Mixing and Segregation Characteristics of Binary Granular Material in Tapered Fluidized Bed: A CFD Study

The particle flow pattern, mixing and granule segregation in a tapered fluidized bed have been studied along with the hydrodynamics. At first the bed of varying total mass and granule fractions is fluidized then the bed is defluidized to freeze the composition, the bed is sectioned to layers and the composition in each layer is determined by sieving. Materials used in the present study are dolomite and glass beads with different B.S.S Sizes. A series of unsteady, three fluid CFD simulations were performed using FLUENTTM 6.2. Simulation parameters viz. solution technique, grid, maximum packing fraction and operating conditions like gas velocity were investigated for relative effects on particle mixing and segregation. Good arrangement of solid volume fraction profile was obtained between the experimental results and simulation results for regular particles.

FUNDAMENTAL STUDIES ON THE HYDRODYNAMICS AND MIXING OF GAS AND SOLID IN A DOWNER REACTOR

The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in both risers and downers.When the flow is in the direction ofgravity(downer),the radial profiles of gas and particle velocity are more uniform than that inthe riser,the solids mixing is very small and the flow pattern approaches plug flow,while theflow is against gravity(riser),the solids backmixing significantly increase and the flow pattern isfar from plug flow.Among many of factors the flow direction has the largest influence onhydrodynamics and axial mixing of gas and solids.

Hydrodynamics and oxygen transfer in a novel extra-loop fluidized bed bioreactor

In this paper, the characteristics of fluid mixing time in a novel extra-loop fluidized bed were studied. The results showed that the mixing time was shortened with the increase of fluid velocity. All the discrete numbers of the reactor were above 0.2. The serial number n was 2.5 -3.0. It was judged accordingly that the reactor fluid state was continous stirred tank reactor （CSTR） mainly. When the inspiratory capacity increased the mixing time of the reactor was shortened. Thus the air input was beneficial for the fluid mixing. During the three phases mixing process, the mixing time of the reactor could be decreased by the n increase of carrier and air loading together, but the change was not significant. The parameters affecting the reactor fluid state were fluid velocity, inspiratory capacity and carrier. KLa could be increased with the air loading increase, and at the same gas/liquid ratio when the pressure drop was high, KL~ value was increased. The amount of carrier complex influence on KLa. As the carrier loading continued to increase, its value had been dropped but the changes was not significant, and optimization condition was found at above 800 1 000 g carrier loading （pouzzolane） or 600 g PVC. Under gas/liquid ratio of 0.8% -5.2%, KLa was （0.62-1.37）×10^-2· s^-1.

Axial Liquid Dispersion Characteristics in Magnetically Stabilized Bed

Axial liquid dispersion was experimentally studied in liquid-solid and gas-liquid-solid magnetically sta- bilized beds using the ferromagnetic catalyst of SRNA-4 as the solid phase. The effects of operating factors and fluid characters, such as superficial liquid velocity, superficial gas velocity, magnetic field intensity, liquid viscosity and surface tension, on axial dispersion coefficients of liquid were investigated. The dispersion coefficients in- creased with the increase of superficial liquid velocity and superficial gas velocity, and decreased with the increase of liquid viscosity, liquid surface tension and magnetic field intensity. A correlation equation of Peclet number was obtained for both liquid-solid and gas-liquid-solid magnetically stabilized bed.

Kinetic Studies for an Aerobic Packed Bed Biofilm Reactor for Treatment of Organic Wastewater with and without Phenol

A laboratory scale aerobic fixed film bioreactor packed with glass beads for biofilm growth was used to evaluate the removal efficiencies of COD and phenol for a carbohydrate—phenol mixture in wastewater. It was done by an indigenous mixed culture inoculums developed after collecting sludge from a return line of an activated sludge plant. The test result on continuous flow in the above biofilm reactor indicated an optimum hydraulic loading range of 4-6.4 m3day-1m-2 for attainment of reasonable amount of COD removal in case of carbohydrate substrate only. The COD removal efficiency, however, gradually depleted from 100% to 54% by gradual increase in organic loading (OLR) from 0.72-4.32 kgday-1m-3, beyond which removal was not significant. For the identical loading conditions, in presence of phenol in the substrate along with carbohydrate, the COD removal was observed varying from 100-40% in the above organic loading range. The COD removal kinetics in presence of phenol also shows a decreasing trend compared to data obtained without the presence of phenol in wastewater that reveals biological inhibition. The experimental data were fitted in a simple plug flow model for evaluating the zero order, first order and Monod form of rate equations to evaluate the kinetics. It was found that Monod type rate equations combining a zero and first order rate expression is the best fit for the above hydraulic and organic loading that gives a best fit half velocity constant value of 35 mgL-1 (R2 = 0.9612).

Effects of Airflow Field on Droplets Diameter inside the Corrugated Packing of a Rotating Packed Bed

Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.

基于DRGs相关指标的福建省某三级医院外科床位优化配置研究

目的分析研究福建省某三级医院外科床位利用情况,为医院床位配置提供分类管理指导和动态调整的科学依据,以提高床位利用效率。方法通过绘制波士顿矩阵图,结合床位利用相关指标、病例组合指数(CMI)、时间消耗指数等DRGs相关指标,综合分析医院外科床位配置情况。结果以时间消耗指数为X轴、床位使用率为Y轴绘制床位利用波士顿矩阵图,使科室床位分类更科学、合理。某三级医院19个外科中,效率型科室有5个,周转型科室有9个,压床型科室有2个,闲置型科室有3个;19个外科中床位数偏少的科室有2个,床位数偏多的科室有9个,床位数合适的科室有8个。结论将床位利用相关指标与DRGs相关指标相结合,对科室床位配置效率进行评价可反映科室收治患者的疾病疑难程度,为优化床位配置和探索“全院一张床”管理模式积累实践经验并提供科学依据。

DRG背景下公立医院床位效率研究

目的分析医院各临床科室床位利用效率,为合理配置科室床位资源提供参考。方法以某三甲专科医院2022年度数据为基础,基于传统床位工作效率指标,引入CMI值进行调整,计算各科室床位的合理区间,结合数据包络分析法(DEA),综合评价各临床科室投入产出效率,得出床位配置优化方向。结果被统计的39个科室中,10个科室床位设置不合理,其中需要增加床位的有5个科室,需要减少床位的有5个科室。结论利用CMI调整病床工作效率指标,结合DEA方法,可为医院动态调整临床科室床位数提供科学依据;医院应合理利用床位资源,科学规划科室床位。

1000 MW超超临界机组精处理系统改造及智能化升级

某电厂2×1000 MW超超临界机组锅炉给水采用加氧处理(OT),利用西安热工研究院“火电厂高速混床运行性能诊断及优化专家系统”对精处理高速混床和再生系统进行诊断,发现运行末期泄漏离子、再生系统缺乏智能监控装置及再生酸碱用量大等问题。应用树脂输送图像智能识别及控制仪(IRIC)和双层多孔板布水装置改造后,树脂体外再生过程实现了智能控制,树脂输送终点识别准确率100%;高速混床平均周期制水量增幅108%,出水Na^(+)和Cl^(-)含量均优于《火力发电机组及蒸汽动力设备水汽质量》(GB/T 12145—2016)要求,经济效益和安全效益显著。

麦-玉耕作秸秆混土还田模式下离散元参数标定

麦-玉一年两熟的江淮、黄淮地区秸秆混土还田保护性耕作模式,麦秸秆-土壤混合的种床缺乏准确的物料相互接触参数,阻碍了机械化玉米精密播种过程中关键部件、种粒、肥料与混合种床相互作用研究,进而制约了机具优化与改进。采用物理与EDEM离散元方法结合研究非连续体麦秸秆-土壤混合物之间相互作用,选用Bonding V2黏结模型搭建柔性麦秸秆段“元颗粒”,选取Hertz-Mindlin with JKR模型对一定湿度的土壤进行参数标定。首先,以圆桶提升麦秸秆和土壤种床混合物堆积角为响应值,采用Plackett-Burman筛选试验和最陡爬坡试验分别对显著影响因素从大到小排序和缩近最佳取值范围。利用Box-Behnken试验构建了显著影响因素与堆积角二阶回归模型,对显著因素交互项进行响应曲面分析,利用Design-Expert软件优化模型并以实测堆积角39.94°为目标响应值,计算得土壤JKR表面能0.500、土壤-秸秆动摩擦系数0.065 8、土壤-秸秆JKR表面能0.262及土壤-土壤动摩擦系数0.155,仿真验证误差1.08%,表明标定的接触模型参数可靠。该研究可为麦-玉保护性耕作模型下混合种床与机具精密播种相互作用研究提供参考和理论依据。

火电厂凝结水精处理系统调试及树脂再生

新建火电厂凝结水精处理系统调试为其投产前必不可少的环节。简述了某火电厂一期1000 MW超超临界机组凝结水精处理系统概况,对高速混床的调试和树脂再生过程的注意事项进行了深入探讨,详细分析了树脂分离传送过程中的粒径控制、分离流量控制、进水流量配比、输送终点判断、再生注意事项等,对树脂再生系统的运行进行了优化。结果表明,调试后的设备运行正常,可以保证凝结水精处理系统长期、安全、经济运行。

气液混合强化在固定床加氢过程中的应用进展

炼油工业作为国民经济的支柱,在创造大量财富的同时,往往存在高能耗、高物耗和高污染的问题。固定床加氢技术是重要清洁炼油技术,在油品质量升级、产品结构调整、原油资源高效利用、生产过程清洁化进程中发挥了重要的作用。提高固定床加氢效率有助于充分利用石油资源、生产清洁燃料和实现生产过程的节能降耗。本文从固定床反应器滴流床加氢和液相加氢过程的氢油两相物料混合特性出发,综述了通过开发新型混氢设备和加氢工艺,强化气液混合过程,提高固定床多相催化加氢效率的应用进展,并提出固定床加氢反应过程气液混合强化技术发展趋势,为炼油化工生产过程提质增效、节能降碳新技术的开发提供参考。

煤化工优质再生水处理工艺优化研究

针对RO+混床工艺处理煤化工优质再生水的周期制水量与处理水库水相比明显偏低,影响回用锅炉补水问题进行了原因分析,并进行了RO+EDI工艺替换RO+混床工艺处理优质再生水的中试研究。试验结果表明:采取RO+EDI工艺处理优质再生水时,再生水回用率可从采用RO+混床工艺的30%提高至100%,产水电导率和硅含量达到相关锅炉进水标准要求,同时吨水产水成本可由1.63元降低至1.02元,工艺优势明显。

钱塘江河口盐官段混合式丁坝修建对水沙及河床影响的实测研究

钱塘江北岸古海塘堤脚加固工程中,辅助围堰施工的临时性管袋黏土混合式丁坝对工程的顺利进行、提高施工效率起着至关重要的作用,然而目前对其周围水沙运动的研究较少,且缺乏相关实测资料。考虑混合式丁坝修建的动态过程,利用无人机拍摄水流视频结合LSPIV(粒子图像测速)处理技术对丁坝修建前、中、后期周围的流场进行分析,并对丁坝附近的地形进行跟踪测量,同时对不同潮差的水流含沙量进行现场测定。结果表明,丁坝具有改变水流方向,减少水流对河岸冲刷的作用,且丁坝越长,挑流作用越明显,为围堰施工提供了较为平缓的水流条件;混合式丁坝对坝后处的促淤效果明显,且坝后地形变化与含沙量密切相关,潮差越大,水体含沙量越高,丁坝后河床淤积幅度越大,有利于提高围堰的施工效率。研究成果对之后相关物理模型和数值模拟的研究提供数据支持。

混床运行周期降低的原因及处理

陕西延长中煤榆林能源化工股份有限公司(简称“榆能化公司”)是中国污水近“零排放”企业之一,原水水质复杂,由地表水、回用水、再生水及少量的污水站产水混合而成。各类回用水占比较大,部分难去除离子长期在水系统内富集,导致脱盐水混床运行周期不稳定、树脂再生频繁、酸碱单耗增加,严重影响装置稳定运行。文章通过对混床进水离子含量、树脂交换容量及再生操作等方面原因分析,发现混床进水电导率是影响混床运行周期的关键因素,并通过对各类回用水进行分质利用等措施,使混床运行周期降低问题得到了有效解决。

低负荷下生物质掺烧比例对循环流化床锅炉燃烧性能的影响

为了研究生物质在低负荷下循环流化床机组深度调峰中的应用潜力,本文结合实验和数值模拟方法,分析不同生物质掺混比例对CFB锅炉内部温度、压力、气体浓度及颗粒动态的影响。研究发现,生物质掺混比为10%、20%时,循环流化床密相区升温速率提高2~8℃/min,但稳定温度随掺混比增加而降低。为深入了解造成这种现象的原因,分别对3种工况进行数值计算后发现:掺烧比由0%提升至20%时,密相区压降由900 Pa减少至700 Pa;CO浓度由10%降低至5%;CO_(2)浓度从17%降低至12%;颗粒浓度降低了18%。相对地,稀相区各组分浓度出现增加,特别是颗粒浓度增加了达38%。表明生物质的掺入促使燃烧区域向炉膛中上部移动。这一发现证明了生物质掺烧能有效提高低负荷下炉内升温特性且满足“双碳”目标下的需求,为低负荷下电网调峰提供了新方法。

煤气发电机组高速混床运行周期优化措施

凝结水精处理系统中高速混床运行周期受多方面因素影响,主要有树脂数量、树脂比例、树脂性能以及运行控制等。针对某钢厂亚临界发电机组2台高速混床运行周期相差较大及高速混床运行压差大的问题,通过优化控制程序,改进高速混床内部结构缺陷以及完善运行控制等措施,提升了2#高速混床的周期制水量。

脉动流化床内青刀豆颗粒的混合特性数值模拟

青刀豆一般采用流化床装置进行速冻。为了解决其床层堵塞和聚集不良的问题,进一步提高青刀豆的混合效率,课题组建立了三维混合脉动流化床模型,将计算流体力学与离散单元法(computational fluid dynamics-discrete element method,CFD-DEM)相结合,探究1,2,4和8 Hz 4种不同频率的脉动进口风速下青刀豆颗粒的流化混合情况。仿真结果表明:脉动流化床对于青刀豆颗粒混合具有一定改善作用,青刀豆颗粒的轴向混合强于径向混合,4 Hz时颗粒混合标准偏差值最小;当进口风速的频率接近颗粒的自主振动频率时,床层膨胀最明显,出现类似“共振”的现象;2 Hz时颗粒径向、轴向混合效果最佳,频率过大或过小对于流态化增强效果不明显。

气固微型流化床反应分析仪的理想流型判据分析

微型流化床因具有气体返混小和可操作性强等优点,在反应动力学测量等领域备受关注。获得流型随操作参数的变化规律,才能实现微型流化床理想流型的有效调控。采用双流体模型耦合考虑结构的相间曳力(又称多尺度CFD)模拟了一系列A类和B类颗粒在不同操作条件下的流化行为,结合颗粒浓度和气体停留时间分布(RTD)特征考察气速、床径和初始床高对气体返混行为的影响。研究表明,当微型流化床在初始鼓泡到湍动流态化之间操作时,才逼近颗粒全混流和气体近似平推流的运动状态。进一步分析气体RTD曲线形状特征(如拖尾、多峰等),提出采用斜度S<0.6作为微型流化床平推流判据,弥补了原判据[满足方差σ_(t)^(2)<0.25且峰高E(t)h>1]的不足,为微型反应分析仪的流型调控奠定了基础。

高速混床树脂分离与输送过程的智能监控

由于缺乏有效的监控手段,电厂凝结水精处理系统的高速混床树脂分离与输送效果较差且很不稳定,严重影响高速混床的运行效果。为此,开发了一种树脂分离与输送智能监控装置。利用该装置,不但可准确判断树脂分离与输送终点,提高树脂分离度,还可根据需要调整阳阴树脂的配比,增加高速混床的周期制水量。2014年将该装置安装在海南某2×350 MW电厂的凝结水精处理系统上,使高速混床运行可靠性显著提高,周期制水量由26 000 m3增加至82 000 m3,再生次数大幅度减少,每年可节约高品质酸碱112 t、除盐水31 000 m3、新鲜水62 000 m3,树脂年补充率降低约3%,产生的直接经济效益约110万元/年。