BIXIN POWDER PRODUCTION IN CONICAL SPOUTED BED UNITS

ABSTRACT

Recent work has demonstrated that the red carotenoid bixin is easily extracted from Bixa orellana seeds by particle attrition and impact rather than by solvent extraction. This technique may require a previous step for drying seeds at a safe temperature to preserve pigment quality. A spouted bed (SB) with a draft tube is the most appropriate equipment to process both seed drying and bixin extraction at low operational costs. Operational parameters of the SB unit are optimized as a function of the powder production rate. The maximum air inlet temperature for drying the seeds is also specified. A high performance liquid chromatography method has been developed for the semi-quantitative determination of bixin content in the powder produced. Results show that this SB unit can be more competitive than ball mill equipment.     

BIXIN POWDER PRODUCTION IN CONICAL SPOUTED BED UNITS

Recent work has demonstrated that the red carotenoid bixin is easily extracted from Bixa orellana seeds by particle attrition and impact rather than by solvent extraction. This technique may require a previous step for drying seeds at a safe temperature to preserve pigment quality. A spouted bed (SB) with a draft tube is the most appropriate equipment to process both seed drying and bixin extraction at low operational costs. Operational parameters of the SB unit are optimized as a function of the powder production rate. The maximum air inlet temperature for drying the seeds is also specified. A high performance liquid chromatography method has been developed for the semi-quantitative determination of bixin content in the powder produced. Results show that this SB unit can be more competitive than ball mill equipment.     

Industrial Trials of Paste Drying in Spouted Beds Under QDMC

Abstract

Spouted bed has been extensively investigated by many authors for years, but the issue of controlling its operation still remains in basic developing stages. The present work consists of the application of an advanced control strategy (QDMC—Quadratic Dynamic Matrix Control) to automate the operation of a large-scale spouted bed dryer. The work on control strategies for spouted bed was motivated by the lack of references on this subject and the encouraging results obtained by Corrêa et al. (Corrêa, N.A.; Freire, J.T.; Corrêa, R.G. Improving operability of spouted beds using a simple optimizing control structure. Brazilian Journal of Chemical Engineering 1999 16 (4), 359–368; Corrêa N.A. Corrêa, R.G.; Freire, J.T. Adaptive control of paste drying in spouted bed using the GPC algorithm. Brazilian Journal of Chemical Engineering 2000 17 (4–7), 639–648; Corrêa, N.A.; Corrêa, R.G.; Freire, J.T. Self-tuning control of egg drying in spouted bed using the GPC algorithm. Drying Technology 2002 20 (4), 813–828.) for a laboratory-scale apparatus. The industrial-scale spouted bed dryer has a height of 4 m and a diameter of 66 cm. The same configuration of data acquisition unit, sensors, and interface developed for the laboratory-scale unit was employed. The dryer is capable of processing up to 20 L/h of pasty material. The powder moisture content (Ys), inferred from measurements of temperature at the exhaustion of the bed bulk, and the powder production rate (Pr), measured on-line by an electronic balance, are the controlled variables. The manipulated variables are: the paste inflow rate (W), regulated by an automatic pump, and the electrical power supply for air heating (P), regulated by a thyristor. The bed pressure drop, the airflow rate, and the information from the environment are monitored by means of an interfaced microcomputer. Experimental runs of drying up to 400 kg/day of an Al₂O₃ 10% aqueous suspension were carried out. The results showed that the QDMC control is robust with respect to the main variables involved and is efficient in maintaining the operation of the bed under the constraints of the system. The major aim concerning the scale-up of spouted bed, which is the determination of the minimum amount of energy required to ensure spout stability, was accomplished by the constrained control strategy.     

Flue Gas Desulfurization by a Powder‐Particle Spouted Bed

The powder‐particle spouted bed process is one of the semi‐dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO₂ removal by a powder‐particle spouted bed, the reaction term is included in one‐dimensional and streamtube models that were presented previously for spouted beds. Hydrated lime is used as the sorbent in this process. The predictions of the models are compared with some published experimental data and it is found that the developed models are valid. The results of two models are compared with each other and their various properties are evaluated. The effects of different operating conditions on SO₂ removal efficiency are also investigated and preferred operating conditions are discussed.     

超细粉在导向管喷动床中的固体循环速率

Ultra-fine powders are difficult to be fluidized due to the strong particle to particle cohesiveness.However, the authors‘ experiments showed that the ultra-fine powder CaCO3 could be stably fluidized in a spouted bed with a draft tube. The effects of geometric and operating parameters on solid circulation rate of ultra-fine powder CaCO3 were investigated in a 120 mm diameter transparent semicircular spouted bed with a draft tube. Three draft tubes with different sizes were used in this study. It was found that the solids circulation rate was mainly dependent on the drawing rate of the gas jet from the nozzle, then on the gas transport capacity in the draft tube. With increasing gas feed rate, distance between the nozzle and the draft tube inlet and draft tube diameter, the solids circulation rate could be increased. Based on the jet theory, a quantitative correlation was proposed for predicting the solid circulation rate of ultra-fine powders in a spouted bed with a draft tube by taking into account the gas transport capacity in the draft tube.     

Cavity formation and breakup forces in conical spouted beds

A method has been developed to deduce a “breakup” force in a packed bed based on measured pressure drop and internal cavity size hysteresis data in a conical spouted bed. The pressure drop over the vertical jet is estimated by the Eulerian-Eulerian two-fluid model using the commercial Fluent software. The pressure drop over the packed bed is extracted from the measured total pressure drop following a flow rate descending process in the spouted bed, while the “breakup” force is determined from the combination of measured total pressure drop and internal jet height following the flow ascending process, the simulated pressure drop over the gas jet and the pressure drop over the loosely packed upper bed section. Such a proposed method can be applied in the future to develop a generalized expression for the “breakup” force in spouted beds and other packed bed systems where a vertical fluid jet is issued into the packed particles.     

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.     

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

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.     

Coal gasification in a spouted bed

Low Btu gas has been produced by gasifying coal in a spouted bed reactor. Coal of size 0.8-3.6 mm is fed continuously to a 0.15 m diameter spouted bed of inerts and gasified using mixtures of steam and air. Tests of the process with Western Canadian coals of free swelling index 0, 4 and 7 are reported. Gases of heating value to 3.61 MJ/m³ were produced at coal throughputs of 0.188 kg/m²s with the reactor operating at atmospheric pressure and temperatures to 930°C. Characteristics of the spouted bed gasifier are presented and results compared to commercial moving and fluidized bed systems. A simple mathematical model based on the two-region spouted bed model of Mathur and Lim is used to predict the effect on steam utilization of bed composition, bed height and diameter, and particle size.     

喷动流化床造粒实验研究

喷动流化床用于粉体造粒，是一种新型的造粒方法。与其它几种造粒方法相比．具有设备投资省、能耗低、设备结构简单等优点。作者经过实验发现，气流雾化器安装于底部或侧部，或是二者结合。可实现对多种粉体的造粒和包衣。气流雾化喷嘴是喷动流化造粒装置的主要部件。为此对气流雾化喷嘴作了一些实验研究。     

DRYING OF PULPS OF TROPICAL FRUITS IN SPOUTED BED: EFFECT OF COMPOSITION ON DRYER PERFORMANCE

Studies on drying of pulps of several tropical fruits in spouted beds had shown advantages in relation to the quality of the products. However, most of the processed pulps presented serious problems of accumulation in the bed and consequently, instability of the spouted bed dynamic. The objective of this work is to analyze the influence of the chemical composition on the spouted bed performance in drying pulps of tropical fruits. Mango pulp “in natura” was used as a standard pulp. Modified pulps were obtained increasing the concentrations of reducer sugars, lipids, fibers, starch and pectin. The effect of these compositions on the fluid-dynamic and efficiency of the powder production was investigated using a factorial design. The operational conditions were maintained fixed in all experiments. The efficiency of powder production, the stable spout pressure drop and the minimum spouting flow rate were the responses analyzed. The statistical analysis of the results showed that the concentration of fibers is not a significant variable for the process. The concentrations of reducer sugars and starch showed significant influence on the fluid dynamic and these concentrations together with the lipids and pectin concentrations showed significant influences on the efficiency of powder production.     

Pressure drop,bed expansion and liquid holdup in a three phase spouted bed contactor

Data on the pressure drop, bed expansion and liquid holdup in a three phase spouted bed contactor with an initial bed height of 243 mm. were obtained as a function of the gas and liquid flowrate. Polyethylene spheres 10 mm. in diameter with a density of 320 kg/m³ were spouted in a 194 mm. column using a 30 mm. nozzle. The spouted bed contactor with gas and liquid mass flow-rates of 2.18 and 1.88 kg/m² sec, respectively had similar pressure drop per unit area of particle surface, total liquid holdup per unit volume of operating bed, and “active” holdup, as a fluidized contactor.     

Side-outlet spouted bed with draft tube: Effect of varying the position of the outlet

The vector form of the Ergun equation was used to numerically predict gas phase streamlines, residence time distributions, chemical conversions and pressure drops in the annulus of a side-outlet spouted bed with an internal draft tube. By varying the position of the side-outlet, it was demonstrated that there exists an optimum location for this outlet at which conversion is a maximum and which shows a greatly improved gas phase residence time distribution in the annulus compared with a conventional spouted bed unit.     

Influence of Drying Techniques on the Characteristics of Chitosan and the Quality of Biopolymer Films

In this work, spouted bed and tray-drying techniques were employed at different drying air temperatures to produce dried chitosan, and the chitosan powder was used to produce biofilms. The products obtained from each drying technique were compared in relation to quality aspects (molecular weight, lightness, and hue angle). The results found for chitosan in spouted bed drying (90°C) showed lower alteration and best quality aspects in relation to the chitosan powder. However, in tray drying under the best condition (60°C) the chitosan molecular weight increased about 50% in relation to the initial value and browning was observed. The biofilms produced from chitosan dried in the spouted bed showed the best mechanical properties (tensile strength of 42 MPa and elongation of 29%) and lower water vapor permeability (3.95 g mm m^?2 kPa^?1 day^?1).     

Simulation of the Hydrodynamics and Drying in a Spouted Bed Dryer

Gas-particle flow behavior in a spouted bed of spherical particles was simulated using the Eulerian-Eulerian two-fluid modeling approach, incorporating a kinetic-frictional constitutive model for dense assemblies of the particulate solid. The interaction between gas and particles was modeled using the Gidaspow drag model and the predicted hydrodynamics is compared with published experimental data. To investigate drying characteristics of particulate solids in axisymmetric spouted beds, a heat and mass transfer model was developed and incorporated into the commercial computational fluid dynamics (CFD) code FLUENT 6.2. The kinetics of drying was described using the classical and diffusional models for surface drying and internal moisture drying, respectively. The overall flow patterns within the spouted bed were predicted well by the model; i.e., a stable spout region, a fountain region, and an annular downcomer region were obtained. Calculated particle velocities and concentrations in the axisymmetric spouted bed were in reasonable agreement with the experimental data of He et al. (Can. J. Chem. Eng. 1994a, 72:229; 1994b, 72:561). Such predictions can provide important information on the flow field, temperature, and species distributions inside the spouted bed for process design and scale-up.     

Removal of SO2 in Semi‐Dry Flue Gas Desulfurization Process with a Powder‐Particle Spouted Bed

Semi‐dry flue gas desulfurization was investigated with several kinds of SO₂ sorbents, such as slaked lime, limestone, Mg(OH)₂ and concrete pile sludge, in a powder‐particle spouted bed. Slurry droplets including sorbent fine particles were fed to a spouted bed of coarse inert particles spouted with hot gas containing SO₂. SO₂ removal efficiency was strongly affected by the approach to saturation temperature, Ca/S molar ratio and particle size of sorbent. Slaked lime showed the highest desulfurization efficiency. In this process, despite very short gas residence time, more than 90% SO₂ removal was easily achieved by choosing appropriate conditions.     

Numerical simulation of two-dimensional spouted bed with draft plates by discrete element method

A discrete element method (DEM)-computational fluid dynamics (CFD) two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates. The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation. The interactions between gas and particles were considered using a twoway coupling method. The motion of particles in the spouted bed with complex geometry was solved by combining DEM and boundary element method (BEM). The minimal spouted velocity was obtained by the BEMDEM-CFD simulation and the variation of the flow pattern in the bed with different superficial gas velocity was studied. The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations. The radial profile of the averaged vertical velocities of particles and the profile of the averaged void fraction in the spout and the annulus were statistically analyzed. The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results. __________ Translated from Chemical Engineering (China), 2007, 35(6): 24–28 [译自: 化学工程]     

Development of a novel fluidized bed ash cooler for circulating fluidized bed boilers: Experimental study and application

A novel bottom ash cooler (BAC) called compound fluidized bed ash cooler (CFBAC) was developed in this paper. The CFBAC combined the major technical features of spouted bed and bubbling bed, and could achieve the selective discharge on the bottom ash. Experiments about the gas-solid flow characteristics of the CFBAC were conducted in a visible cold test rig. The experimental results indicated that the separation chamber working in the spouted bed state had a good particle separation effect on the boiler bottom ash. A small quantity of fluidizing air was needed for the cooling chambers to work in the bubbling bed state. The particle separation effect could be controlled by the fluidizing air flow and physical dimensions such as the height of separation partition. The CFBAC had also been industrially applied in a 300 MW circulating fluidized bed unit. The application showed that the CFBAC had a well separation effect, an excellent adaptability on the bottom ash, a good cooling effect and a large ash discharge capacity over 30 t/h. Compared with the water-cooled BAC, the CFBAC had a better energy conservation performance.     

喷动床发展与现状

介绍了流化床的一个分支——喷动床的发展与现状。首先简述了喷动床的发展史，然后着重讲解了有关喷动床的几个基本概念，并对喷动床的流动特性及其与传统流化床的异同点作了描述。给出了一些喷动床的床型变化及应用实例，并提供了一份有关喷动床研究的较完整的文献清单     

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.