Solid Feed Rate Research Articles

Studies on segregation of binary mixture of solids in a continuous fast fluidized bed

Experimental investigations on the continuous fast fluidized bed were extended for size segregation of binary mixture of solids in the column with air as the separation medium [1]. The feed is either jetsam-rich or flotsam-rich binary mixture of particles of different size, but same density. The variables tested were superficial gas velocity, solids feed rate and feed characteristics. At steady state, there exists physical equilibrium between the evolved flotsam and the residual jetsam when the granular solids are in fluid-like state as in the case of density segregation of solids [1]. Using the analogy of the binary liquid mixtures separation by distillation, the phase diagram was constructed from the experimental observations. The effect of solids feed rate, feed composition, particle size ratio and particle size on equilibrium distribution of the flotsam and jetsam were presented.

Investigation of the bed types and particle residence time in a staged fluidised bed

Perforated plates were added to section the column and a fluidised bed was modified as a counter-current staged fluidised bed. The bed types and particle residence time were investigated in single-stage and two-stage fluidised bed systems. A stable bed (column I.D. = 3 cm, plate opening ratio = 0.2) exists at: 0.55 m/s ≦ gas velocity ≦ 1.70 m/s; 0.05 kg/s m 2 ≦ solids feeding rate ≦ 1.50 kg/s m 2. The bed types in the single-stage bed system and in the two-stage bed system can be different even at the same operating conditions and the differences are due to the different particle accumulating probabilities above the plate. In the particle residence time experiments, the mean residence time increases with the increase of the gas velocity and/or the solids feeding rate. The addition of one plate to the single-stage bed system increases 40% of the mean particle residence time. The one-parameter and two-parameter Continuous Stirred Tank Reactor (CSTR) models were used to predict the particle residence time in both systems. The results indicated that both models could quantitatively predict the particle residence time in the current staged fluidised bed systems.

A physical description of solids transport in flighted rotary dryers

In this paper, a solids transport model for flighted rotary dryers is presented. Emphasis is placed on combining statistical and mechanistic modelling efforts to create a physically motivated compartment model involving pairs of perfectly mixed tank reactors linked in a series arrangement. Here, each tank pair, or cell, aims to physically describe a finite slice of a case study industrial rotary sugar dryer, and is hence governed primarily by flight geometry and dryer operational variables such as rotational speed and dryer inclination. Solids flow paths are structured to properly represent the different modes of transport in the rotary dryer, and values of transport coefficients are based on calculated rates of rotational and axial flows. A solids dispersion variable is used to correlate the model residence time distribution (RTD) prediction with available data from a tracer study conducted during industrial operation of a full-scale raw sugar dryer. RTD results from the model show intuitive responses to variations in solids feed rate, rotational speed and drum inclination.

Design and Modeling of Plug Flow Fluid Bed Dryers

Plug flow fluid bed dryers (PFFBD) have been used for drying of particulate solids such as salts, ion exchange resins, grains, and a variety of other products. The present article describes the use of a mathematical model for the scale-up of lab-scale batch fluidization data to design an industrial-scale PFFBD. Axial dispersion theory was used in conjunction with the tanks-in-series model to describe the non-ideal flow. The model was implemented in Matlab 6.5 and it can be used for easily fluidizing particulate materials. The proposed model is capable of analyzing both the exponential falling rate and constant rate drying periods. The model predicts the required dryer dimensions for a given throughput and desired final moisture content. The model can also be used to study the effect of different process parameters such as solids feed rate, inlet air velocity, and temperature on the required dryer dimensions and it can also be used to predict the moisture and temperature profiles along the length of the PFFBD.

Studies on Gas-Solid Heat Transfer in Cyclone Heat Exchanger

Abstract Cyclones can be used for heating solid particles where the direct contact with the gas is permitted. Since cyclones have potential applications as heat exchangers in fertilizer, polymer powder, pharmaceutical and other industries, study of cyclone as heat exchanger is deemed important. Experiments on air-solid heat transfer were carried out in a cyclone heat exchanger of 100mm inside diameter, using sand. The effects of solid feed rate (0.5-7.5g∕s), cyclone inlet air velocity (9-22m∕s), and four average particle sizes (163-460μm) on the heat transfer rate, exit solid temperature, and heat transfer coefficient have been studied. An empirical correlation has been proposed for the prediction of heat transfer coefficients based on the present experimental data. The proposed correlation predicts the heat transfer coefficients with an error of +10%to−15% for the present data and within an error of +25%to−15% for the data of other investigators.

Modeling of an industrial wet grinding operation using data-driven techniques

The data-driven modeling techniques have been applied to the industrial grinding operation of a lead–zinc ore beneficiation plant to predict the output variables, the key performance indicators (KPIs) for the circuit. Many grinding plants are not adequately equipped with measuring instruments that are used only to measure some of the output parameters leading to a major hindrance towards modeling the operation through the route of first principles. To add to this, for controlling the grinding operation, system identification of the process is a must and poses a critical problem in advanced control as the grinding process behavior is highly non-linear. This necessitates applying some advanced data-driven techniques that are capable of predicting the KPIs within some acceptable limits. A total of six important KPIs considered here are throughput, three size fractions (+150 μm, +63 μm, −38 μm), percentage solids and recirculation load. These KPIs are predicted using three manipulated variables, namely, solid ore feed rate, two water feed rates to two sumps. To capture the nonparametric model for these KPIs, the data-driven techniques used here are several versions of neural networks and wavelets. While using neural network topologies, feed-forward neural networks (FNN) and recurrent neural networks (RNN) are utilized whereas for wavelet-based networks, wavelet frames are used. A well-validated hybrid model, a combination of physical and empirical methodologies, is used to approximate the actual behavior of the plant. A set of data, generated from this hybrid model is used for training the above-mentioned networks whereas another exclusive set of data is used to validate the evolved data-driven models. Merits and demerits of each of these techniques are also presented. Implementation of these techniques based on analysis to the actual plant may influence implementation of control and optimization technologies and thereby enhancing the plant performance tremendously where lack of hardware sensors does not allow them to be a right candidate to take part in systematic exercises for plant performance improvement.

Solids deposition in low-velocity slug flow pneumatic conveying

Solids deposition in the horizontal pipeline of a pneumatic conveying system was studied both mathematically and experimentally. Mathematically modelled results using the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach have demonstrated an intensive exchange of particles between the stationary layer (deposited particles) and the moving slug and a variation of solids concentration and pressure and velocity distributions across the slug. Slug flows were also visualised experimentally through a glass section and analysed by a high-speed video camera. The amount of particle deposition in the pipeline after a conveying was calculated by controlling the solids feeding rate using a rotary valve and by monitoring the solids flow out of the system using dynamic load cells. Experimentally generated data have quantitatively shown a tendency of more solids deposition with lower gas mass flow rate in slug flows except that, below a certain amount of solids mass flow rate, the deposition becomes independent of gas flow rate.

Image Analysis to Obtain the Vibration Amplitude and the Residence Time Distribution of a Vibro-Fluidized Dryer

The determination of the vibration amplitude and the residence time distribution on a vibro-fluidized dryer was carried out using the pulse method. Measuring the dryer displacement through image analysis, the vibration amplitude was determined and the vibro-fluidized bed was classified as a vibrated fluidized bed. The material used was ground eggshell, and tracers were ground eggshell dyed with black ink spray. The mass fraction of the tracer particles in each sample was calculated using image analysis. Two digital photographs were taken for each sample. On each photo, a grey level was specified. As the tracer has a greater percentage of grey level, compared to the non-marked sample, it was possible to count the amount of marked material using the image histogram. The influence of the residence time distribution was studied by varying the amplitude intensity, the solid feed rate and the air flow. It was inferred that the residence time increases as vibration amplitude decreases. Regarding the solid feed rate and the air flow, it was observed that the residence time increases with increase in the solid flow for low values of solid flow and air flow, and decreases with increase in the solid flow for high air flow. An addition of 0.06 m 3 s −1 in the air flow causes a 2.4-fold increase in the residence time.

Solid–liquid transport in a modified co-rotating twin-screw extruder—dynamic simulator and experimental validations

This work presents a dynamic transport model of a solid–liquid media through a twin-screw extruder (TSE). The application under consideration is the solid–liquid extraction of solute from raw plant substrate. Dynamic experiments are performed and compared with the simulated results for step functions on the solid feed rate and on the screw rotating speed. Despite some imperfections, results allow to validate the simulator.

The formation of a suspension bed on dual flow distributors

The formation of suspension beds on a dual flow distributor was studied using mono-sized particles (group D, Geldart, 1973). Three stages are experienced during the formation of a suspension bed: the induced, the growing and the final stage. The discharge mechanisms are raining, weeping, dumping (I) and dumping (II). The operating variables of a suspension bed are the opening ratio of the distributor ( m), the solids feeding rate ( F), the normalised air velocity through the hole ( U o/ U t, where U t is the terminal velocity of a single sphere in the air), the ratio of the diameter of the hole of the perforated plate to the size of the particle ( d o/ d p), and the density of the particles ( ρ p). Their influences on the formation of a suspension bed were examined. Five different types of beds were formed depending on the combination of the operating variables; these can be catagorised as dilute beds, oscillating shallow beds, bubbling beds, slugging beds and flooding beds. The ranges for stable operating conditions using 2-mm polystyrene spheres are mapped, which have the following ranges: 0.31≤ m≤0.52; 0.082 kg/s·m 2≤ F≤0.455 kg/s·m 2 and 0.8≤ U o/ U t≤1.25. A model was developed to simulate the growth of the bed in terms of the net pressure drop across the bed. There is a good qualitative agreement between the experimental pressure drop and model predictions.

Software for the design and simulation of gravity thickeners

Based on the steady state and the transient solutions of the phenomenological theory of sedimentation, a software was developed for the design and simulation of batch and continuous thickening. The paper presents a brief description of the phenomenological theory of sedimentation and its application to batch and continuous thickening with two appropriate initial and boundary conditions. The software permits the simulation of batch sedimentation and the design and simulation of continuous thickeners. For batch thickening, the initial and critical concentration and the height of the initial suspension have to be entered together with the parameters of the flux density function and the effective solid stress. The output is a settling plot showing as many lines of constant concentration as requested and a plot of the concentration profile for several times. For continuous thickening, the program calculates the unit area and the area of a thickener required to treat a given feed rate. The input is the solid feed rate and the required underflow concentration, together with the thickening parameters. One example shows the application.

Drying characteristics of millet in a continuous multistage fluidized bed

The effects of gas velocity, inlet gas temperature and the solid feed rate on the drying efficiency, the outlet solid moisture content, bed temperature in each stage, the outlet gas humidity and temperature in a rectangular acryl multistage fluidized bed (0.172 m×0.192 m×1.5 m-high) with a downcomer (0.04 m-I.D.) were investigated. The experiments were performed by using 1.9 mm millet particles. The final moisture contents of the solids increased with increasing the solid feed rate. The drying efficiency increased with increasing the wetted solid feed rate but decreased with increasing the inlet gas temperature. The drying performance of the multistage fluidized bed was compared with the single-stage fluidized bed and found to be superior under identical operation conditions. The model predicted values were well matched with the experimental data in the multistage fluidized bed dryer.

Process engineering evaluation of the CrossFlow Separator

Hindered-bed separators are often used in the minerals processing industry to classify particles according to size and density. A new technology, known as the Eriez CrossFlow, was recently developed to overcome some of the limitations associated with hydraulic separators. The innovative feature of this unit is a novel feed presentation system that improves separation efficiency and capacity. In the present work, a detailed process engineering evaluation was conducted to determine the basis for the improved performance of this unit. The evaluation included controlled separation tests using well-characterized feeds, particle and liquid tracer experiments and mathematical modeling studies. Data obtained from this work show that the new separator is capable of maintaining good separation efficiencies at higher solid feed rates than traditional designs due to improved hydrodynamics in the separation zone. This paper reviews the operating principle of the Eriez CrossFlow separator, discusses the results of the tracer experiments and modeling studies and presents test data obtained from recent laboratory and plant trials.

Predicting transport velocities

The minimum transport velocity is defined as the minimum gas velocity required for the vertical, dilute phase transport of particles. Literature data for this characteristic gas velocity are correlated in terms of particle properties. Then, it is shown that the same type of correlation holds for transport velocities governing transition toward fast fluidization. The similarity of these equations suggests that coarse particles can be carried over only in the fast fluidization regime. On the contrary, in a limited range of gas velocities, finer solids can be transported with different flow regimes, depending upon solids feed rate to the column. In that case, the solids feed rate governs transition to fast fluidization.

Prediction of Screw Length Required for Polymer Melting and Melting Characteristics

Abstract The previous study on the dynamic processing characteristics of co-rotating twin-screw extruder based on a visible technique (which employed a “transparent” extruder) performed by the authors Wong et al. [1 and 2] had enabled a quantitative treatment to be carried out in the present paper on the melting behaviour of polymer during an extrusion process. The qualitative analysis performed previously [1] had led to the development of a melting model which was capable of revealing some of the fundamental melting behaviour. The model also enabled the determination of the length of screw required for completing melting (Zr). Melting characteristics in terms of effects of solid feeding rate, temperature, screw speed and channel depth on the predicted Zr were discussed to further our understanding on melting performance of polymer melt in intermeshing corotating twin-screw extruder.

Heat transfer in a draft tube spouted bed with bottom solids feed

Detailed temperature measurements were obtained for a draft tube spouted bed of 2.6-mm glass beads with bottom solids feed at different air flow rates, air inlet temperatures, solids feed rates and bed heights. The temperature profiles showed that air temperature drops significantly with the axial position in the spout, while air and solids temperatures are uniform in the annulus. The drop in air temperature along the spout decreases with increasing air flow rate and increases with solids feed rate. A model was adapted for use with the spouted bed configuration studied here and its predictions were compared with the experimental data. In general, the model could accurately predict the temperature profiles in the bed, since the largest deviations were observed for the air temperature in the spout and were always less than 5%. Although the model provided for a low deviation in predictions, air temperature in the spout was systematically over-estimated.

Carrying capacity in a pilot flotation column

Concentrate flow rates were measured for the flotation of −100-mesh Lower Kittaning coal in a computer-controlled 0.076 x 3.5-m pilot flotation column. The variables studied were recovery zone height, airflow and solid feed rates. The specific projected surface areas of the feed, concentrate and tailing streams were determined from the measured particle size distributions. The results obtained show that the concentrate flow rate was independent of recovery zone height but was dependent on the hydrostatic pressure setting (measure of froth depth), gas flow rate, solid loading and particle size. New correlations for column carrying capacity and yield arc provided as a function of bubble surface area flux and the specific particle projected surface area.

Fluidized-bed incineration of solid pellets: Combustion and co-combustion

The UIC experimental facility for combustion of materials in a fluidized-bed combustor is described. The combustion and co-combustion studies made in a heated inert bed, of wood, refuse-derived fuel, peanut-hull, paper, cellulose and cardboard pellets are reviewed and discussed. Coal and propane are used as auxiliary fuels. The investigations cover a range of gas velocities, combustion temperatures, fractional excess air values and solid pellet feed rates. The emission of carbon monoxide in the flue gas is monitored, and for most conditions, its value is well within the limit set by the Illinois Environmental Protection Agency. The carbon combustion efficiency values are found to be quite high, 99.8 + percent, validating the thermal degradation capability of the fluidized-bed incinerator. Further, the thermal combustion efficiencies are also equally high, which reinforces the concept of waste to energy generation.

Application of centrifugal washing for fine-coal cleaning

Froth flotation is now the most commonly used method for cleaning fine-coal fractions in coal-preparation plants. Past research and industrial practice have demonstrated that froth flotation achieves excellent separation efficiencies for fine coals having only a small fraction of middling particles. However, the efficiency of froth flotation decreases sharply as the concentration of middling particles increases. This is due to the flotation of high-ash particles that have a small amount of hydrophobic coal present at the surface. Because gravity-based processes are much more efficient for the treatment of middlings, the application of centrifugal washing for fine-coal cleaning was studied with an emphasis on the primary cleaning of fine-circuit feed. Results are shown of a parametric study that used a semibatch Falcon centrifugal concentrator. The results of the study revealed that separation performance is a function of particle size, bowl geometry, feed solids content and feed rate.

Fine Coal Cleaning by Spiral and Water Washing Cyclone

The performance of three different types of spirals and a 200 mm diameter water washing cyclone have been assessed in open-circuit on-site testwork at the Norwich Park preparation plant on nominally 500 µ x 75 µm sized coal. The study is part of a program investigating alternative methods to heavy media cyclones and froth flotation for removing ash from fine coal from Central Queensland mines in the nominally 3 mm x 75 µm size range. The two spirals specifically developed for treating fine coal showed better cleaning efficiencies than the water washing cyclone on the +75 µm size fraction in the feed (essentially 1 mm top size). Their single start capacity was about half that of the water washing cyclone for the same clean coal ash content. The spirals readily produced a high ash reject (> 81%) in a single stage and, with the appropriate splitter configuration, a small middlings suitable for retreatment. Middlings splitter setting and vortex finder position (for the water washing cyclone) both provided reasonable control of clean ash at intermediate solids feed rates. For the spirals there was a strong correlation between solids feed rate and both clean coal ash content and yield at constant middlings splitter setting. For small cuts to middlings, separation efficiency remained relatively constant over the full range of feed rates. Relative density partition data indicated that less size classification took place in the spirals although the efficiency of both processes decreased sharply below about 125 µm. For a given clean coal ash the capacity and/or recovery of the spirals and water washing cyclone depended on tshe proportion of -75 µm high ash slimes in the feed.