多段分级转化流化床提升管局部固体体积分数分布

在射流流化床与提升管耦合的多段分级转化流化床冷态实验装置上,采用PC6D型颗粒体积分数测量仪,系统研究了提升管中局部固体体积分数径向分布及其轴向发展规律。结果表明:固体体积分数的径向分布为中心区固体体积分数较稀、分布均匀,边壁区为体积分数高、分布陡峭的环核流动结构。提升管中径向颗粒体积分数的轴向发展为:提升管底部,中心区和边壁区固体体积分数随轴向高度的增加而减小,边壁区固体体积分数的减小趋势明显高于中心区;提升管的发展段,边壁区固体体积分数随高度的增加而减小,而中心区固体体积分数几乎不变。提升管所有截面上各径向位置的固体体积分数随表观气速ur,g的减小或固体循环量G S的增加而增大,边壁区固体体积分数受操作条件影响的敏感程度明显高于中心区和过渡区。拟合得到了升管不同径向区域内固体体积分数与截面平均固体体积分数的关系式,误差分析表明该表达式的计算值和实验值吻合较好。     

循环流化床提升管中颗粒速度的径向分布及其沿轴向的发展

采用5光纤速度探头对f100mm?5.1m循环床提升管8个高度截面上11个径向位置的局部颗粒速度进行了实验测试,并采用径向不均匀指数(RNI)对颗粒速度径向分布的不均匀性及其沿轴向的变化进行了定量描述。研究结果表明:在高气速、高颗粒循环量操作时,操作条件对颗粒上升速度和下降速度的径向分布的影响在加速段和充分发展段呈现出不同的规律;颗粒上升速度和下降速度沿轴向的变化在核心区和边壁区也表现出不同的趋势。当颗粒循环速率大于200 kgm-2s-1时,颗粒的加速段长度大大延长,以至于大于提升管的高度(15.1m)。颗粒速度径向分布的不均匀性沿轴向是逐渐增大的,并且与截面平均颗粒速度存在很强的相关性。     

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。     

预热器换热管内粉体物料轴向浓度分布的试验研究

采用光纤探头针对7个不同高度的预热器换热管截面做粉料轴向相对浓度分布测试.研究发现,沿换热管下料点断面向上,同一径向位置的颗粒浓度总是不断减小.换热管边壁区颗粒浓度沿轴向位置升高而减小远比中心区域迅速,当表观气速较小或物料负荷率较高时此现象尤为明显.随换热管截面高度的增高,气固两相流场发展逐步充分而趋于稳定,两者的相对运动速度逐渐变小.气流沿轴向的湍动逐步减弱,中心区和边壁区的颗粒浓度的差异逐渐缓和.改变操作条件对同一轴向断面边壁区颗粒浓度的影响较大,对中心区颗粒浓度的影响较小.增大系统的固气比,轴向不均匀性增大,物料下冲高度增大.     

60米高矩形截面循环流化床内物料分布冷态试验

为研究超高提升管内的气固流动特性,依托四川白马电厂600MW超临界循环流化床锅炉现有钢架,将原有60m高的提升管冷模试验台的上部20m改为矩形截面的循环流化床提升管试验台。本文重点研究了提升管流化风速对上部颗粒浓度的轴向/截面分布特性及其影响因素。试验结果表明：颗粒浓度和颗粒粒径的分布特性与流化风速和几何结构密切相关,在一定初始床料高度下,随着风速的增加,提升管上部的空隙率沿轴向先不变然后减少,并最终呈现倒C形分布;截面浓度从均匀分布逐渐变为近短边壁处的颗粒浓度要明显大于近长边壁处的不均匀分布;平均颗粒粒径则随风速的增加而增大,沿截面分布均匀,但是沿提升管高度方向平均颗粒粒径沿轴向会略微减小,且提升管上部近短边壁的颗粒粒径要稍小于近长边壁的。     

耦合流化床提升管内固含率径向分布及沿轴向的发展

针对催化汽油辅助反应器改质降烯烃工艺,结合提升管与流化床的特点,建立了一套提升管与流化床耦合反应器大型冷态实验装置. 在不同操作条件下,采用PV-4A型光纤密度仪测定了提升管内固含率沿径向的分布规律. 结果表明,固含率径向分布整体上呈现中心小、边壁大的环-核结构分布特征;沿轴向向上,各径向位置上的固含率在颗粒加速区逐渐降低,在充分发展区趋于稳定,在颗粒约束返混区又有所升高;各径向位置上的固含率随表观气速增大或颗粒循环强度减小而减小,且均匀性变好;提升管上部流化床内颗粒静床高度只对颗粒约束返混区内固含率径向分布有影响,而对颗粒加速区和充分发展区的固含率径向分布影响较小;当表观气速较低或颗粒循环强度较大时,颗粒约束返混区上部局部固含率最大值出现在无因次半径f=r/R=0.7附近,此时局部无因次固含率es*=es/ 沿轴向在H>5.33 m时不再具有相似性;通过比较径向不均匀指数,得到轴向各区固含率径向分布趋于均匀的程度依次为：充分发展区>颗粒约束返混区>颗粒加速区. 利用实验数据回归出了局部固含率径向分布关联式,其平均相对误差在6%以内.     

内构件对于提升管中颗粒混合行为的影响

对加设了钝体式内构件的提升管内颗粒的轴径向混合为进行了研究。研究结果表明，内构件的存在并不能明显减少提升管内颗粒的轴向返混，这与提升管内稳定的微观两相结构密切相关，但颗粒的径向混合能力却可大大加强，而且在越高的气速和固含条件下，这种加强作用越明显，其原因是内构件的存在加强了边壁区颗粒的脉动，有利于破坏提升管边壁区的颗粒浓环，促进颗粒的径向交换与混合。     

一种新型入口结构的下行管的流体力学性能

提出了一种新型下行管入口结构. 这种结构设有雾化空间,能够提供适宜的床层密度,剂油初始接触采用逆流、错流方式. 在下行管入口处,颗粒浓度呈管中心高、边壁低的分布;随着颗粒向下运动,中心区颗粒浓度逐渐降低,边壁区颗粒浓度升高. 在下行管完全发展段,颗粒浓度径向分布形式不再随轴向位置发生变化.     

入口结构对18 m气固循环流化床提升管内颗粒流动特性的影响

在高18 m、内径80 mm的循环流化床提升管内分别考察了三种入口结构对颗粒流动特性的影响。实验结果表明:入口结构主要影响提升管底部区域的颗粒流动特性,不同入口结构对颗粒流动影响不同。相同操作条件下,当采用多管式入口结构时,径向上提升管底部区域的颗粒浓度分布相对均匀,轴向上颗粒能够迅速达到充分发展状态,充分发展高度在9 m左右;当采用多孔板入口结构时,径向上提升管底部颗粒浓度差别较大,轴向上颗粒发展较慢,需要更高高度才能达到充分发展,充分发展高度约为11 m;当采用单管式入口结构时,径向上颗粒浓度分布和轴向上颗粒充分发展速度均处于前两者之间,底部颗粒浓度径向分布仍为中间稀、边壁浓的不均匀分布,颗粒浓度轴向充分发展高度约为10 m。     

气固两相上行流动中颗粒加速行为的研究

根据空气－FCC颗粒在16m高循环床提升管内的压力梯度实验数据,对提高升管颗粒加速区的平衡颗粒浓度、颗粒加速区长度以及操作条件的影响进行了系统的分析研究。颗粒的加速导致了颗粒表观浓度沿提升管轴向的不均匀分布,加速区截面上颗粒表观浓度随操作参数的变化明显不同于充分发展段;颗粒加速区长度受操作条件影响非常著,增加颗粒循环量或减小表观气速,都将延长颗粒加速过程,颗粒表观浓度也随之增加;特别地,当提升管底部有大量颗粒聚集和絮状物形成时,颗粒加速区将显著增长,甚至扩展到整个提升管高度。     

入口结构对18 m气固循环流化床提升管内颗粒流动特性的影响

在高18 m、内径80 mm的循环流化床提升管内分别考察了三种入口结构对颗粒流动特性的影响。实验结果表明：入口结构主要影响提升管底部区域的颗粒流动特性,不同入口结构对颗粒流动影响不同。相同操作条件下,当采用多管式入口结构时,径向上提升管底部区域的颗粒浓度分布相对均匀,轴向上颗粒能够迅速达到充分发展状态,充分发展高度在9 m左右;当采用多孔板入口结构时,径向上提升管底部颗粒浓度差别较大,轴向上颗粒发展较慢,需要更高高度才能达到充分发展,充分发展高度约为11 m;当采用单管式入口结构时,径向上颗粒浓度分布和轴向上颗粒充分发展速度均处于前两者之间,底部颗粒浓度径向分布仍为中间稀、边壁浓的不均匀分布,颗粒浓度轴向充分发展高度约为10 m。     

A Comparison of Flow Dynamics and Flow Structure in a Riser and a Downer

Flow development and flow dynamics were systematically investigated using local solids concentration measurements in a pair consisting of a downer (0.1 m I.D., 9.3 m high) and a riser of the same diameter (0.1 m I.D., 15.1 m high). Both statistical and chaos analysis were employed. Values for the Kolmogorov entropy (K), correlation dimension (D), and Hurst exponent (H) were estimated from time series of solids concentration measurements. Axial distributions of chaos parameters were more complex in the downer than those in the riser, especially in the entrance section. Flow in the downer was more uniform with a flatter core in all the radial profiles of chaos parameters. The radial profiles of K varied significantly with increasing axial levels due to different clustering behavior in the wall region of the downer. In both the riser and the downer, anti‐persistent flow in the core region and persistent flow behavior near the wall were identified from the profiles of H. Different flow behavior in the region close to the wall in the downer and riser was characterized from the combination of the three chaos parameters. Relationships between chaos parameters and local time‐averaged solids holdup in the core and wall regions of the developed sections in both the downer and riser were also analyzed.     

Comparative Study of Flow Structure in Circulating Fluidized Bed Risers with FCC and Sand Particles

The combined influences of particle properties and nozzle gas distributor design on the axial and radial flow structure in two 100 mm i.d., 15.1 m and 10.5 m long risers with FCC and sand particles were investigated by measuring the axial pressure gradient profiles, and the axial and radial profiles of solids concentration. The results show that the nozzle gas distributor design has significant effects on the axial and radial flow structure for the FCC and sand particles. At lower superficial gas velocity of less than 8.0 m/s, the upward gas‐solid flow of the sand particles decelerates in various degrees with the disappearing of the nozzle gas distributor effect. The upward gas‐solid flow of the FCC particles, however, occurs without noticeable deceleration within the range of this study. In the acceleration section, the radial distributions of the local solids concentration of the FCC particles are more uniform than those of sand particles under the same operating conditions; while in the fully developed zone, the sand particles have a more uniform radial distribution than the FCC particles. The gas‐solid flow is first developed in the center region, and then extends towards the wall. The overall flow development in the riser mainly depends on the local gas‐solid flow in the wall region.     

Flow patterns in high-velocity fluidized beds and pneumatic conveying

Four flow patterns are identified for gas-solids vertical upward flows. Homogeneous dilute phase flow is characterized by the absence of both radial and axial solids segregation. Heterogeneous dilute phase flow (also called core-annulus flow) is characterized by the absence of axial solids segregation, with solids carried upward in the core and travelling downward near the outer wall due to the formation of particle streamers. Collapsed flow with a lower dense region and an upper dilute region is also referred to as the fast fluidization regime. In this case, the flow structure in the upper dilute region is similar to that in heterogeneous dilute phase flow, while the lower dense region resembles that in a turbulent fluidized bed. Dense phase flow can be reached when the riser is completely occupied by a relatively dense suspension with little axial density variation and no net solids downflow near the riser wall. The transition from fast fluidization to dense phase flow is still not clearly defined.     

Flow development in a gas-solids downer fluidized bed

The development of gas and solids flow structure was studied in a 9.5 m high and 0.10 m diameter, gas-solids cocurrent downflow circulating fluidized bed (downer). Local solids concentration and particle velocity were measured using two separate optical fibre probes at different radial positions on several axial levels along the downer. The results show that the flow development is significantly influenced by the operating conditions. For most of the conditions under which the experiments were conducted, the gas-solids flow reaches its fully developed zone within 3 to 8 m away from the entrance. On the other hand, the development zone can extend as long as the downer itself, under certain conditions. When the solids circulation rate is over 100 kg/m²s, an increasing solids circulation rate largely extends the length of radial flow development. It is found that the flow developments in the core and at the wall are not quite simultaneous. For solids concentration, the core develops more quickly at low gas velocities and the wall region develops faster at high gas velocities. For particle velocity, higher gas velocity speeds up the development of the wall region but does not significantly affect the development of the core region. The wall region is much more sensitive to the change of superficial gas velocity than the core region. At high superficial gas velocities (> 7 m/s), a “semi-dead” region is observed in the fully developed zone adjacent to the wall where the dilute solids are moving at a very low velocity.     

The influence of distributor structure on the solids distribution and flow development in circulating fluidized beds

The influence of distributor structure on solids distribution is studied in two riser circulating fluidized bed reactors with different distributor structures but similar diameters. Optic fibre probes were used for the measurement of local solids distribution. The axial and radial distribution of solids holdup in the riser with a multi‐tube distributor is more uniform than that with a multi‐orifice distributor. The radial profiles of particle velocity in the riser with the multi‐tube distributor are also more uniform than that with the multi‐orifice distributor. In the riser with the multi‐tube distributor, both gas and particles are distributed more uniformly across the section, so that the flow acceleration is much more uniform and faster. The flow development is much faster and the fully developed region is reached early for the riser with the multi‐tube distributor. The distributor design is an important factor for the design of circulating fluidized bed reactor.     

竖直窄通道充分发展段液固流动特性的数值模拟

采用欧拉-欧拉双流体模型,基于水-玻璃珠体系,对长×宽×高尺寸为240 mm×12 mm×1800 mm的竖直窄通道充分发展段内液固两相流动特性进行了数值模拟。结果表明,沿窄通道竖直方向0.7 m以上液固两相流动进入充分发展阶段,在充分发展阶段的窄通道截面上,狭长方向与狭窄方向各位置颗粒速度及浓度均呈中心区域高、贴近边壁区域低的分布趋势;随着入口液速提高,截面各位置颗粒速度均提高,而颗粒浓度在流道中心区域降低,在贴近壁面区域升高;随着初始固相体积分数增加,截面各位置颗粒浓度均提高,而颗粒速度在流道中心区域略有降低,在贴近壁面区域略有升高;在窄通道截面狭长方向两端靠近三边壁影响的区域存在颗粒增浓效应,在截面狭窄方向颗粒速度和浓度分布梯度较大的区域无量纲占比随着入口液速的提高而提高,随着初始固相体积分数的提高而减小。     

气固下行流化床反应器Ⅱ气固两相的流动规律

气固下行流化床反应器气固两相流动过程是比较复杂的，沿轴向气固两相运动可分为第一加速、第二加速和恒速３个运动段，沿径向局部气体速度、颗粒速度和颗粒浓度都具有不同程度的不均匀性。而这种不均匀性是由气固两相顺重力场湍动运动所决定的。和循环床提升管相比，下行管反应器气固两相沿径向分布的不均匀性得到有效地改善，气固可以实现超短接触操作，因而是一种新型高效气固超短接触反应器     

Three‐component solids velocity measurements in the outlet section of a riser

Coincident (simultaneous) three‐component particle velocity measurements performed using two laser Doppler anemometry probes at the outlet section of a 9 m high cylindrical riser are for the first time presented for dilute flow conditions. Near the blinded extension of the T‐outlet a solids vortex is formed. Particle downflow along the riser wall opposite the outlet tube is observed, which is restricted to higher riser heights at higher gas flow rates. Increased velocity fluctuations are observed in the solids vortex and downflow region as well as at heights corresponding to the outlet tube. Contrary to the rest of the riser, in the downflow region time and ensemble velocity averages are not equal. Given the local bending of the streamlines, axial momentum transforms to radial and azimuthal momentum giving rise to the corresponding shear stresses. Turbulence intensity values indicate the edges of the downflow region. © 2016 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 62: 3575–3584, 2016