Particle Cycle Time Research Articles

Solid-fluid mixing behavior of conical spouted beds with internal devices

The effect of draft tubes and fountain confiner on the gas and solids mixing behavior is studied in conical spouted beds. Accordingly, the bed porosity has been determined in different hydrodynamic regimes of 1.1,1.25 and 1.5u/ums, with beds equipped with draft tubes of 0%,56% and 100% opening ratio. These devices significantly affect the gas residence time and particle cycle time distributions, which are further improved by using a fountain confiner, specially when high inlet gas flow rates are desired. The addition of this device was found to remove stagnant gas pockets over the annular zone, while reducing the particle cycle time by 15% with the OSDT configuration at 1.5u/ums. This reduction heavily depends on the distance between the bed surface and the fountain confiner. By including draft tubes, the expected particle cycle time can be more than doubled due to the reduced annular-spot solids circulation. Therefore, it was found that a combination of internal devices and operating flow rate present a promising strategy to control the gas flow pattern, while keeping the distribution of particles cycle times required for each application.

Multiple‐Output Artificial Neural Network to Estimate Solid Cycle Times in Conical Spouted Beds

AbstractKnowledge of cycle times is essential to design spouted beds. Although experiments for determining cycle times are time‐consuming, there is hardly any mechanistic or empirical model for their prediction. Two types of artificial neural networks, namely, single‐ and multiple‐output ones, have been developed to estimate particle cycle times in conical spouted beds. They provide satisfactory cycle time predictions under different configurations. A comparison of single‐output neural networks with multiple‐output ones proves that, although the former fit slightly better the experimental data, the latter provide a reasonable prediction of all cycle times, and therefore, only one neural network is sufficient for their prediction. The maximum cycle is the one of highest sensitivity to all the parameters analyzed.

Computational Fluid Dynamics Evaluation of the Influence of Cone Geometry on Solids Circulation in Spouted Beds

The influence of cone angle on solids circulation was investigated using a computational fluid dynamics (CFD) Euler–Euler multiphase model. The solids mass flow rate in the spout and the average particle cycle time were used to evaluate the solids circulation rate for seven cone angles with different loads of solids. A factorial design was applied to evaluate the effects of cone angle, solids load, and inlet air velocity on particle circulation. The proposed CFD method for measurement of the particle cycle time showed good agreement with experimental data reported in the literature and could be applied to investigate solids circulation for other particles and spouted bed geometries The solids load had the greatest effect on the particle cycle time, followed by the cone angle. Simulation results showed that lower cone angles favored solids circulation in spouted beds and could be used to improve the drying of sorghum in the equipment.

Evaluation of pellet cycle times in a Wurster chamber using a photoluminescence method

Particle cycle time variation in a fluid bed coater is an important parameter that affects inter-particle coating uniformity. For the purpose of analyzing the pellet circulation process, a tracer particle photoluminescence detection system was developed and used in a laboratory scale fluid bed Wurster chamber. In order to tackle the problem of optically dense flow within the Wurster tube, transitions of a photoluminescent pellet were recorded in the down-flow region. Tracer pellets were representative for evaluated populations of pellets in terms of size and density. Pellet cycle time distributions were assessed for processes with varying particle size, gap, fluidizing air flow rate and loading mass. A higher air flow rate and gap decreased the distribution mode whereas a decrease in gap and an increase in the air flow rate and loading mass decreased the magnitude of pellet cycle time variation. Additionally, the variation in the position of tracer pellet successive passes was assessed and the change in transition azimuth was connected to stability of gas–solids flow. We also estimated that for the homogeneous spray case the average circulation process variability contribution to the total coating mass variability is relatively small.

Influence of contactor geometry and draft tube configuration on the cycle time distribution in sawdust conical spouted beds

A study has been carried out on the influence the draft-tube configuration has on the solid circulation in conical spouted beds made up of sawdust. Knowledge on the performance of these fine particles of low density and irregular texture is required for the pyrolysis, gasification or combustion of this waste materials in conical spouted beds. Accordingly, particle cycle times have been monitored for contactors of different geometry (angle and gas inlet diameter) provided with draft-tubes of different configuration (nonporous and open-sided tubes). The study has been carried out according to a factorial design of experiments. Particle cycle times follow an almost exponential distribution for both types of tubes and are highly dependent on the type of draft tube and contactor angle, especially in the range from 36° to 45°. On average, cycles times are twice to triple longer when nonporous tubes are used. Therefore, the open-sided internal device provides stability and ensures high turbulence to beds made up of fine and irregular particles, with their behaviour being similar to stable beds made up of coarse particles in which no draft-tube is required.

Particle Cycle Times in Draft Tube Conical Spouted Beds

A hydrodynamic study of conical spouted beds equipped with draft tube has been carried out for glass beads. Runs have been carried out in conical spouted beds of different geometry according to a factorial design of experiments. The purpose of this design has been to study the effect on particle cycle times and solid circulation rate of the following: the insertion of a draft tube, draft tube configuration, and the different factors of the contactor and particle system. Particle cycle times (average, maximum, and minimum) have been measured in draft tube conical spouted beds for different geometric factors of the contactor (angle and gas inlet diameter), draft tubes (diameter, height of the entrainment zone, and width of the faces) and under different operating conditions. It can be concluded that the hydrodynamics of conical spouted beds with draft tube is influenced by the geometric factors of the draft tube, contactor and operating conditions.

Particle Cycle Times and Solid Circulation Rates in Conical Spouted Beds with Draft Tubes of Different Configuration

Particle cycle times (average, maximum, and minimum) have been measured in draft tube conical spouted beds for different geometric factors of the contactor (angle and gas inlet diameter), draft tubes (diameter, height of the entrainment zone, and width of the faces) and under different operating conditions (particle density). On the basis of the results, the effects of the type of draft tube and different factors of the contactor/draft tube/particle system have been studied, and those of greater influence have been determined. The results show that particle cycle times and solid circulation rates are highly dependent on the type of draft tube, solid density, and contactor angle. Open-sided draft tubes are the ones with the highest solid circulation rate with stable spouting performance. Therefore, this internal device is a suitable option for scaling up spouted beds with a hydrodynamic performance similar to those without tubes.

Cycle time in draft tube conical spouted bed dryer for sludge from paper industry

De-watering of sludge wastes from pulp and paper industry has been studied using a conical spouted bed dryer. Influence of operating parameters such as the presence of a non-porous draft tube, the entrainment zone height, the draft tube diameter to gas inlet diameter ratio and waste moisture content on bed stability have been investigated for drying temperatures ranged from room temperature up to 140°C. In addition, cycle time distribution of particles was determined for different experimental conditions. The drying time to reach given moisture content of the material decreased with increasing both gas inlet diameter and temperature. Although the use of the draft tube slightly raised drying time, it enhanced the uniformity of bed moisture content of treated wastes. The minimum gas spouting velocity required to reach the stable spouted bed regime was found to increase with both higher stagnant bed height and moisture content. The operation with a draft tube narrowed the frequency distribution of particle cycle times, the more the smaller the height of entrainment zone. Moreover, at the same experimental conditions, cycle times were longer when working with the draft tube. Therefore, the conical spouted bed dryer with a non-porous draft tube has been proven to be an effective pre-treatment for handling of sludge wastes from paper industry.

The Prediction of Variability Occurring in Fluidized Bed Coating Equipment. I. The Measurement of Particle Circulation Rates in a Bottom-Spray Fluidized Bed Coater

The purpose of this work was to investigate the effect that changes in design and process variables had on the movement of particles around a fluidized bed coating apparatus. To measure the mean and variance of the particle cycle time distribution (CTD), the number of passages taken by a magnetic tracer particle through the spray zone was measured by a detector coil wound around the partition. The reproducibility of the measurement technique was tested by taking repeated measurements of the tracer particle movement, using similar bed operating conditions, and the method was found to give reproducible results. A series of experiments was carried out by varying operating conditions such as the partition gap, fluidizing air rate, and partition diameter and length, and measuring the change in the rate at which the tracer particle circulated in the coating device. The results of the experiments showed that, over the range of parameters tested in this work, the partition gap had the strongest influence on the rate of particle circulation. Moreover, for the 6-in.-diameter Wurster process used in the current work, the mean circulation time for the 1.1-mm-diameter Nu-Pareil particles was found to vary over the range of 2.2–10.4 sec. In addition, the mean and standard deviation of the CTD could be linearly correlated over a wide range of operating conditions, with a correlation coefficient of 0.80. Finally, an estimate of the variability in mass coating uniformity was made based on the results from the cycle time distributions. It was concluded that the effect of variability in the CTD could account for only a small fraction of the variability in the observed mass coating distribution.

Measurement of particle movement in a spouted bed using a new microprocessor based technique

AbstractA new experimental technique for measuring particle cycle times, times of occurrence of particles at different levels, and particle velocities in the spout of a spouted bed is described. A magnetized marker particle and search coil or coils are employed together with a microprocessor system for ease of data collection and processing. The magnetic particles have the same diameter, density and similar surface texture to bed particles to ensure proper representation.Data is presented on distributions of cycle time and particle velocity and implied particle mass circulation rates at different levels in a spouted bed. Comparisons are made with photographic and laser–doppler anemometry techniques.

Particle cycle times in a spouted bed of polydisperse particles

Particle cycle times in a spouted bed of polydisperse particles