流化床提升管中脱油油砂颗粒固含率的轴向分布

针对油砂直接流化焦化工艺,建立了一套大型冷模提升管循环流化床装置. 粒度测试结果表明,该脱油油砂颗粒属宽筛分混合颗粒,且细颗粒含量较多,粒度分布宽(1~>2000 mm). 在不同操作条件下,采用多点压力密度测量仪测定了提升管内压力梯度和截面平均固含率沿提升管轴向的分布. 实验结果表明,脱油油砂颗粒在提升管内截面的平均固含率随表观气速增大而减小,随颗粒循环强度增大而增大;固含率沿提升管轴向的分布为C型,即上下两端较浓、中间较稀,且沿提升管自上而下分为3个区域：颗粒约束返混区(>12 m)、充分发展区(4~12 m)和颗粒加速区(<4 m);在相同操作条件下,脱油油砂颗粒在提升管内截面的平均固含率高于FCC颗粒,加速段与约束返混段长度大于FCC颗粒;确定了脱油油砂颗粒在提升管内截面平均固含率的影响参数为ep', Fr及Hr/Dr;通过实验数据回归得到提升管内截面平均固含率轴向分布的经验模型,计算与实验值吻合较好.     

高密度下行床内颗粒浓度径向分布的研究

在自行设计的一套下行循环流化床内进行了低气速、高浓度下行床内颗粒浓度的分布研究。实验分别采用了硅胶和FCC颗粒,在床层截面平均浓度最高到12％范围内进行了下行床不同截面上颗粒浓度径向分布的研究,并进一步分析了床层颗粒浓度对稀相中心区、环形浓相区浓度径向分布的影响。研究表明,在同一截面,随着床层颗粒平均浓度的增加,浓度分布趋于均匀;在截面平均浓度相近,浓度的径向分布沿轴向从上到下逐渐趋于均匀。颗粒的相对浓度的最大值随截面平均浓度的增加而减小,其在径向的位置基本不变。实验还发现,床层截面平均浓度的增加,浓相区内颗粒浓度的分布更均匀,而对稀相区内颗粒浓度分布没有明显的影响。     

气固错流移动颗粒床过滤器压降特性研究

研究了错流移动颗粒床过滤器操作压降与过滤介质特性、表现过滤气速、颗粒层移动速度和床层粉尘沉积量之间的关系。结果表明，无粉尘沉积时，床层压降可以用Ergun方程计算。颗粒层移动速度的变化并不会造成床层压降的显著变化。除尘过程中，床层内粉尘沉积量随气体中粉尘浓度的增大、颗粒层移动速度的减小而增加，同时将导致床层压降的显著增大。错流移动床除尘操作压降可以用带修正项的Ergun方程计算，其修正项为比沉积率和颗粒层空欧率的函数。在实验数据范围内，该方程的计算结果与实验数据最大偏差小于15％。     

流化床-提升管耦合反应器内沥青颗粒的流动特性

针对重油残渣(沥青颗粒)气化制氢工艺,在流化床-提升管耦合反应器大型冷模实验装置上,考察了不同操作条件下沥青颗粒体系在耦合反应器内截面平均密度的轴向分布. 结果表明,对单组分沥青颗粒体系,耦合反应器适宜的操作条件为：提升管表观气速ug,r=0.70~1.76 m/s;与A类颗粒相比,沥青颗粒在耦合反应器内的流动特性呈现不同的特点,整个反应器沿轴向可分为底部流化床密相区、提升管底部低密度区、提升管颗粒密度重整区、提升管加速区、充分发展区和出口约束区6个区域;反应器内截面平均密度随颗粒质量流率增大而增大,随表观气速增大而减小;确定了耦合反应器内提升管区域截面平均固含率的影响参数为ep', Fr及H/Dr,并利用实验数据回归了平均固含率的轴向分布经验模型,其计算值与实验值吻合较好.     

气固逆流下行流化床中颗粒速度的径向与轴向分布

在内径90 mm、高7 m的逆流下行床冷态实验装置中,研究了气固逆流下行床中循环锅炉灰(dp=300 mm)颗粒速度的径向分布及其沿轴向发展. 结果表明,局部颗粒速度沿径向分布是不均匀的,在完全发展区,颗粒速度中心和边壁低、在r/R=0.85附近颗粒速度最大. 由大量实验数据回归出预测充分发展段局部颗粒速度的关联式,该公式计算值与实验值的平均相对偏差小于±11%. 不同径向位置的局部颗粒速度沿轴向的变化趋势不同,边壁区域(r/R>0.622)颗粒速度沿轴向单调递增,而中心区域(0相似文献   

提升管与气-固环流床层耦合反应器的流体力学特性及流动模型

针对催化汽油辅助反应器改质降烯烃技术,在一套提升管与气-固环流床层耦合反应器大型冷模实验装置上,研究了上部环流床层的流体力学特性。结果表明,在环流床层与提升管耦合操作的情况下,床层内颗粒环流存在两种推动力,分别为静压差推动力和颗粒喷射推动力;环隙与导流筒之间的整体平均固含率差随导流筒表观气速增加而增加,随颗粒外循环强度增加而降低;颗粒环流速度随导流筒表观气速和颗粒外循环强度增加而增加。通过对环流床层进行动量衡算,建立了提升管与环流床层耦合流动的数学模型,模型平均相对误差在15.95％以内。     

下行气固两相流充分发展段的颗粒浓度

在较宽的操作条件范围内采用光纤颗粒浓度探头测定了下行管(φ100 mm×9.5 m)充分发展段内的真实颗粒浓度,并结合文献上的大量实验数据,系统研究了操作条件、颗粒直径和床层直径对下行气固两相流充分发展段内真实颗粒浓度的影响.结果表明,当操作气速一定时,充分发展段内的颗粒浓度随着颗粒循环速率的增大而线性增加.颗粒直径对下行床充分发展段内颗粒浓度的影响随操作气速的增加而逐渐减弱.床层直径对下行床充分发展段内的颗粒浓度基本上没有影响.所提出的预测关联式能很好地拟合本文及文献上的实验数据.     

石油焦燃烧器环流混合段内床层的轴向密度分布

采用气-固环流反应器与输送床烧焦管相结合的结构形式,建立了一套适应石油焦或气化余焦燃烧要求的大型冷态实验装置. 在不同操作条件下,采用差压变送器测定了环流混合段内环区及外环区内床层轴向压力梯度及密度的分布规律. 结果表明,内环床层密度分布可分为底部密相区和上部湍流扩散区;内环颗粒循环强度对底部密相区的密度分布影响较小,只对导流筒上部湍流扩散区有影响;随着内环表观气速的增大,整个内环床层密度均降低. 外环床层密度分布与内环的表观气速、颗粒循环强度和外环床层密相料位高度有关. 利用实验数据回归出了内环和外环轴向颗粒密度分布的经验模型,其计算值与实验值吻合较好.     

微小流化床流化特性分析

在内径4.3, 5.5, 10.5, 15.5, 20.5和25.5 mm的6个气固微小流化床中,考察了石英砂和不同粒径的催化裂化催化剂的流化特性. 研究了流化床尺寸、颗粒及流化介质物性对微小流化床床层压降及最小流化速度的影响. 结果表明,不同颗粒及流化介质的微小流化床床层压降实验值均小于计算值. 传统的压降关联式不能直接用于微小流化床. 其最小流化速度随床径减小呈指数增大,在高径比1:1~3:1范围内,最小流化速度随料高增大近似呈线性增大,其增大速度随床径增大而变缓. 基于实验数据得出了微小流化床最小流化速度的关联式.     

组合约束型提升管出口气固分布器的压降

在一套组合约束型提升管冷态实验装置上,通过实验研究了不同操作条件下提升管出口气固分布器的压降,并与常规气体分布器压降进行了对比。实验结果表明,在零床层及有床层的操作模式下,气固分布器压降均随提升管内表观气速和颗粒循环强度的增加而增大,在颗粒循环强度较低时,气固分布器压降曲线变化的斜率随着表观气速的增加而增大,在颗粒循环强度较高时,气固分布器压降曲线变化的斜率随着表观气速的增加而减小;随着开孔率及上部流化床层压降增加,气固分布器压降呈降低趋势,当流化床层压降达到一定程度后,分布器各孔方可实现有效布气,此后气固分布器压降趋于近似不变;在相同表观气速及开孔率下,气固分布器压降大于常规气体分布器压降。     

Hydrodynamics of a gas-driven gas-liquid-solid spouted bed with a draft tube

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.     

循环流化床内颗粒的加速作用及气固两相间的动量交换

根据对气固两相流动特性的分析,表明在循环流化床提升管内,颗粒的加速运动及气固两相间的动量交换对床层各项参数具有明显的影响。由于颗粒聚集,减小了气固两相间的相互作用,使曳力系数小于单颗粒标准曳力系数(C_D/C_(DS)<1.0)。从而使颗粒具有较长的加速段,其加速压降在总压降中所占的分率不可忽略。考虑颗粒加速作用及由于颗粒聚集使气固两相相互作用力减小的事实后,用一维轴向稳态流动的模型可以获得截面平均空隙率、平均颗粒速度以及曳力系数等参数及其轴向分布规律,并与实验直接测定结果吻合很好。通过对大量数据的分析,表明C_D/C_(DS)可用下述经验关联式表示:C_D/C_(DS)=1.68(ε)~(0.253)(Re_(?)/Re_t)~(-1.213)(d_P/D)~(0.105)     

气固两相流中颗粒时均速度的测量新方法

根据互相关测速技术提出了一种测量颗粒时均速度的新方法，与Aguillon和Nieuwland提出的方法相比，本方法不仅考虑了采样时间内向上及向下运动颗粒微元体的速度和数量变化，而且还考虑了所测颗粒微元体的浓度变化. 为了比较几种测量方法间的差别，采用PV4A型光纤测量仪，在循环流化床冷态实验装置上测量了不同操作条件下的颗粒速度，并对3种方法的计算结果进行了对比. 结果表明，在高气速、低颗粒浓度条件下，3种方法计算的颗粒时均速度相差较小，而在低气速、高颗粒浓度条件下，3种方法计算的颗粒时均速度相差较大，并且本文方法所计算的颗粒质量流率与实际测量值最接近.     

Position and velocity of a large particle in a gas/solid riser using the radioactive particle tracking technique

The flow behavior of the solids phase in the fully developed region of a laboratory-scale circulating fluidized bed riser was studied using an assembly of sixteen NaI detectors to determine the position of a 500 μm radioactive particle, 100 times/s. The particle location was inferred from the number of γ-rays recorded by the assembly. The knowledge of the instantaneous positions enabled the determination of the instantaneous and mean velocity fields. Tests were conducted in a 0.082 m diameter, 7 m tall riser using 150 μm silica sand particles. Data were obtained at a gas superficial velocity of 4 m/s and solids mass fluxes from 23 to 75 kg/m²·s. Radial profiles of axial particle velocity showed that the solids velocity decreased with increasing solids circulation rates. Correspondingly, turbulent particle velocities and solids dispersion coefficient in the longitudinal direction were found to decrease as the solids circulation rate increased. The cross-sectional area where, on average, solids downflow took place, increased with increasing solids circulation rate.     

GAS-SOLIDS FLOW PATTERNS IN A CONCURRENT DOWNFLOW FAST FLUIDIZED BED(CDFFB)

Radial profiles of solid concentration and velocity for concurrent downward gas-solid suspension in a140mm inside diameter fast fluidized bed were investigated.The influence of gas velocity,solid circulating rateand axial position on radial profiles of solid concentration and particle velocity has been examined.It hasbeen found that an annular region of high solid concentration exists at r/R=0.94.At both the center and wallregion,the solid concentration and the particle velocities are relatively low.The shape of radial solid con-centration profile curves is mainly dependent on the cross-section averaged voidage,and the shape of radialparticle velocity profile is mainly affected by the gas velocity and cross-section averaged voidage.Based on the radial profiles of solid concentration and particle velocity,the solid mass flux profile and thenonuniformity of solids flow are discussed in this paper.It is shown that solids flow in CDFFB is much moreuniform than that in UFFB.     

液固循环流化床中颗粒轴向速度的实验研究

利用超声多普勒测速仪实验测量了液固循环流化床中不同径向位置处颗粒瞬态轴向速度，研究了其概率密度分布特征。采用瞬态速度的标准偏差衡量瞬态速度的波动程度，考察了不同操作形式下的颗粒时均轴向速度的径向分布以及表观液速和颗粒循环速率等操作条件对速度波动程度和速度均衡径向分布的影响，利用相间作用力对两种分布的特点进行了机理分析，并对液固和气固循环流化床中颗粒的流动行为进行了比较。     

A Novel Model for Predicting the Dense Phase Behavior of 3D Gas‐Solid Fluidized Beds

A novel phenomenological discrete bubble model was developed and tested for prediction of the hydrodynamic behavior of the dense phase of a 3D gas‐solid cylindrical fluidized bed. The mirror image technique was applied to take into account the effects of the bed wall. The simulation results were validated against experimental data reported in the literature that were obtained by positron emission particle tracking. The time‐averaged velocity profiles of particles predicted by the developed model were found to agree well with experimental data. The initial bubble diameter had no significant influence on the time‐averaged circulating pattern of solids in the bed. The model predictions clearly indicate that the developed model can fairly predict the hydrodynamic behavior of the dense phase of 3D gas‐solid cylindrical fluidized beds.     

Annular wall layer thickness in circulating fluidized bed risers

The thickness of downward-flowing annular wall layers in circulating fluidized bed risers has been determined in the literature based on measured radial profiles of both local particle velocity and solids flux. The thickness of the wall layer is shown to be larger based on solids flux profiles than when based on particle velocity profiles, because fluctuations in local instantaneous particle velocity are correlated with fluctuations in local solids concentration. A new correlation is developed to predict the time-average thickness of the downflowing particle streamer layer based on solids flux measurements as a function of the cross-sectional average voidage. It successfully accounts for the variation of the wall layer thickness with axial location and solids circulation rate.     

Effects of temperature on local two-phase flow structure in bubbling and turbulent fluidized beds of FCC particles

A novel high temperature optical fiber probe has been developed to study the effects of bed temperature on the local two-phase flow structure in a pilot scale fluidized bed of the FCC particles with bed temperatures ranging from 25°C to 420°C, covering both the bubbling and turbulent fluidization regimes. The results show that fluidization is enhanced and fluctuations of the local two-phase flow structure become more intense with increasing bed temperature. At constant superficial gas velocities, the averaged local particle concentration, the dense phase fraction and particle concentration in the dense phase decrease with increasing bed temperature, whereas both the frequency of the dilute/dense phase cycle and the ratio of the dilute phase duration to the dense phase duration increase. In addition, the effects of temperature on the dilute phase depend on superficial gas velocity. The conventional two-phase models fail to predict these changes of the local flow structure with temperature, which may be explained by the fact that the role of interparticle forces is neglected at different bed temperatures. Indeed, fluidization behaviors of the FCC particles tested increasingly shift from typical Geldart A towards B with increasing temperature due to a decrease of the interparticle attractive forces and a simultaneous increase of interparticle repulsive forces.