微型流化床内气体返混

微型流化床基础和应用在近几年受到越来越多的关注。针对微型流化床对气固反应分析的应用要求,利用脉冲示踪法研究了内径10 mm和21 mm两种尺寸微型流化床中的气体返混特性,具体考察了管内径、颗粒静床高度、床料颗粒粒径和气体表观流速对气体返混程度的影响。结果表明:随着床内径、颗粒静床高度和表观气速的减小和床料颗粒粒径的增大,气体在床内的返混程度减小。使用粒径约270 μm粗颗粒时,两种床径的浅层微型流化床中的气体返混程度都较小,对应的Peclet数在27以上,证明了床内气体流动接近平推流,从而为利用微型流化床最小化气体返混对反应测试的影响,获得近本征反应动力学参数提供了流动特性的保障。     

循环流化床提升管中固体颗粒停留时间的分布

在内径１４０ｍｍ，高１０ｍ的循环流化床提升管中，采用磷光颗粒示踪法对床内固体颗粒的停留时间分布进行了测定。在气速１．５～９．０ｍ／ｓ，固体循环量１０～１４０ｋｇ／ｍ２ｓ的范围内，实验测得的停留时间分布曲线均有明显的双峰分布。这种双峰分布是由于提升管中弥散颗粒和颗粒团共同作用的结果。本文提出的一维两组分扩散叠加模型可较好地描述提升管中固体的混合行为。考察了在实验条件下，操作条件对固体混合行为的影响。发现：气速及固含对颗粒的轴向Ｐｅｃｌｅｔ数影响不大，提升管中颗粒的返混主要是由于颗粒团引起的。将研究结果与近期文献报道的其他研究进行了对比     

二维三相循环流化床液体停留时间分布的研究

用脉冲示踪法对二维三相循环流化床液体停留时间分布(RTD)进行了测定。在气速2～3m／s,液体循环量0～0．35m^3／h,固体循环量1．5～1．75g／s的范围内测得的液体停留时间分布曲线均有明显的3峰分布。其中前两峰分布是由于提升管中颗粒与液体之间和液体与气体之间共同作用改变了液体轴向速度分散程度的结果。第三个峰的分布是由于液体进入循环仓循环后在出口处检测的RTD曲线,并且提出一维两组分扩散物理叠加模型,模型的预测结果与实验获锝的RTD曲线平均误差小于5％,可较好地描述提升管中液体停留时间分布曲线。     

变孔径分布板减小液固流化床中液相返混

引言流化床亲合色谱蛋白质分离新方法综合了亲和吸附的快速、高选择性与液固流化床液相负荷大、传质速率高等优点,尤其是生物细胞可随液相穿透空隙率较大的吸附剂颗粒床层,因此该方法是构成连续分离-反应相耦合的蛋白质生产工艺的有效手段．但不足之处是流化床内的液相返混会严重影响分离效率,因此必须采取措施加以抑制．国外有采用磁稳定流化床来减小液相返混,但要添加体积比44％的磁性颗粒且要在75G_s的磁通密度下操作,有可能影响产品的生物活性．鉴于此,可采取不外加场源的稳定化措施来减小液相返混．本文通过对液固流化床液相返…     

循环流化床锅炉返料系统改造及应用

河南龙宇煤化工有限公司50万t/a甲醇装置一期配套3台130t/h的高温高压循环流化床锅炉。针对循环流化床锅炉管式返料组件多次出现配风管弯曲、变形、风管盲板脱落而引起锅炉停炉和结焦等问题,实施了锅炉返料系统的技术改造,由原来的管式配风改造为布风板加风帽配风。改造后的试运行效果表明:1返料系统运行稳定,再未出现锅炉停炉问题;2每年可节省更换返料风管的费用7.2万元、系统再次启动的费用800万元。     

流化床返料器控制与调节

非机械阀已经广泛应用于循环流化床锅炉完成固体颗粒从低压区向高压区的传输且具有压力密封作用。本文详细介绍了一种新型流化床返料器,通过试验结果分析表明,该流化床返烊器具有良好的物料循环量的控制与调节性能。     

流动反应器内返混研究

以多釜串联模型为主体,采用示踪法.对不同搅拌速率和不同流体流量下四联釜流动反应器内的返混状况进行了测定,建立了该系统的数学模型.结果表明,搅拌速率及流体流量影响系统返混程度大小,在实际的生产过程中,可以通过调节上述2个可控制的因素,对反应的过程进行控制和调节,使反应向着最有利的方向发展.     

循环流化床锅炉返料量减少的问题处理及对策

循环流化床锅炉系统改造后,出现返料风压突然降低以及返料器中基本没有返料的现象,经反复调整仍无效果。停车检修后,对返料风机选型、物料分离系统和返料装置进行了细致排查,发现是由于返料器风帽用错及脱落过多而引起。最后,对循环流化床锅炉分离返料常见的故障进行了简单分析。     

循环流化床锅炉密封返料装置输送特性及故障分析

探讨了流化风量，松动风量和狭缝高度对流化密封返料器工作性能的影响，分析返料器常见故障的原因，并以广西某化肥厂25t/h循环流化床锅炉为例，提出了相应的解决措施。     

大颗粒流化床停留时间分布的研究

通过对流化床尿素造粒的冷模研究，对4种与尿素有类似流化特性的大颗粒物料在两级矩形流化床内的停留时间分布进行了系统的实验研究，分别考察了气速、床高（高径比）、粒径、物料流量等操作变量对停留时间分布的影响。气速是影响停留时间分布的主要因素，随着气速的增加，物料在床内的混合加剧，并同时伴有循环流。大颗粒床层混合程度较差时，更易出现腾涌现象。停留时间分布的测定为流化床造粒器的工业设计提供了基础数据。     

Residence Time Distribution of Solids in a Fluidized Bed

Experimental investigation on RTD of solids is carried out in a single‐stage fluidized bed provided with an internal, using uniformly sized particles and a binary solid mixture, varying gas flow rate, solids rate, bed height, dilution and the bed geometry. The effect of these variables on first and second moments as well as on F‐curves has been determined. Using a binary solid mixture or an internal inside the bed is found to reduce backmixing of solids. The data is fitted to FTEM and the values of N obtained were compared for different variables.     

内置螺旋挡板流化床颗粒停留时间分布

采用脉冲示踪法在内置螺旋挡板冷态鼓泡流化床上研究了螺旋挡板、加料速率、流化风速、颗粒粒径和床料高度对颗粒在流化床内停留时间分布的影响. 结果表明,颗粒停留时间的无量纲方差从无螺旋挡板时的0.558减小到有螺旋挡板时的0.085,螺旋挡板可有效抑制颗粒返混,增大颗粒运动的平推流趋势;加料速率增大为约2倍时,停留时间减小为约50%,流动更趋向于平推流;床料高度增加,颗粒返混加剧,颗粒平均停留时间及无量纲方差均增大,颗粒运动向全混流靠近;随流化风速增大,颗粒平均停留时间变长;实验范围内,颗粒粒径对颗粒停留时间分布影响不大.     

Measurement of Residence Time Distributions in a Continuously Operated Spouted Bed

Continuous gas-solid processes are applied in many industries with particulate products, e.g. for granulation or coating. In this contribution, the residence time behavior in a continuously operated prismatic spouted bed was determined by applying an impulse of magnetizable tracer particles. Experiments were performed with the original configuration and with separation plates including mouse holes of varying size between the different chambers of the ProCell 25 apparatus. It is shown that the shape of the residence time distribution is influenced by the separation plates. In order to quantify the backmixing between the chambers, discontinuous experiments were performed, and the bed mass distribution and the distribution of the tracer were measured and compared to the initial conditions.     

Drying Sawdust in a Pulsed Fluidized Bed

The objective of this work was the experimental and theoretical study of sawdust drying, in batch and continuous experiences, using a pulsed fluidized bed dryer.

In the batch experiences, a 2³ factorial design was used to determine the kinetics of drying, the critical moisture content, and the effective coefficients of both diffusivity and heat transfer, all of them as a function of the velocity and temperature of the air, the speed of turning of the slotted plate that generates the air pulses in the dryer, using sawdust with 65% moisture in each run.

In the continuous operation, a 2³ factorial design was used to study the effect of the solid flow and the velocity and temperature of the air on both the product moisture and the distribution of residence times. In order to determine these last ones, digital image processing was used, utilizing sawdust colored by a solution of methylene blue as tracer.

The statistically significant factors were the velocity and the temperature of the heating air, for both the continuous and batch operations. Although the speed of turn of the slotted plate was not significant, it was observed that the air pulses increased the movement of particles, facilitating its fluidization, especially at the beginning of drying.

The heat transfer coefficients were adjusted according to the equation Nu = 0.0014 Re_p^1.52, whose standard deviation of fit is 0.145.

The period of decreasing rate was adjusted to several diffusivity models, giving the best fit the simplified variable diffusivity model (SVDM). The curve of distribution of residence times was adjusted using the model of tanks in series, with values between 2.6 and 5 tanks.     

Drying Sawdust in a Pulsed Fluidized Bed

The objective of this work was the experimental and theoretical study of sawdust drying, in batch and continuous experiences, using a pulsed fluidized bed dryer.

In the batch experiences, a 2³ factorial design was used to determine the kinetics of drying, the critical moisture content, and the effective coefficients of both diffusivity and heat transfer, all of them as a function of the velocity and temperature of the air, the speed of turning of the slotted plate that generates the air pulses in the dryer, using sawdust with 65% moisture in each run.

In the continuous operation, a 2³ factorial design was used to study the effect of the solid flow and the velocity and temperature of the air on both the product moisture and the distribution of residence times. In order to determine these last ones, digital image processing was used, utilizing sawdust colored by a solution of methylene blue as tracer.

The statistically significant factors were the velocity and the temperature of the heating air, for both the continuous and batch operations. Although the speed of turn of the slotted plate was not significant, it was observed that the air pulses increased the movement of particles, facilitating its fluidization, especially at the beginning of drying.

The heat transfer coefficients were adjusted according to the equation Nu = 0.0014 Re _p ^1.52, whose standard deviation of fit is 0.145.

The period of decreasing rate was adjusted to several diffusivity models, giving the best fit the simplified variable diffusivity model (SVDM). The curve of distribution of residence times was adjusted using the model of tanks in series, with values between 2.6 and 5 tanks.     

连续进出料鼓泡流化床颗粒停留时间分布

针对双流化床气化或双床热解气化工艺中鼓泡床反应器的设计,采用脉冲法研究了Geldart B类固体颗粒在连续颗粒进料和出料的矩形流化床内的停留时间分布(RTD),考察了气速、床料高度、粒径、物料流率等操作参数对RTD的影响. 结果表明,物料流率、床料高度、粒径是影响颗粒RTD的主要因素,而气速则是次要因素. 随物料流率和粒径增加,鼓泡床内颗粒流动向平推流靠近;随床料高度增加,物料在床内的混合更加充分,颗粒流动向全混流靠近. 根据实验结果,推荐采用比理想平推流时间低9%~18%计算平均颗粒停留时间.     

Drying Kinetics in the Riser of Circulating Fluidized Bed with Internals

Solid particles were dried in the riser of circulating fluidized bed with internals to study the drying kinetics. Experiments were conducted in a circulating fluidized bed, having perforated plates as internals covering wide range in the operating parameters. The effects of various operating parameters, i.e., initial moisture content, temperature, and flow rate, of the heating medium and solid circulation rate on the rate of drying have been critically examined. It has been observed from the present investigation that the presence of internals enhances the solids holdup in the riser of circulating fluidized bed. The drying efficiency of a circulating fluidized bed with internals has been compared with the drying performance of a circulating fluidized bed without internals under the same operating conditions.     

低密度循环流化床局部颗粒速度的轴径向分布的研究

在高8m,内径186mm的循环流化床中,利用光纤激光多普勒测速仪测量了FCC颗粒的局部速度沿轴径向的分布。实验结果表明:局部颗粒速度沿径向分布是不均匀的,床中心区域分布比较平坦,近壁环形区域分布较陡,颗粒沿轴向运动有较长的加速段。由实验数据回归得到预测低密度循环流化床局部颗粒速度的经验关联式。