共查询到20条相似文献,搜索用时 15 毫秒
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应用自行开发的微电导探针测试技术,以玻璃珠(dp=0.48 mm, ρs=2460 kg8226;m-3)和苯乙烯颗粒(dp=1.45mm,ρs=1264 kg8226;m-3)为固相,空气为气相,水及0.05%、0.20% (质量)SCMC(羧甲基纤维素钠)水溶液为液相,对三相循环流化床(TCFB)的各相局部含率进行了同时测定.考察了不同表观液体速度、辅助液体速度、液体黏度及颗粒密度对局部相含率轴径向分布的影响. 在不同操作条件下,获得了1286套局部相含率实验数据. 给出了局部固含率和局部气含率与操作条件、流体物性及床层轴径向位置的关联式,关联式的计算值与实验值吻合较好. 相似文献
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设计了实现液固外循环流化床中颗粒正常循环的关键部件——喷嘴,利用CCD图像采集分析系统,获得了其换热管束内固体颗粒的分布情况,考察了液体流量、口径比、喷嘴安装位置、颗粒直径、颗粒初始加入量以及液体黏度对液固外循环流化床换热器管束内含固体积分数的影响。结果表明:口径比及喷嘴安装位置对提高管束内的含固体积分数都存在一个最佳值,颗粒直径、颗粒初始加入量以及液体黏度对管束内含固体积分数也具有较大的影响,同时还通过对实验数据的综合分析,得到了喷嘴在最佳安装位置下液固外循环流化床内含固体积分数的经验关联式。 相似文献
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Ying Zheng 《加拿大化工杂志》2001,79(4):564-569
Although axial liquid dispersion has been studied extensively in particulate fluidized beds, no data has been reported previously in a liquid–solid circulating fluidized bed (LSCFb). In this work, the axial liquid dispersions at various radial positions were measured in an LSCFB of 76 mm in diameter and 3.0 m in height using a dual conductivity probe. The results reveal that the axial liquid dispersion is affected not only by the operating conditions but by the radial positions as well. A local axial dispersion model is proposed to describe the axial liquid dispersion at various radial positions. The local axial liquid dispersion coefficients determined by the proposed model are greater at the axis than near the wall region of the riser. This nonuniformity of axial liquid dispersion is believed to be caused by the radial nonuniform distribution of liquid velocity, and bed voidage in the LSCFB can significantly affect the axial liquid dispersion. 相似文献
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气液固三相循环流化床中气固相含率轴径向的分布 总被引:4,自引:0,他引:4
对气液固三相循环流化床中气固相含率沿轴径向的分布进行了实验研究和模拟。实验结果表明:与膨胀床相比,三相循环流化床内的相间接触较为充分;固含率轴向分布的一维沉降-扩散模型模拟值与实验值吻合较好。 相似文献
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气液固循环流化床颗粒分布板实验研究 总被引:10,自引:2,他引:8
设计了用于气液固三相循环流化床换热器的固体颗粒分布板。采用功能强大的CCD图像采集分析系统,获得颗粒的分布和运动规律,考察了安装高度、运行参数等对分布板颗粒分布性能的影响。研究表明,分布板的安装高度、液体和气体流量、颗粒体积分数等对颗粒的速度和固含率分布有较大影响,得到了使固体颗粒在管束中分布效果较好的设计参数,以指导工程应用。 相似文献
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S.A. Razzak 《Powder Technology》2010,199(1):77-5662
Axial distribution of phase holdups was studied in the riser of a gas-liquid-solid circulating fluidized bed (GLSCFB). The effects of gas and liquid superficial velocities as well as solids circulation rate on radial distribution of phase holdups at different axial locations were investigated. Electrical resistance tomography (ERT) and optical fiber probe were employed online in the experiments for a precise determination of phase holdups. An empirical model was developed for the determination of gas bubbles in analysis of data obtained by fiber optic sensor. Gas holdup was higher at the central region of the riser and increased axially due to coalescence of small bubbles and decrease of hydrostatic pressure at higher levels in the riser. This led to an increase in solids holdup in regions close to the wall which was slightly higher than the solids holdup at the wall. Both solids and liquid holdups were lower in the central region and increased radially towards the wall. Gas holdup decreased with increasing solids circulation rate but opposite trend was observed for solids holdup. Solids circulation rate had negligible effect on liquid holdup at lower axial locations compared to top of the riser. Cross-sectional average of solids, gas and liquid holdups did not change significantly at higher liquid superficial velocities. 相似文献
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应用开发的微电导探针测试技术,对小尺寸颗粒玻璃珠(粒径分别为0.48、0.80、1.25 mm)和1.45 mm苯乙烯树脂为固相,空气和水分别为气相和液相的三相流化床的各相局部含率进行了同时测定.在较宽操作条件下,获得了一系列局部相含率实验数据.通过对实验数据研究发现:在充分发展段,局部固含率在r/R=0.75~0.85范围内有一个极大值,床层截面平均气含率随表观液速的变化存在一个极小值.在气体分布器区,在距气体分布器轴向一定距离范围内,三相局部含率的径向分布存在明显的不对称分布.随着轴向距离的增加,局部气含率径向不对称分布逐渐消失,最终过渡到对称分布,而局部固含率的径向不对称分布消失得不明显. 相似文献
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A simple hydrodynamic model for Circulating Fluidized Beds has been developed. The mathematical model, based on the core-annulus flow structure, is shown to be able to predict the two-phase flow characteristics and it requires only two measurable steady-state parameters, namely the experimental average voidage profile along the riser, or equivalently the pressure distribution, and the net solids circulation rate. The model has been successfully tested using recently obtained literature data covering a variety of reactor configurations and operating conditions. 相似文献
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考虑到循环流化床中分散颗粒和颗粒聚团同时存在的多尺度结构,确定了密相和稀相加速度与计算网格局部参数之间的关系,建立了多尺度曳力消耗能量最小的稳定性条件,基于双变量极值理论,构建了考虑颗粒团聚效应的多尺度气固相间曳力模型。结合双流体模型,对循环流化床内气固流动特性以及颗粒聚团特性进行了模拟研究。通过与实验值比较,考虑颗粒聚团影响的计算模型可以更好地贴近实验结果,颗粒聚团直径随颗粒浓度增大呈现先增大后减小的分布趋势,气体和颗粒的加速度在模拟中与重力加速度同处一个数量级,求解过程中不能被忽略。 相似文献
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Shilapuram VidyasagarK. Krishnaiah P.S.T. Sai 《Chemical Engineering and Processing: Process Intensification》2011,50(1):42-52
Experiments were conducted in a liquid-solid circulating fluidized bed to study the effect of liquid viscosity and solids inventory on pressure gradient, critical transitional liquid velocity, onset average solids holdup, axial solids holdup distribution, average solids holdup and solids circulation rate in circulating fluidization regime with riser operated in fixed inventory mode. The results indicate that critical transitional liquid velocity decreases with increase in liquid viscosity. The onset average solids holdup, on the other hand, increases with increase in either auxiliary liquid velocity or solids inventory. The variation of axial solids holdup distribution, average solids holdup and solids circulation rate with liquid viscosity when solid inventory was 0.15 m was dissimilar with either 0.25 m or 0.35 m solid inventory. Correlations were proposed for estimating the average solids holdup and are satisfactorily compared with experimental values. 相似文献
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The axial concentration distribution of the hydrophilic and hydrophobic particles, corresponding to poor and good attachment to rising bubbles in water, was investigated in a gas‐liquid‐solid fluidized bed. The sedimentation‐dispersion model depicted satisfactorily the axial distribution of solids holdup by modifying only the terminal settling velocity, which considered the effect of an additional drag force resulting from the attached rising bubbles. This model explained correctly the different phenomena, i.e. solids holdup decreased with increasing the axial height in the non‐attached system, but increased in the attached system. 相似文献
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While many fundamental studies have been carried out in relatively low density circulating fluidized beds (LDCFB), there has been little reported fundamental study of the high density (including high solids flux and/or high solids concentration) circulating fluidized bed (HDCFB), although many commercial CFB setups are operating under high density conditions. Catalytic gas-phase reactions tend to require higher gas velocity and higher solids flux and/or concentration than gas-solids reactions, and therefore it is necessary to make a distinction between the two types of operations. The study of hydrodynamics and other fundamentals of HDCFB will help in understanding the fundamentals and thus improving the design and operation of existing HDCFB reactors such as FCC risers, and may also lead to other applications requiring even higher solids/gas feed ratios and/or higher solids concentration in the riser. On the other hand, high density operation can only be achieved by properly choosing the gas blower, solids feeding system and CFB geometry to avoid the instabilities resulting from insufficient pressure head from the gas blower and downcomers. 相似文献
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气液固流化床是一类重要的多相反应器,在化工及相关过程工业中有着广泛的应用。然而,由于对该类反应器内复杂的多相流动结构的定量描述十分有限,目前其设计和放大仍主要依赖经验,致使放大成功率低,反应结果达不到预期效果。因此,建立和完善气液固流化床内的三相流动机理模型,是实现该类反应器科学设计和放大的关键环节。对气液固流化床内的三相流动机理模型的研究进展进行了分析,着重总结了三相流动介尺度机理模型研究的新进展,并指出了存在的问题和进一步研究的方向,希望为该类反应器的基础研究和工业应用提供参考。 相似文献
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Solids motion and holdup profiles in liquid fluidized beds 总被引:1,自引:0,他引:1
Non-invasive gamma rays-based techniques, computer tomography and computer-aided radioactive particle tracking, were used to measure solid holdup and solid velocity profiles in liquid-solid fluidized beds. The time averaged velocity measurements indicated that multiple circulation cells exist in the column. The solid motion was upward in the center and downward near the walls in the fully developed part of the column. The flow pattern is reversed in the entry region of the column. The solid holdup values increase slightly with the increase in radial position in the fully developed region. The average values of holdup in the column were in agreement with other measurements and with the modified Richardson-Zaki equation. The solids mean velocities and eddy diffusivities increase with increase in liquid superficial velocity, column size, particle size and density. Distributor-type affects the mean velocity and turbulence parameters while the column height has a relatively minor effect. The solids motion and turbulence parameters presented here are useful for validation of CFD models. 相似文献
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The bypassing of a portion of the inlet spout gas to the annular region of spouted and spout-fluid beds can have a critical effect on processes requiring accurate control of the spout gas residence time even when a draft tube is utilized. A modification to the spout-fluid bed with draft tube called the Internally Circulating Fluidized Bed or ICFB is proposed which eliminates this bypassing problem. Experiments were conducted on a cold 20 cm diameter semi-cylindrical unit to define the operational characteristics of the ICFB with particular emphasis on the gas and solids flow behavior. The solids and gas flow rates in the unit were successfully related by a published correlation which was developed for the cocurrent flow of gases and solids through orifices. 相似文献
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The axial pressure drop profile and the radial solids distribution were measured in a circulating fluidized bed for evaluating the effects of return gas-solids stream position on the riser flow properties.The saturation carrying capacity of gas for Geldart B typed particles and the flow mode of return gas-solids stream in the bed were discussed.It was found that arranging the inlet at a higher position of the riser would make the bottom bed leaner when U0 was high and Gs was low.When Gs increased,the longer influenced region of return particles and a small air-staging through lifting the loosening air injection position made the bottom bed become denser significantly.The deceleration and residence of return particles caused a relatively denser but asymmetrical region in the vicinity of inlet.But much more symmetrical solids distribution profile was found in the upper and lower regions far away from the inlet.The effects of inlet height on the flow properties of the riser with air-staging also were analyzed.The secondary air injection below the solids inlet could not cut off the solids exchange in the bed.The bed solids concentration increased when the particles inlet moved to a higher position of the bed when air-staging was adopted.Using CO2 as tracer,the dispersion of the loop-seal-fluidizing air for transmitting the return particles was investigated.It was found that the loop-seal fluidizing air dispersion rate was low but can be enhanced by the secondary air injection. 相似文献