Attrition rate of CO2 adsorbent in bubbling fluidized beds

Particle attrition induced by bubbles in a bubbling fluidized bed was investigated with CO₂ adsorbent particles (0.128 mm in diameter, 1770 kg/m³ in apparent density). The theoretical relationship between the rate of attrition by gas jets on the perforated plate distributor (R_a,j) and the rate of attrition by bubbles (R_a,b) in the bed was revealed that the rate constant of attrition by bubbles (K_a,b) was the product of the rate constant of attrition by gas jets (C_a) and dimensionless particle diameter (d_pbc). An attrition tube (0.035 m-i.d.) using the perforated-plate distributor designed for reducing the attrition by gas jets was employed as the fluidized bed, and the air as the fluidizing gas. The mode of attrition by bubbles was identified as abrasion. The rate of attrition by bubbles (R_a,b) was linearly proportional to the power given to the bed solids by bubbles. The top size of the fine particles formed by attrition (d_pm,ab) increased exponentially with an increase of bed mass and gas velocity. The effects of temperature, pressure, and area of internal surface contacting particle bed on the R_a,b and d_pm,ab were negligible under the tested condition. Empirical relationships on R_a,b and d_pm,ab were proposed based on the experimental data. When both jet and bubble attrition were significant, there existed the static bed heights that gave respectively the minimum attrition rate and the minimum of the top size of fine particles formed by attrition. Each optimal static bed heights increased with an increase of the orifice jet velocity of the perforated plate distributor.     

气体分布板开孔结构对流化干燥滞留率的影响

滞留率是确定流化干燥死床点的重要参数。针对气体分布板开直孔和开斜孔的惰性粒子流化床干燥器，以洗衣粉悬浮液为对象，考查了进料量、惰性粒子直径、进风温度、静床高、进风速度以及物料初始浓度对干燥器滞留率的影响，分析了气体分布板开直孔和开斜孔时干燥器滞留率的大小，并以气体分布板开斜孔为例，测定了干燥器的生产能力与板开孔率之间的关系曲线。结果表明，滞留率随进料量和物料初始浓度的提高而增大，随惰性粒子直径、进风温度、静床高和进风速度的提高而减小；若将气体分布板的孔道由直孔改为斜孔，并在此基础上适当增加板的开孔率，可有效降低干燥器的滞留率，提高干燥器的生产能力。     

Magnetite particle surface attrition model in dense phase gas–solid fluidized bed for dry coal beneficiation

Dense-phase high-density fluidized bed has received considerable attention worldwide due to the urgent need for an efficient dry separation technology. This study on magnetite particle attrition model and size distribution change rule in a dense-phase gas–solid fluidized bed for dry beneficiation analyzes the complex process of magnetite particle attrition and fine particle generation. A model of magnetite particle attrition rate is established, with the particle attrition rate leveling off gradually with the attrition time in the dense-phase gas–solid fluidized bed. Magnetite particle attrition in the dense-phase gas–solid fluidized bed is consistent with Rittinger’s surface theory, where the change in surface area of magnetite particles is proportional to the total excess kinetic energy consumed and the total attrition time. An attrition experiment of magnetite particles is conducted in a laboratory-scale dense-phase gas–solid fluidized bed for dry beneficiation.     

Bed pressure drop of a bubbling fluidized-bed with overflow solid discharge

The pressure drop of a bubbling fluidized-bed that employed an in-bed inlet and an overflow outlet for continuous flow of solid particles was investigated with variation in the particle size and density, the solid flow rate and the gas velocity. The bed pressure drop decreased with increasing the gas velocity, but increased with the solid flow rate. The characteristics in lifting the solid particles vertically to the level of the overflow outlet by bubbles appeared different from the ones of particle entrainment and bed expansion. Regardless of size and density of particles, bed height in minimum fluidizing condition (pressure head by solid bed weight, H_mf,f) decreased with increasing the volume flow rate of bubble but increased with the mass flow rate of solid particles. The nominal vertical height from H_mf,f to the level of the overflow outlet that the particles should overcome in the course of discharging out of the fluidized-bed with the aid of bubbles increased as either the volume flow rate of bubble increased or the mass flow rate of solid particles decreased. The power consumed while bubbles lifted particles to be discharged appeared to be same at the fixed volume flow rate of bubble. A correlation was proposed successful even for predicting the bed pressure drop of the recycle chamber of the loop seal and the external solid circulation rate in the circulating fluidized-bed system.     

Sulfation and attrition of calcium sorbent in a bubbling fluidized bed

A bubbling fluidized bed reactor was used as a desulfurization apparatus in this study. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. The effects of the operating parameters of the flue gas desulfurization including relative humidity, temperature, superficial gas velocity, and the particle size of calcium sorbent on SO₂ removal efficiency and calcium sorbent conversion and attrition rate in the fluidized bed were investigated. It was found that the temperature effect in our system was negligible from 40 to 65°C. A higher relative humidity had a higher calcium conversion and a higher sulfur dioxide removal efficiency. Moreover, a smaller particle size of calcium sorbent had a lower calcium conversion in the cyclone but a higher sulfur dioxide removal efficiency. A lower superficial gas velocity resulted in a higher sulfur dioxide removal efficiency and a higher calcium conversion, thus, the total volume of the flue gas treated was maximum near the minimum fluidization velocity. Finally, an attrition rate model proposed in this study could predict the elutriation rate satisfactorily.     

The Unique Phase Doppler Particle Analyzer Application and Analysis of Solid Particle Flow in the Fluidized Bed Combustor (FBC) Cold Model

The hydrodynamic effects of varying operating parameters in the fluidized bed combustor (FBC) have been of great interest to the FBC design and manufacturing process. Some experiments to investigate the gas/particle flows in the gaseous fluidized bed were performed with the laser-based phase Doppler particle analyzer (PDPA). In the experiments, the PDPA was used to measure the vertical component of fluidizing particle velocity at one specific position point. The robust experimental design method was used to evaluate the experimental conditions and to analyze the experimental results. An empirical model for the particle velocity vertical component V_y with particle size (S) and fluidizing airflow rate (R) as variables was developed for the FBC cold model. From the model, it was found that vertical component V_y has a strong linear relationship with the fluidizing airflow rate (R), while particle size (S) has less linear relationship to V_y. It can also be seen that V_y increased when fluidizing airflow rate increased and V_y decreased when particle size increased.     

Bed expansion and fluctuation in cylindrical gas solid fluidized beds with stirred promoters

A profound and fundamental understanding of bed dynamics such as bed expansion ratio and bed fluctuation ratio of irregular particles of binary mixtures has been made in a cylindrical fluidized column for gas solid systems, resulting in a predictive model for fluidized beds. In the present work attempt has been made to study the effect of various system parameters (viz. rotational speed of the promoter, initial static bed height, superficial velocity of the fluidizing medium, particle size and density) on the bed dynamics through experimentation. The correlations for the bed dynamics have been developed on the basis of dimensional analysis. It was observed that the calculated values of bed dynamics agree well with the experimental values in most of the cases.     

Experimental study on fluidization characteristics of different-sized particles in a U-type reduction chamber

A novel fluidized bed reactor, which is an improvement of the loop seal, was applied successfully to iron ore reduction roasting. For this U-type reduction chamber, the fluid dynamic behaviors of different-sized particles were investigated via a cold experimental apparatus using the pressure measurement method in this study. The results showed that the measured U_mf of 71, 101 and 147 μm-sized particles were 0.033, 0.040 and 0.059 m/s, while the U_c were 0.167, 0.190 and 0.223 m/s, respectively, demonstrating that the decrease of particle size caused a rapid transition from both the fixed to bubbling regime, and the bubbling to turbulent flow regime. Under stable operation, the pressure drop, average solids holdup and axial nonuniformity index across the FC increased when particle size increased, along with the solids height and pressure drop gradient in the SC, though the differential pressure fluctuation decreased. These consequences indicated that larger particle size promotes the opportunity for particle mixing and contacting, accordingly increasing the preferential formation of the particle aggregation and deteriorating the reduction performance. These can provide guidelines for the regulation and control of industrial iron ore fluidized bed roasting.     

气体分布板开孔结构对流化床干燥性能的影响

针对惰性粒子流化床干燥器，以洗衣粉悬浮液为对象，先后进行了气体分布板开直孔和开斜孔的流化干燥实验。通过测定干燥器的流体力学特性曲线，以及在相同进料量、进风温度、进风速度或惰性粒子直径条件下的体积传热系数曲线和热效率曲线，考察和分析了气体分布板两种不同的开孔结构对干燥器流体力学和传热性能的影响。结果表明，气体分布板开斜孔的床内气流阻力要高于开直孔的气流阻力，但其体积传热系数和热效率相对较高，即斜孔较直孔更加有利于床内传热。在此基础上，对惰性粒子流化床干燥器的生产调节措施进行了初步探讨。     

Modelling the transport disengagement height in fluidized beds

Bubbles bursting at the surface of a bubbling gas fluidized bed (BFB) project particles into the freeboard. Coarser particles fall back, the solids loading declines with height in the freeboard, and fines are ultimately carried over. The height of declining solids loading is the transport disengagement height (TDH), measured in this research by positron emission particle tracking, and modelled from a balance of forces on ejected particles. Model predictions and PEPT-data are in good agreement. Almost all of the empirical equations overestimate the TDH.     

Effect of level of overflow solid outlet on pressure drop of a bubbling fluidized-bed

The effect of level of the overflow outlet for continuous flow of solid particles on the pressure drop of a bubbling fluidized-bed that employed an in-bed inlet for solid feed was investigated with changing solid properties, solid feed rate, gas velocity, and level of the overflow outlet. The pressure drop of fluidized-bed (Δp_bed,f) decreased with increasing gas velocity, but increased with either solid feed rate or level of the overflow solid outlet (L). The Δp_bed,f/L increased with L. Irrespective of particle size and density, bed height converted for minimum fluidization condition (pressure head by bed weight, H_mf,f) decreased with increasing the volume flow rate of bubble but increased with either the solid feed rate or the level of the overflow solid outlet. The nominal vertical height, height between the H_mf,f and the level of the overflow outlet, that bubbles transported particles while drawing the solid particles out of the fluidized-bed increased as either the volume flow rate of bubble or level of the overflow outlet increased. However, it decreased as the solid feed rate increased. It appeared that the power of bubble for lifting solid to be discharged through the overflow outlet was same at the fixed volume flow rate of bubble, solid feed rate, and level of the overflow solid exit. The power of bubble increased with the level of the overflow outlet but not linearly. The correlation proposed for the pressure drop across the bubbling fluidized-bed was useful to predict the pressure drop across the recycle chamber of the loop seal and the external solid circulation rate in the circulating fluidized-bed system.     

Experimental and theoretical study on hydrodynamic characteristics of tapered fluidized beds

A novel fluidized bed ash cooler was developed for circulating fluidized bed boilers based on a proposed modified tapered fluidized bed. A cold model was built to study the hydrodynamic characteristics of the modified tapered fluidized bed, and its critical superficial gas velocity u_mf and critical velocity for full fluidization u_mff were particularly studied. The effects of taper angle α, static bed height H, air inlet section width δ and particle size d_p on the u_mf and u_mff were experimentally investigated. Furthermore, a theoretical model and an empirical correlation have been proposed to predict the u_mf and u_mff, respectively. The predicting capabilities of the model and correlation have been experimentally discussed. And the predicting capability of the model has also been compared with that of an existing representative model. It is found that both the u_mf and u_mff increase with the increase of taper angle α, static bed height H and particle size d_p, but decrease with the increase of air inlet section width δ, respectively. Additionally, the predicted values of u_mf and u_mff compare well with the experimental data, and the model has a better capability than the existing representative model in predicting the u_mf of the modified bed.     

Heat transfer and the combustion temperature of coke particles in a fluidized bed

The temperature of carbon particles undergoing combustion in a fluidized bed is measured. Heat-transfer laws are ascertained.Notation a diffusivity of air - c heat capacity of air - D diffusion coefficient of oxygen in air - d₀, d initial and running diameters of carbon sphere - d_i diameter of inert particles - k rate constant for carbon monoxide combustion - q calorific value of carbon oxidation to CO₂ - T temperature difference between burning particle and fluidized bed - X, X_n oxygen concentration in the fluidized bed and on the surface of the burning particle - Z, Z_n running concentration of carbon monoxide and concentration on the surface of the burning particle - heat-transfer coefficient between fluidized bed and burning particle - _m maximum heat-transfer coefficient between fluidized bed and a stationary body submerged in the bed - masstransfer coefficient between fluidized bed and burning particle - thermal conductivity of air - kinematic viscosity of air - ₀, gr, ₄ density of oxygen, air, and inert material - relative thickness of burning gas layer - relative thickness of diffusion boundary layer Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 21–27, January, 1982.     

Gas flow influences on bubbling and flow characteristics of fluidized bed with immersed tube under electrostatic effects

Industrial bubbling fluidized beds are used to fluidize particles. When particles are fluidized, electrostatic effects will cause the particles to form obvious agglomerates, thus reducing fluidization performance. For better fluidization performance, internal component immersed tubes are usually placed in fluidized bed to limit the bubble size and reduce particle agglomerates. Meanwhile, pulsed gas flow can increase particle disturbance, which is also an effective method to reduce particle agglomerates. In this paper, the CFD-DEM model under electrostatic effects is constructed to research the bubbling and flow characteristics in fluidized beds. Firstly, particle mixing qualities with and without the immersed tube are compared. Then, the effects of different superficial gas velocities are investigated with an immersed tube. Finally, different frequencies are applied to study the energy loss and flow characteristics around the immersed tube. The results show that the addition of the immersed tube can reduce bubble size to facilitate particle mixing. Due to the obstruction of the immersed tube, the bubbles are generated near the wall. As the superficial gas velocity increases, the larger bubbles are generated. Moreover, the electrostatic force applied to the particles varies periodically with the frequency of incoming pulsed gas flow, with fluctuations maximal at 2.5 Hz.     

FLUIDIZATION BEHAVIOR OF STICKY PARTICLES

To obtain fundamental Information on the fluidization behavior of sticky particles, a visually observable fluidized bed, which can be operated under conditions in which agglomeration of the bed materials occurs, was designed and constructed. Polyethylene particles with a softening temperature of 117.2^°C and melting temperature of 124.4^°C, in sizes from 850 to 50 μm, were chosen as the bed material. Two types of fluidizing gas distributors were used: a porous plate and a porous plate with an independently fed jet at the center. The agglomeration rate was measured at different jet and bed temperatures, particle sizes, and residence times in the fluidized bed.

The amount of agglomerates generated increased linearly with residence time and increased exponentially with either auxiliary air or jet air temperature. The agglomerates were formed from the whole range of particle sizes, but fine particles enhanced the agglomeration rate. A set of operating conditions must be properly chosen; otherwise, excessive agglomeration can lead to catastrophic sintering and defluidization.     

A model on desulfurization characteristics of an entrained bed-bubbling bed hot gas cleanup system for IGCC

A mathematical model has been developed to predict performance of a continuous entrained-bed and bubbling fluidized-bed hot gas desulfurization system in IGCC. The model combines the particle residence time with the kinetic rate in each reactor. The model has been applied to the KIER’s laboratory scale fluidized bed process. The present model provided a reasonable fit in predicting experimental results that the outlet concentration of H₂S from the desulfurizer and SO₂ from the regenerator increased nearly proportionally to the inlet concentration of H₂S to the desulfurizer. The model also could predict well the outlet concentration of O₂ from the regenerator to decrease as the inlet concentration of H₂S to the desulfurizer increased. The present model predicted with reasonable accuracy mean diameter of bed particles and sulfur content of particles in desulfurizer and regenerator.     

The Unique Phase Doppler Particle Analyzer Application and Analysis of Solid Particle Flow in the Fluidized Bed Combustor (FBC) Cold Model

The hydrodynamic effects of varying operating parameters in the fluidized bed combustor (FBC) have been of great interest to the FBC design and manufacturing process. Some experiments to investigate the gas/particle flows in the gaseous fluidized bed were performed with the laser-based phase Doppler particle analyzer (PDPA). In the experiments, the PDPA was used to measure the vertical component of fluidizing particle velocity at one specific position point. The robust experimental design method was used to evaluate the experimental conditions and to analyze the experimental results. An empirical model for the particle velocity vertical component V_y with particle size (S) and fluidizing airflow rate (R) as variables was developed for the FBC cold model. From the model, it was found that vertical component V_y has a strong linear relationship with the fluidizing airflow rate (R), while particle size (S) has less linear relationship to V_y. It can also be seen that V_y increased when fluidizing airflow rate increased and V_y decreased when particle size increased.     

Fluidization behavior of glass beads under different vibration modules

The expansion of free bubbling gas fluidized beds has been investigated experimentally in a two-dimensional perspex-walled bed. Glass beads were fluidized with dried air at varying gas velocities, while the bed was vibrated at different frequencies, amplitudes and directions to study their effects on the fluidization quality. The experimental results showed that the particle flow pattern depends on the vibration direction, especially at superficial gas velocities less than the minimum fluidization velocity U_mf. The effect of horizontal vibration on fluidization behavior of glass beads exists at superficial gas velocities less than U_mf, while the effect of vertical vibration on fluidization behavior still exists even at higher superficial gas velocities than U_mf.     

The impact of vertical internals array on the key hydrodynamic parameters in a gas-solid fluidized bed using an advance optical fiber probe

The effect of a circular configuration of intense vertical immersed tubes on the hydrodynamic parameters has been investigated in a gas-solid fluidized bed of 0.14?m inside diameter. The experiments were performed using glass beads solid particles of 365?μm average particle size, with a solid density of 2500?kg/m³ (Geldart B). An advanced optical fiber probe technique was used to study the behavior of six essential local hydrodynamic parameters (i.e., local solids holdup, particles velocity, bubble rise velocity, bubble frequency, and bubble mean chord length) in the presence of vertical immersed tubes. The experimental measurements were carried out at six radial positions and three axial heights, which represent the three key zones of the bed: near the distributor plate, the middle of the fluidizing bed, and near the freeboard of the column. Furthermore, four superficial gas velocities (u/u_mf?=?1.6, 1.76, 1.96, and 2.14) were employed to study the effect of operating conditions. The experimental results demonstrated that the vertical internals had a significant effect on all the studied local hydrodynamic characteristics such that when using internals, both the solids holdup and bubble mean chord length decreased, while the particles velocity, bubble rise velocity, and bubble frequency increased. The measured values of averaged bubble rise velocities and averaged bubble chord lengths at different axial heights and superficial gas velocities have been compared with most used correlations available in the literature. It was found that the measured values are in good agreement with values calculated using predicted correlation for the case without vertical internals. While, the absolute percentage relative error between the measured and calculated values of these two hydrodynamic parameters indicate large differences for the case of vertical internals.     

A study of gas and solid mixing behaviors in a three partitioned fluidized bed

A previously unknown partitioned fluidized bed gasifier (PtFBG) has been developed for improving coal gasification performance. The basic concept of the PtFBG is a fluidized bed divided into two parts, a gasifier and a combustor, by a partitioned wall. Char is burnt in the combustor and the generated heat is supplied to the gasifier along with the bed materials. During that time, highly concentrated CO₂ is inevitably generated in the combustor. Therefore, vigorous solid mixing is an essential precondition as well as minimizing horizontal gas mixing. In this study, gas and solid mixing behaviors were verified in a cold model three partitioned fluidized bed (3-PtFB). Glass beads with an average diameter of 150 μm and a particle density of 2500 kg/m³ were used as bed materials. For the gas mixing experiments, CO₂ and N₂ were introduced into the beds through each distributor. Then, outlet gas flow rates and concentrations were measured by gas flow meters and an IR gas analyzer respectively. The calculated gas exchange ratios ranged from 3% to 10% with varying gas flow rates. For the solid mixing experiments, 1000 μm polypropylene particles with a density of 883 kg/m³ were continuously fed into the reactor. Then, the polypropylene particles were distributed to the entire beds evenly. Solid mixing behaviors were very analogous to liquid mixing behaviors in a continuous stirred tank reactor (CSTR).