双喷嘴矩形导流管喷动床脱硫性能的研究

针对半干法烟气脱硫方法,提出了一种新型的双喷嘴矩形导流管喷动床半干法烟气脱硫装置。在不同的钙硫摩尔比、静床层高度、表观气速、绝热饱和温差下,以消石灰为脱硫剂,研究了该装置的脱硫性能,并与未加导流管的双喷嘴矩形喷动床的脱硫性能进行了比较;研究了不同脱硫剂流量下导流管喷动床的喷动压降。实验结果表明:脱硫率与钙硫摩尔比、静床层高度成正比,与绝热饱和温差、表观气速成反比;喷动压降与脱硫剂流量成反比。并最终得出了实验条件下双喷嘴矩形导流管喷动床的最佳操作范围和脱硫率关联式。     

小波分析方法在喷动床流型识别中的应用

在直径150 mm、静床层高280 mm的柱锥形喷动床中,采用平均粒径为1 mm、密度为2 770 kg/m~3的刚玉球为实验固相,采集不同气速下无导流管和带开孔导流管喷动床中的压力信号,通过小波分析与功率谱相结合的方法表征柱锥形喷动床的流型转变。首先利用平均压力法测得本实验条件下无导流管和带开孔导流管喷动床的最小喷动速度分别为0.57,0.50 m/s,然后采用Daubechies2小波对压力信号进行7层小波分解得出能反映喷动床流动特性的主频信号,再对主频信号进行功率谱分析。结果表明:无导流管和带开孔导流管喷动床的主频分别出现在D3(6.25—12.5 Hz)和D2(12.5—25 Hz)频段,且主频信号的功率谱图可以表征喷动床的3种流型:固定床、稳定喷动和不稳定喷动;开孔导流管喷动床的操作弹性(1相似文献   

双喷嘴矩形喷动床流动性能实验研究

在120 mm×240 mm的双喷嘴矩形不锈钢床内,对新型双喷嘴矩形导流管喷动床的最小喷动速度和喷动高度进行了研究,考察了喷动气速、粒径、静床层高度、导流管直径、导流管安装位置对最小喷动速度和喷动高度的影响。结果表明:最小喷动速度随颗粒直径、导流管直径、导喷距的增大而增大,随静床层高度的增大而减小;喷动高度随喷动气速的增大而增大,随导流管直径的增大而减小,受静床层高度和导喷距的影响不大,并得出了最小喷动速度的关联式。     

二维导流管喷动床的流动特征

带导流管的二维喷动床(2-DSBDP)是传统喷动床的改进型式,矩形床内设置的与床同厚的垂直导流管可以控制固体颗粒的循环速率, 同时使下行区中的气固移动床维持平推流. 本文实验测定了不同表观气速、床层高度、固体颗粒与气体入口尺寸时, 二维导流管喷动床的床压降及相应的空隙率,藉以阐述2-DSBDP的流动特征.     

液固导流管喷动流化床流型及流型转变的实验研究

以粒径为0.9mm的铜颗粒为流化颗粒,常温水为流化介质,在截面为59.2×15.6mm的矩形床中,对液固导流管喷动流化床的流型及流型转变进行实验了研究。通过对床层压降流量曲线的分析并结合实验观察,确定了液固导向管喷动流化床的流型及流型的划分,提出了流型图。研究结果对进一步开展导流管喷动流化床电极研究有重要的参考意义。     

导流管的不同形式对喷动床颗粒循环量的影响

对于导流管喷动床,导流管的形式对颗粒物料的循环量影响不能忽略.研究了四种不同形式的导流管在导流管不同的安装高度、不同的床层料位高度以及不同的吹松气量对颗粒循环量的影响.结果表明:增加床层料位高度,在一定范围内增加导流管安装高度和吹松气量,会增大颗粒循环量;导流管形式对颗粒循环量影响至关重要.     

开孔导流管喷动床烟气脱硫技术实验研究

研究了一种新型的半干法脱硫开孔导流管喷动床。在相同静床层高度下,研究了其最小喷动速度、最大喷动压降、喷动高度;在相同钙硫摩尔比、入口SO2质量浓度、进气温度、绝热饱和温差条件下,以消石灰为脱硫剂,研究了其脱硫性能。实验结果表明,与传统柱锥型喷动床相比,开孔导流管喷动床具有更好的流体力学性能和脱硫效率。实验条件下最适宜的操作条件为:钙硫摩尔比为0.9—2.5,进气温度为120—130℃,绝热饱和温差为10℃。     

矩形导流管喷动床下行区的床层压降

带导流管的矩形喷动床是传统喷动床的改进型式,矩形床内设置的与床同厚的垂直导流管,可以控制固体颗粒的内循环速率,同时使下行区中的气固移动床维持平推流.本文实验测定了不同表观气速、床层重量、不同固体颗粒与气体入口形式与尺寸时,矩形导流管喷动床下行区的床层压降,以考察其流动特征.实验结果表明,下行区存在床层压降的轴向分布,气固流动处于负压差下移上流区,且气固滑移速度自下而上是逐渐下降的.下行区颗粒床层的压降以及颗粒的移动下输,受到喷动床表观气速、床高、喷嘴尺寸、物料种类和颗粒直径的不同影响.     

二维导流管喷动床离散颗粒动力学模拟

采用离散单元法(DEM)-计算流体力学(CFD)双向耦合数值方法对二维导流管喷动床进行了模拟,颗粒的运动通过DEM模型描述,而气体的运动用Navier-Stokes方程进行求解,气体和固体颗粒之间的相互作用通过曳力形式传递。文中将DEM和边界元方法(BEM)结合起来解决颗粒在具有复杂边界设备内的运动。通过采用BEM+DEM-CFD相结合的方法进行模拟计算,得到了喷动床的最小喷动速度,研究了不同表观气速下床内的流型,得到了二维导流管喷动床的床层压降与表观气速的关系,统计分析了喷射区、环隙区内颗粒的运动速度和相应的空隙率,全面地描述了二维导流管喷动床内的气固流动特征。     

带导流管液固喷动床的最小喷动速度研究

在截面为矩形有机玻璃喷动床内，使用四种粒径的窄筛分球形玻璃珠，以常温水作为喷动和辅助液体。综合考虑床体的几何尺寸、操作参数以及液体和颗粒的物性特征，系统研究带导流管喷动床的最小喷动速度，得出最小喷动速度的经验公式，为设计和操作提供参考。     

An Experimental Study on the Influence of Using a Draft Tube in a Continuous Spouted Bed Dryer

Further increasing the production of processed biofuel also increases the demands on drying capacity. With the aim of increasing the heat capacity flow, experimental tests have been performed on the process of drying sawdust in a continuous spouted bed dryer with nine different draft tube designs. The results showed that a draft tube with an increased length and an increased disengagement height decreased the dry substances’ flow rate throughout the dryer. The results also showed that the mass of the material in the dryer was approximately the same in all the tests. This means that the draft tubes, no matter their size, do not influence the amount of material in the dryer.     

Drying characteristics of a draft tube spouted bed

Using the results of earlier work on the flow pattern of gas and solids in a draft-tube spouted bed, the drying characteristics of such a spouted bed are discussed. Paddy (unpeeled rice) was dried in a 30 cm bed with a 5.5 cm draft tube and temperatures and moisture content of solid and gas phase were measured as a function of drying time at various points in the system. It appears that the (constant) drying rate is determined by the heat transfer in the recirculation zone (just above the air inlet) and in the draft tube. After the short and rapid heating in the tube, the temperature and moisture gradients in the particle equilibrate in the annulus. It is concluded that a draft-tube spouted bed is a promising dryer design for heat-sensitive particles with slow intra-particle mass transfer coefficients.     

Grain Drying in a Paraboloid-Based Spouted Bed with and without Draft Tube

In this study, grain drying in a spherical-based spouted bed (SBSB), a cone-based spouted bed (CBSB), and a paraboloid-based spouted bed (PBSB) with and without draft tube was investigated. Spouted-bed bases with the same volume in different shapes—spherical, cone, and paraboloid—were used for the drying experiments to investigate the effect of the spouted-bed base shape on drying. The drying experiments were carried out with perforated and solid draft tubes. The effects of the distance between the gas inlet nozzle and the bottom of the draft tube (entrainment zone height) and the draft tube diameter as geometric parameters on drying were also investigated. It was seen that the geometrical shape of the contactor base influenced the drying time. The highest drying rate was achieved for drying in a paraboloid-based spouted bed. The results also showed that using a draft tube caused a significant increase in drying time. Because the perforated draft tube allows a higher gas flow rate through the annulus, it decreases the drying time when compared with the solid draft tube. Drying time decreased slightly with the decreasing height of the entrainment zone but draft tube diameter did not have a considerable effect on drying.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20-25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

Drying of Biomass in a Conical Spouted Bed with Different Types of Internal Devices

The drying of sawdust was studied in a conical spouted bed pilot plant in order to adapt this feed for the pyrolysis process. Air at different temperatures was used and the effect of sawdust particle size and operating gas velocity was studied. Batch operation was performed with no internal device and with nonporous and open-sided draft tubes in order to ascertain the optimum configuration of the contactor. Although the nonporous draft tube required the lowest minimum spouting velocity, its performance was poor due to deficient gas–solid contact. Configurations with open-sided draft tubes and with no internal devices had higher efficiencies because of their better contacts. An increase in air temperature resulted in a reduction in drying time but the operating conditions need to be fine-tuned to ensure proper energy efficiency.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

Abstract

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

Drying of Liquid Feedstocks in a Spout‐Fluid‐Bed with Draft‐Tube Submerged in Inert Solids: Hydrodynamics and Drying Performance

A spout‐fluid bed with draft tube submerged in a bed of polypropylene beads was used for drying maltodextrin solutions. The hydrodynamics of the dryer were studied by determining the annular air flow vertical profile at different spouting velocities, using an additional air flow rate through the annulus equivalent to 0.5 U_mf. The drying performance of the dryer was studied through the determination of several dryer response parameters (product moisture, evaporative capacity and volumetric evaporative capacity). These parameters were compared with those obtained in a conventional spouted bed with inert solids and a spray dryer.     

导向管直径对喷动床流动特性影响的计算颗粒流体力学数值模拟

导向管喷动床是较为常见的一种喷动床改进床型,通过阻断喷动区与环隙区气固接触来提高颗粒循环的规律性与稳定性。本文采用计算颗粒流体力学（CPFD）方法对于直径150mm的柱锥式导向管喷动床进行了数值模拟研究,考察了导向管直径对于喷动床内颗粒流动特性的影响,从环隙区死区分布、颗粒速度分布、固体循环量等方面分析了具有不同直径导向管喷动床的运行状态。结果表明,加入导向管在减少床内死区的同时也降低了运行时的固体循环量,对于本次采用的喷动床结构尺寸与运行参数,只有在导向管直径为40～60mm时才能保证床内具有良好喷动状态,综合考虑各因素,选用直径50～55mm的导向管最为合适。对于具有类似结构与运行条件的柱锥喷动床,导向管直径可考虑选为无导向管运行时喷动区直径的1.2～1.375倍。     

A Draft-Tube Conical Spouted Bed for Drying Fine Particles

A study has been conducted on the performance of a draft tube conical spouted bed for drying fine particles. Batch operation has been performed with nonporous, porous, and open-sided draft tubes in order to ascertain the optimum configuration of this internal device. The nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the drying efficiency of the open-sided draft tube are superior to any other spouted bed configuration. Moreover, it allows for reducing the height of the fountain and, consequently, the height of the drying equipment.     

Simulations of flow behavior of gas and particles in spouted bed with a porous draft tube

Flow behaviors of particles in a two-dimensional spouted bed with a porous draft plates are studied using a fluid dynamic computation with kinetic-frictional stresses models. Gas flow through the porous draft tube is simulated by Brinkman-Darcy-Forchheimer formulation. The distributions of concentration and velocities of particles are predicted. Simulated results predict the solid circulation rate and gas flux rate measured in the spouted bed with a porous draft tube (Ishikura et al., 2003). The solid circulation rate in the spouted bed with a porous draft tube is larger than that with a non-porous draft tube. The predicted bed pressure drop with the porous draft tube is high in comparison to the spouted bed with non-porous draft tube. The effect of the porosity of the porous draft tube on distributions of gas flux rate through the annulus and solid circulation rate are discussed.