Fluidization Air Research Articles

High-temperature air fluidization improves cooking and eating quality and storage stability of brown rice

Brown rice contains many valuable active ingredients; but due to its long cooking time, hard texture, heavy rice bran taste, and short shelf life, it is not widely accepted by consumers. Herein, we developed a novel processing technology so-called high-temperature air fluidization (HTAF) to treat brown rice. The effects of the HTAF treatment at 120 °C, 130 °C, and 140 °C for 60 s at a feed rate of 80 kg/h on the quality of brown rice were investigated. The results showed that the treatment with HTAF caused fissures to form on the surface and the interior of brown rice, and these fissures appeared to facilitate the penetration of water into the rice kernels during soaking. The optimal HTAF treatment temperature was 130 °C, the water adsorption of HTAF-treated brown rice at 130 °C (TBR-130) was increased to 25.3% after soaking for 160 min, which was higher than that of white rice and untreated brown rice (UBR; 13.7%). The optimal cooking time for TBR-130 was also 5 min shorter than that for UBR. The results further showed that TBR-130 had a larger degree of volume expansion compared to that of UBR, and cooked TBR-130 had softer texture than cooked UBR. The cohesiveness and sensory quality of TBR-130 were also higher than those of UBR, and the content of flavor compounds in TBR-130 was similar to that of white rice. HTAF caused no obvious damages to the main active components or nutritional components of TBR-130. Finally, TBR-130 had better chromaticity and higher storage stability than UBR. These results demonstrate that the HTAF treatment can improve cooking and eating quality and storage stability without causing obvious damages to nutritional quality of brown rice. This technology may play important roles in an attempt to promote the use of brown rice as staple foods.

Numerical study of the hydrodynamics and heat transfer characteristics of gas–solid in a slit-less rotating fluidized bed in static geometry

A rotating fluidized bed in static geometry (RFB-SG) without slits is presented in this paper as a research objective. The concept of RFB-SG is highly beneficial in numerous industrial operations such as granular drying, particle coating, mixing, agglomeration, and combustion. In this study, a three-dimensional CFD model is developed using the commercial software ANSYS FLUENT 14.5, to investigate hydrodynamics and heat transfer characteristics of gas–solid in the vortex chamber. The analysis of the flow pattern of gas–solid and the prediction of fluidization capacity have been made, using appropriate parameters. The findings showed that the significant factors, such as inlet air velocity, solid-bed thickness, the volume fraction of solids, solids pressure, and heat transfer coefficient, influenced the reactor capacity. It is observed that the solid inventories of 300 and 500 g have been fluidized perfectly at inlet air velocities of 30 m s−1 and 44 m s−1, respectively. The overall operating and drying costs are found to be decreased due to the reduction in fluidization air requirements.

Phenol removal using pulsation bubble column with inverse fluidization airlift loop reactor

Phenol and phenolic compounds are omnipresent organic contaminants which are sent out to water bodies and wastewater systems produced from industrial processes, and they require specific attention due to their extraordinary features such as high toxicity, carcinogenic characteristics, and ability to accumulate, which affects the health of humans and the environment. In this practical study, the integrated system of a pulsation bubble column with an inverse fluidization air loop reactor was tested to remove phenol. The test platform was made and operated with a bubble column containing at its upper end an electrical solenoid valve engaged via at least two timers, and connected to the air loop reactor consisting of an outer rectangular tube and an internal draft tube by one-way valve, where the granular activated carbon is put as an adsorbent material in the annulus region between the inner and outer tube. The effects of various parameters [molar ratio of Phenol to H2O2 (1/10, 1/15 and 1/20), airflow rate (5-20 L/min), remediation time (5-60 min), initial phenol concentration (10- 150 mg L-1) have been studied. Removing 90% of the contaminated phenol as a result of this study may represent a partial solution to the ecological problem.

Ultrathin coating of particles in fluidized bed using submicron droplet aerosol

In this work, we demonstrate that particles can be coated in a fluidized bed with coating solution provided by a novel aerosol generator. Aerosol droplets are smaller than 1μm in volume-based diameter, hence they are very much smaller than droplets in conventional spray fluidized bed processes (around 40μm). A proof-of-principle experiment with 30% aqueous coating solution of sodium benzoate and γ-Al2O3 core particles in 150mm fluidized bed fed with droplet aerosol supplied from the chamber side is presented. To simultaneously coat and dry the particles, inlet of fluidization air was at 50°C. Moreover, Monte Carlo simulations of coating with small aerosol and large spray droplets were conducted. Due to dramatically smaller building blocks, ultrathin particle coating of high-resolution (very small layer thickness) can be attained with the new aerosol process, with the potential of even going nanoscale. Full coverage of particles is reached substantially faster than in the conventional process, so that material demand is much lower and sensitive materials can be processed in short residence time. Solids yield of around 30% was much higher than expected, that is considered to be technically viable and may be enhanced by the recycling of entrained solids or better equipment design.

Simultaneous drying of pet food pellets and Salmonella inactivation by 395 nm light pulses in an LED reactor

Contamination by Salmonella is one of the major reasons for food recalls and outbreaks. This study developed a pulsed light emitting diode (LED) reactor to dry pet food pellets and to inactivate Salmonella. Three treatment modes were tested: 395 nm LED treatment alone (mode 1), vibration + mild hot air (50 °C) fluidization (mode 2), and 395 nm LED treatment + vibration + mild hot air (50 °C) fluidization (mode 3). Significant drying of the pet food pellets was observed in all the three modes. The average log reductions in Salmonella on the pet food pellets after 30 min treatments with modes 1, 2, and 3 were 1.2, 0.33, and 2.26, respectively. This study shows that 395 nm light pulses with mild hot air fluidization inactivated Salmonella while producing a low-moisture food product simultaneously.

Recovery of Copper Values from Discarded Printed Circuit Boards

In the present study, discarded random access memory cards were evaluated as a secondary copper source. Both air and water fluidization process were investigated as the pretreatment steps followed by thermal exposure. A significant reduction of plastic/resin content from ~ 62% in feed to ~ 9% was attained in the underflow fraction of the water fluidization. Formation of the molten mass was observed at a thermal exposure of 1100 °C, whereas at 800 °C, a discrete structure with copper purity of 90.2% was attained. The adopted process provided an alternative pathway to recover metals without using any external additive and minimal gas generation because of the effective removal of epoxy resin. The experimental data revealed that 91% of copper values, i.e., ~ 31 g concentrate, could be recovered from 100 g of the RAM boards. The overflow product comprised of a calorific value of 4.5 × 106 J/kg and could be further used.

Numerical investigation of gas–solid flow behavior in a novel integral multi-jet spout-fluidized bed

A novel integral multi-jet spout-fluidized bed (IMJSFB) is designed so as to reduce the dead zone at the bottom of the annulus and omit auxiliary equipment for bypass fluidizing air. The gas–solid flow behavior in the IMJSFB was numerically simulated using an Eulerian–Eulerian two-fluid model. A number of slits (4) were formed on the cone side of the cylindrical spouted bed to form an auxiliary multi-jet structure, which can create spoiler effects on the boundary of the pyramidal. The distributions of particle velocity and concentration in the IMJSFB were obtained by numerical simulation. The CFD results show that, compared with the conventional spouted beds, the IMJSFB structure can effectively enhance the particle’s velocity in the annulus of the spouted bed (especially in destroying flow dead zone at the annulus). The enhanced particle motion significantly decreases the volume fraction of the boundary layer on the cone. The particle concentration and velocity distribution along the radial direction become more uniform, and the decrease in value of the coefficient of variation (CV) of the particles’ velocity is 22.9% in IMJSFB. The turbulent kinetic energy of the gas phase can be significantly enhanced and the strengthening effect on the turbulent kinetic energy of the gas remains good with the increase of the bed height.

Investigation of Ash-Related Issues During Combustion of Maize Straw and Wood Biomass Blends in Lab-Scale Bubbling Fluidized Bed Reactor

Abstract During the combustion of solid fuels, the undesired effects of ash transformation include bed agglomeration, slagging, and fouling processes. In particular, a problematic consequence of bed agglomeration is the defluidization process, resulting from the disappearance of gaseous bubbles that are created behind air distributors. Different solutions can be applied against the agglomeration process. One possible method is to apply some additives that influence the ash behavior, thus inhibiting the agglomeration process. This paper presents the results of investigations into ash-related issues in a laboratory-scale bubbling fluidized bed (BFB) reactor. In particular, the impact of additives (kaolin, halloysite, fly ash, and the residuals from wet desulfurization system (IMOS)) on bed agglomeration was investigated. It was found that the addition of these compounds increased the defluidization time from ∼109 min (without additive) to ∼285 min in the BFB (with the addition of 0.1 g/min of kaolin). The morphology of additive (kaolin and halloysite) transformation after their addition into the combustion chamber was discussed. Another interesting phenomenon is that residuals from the IMOS exhibited the ability to be an additive against the agglomeration process. The defluidization time can be also significantly increased by the simultaneous application of the additive and the control of fluidization air velocity. The procedure of periodical bed moving by impulse primary air feeding against defluidization (PADM) is suggested and discussed. The PADM procedure resulted in a 36% reduction of additive, thus reducing the cost of measures against ash-related issues.

Control of pellets coating in a Wurster fluidised bed by means of electrical capacitance tomography

Wurster fluidised bed is commonly used for coating pellets in the pharmaceutical industry. Normally, the control in a Wurster fluidised bed for coating is based on point-based measurement, that is, pressure and optical probes. However, the point-based measurement methods only provide local flow information and cannot reveal the cross-sectional flow dynamics characteristics and it is difficult to control the whole process with limited data. In this paper, electrical capacitance tomography (ECT) is applied to reconstruct the solids distribution in a lab-scale Wurster fluidised bed for coating pellets and the measurements are used in a control loop of the process. The flow regime is identified from the ECT images using a simple but efficient approach. The objective of control is to keep stable minimum fluidisation and avoid undesired flow regime in the region between the outside wall and the Wurster tube, such as intermittent, plug and defluidisation. To achieve this target, a PID controller is applied to keep a low volume fraction in the annular region by adjusting the fluidisation air rate, and bang-bang control is applied to a peristaltic pump used for spraying coating solutions based on the detected flow regime. It has been found that the proposed control scheme based on the ECT measurement is effective for keeping a stable flow regime, reducing the degree of pellets agglomeration and avoiding defluidisation.

Experimental Analysis of Low-rank Fuel Drying Characteristics

Drying technology of low rank coal, which is the leading technology of low rank coal thermal chemical processing, plays an important role for the efficient use of low rank coal. It has made clear the influence factors of low rank coal drying process and effect of related factors by studying low rank coal occurrence form of moisture and the drying mechanism. In the paper, it has carried on the experimental study in drying characteristic under the condition of fluidized drying in the tube furnace with YuZhou Long-flame coal as the research object, and obtained the correlation curve of the particle size, fluidization velocity, drying temperature, drying rate and the influence factors. At last, according to the experiment and the system economy, the drying process parameters are optimized: the drying temperature is 210 °C, the fluidization air velocity is 1.6 m/s, the drying time is 5 minutes.

Process simulation of a dual fluidized bed chemical looping air separation with Mn-based oxygen carrier

Chemical looping air separation (CLAS), a simple and efficient oxygen production technology, can be efficiently integrated with the moderate or intense low-oxygen dilution (MILD) combustion and oxy-fuel combustion technologies. Mn-based oxygen carrier is considered to be a hopeful candidate for the CLAS, but its redox kinetics has rarely been reported. In this work, the most suitable kinetic mechanisms for reduction and oxidation reactions are determined by thermogravimetric analyses. By coupling the obtained redox reaction kinetics and gas-solid flow hydrodynamics, a one-dimensional model of the interconnected fast fluidized bed and bubbling fluidized bed is built using sequential modular approach for simulating the chemical and physical phenomena in the CLAS process. The effects of main operation parameters on the CLAS performance are investigated by sensitivity analyses. The mole fraction of generated oxygen is found increasing with the increments of reduction temperature and air flow rate. Moreover, the system specific power consumption (SPC) is decreased when the temperatures of the two fluidized beds are similar. SPC can be as low as 0.076 kWh/m3 at the oxidation and reduction temperatures of 770 °C, the air flow rate of 50 Nm3/h, and the CO2 flow rate of 23 Nm3/h, which is 18% of the energy requirement of conventional cryogenic air separation system.

Valorization of anaerobic digestion liquid residue through the production of organic fertilizer by fluidized bed granulation

In this work the feasibility of developing a solid fertilizer by fluidized bed granulation, using digestate (liquid residue from anaerobic digestion) as binder and different minerals as seeds is analysed. Full characterization of the selected mineral particles and the liquid digestate was performed. Particularly, phosphorous and potassium content was assayed before and after granulation. Friability and breakage strength of product granules were tested as well. Also, the process operating conditions (bed temperature, fluidization air temperature and flowrate, digestate temperature and flowrate, etc.) that enable stable operation and the production of completely coated granules were successfully established for lab- and pilot-scale granulation units.

Experimental and Numerical Investigations on the Fluidized Heat Absorption inside Quartz Glass and Metal Tubes

Air as a heat transfer fluid has been widely studied in concentrated solar-power generations, but the solar energy absorbed by air inside transparent and opaque tubes has not been comparatively investigated. The heat transfer was studied experimentally and numerically for a fluidized granular bed air receiver with a non-uniform energy flux and the fluidization occurs inside cylindrical metal and quartz glass tubes. The experiments were conducted in a solar simulator with 19 xenon short-arc lamps and showed that the thermal efficiencies in the quartz tube are higher than those in the metal tube. A numerical model was established to study the fluidized heat transport inside the quartz tube, which includes effective thermal conductivities for the conduction, the Syamlal–O’Brien drag model to describe the pressure drop, a modified P-1 model for the radiation, and a two-fluid model (TFM) for gas–solid two-phase flow. The local thermal non-equilibrium model is used to relate the air temperatures to particle temperatures. Comparisons with experimental data show that this model can be used to predict the heat transport inside the quartz glass tube. The maximum relative error was 7.7% when the current is 100 A and the air mass flow rate is 0.53 g/s.

Impact of sodium salts on agglomeration in a laboratory fluidized bed

When using biomass as fuel for power and heat production, compounds in the biomass ash may cause problems for fluidized bed boilers, such as corrosion and agglomeration. Especially high alkali biomass has been shown to cause agglomeration that may lead to defluidization. Many laboratory scale studies have been done to clarify which compounds cause agglomeration and to identify actions to minimize the agglomeration tendency. However, most studies have used fuels or ashes; only a few studies using pure alkali salts can be found. To be able to study the agglomeration mechanisms in more detail, pure alkali salts were fed into a quartz bed as a function of time at different bed temperatures. Each test was terminated either at the point of defluidization or after a certain amount of salt had been fed. Samples of agglomerates and bed material were analyzed by SEM/EDX after the tests. The results showed that Na2CO3 reacted with the bed material to form sodium silicate, while NaCl, as well as Na2SO4, melted and glued the bed particles together. However, when water was added to the fluidization air, NaCl also reacted with the bed material, forming sodium silicate at temperatures above the melting point of NaCl. The amount of melt causing defluidization was calculated (based on analysis) to be around 0.10–0.13 wt% for the melting compounds. Furthermore, the amount of sodium silicate melt that was formed in the tests with Na2CO3 was calculated (based on fed Na2CO3) to be much higher (0.59–0.96 wt%) at defluidization.

A pressure drop model of U-typed reduction chamber for iron ore suspension roasting

A pressure drop model for a U-typed reduction chamber was proposed from the pressure balance law to predict pressure in the bottom of fluidization chamber under its stable operation state. During steady roasting, the feeding particles descend in moving-bed mode in the supply chamber, while the particles move upwards in fluidization mode in the fluidization chamber. A cold test system was established and operated to study the performance of the U-typed reduction chamber using alumina particles with average diameters of 70.77 μm, 101.09 μm and 146.66 μm, respectively. Experiments revealed that the pressure in the bottom part of fluidization chamber decreased with the increased fluidizing air velocity, while increased with the increase of delivery rate. Besides, the particles height of supply chamber would be automatically adjusted according to the system pressure balance. The simulated pressure drop was in good agreement with experimental data giving an average deviation of 7.30%, demonstrating the validity of proposed algebraic model. Therefore, it can be used to predict the pressure in the bottom of fluidization chamber for the U-typed reduction chamber.

Evaluation of new parboiled rice process using humidified hot air fluidized bed drying

This study aims to experimentally investigate the drying characteristics and quality of a paddy dried by hot air (HA) and humidified hot air (HHA) fluidization technique. Qualities such as head rice yield (HRY), white belly, degree of gelatinization (DSG), and color of dried paddy were evaluated. A paddy with an initial moisture content of 14% d.b. was soaked in hot water at a temperature of 70 °C for 5 h then dried at a temperature of 130,150, and 170 °C, relative humidity in the range of 0.3–12%, an air velocity of 3.9 m/s, and a bed height of 10 cm. The results showed that the drying time of the paddy in the HHA condition took longer than the HA drying condition. Because HHA provided a higher grain temperature and a slow rate of drying, the degree of starch gelatinization was significantly higher when compared to HA. The subsequent HRY was relatively higher than using HA drying. However, the color of the sample obtained from the HHA condition was relatively browner, but the parboiled rice product still had a light brown color for the drying temperature range used in this study. To produce parboiled rice, HHA could be operated up to the temperature of 170 °C, relative humidity of 6%, and DOM of 10%.

CHARACTERIZATION OF AN EXPERIMENTAL FACILITY FOR BUBBLING FLUIDIZED BED COMBUSTOR

Fluidized bed technology offers an attractive way for energy production with clean environment by the combustion of even low-grade waste derived fuels (WDF). This paper reports experimental results concerning the characterization of a small-scale bubbling atmospheric fluidized bed combustor with WDF batch feeding. The combustor having 0.215 m inner diameter and 1.88 m height is equipped with a packed-bed sandwich-type fluidizing air distributor. The experimental fluidized bed combustor (EFBC) is provided with facility items necessary for the operation, control, and measurements. Results of the measured fluidized bed pressure drop and temperature were investigated for cold flow, hot flow, and combustion tests during the characterization procedure. The results of these tests clearly indicated the good fluidization characteristics inherent to well-controlled operation of the EFBC facility. The characterization tests also indicated the reproducible and safe operation characteristics of the EFBC facility without appreciable leakage of fluidizing air and exhaust gases. Moreover, the obtained uniformity of the fluidized bed temperature together with the high estimated values of bed-to-immersed cooling coil heat transfer coefficient, added more evidence on the good combustion characteristics of the investigated EFBC facility.

Inline acoustic monitoring to determine fluidized bed performance during pharmaceutical coating

Fluidized beds are used by pharmaceutical manufacturers for multi-particulate drug coating. They provide effective mass and heat transfer; however, unit optimization can be difficult due to the multivariate nature of a fluidized bed system. This research explores the use of passive acoustic emissions monitoring as a method to improve temperature management during pellet coating. A piezoelectric microphone was placed inside the exhaust of a conical top spray fluidized bed. Spherical 1000 μm pellets were coated while recording acoustic emissions. Fluidization air temperature was adjusted between trials as a controlled variable to determine if pellet drying rate could be extracted from the data. During each trial, pellets became damp as the coating solution was applied. Drying stages were used to remove moisture whereby pellet fluidization continued without spraying. The moving standard deviation of the acoustic emissions increased by approximately 40 mV during each 2-min coating stage. The emissions then decreased during drying. This decrease was at a rate proportional to pellet drying independently measured at each controlled temperature. The overall coating-drying emissions profile was similar for trials using either sugar or Acryl-EZE® coating solutions. Passive acoustic emissions monitoring is non-invasive and provides reliable coating and drying information during fluidized bed operation.

Statistic model for predicting cluster movement in circulating fluidized bed (CFB) risers

Abstract This study aims to develop a statistic model which can predict the cluster movement in a circulating fluidized bed (CFB) riser accurately and fast. The statistic model takes the CFD–DEM results as samples to make the statistical analysis of the particle movement in a two dimensional (2D) CFB riser. The model combines a stochastic cluster developing model (SCDM) with a Markov chain model (MCM) of particles. The Markov process of particles, the image recognition of clusters and the stochastic cluster moving and shaping sub-models are introduced in detail. Four representative cases with different fluidized air velocities are simulated using the CFD–DEM and the SCDM–MCM separately. Results show that the computing speed of the SCDM–MCM is approximately 60 times faster than that of the CFD–DEM, and the SCDM–MCM successfully simulates the development and the noticeable rectangular-shaped structures of clusters, which is consistent with the description of the cluster shaping sub-model. Besides, the SCDM–MCM introduces the instantaneous disturbance of clusters to the movement of particles, which is reflected in the good comparison between the SCDM–MCM and the CFD–DEM simulated particle RTDs and particle mixing curves.

Numerical simulation and optimization of hydrodynamics in a novel integral multi-jet spout-fluidized bed

The hydrodynamics in a novel integral multi-jet spout-fluidized bed was simulated using both Eulerian-Eulerian approach and the kinetic theory of granular flows. The effect of side jet number and side jet width on gas-solid two phase flow in the integral multi-jet spout-fluidized bed (IMJSFB) was investigated. The CFD results show that when the number of side jet is greater than 1 (N = 2–5), a wave-like spout and stable spout structure is formed in the IMJSFB. Compared with simulation results in the single nozzle spouted bed, the profiles of particles' velocity and concentration along the radial direction in the IMJSFB become relatively flatter. The integral uniformity of particle velocity distribution in spouted bed can be enhanced by increasing δ/Di. The particle flow factor (η) decreases first and then increases with the increase of δ/Di, and η reaches its minimum value when δ/Di = 0.208. On the whole, there is a set of optimal design parameters of side jet (N = 4, δ/Di = 0.208), at which, the fluidization quality particle phase in spout-fluidized bed reaches the optimum state while the bypass fluidizing air supply auxiliary equipment is omitted. The fluidization quality of particles in annulus can be significantly enhanced in the IMJSFB while the bypass fluidizing air supply auxiliary equipment is omitted.