Open-sided Draft Tube Research Articles

Spout geometry of fine particle conical spouted beds equipped with internal devices

The size and geometry of the spout are crucial parameters for the design and scaling-up of spouted beds because they condition heat and mass transfer rates. It is well-established in the literature that spouted beds without draft tube show axisymmetric spout shape, but this does not occur with open-sided draft tubes. Particle velocity has been measured at several bed heights and angular coordinates, under different geometric parameters and operating conditions, to determine the location of the spout-annulus interface in beds provided with open-sided draft tubes. Narrow draft tube wall slits and low air velocities lead to spouts of small size and triangular shape. The greatest spout expansion (high air velocities and wide draft tube wall slits) leads to a Reuleaux triangle shape, in which the spout swallows the tube. The results allow a better understanding of fine particle hydrodynamics in conical spouted beds, which is essential information for their scaling-up.

Search for Operating Conditions in the Thermal Pistachio Splitting in Fountain Confined Conical Spouted Beds

AbstractThe worldwide consumption of pistachio nuts has been increasing over the last decades due to their high nutritional value. Given that only split nuts are commercialised, the closed-shell nuts, which account for most of the harvested ones, must be split by mechanical or thermal processes. However, there is hardly any information about the splitting mechanism based on thermal treatments. Accordingly, the thermal splitting of pistachio nuts in conical spouted beds has been approached, and the effect of the air inlet temperature, the draft tube aperture ratio and the air inlet diameter on the splitting mechanism has been analysed. Batch drying tests have been carried out in the proposed technology at an air inlet temperature range of 40–120 $${}^{\circ }\text {C}$$ ∘ C using configurations with and without draft tube. The operating temperature and dryer configuration that allows attaining up to 60% of split pistachios and preserving their quality are 80 $${}^{\circ }\text {C}$$ ∘ C , an inlet diameter of 0.05 m and an open-sided draft tube with an aperture ratio of 80%.

Bed symmetry in the fountain confined conical spouted beds with open-sided draft tubes

Bed symmetry has been analysed in fountain confined conical spouted beds operating with fine particles. Thus, vertical particle velocities and the spout shape have been determined in a wide range of spouting air velocities and bed configurations. Bed symmetry is widely accepted in the spouted beds without draft tubes or with nonporous ones, but this is not the case when open-sided draft tubes are used. Thus, radial particle velocity profiles differ depending on the cross-sectional angular plane considered in the open-sided draft tubes. The spout expands preferentially along the tube opened surface, and is wider as spouting air velocity and aperture ratio are increased. The literature correlations proposed for the average spout diameter have been analysed and no one is valid for estimating this parameter in the whole range of spouting air velocities and configurations analysed in these systems operating with fine particles.

Effect of operating conditions on the hydrodynamics in fountain confined conical spouted beds

Spouted bed stability and operation is greatly affected by particle features. Accordingly, the hydrodynamic behaviour of conical spouted beds has been studied for fine particles differing in size and density in a wide range of inlet air flow rates. This knowledge is essential for a successful scaling up and industrial implementation of the spouted bed. Therefore, the effect air velocity and solid properties (density and size) have on local solid velocity has been ascertained in a fountain confined conical spouted bed using a borescope technique (Particle Tracking Velocimetry, PTV) applied to several bed configurations. The results show a close relationship between the inlet air velocity and the local solid velocity, with the gas-solid contact being especially vigorous in the configurations without draft tube and with the open-sided draft tube. The solid circulation flow rate is lowest when a nonporous draft tube is used due to the low solid vertical velocities in the annulus, even at high air flow rates. Nevertheless, vertical velocities in the annular zone increase when particle size and density are increased, although these velocities are lower in the spout and fountain regions due to the higher momentum exchange required for their acceleration.

Estimation of the minimum spouting velocity and pressure drop in open-sided draft tube spouted beds using genetic programming

Explicit dimensionless models are proposed for estimating the minimum spouting velocity, operating pressure drop and peak pressure drop in open-sided draft tubes spouted bed using the genetic programming (GP). The models are developed based on 664 experimental data for minimum spouting velocity, 660 for peak pressure drop and 652 for operating pressure drop. The parameters of significant influence are considered as GP input variables, and reliable semi-empirical correlations have been obtained. The models predict the hydrodynamic parameters analyzed with average absolute relative errors of 12.90%, 15.99% and 10.92% for the minimum spouting velocity, peak pressure drop and operating pressure drop, respectively. A comparison of literature correlations with the present ones shows that the latter lead to considerably lower errors from the experimental data. The prediction capability of the new models was evaluated in a range of operating and geometric conditions and a close agreement with the experimental data was observed.

Fine particle flow pattern and region delimitation in fountain confined conical spouted beds

A novel borescopic technique together with the monitoring of pressure fluctuation signals (power spectral distribution, PSD) has been used to track fine particles and characterize solid flow dynamics in fountain confined conical spouted beds. Radial and axial particle velocity profiles have been obtained for different configurations, and spout-annulus and fountain core-periphery interfaces have been delineated. The downward particle velocities in the annulus peak at intermediate positions in this zone, whereas the upward velocities in the dilute zones (spout and fountain core) peak at the axis or close to this position. Among the different configurations analysed in this work, the system without draft tube shows the greatest vertical particle velocities in almost all the different radial and axial positions. The evolution of the spout size along the bed depends on the configuration used, but all of them differ from those commonly reported in the literature. Thus, the spout expands from the bed bottom to the surface, without any neck at an intermediate bed level. Furthermore, the cross-sectional spout shape has been delineated in the systems with open-sided draft tube, and significant spout expansion is observed due to air percolation from the spout into the annulus through the opened faces. Finally, the average spout diameters of the systems without draft tube and with open-sided draft tubes have been compared with those predicted by literature correlations. Those proposed by San José et al. and Volpicelli et al. provide the best fit for the configurations without draft tube and with open-sided draft tube, with their relative errors being 9.83% and 8.88%, respectively.

Smart computing approach for design and scale-up of conical spouted beds with open-sided draft tubes

Open-sided draft tubes provide an optimal gas distribution through a cross flow pattern between the spout and the annulus in conical spouted beds. The design, optimization, control, and scale-up of the spouted beds require precise information on operating and peak pressure drops. In this study, a multi-layer perceptron (MLP) neural network was employed for accurate prediction of these hydrodynamic characteristics. A relatively huge number of experiments were accomplished and the most influential dimensionless groups were extracted using the Buckingham-pi theorem. Then, the dimensionless groups were used for developing the MLP model for simultaneous estimation of operating and peak pressure drops. The iterative constructive technique confirmed that 4-14-2 is the best structure for the MLP model in terms of absolute average relative deviation (AARD%), mean square error (MSE), and regression coefficient (R2). The developed MLP approach has an excellent capacity to predict the transformed operating (MSE=0.00039, AARD%=1.30, and R2=0.76099) and peak (MSE=0.22933, AARD%=11.88, and R2=0.89867) pressure drops.

Design Factors in Fountain Confined Conical Spouted Beds

The design factors of fountain confined conical spouted beds have been assessed in order to determine their best combination for scaling up and enhancing fine particle retention. The results evidence that the length of the confiner and the height of the draft tube entrainment zone are the key design factors, causing the highest entrainment reduction. Thus, the optimum confiner length is within the range of 2-3 times the bed surface diameter and the desirable height of the entrainment zone is approximately 1-2 times the tube diameter. This study also concludes that the best system for attaining high stability with minimum elutriation is the one equipped with an open-sided draft tube with an aperture ratio of around 20%.

Influence of the fountain confiner in a conical spouted bed dryer

The drying of fine sand particles (below 1 mm) has been studied in a conical spouted bed fitted with a draft tube in order to ascertain the performance of a new internal device to confine the fountain. Accordingly, batch runs have been carried out using three types of draft tubes, with confiner and without it under ambient conditions. Their performances have been compared in order to ascertain the optimum configuration. The results evidence that the systems with the confiner perform much better than those without it. Thus, the drying time decreases considerably and the pressure drop and air flow rate decrease slightly when the confiner is used. The drying performance of the open-sided draft tube is superior to any other configuration, i.e., the drying time required with this tube is the shortest. Nonporous draft tubes are the worst option due to their poor gas-solid contact. Porous draft tubes have an intermediate performance.

A new fountain confinement device for fluidizing fine and ultrafine sands in conical spouted beds

A study has been carried out on the hydrodynamic performance of a fountain confinement device used in conical spouted beds for the treatment of Geldart A and B type particles. Stability and particle elutriation have been analysed for beds provided only with this device and those provided with this device and two types of draft tubes, namely, open sided draft tube and nonporous draft tube. Stability is greatly improved when only the fountain confiner is used, but the draft tubes are required for significantly avoiding bed elutriation in spouted beds. The modified conical spouted bed has been located in a map of operating conditions together with the remaining gas-solid contact regimes. The fountain confiner provides a dramatic increase in the applicability range of spouted beds. Thus, unlike the traditional use of spouted beds for Geldart D type particles, this device allows operation with Geldart A, B and D particles, with a small fraction of C particles.

CFD-DEM simulation of a conical spouted bed with open-sided draft tube containing fine particles

Abstract A full 3D model of a conical spouted bed equipped with an open-sided draft tube was simulated using CFD-DEM embedded in a commercial CFD code ANSYS-FLUENT. The dense discrete phase model (DDPM) with DEM closure for particle–particle interaction available in the FLUENT was used for the particulate phase. The dispersed k-e turbulent model was used in the computational model for the gas phase. The geometry used in the simulation for both the contactor and the open-sided draft tube was identical to that of a pilot plant in which the hydrodynamic studies were carried out. The influence of the open-sided draft tube was studied by using two configurations, one flushed with the bed surface and the other one protruding above the bed surface. The CFD-DEM results indicated that the accuracy of model predictions significantly depends on the modification in the Gidaspow drag function. The predicted pressure drops and fountain heights were consistent with the experimental data. New aspects of particle flow pattern, axial solid velocity, solid volume fraction in the bed, and power spectral density have also been discussed.

Minimum spouting velocity for conical spouted beds of vegetable waste biomasses

Spouted beds are an interesting alternative for the treatment of biomass for energy purposes, given that the insertion of a draft-tube allows large-scale handling of solids with a wide range of sizes and diverse properties. The hydrodynamic correlations proposed in the literature have not been validated with particles of low density and shape factor. Therefore, a detailed experimental study has been conducted using five types of biomasses and different combinations of the contactor geometric factors. The correlations in the literature for plain conical spouted beds and for those provided with nonporous and open-sided draft-tubes have been taken as a starting point and, based on the experimental results, they have been modified in order to account for the properties of the solids. Two strategies have been considered in the methodology for modifying the coefficients in the literature correlations. Both are based on the introduction of coefficients one by one based on a hypothesis test. Accordingly, new correlations based on existing ones have been proposed, with the number of coefficients modified being minimum.

Operating and Peak Pressure Drops in Conical Spouted Beds Equipped with Draft Tubes of Different Configuration

Operating and peak pressure drops have been studied in conical spouted beds equipped with draft tubes of different configuration using materials of different size. The draft tubes used are nonporous and open-sided ones. Based on an experimental design, the factors of greater influence on both pressure drops have been determined and general correlations valid for fine and coarse materials have been proposed for predicting the operating pressure drop and peak pressure drop with each type of draft tube. The results show that conical spouted beds equipped with draft tubes give way to lower operating and peak pressure drops than those without draft tube. A comparison of draft tube systems reveals that nonporous tubes give way to the lowest values of both pressure drops, but the solid circulation rates and the gas–solid contact efficiency are poorer than those with open-sided draft tube systems.

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.

Influence of the Geometric Factors of Conical Contactors and Draft Tubes on the Performance of Draft Tube Conical Spouted Beds

A hydrodynamic study of conical spouted beds equipped with draft tube has been carried out for Geldart group D particles. Based on a design of experiments, the performance of conical spouted beds provided with draft tube has been studied by measuring different hydrodynamic parameters (minimum spouting velocity, operation pressure drop, solid circulation rate) and the influence of the geometric factors of conical contactors and draft tubes (open-sided draft tubes), and particle properties on these hydrodynamic parameters. The results show that the factors studied (bed height, angle, inlet diameter, width of the draft tube faces, particle diameter) have great influence on the hydrodynamic parameters.

Minimum Spouting Velocity of Conical Spouted Beds Equipped with Draft Tubes of Different Configuration

The hydrodynamics and the influence of the geometric and operating factors on the minimum spouting velocity have been studied in draft tube conical spouted beds with materials of different size and density. Two draft tube configurations have been used: nonporous and open-sided tubes. Based on an experimental design, the factors of greater influence have been extracted and the general correlations valid for fine and coarse materials have been proposed for predicting the minimum spouting velocity for each type of draft tube. A comparison of the velocities with and without a tube reveals that the nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the gas–solid contact efficiency of the open-sided draft tube outperform any other spouted bed configuration, especially for fine particles. Consequently, open-sided draft tubes allow stable operation with fine particles and high solid circulation rates in conical spouted beds.

Drying of Biomass in a Conical Spouted Bed with Different Types of Internal Devices

The drying of sawdust was studied in a conical spouted bed pilot plant in order to adapt this feed for the pyrolysis process. Air at different temperatures was used and the effect of sawdust particle size and operating gas velocity was studied. Batch operation was performed with no internal device and with nonporous and open-sided draft tubes in order to ascertain the optimum configuration of the contactor. Although the nonporous draft tube required the lowest minimum spouting velocity, its performance was poor due to deficient gas–solid contact. Configurations with open-sided draft tubes and with no internal devices had higher efficiencies because of their better contacts. An increase in air temperature resulted in a reduction in drying time but the operating conditions need to be fine-tuned to ensure proper energy efficiency.

Effect of Temperature on Fine Particle Drying in a Draft‐Tube Conical Spouted Bed

AbstractThe performance of a draft‐tube conical spouted bed for drying fine particles under batch operating conditions has been assessed at several temperatures using nonporous and open‐sided draft tubes, and the results have been compared with those obtained when operating without a draft tube. In order to ascertain the influence of temperature on drying, experimental runs have been carried out in the 25–300 °C temperature range. The open‐sided draft tube provides the best performance due to the excellent gas‐solid contact attained with this device, which enables shorter drying times. A maximum air temperature of 200 °C is recommended for energy optimization. An open‐sided tube protruding above the stagnant bed by at least 2/3 of the latter's height produces much lower and denser fountains than a tube flush with the upper surface of the bed.

A Draft-Tube Conical Spouted Bed for Drying Fine Particles

A study has been conducted on the performance of a draft tube conical spouted bed for drying fine particles. Batch operation has been performed with nonporous, porous, and open-sided draft tubes in order to ascertain the optimum configuration of this internal device. The nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the drying efficiency of the open-sided draft tube are superior to any other spouted bed configuration. Moreover, it allows for reducing the height of the fountain and, consequently, the height of the drying equipment.