共查询到20条相似文献,搜索用时 578 毫秒
1.
在循环流化床(CFB)煤燃烧/热解双反应器冷态实验装置上,以硅胶和电厂锅炉灰为实验物料,考察了立管内的气固流动特性,其中立管的内径44mm、高3m。研究结果表明,立管内的气固流动形态为移动床流动,Leung的立管流动模型适合对该系统中立管内移动床流动的描述,经拟合分别得到了立管内气、同速率以及气同相对速率与固体速率之间的经验方程,对热态实验过程中判断立管内的气固流动型态以及料封的稳定性均具有一定的参考价值。 相似文献
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Dynamics of gas-particle flow in circulating fluidized beds 总被引:3,自引:0,他引:3
A. Srivastava K. Agrawal S. Sundaresan S.B. Reddy Karri T.M. Knowlton 《Powder Technology》1998,100(2-3):173-182
The flow of gas—particle mixtures in a circulating fluidized bed has been studied, probing the flow behavior under both stable and unstable operating conditions. A novel feature of our work is the use of electrical capacitance tomography to image particle distribution over the cross-section at one elevation in the standpipe. In addition, we have also obtained data on pressure profile and aeration rate in the standpipe, particle circulation rate in the circulating fluidized bed and riser gas flow rate under various operating conditions. Here, we report experimental results obtained for two different particles, both belonging to Geldart type A. At low aeration rates, a stable dense phase flow is obtained in the standpipe. At high aeration rates, the flow became unstable, manifesting low frequency oscillations in the flow characteristics. Our results suggest that, under conditions explored in the present study, this instability originates in the standpipe and that any attempt to model it should consider the interaction between the various components of the circulating fluidized bed system. 相似文献
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负压差立管内的气固两相流 总被引:8,自引:3,他引:5
在φ800 mm×12000 mm流化床实验装置上对150 mm×11500 mm负压差立管内气固两相流的轴向压力、空隙率和气体流动特性进行了测量和分析.立管出口无约束淹没在密相流化床内,颗粒质量流率范围Gs<1200 kg8226;m-28226;s-1.立管内气固两相流态有两种存在形式,当颗粒质量流率Gs<200~250 kg8226;m-28226;s-1时,流态是稀密两相共存形式;当Gs>200~250 kg8226;m-28226;s-1时,流态是浓相输送流态.两种流态之间可以相互转换,主要取决于颗粒质量流率的变化.影响立管内气固两相流的轴向压力、空隙率分布、气相的流动特性和气固流态存在形式的主要参数是颗粒质量流率Gs、旋风分离器入口速度Vi、下端流化床流化速度uf,质量流率Gs是主要的影响因素. 相似文献
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垂直立管中催化剂流动特性的实验研究 总被引:4,自引:1,他引:3
对垂直立管中催化剂的流动性能进行了实验研究,测定了各种操作条件下立管中的轴向压力分布、催化剂循环速率以及附加吹气的影响. 实验结果表明,立管中的气固流动存在分别处于负压差下移下流区的"脱气段"和处于正压差下移下流区的"持气段"两种流动状态;下料阀开度对固体循环流率有明显的约束作用,且使"持气段"总压降增加较"脱气段"更为明显;对立管引入附加吹气有明显的增压作用,并使立管的压力分布有较大的改变. 根据实验结果及分析,对垂直立管的管形设计和催化剂在垂直立管中的密相输送提出了分析与建议. 相似文献
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采用计算颗粒流体力学对密相输运床返料系统内的气固流动行为进行了数值模拟,分析了曳力模型和颗粒最大堆积浓度等参数对模拟结果的影响,确定了合适的模型参数。通过对比3组工况的模拟结果,获得了与实验结果基本一致的立管压力分布和固体循环流率随充气条件的变化规律,并分析了立管内压力梯度分布、气体流动方向、颗粒浓度分布等。结果表明立管充气口处压力梯度绝对值为局部最大值;当立管充气口气量为零时,会使充气口上方一段距离的压力梯度绝对值较小;充气量增大到一定值时会在充气口附近形成明显的气泡。当缺少立管高位充气时,会导致立管下部区域形成大的压力梯度,增加颗粒下落阻力。充气松动颗粒的作用仅对充气口附近区域有一定影响,更大的作用是在立管内形成均匀的压力梯度分布,使立管内气固流动状态保持上下一致。在制定充气方案时,应根据固体循环流率确定立管压降,补充合适气体量以维持气体下行速度均衡,使得各段的平均压力梯度相同。 相似文献
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Sheng Chen Cong Xu Dezheng Wang Yong Jin 《Chemical Engineering Communications》2013,200(12):1598-1620
A stress distribution model for a liquid-solid circulating moving bed reactor that consists of a bottom reaction chamber, a top regeneration chamber, a coupling standpipe, a particle transportation system, and a bottom standpipe is established based on the equations of continuity and momentum balance. Simulations show that the stress concentration regions are at the bottom of the regeneration chamber and the coupling standpipe. To reduce the maximal stress and increase the operation flexibility in a reactor for the 2000-ton-per-year production of linear alkylbenzene, the regeneration chamber should have a low height-to-radius ratio (about 9), a suitable half-conical angle between 28° and 35°, and standpipe radius of about 0.05 m. 相似文献
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Sheng Chen Minghan Han Cong Xu Dezheng Wang Yong Jin 《Chemical Engineering Communications》2005,192(12):1598-1620
A stress distribution model for a liquid-solid circulating moving bed reactor that consists of a bottom reaction chamber, a top regeneration chamber, a coupling standpipe, a particle transportation system, and a bottom standpipe is established based on the equations of continuity and momentum balance. Simulations show that the stress concentration regions are at the bottom of the regeneration chamber and the coupling standpipe. To reduce the maximal stress and increase the operation flexibility in a reactor for the 2000-ton-per-year production of linear alkylbenzene, the regeneration chamber should have a low height-to-radius ratio (about 9), a suitable half-conical angle between 28° and 35°, and standpipe radius of about 0.05 m. 相似文献
10.
A method of analysing solids downflow through standpipe and slide valve in the moving bed mode is presented. The method is based on combining Yoon and Kunii equations for moving-bed flow with a proposed modified orifice equation for gas—solid flow. The analysis correctly predicts the observed trend of the effects of gas injection into the standpipe. It also provides quantitative prediction of the conditions for transition from moving-bed flow to dense phase fluidized solids flow and to lean phase “streaming flow”. The latter flow pattern refers to solids streaming down a tube at high voidage typified by the discharge of solid down a tube with no constriction at the lower end of the tube. Further work is required to test the general applicability of the present analysis and to extend the analysis to yield a generalized quantitative flow regime diagram for downflow of solids in a pipe. 相似文献
11.
Effect of Sudden Increase of Solid Feed Rate on the Arching in Hoppers Connected to a Standpipe with Interstitial Gas Flow
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In this paper, a model is proposed for the prediction of the width of arching in hoppers resulted from sudden changes in solid feed rates. Such changes in solid feed rate usually come from the collision on the surface of the moving-bed in the standpipe. The model also takes into accountthe effect of the powder height in the standpipe of the hopper. The model proves to be adaptable for predicting operational conditions to avoid vxching by keeping constant powder height in the main standpipe wlth interstitial gas flow. 相似文献
12.
Effect of Sudden Increase of Solid Feed Rate on the Arching in Hoppers Connected to a Standpipe with Interstitial Gas Flow
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In this paper , a model is proposed for the prediction of the width of arching in hoppers resulted from sudden changes in solid feed rates. Such changes in solid feed rate usually come from the collision on the surface of the moving-bed in the standpipe. The model also takes into account the effect of the powder height in the standpipe of the hopper. The model proves to be adaptable for predicting operational conditions to avoid arching by keeping constant powder height in the main standpipe with interstitial gas flow. 相似文献
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The liquid-solid circulating moving bed reactor is a novel one, which consists of two reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through a coupling standpipe and to the particle transport system through a bottom standpipe, and are then conveyed into the upper reaction chamber through a riser. A stress distribution model based on the equations of continuity and momentum balance in the reactor is established and used for simulations which shows that the stress concentration regions are at the coupling standpipe and the bottom of the regeneration chamber. To reduce the largest stress in the stress concentration regions and to minimize catalyst consumption, the regeneration chamber should be designed to give a low ratio of height to diameter. Zoning diagrams of the flow patterns in the bottom standpipe are proposed and the flow patterns can be readily deduced from the pressure gradient. 相似文献
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本文给出利用料斗中体均压力梯度与立管压力梯度的关系判别压力控制区、气泡控制区、气栓控制区和悬料区的方法。在气栓控制区,料斗中体均压力梯度有如下关系[(一dP/dz)]hplug=0.241pbmfg而且,散体颗粒平均质量流率可以用Beverloo方程来预测。在此基础上,讨论了料斗中体均压力梯度对散体颗粒通过孔口平均质量流率的影响,并给出预测平均质量流率的关联式。给出一种新的立管约束条件,即料斗阀的设计方法和操作范围。 相似文献
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For downflow of cohesive solids in a standpipe in the absence of pressure gradient, the flow, no-flow criterion of Jenike (1964) can be applied to determine the minimum diameter for no arching to occur. In this paper Jenike's analysis is extended to account for the presence of pressure gradient in the standpipe. An equation for estimating minimum pipe diameter for smooth flow is presented. For design we suggest that the minimum diameter in the absence of pressure gradient should be measured and our equation is to be applied to extrapolate to the real situation with a finite pressure gradient.The present work is relevant to recent usage of standpipes in oil-shale processing and coal power plants. 相似文献
17.
Juchirl Park Yue Huang Richard Turton Parviz Famouri Edward J. Boyle 《Powder Technology》2005,150(3):176-184
Circulating fluidized beds (CFBs) are used widely in the chemical industry. Knowing or estimating the bed height in the standpipe and the solids circulation rate are essential for effective control of the system. This paper incorporates a 2-region model to calculate the bed height in the standpipe with a Kalman filter algorithm to estimate the solids circulation rate (SCR). Simulations of both the standpipe bed height and SCR were compared with experimental data and shown to give good agreement.
In addition, a neural network method was applied to model the entire cold flow CFB system and measured data sets were used to train the neurons of the network. Finally, a linear controller was applied to control both the bed height and solids circulation rate to desired set points. Simulations were performed for both positive and negative step inputs for both variables and satisfactory control was demonstrated using this controller in combination with the neutral network and Kalman estimator. 相似文献
18.
Darsh T. Wasan 《Powder Technology》1977,18(1):1-6
Industrial standpipes for gas—solid recirculation systems are often installed with slide valves at their lower end for control of solid flow and pressure balance. By combining the equations for gas—solid dense phase flow with equations for flow of fluidized solids through an orifice, a set of equations is presented for standpipe design. The equations permit quantitative design of a standpipe and can be used to predict the effects of terminal pressure, slide valve opening position and aeration rate on gas and solid circulation rates, flow pattern and pressure profile in standpipes. 相似文献
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The standpipe has become a standard element of most circulation loops. In the past, standpipes have been thought of as a device to only allow solids to transfer from a low to a higher-pressure region. However, it also has another function in a solids circulation loop. It is also the device that adjusts its operation to balance the pressure around the solids circulation loop. An overflow standpipe adjusts the pressure drop across it by raising or lowering the solids level in the standpipe. However, the operation of the underflow standpipe is more complex. This self-adjusting function can cause underflow standpipe pressure drops to be negative, which seems counter-intuitive. How an underflow standpipe operating with a negative pressure build can occur in a circulation loop is described below using two commercial unit examples as illustrations of this phenomenon. 相似文献
20.
在无负压差的环境下,采用PV6D型颗粒速度测量仪,考察了垂直立管中FCC催化剂颗粒移动床的蠕动流动特性. 结果表明,颗粒质量流率较小时立管中颗粒流动具有明显的蠕动流动特性,可划分为两种流态,拟气固雷诺数Re<500时为间歇式蠕动流动,5004000时颗粒的蠕动流动转变为密相流化流动. 立管中颗粒的蠕动流动主要是出口区颗粒成拱与崩塌交替进行产生的,其次为颗粒与器壁滑动摩擦力的不稳定性变化起作用. 微观上颗粒流动的蠕动行为是颗粒之间力链作用变化的结果. 相似文献