Continuous Drying of Slurry in a Jet Spouted Bed

ABSTRACT

he performance of a laboratory scale jet spouted bed (JSB) for drying rice flour slurry was studied. The bed consisted of ceramic balls (5028 mm diameter) and the rice flour slurry was sprayed onto the moving particle surface near the inlet part. All the experiments were carried out at the jet spouting regime. This regime has high bed void fraction and violent movement and collision of bed particles. As a result, the dried product layer is attrited from particle surface as a fine powder and entrained from the bed by the spouting air. The experimental result were presented to show the effects of static bed height, inlet air flow rate and temperature, and feed concentration and flow rate on the outlet air temperature, thernal efficiency, and mean particle size and moisture content of the product. Asimple mathematical model, which is based on the conservation of mass and energy equations, was developed. Predicted results agreed well with those obtained from the experiment.     

DRYING OF POWDERY MATERIALS IN A PULSED FLUID BED DRYER

ABSTRACT

Drying of recycled polypropylene powder was studied experimentally in a laboratory pulsed fluid bed dryer (PFB) with relocated air stream. It was proved that fluidization of fine particles having a large specific surface area and a broad size distribution is technically feasible when using the composite supporting grid. Drying and hydrodynamic characteristics for a pulsed fluid bed of fine particles are found to be similar to the ones for coarse particles. Equations for minimum pulsed fluidization velocity, pressure drop, and surface and volumetric heat transfer coefficients are given.     

Fluidized bed film coating of cohesive Geldart group C powders

The difficulty of coating cohesive Geldart group C powders in a conventional fluidized bed is attributed to strong inter-particle force between fine particles leading to poor fluidization behavior. Dry coating approach involving deposition of nanosize particles on the surface of group C powders is considered to reduce the interparticle force and improve the fluidization behavior of fine powders. Polymer film coating at an individual particle level is achieved on these pre-coated fine powders in a commercially available spouting fluidized bed (MiniGlatt). The effect of operating conditions such as inlet air temperature, polymer concentration, polymer weight ratio, water percentage in solvent and spray rate of coating solution on the quality of film coating are investigated. Experimental results demonstrate that the quality of film coating goes down as polymer concentration in coating solution goes higher, whereas the lower inlet air temperature is found to enhance polymer film generation and coating quality. It is also observed that the higher polymer weight ratio promotes agglomeration without affecting the coating quality to a great extent. An optimum water ratio in acetone-water solvent as well as spray rate can be optimized to achieve superior coating quality with acceptable agglomeration ratio.Graphical abstractDry coating approach involving deposition of nanosize particles on the surface of group C powders is considered to reduce the interparticle force and improve the fluidization behavior of fine powders. Polymer film coating at an individual particle level is achieved on these pre-coated fine powders in a commercially available spouting fluidized bed (MiniGlatt). The effect of operating conditions such as inlet air temperature, polymer concentration, polymer weight ratio, water percentage in solvent and spray rate of coating solution on the quality of film coating are investigated. Experimental results demonstrate that the quality of film coating goes down as polymer concentration in coating solution goes higher, whereas the lower inlet air temperature is found to enhance polymer film generation and coating quality.

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Figure: SEM images of Aluminum-1 particles coated to investigate the effect of polymer concentration. (a, b) Spray rate 2.11 ml/min, polymer concentration 4%, inlet air temperature 40 °C, polymer weight ratio 4% and water in solvent 0%; (c, d) spray rate 2.11 ml/min, polymer concentration 16%, inlet air temperature 40 °C, polymer weight ratio 4% and water in solvent 0%.     

Kinetics of Adsorption of Uranium from Seawater by Humic Acids

Abstract

The kinetics of the adsorption of uranium from seawater by humic acids fixed onto a polymer matrix was measured in a fluidized bed as a function of the grain size of the adsorbent and the flow velocity of the seawater. The adsorption rate was found to be governed by the diffusion of the uranium ions through the hydrodynamic surface layer of the adsorbent which is always formed in laminar flows of liquids. The measured rate constants are interpreted in terms of effective diffusion coefficients of 3.6 × 10^?5 cm²/s for uranyl ions and 1.8 × 10^?5 cm²/s for tricarbonatouranate ions in the surface layer. As a consequence of this kinetic behavior, the geometry of the adsorbent as well as the velocity of the water flow are relevant parameters for the amount of adsorbent needed for a projected extraction rate. This conclusion applies to all adsorption processes where diffusion through the hydrodynamic layer is the rate-determining kinetic step.     

SUBLIMATION OF PURE SUBSTANCES IN GAS FLUIDIZED BEDS AT ATMOSHPERIC PRESSURE.

This paper deals with the sublimation of large bodies, or “objects”, made up from a pure substance in a bubbling gas fluidized bed of considerably smaller particles, or “fines”. The influence of such parameters as the gas velocity, the bed temperature, the size and the adsorption capacity of the fines has been investigated.

The results obtained clearly show that the rate of sublimation in fluidized beds is far higher than in air alone. It increases with increasing bed temperature, decreasing particle size, increasing powder mass capacity, and roughly varies as a parabolic function of time. It has also been observed that the temperature difference between the bed and the object surface, or “temperature depression”, depends on the fines characteristics as well as on bed temperature, but is independent of gas velocity when good solid mixing conditions are achieved.

Bed-to-object heat and mass transfer coefficients have been deduced from data points and attempts have been made to provide a reasonable theory to account for them. After a complete examination, the idea of interpreting transport phenomena based on a well-adapted “surface renewal model” has been proposed.     

用于乙醇脱水的生物质吸附性能

The adsorption capability of paddy flour and maize flour for gaseous phase selective adsorption for ethanol dehydration was investigated via a bench-test fixed-bed adsorber at constant temperature. Ethanol concentration in the feed was 93.4% (mass) and each of the dried biomass was used as adsorbent, and breakthrough curves and temperature distribution in adsorptive bed were obtained for different bed depths,superficial velocities, granularities of adsorbent and temperatures. Bed pressure drop curves for different bed depths and superficial velocities were also measured. A product of ethanol purity of 99.5% (mass) could be obtained through both kinds of biomass adsorbent. When 99.5% (mass) of ethanol purity is defined as the breakthrough point, the production capacity for either adsorbent was within 0.0915-0.2256 (gram product/gram adsorbent). Tests on pure ethanol adsorption were also performed to extrapolate the selectivity of both adsorbents.     

Temperature-Swing Gas Separation with Electrothermal Desorption Step

Abstract

Results of an experimental investigation of a new method for heating adsorbent beds in the desorption step owing to Joule's heat generated inside the adsorbent particles by passing an electric current through them are presented. Desorption of a previously saturated bed and cyclic separation with the electric potential applied to a fibrous activated carbon bed was performed.     

INFLUENCE OF THE PARTICLE SIZE AND SUPERFICIAL GAS VELOCITY ON THE SUBLIMATION OF PURE SUBSTANCES IN FLUIDIZED BEDS OF DIFFERENT SIZES

Abstract

In the present study the sublimation of large solid carbon dioxide particles inside fluidized beds of fine particles is investigated. A model which takes the surface area of the sublimable particles into account is used to describe the sublimation kinetics. Based on this model, the results of different experiments, namely single particle experiments using a precision scale, batch experiments in a laboratory-scale fluidized bed and continuous experiments in a larger circulating fluidized bed are compared. The main focus of the study is to evaluate the influences of the particle size, of the inert bed material, of the bed temperature and of the superficial gas velocity, respectively.     

DRYING EXPERIMENTS WITH ALO(OH) SUSPENSION OF HIGH PURITY AND FINE PARTICULATE SIZE TO DESIGN AN INDUSTRIAL SCALE DRYER

ABSTRACT

AIO(OH) suspension of high purity and fine particle size was dried in a Mechanically Spouted Bed (MSB) dryer with inert particles. During drying the maximum required moisture content and the mean particle size of the dried product had to be taken into consideration. Also another important aspect was to avoid contamination of the dried solid with metals. PTFE cylinders of 8 mm in diameter and of 8 mm in height were used as inert particles, and also the whole dryer itself was coated with teflon. As a result of the drying experiments the optimum values of the process parameters were used for scaling-up. The specific rate of evaporation in the drying zone of the inert bed was the basis of the calculations. The suspension with capacity of 125 kg/h was successfully dried in the designed industrial scale MSB dryer with inert panicles and the required quality of the material was produced.     

Predicting the dynamics and performance of a polymer–clay based composite in a fixed bed system for the removal of lead (II) ion

A polymer–clay based composite adsorbent was prepared from locally obtained kaolinite clay and polyvinyl alcohol. The composite adsorbent was used to remove lead (II) ions from aqueous solution in a fixed bed mode. The increase in bed height and initial metal ion concentration increased the adsorption capacity of lead (II) and the volume of aqueous solution treated at 50% breakthrough. However, the adsorption capacity was reduced by almost 16.5% with the simultaneous presence of Ca²⁺/Pb²⁺ and Na⁺/Pb²⁺ in the aqueous solution. Regeneration of the adsorbent with 0.1 M of HCl also reduced its adsorption capacity to 75.1%. Adsorption of lead (II) ions onto the polymer–clay composite adsorbent in the presence of Na⁺ and Ca²⁺ electrolyte increased the rate of mass transfer, probably due to competition between cationic species in solution for adsorption sites. Regeneration further increased the rate of mass transfer as a result of reduced adsorption sites after the regeneration process. The length of the mass transfer zone was found to increase with increasing bed height but did not change with increasing the initial metal ion concentration. The models of Yoon–Nelson, Thomas, and Clark were found to give good fit to adsorption data. On the other hand, Bohart–Adams model was found to be a poor predictor for the column operation. The polymer–clay composite adsorbent has a good potential for the removal of lead (II) ions from highly polluted aqueous solutions.     

HEAT AND MASS TRANSFER DURING DRYING OF A LIQUID FILM FROM THE SURFACE OF A SINGLE INERT PARTICLE

ABSTRACT

This paper presents the results of theoretical and experimental studies on drying of aqueous suspensions of finely dispersed solids sprayed over the surface of an inert ceramic sphere. The effects of temperature and air velocity on kinetics of heat and mass transfer as well as peeling off the layer of a dry material from the sphere surface are described. The mathematical model of a drying process based on simplified ?gradientless? approach to transfer phenomena is proposed. The adequacy of the model developed for drying of the wet coat from a single sphere to the real drying process taking place in a bed of particulate carrier is confirmed by results of drying of several organic dyestuffs in an industrial spouted bed dryer with inert particles.     

Simulation of Drying on the Basis of Nonequilibrium Thermodynamics of Beterogeneous Multiphase Polydispersed Systems.Formation of the Morphological Structure of Emulsive Elastomers Using Method of Spray - Drying for Latexes

ABSTRACT

The process and the technology of fine - dispersed rubber powder production on the basts of spray - drying for latexes were considered. The practical recommendations on usage of physical modification method for elastomers on the basis of interaction mechanism between solid -phase dispersed filler and polymeric panicles were given.

The mathematical model for latex drops during drying in the presence of structured adsorptive layer of surface active substances on the surface of drops was worked out, that allowed us to give the recommendations for production of monolithic particles.     

Removal of Carbon Dioxide from Light Gas Mixtures using a Porous Strontium(II) Silicoaluminophosphate Fixed Bed: Closed Volume and Portable Applications

A Sr²⁺ -SAPO-34 bed was assembled to study CO₂ dynamic adsorption under conditions that emulate those found in closed volume and portable applications. Although the surface area was reduced by 7% during pelletization, adsorption capacities estimated from breakthrough curves compared well with static volumetric adsorption data. Modeling of the breakthrough adsorption was achieved using a Linear Driving Force mass transfer rate model, showing good agreement with the experimental data and confirming fast kinetics and efficient use of the bed. Fast kinetics were also evidenced by the length of the unused section of the bed as calculated from a Mass Transfer Zone model. Adsorption capacity degradation was not observed after multiple regeneration cycles. Apparent and equilibrium adsorption isotherm data estimated from the bed and static volumetric experiments at 25° C were compared to that of 5A Zeolite. These showed that Sr²⁺ -SAPO-34 is a superior adsorbent for CO₂ removal in the low partial pressure range (<1500 ppm). CO₂ and H₂ O multicomponent adsorption breakthrough curves were also gathered for a CO₂ inlet concentration of 1000 ppm and dew points of ?5 and 8° C. The addition of moisture resulted in a decrease in total processed gas volume by 31 and 47%, respectively.     

Efficient Cycle Recovery of Hydrogen from a Low Concentration Pyrolysis Gas Stream by Pressure Swing Adsorption – An Experimental Evaluation

Breakthrough curves, cycle mass balances, and cycle bed productivities (mg H₂ per gram of adsorbent) on three dual adsorbent amounts (g) of 2,892, 1,963, and 1,013 respectively each filling 200 cm, 135 cm, and 70 cm of a 5.0 cm internal diameter stainless steel pipe were performed. The approximate optimum (sludge pyrolysis) synthesis gas with composition in volume % of 45% H₂/35% CO/20% CH₄ was used as the feed gas with molecular sieve 5 Å and activated carbon as adsorbents. Impurity breakthroughs occurred at ～14.9, 12.3, and 5.0 minutes respectively for % cycle recoveries of 72.2, 65.0, and 60.2 using 2,892, 1,962, and 1,013 g of adsorbent respectively. Our results indicated that basing % recycle recovery on cycle bed productivity can enable efficient hydrogen recovery with savings on adsorbent amount. An optimum cycle bed productivity of 2.3 mg H₂/g of adsorbent corresponded to a cycle recovery of 66.2% for 2,300 g of adsorbent used. Only 1.7 mg H₂/g of adsorbent was obtained for a cycle recovery of 72.2% requiring up to 2,800 g of adsorbent. This makes economic sense in the pressure swing adsorption separation of hydrogen from traditionally low hydrogen concentration biomass sources.     

Operation Strategies for Simulated Moving Bed in the Presence of Adsorbent Ageing

Abstract

The effect of adsorbent ageing on the operation of Simulated Moving Bed (SMB) units is addressed, for two different systems (linear and non‐linear isotherms). Two different consequences of adsorbent deactivation are considered, one involving the loss of adsorption equilibrium capacity and the other related to the increase of mass transfer resistance. For each of these cases one direct and straightforward compensation measure is presented: the increase of the solid velocity (decrease of switching time) to compensate the adsorbent capacity decline and the decrease of solid and internal flow rates to compensate the mass transfer resistances increase. It is possible to compensate the adsorbent capacity decline, maintaining all SMB performance parameters, limited to the reduced contact time when high solid velocities are used. In the second case, when mass transfer resistance increases, it has been shown that the direct compensation strategy would lead to a decrease of productivity, to keep the same purity and recovery as with fresh adsorbent.

Another possible corrective method to the ageing problem is the use of variable switching times in the non‐conventional “modus operandi”‐Varicol, a sort of re‐arrangement of the SMB columns distribution by sections, here tested for the case of adsorbent capacity decline case as a consequence of adsorbent ageing mechanisms.     

Extraction of Uranium from Seawater Using Magnetic Adsorbents

Abstract

A new process for the extraction of uranium from seawater was developed. In the process, uranium adsorption is effected using powdered magnetic adsorbents; the adsorbents are then separated from seawater using magnetic separation technology. This process is superior to a column method using a granulated hydrous titanium oxide adsorber bed in the following ways: (1) a higher rate of adsorption is realized because smaller particles are used in the uranium adsorption; and (2) blocking, which is inevitable in an adsorber bed, is eliminated.

The composite hydrous titanium-iron oxide as a magnetic adsorbent having high uranium adsorption capacity and magnetization can be prepared by adding urea to a mixed solution of titanium sulfate and ferrous sulfate. Adsorption and desorption of uranium and the removal of the adsorbent using a small-scale uranium extraction plant (about 15 m³/d) is reported, and the feasibility of uranium extraction from seawater by this process is demonstrated.     

Carbon Di-Oxide Removal with Mesoporous Adsorbents in a Single Column Pressure Swing Adsorber

Abstract

A five-step PSA cycle was studied for CO₂ separation from CO₂-N₂ gas mixture in a single column at elevated temperatures using Poly-ethyleneimine (PEI) impregnated mesoporous silica SBA-15 as adsorbent. The PSA cycle study included a strong adsorptive rinse step in which the strongly adsorbed component, i.e., CO₂ was used for rinsing the adsorbent bed in order to increase the purity of CO₂ product. The study indicates that the adsorbent is regenerable under typical PSA conditions. The productivity of the adsorbent studied for CO₂ separation was found to be comparable with commercial zeolite adsorbents as reported in literature.     

THESES/DISSERTATIONS/1963-1983, POLAND

ABSTRACT

A fluidized bed of inert particles lpar;packing)--> can be used advantageously for the drying of paste-like materials of high moisture content. Wet pasty material is fed into a fluidized bed of chemically inert coarse particles. The wet material coats the surface of the inert particles. Drying takes place mainly in the thin layer formed on the surface of particles. After reaching a certain moisture content, the dried material film breaks off the surface of the packing particles, and leave the fluidized bed as a fine powder in the exit gas stream.

Experiments were performed using different organic and inorganic materials e.g. raw materials from human and veterinary     

HEAT AND MASS TRANSFER IN THE ADSORBENT BED OF AN ADSORPTION HEAT PUMP

The heat and mass transfer equations governing an adsorbent bed in an adsorption heat pump and the mass balance equation for the adsorbent particles in the adsorbent bed were solved numerically to simulate the cycle of a basic adsorption heat pump, which includes isobaric adsorption, isosteric heating, isobaric desorption, and isosteric cooling processes. The finite difference method was used to solve the set of governing equations, which are highly nonlinear and coupled. The pressures of the evaporator and condenser were 2 and 20 kPa, respectively, and the regeneration temperature of the bed was 403 K. Changes in the temperature, adsorptive pressure, and adsorbate concentration in the adsorbent bed at different steps of the cycle were determined. The basic simulated cycle is presented in a Clausius-Clapeyron diagram, which illustrates the changes in average pressure and temperature of the adsorbent bed throughout the cycle. The results of the simulation indicated that the most time-consuming processes in the adsorption heat pump cycle were isobaric adsorption and isobaric desorption. The high thermal resistance of the bed slows down heat transfer, prolonging adsorption and desorption processes.