Effects Of Static Bed Height Research Articles

Adsorption-absorption technique for effective CO2 capture

ABSTRACT This paper presents a study on the removal of CO2 gas from gas mixture (CO2/N2) of 14% CO2 using adsorption onto zeolite 13X in a fluidized bed at 298 K and 1 atm pressure. The effects of static bed height (5–25 cm) and rate of flow of the gas mixture (6–14 L/min) on the breakthrough time were studied. The desorption of CO2 was performed by absorbing the adsorbed CO2 molecules using NaOH solution (0.1 M). The absorption process which was accompanied with chemical reaction achieved two objectives. The first was converting CO2 gas into a valuable substance (Na2CO3) which could be used in many industries. The second was the storage of CO2 gas in what was called a chemical carrier which could emit the gas when it was needed. The effect of static bed height (5–25 cm) on the absorption process in the fluidized bed was also studied. For the adsorption process, the results showed that the breakthrough time increased with decreasing the flow rate but with increasing the static bed height. In the desorption process, the total amount of absorbed CO2 molecules was 396 mg, achieving a recovery of 90.8% at 5 cm static bed height.

An XCT study on three-dimensional characteristics of a spout-fluid bed

Spout-fluid beds are widely used in the chemical and petrochemical industries for excellent mixing and heat and mass transfer properties. Understanding the behavior of jets in spout-fluid beds is crucial for optimizing these processes. In this paper, we present a novel experimental method for studying the three-dimensional characteristics of jets in spout-fluid beds using X-ray computed tomography. By employing a gas–solid flow parameter measurement system, we propose an accurate experimental fitting method for voxel voidage values, enabling the three-dimensional reconstruction of the time-averaged voidage in the entire flow field of a spout-fluid bed. These data are then used to develop an image processing algorithm for identifying and quantifying gas jets in the flow field, allowing for measures of jet length, volume, and diameter. We further investigate the effects of static bed height, spouting gas velocity, and fluidizing gas flowrate on the three-dimensional characteristics of jets.

Oxygen Carrier Circulation Rate for Novel Cold Flow Chemical Looping Reactors

To achieve net-zero emissions by the year 2050, carbon capture, utilization, and storage technologies must be implemented to decarbonize sectors with hard-to-abate emissions. Pressurized chemical looping (PCL) with a novel reactor design called a plug flow with internal recirculation (PFIR) fluidized bed is proposed as an attractive carbon capture technology to decarbonize small- and medium-scale emitters. The objective of this work is to examine the solid circulation rate between redox reactors in a cold flow chemical looping facility using an energy balance approach. The effects of static bed height, weir opening height, purge configuration, and gas flow rate on solid circulation rate were investigated. It was determined that parameters that greatly affected the total gas momentum, such as the fluidization ratio or number of purge rows, tended to also have a large effect on solid circulation rate. Parameters that had a small effect on total gas momentum, such as bed height, did not have a measurable effect on solid circulation rate. It was noted that parameters that posed a restriction to solids flow, such as a vertical purge jet or the weir itself, decreased the solid circulation rate compared to similar tests without restrictions.

Experimental investigation of spout incoherence in a spouted bed

Spout incoherence is a typical instability phenomenon in spouted beds, in which the particles in the spout region move upward as groups, leading to poor spouting stability and efficiency. In this paper, the moving particle blockage in the spout region is measured to quantify the spout incoherence for the first time, by means of depicting the regularity, frequency and particle blockage length of the spout incoherence phenomenon. Specifically, the particle blockage is quantified using the particle concentration obtained by image processing method based on intensity differences between gas and solid phase in the spout centreline. The centreline of the spout channel is located by the particle velocity vector field. The method is validated by visual observation and frequency analysis. Then, the effects of static bed height and spouting velocity on the spout incoherence are investigated, respectively. The results show that the main features of spout incoherence, including frequency, regularity and particle blockage length, remain constant with varying spouting velocity in the investigated range. The results reveal that the static bed height has significant effects on the spout incoherence, and the increasing bed height reduces the frequency and particle blockage length of spout incoherence. This work quantifies the spout incoherence and unveil many interesting mysteries of the spout incoherence in spouted beds.

Investigation of Bubble Behavior in Gas‐Solid Fluidized Beds with Different Gas Distributors

AbstractThe behavior of gas bubbles in a gas‐solid fluidized bed was investigated by computational fluid dynamics simulation. A two‐phase flow model incorporating the kinetic theory of granular flow was used to study the effect of gas distributor design on the size distribution and the rise velocity of gas bubbles in the bed column. The experiments were conducted on four gas distributors with different orifice sizes and pitches. The geometry of the gas distributor had a significant influence on the bubble behavior in the gas‐solid fluidized bed. The effects of static bed height and superficial gas velocity were also considered. Bubble diameter and bubble rise velocity increased with gas velocity. However, at low bed height, the deviation in bubble size was indistinct because at higher gas velocity the rising tendency of the bubble formed just above the gas distributor increased and the probability of bubble coalescence decreased.

Experimental study on fluidization, mixing and separation characteristics of binary mixtures of particles in a cold fluidized bed for biomass fast pyrolysis

To guarantee the uniform mixing of biomass and inert particles in the fluidized bed reactor for the full and complete reaction during the biomass fast pyrolysis process, a visualized cold fluidized bed experimental apparatus was set up to investigate the effects of static bed height, moisture content and particle diameter on the fluidization quality of single component particles, and the mixed volume ratio on the fluidization characteristics of binary mixtures. The results showed that the appropriate static bed height was significant for the stability of the fluidized bed. As the moisture content increased, the minimum fluidization velocity increased rapidly while the fluidization index continued to decrease. In addition, the fluidization performed on binary mixtures of larch/quartz sand-2 indicated that the same minimum fluidization velocity was the key parameter for the two kinds of particles to be fully fluidized simultaneously, avoiding the semi-fluidization phenomenon. The mixed volume ratio of larch (M = 10.3%)/quartz sand-2 and superficial gas velocity range were also the important factors affecting fluidization and mixing quality, and the optimal value were 1: 3 and 3–5 umf, respectively.

Intensification of waste gangue removal from 6–1 mm fine-sized iron ores based on density-based dry vibrated separation and upgrading

Density-based dry separation with a vibrated fluidized bed was performed to investigate the segregation and separation of 6–1 mm fine-sized iron ore through the removal intensification of waste gangue. The 6–3 mm and 3–1 mm iron ore samples were a typical hematite with total Fe-grades of 46.5% and 46.2%, respectively. The effects of static bed height (Hs), vibration amplitude (A), and frequency (f) on the fluidization characteristics of the fine-sized iron ore were experimentally studied. Fluidization tests indicated that the appropriate operational factors of Hs = 80–110 mm, A = 1.5–2.5 mm, and f = 13–17 Hz should be adjusted to ensure fluidization stability. The separation performance of the fine-sized iron ore was studied under various operational conditions. The highest concentrate recoveries were 74.2% and 69.1% under the optimal operational factors for the 6–3 and 3–1 mm iron ore samples, respectively. The actual segregation processes of the iron ore particles obtained using a high-speed dynamic camera validated the separation results. This work aims to provide laboratory-scale experimental results for the discharging intensification of waste gangue from raw fine-sized iron ores using an efficient dry-based separation technology.

Deciphering conical spouted bed hydrodynamics using high intensity microphone

Pressure fluctuations emanating from three dimensional (3D) conical spouted bed using dense zirconia particles (6200 kg/m3) were investigated via high intensity microphone. The effects of static bed height and gas velocity on the spouted bed hydrodynamics were studied. Studies reveal that unprocessed pressure signals are adequate to decipher the various hydrodynamic regimes of the spouted bed. Simple root mean square (RMS) of pressure fluctuation signals can be used to identify the spouted bed hydrodynamic regimes. Pressure fluctuation signals were further analyzed in the frequency domain and the analysis shows drastic lowering of peak intensity of power spectral density at minimum spouting velocity. The differentiating factor of the present study being that the pressure signals exhibit distinctly identifiable general trend associated with various spouted bed regimes and such trend is further confirmed by the frequency analysis. This very feature could be useful tool in fabricating TRISO particles in single batch process. Experimental data on minimum spouting velocity (Ums) was compared with relevant correlations and the results were discussed.

Estimation of Minimum Spouting Velocity in a Rectangular Spouted Bed

A study was conducted to explore the effects of static bed height, nozzle diameter, cone angle, and particle properties on the minimum spouting velocity in a 4 in × 1 in rectangular spouted bed. Tests were conducted with various solids materials (including 871 μm HPDE pellets, 3.2 mm nylon beads, 707 μm glass beads, and 1.5 mm alumina spheres), two gas inlet nozzle diameters, and two cone angles. Experimentally obtained minimum spouting velocities were compared to existing published correlations developed for cylindrical spouted beds. In each case, it was determined that the existing correlations did not adequately predict the minimum spouting velocity for a rectangular spouted bed. A new correlation is proposed.

Study of Pressure Drop in the 2D Spouted Bed with Conical Base of Binary Particle Mixtures: Effects of Particle Size and Density

In this study, the pressure drop for the binary mixtures of particles differing in size and density in a pseudo-2D spouted bed was experimentally studied. A binary mixture of solid particles including sand, Gypsum, and polyurethane was used in the experimental setup. Effects of static bed height, cone angle, particles diameter, and a particles weight fraction on the bed pressure drop were evaluated. The relationship between the peak pressure drops of the binary mixtures to the minimum spouting velocity was discussed. The trend of variation of pressure drop versus superficial gas velocities for binary particle mixtures in the spouted beds was found to be similar with that for the single sized particle system. The particles that sink to the bed bottom are called jetsam, whereas those gathered at the upper section of the bed are called flotsam. At the same air velocity for jetsam and flotsam rich systems, the maximum pressure drop in the jetsam rich system was larger than the flotsam one. The measured values of minimum spouting velocity were compared with some empirical correlations for single sized particles in spouted beds.

Influence of pressure on fluidized bed gasifier: Specific coal throughput and particle behavior

In this work, the influence of pressure on specific coal throughput and particle behavior was investigated. Firstly, mono-gasification of Jincheng anthracite (JCA) and meat and bone meal (MBM) and co-gasification of JCA and MBM were performed in pressurized fluidized bed gasifier pilot plant with a pressure of 0.1–2.6 MPa and a temperature of 900–1050 °C (mono-gasification of MBM at about 750 °C). It was found that the specific coal throughput is approximately directly proportional to the pressure to the power of 0.6–0.75 and co-gasification leads to successful thermochemical conversion of JCA as opposed to mono-gasification. Furthermore, a series of experiments, in a Pseudo-2D cold mode of a pressurized fluidized bed gasifier using an optic fiber probe system, have been performed to investigate the effects of pressure, fluidizing-gas velocity and static bed height on the particle behavior. The bed material used in this study was polystyrene having average diameter of 1.32 mm. It was found that the effect of pressure on vertical local-particle velocities (Vp) at low bed height (LBH) can be ignored at identical excess fluidizing-gas velocity while Vp at high bed height (HBH) decrease slightly with pressure in the lower pressure range (evidently below approximately 1.2 MPa) and increase thereafter. The effects of the fluidizing-gas velocity on Vp at LBH and HBH are also different. However, the effects of static bed height on Vp both at LBH and HBH are the same under pressure.

Influence of inlet air distributor geometry on the fluid dynamics of conical spouted beds: A CFD study

The spouted bed presents limitations in terms of scale-up. Furthermore, its stability depends on its geometry as well as the properties of the fluid and solid phases. CFD provides an important tool to improve understanding of these aspects, enabling a wide range of information to be obtained rapidly and at low cost. In this work, CFD simulation was used to evaluate the effects of different inlet air distributors (Venturi and straight tube) and the effects of static bed height on the fluid and solid dynamics of a conical spouted bed. Simulations were performed using the two-dimensional Euler-Euler approach. In order to evaluate the fluid dynamics model, static pressure data obtained by simulation were compared with experimental data obtained with the Venturi distributor. The fluid and solid dynamics of the conical spouted bed were obtained by CFD simulation. The results showed that the pressure drop was lower for the straight tube air distributor, while the Venturi air distributor provided higher stability and a more homogenous air distribution at the bed entrance.

Beneficiation of coarse particulate iron ore by using a dry density-based fluidized bed separator

A dry density-based fluidized bed separator was used to beneficiate coarse particulate iron ore. The atomized iron powder and zircon sand, with specific size fractions of 150–75 and 250–150μm, were mixed in certain proportion to form a binary dense media. The results indicated that the binary dense media efficiently formed stable fluidization within the fluidized bed for subsequent separation of iron ore particles. The theoretical separation density of 3.5–4.0g/cm3 was determined by investigating the relationships among particle size, density distribution, and total Fe-grade in the iron ore sample. The effects of static bed height, operational gas velocity, and weight proportion of the atomized iron powder in the binary dense media on the stability of bed density were studied to determine the appropriate operational conditions. The stability of bed density was maintained under the condition with a static bed height of 80–90mm, an operational gas velocity of 1.6–2.0Umf, and a weight proportion of the atomized iron powder in the binary dense media of 90%. The effects of static bed height, gas velocity, and size fraction of iron ore particles on the dry separation efficiency were also investigated to determine the optimum separation performance. The optimum total Fe-grade and satisfactory recovery were achieved at appropriate static bed height and gas velocity. The separation efficiency of coarse iron ore particles gradually decreased with decreasing size fraction. This study aims to provide an alternative approach for improving the quality of coarse particulate iron ore.

Novel Concept of Fluidized Bed Reactor Design for Highly Efficient Internal Heat Transfer

A novel double pipe fluidized bed (DPFB) reactor was used in the present study to supply heat energy during fast pyrolysis. The steady state heat transfer model of the DPFB was developed where classical equations of heat transfer inside the fluidized bed and that of wall-to-bed were considered. The sensitivity analysis showed that contact time was a critical parameter to the overall heat transfer coefficient. The model provided good predicting accuracy on temperature calculations by deviating from measured data within +20%. The simulation of DPFB was conducted based on the model and results showed that the heat exchange mainly occurred in the bed phase. Both reducing contact time and increasing Reynolds number would improve heat transfer significantly. The effect of static bed height on outlet temperatures of DPFB could be observed under high inlet temperature difference, which illustrated the importance of the annular fluidized bed in heat transfer enhancement.

The study of solid circulation rate in a compartmented fluidized bed gasifier (CFBG)

Biomass waste has been abundantly available in Malaysia since the booming of palm oil industry. In order to tackle this issue, gasification is seen a promising technology to convert waste into energy. In view of the heat requirement for endothermic gasification reaction as well as the complex design and operation of multiple fluidized beds, compartmented fluidized bed gasifier (CFBG) with the combustor and the gasifier as separate compartments is proposed. As such, solid circulation rate (SCR) is one of the essential parameters for steady gasification and combustion to be realized in their respective compartments. Experimental and numerical studies (CFD) on the effect of static bed height, main bed aeration, riser aeration and v-valve aeration on SCR have been conducted in a cold- flow CFBG model with only river sand as the fluidizing medium. At lower operating range, the numerical simulations under-predict the SCR as compared to that of the experimental results. Also, it predicts slightly different trends over the range. On the other hand, at higher operating range, the numerical simulations are able to capture those trends as observed in the experimental results at the lower operating range. Overall, the numerical results compare reasonably well with that of the experimental works.

Density-based separation performance of a secondary air-distribution fluidized bed separator (SADFBS) for producing ultra-low-ash clean coal

Stable fluidization with consistent flow and a reasonable separating density are keys to the highly efficient separation in a secondary air-distribution fluidized bed separator (SADFBS). In this study, a binary dense medium was formed by mixing fine coal with magnetite powders. The optimum secondary air-distribution layer (SAL) height of 13mm was obtained by verifying the density uniformity of the bed. The suitable static bed height of 60–100mm was determined by comparing the fluctuation of bed pressure drops. In addition, the distribution characteristics of the fine coal particles in various bed layers indicated that the feeding fine coal content should be not more than 10%, which was verified by the bubbling performance in the bed. Box–Behnken Response Surface Methodology (BB-RSM) was employed to evaluate the effects of static bed height (Hs), fluidization number (N), and feeding fine coal content (P) on the combustible material recovery θ of feed coal. Based on the experimental data, a mathematical model was established to describe the relationship between combustible material recovery and the operational factors. The influential degree of various factors on θ was N>Hs>P. The separation results of SADFBS suggested that θ value was maximized when Hs=100mm, N=1.45, and P=4%, which showed a good separation performance. The ash content of clean coal reached the lowest value of 2.65% when Hs=80mm, N=1.70 and P=7%, with a yield of 64.89% and a combustible material recovery of 74.86%. The product is generally considered to be ultra-low-ash clean coal which is the raw materials for activated carbon production.

CFD Simulations of Hydrodynamics of Conical Spouted Bed Nuclear Fuel Coaters

AbstractThe ability of the two fluid method (TFM) to predict the gas‐solid flow phenomenon in conical spouted beds operated with high density (6050 kg m−3) particles simulating the nuclear fuel coating conditions is investigated. The effects of geometric and operational factors, such as conical angle and static bed height, are also assessed. The results show that TFM predicts the time‐averaged bed pressure drop quite well. The qualitative variation of the particle velocity, solids volume fraction, and axial particle flux with axial height are captured by the simulations. The simulated trends observed in the investigation of the effects of static bed height and conical angle on the particle velocity, solids volume fraction, and axial particle flux agree well with those of the experimental measurements.

Development of parallel DEM for the open source code MFIX

Abstract The paper presents the development of a parallel Discrete Element Method (DEM) solver for the open source code, Multiphase Flow with Interphase eXchange (MFIX) based on the domain decomposition method. The performance of the code was evaluated by simulating a bubbling fluidized bed with 2.5 million particles. The DEM solver shows strong scalability up to 256 processors with an efficiency of 81%. Further, to analyze weak scaling, the static height of the fluidized bed was increased to hold 5 and 10 million particles. The results show that global communication cost increases with problem size while the computational cost remains constant. Further, the effects of static bed height on the bubble hydrodynamics and mixing characteristics are analyzed.

Fluidization of micronic particles in a conical fluidized bed: Experimental and numerical study of static bed height effect

AbstractThe numerical simulations and experimental data of bed hydrodynamics in a conical fluidized bed unit are compared. Experimental studies have been carried out in a bed containing TiO2 particles belonging to A/C boundary of Geldart's classification with a wide particle‐size distribution. Thus, pressure measurements and an optical fiber technique allowed determining the effect of static bed height on the fluidization characteristics of micronic particles. Numerical simulations have then been performed to evaluate the sensitivity of gas‐solids drag models. The Eulerian multiphase model has been used with different drag models and three boundary conditions (BC) consisting of no‐slip, partial‐slip, and free‐slip. The numerical predictions using the Gidaspow drag model and partial‐slip BC agreed reasonably well with the experimental bed pressure drop measurements. The simulation results obtained for bed expansion ratio show that the Gidaspow model with the free‐slip BC best fit with the experimental data. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Experimental studies and empirical models for the prediction of bed expansion in gas–solid tapered fluidized beds

Studies in the expansion behaviour of tapered fluidized bed systems are important for specifying the height of the bed. Data have been obtained on the expanded heights of tapered fluidized beds and bed expansion ratios for spherical and non-spherical particles have been calculated. Based on dimensional analysis, models have been developed as a function of geometry of tapered bed, static bed height, particle diameter, density of solid and gas and superficial velocity of the fluidizing medium. The data used to derive the models cover a wide range of operating conditions, with varying fluidization velocities. Effects of static bed height, particle diameter, density, tapered angle and superficial gas velocity over minimum fluidization velocity on bed expansion ratios have been investigated experimentally. A comparison has been made between the calculated values of bed expansion ratios using proposed models and the experimental data. It has been seen that calculated values by models agree well with the experimental values. Models have also been compared with literature data of conventional bed and found its applicability at higher gas velocities with good accuracy.