煤粉料仓通气下料流动行为

在可视化有机玻璃料仓系统上对煤粉下料过程及其特性进行了实验研究。研究表明,煤粉介质粒径小、比表面积大,属于黏附性非自由流动粉体,下料流动困难;料仓通气技术可以显著改善煤粉流动性从而促进料仓下料,但过量通气反而会抑制煤粉下料。通过分析下料过程中料仓壁面的压力信号,揭示了料仓压力分布特性,分析了超侧压现象并定义了压力转换面。实验发现,通气可以在一定程度内减小超侧压幅度,扩大煤粉流化疏松区域,提升转换面高度。此外,研究还发现通气下料过程中存在气体穿透现象,穿透临界高度随通气量的增加而提高,并且穿透后煤粉下料流率降低。     

不同载气供料对煤粉料仓下料的影响

煤粉料仓下料是气流床粉煤气化工艺中粉体供料单元的重要组成部分,其安全稳定运行具有重大的经济意义。在煤粉循环供料系统上,研究了以空气和CO2为载气的气力输送供料对料仓内煤粉重力下料和通气下料的影响。研究表明,料仓内粉体的堆积或流化状态对后续粉体的流动行为影响明显。对于重力下料,CO2供料后的重力下料过程中煤粉床层空隙率较高,下料流率较大;对于通气下料,空气供料后煤粉难以被CO2气体流化,从而对应较低的下料流率。     

不同载气供料对煤粉料仓下料的影响

煤粉料仓下料是气流床粉煤气化工艺中粉体供料单元的重要组成部分,其安全稳定运行具有重大的经济意义。在煤粉循环供料系统上,研究了以空气和CO₂为载气的气力输送供料对料仓内煤粉重力下料和通气下料的影响。研究表明,料仓内粉体的堆积或流化状态对后续粉体的流动行为影响明显。对于重力下料,CO₂供料后的重力下料过程中煤粉床层空隙率较高,下料流率较大;对于通气下料,空气供料后煤粉难以被CO₂气体流化,从而对应较低的下料流率。     

复杂流道结构料仓的下料流率预测

在实验室搭建的有机玻璃料仓下料平台上，分别以自由流动粉体玻璃微珠和黏附性粉体煤粉和聚氯乙烯为实验介质，针对无改流体(No-In)、封闭改流体(Con-In)和开放改流体(Ucon-In)三种情况所形成的不同流道结构，开展了粉体料仓下料及其流率建模研究，定量分析了改流体对粉体下料流率的促进作用，对比给出了玻璃微珠、煤粉和聚氯乙烯在不同流道结构料仓内的下料特性。研究表明，改流体的引入有利于提高料仓下料流率，Con-In促进流动效果最明显，对于流动性弱的煤粉，下料流率提升幅度达到最大的58%。基于剪切摩擦区的概念，提出流率校正因子F对最小能量理论方程进行了修正，将理想的料仓下料模型拓展至实际下料过程。进一步，对于Con-In，根据流道结构特征结合对粉体的受力分析，修正了模型中的锥角项；对于Ucon-In，基于粉体下料流动竞争机制，提出分阶段下料模式并关联了内层和夹层的下料流率，最终建立了复杂流道结构料仓的下料流率预测模型。该模型综合考虑了粉体物性、下料流型和流道结构的影响，可有效预测自由流动粉体和黏附性粉体流经传统料仓(No-In)和改流体料仓(包括Con-In和Ucon-In)的粉体下料流率，且预测偏差<10%。     

CPFD在细颗粒料仓下料中的应用

借助计算颗粒流体力学(CPFD)的数值模拟方法,研究了细颗粒玻璃微珠在不同结构料仓内的下料特性,获得了料仓出口直径和半锥角对颗粒下料流动的影响。在实验室可视化下料平台开展了验证实验,模拟结果与实验结果吻合较好。模拟结果表明:下料流率与料仓出口直径2.5次方呈正比;料仓半锥角增大,下料流型从质量流过渡至漏斗流。CPFD模拟给出了料仓下料过程的细节信息,并获得了料仓结构对颗粒流动形态转变的临界面相对高度的影响。     

粉煤在流化料仓中的下料特性

在自行设计的有机玻璃流化料仓系统上对粉煤下料过程及其特性进行了实验研究。研究发现，在筒仓段与料斗段连接处上方存在一个临界面。在临界面以上的筒仓段，粉煤以柱塞流形式下料，在临界面以下，粉煤以不定向螺旋运动下料。研究结果表明，料斗下部的流化气对下料稳定性和下料流率有重要影响，存在最佳流化气位置区间和最佳流化气表观气速范围，当流化气补气位置太低，在补气位置附近易形成气压平衡拱。研究还表明，增加料仓压力能提高粉煤下料流率，改善下料稳定性，减弱流化气补气位置及气速对下料的影响，阻止气压平衡拱生成。     

电容层析成像在煤粉料仓下料中的应用

煤粉料仓下料是气流床粉煤气化工艺中粉体供料单元的重要组成部分,其安全稳定运行具有重大的经济意义。提出将电容层析成像（ECT）技术用于煤粉料仓下料,从而实现研究手段的可视化。在煤粉料仓下料系统上,通过线性反投影算法及图片累加技术,获得料仓出口管道截面的相对颗粒浓度分布图像和下料过程的二维流型图;对比分析了称重信号和ECT信号的时间序列曲线,并通过RSD统计方法定量描述煤粉下料的波动程度。结果表明,ECT研究与煤粉下料分区理论吻合良好,借助ECT可充分认识煤粉下料流型和气固作用特征。     

补气料仓中宽筛分粒煤的下料特性

在自行设计的有机玻璃补气料仓系统上对宽筛分粒煤下料特性进行了实验研究,结果表明,料仓出口直径、粒煤粒径和外水分对宽筛分粒煤在补气料仓中的下料特性有显著影响.宽筛分粒煤的下料流率随料仓出口直径的增大而增加,但增加量随着补气量的增加而减小.增加宽筛分粒煤的平均粒径使料仓出口有效尺寸减小,导致物料下料流率减小.增加宽筛分粒煤...     

粉体料仓的卸料问题

<正>料仓能否保持连续、平稳和顺畅卸料是水泥生产正常运行的基础,更是下级给料计量设备稳定运行和准确计量控制的关键影响因素。但在工程设计中却常常不被重视,由于下料仓问题导致计量设备不能正常工作的现象较为常见,尤其对于煤粉和粉煤灰系统更为突出。本文对此进行讨论,希望为料仓的设计和选用提供有益的参考。1料仓中物料卸料的主要形态粉体物料在料仓中实际卸料流动状态往往比较     

简易粉状物料料仓助卸器—锥形嵌入体的应用

在料仓内距卸料口一定高度处,设置一个三角锥形的嵌入体,防止物料起拱,減少物料料柱压力和形成环形卸料带,大大改善料仓内物料的流动情况。经十年多的现场应用,证明下料均匀,生产稳定。     

Effect of powder properties on discharge characteristics of cohesive carbonaceous fuel powders from a top discharge blow tank at high pressure

Abstract

Discharge experiments of two cohesive carbonaceous fuel powders (anthracite coal and petroleum coke) were carried out in a top discharge blow tank experimental system with design pressure up to 6.4?MPa. The effects of powder properties (particle size and powder category) on the discharge characteristics (including solid discharge rate, solids loading ratio, and discharge stability) from the top discharge blow tank at high pressure were investigated. Meanwhile, shear tests with a ShearTrac II shear tester were performed to investigate the flowability of these two cohesive powders. The results indicate that there exists a near-linear relationship between major consolidation stress and flow function (FF). As particle size decreases, the values of FF decrease and powder flowability becomes worse. However, as particle size decreases, the particle suspension velocity decreases correspondingly, and the gas permeability becomes worse and gas maintain ability becomes better, which contribute to higher solid discharge rate and better discharge stability, whereas solids loading ratio may have opposite variation tendency. Compared to petroleum coke with similar particle size, anthracite coal has better flowability and can obtain higher solid discharge rate and solids loading ratio, as well as better discharge stability. During the discharge processes of petroleum coke, it was found that as the number of discharge experiment increases, the discharge stability decreases correspondingly. After petroleum coke being discharged continuously for 4–6 times, the discharge process could not start again, adhesion phenomena of petroleum coke to the wall of conveying pipelines could be observed.     

背压对U阀排料特性的影响

实验研究了背压对U阀排料特性的影响,建立了可调节背压的立管?U阀实验平台,发现随背压增大,U阀排料速率明显减小,进气速率对排料速率的调控能力变弱,且背压波动时,孔口的高度越小,U阀的运行越稳定. 针对本实验装置,背压小于7 kPa时,U阀孔口高度小于0.11 m,背压大于13 kPa时,孔口高度大于0.15 m,使U阀获得良好的排料特性. 根据实验数据和理论分析建立了U阀排料速率与背压、进气速率和孔口高度之间的经验方程,计算值与实验值的平均相对误差为20.9%.     

On the role and the origin of the gas pressure gradient in the discharge of fine solids from hoppers

The Brown and Richards (Principles of Powder Mechanics, Pergamon Press, Oxford, UK, 1970) correlation for the discharge rate of fine powders from a hopper was modified to account for the gas pressure gradient near the outlet. According to Donsı̀ et al. (Chem. Eng. Sci. 52 (1997) 4291) there is a transition between a granular flow region and a suspended flow region near the hopper outlet. Brown and Richards (1970) stated that the particle discharge rate depends on the flow conditions just above this transition surface. In the modified equation that is developed to account for the gas pressure, a term including the gas pressure gradient at this surface appears. The gas pressure gradient is evaluated from the literature experimental results by considering the Donsı̀ et al. (1997) finding that a significant part of the gas pressure gradient near the hopper outlet is due to the suspended motion. Furthermore, a simplified analysis is carried out to evaluate from the experimental results the voidage variation within the solids phase that is responsible for the onset of the gas pressure gradient.     

偏心楔形喂料斗卸料过程中颗粒流动特性

采用三维离散单元法,研究了偏心楔形喂料斗中不同粒径颗粒卸料过程的流场分布,建立了适用于偏心楔形喂料斗的整体流系数模型,分析了料斗卸料流型以及卸料流型与卸料质量流率的相关性,并通过实验验证了离散元模型的可靠性。结果表明：偏心楔形喂料斗内颗粒流场分布以靠近喂料管口区域为高速区,并呈辐射状朝远离垂直壁面端的料斗上部低速区过渡,高速区颗粒流场的整体一致性好,低速区颗粒流场呈局部涡流状;颗粒粒径增大,颗粒整体流动性变差,高速区域范围减小,低速区域范围增大,过渡区域变模糊;当颗粒粒径不大于10 mm时,整体流系数与颗粒粒径呈线性负相关,卸料质量流率与整体流系数呈线性正相关。     

GPU-based discrete element simulation on flow stability of flat-bottomed hopper

In this study, the flow stability of the flat-bottomed hopper was investigated via GPU-based discrete element method(DEM) simulation. With the material height inside the hopper reducing, the fluctuation of the flow rate indicates an unstable discharge. The flow regions of the unstable discharge were compared with that of the stable discharge, a key transformation zone, where the voidage showed the largest difference between unstable and stable discharge, was revealed. To identify the relevance of the key transformation zone and the hopper flow stability, the voidage variation of the key transformation zone with material height reducing was studied.A sharp increase in the voidage in the key transformation zone was considered to be the standard for judging the unstable hopper flow, and the ‘Top–Bottom effect' of the hopper was defined, which indicated the hopper flow was unstable when the hopper only had the top area and the bottom area, because the voidage of particles in the top area and the bottom area were both variables.     

Pneumatic transport characteristics of coarse size pulverized coal for the application of fast circulating fluidized bed gasification

The pneumatic transport characteristics of pulverized coal with very coarse grain size were investigated, especially related to fast circulating fluidized bed gasifier. The lock hopper system was used along with the top discharge blow tank technology to examine the transportation characteristics of pulverized coal. The most important factors among the pulverized coal transportation properties were mass flow rate of pulverized coal and the solid loading ratio, which changed with the amount of fluidization nitrogen and differential pressure between injection hopper and gasifier. The mass flow rate of the pulverized coal and the solid loading ratio were linearly proportional to changes in differential pressure, and were inversely proportional to changes in the amount of fluidization nitrogen. In the case of extended transport line, similar feeding characteristics were obtained by increasing the differential pressure while the level of fluidization nitrogen was kept constant. Pressure losses were observed with changes in the mass flow rate of pulverized coal, solid loading ratio, and the transport gas density in horizontal and vertical, both upward and downward, straight pipelines and at bends. Characteristics of pressure losses under various operating conditions were correlated with the nondimensional numbers such as the Reynolds number, Froude number, solid/gas density ratio, and solid loading ratio. Such correlations were reasonably consistent with the experimental results.