Agglomeration processes wetting

Mechanistic Understanding of the Wet Agglomeration Process and the Power Consumption Profile... 

Some Hints Concerning the Wet Agglomeration Process in a High-Shear Mixer to Avoid Problems... 

The agglomeration process is a dynamic process where a droplet is created by a two-fluid nozzle, and deposited on the randomly fluidized particle. The binder solvent evaporates, leaving behind the binder. Before all of the solvent is evaporated, other randomized particles form bonds on the wet site. This process is repeated numerous times to produce desired agglomerated product. There are number of process variables that control the agglomeration. Process variables most important to consider are listed as follows ... 

Drying a wet product in a fluid bed is a separate topic, but during the granulation process it becomes an integral part of the process, hence understanding fluid bed drying is important before we review the agglomeration process. 

A simple example of immiscible liquid wetting is the addition of oil to a fine coal suspension to agglomerate and remove the carbon constituents while the inorganic impurities (ash constituents) remain in suspension and are rejected. A number of such coal cleaning processes, such as the Trent Process [3], the Convertol Process [4] and the Spherical Agglomeration Process [5], have been developed and used in this century. As discussed below, developments of the latter process have shown that many other applications are possible for immiscible liquid wetting. 

With particles that are formed by an agglomeration process, there is internal surface area which can be wet by the solvent. A simplified case of internal porosity is that of a horizontal capillary where gravity can be neglected. The rate of penetration of a liquid into the tube, dl dt, is given by the Washburn equation [14] ... 

Pelletized granular resins can be obtained by agglomeration of fine-cut resins. The agglomeration process increases the powder flow and apparent density. The goal of this process is to make the small PTFE particles adhere together. Essentially, there are two processes of agglomeration namely, dry and wet techniques [24]. 

Wet agglomerates are very often bonded by a combination of the above two mechanisms. In that case partial volumes exist which are completely filled with the liquid while in others liquid bridges prevail. Technically it is almost impossible to attain 100 % saturation because there is a high probability that during the agglomeration process air is trapped in some pores. 

The technique that lends itself best to small-scale evaluation is low pressure agglomeration (Chapter 5, Fig. 5.10, and Section 6.2.2), which may be followed by spheroni-zation. Since in this method of pressure agglomeration a wet mixture is passed through the openings of a screen or a thin perforated sheet, very little pressure is exerted and it is essentially a shaping process [B.97]. Therefore, even if tests are performed on a small perforated die, in regard to product characteristics, the results are also representative for larger units. 

Because, in most cases, binder added for growth agglomeration is liquid, the discharge from equipment in which size enlargement occurs is moist (green) and only temporarily bonded by the effects of surface tension and capillary forces. With few exceptions (e.g., pan and some fluid bed agglomerators) a wide size distribution is obtained which, without removal of over- and under-sized material, is not acceptable as product. Since separation techniques that do not blind when processing wet solids. 

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