SPOUTED BED DRYING OF SLUDGE FROM METALS FINISHING INDUSTRIES WASTEWATER TREATMENT PLANTS

ABSTRACT

A 0.15 m diameter half cylindrical spouted bed was used to dry a ferric hydroxide - zinc hydroxide sludge with a moisture content of 83.4 % wet basis. Heat for drying was provided by an electrical air preheater. The sludge was fed through an air cooled feeder into the spout and dried product was removed by elutriation; it was captured by a cyclone and baghouse. The mechanisms of drying and the performance of the drier were studied as a function of the operating variables. A glass front panel was used for visual observation of the system to elucidate the drying mechanisms, a stainless steel panel was used at other times.

The study showed that a spouted bed drier could produce a consistent fine powder product with a mechanically simple and reliable design. A cost comparison of a spouted bed with other driers for a typical metals finishing installation shows that the spouted bed is cost competitive with conventional technology.     

Drying of industrial sludge waste in a conical spouted bed dryer. Effect of air temperature and air velocity

To determine the performance of a conical spouted bed dryer for the drying of sludge waste, an experimental study of drying in a spouted bed regime was performed under different experimental conditions. The drying performance was determined based on the time evolution of solid moisture content, and the influence of operating conditions (inlet air temperature, air flow rate, and bed mass) on the drying rate of sludge waste in spouted beds of a conical geometry was analyzed.     

Microwave-Assisted Spouted Bed Drying of Lettuce Cubes

Microwave-assisted spouted bed (MSBD) drying of lettuce cubes was investigated experimentally. Response surface methodology was used to optimize the process with spouting air temperature, microwave power level, and superficial air velocity. The dried product obtained was compared with that obtained using other drying technologies such as hot air drying, air spouted bed drying, vacuum microwave drying, and vacuum freeze drying. The comparison is based on the rehydration ratio, chlorophyll content of the product, color, and the drying time required.     

DRYING OF SUSPENSIONS IN A MODIFIED SPOUTED BED DRIER WITH AN INERT PACKING

Authors summarize results of drying experiments carried out in aim to investigate effects of operational and process-conditions on the drying output and the product quality. The studies were performed in a laboratory-size spouted bed drier of a new construction with tangentional air inlet and with an inner conveyor screw maintaining the spouted bed recirculation of the inert particles

Effects of parameters assuring intensive gas-solid contact were studied, such as the inlet air-velocity, the recirculation of inert particles as well as chemical and physical properties of the inert material.

Various chemical suspensions (e.g. fine grain inorganic-salt pulps, waste products), biologically active materials (e.g, suspension of yeast) food products were used in preliminary experiments which showed effectiveness of this dryin5 method. On this basis two rode1 materials (cobalt-carbonate suspension and pulp of zinc--carbonate) were chosen for detailed experiments.

As a result cf these studies main optimal operational and process pszramters.have been obtained.     

SLURRY DRYING IN GAS-PARTICLE CONTACTORS: FLUID-DYNAMICS AND CAPACITY ANALYSIS

The fluid-dynamic characteristics and evaporation capacities of several substrates (pure water, a mixture of water and carbohydrates, and apple pulps with maltodextrines) for conical spouted bed, fluidized bed and pneumatic dryers was compared.

For fluidized and spouted beds, the presence of fluids increased the fluid-dynamics parameters over the values when only inert particles were present in the beds. In both cases it was proposed correlations to predict those effects. In the spouted bed drier, increasing the load of inert particles resulted in a slight increase of the water evaporation capacity, while in the fluidized bed drier the effect was more marked. For fluidized and spouted beds, under similar operation conditions, the maximums of the suspension drying capacities are lower than the values of water evaporation, but for pneumatic drying this effect was the opposite. In general terms, the maximal capacities of fluidized bed dryers are higher than those observed in the spouted bed dryers.     

HYDRODYNAMICS AND MASS TRANSFER IN A SPOUTED BED DRYER

The disposal of sludge generated by water treatment plants poses major financial and environmental problems. Drying of the sludge is an essential pan of any disposal process which may include incinerating, landfilling or upgrading. In the present study, experiments were carried out to investigate the drying of sludge in a spouted bed and to characterize the hydrodynamics and mass transfer mechanisms. The effect of bed moisture content on the minimum spouting velocity (U_ms) was examined for sludge granules. U_ms was found to increase with increasing the moisture content of the sludge particles. The gas phase mass transfer coefficient in the dryer was determined using porous calcined alumina particles and the results were compared with predictions by correlations available in the literature. The existing correlations gave poor predictions for the mass transfer coefficient. A new correlation for the mass transfer coefficient in a spouted bed dryer was developed based on the experimental results.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20-25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

DRYING OF SUSPENSIONS IN A MODIFIED SPOUTED BED DRIER WITH AN INERT PACKING

Authors summarize results of drying experiments carried out in aim to investigate effects of operational and process-conditions on the drying output and the product quality. The studies were performed in a laboratory-size spouted bed drier of a new construction with tangentional air inlet and with an inner conveyor screw maintaining the spouted bed recirculation of the inert particles

Effects of parameters assuring intensive gas-solid contact were studied, such as the inlet air-velocity, the recirculation of inert particles as well as chemical and physical properties of the inert material.

Various chemical suspensions (e.g. fine grain inorganic-salt pulps, waste products), biologically active materials (e.g, suspension of yeast) food products were used in preliminary experiments which showed effectiveness of this dryin5 method. On this basis two rode1 materials (cobalt-carbonate suspension and pulp of zinc--carbonate) were chosen for detailed experiments.

As a result cf these studies main optimal operational and process pszramters.have been obtained.     

Drying of Liquid Feedstocks in a Spout‐Fluid‐Bed with Draft‐Tube Submerged in Inert Solids: Hydrodynamics and Drying Performance

A spout‐fluid bed with draft tube submerged in a bed of polypropylene beads was used for drying maltodextrin solutions. The hydrodynamics of the dryer were studied by determining the annular air flow vertical profile at different spouting velocities, using an additional air flow rate through the annulus equivalent to 0.5 U_mf. The drying performance of the dryer was studied through the determination of several dryer response parameters (product moisture, evaporative capacity and volumetric evaporative capacity). These parameters were compared with those obtained in a conventional spouted bed with inert solids and a spray dryer.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

Abstract

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

Batch drying kinetics of corn in a novel rotating jet spouted bed

The batch drying kinetics of corn as a test material were investigated experimentally in a novel rotating jet spouted bed (RJSB) using both continuous and intermittent (on/off) spouting and heating schemes. The parameters investigated include inlet air temperature, bed height, superficial air velocity, nozzle diameter, distributor rotational speed and intermittency of spouting and heat input. The results indicate that the drying kinetics are comparable with conventional spouted and fluidized beds for slow drying materials and that intermittent drying can save up to 40% of the thermal energy as well as air consumption with better quality product.     

HYDRODYNAMICS AND MASS TRANSFER IN A SPOUTED BED DRYER

ABSTRACT

The disposal of sludge generated by water treatment plants poses major financial and environmental problems. Drying of the sludge is an essential pan of any disposal process which may include incinerating, landfilling or upgrading. In the present study, experiments were carried out to investigate the drying of sludge in a spouted bed and to characterize the hydrodynamics and mass transfer mechanisms. The effect of bed moisture content on the minimum spouting velocity (U_ms) was examined for sludge granules. U_ms was found to increase with increasing the moisture content of the sludge particles. The gas phase mass transfer coefficient in the dryer was determined using porous calcined alumina particles and the results were compared with predictions by correlations available in the literature. The existing correlations gave poor predictions for the mass transfer coefficient. A new correlation for the mass transfer coefficient in a spouted bed dryer was developed based on the experimental results.     

BATCH DRYING OF SHELLED CORN IN TWO-DIMENSIONAL SPOUTED BEDS WITH DRAFT PLATES

Geometrically similar spouted beds with draft plates were used to obtain the drying characteristics of freshly harvested shelled corn with 0.28 to 0.31 kg/kg initial moisture content at different air inlet temperatures and bed heights. Thermal equilibrium between air and grains was achieved at minimum spouting conditions. The drying kinetics of shelled corn in a drafted two-dimensional spouted bed was found to be of the "thin layer" type. Expressions for the model parameters in Page's equation accounting for the bed geometry, grain moisture content, and drying conditions were developed.     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

COMBINED MICROWAVE AND SPOUTED BED DRYING OF DICED APPLES: EFFECT OF DRYING CONDITIONS ON DRYING KINETICS AND PRODUCT TEMPERATURE

ABSTRACT

The influence of microwave power (0 to 8.0 W/g, dry basis) and hot air temperature (25°C to 95 °C) on drying rate and product temperature of diced apples (from 31 % to 5% moisture content, dry basis) in a laboratory microwave and spouted-bed combined dryer was investigated. Product temperature initially increased sharply to a plateau about 12 to 15°C above the spouted bed air temperature at a microwave input power 6.4 W/g. This temperature remained almost constant thereafter. Uniform microwave heating was achieved as evidenced by uniform product color and product temperature. Drying rates increased with increasing spouted-bed air temperature or microwave power level, But higher microwave power caused more darkening of the product. Drying of the diced apples in the microwave and spouted bed drying system exhibited two falling rates periods. The influence of air temperature on effective moisture diffusivity followed an Arrhenius type equation. The activation energies were 23.7 kJ/mol and 26.7 kJ/mol for the first and second falling rate periods, respectively.     

COMBINED MICROWAVE AND SPOUTED BED DRYING OF DICED APPLES: EFFECT OF DRYING CONDITIONS ON DRYING KINETICS AND PRODUCT TEMPERATURE

The influence of microwave power (0 to 8.0 W/g, dry basis) and hot air temperature (25°C to 95 °C) on drying rate and product temperature of diced apples (from 31 % to 5% moisture content, dry basis) in a laboratory microwave and spouted-bed combined dryer was investigated. Product temperature initially increased sharply to a plateau about 12 to 15°C above the spouted bed air temperature at a microwave input power 6.4 W/g. This temperature remained almost constant thereafter. Uniform microwave heating was achieved as evidenced by uniform product color and product temperature. Drying rates increased with increasing spouted-bed air temperature or microwave power level, But higher microwave power caused more darkening of the product. Drying of the diced apples in the microwave and spouted bed drying system exhibited two falling rates periods. The influence of air temperature on effective moisture diffusivity followed an Arrhenius type equation. The activation energies were 23.7 kJ/mol and 26.7 kJ/mol for the first and second falling rate periods, respectively.     

Physicochemical Properties of Phytopharmaceutical Preparations as Affected by Drying Methods and Carriers

This article reports a study of the effects of the drying methods and drying carriers on system performance and physicochemical properties of spray- and spouted bed–dried phytopharmaceutical preparations from Bidens pilosa L. Colloidal silicon dioxide, β-cyclodextrin, maltodextrin dextrose equivalent (DE) 10, and microcrystalline cellulose were used as drying carriers. The dried product was characterized by the particle size and morphology, total flavonoid content, solubility, flowability, and water activity. High-performance liquid chromatography (HPLC) was used to detect four marker compounds previously reported for this plant. Spray and spouted bed drying systems were compared through energetic efficiency, product recovery, elutriation, and product accumulation. The crystalline state of the powders was assessed by X-ray diffraction. Results showed high degradation rates for total flavonoid content and marker compounds during spouted bed drying. Depending on the drying carrier added to extractive solutions, different degrees of protection from degradation were conferred, and the physical characteristics of the product were changed accordingly. The lowest flavonoid degradation (8.6%) and the higher concentration of marker compounds were obtained using β-cyclodextrin as the drying carrier. Particle size was higher when a blend of Aerosil (Evonik Degussa, Hanau, Germany) and cellulose was employed as the drying carrier. A maximum product recovery of 86.9% was achieved by spray drying and 72.9% by spouted bed drying with the Aerosil : cellulose composition.     

BATCH DRYING OF SHELLED CORN IN TWO-DIMENSIONAL SPOUTED BEDS WITH DRAFT PLATES

ABSTRACT

Geometrically similar spouted beds with draft plates were used to obtain the drying characteristics of freshly harvested shelled corn with 0.28 to 0.31 kg/kg initial moisture content at different air inlet temperatures and bed heights. Thermal equilibrium between air and grains was achieved at minimum spouting conditions. The drying kinetics of shelled corn in a drafted two-dimensional spouted bed was found to be of the "thin layer" type. Expressions for the model parameters in Page's equation accounting for the bed geometry, grain moisture content, and drying conditions were developed.     

Behaviour of a conical spouted-bed dryer for animal blood

A 60° conical bed of inert particles spouted with hot air has been used as a medium for drying animal blood into a powder with little thermal degradation. The spouting and drying performances of the dryer were investigated. A feature of considerable practical significance is the existence of an initial regime of incomplete spouting in which the solids in the annulus are partly held stagnant by friction, causing a reduced pressure drop. A model of the drying process was developed to predict the variations in maximum throughput and product properties with changes in operating conditions. Good agreement between predictions and experimental results was found.     

A MATHEMATICAL MODEL FOR CONTINUOUS DRYING OF GRAINS IN A SPOUTED BED DRYER

A mathematical model for a continuous spouted bed dryer has been presented to predict moisture content, air and grain temperatures as well as energy consumption. To better understand the interactive influence of processes in each region of the spouted bed, solution schemes for the spout and downcomer were treated separately. The behavior of dryer was investigated experimentally and found that the dryer behaved differently from an ideal plug flow. The drying rate as simulated by the model is almost constant during grain movement in the dryer. Absence of airflow in the downcomer leads to a tempering process that takes place in the downcomer while intense heat and mass transfer occurs mainly in the spout due to the high airflow rate there. Furthermore, by considering the predicted grain temperature history as one of the indicators of product quality, one can, in principle, design appropriate successive processes in a continuous spouted bed dryer to minimize product damage.