Fluidization Of Cohesive Particles Research Articles

Fluidization of Swelling Particles at Elevated Temperatures

Semicrystalline polymer (e.g., polyethylene and polypropylene) particles may swell in solvent at elevated temperatures, inducing flow instability in operation, reactor blockage, and undesired product. Understanding the fluidization behavior of swelling particles at elevated temperatures is therefore of great significance. This work conducts an experimental study on the fluidization of polyethylene particles in an elevated-temperature liquid–solid fluidized bed. With the increase in temperature, particle swelling develops over two phases, i.e., non-cohesive swelling and cohesive swelling, which is different from the fluidization of cohesive particles in gas–solid systems. Four regimes can be identified through static bed height and pressure drop measurements, i.e., stable fluidization, noncohesive-swelling fluidization, cohesive-swelling fluidization, and full defluidization. A phase diagram was then obtained to demarcate these regimes. Furthermore, an energy balance model was proposed to predict the initial agglomerating temperature Tag of swelling particles for early warning of abnormal fluidization in practical operation.

On the fluidization of cohesive powders: Differences and similarities between micro‐ and nano‐sized particle gas–solid fluidization

AbstractThe fluidization of cohesive powders has been extensively researched over the years. When looking at literature on the fluidization of cohesive particles, one will often find papers concerned with only micro‐ or only nano‐sized powders. It is, however, unclear whether they should be treated differently at all. In this paper, we look at differences and similarities between cohesive powders across the size range of several nanometres to 10s of micrometres. Classification of fluidization behaviour based on particle size was found to be troublesome since cohesive powders form agglomerates and using the properties of these agglomerates introduces new problems. When looking at inter‐particle forces, it is found that van der Waals forces dominate across the entire size range that is considered. Furthermore, when looking into agglomeration and modelling thereof, it was found that there is a fundamental difference between the size ranges in the way they agglomerate. Where the transition between the types of agglomeration is located is, however, unknown. Finally, how models are made and agglomerate sizes are measured is currently insufficient to accurately predict or measure their sizes consistently.

Effects of pulsating air flow in fluid bed agglomeration of starch particles

Fluid bed agglomeration is commonly used to improve the instant properties and flowability of cohesive food powders. However, fluidization of cohesive particles is characterized by cracks and channeling, but air pulsation systems can be attached to the fluid bed in order to improve bed homogeneity. The aim of this study was to investigate the influence of air pulsation frequencies, at (0, 5, 10 and 15) Hz, in fluid bed agglomeration of cassava starch and cornstarch particles. The particles size increased with agglomeration, resulting in the decreasing of wetting time and higher flowability. The solving of Population Balance Equations achieved the experimental aggregation kernel constants. The pulsation of (5 and 10) Hz resulted in the higher agglomeration rates, for both cassava and cornstarch study, respectively. The evaluation of the experimental PBE kernel constants were useful to measure the aggregation rate and to compare the performance of a fluid bed granulator.

Effects of adding different size particles on fluidization of cohesive particles

The fluidization of SiC cohesive particles of different sizes shows that (1) the fluidized characteristics is greatly affected by the size of particles, and the smaller the size of particles, the bigger the interparticle force, the worse the fluidized behavior; (2) SiC of average size larger than 10 μm can be fluidized by increasing gas velocity, but SiC (5 μm) cannot be fluidized. Particle agglomeration number Ae, which can be used to describe the fluidized behavior of particles is proposed based on interaction between the agglomerate body and the outer-most particles cohered. The calculation of particle agglomeration number Ae shows that cohesive particles can be fluidized if particle agglomeration number Ae≤40 000. SiC5 may be fluidized with the method of adding particles, and optimum additive amount can be calculated by particle agglomeration number Ae.