带翼阀旋风分离器料腿内动态压力的分析研究

在大型流化床装置上,采用动态压力传感器测定了翼阀置于流化床的稀相空间和密相空间两种情况时料腿内的动态压力。通过对二级料腿稳定排料和周期性排料的数据分析得出,料腿内动态压力的变化与料腿内颗粒质量流率的大小密切相关,翼阀埋没在密相时料腿内的压力波动比较平缓,料腿的周期性排料时压力波动频率约0.01Hz,料腿内稀相段压力波幅比密相段略小,料腿内压力波动的原因是由于气固两相在快速下行过程中存在密度差和速度差。     

双气路循环流化床压力平衡的实验研究

在Φ800mm×12000mm流化床装置上,用多点压力测量仪对双气路循环流化床各部分的压力分布进行了实验。实验结果表明,颗粒单循环回路的压力平衡图与装置的运行状态、颗粒的循环量密切相关。整个颗粒的循环回路压力曲线呈双8字缠绕式,随质量流率的减少形状发生畸变;补气循环回路与不补气循环回路的压力分布相似,但料腿沉降段的压力降低;提升管内没有明显的稀密相交界面,而料腿内存在着稀密相的交界面,料腿下部的高密度移动床是保证流化床正常运转的必要条件。     

提升管内气固流动的小波分析

对由光纤探头获得的提升管循环流化床内颗粒体积分数的瞬态信号,采用Dauchveies小波(db4)进行15层的小波分解,并计算各尺度能量分率,以研究提升管底部浓相段与顶部稀相段气固流动结构。结果表明:颗粒速度、体积分数、能量分率在径向分布都呈典型的环核结构;底部浓相段和顶部稀相段的高、中、低频能量分率基本相同,分别在10%,60%,30%左右,说明提升管内大多数的颗粒以聚团形式或密度较大的颗粒群的形式在流化床内流动。操作条件的改变对稀密段气固流动结构的影响不同:颗粒循环流率的改变对密相段的流动影响较大,而气体速度的变化对稀相段的流动影响较大。     

循环流化床下料立管内气固两相流动状态与压力脉动的关系

在15 m高的大型气固循环流化床上对内径90和42 mm的下料立管内气固两相流的动态压力进行了测量. 实验结果表明,负压差下料立管内的气固两相流动存在着低频压力脉动,压力脉动的强度可以用动态压力的标准方差(Standard deviation, Sd)来表征,且与立管下料的流动状态密切相关. 立管下料的流动状态依据颗粒质量流量通量的大小有浓相输送状态和稀密两相共存两种状态. 浓相输送状态的压力脉动强度较大,是下行颗粒压缩其夹带气体引起气固两相强烈相互作用导致的;稀密两相共存状态的压力脉动强度较小,是密相段排料的不稳定性和稀相段较弱的气固相互作用共同引起的. 立管下料的压力脉动强度随颗粒质量流量通量的增加而增大,对于浓相输送状态,在实验操作范围内[Gs'=550~850 kg/(m2×s)],压力脉动的强度与立管下料质量流量通量近似成Sd=0.00875Gs'-4.77的线性关系.     

气固两相流内中空多孔催化剂性能的数值模拟

气固流态化过程中流体和颗粒分别聚集,形成稀密两相,严重限制其传质效率和反应速率的提高。针对此问题,本工作设计了一种中空多孔结构的催化剂颗粒,通过模拟方法研究该颗粒对稀密两相气相传质与反应的影响,及其在稀密相间转换的时间尺度。结果表明,一定的流动强度时,在颗粒稀密相转换的时间尺度内,中空多孔结构的颗粒能够有效地在稀相存储反应气体,并在密相释放,为密相提供额外的反应气体,增强体系的整体反应效率。当催化反应速率高于传质速率时,在所研究的流动条件下中空多孔颗粒体系的反应效率比实心球形颗粒体系高出26.92%~29.55%。可以预见在稀密相分布更广的大型气固流化床反应器中,中空多孔结构的催化剂颗粒能够更为有效地提高反应器的整体效率。     

循环流化床中流动结构的动态变化

采用激光相位多普勒粒子分析仪（ＰＤＰＡ）测量了二维循环流化床中局部颗粒运动行为及流动结构．通过将ＰＤＰＡ采集的数据进行动态图形化处理，研究了稀、密相的结构以及颗粒聚团的形成和分解．研究结果表明：在循环流化床中不仅存在稀、密两相的不均匀流动结构，而且密相和稀相自身内部也存在不均匀性；颗粒聚团的形成和分解是一个动态过程，颗粒间不同速度造成颗粒相互碰撞，密相能够分解形成稀相，稀相能够合并成为密相．在流动过程中稀相、密相及介于稀、密相间的乳相以动态的形式存在和分解，形成复杂的动态流动结构．     

CFB密相区内颗粒横向扩散对燃烧的影响

循环流化床(CFB)床内燃料颗粒的扩散、混和，特别是复杂的密相区内的混和特性在很大程度上影响了燃烧状况，密相区颗粒横向扩散的规律，对于循环流化床的设计具有重要意义，在循环流化床密相区颗粒横向扩散实验研究的基础上，总结了密相区内颗粒横向扩散系数的经验公式，以此为基础，研究了密相区内碳的分布规律，并建立了相应的燃烧模型，模型包括两个子模型，即密相区二维流动及燃烧子模型、稀相区一维流动及燃烧子模型。通过模型定性模拟了流化风速、给料点布置对床内燃烧的影响，有效地反映了实际情况，并确认了将密相区颗粒横向扩散规律引入现有循环流化床燃烧模型的重要意义。     

提升管内气粒流动行为的数值模拟

采用描述密相湍流气粒流动规律的k-ε-kp-εp-Θ双流体模型对不同尺度和操作条件下的提升管内的定常流动进行了计算流体力学数值模拟，获取了各种工况下有关颗粒速度、体积分率和质量流率分布等宏观流动行为的大量信息，并与相应条件下的实验数据取得了较好的吻合。此外还通过对大量模拟数据的分析获得了提升管内宏观流动规律的综合图像。该模型描述了密相湍流气粒流动规律，预测出了描述单颗粒脉动能大小的颗粒拟温度田和表征颗粒在介观尺度上脉动大小的颗粒湍动能江在床内的分布。分析表明：不同流动参数对颗粒在微观和介观尺度上的脉动有不同程度的影响；固含率对颗粒相的脉动行为和颗粒的质量扩散行为有重要的影响。     

渐缩下料段对其上矩形移动床内床层颗粒流动的影响

本文从Ｎｅｄｄｅｒｍａｎ等人的颗粒流动学基本理论出发，结合Ｐｏｌｄｅｒｍａｎ等人对渐缩下料段同颗粒流动分布的研究结果，建立了矩形移动床床内颗粒流动速度分布的关系式，提出了渐缩下料段对其上床层颗粒流动影响临界高度的概念，并分析了改变渐缩下料段几何形状及颗粒与渐缩下料段壁面的摩擦角等因素对临界高度的影响，以期为有效利用移动床提供指导。     

油页岩循环流化床燃烧室密相区物料颗粒与燃烧特性

在 65t/h油页岩循环流化床锅炉上进行了燃烧室密相区物料特性与燃烧特性的工业试验。得到了极具片状结构特点的油页岩颗粒特性 ,经燃烧破碎磨损后的密相区床料和循环物料的颗粒特性与燃烧特性及相应的锅炉运行参数。试验结果对油页岩循环流化床锅炉的放大设计与运行调节具有一定的参考价值。同时为进一步建立油页岩循环流化床燃烧室密相区的流动、燃烧、传热、磨损、扬析与夹带模型奠定了基础。     

流化床中旋风下料管的物理模型

In most industrial fluidization units, two- or three-stage cyclone systems are used to clean the product gases. To return the solids to the bed, these cyclones are fitted with diplegs. By pass of gas from the bed through the dipleg is partially overcome by the back pressure build-up in the dipleg and by adding a trickle valve at the bottom of the dipleg. Diplegs of primary cyclones, operating at a high solid loading behave differently from diplegs of secondary and tertiary cyclones which operate at low solid loading. Both types have been investigated by pressure drop measurements, visual observation and by measurements of the air flow rate flowing up the riser. The primary dipleg was also studied using electrical capacitance tomography. The results are reported hereafter and will give a first indication towards the right design of the dipleg and the selection of the trickle valve. The influence of gas flow in the dipleg on the conversion in a catalytic fluidized bed reactor is found to be negligible.     

负压差立管下料过程压力脉动的传递性实验与分析

在高13m大型循环流化床装置上,对φ150 mm×900 mm负压差立管内气固两相流的动态压力进行了轴向多点测量,并用标准偏差进行了分析,主要研究立管下料过程的动态传递特性.实验表明负压差立管内存在明显的压力脉动现象,这种压力脉动具有一定的传递性.颗粒质量流率比较小时是稀密两相共存流态,稀相区的压力脉动主要受进料流量振荡的影响,向下传递;密相区的压力脉动主要受立管的波动性排料影响,向上传递;随着颗粒质量流率的增加达到浓相输送流态时,上部是连续式浓相输送流态,下部是密相波浪式输送流态,立管的压力脉动主要受进口流量振荡和排料过程压缩气体作用,向下传递.对立管的压力脉动进行标准偏差分析表明脉动压力传递沿颗粒的流动方向上具有幅值增大特性.在立管内流态从稀密两相共存流态转变为浓相输送流态时,由于颗粒压缩气体分量最大,压力脉动幅值最大,减小或增加颗粒质量流率,压力脉动幅度均降低.     

Numerical and Experimental Study of Catalyst Loading and Body Effects on a Gas‐Liquid Trickle‐Flow Bed

The influence of tortuosity and fluid volume fractions on trickle‐flow bed performance was analyzed. Hydrodynamics of the gas‐liquid downward flow through trickle beds, filled with industrial trilobe catalysts, were investigated experimentally and numerically. The pressure drop and liquid holdup were measured at different gas and liquid velocities and in two different loading methods, namely, sock and dense catalyst loading. The effect of sharp corners on hydrodynamic parameters was considered in a bed with rectangular cross section. The reactor was simulated, considering a three‐phase model, appropriate porosity function, and interfacial forces based on the Eulerian‐Eulerian approach. Computational fluid dynamics (CFD) simulation results for pressure drop and liquid holdup agreed well with experimental data. Finally, the velocity distribution in two types of loading and the effect of bed geometry in CFD results demonstrated that pressure drop and liquid holdup were reduced compared to a cylindrical one due to high voidage at sharp corners.     

旋流筛板式气固挡板流化床内压力脉动特性

在表观气速Ug=0.04~1.14 m/s时,采用旋流筛板构型的挡板式内构件,通过对比分析旋流筛板式气固挡板流化床与自由床内流动现象、压差脉动标准偏差和压力脉动标准偏差等参数,确定了旋流筛板式气固挡板流化床能有效破碎气泡的流动与操作条件。结果表明,构件下方区域颗粒随表观气速增加而不断转移至构件上方床层,造成构件下方区域密相床层高度持续降低,该区域出现3种流动状态并直接决定构件是否能破碎气泡。当Ug<0.44 m/s时,构件下方区域密相床层料位较高,形成下部为密相床层、上部为密相与大气泡交替通过构件的鼓泡床,此时构件具有抑制气泡生长并破碎气泡的作用,全床压差脉动及压力脉动标准偏差低于相同条件下的自由床;当0.44≤Ug<0.66 m/s时,密相床层料位较低,形成下部为密相床层、上部为单一稀相的湍动床,此时构件不再直接抑制气泡生长或破碎气泡,但构件下方密相床层的存在能降低构件下方及构件上方一定高度内床层的压力脉动强度;当Ug≥0.66 m/s后,密相床层完全消失,形成气体为连续相的稀相流化状态,构件不能破碎气泡、降低床层压力和压差脉动强度。     

Trickle bed reactor diluted with fine particles and coiled tubular flow-type reactor for kinetic measurements without external effects

Gas and liquid velocities in laboratory scale trickle bed reactors are one or two orders of magnitude lower than those in commercial reactors. Then, the kinetic data may include the external effects. This shortcoming of laboratory scale trickle bed reactor can be resolved by diluting the catalyst bed with fine inert particles. The catalyst bed dilution increases dynamic liquid holdup, pressure drop, gas–liquid mass transfer coefficient. Hydrogenation of 2-phenylpropene on Pd/Al₂O₃ was performed with the trickle bed reactor diluted with fine inert particles and the coiled tubular flow-type reactor to compare the kinetics with that of the basket type batch reactor. The trickle bed reactor diluted with fine inert particles is suitable to obtain the reaction rate without external effects even if the liquid velocity is low. The coiled tubular flow-type reactor should be used at high gas velocities.     

Apparent drag reduction phenomenon in the defluidized packed dense bed of the multisolid pneumatic transport bed

Experiments were performed to study the pressure drop behavior in the packed bed of dense particles in the multisolid pneumatic transport bed (MPTB). The packed bed under extensive analysis is established by fluidizing and then defluidizing the dense particle bed by increasing and then decreasing the air flow rate at a constant fine particle flow rate. The pressure drop in a packed bed established in this manner initially decreases significantly and then increases as the fine particle flow rate increases at a given air flow rate. This behavior signifies the apparent drag reduction phenomenon in the defluidized packed bed. The classical pressure drop equation by Ergun[1] was modified to account for this phenomenon.     

移动床贴壁现象的研究

在错流区高度为430 mm,横向宽度分别为400 mm,200 mm,105 mm的三种不同尺寸的矩形二维移动床内对贴壁现象进行了研究.实验结果表明,随着错流气速的增加床层压降也增加,当压降超过一定值时,移动床内近下流面的部分颗粒将停止下移,发生贴壁;贴壁颗粒层的厚度与床层压降呈线性关系,在相同错流气速下宽床层的贴壁厚度大于窄床层,但无因次化贴壁厚度大致相同.通过力平衡分析建立了贴壁现象的数学模型,可计算不同压降下贴壁颗粒层的厚度,并获得贴壁临界压降值的计算式,模型计算值与实验值基本相符.     

Hydrodynamics in a pilot‐scale cocurrent trickle‐bed reactor at low gas velocities

Hydrodynamic data obtained from laboratory‐scale trickle‐beds often fail to accurately represent industrial‐scale systems with high packing aspect ratios and column‐to‐particle diameter ratios. In this study, pressure drop, liquid holdup, and flow regime transition were investigated in a pilot‐scale trickle‐bed column of 33 cm ID and 2.45 m bed height packed with 1.6 mm × 8.4 ± 1.4 mm cylindrical extrudates for air‐water mass superficial velocities of 0.0023 – 0.094 kg/m²s and 4.5 – 45 kg/m²s, respectively, at atmospheric pressure. Significant deviation was observed from pressure drop and liquid holdup correlations at low liquid flows rates, corresponding to gravity‐driven flow limit. Likewise, liquid saturation is overestimated by correlations at high liquid flow rates, owing to significantly reduced wall effects. Lastly, trickle‐to‐dispersed bubble flow and trickle‐to‐pulsing flow regime transitions are reported using a combination of visual observations and analysis of the magnitude of local pressure fluctuations within the column. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2560–2569, 2018