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Rice fissuring during the drying process may decrease the head rice yield after milling. To better understand the rice fissure formation, a 3D body fitted mathematical model was developed based on ...

During drying, hydrodynamics of fluidized beds can vary due to moisture evaporation. It is of practical importance to quantify the fluidized bed hydrodynamics by analysis of pressure fluctuations, especially when drying cohesive materials. In this study, spent liquor from a fermentation process for the production of yeast was mixed with corn bran at different mass ratios, and used as the fluidizing material of various stickiness levels. Local bed pressure fluctuations and the dryer exhaust air temperature as well as relative humidity were monitored over the course of drying. The pressure fluctuation data were analyzed using statistical methods. The bed hydrodynamic behavior was interpreted in terms of the time-averaged bed-pressure drop and its standard deviation. The transition from channeling to uniform fluidization occurs when both the average pressure drop and the standard deviation vary little with time. Also, the average values of the bed-pressure drop within short periods in reference to the ideal ...

To utilize the spent liquor from yeast fermentation, sorption drying in a thin static layer was proposed in which the corn bran serving as a solid carrier adsorbs the viscid liquor, and wet granules are then dried in a fixed bed by the hot air stream. A parametric study was conducted to investigate the effects of weight ratio, drying air temperature, air velocity, and layer thickness on the drying kinetics. Experimental results show that a low critical moisture content exists in the drying process, so the majority of moisture was removed during the constant drying rate period. Drying air temperature and layer thickness were two important parameters governing the drying process. In addition to expected effects from convective drying of capillary-porous materials, it was found that the conditioning period during which the spent liquor–bran mixture is left for conditioning markedly improves the drying rate. The possible mechanisms leading to this phenomenon were put forward.

Wet beneficiation of minerals necessarily requires removal of large amounts of water—typically contaminated—before further processing of the concentrated ores can be carried out. Often such concentrates are transported over large instances by ground or sea transport. For economic reasons dewatering/drying are essential unit operations. Often the capacity requirements of the mining operations are very large, the product processed has low unit value, and the material is abrasive. The selection of dryers is often arbitrary. No clear guidelines can be found by noting current practices in different countries. This article provides a global view of the types of dewatering equipment and dryers currently used in the mineral processing industries, provides guidelines for selection of drying systems, and recommends emerging innovative technologies, such as superheated steam and pulse combustion drying for future applications in this industry. A few case studies are examined.

The bubbling flow in a 2D pulsed fluidized bed is simulated using a developed Eulerian-Eulerian two-fluid modeling approach. Parametric studies are carried on for pulsed inflow of the gas phase with rectangular and sawtooth patterns where three pulsating frequencies of 0.4, 4, and 40 Hz are used. The flow instabilities are observed to develop in the pulsed fluidized bed and the mechanisms leading to the instabilities are discussed. The formation, coalescence, split-up of air bubbles, and their trailing wakes inside the bed are described and discussed in detail. Bubble rising velocity and size are obtained and analyzed. Bed expansion and fluctuation ratio are calculated to evaluate the pulsed fluidization quality. Numerical results improve the understanding of the pulsed fluidization.

The hydrocyclone is a mechanical separation device that is used widely in mineral processing. The solid particles in mineral slurries are separated according to their density, size, and shape by the centrifugal force generated by an induced vortex motion in a cylinder-on-cone vessel. The larger and denser particles move closer to the wall region due to their greater inertia and descend by gravity; a higher concentration suspension is thus collected at the bottom of the hydrocyclone. The cleaned liquid and hydrodynamically smaller particles exit through an overflow outlet at the top of the hydrocyclone. Higher velocities, within limit, generally yield higher collection efficiency. However, higher stream velocities cause severe erosion of the internal wall of hydrocyclones as mineral slurries generally are abrasive. The objective of this study is to use the computational fluid dynamic (CFD) technique to model the turbulent swirling flow and predict regions of significant wear and how they are influenced by ...

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simula...

Spray drying of a concentrated common salt (NaCl) solution carried out in the intense oscillating high-temperature turbulent flow field generated in the tailpipe of a pulse combustor was simulated. Simulation of such transport process problems is especially crucial since the environmental conditions are too hostile for detailed and reliable measurements. The momentum, heat, and mass transfer processes between the gas and droplet phases during drying were simulated using a computational fluid dynamic solver. The simulated profiles of flow field, temperature, and humidity of gaseous phase, and particle trajectories in a drying chamber are presented and discussed. The effects of gas temperature, pulse frequency and amplitude, and gas mass flow rate on the transient flow patterns, droplet trajectories, and overall dryer performance were investigated. Different turbulence models were also tested. Simulation results show that the flow field and droplet drying conditions vary widely during a single pulsating per...

Spray drying of NaCl solution was carried out under an intense oscillating flow field generated by a pulse combustor. A pulse combustion spray drying system was constructed. An optical analyzer was used to measure the particle diameter distribution of droplets atomized by a pulsating flow. The momentum, heat and mass transfer in both gaseous and particulate phases during spray drying inside the drying chamber were simulated using the computational fluid dynamics method. The simulated profiles of flow field, temperature and humidity of the gaseous phase, as well as the particulate phase, in the drying chamber were presented. The simulation showed changes of the flow field and particle trajectories in the drying chamber during one pulsating period. A large-scale vortex was observed in the upper part of the drying chamber because of the unstable state of flow field and particle trajectories. Short drying time and large evaporation rate are characteristics of pulsating spray drying. The influence of ...

The Chinese Drying Conference (CDC) series is hosted by China Drying Technology Division under The Chemical Engineering Committee of the Chemical Industry and Engineering Society of China (CIESC). ...