Open-sided Tubes Research Articles

Draft tube design based on a borescopic technique in conical spouted beds

Draft tubes have emerged as promising internal devices to overcome the scale up limitations of the spouted bed. Although only a few parameters define draft tubes, the design of these devices is complex and remains a challenging task, as knowledge concerning the gas–solid flow pattern in the spouted bed is required for a proper implementation. Therefore, this study aims to propose a new criterion for the design of draft tubes (nonporous and open-sided) based on the average spout diameter measured by a borescopic technique in conical spouted beds without draft tube. Based on the radial and axial particle velocity profiles, hydrodynamic analysis, and cycle time distributions, the new configurations are compared with those without tube and with conventional draft tubes. The new open-sided tube provides maximum particle velocities of 480.90 ± 14.60 mm/s in the spout and 90.10 ± 4.40 mm/s in the annulus. These values are lower and higher than the particle velocities obtained without draft tube in the spout and annulus regions, respectively, which means it modifies particle residence time in these regions. The new open-sided tube provides a more efficient gas–solid contact than any conventional one, with spouting behaviour being very similar to the configuration without tube (differences in the minimum spouting velocity being in the 2–6% range), which is a key aspect for scale up purposes.

Drying of particulate materials in draft tube conical spouted beds: Energy analysis

Drying is a highly energy-intensive process and dryers are considered one of the most energy-consuming industrial equipment. Nevertheless, the energy contribution of the draft tube in the spouted bed has hardly been studied. This equipment is widely recognized as a versatile and efficient gas-solid contact method for several chemical and physical operations. Thus, the objective of this study is to perform an energy analysis of a draft tube conical spouted bed for particulate materials. Drying of alumina, soybean, and barley has been performed with three different configurations: without tube and with nonporous and open-sided tubes. Energy Efficiency, Drying Efficiency, and Specific Energy Consumption have been the parameters considered for energy analysis. The nonporous tube provided the best energy performance for diffusive materials, such as barley and soybean particles, with reductions in the energy consumption in the range from 31.60% to 42.40% in relation to configuration without tube. The configurations with open-sided tube and without tube provided similar energy performance for all materials. Therefore, this study contributes to support that draft tubes are promising devices for improving energy issues in the spouted bed, mainly in the processing of low moisture materials.

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.

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.