Pressure agglomeration

Therefore, it was the author s intent to cover—for the first time in a textbook on agglomeration—the fundamentals in considerable detail and to introduce the multitude of agglomeration techniques as well as applications that have been developed during the past 100 years and, more specifically, during the most recent four to five decades. In Chapter 4 (Industrial Size Enlargement Equipment and Processes) as well as Chapter 5 ([Some Selected] Industrial Applications of Agglomeration) pressure agglomeration and, explicitly, roller presses have been covered in particular detail because of the author s past and present involvement as an expert in this area. 

In contrast to tumbling agglomeration where no external forces are applied, in pressure agglomeration pressure forces act on a confined mass of particulate solids, which is then shaped and densified (Engelleitner, 1994). Pressure... 

Conventional granulation processes can be classified as agitation methods (tumbling agglomeration and mixer agglomeration), pressure methods (compaction, extrusion, and rolling), thermal methods (sintering), spray and... 

Then tire pressure is reduced to transfonn tire frozen liquid to a vapour and to remove it. Freeze drying is commonly used to make powders tliat are not agglomerated. 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

H. H. Hausner, "Compacting and Sintering of Metal Powder Without the Apphcation of Pressure," International Symposium Agglomeration, Apr. 12-14,1961. 

When the void space in an agglomerate is completely filled with a Hquid (Fig. Ic), the capillary state of wetting is reached, and the tensile strength of the wet particle matrix arises from the pressure deficiency in the Hquid network owing to the concave Hquid interfaces at the agglomerate surface. This pressure deficiency can be calculated from the Laplace equation for chcular capillaries to yield, for Hquids which completely wet the particles ... 

The success of the compaction operation depends pardy on the effective utilization and transmission of appHed forces and pardy on the physical properties and condition of the mixture being compressed. Friction at the die surface opposes the transmission of the appHed pressure in this region, results in unequal distribution of forces within the compact, and hence leads to density and strength maldistribution within the agglomerate (70). Lubricants, both external ones appHed to the mold surfaces and internal ones mixed with the powder, are often used to reduce undesirable friction effects (71). For strong compacts, external lubricants are preferable as they do not interfere with the optimum cohesion of clean particulate surfaces. Binder materials maybe used to improve strength and also to act as lubricants. 

Stressing by the Surrounding Medium. Size reduction is effected by shearing forces or pressure waves (Fig. 3f). The amount of energy that can be transferred is very limited and this method is used mainly to break agglomerates. 

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... 

Agglomerate porosity can be measured by gas adsorption or mercuiy porosimetiy. However, any breakage or compression of the granules under high pressure during porosimetiy can invahdate the results. 

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