Modeling and simulation of polypropylene particle size distribution in industrial horizontal stirred bed reactors

This work aims at developing a steady-state particle size distribution (PSD) model for predicting the size distribution of polypropylene particles in the outflow streams of propylene gas-phase horizontal stirred bed reactors (HSBR), on the one hand and investigating the effect of the catalyst residence time distribution (RTD) on the polymer PSD, on the other hand. The polymer multilayer model (PMLM) is used to describe the growth of a single particle. Knowing the PSD and RTD of a Ziegler–Natta type of catalyst and polymerization kinetics, this model allows calculating the polymer PSD of propylene polymerization in the HSBRs. The calculated polypropylene PSDs agree well with those obtained from the industrial reactors. The results reveal that both the PSD and the RTD of the catalyst affect the polymer PSD but in different manners. The effect of RTD on the PSD is less significant in the case of a nonuniform size catalyst feed. This model also allows investigating the effects of other process parameters on the polymer PSD under steady-state conditions, including intraparticle mass- and heat-transfer limitations, initial catalyst size, and polymer crystallinity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Two-area model for bubble distribution in a turbulent fluidized bed of fine particles

The flow behavior of gas and solid was investigated in FCC simulator of φ710×4000/φ870×11000mm.The axial and radial distributions were detected with matrix fiber-opticprobes.It was found that the distribution of bubble diameter in the turbulent region of the fluidizedbed of fine particles was different from the results reported for lab-scale experiments.Radially therewere three areas,i.e.,the central(r/R=0-0.4),the intermittent or stable(r/R=0.4-0.8)and thenear wall(r/R=0.8-1.0)areas respectively.It was noticed that bubbles were almost non-existing atthe near wall area.Hence,according to the coalescence and splitting theory of bubbles,a two-areamodel of bubble diameter distribution was proposed and a dimensionless parameter(γ_M)regarded asan index for'quality'of fluidization was deduced.     

催化裂化流化床内构件的研究进展

介绍了近年来催化裂化流化床中内构件的研究现状,主要包括挡板、垂直管束和填料。阐述了气、固两相在装有不同内构件的流化床中的流动特点,指明了各类内构件的优缺点。并详细阐述了挡板式和填料式内构件的改进历程,根据现有内构件存在的优缺点提出了新的内构件的开发方向。     

气液固循环流化床颗粒分布板实验研究

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。     

The effect of adsorption on mass transfer in fluidized bed catalytic reactors

Tracer gas residence time distributions (RTD) in a laboratory scale fluidized bed system have been measured for pulses of three different tracer gases (methane, ethane and propane) at different temperatures in the range 323 to 435 K. The fluidized solid was a commercial zeolite based FCC catalyst (CBZ‐2), and measurements were carried out in a superficial air velocity range of 0.01 to 0.04 m/s. The data were interpreted with two‐phase dense phase dispersion models for adsorptive tracers, available in the literature. In addition, modified models were considered by assuming a stationary dense phase and neglecting axial dispersion in this phase. Mean residence time, μ₁, and the variance of the residence time, σ², of RTD data were calculated for each experimental run. Applying the moment technique in the Laplace domain, the differential equations for all models considered were analytically solved. Mass transfer coefficients obtained from dynamic experiments were compared with the values estimated from the relations available in the literature. It was found that methods considering convective flux alone between the bubble and emulsion phases give closer values to the experimental ones than the methods also including the diffusive flux.     

流化床一步制粒法的工艺优化

采用流化床一步制粒法制备工业压片颗粒,讨论了流化床设备工艺参数(进风风量、进风温度,喷雾速率和喷雾压力)对颗粒形成的(粒径分布和休止角)影响。结果表明,最佳实验条件为风机频率23~35 Hz,进风温度60℃,喷雾速率10 mL/min,喷雾压力1.5 MPa时,所得颗粒粒径分布最优,流动性最好。     

高温烟气颗粒物在线检测装置性能评价

为评价高温工况下颗粒物在线检测装置的性能,在催化裂化高温烟气过滤实验装置上使用光学在线颗粒物检测装置测定了过滤器下游烟气中的催化剂浓度及粒径分布,同时用离线式粉尘等动采样装置和Coulter粒径分析仪测量过滤器上游与下游的催化剂浓度和粒径分布,对在线式的测量结果进行验证。考虑了温度对在线式测量结果的影响。实验结果表明:在线式检测装置可以在操作温度320~465℃,操作压力0.21 MPa工况下实现稳定的测量,在线式测量结果和离线式测量结果吻合很好,实验和计算模拟结果表明操作温度对实验测量的影响可以忽略。在此基础上,针对煤化工行业的实际工况,提出了利用迭代方式来获得在线测量结果修正值的方法,该方法对煤化工工艺中高温气体管道内颗粒物的在线测定同样具有指导意义。     

Limestone particle attrition and size distribution in a small circulating fluidized bed

Limestone particle attrition was investigated in a small circulating fluidized bed reactor at temperatures from 25 to 850 °C, 1 atm pressure and superficial gas velocities from 4.8 to 6.2 m/s. The effects of operating time, superficial gas velocity and temperature were studied with fresh limestone. No calcination or sulfation occurred at temperatures ?580 °C, whereas calcination and sulfation affected attrition at 850 °C. Increasing the temperature (while maintaining the same superficial gas velocity) reduced attrition if there was negligible calcination. Attrition was high initially, but after ∼24 h, the rate of mass change became constant. The ratio of initial mean particle diameter to that at later times increased linearly with time and with (U_g − U_mf)², while decreasing exponentially with temperature, with an activation energy for fresh limestone of −4.3 kJ/mol. The attrition followed Rittinger’s surface theory [Beke B. Comminution. Budapest: Akademiai Kiado, 1964; Ray YC, Jiang TS, Wen CY. Particle attrition phenomena in a fluidized bed. Powder Technol 1987a; 49:193-206]. The change of surface area of limestone particles was proportional to the total excess kinetic energy consumed and to the total attrition time, whereas the change of surface area decreased exponentially with increasing temperature. At 850 °C, the attrition rate of calcined lime was highest, whereas the attrition rate was lowest for sulfated particles. When online impact attrition was introduced, the attrition rate was about an order of magnitude higher than without impacts.     

酵母悬浮液进料时膨胀床空隙率和粒径分布的动态变化

引言 膨胀床吸附技术可以直接从细胞破碎液(未澄清液)中提取目标产物[1-3],而无需预先进行固液分离操作,具有快速、高效和集成化的特点.在实际应用中,料液中细胞(碎片)的存在将会影响到膨胀床的床层稳定性和操作性能[4-6].     

Deep learning-based tomographic imaging of ECT for characterizing particle distribution in circulating fluidized bed

The gas and solids in a circulating fluidized bed (CFB) are heterogeneously dispersed and a multiscale flow regime may form both in time and space. Accurate measurement of the fluidizing process is significant for investigating the multiscale gas–solid flow characteristics and the design, optimization, and control of CFBs in various applications. This article develops a deep learning-based tomographic imaging of electrical capacitance tomography (ECT) to characterize the particle concentration distribution in a CFB. The deep tomographic imaging approach is realized through training a well-designed convolutional neural network (CNN) with the numerically built dataset. Simulation results demonstrate that the average values of the relative image errors reconstructed by CNN in the test set are 0.1110 and 0.1114 for the 60 and 100 mm pipes, respectively, which are better than the average values of 0.1819 and 0.2519 by the Landweber algorithm. With the verification of the trained model based on the prepared data can image the unseen typical flow patterns better than Landweber, it is further used to investigate the particle flow characteristics of a lab-scale CFB. Experimental results reveal that the developed deep tomographic imaging of ECT can successfully measure the fluidized particle distribution in both the 60 and 100 mm pipes, showing good prediction and generality of the designed CNN model. A flow regime transformation from “annular” flow to “core-annular” flow and pneumatic conveying is observed under the tested conditions. Besides, the flow regime would be highly affected by the fluidized gas flow rate and the initial bed height.     

高岭土浆液粒度影响因素的研究

高岭土是半合成FCC催化剂的重要载体,其浆液粒度对催化剂性能有较大影响。高岭土作为载体是半合成FCC催化剂的重要组成部分,其浆液粒度的性能已引起广泛重视。考察了打浆时间对高岭土浆液粒度性能的影响,发现粒度随打浆时间的增加而减小,但是达到一定的时间后高岭土的粒度基本不变。进一步研究了分散剂对高岭土浆液粒度的影响,结果表明,加入分散剂有利于降低高岭土的粒度,提高打浆效率,有利于打浆过程,但加入一定量后,降低粒度的效果不明显。工业生产过程中,可以考虑加入适量的分散剂提高打浆效率,降低浆液粒度。     

网格尺寸对循环流化床内气固两相流动的影响

将基于能量最小多尺度方法(EMMS)的曳力模型耦合到双流体模型中,并针对循环流化床内的气固两流动进行了模拟研究。采用全滑移壁面边界条件处理颗粒相,考察了3种网格尺度对轴向空隙率和出口颗粒循环量等气固流动特性的影响。计算结果表明,应用EMMS曳力模型处理相间作用力,同时在采用全滑移壁面边界条件处理颗粒相时,双流体模型能够正确预测轴向空隙率分布。采用网格尺寸为2.325 mm×20 mm时,模拟结果和实测数据吻合较好,表明在循环流化床的数值模拟中选择恰当的网格尺度是极为重要的。     

Using stereo XPTV to determine cylindrical particle distribution and velocity in a binary fluidized bed

Nonspherical particles are commonly found when processing biomass or municipal solid waste. In this study, cylindrical particles are used as generic nonspherical particles and are co-fluidized with small spherical particles. X-ray particle tracking velocimetry is used to track the three-dimensional particle position and velocity of a single tagged cylindrical particle over a long time period in the binary fluidized bed. The effects of superficial gas velocity (u _f), cylindrical particle mass fraction (α), particle sphericity (Φ), and bed material size on the cylindrical tracer particle location and velocity are investigated. Overall, the cylindrical particles are found in the near-wall region more often than in the bed center region. Increasing the superficial gas velocity u _f provide a slight improvement in the uniformity of the vertical and horizontal distributions. Increasing the cylindrical particle mass fraction α causes the bed mixing conditions to transition from complete mixing into partial mixing. © 2018 American Institute of Chemical Engineers AIChE J, 65: 520–535, 2019     

循环流化床预还原粉铁矿的动力学分析与计算

基于循环流化床（CFB）一维流动模型及界面反应控制的未反应收缩核模型,建立了CFB连续还原粉铁矿的数学模型,同时考虑了气相与固相的转化过程及粉铁矿的宽筛分特性,并与文献中的实验数据进行了对比,结果显示该模型能够较好地反映CFB内的流动及还原反应规律。在此基础上,针对某工业尺度反应器,又分别研究了气速、反应物成分、循环比等因素对反应器内运行特性的影响规律。结果表明：一定条件下,增大气速和降低还原气体的氧化度可以不同程度地增加固相的转化速率,但前者降低了气体的利用率,而后者增加了气体利用率;控制合适的循环比可以保证固相还原程度更为均匀。     

Experiments on particle cluster behaviors in a fast fluidized bed

A three-dimensional (3D) fast fluidized bed with the riser of 3.0 m in height and 0.1 m in inner diameter was established to experimentally study the cluster behaviors ofGeldart B particles.Five kinds of quartz sand particles (dp =0.100,0.139,0.177,0.250 and 0.375 mm and ρp =2480 kg·m-3) were respectively investigated,with the total mass of the bed material kept as 10 kg.The superficial gas velocity in the riser ranges from 2.486 to 5.594 m·s-1 and the solid mass flux alters from 30 to 70 kg· (m 2· s)-1.Cluster characteristics and evolutionary processes in the different positions of the riser were captured by the cluster visualization systems and analyzed by the self-developed binary image processing.The results found four typical cluster structures in the riser,i.e.,the macro stripe-shaped cluster,saddle-shaped cluster,U-shaped cluster and the micro cluster.The increasing superficial gas velocity and particle sizes result in the increasing average cluster size and the decreasing cluster time fraction,while the solid mass flux in the riser have the reverse influences on the cluster size and time fraction.Additionally,clusters in the upper region of the riser often have the larger size and time fraction than that in the lower region.All these effects of operating conditions on clusters become less obvious when particle size is less than 0.100 mm.     

流化床与沸腾床内部微生物群落演变与分析

用流化床反应器和沸腾床反应器处理焦化废水,对两种反应器运行效能及微生物群落变化进行对比研究。结果表明,提高污泥负荷后流化床COD去除率优于沸腾床反应器。提高进水污泥负荷对沸腾床内微生物的冲击更大,致使其种群丰富程度下降明显。研究结果证明,流化床在宏观去除率、维持菌种丰富度方面具有较大优势。     

The influence of particle size and density on the radial gas mixing in the dilute region of the circulating fluidized bed

A cold model of a CFB, having a 0.120m ID, 5.75m high riser, was operated at a superficial gas velocity of 6m/s and at average solids mass fluxes varying in the range between 16 and 55kg/sm². A stream of carbon dioxide was injected continuously at a fixed position along the riser axis and used as tracer gas. Three solids, belonging to groups A and B of Geldart's classification, were selected in order to investigate separately, the effect of particle size and density on the radial mixing of the gas phase. The intensity of radial gas dispersion reduced when larger or heavier particles were used. The differences in the values of radial dispersion coefficient and Peclet number were explained, taking into account the role of the particle size with respect to the scale of gas turbulence.     

磁场流化床的研究与应用

介绍了磁场流化床的基本原理以及近年来在基础研究和应用研究两个方面取得的进展及成果,综述了磁场流化床在化工环保、生化工程、能源三个领域的应用现状并分析了其工业化前景及存在的问题。     

多段分级转化流化床提升管速度场的研究

针对流化床煤气化过程中需要长气固接触时间和高固体浓度,开发了耦合灰熔聚流化床和提升管的多段分级转化流化床。为了研究多段分级转化流化床提升管中局部颗粒速度的径向、轴向分布,在不同的操作条件下,采用PV-6型颗粒速度测量仪在冷态实验装置中系统测定提升管内局部颗粒速度。实验结果表明:提升管中任何径向、轴向位置的颗粒速度随着操作气速的增大而增大,随循环量的增加而减小。操作条件对中心区颗粒速度变化的影响明显高于边壁区。颗粒的加速首先发生在提升管中心区域,然后向边壁区域扩展。颗粒速度径向分布的不均匀性沿轴向逐渐增大,并且受操作气速影响比较大。