列管式回转窑物料停留时间的分析

为了能较精确地预测列管式回转窑的物料停留时间,通过理论分析内部构件对物料填充率及停留时间的影响,并通过Φ500mm×8 100mm回转窑上对三种物料进行物料停留时间试验,提出在列管式回转窑填充率15%~25%时,动态安息角对物料停留时间的影响,并提出原煤、油砂物料的近似计算值,基本符合原煤、油砂实际生产设备的运行数据。该结果可为列管式回转窑的物料的停留时间提供参考。     

直热式转筒干燥过程物料停留时间理论推导

为了对物料在直热式转筒干燥机内理想扬料板作用下停留时间进行计算研究,根据扬料板作用下的物料在转筒内撒落分布均匀状态,建立了理想扬料板的截面方程,采用建立的理想扬料板的截面方程,导出了随着转筒转动到不同位置的扬料板持料量,在此基础上,分析物料在直热式转筒干燥机内的实际运动情况,建立转筒内物料运动的数学模型,导出物料在转筒内的停留时间,对现有停留时间计算方法进行了修正。研究为扬料板作用下直热式转筒干燥过程物料停留时间的计算提供一种参考。     

双转子连续混炼机停留时间的测定

采用示踪剂法测定了双转子连续混炼机的物料停留时间分布曲线，讨论了影响物料停留时间分布曲线的因素。结果发现：混炼机产量越大，停留时间越短，分布曲线的分布越窄；而混炼机的转速对停留时间分布的影响不大。     

变径炭素回转窑内物料平均停留时间的计算

在前人厚度变化公式基础上推导出适用于窑尾扩径和增设翻料装置的炭素回转窑内物料平均停留时间的计算公式,同时建立了实验室回转窑模型,进行了冷态实验。将物料停留时间的计算值与变径回转窑模型实验测试值作了比较。结果表明,公式计算值与实验测试值比较吻合,误差范围在-15％～12％内,并且计算中不需要引入修正系数;回转窑转速和斜度的增加均使物料平均停留时间缩短,而窑尾挡料圈高度的增加可以使平均停留时间缩短,也可以使平均停留时间延长。     

假塑性流体在双螺带桨搅拌釜内停留时间分布

采用电导率法研究了羧甲基纤维素水溶液假塑性流体在双螺带搅拌釜内的停留时间分布(RTD)情况,考察了物料黏度、流量、搅拌转速和转向对停留时间分布的影响.发现假塑性流体在釜内的停留时间分布类似于全混釜,但有一定的拖尾现象.物料黏度对平均停留时间和当量全混釜数影响不大;随着流量增大,平均停留时间减小,而当量全混釜数基本不变;...     

碳纤维复合材料回收装置中物料停留时间研究

为保证所回收的碳纤维能及时有效地被排出,用EPE泡沫为示踪物料,在建立热氧裂解法回收碳纤维的装置上,用实验法测定了卧式流化床反应器的流化曲线。经分析流化曲线得出临界流化速度和带出速度并经公式计算确定了临界流化速度和带出速度,考察不同形状物料及混合物料在主反应器内的停留时间。结果表明,流化床内临界流化速度为0.15m/s,颗粒带出速度为0.24m/s;物料形状对其在床内停留时间影响较大;单一形状物料在流化床内停留时间由长到短依次为圆柱体、长方体和球体;球体物料最易排出;混合物料在床内停留时间由长到短依次为球体与圆柱体混合物料、长方体与球体混合物料和长方体与圆柱体混合物料;长方体与圆柱体混合物易排出;为使回收碳纤维尽快排出流化床,可采用长方体和圆柱体混合物料或单一的球形物料进行热试验研究。     

连续级式理想混合反应器中物料的短路问题及计算方法

<正> 一、前言化工生产中所使用的连续级式混合反应器,均存在着反应物料的短路现象。所谓短路,系指在反应器中进行反应的物料,并不都是达到了应有的反应停留时间。一部分物料在应有停留时间之前即已溢流出去;而另一部分则较应有停留时间为长。在生产和设计上,往往需要了解两者之间的定量关系,     

SLC-S分解炉增加物料进口时气固两相流场的数值模拟

以SLC-S分解炉为基准模型,新增一个物料进口,分别对两物料进口在不同的相对位置时的气固两相流场进行了数值模拟.对连续相、颗粒相的计算分别采用k-ε双方程湍流模型和离散相模型,对离散相与湍流之间的相互作用采用随机跟踪模型.模拟所得的气流场分布规律与模型实测结果吻合较好,而且所预测的固、气停留时间以及固气停留时间比值与模型实验预测值相一致.对结构进行优化的模拟结果表明:当两物料进口之间的水平投影夹角大于或等于135°时,尤其是在157.5°时,物料在分解炉内的分散状况皆良好,物料停留时间的绝对值和固气停留时间比值皆很高,为适宜的夹角范围.     

不同角度内模填充衣架型机头的数值模拟

利用Polyflow软件对填充了不同角度内模的衣架型机头流道进行了模拟。研究了不同内模夹角对流道压力分布、出口压力、出口速度以及流道内流体停留时间的影响。结果表明:不同角度内模填充机头流道后,流道压力分布、出口压力和出口速度无明显改变;流道内物料主要停留在歧管端部;通过改变内模夹角,可以改变物料最大停留时间及停留面积,内模夹角为40°时,流道内最大停留时间短,物料停留少。     

新型离心力卸料离心机的研究

本文将原为直锥形转鼓的离心力卸料离心机改为阶梯锥形转鼓的新型离心力卸料离心机。这样延长了物料在转鼓内停留时间，提高了分离质量。经计算物料在转鼓内停留时间增加约两倍，经实测分离质量明显提高。     

循环浆态床气体停留时间分布的研究

研究了循环浆态床气流段的气流量和液体循环量对气体停留时间分布的影响。实验结果表明,减小气流量或者增加液体循环量,气体返混程度变大,气体平均停留时间增长。建立模型模拟循环浆态床气流段气体停留时间分布,得到停留时间分布密度函数和物料分率p与射流相似准数Ct和气液动量比准数Cr的关联式。从关联式看出,气液动量比准数Cr越小,物料分率p越大,表明循环液体流量越大,气体停留时间分布越接近于全混流。这一结论与实验结果相符。     

外循环反应器停留时间分布的计算

本文对外循环反应器的停留时间分布进行了分析和计算。推导了计算公式。通过电子计算机计算,得出了在不同循环比下的停留时间分布数据。提出了在某些情况下外循环反应器停留时间分布的简化计算方法。     

带固体循环系统气流干燥器停留时间分布的计算

本文就具有固体循环系统的气流干燥器停留时间分布规律进行了研究,提出了停留时间分布密度的计算公式。通过计算,得出了在不同的循环比下停留时间分布的计算结果。     

Fluidization behavior in a circulating slugging fluidized bed reactor. Part I: Residence time and residence time distribution of polyethylene solids

Square nosed slugging fluidization behavior in a circulating fluidized bed riser using a polyethylene powder with a very wide particle size distribution was studied. In square nosed slugging fluidization the extent of mixing of particles of different size depends on the riser diameter, gas velocity, hold up and solids flux in the riser. Depending on the operating conditions the particle residence time distribution of a riser in the slugging fluidization regime can vary from that of a plug flow reactor to that of a well-mixed system.Higher gas velocities cause shorter particle residence times because of a significant decrease in the hold-up of particles in the riser at higher gas velocities. A higher solids flux also shortens the average residence time. Both influences have been quantified for a given polyethylene-air system.Residence time and residence time distribution were determined for different particle size and the influence of gas velocity, solids flux, hold up and riser diameter was studied. When comparing data from segregation and residence time experiments it is clear that segregation data can predict the spread in residence time as a function of overall residence time, particle size and gas velocity. The differential velocity between small and large particles found in the segregation experiments can predict the spread in residence time as found in the residence time distribution experiments with a powder with a broad particle size distribution. Raining of particles through the slugs was studied as a function of plug length, gas velocity and pulse length. It was found that raining is not the determining mechanism for segregation of particles.     

The influence of the riser exit on the particle residence time distribution in a circulating fluidised bed riser

This paper reports measurements of the influence of riser exit geometry upon the particle residence time distribution in the riser of a square cross section, cold model, circulating fluidised bed. The bed is operated within the fast fluidisation regime. The fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002) 127-142) was used to measure the residence time distribution.The geometry of the riser exit is shown to have a modest but consistent influence upon the particle RTD; the influence of operating conditions, i.e. superficial gas velocity and solids flux is more significant.Increasing the refluxing effect of the riser exit increases the mean, variance and breakthrough time and decreases the coefficient of variation of the residence time distribution. Changes in reflux do not have a systematic effect upon the skewness of the RTD.     

Influence of ring-type internals on the solids residence time distribution in the fuel reactor of a dual circulating fluidized bed system for chemical looping combustion

The intensification of gas-solids contact in the fuel reactor of a chemical looping combustion system is enhanced with the installation of ring-type internals. This can be a key issue for achieving the necessary fuel conversion rates. Wedged rings, previously designed and tested, were found to increase the particle concentration in the counter current section of the fuel reactor and hence, to achieve a more homogeneous particles concentration along this zone. The present work investigates the effect of the mentioned internals on the residence time distribution of particles in the fuel reactor of a dual circulating fluidized bed system for chemical looping. The study was carried out in a cold flow model especially designed for the fluid-dynamic analysis of the system equipped with a recently developed residence time measurement device based on the detection of ferromagnetic tracer particles through inductance measurement. Ring internals proved the positive effect on the particles residence time, the residence time distribution is more symmetric and shows lower dispersion, the flow pattern is more plug-flow-like, these effects are intensified with the reduction of the aperture ratio of the rings. On the other hand, the upward particle transport in the counter-current zone of the fuel reactor also increases with the installation of the rings, increasing the bypass flow of solids through the fuel reactor's return loop (internal circulation). For high internal circulation rates the solids residence time distribution of the fuel reactor is dominated by the bypass effect. The findings may be used for focused design improvement of the investigated fluidized bed system.     

循环流化床气体返混及停留时间的分布

本文采用脉冲示踪技术,研究了直径140 mm循环流化床内气体的返混特性及其停留时间分布规律,并通过一维轴向扩散模型,得到了气体轴向扩散系数。实验结果表明,在循环流态化条件下,气体轴向流动明显偏离于平推流,并且随操作气速增大或颗粒循环速率的减小,气体轴向返混程度减小。     

高密度液固循环流化床流动特性研究及数值模拟

在φ80 mm×8000 mm的液固循环流化床提升管中,利用实心玻璃珠和常温水,采用实验和数值模拟相结合的方法对高密度液固循环流化床的流动特性进行了考察。实验发现,高密度液固提升管中,颗粒固含率和颗粒速度径向分布均为抛物线分布,轴向平均固含率分布总体上为下浓上稀的波动形式分布,颗粒在提升管中的流动表现出加速-减速-再加速直至充分发展的过程。这种分布特征与较高颗粒浓度、较高表观液速和颗粒循环速率及喷管式液体分布器的影响有关。液固提升管中固体颗粒的停留时间分布曲线均为尖而窄、较对称且没有明显拖尾的单峰分布,这表明颗粒基本是以弥散颗粒形式存在,颗粒停留时间分布较为均匀。通过将数值模拟结果与实验结果进行比较发现,模拟值与实验值吻合较好,说明所建立的数学模型较为合理,进一步通过数值模拟实验对颗粒密度和颗粒粒径对流动特性的影响规律进行了考察。     

固体返料气流-流化组合干燥器的湿含量分布

分析了固体返料气流 -流化组合式干燥器出口粒子湿含量分布特性 ,建立了湿含量分布密度函数 ,并就硫酸亚铁的干燥过程进行了模拟计算 结果表明 ,具有降速段的流化床干燥器的优化设计 ,除了应满足干燥过程的热量供求平衡并由此确定流化床底面积外 .还应满足 :①保证湿分传质汽化所需的停留干燥时间 ,应根据干燥所需的平均停留时间来确定流化床容积 ;②控制湿含量的分散程度 ,应由干燥产品的均匀性指标来确定流化床室数 .     

Paste Residence Time in a Spouted Bed Dryer. IV: Effect of the Inert Particle Size Distribution

The residence time distribution and mean residence time of a 10% sodium bicarbonate solution that is dried in a conventional spouted bed with inert bodies were measured with the stimulus-response method. Methylene blue was used as a chemical tracer, and the effects of the paste feed mode, size distribution of the inert bodies, and mean particle size on the residence times and dried powder properties were investigated. The results showed that the residence time distributions could be best reproduced with the perfect mixing cell model or N = 1 for the continuous stirred tank reactor in a series model. The mean residence times ranged from 6.04 to 12.90 min and were significantly affected by the factors studied. Analysis of variance on the experimental data showed that mean residence times were affected by the mean diameter of the inert bodies at a significance level of 1% and by the size distribution at a level of 5%. Moreover, altering the paste feed from dripping to pneumatic atomization affected mean residence time at a 5% significance level. The dried powder characteristics proved to be adequate for further industrial manipulation, as demonstrated by the low moisture content, narrow range of particle size, and good flow properties. The results of this research are significant in the study of the drying of heat-sensitive materials because it shows that by simultaneously changing the size distribution and average size of the inert bodies, the mean residence times of a paste can be reduced by half, thus decreasing losses due to degradation.