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The Impacts of Biomass Pretreatment Methods on Bio-oil Production
Published in Jaya Shankar Tumuluru, Biomass Preprocessing and Pretreatments for Production of Biofuels, 2018
Air classification is a mechanical approach to roughly separate particles with air flow. It has accomplished the separation of particles below 100 to 300 microns which sieving cannot effectively complete (Voshell, 2015). After air classification, the particles with different size and density are separated into the fine product and coarse product, respectively, collected from the top/side and bottom outlets of air classifier. Particle size, shape, and density are the main physical properties, impacting the separation effect. However, for uniformed materials, individual particles have similar density that avoids the influence of density on separation. When the density of the particle is approximating the same, size, and shape are the main factors influencing the classification result. It was reported that the possibility of flaky particle to be collected as the fine product is more than spherical particle because of different drag coefficient (Johansson and Evertssonn, 2014).
Solid—Fluid Systems
Published in Enrique Ortega-Rivas, Unit Operations of Particulate Solids, 2016
Air classification is a method of separating powdery, granular, or fibrous materials in accordance with the settling velocity and combined with the influence of particle size, particle density, and particle shape. The procedure of winnowing or aspiration is a traditional way of separating chaff from grain after threshing and is one of the simplest forms of air classification. Ideally, the separation effect of an air classifier should be such that all particles that exceed the cut point are transported into the coarse fraction and the smaller particles are transported to the fines fraction. In this sense, air classification basically consists of dividing particle size distributions of given powders and, as such, is a technique commonly used in combination with size reduction equipment, normally to eliminate fines that may affect properties like wettability and dispersibility. The major interest in air classification is that it provides a means for separating small particles, in a dry manner, which cannot be readily achieved by sieving, that is, below 50 μm. Ortega-Rivas and Svarovsky (2000) report a successful sharp split of the particle size distribution of calcium carbonate, into a fine fraction with mean particle size as fine as 6 μm.
Introduction to Ceramic Fabrication Approaches Including Powder Processing
Published in David W. Richerson, William E. Lee, Modern Ceramic Engineering, 2018
David W. Richerson, William E. Lee
Air classification is frequently linked directly to milling, crushing, grinding, or other comminution equipment in a closed circuit. Particles from the mill are discharged directly into the air classifier. The fines are separated, and the coarse is returned to the mill for further grinding. One type of unit combines size reduction and classification into a single piece of equipment. The coarse powder particles are carried by high-velocity air through two opposing nozzles. Where the two air streams meet, particles strike each other and are shattered into smaller particles. The air carrying the particles flows vertically. Large particles pass through a centrifugal-type air classifier at the top of the unit, where additional controlled sizing is accomplished.
Particle Classification Optimization of a Circulating Air Classifier
Published in Mineral Processing and Extractive Metallurgy Review, 2019
C. Eswaraiah, Rahul K. Soni, Sunil Kumar Tripathy, L.O. Filippov
The schematic representation of a circulating air classifier used in this study is shown in Figure 2. The height and diameter of the classifier considered were 0.95 m and 0.51 m, respectively. The advantage of a circulating air classifier is that it does not require external air from a compressor or blower to suspend the particles, as an internal fan itself induces the desired air flow. The solid feed enters the classifier via a vibratory feeder and falls on a rotating disc, where it is radially discharged toward the wall with the help of rotating guide vanes. The guide vanes in the classifer had few fixed angular positions out of which 13, 39, and 65° were chosen for the experiment where lower and higher values indicate vane orientation in tangential and radial direction, respectively. The coarse particles settle along the surface of the upper inner cone, where gravity causes them to flow downwards within the inner cone. The coarse particles are then thrown against the wall due to their high centrifugal force and simultaneously fall against the entering air stream and get collected at the air inlet section. Due to the drag force, fine particles are carried along with the airflow into the annular region of the classifier and get collected at the air outlet section. However, the detailed experimental procedure and other internal details of a circulating air classifier can be found elsewhere (Eswaraiah et al. 2008).