共查询到20条相似文献,搜索用时 15 毫秒
1.
Jin Hee Jeon Sang Done Kim Seung Jae Kim Yong Kang 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2351-2360
The effects of gas velocities to draft tube (26.64–52.54 cm/s) and to annulus section (8.14–11.84 cm/s) on solid circulation rate and gas bypassing fractions were determined in a square internally circulating fluidized bed reactor with an orifice-type square draft tube. The solid circulation rate and gas bypassing fraction from the annulus section to the draft tube increase but gas bypassing fraction from the draft tube to the annulus section decreases with increasing gas velocity to the draft tube. With increasing gas velocity to the annulus section, the solid circulation rate and gas bypassing fraction from the draft tube to the annulus section increase but, gas bypassing fraction from the annulus section to the draft tube decreases. The solids circulation rate was correlated with the pressure drop across the orifice and the opening area ratio based on the orifice theory. The gas bypassing fraction was correlated with gas velocities to the fluidized and the moving beds. Based on the gas bypassing fraction data, the gas flow rates across the orifice were correlated with gas velocities to the fluidized and the moving beds, opening area ratio, particle size and solids height in the bed. 相似文献
2.
Hong-Sik Ahn Woon-Jae Lee Sang-Done KimDg Byung-Ho Song 《Korean Journal of Chemical Engineering》1999,16(5):618-623
The effects of orifice diameter in the draft tube, particle size, gas velocities and bed height on the circulation rate of
solids and gas bypassing between the draft tube and annulus have been determined in an internally circulating fluidized bed
(i.d., 0.3 m ; height, 2.5 m) with an orifice-type draft tube. A conical shape gas separator has been employed above the draft
tube to facilitate the separation of gases from the two beds. The circulation rate of solids and the quantity of gas bypass
from the annulus to draft tube show their minimums when the static bed height is around the bottom of the separator. The circulation
rate of solids increases with an increase in orifice diameter in the draft tube. At fixed aeration to the annulus, gas bypassing
from the draft tube to annulus sections decreases, whereas reverse gas bypassing from the annulus to the draft tube increases
with increasing the inlet gas velocity to the draft tube. The obtained solids circulation rate has been correlated by a relationship
developed for the cocurrent flow of gas and solid through the orifice. 相似文献
3.
Chen Yeon Chu 《Powder Technology》2005,154(1):14-23
An internally circulating fluidized bed reactor (ICFBR) 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, particle size of the calcium sorbent, inlet concentration of SO2, difference between the superficial gas velocities in the draft tube and the annulus, and superficial gas velocity in the draft tube on SO2 removal efficiency (RE) were investigated. It was found that when the relative humidity (RH) was varied from 40% to 80%, the steady state RE had a largest value of approximately 15% when the relative humidity was 60%. When RH = 50%, 60% and 70%, RE decreased initially and then increased. After that RE decreased again until a steady state was reached. In addition, RE decreased with increasing calcium particle size or inlet SO2 concentration. A larger difference between the superficial gas velocities in the draft tube and the annulus had a higher RE resulting from increasing reactivity of the calcium sorbent caused by a higher attrition rate. Moreover, a higher attrition rate had a higher total volume of the flue gas treated. Finally, a model to predict the steady state RE in ICFBR was proposed. It assumed that the draft tube section was a bubbling fluidized bed while the annulus section was a moving bed. In addition, the effects of the calcium sorbent conversion, attrition rate and gas-bypassing fractions on RE were also taken into account in this model. It was found that the values of RE predicted by this model agreed with the experimental results. 相似文献
4.
Woon-Jae Lee Yong-Jun Cho Jung-Rae Kim Sang Done Kim 《Korean Journal of Chemical Engineering》1992,9(4):206-211
The effects of gas velocity to draft tube (3–6 Um), bed temperature (800–900°C) and excess air ratio (0–30%) on the total entrainment rate, overall combustion efficiency and heat transfer coefficient have been determined in an internally circulating fluidized bed combustor with a draft tube. The total entrainment rate increases with an increase in gas velocity to draft tube, but decreases with increasing bed temperature and excess air ratio. The overall combustion efficiency increases with increasing excess air ratio, but decreases with increasing gas velocity to draft tube. The overall combustion efficiency obtained in internally circulating fluidized beds was found to be somewhat higher than that in a bubbling fluidized bed combustor. 相似文献
5.
The liquid dispersion and bubble distribution in the radial direction have been investigated in the riser of a three‐phase circulating fluidized bed whose diameter is 0.102m and 3.5m in height. Effects of gas and liquid velocities and solid circulation rate have been determined. It has been found that the radial distribution of bubbles is related closely to the liquid dispersion in the radial direction. The size and rising velocity of bubbles tend to increase as the radial position approaches to the center of the riser. The bubble size increases with increasing UG, but it decreases with increasing UL or GS in all radial positions. The radial dispersion coefficient of the liquid phase increases with increasing UG or GS, however, it tends to decrease with increasing UL. The value of Dr has been well correlated in terms of dimensionless groups based on the isotropic turbulence model. 相似文献
6.
针对开发适用于化学气相沉积反应动力学研究的微型流化床反应分析仪的应用需求,研究了外径为30 mm的内循环微型流化床中气固流动特性,具体考察了中心射流管伸入高度、内导流管直径和颗粒装载量对实现固体物料内循环的最小操作气速和导流管与环隙区间窜气的影响。结果表明,随着射流管伸入高度的增大,实现颗粒内循环流动的最小操作气速变大;存在最优的导流管直径(20 mm),使得实现颗粒环流的最小操作气速较小;增大颗粒装载量有利于降低颗粒内循环的最小操作气速。通过检测示踪气体在环隙区内的质谱信号,发现在所考察的参数范围内,反应器底部不存在导流管区向环隙区的窜气;在反应器上部,由于颗粒对气体的夹带,环隙区上部总能检测到示踪气体,且窜气特性随操作气速的增大而增强。研究结果可为设计适用于化学气相沉积反应的内循环微型流化床反应器提供参考。 相似文献
7.
Numerical Simulations of Solid Circulation Characteristics in an Internally Circulating Elevated Fluidized Bed
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Muhammad Hassan M. Philip Schwarz Muhammad Rafique Yuqing Feng Guodong Liu Peter J. Witt Shuai Wang Huilin Lu 《化学工程与技术》2017,40(4):769-777
A twin‐chamber internally circulating elevated fluidized bed (EFB) with one chamber elevated higher than the other within a single vessel is simulated using a two‐fluid model. Two EFB configurations termed as reaction chamber (RC)‐elevated and heat exchange chamber (HEC)‐elevated is evaluated. The effect of chamber elevation, variation of superficial velocities, and interchanging the two chambers are investigated and the results are quantified in terms of solid flux Gs. By increasing the RC gas velocity UR at constant HEC velocity UH, Gs is increased in both EFBs while an opposite behavior is observed by increasing UH at constant UR. Variation of the chamber elevation as well as interchanging the chambers also affects the performance of the two EFBs. 相似文献
8.
Based on the combustion characteristics of petroleum coke, a coupled gas-solid fluidized bed combustor is proposed in this work. The overall circulating system of the fluidized bed mainly consists of a dense-phase airlift loop section and a dilute-phase riser section. In different operating conditions, the particle flow behaviors in the airlift loop section were investigated systematically by using optical fiber probe. The experimental results show that the airlift loop section can be divided into four regions, namely, the draft tube, the annulus, the bottom region and the particle diffluence region, in which the average cross-sectional solids fraction and the particle velocity are different. The overall solids fraction difference between the draft tube and the annulus provides a driving force for particle circulation flow in the airlift loop section, and the driving force increases with increasing the superficial gas velocity in the draft tube. The ratio of the particle mass flux in the annulus to that in the riser ranges from 8 to 16. The particle circular velocity in the annulus also increases with increasing the superficial gas velocity in the draft tube. Moreover, a model about the particle circular velocity is established on the basis of energy equilibrium principle. 相似文献
9.
Jin Hwan Bang Yong Jeon Kim Won Namkung Sang Done Kim 《Korean Journal of Chemical Engineering》1999,16(5):624-629
In a downer reactor (0.1 m-I.D.x3.5 m-high), the effects of gas velocity (1.6-4.5 m/s), solids circulation rate (0–40kg/m2s) and particle size (84, 164 Μm) on the gas mixing coefficient have been determined. The radial dispersion coefficient(D
r
) decreases and the radial Peclet number (Per) increases as gas velocity increases. At lower gas velocities, Dr in the bed of particles is lower than that of gas flow only, but the reverse trend is observed at higher gas velocities.
Gas mixing in the reactor of smaller particle size varies significantly with gas velocity, whereas gas mixing varies smoothly
in the reactor of larger particle size. At lower gas velocities, Dr increases with increasing solids circulation rate (Gs), however, Dr decreases with increasing Gs at higher gas velocities. Based on the obtained Dr values, the downer reactor is found to be a good gas-solids contacting reactor having good radial gas mixing. 相似文献
10.
A cylindrical gas-liquid-solid spouted bed, driven exclusively by gas flow, has been developed with a high potential for use in biochemical processes, such as a biological wastewater treatment. A plexiglass column with a 152 mm inner diameter was used in combination with a 53 mm inner diameter plexiglass draft tube. Three particle types were studied with densities ranging from 1044 kg/m3-1485 kg/m3 and average particle sizes ranging from 0.7-2.5 mm. Four flow regimes were observed when increasing the gas velocity, including fixed bed, semispouted bed, full spouted bed, and internal circulating fluidized bed. The transition gas velocities between those regimes were experimentally measured and termed as minimum spouting velocity, full spouting velocity, and minimum circulating velocity, respectively. A measurement of the downward particle flux in the annulus was used to identify the minimum spouting velocity, while the particle velocity and dense phase retraction in the annulus were monitored for the full spouting and minimum circulating velocities. All regime transition velocities increased with more dense particles and longer draft tubes. The minimum spouting velocity and full spouting velocity were not affected when varying the nozzle-tube gap, while the minimum circulating velocity increased with longer nozzle-tube gaps. Experiments without a draft tube were carried, though the spouting stability was significantly reduced without the draft tube. 相似文献
11.
Young Hean Choung Ki Chul Cho Won Joon Choi Soo Gon Kim Young Suk Han Kwang Joong Oh 《Korean Journal of Chemical Engineering》2007,24(4):660-663
Fluidized bed pyrolysis has been recognized as an innovative technology for sewage sludge treatment. The physical and attrition
properties of sewage sludge are changed through the fluidized bed pyrolysis. The minimum fluidization velocities and attribution
rate constants for sewage sludge and sludge based-char were obtained from pressure drop and attribution tests. As a result,
sewage sludge with 20% moisture content and char were classified as Geldart B solids and the superficial gas velocity for
bubbling fluidization was 0.2142-0.8755 m/s. In addition, attribution of the sewage sludge and char was more affected by particle
size than by material type. The equations for the overall attrition rate constants are K
a
× 105 = 1.09U − 14.82 for sludge and ln k
a
= 0.1(U−U
mf
)− 13.63 for char, respectively. 相似文献
12.
Results of an experimental study on the aerodynamics of a vertically vibrated fluidized bed of cross-section 0.2 × 0.2 m are presented and discussed. Variables studied included frequency (0-105 s?1), amplitude (0-5xl0?3 m), bed height (12.5-100×10?3 m), particle size (900-3900 μm), particle density (570-890 kgm?3), particle shape factor (0.55-1.00) and the particle surface characteristics, i.e. presence of surface moisture. The effect of vibrational parameters on the fluidized bed pressure drop, the newly defined minimum mixing velocity, Umm and overall aerodynamic behaviour of the bed is discussed on the basis of quantitative as well as visual observations. Empirical correlations are proposed for δPmf and Umm, which were both found to decrease significantly with increase in the vibrational acceleration. 相似文献
13.
A spout‐fluid bed with draft tube submerged in a bed of polypropylene beads was used for drying maltodextrin solutions. The hydrodynamics of the dryer were studied by determining the annular air flow vertical profile at different spouting velocities, using an additional air flow rate through the annulus equivalent to 0.5 Umf. The drying performance of the dryer was studied through the determination of several dryer response parameters (product moisture, evaporative capacity and volumetric evaporative capacity). These parameters were compared with those obtained in a conventional spouted bed with inert solids and a spray dryer. 相似文献
14.
The effects of ratio of draft tube to reactor diameter (Dd/D), liquid nozzle diameter (dN), aeration tube diameter (dG) and immersion height of the two-fluid nozzle into the draft tube (HN) on overall and annulus gas holdups for the air-water system were evaluated experimentally in a reversed flow jet loop reactor over wide ranges of gas and liquid flow rates. Both the gas holdups increased with increasing gas and liquid flow rates and with decreasing dN and HN. The influence of dG on gas holdups is found to vary with gas flow rates. Correlations are proposed to predict gas holdups. 相似文献
15.
In order to investigate the suspension behaviour of solid particles in bubble columns without and with draft tube, minimum gas velocities for generating and maintaining complete solid suspension were determined. Experiments were carried out in a bubble column with a diameter of 200 mm and a height of 2 500 mm. The bubble column could be equipped with a draft tube with a diameter of 120 mm and a length of 1 500 mm. The state of suspension was determined by measuring the hydrostatic pressure as a result of suspended solid particles with an inductive pressure gauge. Solid content εs, solid density ?s, particle size dp, particle shape, particle size distribution, and solid wettability were varied. Furthermore measurements of integral gas holdup were carried out. 相似文献
16.
Several fractions of a silica—alumina catalyst and an impregnated catalyst were fluidized with air to check published bubble point correlations and to determine the expansion of the dense phase in the bubbling region. The minimum bubbling velocities were fairly close to those reported by Geldart and others, but Umb varied with only the 0.6 power of the particle size. The dense phase expansion was significant even at velocities much above Umb and corresponded to relative velocities up to 2 – 3 times Umf. 相似文献
17.
The effects of the Uo, PA/[PA+SA] ratio, total solid inventory and fluidizing velocity of loopseal on the axial solid holdup and the solid circulation
rate have been determined with different particle sizes (174, 199, 281, 377 μm) and particle types (silica sand: narrow PSD,
coal ash: wide PSD) in a CFB reactor with 3-loops. A simple model for solid hold-up based on the previous works was in agreement
with the experimental data. With increasing Uo, Gs increased exponentially, and in the center-loop, Gs was 1.5 times larger than that found in the other side-loops. As the PA/[PA+SA] ratio increased, and as SA injection port
was placed at a lower part in the riser, the axial solid holdup and Gs increased. With increasing fluidizing velocity of loopseal to about 1.5umf, Gs somewhat increased, but above the gas velocity of 1.5umf, the loopseal lost the ability of the control ofGs. The following correlation for the solid circulation rate in the CFB was developed with good accuracy; G, = ϕ,[PA/TA]2+[H
l
/H
l
]0.5[Ar]-188[Fr]2k+[KU1/U
l
]3-45 相似文献
18.
Fukuji Yamashita 《Korean Journal of Chemical Engineering》1999,16(6):789-794
The effects of the geometrical parameters of draft tubes and the clear liquid height on the average gas holdup EG in a 0.16 m I.D. bubble column for gas dispersion into the tubes were experimentally studied in an airtap water system. The
gas holdup depended on the superficial gas velocity U(ING), the kinds of gas spargers, the diameter and length of the draft
tubes, clearance Cb between the lower end of the draft tube and the bottom of the bubble column, and the clear liquid height HL. EG increased with decreasing hole diameter of the gas sparger at a small gas velocity UG, but did not depend on the kinds of gas spargers at a large UG. EG decreased with increasing clear liquid height HL. The effect of HL on EG was well expressed by the modified three-region model. The experimental data of EG were correlated. 相似文献
19.
The effects of gas velocity, annulus gap on solid (εs) and gas phase holdups (εg), UV light transmittance and photocatalytic reduction of TCE (trichloroethylene) over TiO2/silica gel photocatalyst have been determined in an annulus fluidized bed photoreactor. The optimum TCE reduction efficiency
exhibits at εs/εg of 0.48, annulus gap of 8 mm and UV light transmittance around 0.20. The most pronounced effects on TCE conversion are found
to be gas velocity (Ug) and annular gap in the photoreactor. 相似文献
20.
Hydrodynamic measurements were obtained in a flat-based half-cylindrical column of diameter 0.91 m and inlet orifice diameters of 76 to 114 mm. Beds of 3.5 to 6.7 mm diameter particles with static depths of 0.53 to 1.83 m were spouted with air. In agreement with measurements by earlier workers in smaller columns, it was found necessary to operate with inlet orifice diameters less than about 30 times the mean particle diameter in order to be able to achieve stable spouting. Correlations for minimum spouting velocity developed on small vessels generally gave poor predictions for the large diameter vessel employed in this work and failed to predict the observed dependence of Ums on the static bed height. Substantial dead regions where particles were stagnant were observed in the lower outer portion of the vessel. Other aspects of behaviour studied, including spout diameters and shapes, fountain heights, pressure profiles and gas velocities in the annulus, were qualitatively similar to those in smaller columns, although equations developed for the smaller vessels did not always provide accurate predictions. 相似文献