hundred to a thousand higher than that of nickel. Therefore, if the utilization of Raney-nickel particles below 10 jum size approaches 100%, it is clear that Pt-activated porous soot particles must be by a factor of from 10 to 30 smaller than Raney-nickel particles to achieve full utilization, that is, vanishing fuel starvation of the catalyst. This happens to be the case with soot agglomerates that are by their very nature of correct size (dv < 0.1 /im) (150, 151). 

Depending on the microorganism, various types of cereal substrates were employed during SSF experiments. Spent malt grains (SMG) were added to some substrates and served as an internal support. Substrates without SMG in most cases led to agglomeration of substrate particles and created a more compact mass, which in turn interfered with microbial respiration and negatively affected substrate utilization. The presence of SMG improved the bioconversion of linoleic acid from substrates to GLA (Certik et al, 2006). Substrates with internal support not only provided better respiration and... 

---