纤维素酶水解反应器的开发与放大

以木质纤维素生产燃料乙醇为背景,在考察玉米秸秆同步糖化与发酵反应特征基础上,给出了合适的反应器构型:螺带型搅拌槽;直径0.2～0.8m,高径比1～2,转速20～120r/min,着重从冷模实验对搅拌槽性能进行了考察,为反应器放大提供必要的基础。实验结果发现,层流流动条件下,随流体剪切稀化性质增强,搅拌功率(Np)显著降低,而无因次混合时间(Ntm)则变化不大;给出适用于强剪切稀化流体的Metzner常数Ks关联式,且Ks与搅拌槽直径无关;对于几何相似的螺带桨,随着搅拌槽直径增大,若保持相同的单位体积功率,Ntm是相同的,这为我们提供了一个螺带型搅拌槽的放大准则;搅拌槽功耗及Ntm随着搅拌槽高径比的增大而增大;最后采用数值计算方法对搅拌槽内分散混合效率进行了考察,发现,根据混合效率的不同,可将螺带型搅拌槽分成几个不同的区域,搅拌槽内体积平均分散混合效率接近于0.5(简单剪切流)。纤维素酶水解反应器的放大,小试给出关键参数(单位体积生产能力),冷模实验提供混合性能、几何结构设计基础,经验判据与CFD相结合,关注基本流型的尺寸效应,兼顾单位体积功率及最大剪切速率。     

带转动挡板的搅拌萃取塔连续相停留时间分布研究

为获取带转动挡板的搅拌萃取塔内部流体流动状况，采用脉冲示踪法对塔内连续相停留时间分布(RTD)进行研究，并结合轴向返混模型得到了连续相的返混系数。结果表明，随着连续相体积流量、总流量或连续相与分散相体积流量比值的增大，连续相RTD曲线收窄、峰值明显增大、连续相停留时间和返混系数均减小；改变分散相体积流量，连续相RTD以及返混系数基本不变。此外，改变搅拌转速对连续相RTD影响较小。将返混系数与操作条件和物性参数进行关联，关联式最大偏差为19.8%、平均偏差为7.7%，表明关联式可用于带转动挡板的搅拌萃取塔的连续相轴向返混程度的评估。     

组合桨搅拌器的宏观混合特性

分别以浓度为１％，２％，３％，３．５％的羧甲基纤维素溶液为实验，采用测温法，测定了正交双层三角桨－单螺带桨，正交双层三角桨－内外单螺带桨．锚式桨－三叶推进器．锚式桨－内外单螺带４种组合桨拌器的宏观混合时间，无量钢数Ｃ１，Ｃ２，Ｃ３，Ｃ４综合评判了它们的宏观混合性能，实验证明，前２种组合桨搅拌器在不同流域内都使搅拌介质达到良好的宏观混合，且功率消耗低，混合效率高，具有明显的节能优势，对搅拌变粘度体系     

ECM30双转子连续混炼机转子及嵌入块结构对分散混合性能的影响

计算比较了双转子连续混炼机不同转子结构和嵌入块时的轴向速度分布、剪切应力和混合指数的分布，得到了转子结构和嵌入块的嵌入深度对ECM30双转子连续混炼机分散混合性能的影响。转子螺棱交汇区的长度减小，其流场的剪切作用增强，拉伸作用减小；转子螺棱包角增加，转子的返混能力增加，剪切和拉伸作用减小。增加嵌入块的高度，返混能力增强，剪切作用增加，拉伸作用减小。     

搅拌槽内具滑移特性非牛顿流体的搅拌功率及混合特性研究

在直径为0.48m的搅拌槽内考察了包括CBY、45°斜叶桨及螺带在内的五种搅拌桨对三种不同流变特性的具有滑移现象的非牛顿高黏流体混合效果的影响。首先采用HAAKERS150流变仪对三种流体的流变特性进行测定和表征,比较各种桨型在液位与槽径比H/T为0.28～0.52内的混合效果,得出不同流体中适宜的搅拌桨型及桨型适宜的混合液位范围。结果表明,在具有滑移特性的流体中各种桨型的Metzner常数通常高于经验数值;螺带桨在很宽的表观黏度范围及较宽的雷诺数范围下均表现出较好的混合效果,而CBY及45°斜叶桨型只适用于流体表观黏度较小而雷诺数相对较高的情形。在液位最低时,流体的混合时间和混合能并非最低,各种桨型的最佳操作液位在槽径的0.35～0.43倍内。     

羟乙基纤维素水溶液黏度稳定性及其抗酶解性能试验

在不同的羟乙基纤维素(HEC)水溶液样品中分别添加防腐杀菌剂和纤维素酶,考察存放不同时间后HEC水溶液的黏度稳定性和酶解稳定性。结果表明:在不添加防腐杀菌剂的情况下,防酶型HEC水溶液的黏度可较长时间保持稳定,而非防酶型的HEC水溶液的黏度随存放时间的延长出现明显下降;添加防腐杀菌剂后,防酶型和非防酶型HEC水溶液均有良好的黏度稳定性。添加纤维素酶后,防酶和非防酶型的HEC水溶液均会发生降解以致其黏度下降,其中非防酶型的黏度下降最快,并明显伴有还原糖的产生。研究结果可为HEC生产与应用企业测试产品性能与质量、制定水性涂料用HEC的行标或国标提供参考。     

三维上流式反应器床层流动和返混特性

采用内径为280 mm的上流式反应器,以空气模拟气相、甘油和水混合溶液模拟渣油。用3种不同粒径的氧化铝球形工业催化剂颗粒为填充颗粒,考察了不同模拟物系的颗粒粒径、颗粒密度、液相黏度、不同床层的高径比和不同操作条件对上流式反应器内床层压降及其波动、床层轴向返混的影响规律。得到模拟工业运行物系和操作条件的上流式反应器床层总压降关联式,相对误差在12%以内。床层总压降均随床层高径比、颗粒密度和液相黏度增加而增大,但随颗粒粒径的增大而减小,床层压降波动随表观气速增加而增大。填充颗粒粒径越小、颗粒密度越小、高径比越大,床层内轴向返混越严重;床层内压降和轴向返混均随表观气速的增加而增大。     

聚酰胺酸聚合物反应热分析与反应釜设计探讨

目前市场上常用的高分子聚合釜,为间歇式双螺带聚合釜,一般来说,这种搅拌方式,能够满足充分混合和聚合反应的要求,但是在高黏度工况下难于及时将反应热传递到反应系统外,也较难满足批量化的大生产需求。对于高黏度聚合体,需要核算聚合反应热,及时将反应热量传递到系统外,才能够得到分子量分布范围比较窄的理想聚合体。本文结合聚酰亚胺纤维生产的工艺技术条件,给出一种适合高黏度较高分子量的聚合反应釜设计方案,在满足高黏度聚合体分散、均混、聚合的同时,有效降低搅拌功率、及时将反应热传递到系统外。     

三维上流式反应器床层流动和返混特性

采用内径为280 mm的上流式反应器,以空气模拟气相、甘油和水混合溶液模拟渣油。用3种不同粒径的氧化铝球形工业催化剂颗粒为填充颗粒,考察了不同模拟物系的颗粒粒径、颗粒密度、液相黏度、不同床层的高径比和不同操作条件对上流式反应器内床层压降及其波动、床层轴向返混的影响规律。得到模拟工业运行物系和操作条件的上流式反应器床层总压降关联式,相对误差在12%以内。床层总压降均随床层高径比、颗粒密度和液相黏度增加而增大,但随颗粒粒径的增大而减小,床层压降波动随表观气速增加而增大。填充颗粒粒径越小、颗粒密度越小、高径比越大,床层内轴向返混越严重;床层内压降和轴向返混均随表观气速的增加而增大。     

BR生产中首釜桨型选择问题的探讨

根据合成高聚物的桨型选择的基本原则,以首釜液体不属于高粘液体为前提,提出了BR生产中首釜聚合工艺对混合的三要素。通过小试用框式桨和螺带桨的混合状态及混合时间的测定,生产装置操作数据与产品性能的分析,指出首釜由框式桨改为螺带桨是有效的。并提出了开发大尺寸轴向流较之螺带式桨相当或稍逊,而微尺寸混合较强的新桨型的建议。     

Prediction of screw conveyor performance using the Discrete Element Method (DEM)

Screw conveyors are used extensively in agriculture and industry for transporting and/or elevating bulk materials over short to medium distances. They are very effective conveying devices for dry particulate solids, giving good control over the throughput. Despite their apparent simplicity, the mechanics of the transportation action is very complex and designers have tended to rely heavily on empirical performance data. The performance of a screw conveyor is affected by the operating conditions, such as: the rotational speed of the screw; the inclination of the screw conveyor; and the volumetric fill level of the bulk material. In this paper we examine how these operating conditions influence the performance of a screw conveyor by applying the Discrete Element Method (DEM) to simulate a single-pitch screw conveyor with periodic boundary conditions. The DEM modelling gives predictions of screw conveyor performance in terms of variations of: particle speeds, mass flow rate, energy dissipation and power consumption, due to changes in the operating conditions.     

Study of Residence Time Distribution in a Pilot-Scale Screw Conveyor Dryer

The screw conveyor dryer (SCD) finds varied applications in the process industries either as a pre-dryer or for post-drying operation. In certain cases, it can be used as the main dryer. The full potential of SCD has not been exploited for the lack of its understanding. The conveying of paste or particles through a screw conveyor may follow a near plug flow behavior; however, it is essential to ascertain a desired level of inter-particle mixing during the course of drying/conveying so as to obtain the desired drying conditions. The effects of feed rate (15–176 kg/h) and screw speed (10.8–28 rpm) on the RTD were studied for the conveying of sand in a pilot-scale SCD using pulse input of a tracer (dye-coated sand). Two new parameters defining the relative stagnancy and screw effectiveness were introduced to study the flow performance of SCD. The flow in the SCD approaches plug flow with an increase in feed rate or by decrease in the screw speed. A low value of the holdback, a parameter of relative stagnancy, indicates the flow in SCD to be near plug flow. Mean residence time was found to be 3 to 4 times longer than the linear residence time due to lower values of screw effectiveness (0.24–0.32).     

螺旋输送器中颗粒混合过程的模拟

采用离散单元法（discrete element method,DEM）模拟了工业尺度螺旋输送器中两种不同密度与粒径的颗粒的流动状态与混合过程。采用Lacey混合指标的定量分析表明,该输送器的混合性能强烈地依赖于操作条件和结构尺寸,转速和物料的添加速率对混合效果影响最大,其次是混合段螺距和物料粒径。根据工业生产的具体要求,可参考上述发现合理地选择技术参数、提高混合效率、降低能耗。     

Analysis and experimental evaluation of twin screw extruders

Twin screw extruders can he classified according to their geometrical configuration. The main distinction is made between intermeshing and nonintermeshing extruders. Another distinguishing characteristic is the sense of rotation. The most important characteristics of the various twin screw extruders are examined, with particular emphasis on the effect of screw geometry on the conveying characteristics. A brief review is given of the state of the art in theoretical analysis of twin screw extruders. Experiments with two lab scale, intermeshing twin screw extruders are described, one co- and one counterrotating. Results are presented on power consumption, residence time distribution, and mixing characteristics of the two extruders. The counterrotating extruder exhibits a narrower residence time distribution and better dispersive mixing capability. The corotating extruder showed a better distributive mixing capability. These results can be explained in terms of the conveying and mixing mechanisms in both extruders. The overall extruder performance seems to be dominated by the effect of the intenneshing region. Any realistic, theoretical analysis of twin screw extruders should be centered around the flow behavior and mixing characteristics of the intermeshing region. The corotating extruder appears to be best suited for melt blending operations, while the counterrotating extruder seems to be preferred in operations where solid fillers have to be dispersed in a polymer matrix.     

聚乳酸用单螺杆挤出机熔体输送段数值模拟研究

运用Polyflow分别对聚乳酸(PLA)用3种不同结构类型单螺杆挤出机熔体输送段进行模拟,在流场分析的基础上,分析3种螺杆的混合性能。结果表明,在相同工艺条件下,普通型单螺杆和菠萝型单螺杆熔体轴向速度波动较大,且产生局部回流区域,不利于熔体的输送;菠萝型螺杆产生的流场速度和熔体黏度较高,使得物料在流场中受到更高的剪切速率,因此挤出产物的分散混合性能更好;挤出过程中,PLA熔体的黏度变化与流动速度变化存在一致性,随着流动速度逐渐增大,熔体受到的剪切作用逐渐增强,使黏度降低,流动性变好。     

双转子连续混炼机混合过程物理模型的建立

建立了双转子连续混炼混合过程的物理模型，分析了影响其混炼段融体输送过程和混合过程的主要因素，并提出：转子混炼段融体输送量与转子螺棱几何形状，物料粘度，混炼段融体压降等有关；转子对物料的混合过程与转子组合（螺棱交汇区长度）转子螺棱几何形状，转子转速等因素有关。     

Numerical Simulation of Extrusion Characteristics for Co-rotating Tri-Screw Extruder

The flow of polyethylene melt in new tri-screw extruder was simulated using the finite element method (FEM). A special study of flow in central region was performed by analysis of the velocity, pressure, and resident time distribution (RTD). The extrusion characteristics of tri-screw extruder, namely the abilities of material conveying, mixing, and power consumption, were compared with those of twin screw extruder. The results showed that there was circumfluence in central region but no stagnation in it. Tri-screw extruder had better operative abilities and high productivity ratio than twin screw extruder in the aspect of material conveying and mixing.     

行星螺杆挤出机加工性能的实验研究

行星螺杆挤出机由于其高产、高效,具有优异的塑化和混合性能等特点在塑料加工领域得到越来越广泛的应用。利用自行开发的行星螺杆挤出机实验装置,研究了不同的口模直径、行星螺杆数量等结构参数条件下,喂料速度、主螺杆转速等工艺参数对于行星螺杆挤出机的机头压力、熔体温度、物料最短停留时间和功耗等影响。     

Theoretical analysis of residence time distribution functions and strain distribution functions in plasticating screw extruders

The residence time distribution (RTD) function in a single screw plasticating extruder was theoretically calculated. The calculation is based on the solids conveying, melting, and melt conveying models in extruders. The screw channel is divided into small axial increments and the path of each exiting fluid particle is followed from hopper to die. In addition to the residence times the total shear deformation or strain imposed on the fluid particles was also calculated. This together with the RTD function has led to the definition and calculation of the strain distribution function (SDF). This function is proposed for quantitative characterization of the mixing performance of screw extruders as well as other laminar mixers. Some simple idealized batch and continuous laminar mixers are analyzed in terms of the SDF. Finally, the effect of extruder operating conditions and screw design on the RTD and SDF were investigated by computer simulations.