Particulate matter agglomeration

Concentrations of particulate matter and S02, accordingly, are the highest in cities with extremely high population densities, low technical standards and an excessive use of two wheelers, as is the case for Asian agglomerations. The worst conditions are observed in Delhi, Beijing, Tehran and Mumbai. But Western European cities also... 

Various dry powder attributes are assessed at release and on stability. These include physieal eharaeteristies sueh as appearance, content uniformity, delivered dose uniformity, and partiele size distribution. Chemieal attributes that may be assessed include drug eontent, purity, and identity, as well as the water content. Dry powders may also undergo mieroseopie evaluation for foreign particulate matter, unusual agglomeration, and partiele size. Mierobial limits should also be examined, including the total aerobie, yeast, and mold eounts. The presence of specific pathogens should be ruled out. The dry powders may be dissolved to test for pH. 

Abstract Recent estimates delivered by the European Environment Agency indicate that exposure to atmospheric particulate matter (PM) causes approximately three million deaths per year in the world. Exceedances of PM thresholds have been reported by the majority of the European Union member countries, mainly in urban agglomerations where human exposure is also higher. 

Emissions from biomass-fueled boilers can be controlled by a variety of methods. The control systems needed depend mainly on the composition of the feedstock. First, good combustion control is essential to maximize combustion and to minimize emissions of unburned hydrocarbons and carbon monoxide. Efficient removal of particulate matter in the flue gases can be achieved by various combinations of cyclonic separation, electrostatic precipitation, agglomeration, and filtration. Removal of acid gas emissions can be achieved by flue gas scrubbing and treatment with lime. There are several approaches to the control of NO, emissions (Clearwater and Hill, 1991). Combustion control techniques include use of staged combustion, low excess... 

From Latin gra i//a=grain, particle. Any kind of relatively coarse particulate matter. In size enlargement, synonymous with agglomeration in a size range of approximately 0.1-10 mm. Also sometimes used for other sizes, larger or smaller (typical in industry). 

Agglomeration by extrusion of plastic material or of particulate matter containing binders through bores of dies in pelleting machines . 

In addition to these four typical binding mechanisms (Figure 14a to d), whereby bonding occurs at the coordination points, three other models exist. Form-closed bonds (e) are only possible if the particulate matter is shaped such that, somehow, it can interlock and capillary forces (f) can only become effective in a disperse system which is filled with a liquid that forms concave menisci at the pore ends. In the third case, particles forming the agglomerate are embedded in a matrix of binder the model can also be depicted by Figure 14(f) where the dark areas represent the binder matrix. 

Pressure agglomeration methods which use sometimes very high forces to consolidate the particulate matter can be applied for larger feed sizes. 

The type of movement required for mixing particulate matter also produces ideal conditions for agglomeration by coalescence. Therefore, unwanted agglomeration is often observed in powder mixers, especially if the particle size of the solids is small and/or a small amount of moisture is present. Considerable problems can arise if components of the bulk mass have different particle sizes because, in that case, the smaller fractions may selectively agglomerate, thus making it impossible to obtain an ideal mixture. Such selective agglomeration is of particular concern in the pharmaceutical industry where an extremely small amount of a finely divided active substance must often be mixed uniformly and reliably with a relatively large amount of inert filler material. 

As a result of the mechanical action of mixing tools, turbulent or high intensity mixers do create fast moving, aerated, particulate matter systems. Therefore, interparticle collision and coalescence take place in a very similar fashion to that in suspended solids agglomerators. The main difference between the two methods is that in mixers particle movement is caused by mechanical forces while in suspended solids agglomerators drag forces induced by a flow of gas are the principal reason for movement of the bed of particulate matter, coalescence of particles, and agglomeration. 

The most versatile methods of pressure agglomeration use high forces (Figure 179) to compact particulate matter into tablets and briquettes of specific size and shape or compacts. 

Particulate matter Since pressure agglomeration between counter-currently rotating rollers deals with particulate matter, results of this theory are only applicable in a general way. If smooth rollers are used, a very close correlation can be obtained. Today, however, roller surfaces for agglomeration are in most cases equipped with some sort of a profile in order to improve the bite on the material which is a never-ending problem because of the noncontinuity of particulate matter. In the case of surface profiliations zones (2) and (3) cannot freely develop due to interlocking between the material and roller surface. This is most pronounced for briquetting. 

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