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1 INTRODUCTIONThe determination of the solids hold-up and local solidfluxes is of paramount importance in the study ofthe hydrodynamics of a two-phase flow.Several tech-niques have been used during the past decades(Table1).These methods can be classified in two groups,depending on their possible disturbance of the two- 相似文献
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在耦合流化床反应器大型冷模实验装置上,考察了不同表观气速下FCC颗粒在耦合流化床内截面平均密度的轴向分布. 结果表明,反应器轴向固含率可分为底部流化床区域和上部提升管区域. 前者的密相区平均固含率随表观气速增大而减小;后者的平均固含率随表观气速Ug增大而增大,Ug<0.58 m/s时固含率分布均匀,Ug=0.70~1.04 m/s时提升管出口出现约束返混区(>8.62 m),Ug>1.16 m/s时提升管底部出现密度重整区(3.82~4.57 m)、加速平稳区(4.57~8.62 m)和出口返混区(>8.62 m). 确定了耦合反应器内提升管区域截面平均固含率的影响参数,并利用实验数据回归了平均固含率的轴向分布经验模型,计算值与实验值吻合较好. 相似文献
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《化学工业与工程技术》2017,(2):8-15
基于欧拉双流体模型和颗粒流动理论对实验室规模的循环流化床气化炉进行了全三维模拟,考察了炉内压力和固体颗粒的分布特征,并进一步比较了操作条件对炉内气固两相循环流动的影响差异。模拟结果表明:提升管内呈上稀下浓的颗粒分布,径向处存在边壁浓中心稀的环合结构,下降管内能够形成堆积较为密实的料封,模拟得到的系统压力环路与试验值较吻合。藏量、粒径和入口气速均会影响炉内的固体颗粒浓度和压力分布,合适的粒径和入口气速条件与颗粒终端速度的匹配是影响炉内稳定循环流化的关键因素。 相似文献
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<正>循环喷动流化床由于循环管(导向管)的引入,显著地提高了射流床的操作能力、传热传质特性及接触效率,因而被广泛地应用于化工过程,如:颗粒涂层、煤气化和石油烃类的热裂解)。 鉴于循环喷动流化床的广泛应用,许多研究者对床层的气固流动循性进行了研究,但是由于实验的几何参数、特性参数及操作参数的不同,实验结果存在着较大的差异,有关固体循环速率的数学模型报道很少,已有的模型也因假设条件太多及考虑影响因素不全而不具有普遍的适用性,本文通过研究几何参数、操作参数及物性参数对固体循环速率的影响,进而得出综合考虑以上参数在内的预测固体循环速率的定量方程,为工程设计提供重要信息。 相似文献
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电容层析成像技术在线测量气固流化床空隙率的研究 总被引：6，自引：0，他引：6
基于电容层析成像技术，提出了一种在线测量气固流化床空隙率的新方法。建立了相应的12电极电容层析成像气固流化床空隙率测量系统，可同时实现气固 流化床空隙率分布的在线显示和整体空隙率测量。选择加权反投影算法进行图像重建以保证空隙率分布显示的实时性和有效性。采用Tikhonov正则化原理和ART算法相结合的组合型新图像重建算法来实现整体空隙率的测量。Tikhonov正则化原理用于克服图像重建过程中的不适定问题，ART算法用于提高最终重建图像的质量。研究表明以上提出的空隙率测量新方法是有效的。空隙率分布在线测量的速度可达25幅／秒以上，整体空隙率测量的最大误差可小于5％。 相似文献
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循环床提升管中粗重颗粒浓度的轴向分布 总被引：2，自引：0，他引：2
在10m高提升管中对空气-沙子体系的压力梯度进行系统测试,研究了粗重颗粒平均颗粒浓度云的轴向分布及操作条件对它的影响。结果表明,粗重颗粒的^εs在相同操作条件下显著低于FCC颗粒;随操作条件的不同,沙子颗粒表现出与FCC显著不同的轴向分布形态。高气速下粗重颗粒^εs的轴向分布与FCC相似表现为单调下降或直线形关系;但在表观气速Ug降低至某一临界值后,粗重颗粒^εs的轴向分布呈现出波动形式,表明沙子颗粒在提升管中的流动是一个加速-减速-再加速直至充分发展的过程。随Ug减小或Gs增大,提升管各截面上云升高;当^εs的轴向分布为波动形式时,提升管底部截面和中部颗粒聚集截面上^εs的变化较其它截面更为显著。 相似文献
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在内径１１０ｍｍ高６ｍ的下料管循环流化床的冷模实验装置内，采用ＦＣＣ催化剂和硅胶球物料，并通过气固并流下行中气固间相互作用的分析，提出了气体流动方程，并以气体示踪法实验证实了其可靠性。 相似文献
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The distributions of the three phases in gas–liquid–solid circulating fluidized beds (GLSCFB) were studied using a novel measurement technique that combines electrical resistance tomography (ERT) and optical fibre probe. The introduction of gas into a liquid–solid circulating fluidized bed (LSCFB), thus forming a GLSCFB, caused the increase of solids holdup due to the significantly decreased available buoyancy with the lower density of the gas, even with a somewhat increased liquid velocity due to the decreased liquid holdup giving space for the gas holdup. The gas passed through the riser in the form of bubbles, which tended to flow more through the central region of the riser, leading to more radial non‐uniformity in radial holdup of the phases. The gas velocity has the most significant effect on the gas phase holdup. While the gas velocity also has an obvious effect to the solids holdups, the liquid flow rate had a much more considerable effect on the phase holdups. The solids circulation rate also had a significant effect on the phase holdups, with increasing solids circulation rate causing much more increased solids holdup in the central region than close to the wall. A correlation was developed for the relative radial distributions of solids holdup in GLSCFB, as such radial profiles were found similar over a wide range of operating conditions, like those in a typical gas–solid circulating fluidized beds (GSCFB). Finally, the axial solids profiles in a GLSCFB was found to be much closer to those in an LSCFB which are very uniform, than those found in a GSCFB which are less uniform and sometime having a S shape. Water was used as the continuous and conductive phase, air was the gas phase and glass bead and lava rock particles were used as the solid and non‐conductive phase. 相似文献
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Jian Li Zheng Tang Biao Zhang Chuanlong Xu 《American Institute of Chemical Engineers》2023,69(5):e18055
The gas and solids in a circulating fluidized bed (CFB) are heterogeneously dispersed and a multiscale flow regime may form both in time and space. Accurate measurement of the fluidizing process is significant for investigating the multiscale gas–solid flow characteristics and the design, optimization, and control of CFBs in various applications. This article develops a deep learning-based tomographic imaging of electrical capacitance tomography (ECT) to characterize the particle concentration distribution in a CFB. The deep tomographic imaging approach is realized through training a well-designed convolutional neural network (CNN) with the numerically built dataset. Simulation results demonstrate that the average values of the relative image errors reconstructed by CNN in the test set are 0.1110 and 0.1114 for the 60 and 100 mm pipes, respectively, which are better than the average values of 0.1819 and 0.2519 by the Landweber algorithm. With the verification of the trained model based on the prepared data can image the unseen typical flow patterns better than Landweber, it is further used to investigate the particle flow characteristics of a lab-scale CFB. Experimental results reveal that the developed deep tomographic imaging of ECT can successfully measure the fluidized particle distribution in both the 60 and 100 mm pipes, showing good prediction and generality of the designed CNN model. A flow regime transformation from “annular” flow to “core-annular” flow and pneumatic conveying is observed under the tested conditions. Besides, the flow regime would be highly affected by the fluidized gas flow rate and the initial bed height. 相似文献
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Abdelwahid Azzi Hiba Bouyahiaoui Abdallah S. Berrouk Andrew Hunt Ian S. Lowndes 《加拿大化工杂志》2020,98(8):1835-1848
The temporal and cross-sectional distributions of particles in a 127 mm diameter fluidized bed have been obtained using a new generation, high-speed electrical capacitance tomography. Two planes of eight electrodes were used and mounted at 160 and 660 mm from the gas distributor which was a 3 mm thick porous plastic plate (maximum pore size of 50-70 μ m). 3 mm diameter, nearly-spherical polyethylene granules made up the bed. Experiments at sampling frequencies of 200-2000 cross-sections per second and gas superficial velocities from just below the minimum fluidization to 83% above minimum fluidization velocities were used. The time series of the cross-sectional average void fractions have been examined both directly and in amplitude and frequency space. The last two used probability density functions and power spectral densities. The information gathered shows that the fluidized bed was operating in the slugging mode, which is not surprising given the size of the particles. It has been found that an increase in the excess gas velocity above the minimum fluidization velocity resulted in an increase in the mean void fraction, an increase in the length and velocity of the slug bubbles as well as the bed height, and a slight decrease in the slug frequency. The results are presented in a level of detail suitable for comparison with later numerical simulation. 相似文献
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用于两相流流型显示和空隙率测量的电容层析成像技术 总被引：9，自引：4，他引：9
引 言两相流流型的实时显示和空隙率的在线测量对两相流系统的控制、运行乃至机理研究等均具有重要意义 ,一直是两相流领域中重要的研究方向 .现已提出多种实现流型显示和空隙率测量的方法 ,例如用于流型显示的核辐射线法和光学法 ,用于空隙率 (或浓度 )测量的机理估算法、核辐射线法、电学法、光学法、微波法、热学法和核磁共振法等 ,但是总的来讲还未能满足应用要求 ,实际应用的例子也较少[1] .电容层析成像 (ｅｌｅｃｔｒｉｃａｌｃａｐａｃｉｔａｎｃｅｔｏｍｏｇｒａｐｈｙ ,简记ＥＣＴ)技术由于可在不干扰流场的情况下获取反映两相流… 相似文献
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在内径１１０ｍｍ的下料管循环流化床中，采用ＦＣＣ（流化床催化裂化催化剂）、硅胶球颗粒时，对下料管中颗粒局部速度、局部浓度的测量基础上，研究了床层截面平均颗粒浓度，截面平均颗粒速度的轴向和径向分布，并回归得到求取床层颗粒浓度的关联式，为气固下行反应器设计开发提供了理论依据。 相似文献
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Qiang Guo Mao Ye Wuqiang Yang Zhongmin Liu 《American Institute of Chemical Engineers》2019,65(6):e16583
Electrical capacitance tomography has been widely used to obtain key hydrodynamic parameters of gas–solid fluidized beds, which is normally realized by first reconstructing images and then by analyzing these images. This indirect approach is time-consuming and hence difficult for on-line monitoring. Meanwhile, considering recurrence of similar flow patterns in fluidized beds, most of these calculations are repetitive and should be avoided. Here, we develop a machine learning approach to address these problems. First, superficial gas velocity linear-increasing strategy is used to perform high-throughput experiments to collect a large amount of training samples. These samples are used to train the map from normalized capacitance measurements to key parameters that obtained by an iterative image reconstruction algorithm off-line. The trained model can then be used for on-line monitoring. Preliminary tests revealed that the trained models show good prediction and generality for the estimation of the overall solid concentration and the equivalent bubble diameter. 相似文献
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In the last few years, the downer has been proposed as a new reactor for gas/solids reactions. Compared to state-of-the-art riser reactors, the cocurrent downflow of gas and solids should lead to a more uniform flow structure, close to plug flow. Experimental studies showed, that the gas/solids distributor at the top of the reactor is significantly influencing the flow pattern in a downer reactor. Local information about the solids concentration is indispensable for a thorough characterization of the flow structure in gas/solids flows. To obtain this information, x-ray computed tomography has been used for the experimental investigations. 相似文献
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Measurement of particle concentration in a Wurster fluidized bed by electrical capacitance tomography sensors 
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下载免费PDF全文 Ruihuan Ge Jiamin Ye Haigang Wang Wuqiang Yang 《American Institute of Chemical Engineers》2014,60(12):4051-4064
It is essential to measure and monitor the particle flow characteristics in a Wurster fluidized bed to understand and optimize the coating processes. In this article, two electrical capacitance tomography (ECT) sensors are used to measure the particle concentration in different regions in a Wurster fluidized bed for the “cold” particle flows. One ECT sensor has a 12‐4 internal‐external electrodes and another has eight electrodes. The 12‐4‐electrode ECT sensor is used to measure the particle concentration in the annular fluidization region (outside of the Wurster tube) and the eight‐electrode ECT sensor is used to measure the particle flow in the central region (inside the Wurster tube). The effect of particle type, particle moisture, fluidization velocity, and geometrical parameters on the Wurster fluidization process is studied based on the two ECT measurements. The radial particle concentration profiles in the annular fluidization and central flow regions with different operation parameters are given. Fast Fourier Transform analysis of the particle concentration in the Wurster tube is performed with different superficial air velocities. The optimum operating ranges of the Wurster fluidization process for different particles are given. In the end of the article, computational fluids dynamics simulation results are given and used to compare with the measurement results by ECT for a typical Wurster fluidized bed. © 2014 American Institute of Chemical Engineers AIChE J 60: 4051–4064, 2014 相似文献