颗粒层非稳态过滤捕集效率的研究

为计算颗粒层非稳态过滤效率,通过改进经典过滤理论模型,考虑颗粒在过滤介质中的沉积,理论推导得出非稳态过滤效率的计算公式,而经典颗粒层过滤效率计算公式仅为此计算公式的特例。因为理论计算公式是隐函数,不便于工程实际应用,所以,在常温条件下,对非稳态过滤时的过滤时间、过滤风速、过滤层厚度、粉尘浓度和颗粒层滤料均粒径等五个因素进行了正交实验研究。采用多元回归的方法得出各影响因素与过滤效率呈显性关系的效率关联计算公式,其计算结果与实验测试结果基本吻合。     

新型颗粒层过滤性能的宏观数学模型

根据固定床颗粒层内气流含尘浓度的连续方程、颗粒层过滤规律和新型颗粒层的过滤特点,建立了固定床颗粒层过滤过程和新型颗粒层过滤性能的宏观数学模型;根据颗粒层的过滤机理和实际灰尘颗粒粒径的分布状态,在实验的基础上,修正了过滤速度对颗粒层过滤效率的影响;根据实验结果对过滤效率方程式、床层压降方程式中的特征参数进行了回归,得到了具体过滤介质的颗粒层宏观过滤数学模型。模型表明新型颗粒层过滤过程是一个不随过滤时间变化的准稳态过程,只与过滤介质特性和循环清灰周期有关,模型计算值能准确地反映颗粒层的过滤性能。     

长纤维过滤器过滤过程的数值模拟

在长纤维束过滤器动力学模型和现场实验数据的基础上,利用Comsol Mulitiphysics仿真软件对长纤维束过滤器过滤过程进行数值模拟。将3类仿真曲线(滤出水颗粒浓度随时间的变化曲线、滤液浓度沿滤层的变化曲线、滤床各层比积泥量的变化曲线)与实验所得的真实曲线分别进行对比,两者比较接近。说明该过滤过程模型可用于影响长纤维束过滤器运行特性中单个或多个变化因素(初始滤速、纤维束装填密度、流入浓度和纤维丝直径等)实验结果的估算,可作为长纤维过滤器的实验研究、操作优化和结构设计的参考。     

湿式纤维层非稳态过滤净化阻力的研究

在干式纤维层过滤净化阻力的理论基础上,提出清洗水均匀分布于纤维丝表面的基本假设,使湿式过滤中对液滴、液膜、液珠的分析简单具体化。并通过实验结论归纳出净化阻力随时间的变化规律,导出湿式纤维层非稳态过滤净化阻力的表达式,并用实验验证了其准确性。     

固定床中粒状脱硫剂除尘效率的研究

建立了非稳态过滤下的固定床颗粒层除尘效率模型.该模型尽可能地包含了影响固定床颗粒层除尘的参数,反映了沉积粉尘对除尘效率的影响;研究了以粒状脱硫剂为滤料的固定床在不同颗粒层厚度、空床气速、粒径下的除尘效率.结果表明,在颗粒层厚度为400～800 cm、空床气速≤0.4 m/s的条件下,颗粒层的除尘效率可达90％以上.     

褶型筒式空气过滤器过滤压降的数值模拟

基于计算流体力学(CFD),采用FLUENT中的多孔介质模型对褶型空气过滤器进行数值模拟研究,通过模拟计算和实验研究得到了空气过滤器的一些阻力性能。结果表明,褶型空气过滤器在过滤气体中的杂质时,过滤器的阻力随着进口风量的增大而增大;而增加过滤器的褶数会增大过滤器的过滤面积,过滤器的过滤面积增大之后过滤器的过滤速度会相应减小,由此可以减小过滤器的阻力。但是增加过滤器的褶数之后会相应的改变过滤器滤芯的褶间距,褶间距的大小会对气流的流动产生影响。气流的流动会影响过滤器的阻力。这些研究可以为过滤器滤芯的设计及应用提供一定的依据。     

旋风除尘器流场及浓度场实验与模拟

在研究旋风除尘器内气固两相的运动状况及分离机理方面,计算机模拟替代部分实验的方法能够优化设计旋风除尘器结构参数,提高其对微细颗粒的捕集效率,减少运行压力损失。本研究采用RSM模型和随机轨道模型对旋风除尘器内流场及浓度场进行模拟及实验。研究表明,旋风除尘器压力损失模拟结果与实验结果吻合较好,对于大于5μm的颗粒其捕集效率模拟结果与实验结果基本吻合;旋风除尘器外壁的颗粒浓度呈螺旋带状分布;如将排气管管径减少至原直径0.8倍,可使其对2μm颗粒捕集效率提高6.6%,但压力损失提高36.5%;颗粒的凝并作用有利于提高旋风除尘器微细颗粒的捕集效率。     

中空纤维微滤膜污染及阻力分析

选用0.1μm的PVDF中空纤维内压式微滤膜组件,在死端微滤工况下,研究了酵母(平均粒径5.3 μm)和高岭土(平均粒径0.7μm)体系在浓度和压力变化时的污染机理及过滤阻力、膜渗透通量的变化规律性.通过恒压堵塞定律积分式的具体形式与实验数据的拟合及根据堵塞过滤定律计算的结果都表明:死端微滤时,酵母体系和高岭土体系均符合滤饼过滤机理.     

新型电袋复合除尘器性能研究

为了提高布袋除尘器对细微粒子的捕集效率,同时降低压力损失,提出了一种新型的电袋复合除尘器,并利用这种新型的除尘器对2 500目的超细滑石粉进行了实验研究。通过普通布袋过滤、电袋复合过滤的对比实验研究,得到了电场强度、气布比、压损、清灰周期和除尘效率等参数的变化规律。实验结果表明,使用新型的复合除尘器过滤粉尘时,粉尘在进入袋室之前就被荷电,通过在滤料表面施加较强的静电场,使得被处理粉尘在滤料的表面有序堆积和排列,能有效地降低压力损失,提高过滤风速,除尘效率均达到97%以上。Vf=3.5 m/min,U=12.3 kV时,新型复合除尘器与普通布袋过滤相比压力损失降低了90 Pa;PM2.5的捕集效率提高了5.9%;清灰周期从10 min延长至36 min。     

多孔介质过滤细颗粒

以活性炭为过滤介质,利用其多孔结构脱除细颗粒,实现低压降除尘工艺。研究活性炭颗粒粒径、滤层厚度以及表观过滤风速等条件对多孔介质过滤细颗粒效果的影响,并通过表面光滑的不锈钢珠进行实验作对比,分析多孔介质过滤细颗粒的机理。结果表明:活性炭颗粒对细颗粒的过滤效率明显高于表面光滑的不锈钢珠。过滤效率随活性炭颗粒粒径和表观过滤风速的减小而增加,当粒径从1.5 mm降至0.45 mm时,平均过滤率从53.17%升至80.34%,当表观风速从26.54 cm·s~(-1)降到1.66 cm·s~(-1)时,平均过滤率从41.89%升至75.24%。过滤效率随滤层厚度的增加明显增加,当层厚从60 mm增加到140 mm时,过滤效率从47.62%增大到70.78%。不同实验条件下,过滤压降都没有随时间有明显变化,细颗粒没有在活性炭颗粒表层形成粉尘层。活性炭颗粒床主要是依靠细颗粒扩散、惯性碰撞和拦截效应沉积在活性炭多孔结构内,从而脱除细颗粒。     

Feasibility of granular bed filtration of an aerosol of ultrafine metallic particles including a pressure drop regeneration system

A process for filtering an aerosol of ultrafine metallic particles (UFP) has been designed and tested, based on the principle of a multistage granular bed. The filtration system comprised a succession of granular beds of varying thickness composed of glass beads of different diameters. This system allows the pressure drop to be regenerated during filtration (“on-line” mode) using a vibrating probe. Tests monitoring the pressure drop were conducted on a “10-L/min” low airflow rate device and on a “100-m³/hr” prototype. Granular bed unclogging is automated on the latter. The cyclic operation and filtration performances are similar to that of filter medium-based industrial dust collectors.

Implications:?Filtration of ultrafine metallic particles generated by different industrial processes such as arc welding, metal cutting, or spraying constitutes a difficult problem due to the high filter clogging properties of these particles and to the high temperatures generally encountered. Granular beds represent an advantageous means of filtering these aerosols with difficult properties.     

Filtration Properties of Fly Ash from Fluidized Bed Combustion

Some of the features of the fluidized-bed combustion (FBC) process have a direct bearing on the particulate properties that most strongly influence filtering pressure drop. A laboratory program was conducted to experimentally determine the relative pressure drop characteristics of ashes from the TVA-EPRI 20-MW bubbling bed, atmospheric pressure FBC (AFBC) pilot plant and six pulverized-coal combustion (PC) units. The combined influences of measured particle and dust cake properties on filtering pressure drop were estimated with existing filtration theories. These theories predict a higher pressure drop for a dust cake produced with the AFBC ash than for one consisting of any of the PC ashes. Laboratory measurements were made of the flow resistance of idealized, simulated dust cakes to confirm these predictions. Field operating data from the fabric filters collecting some of the tested ashes were available to validate the laboratory results. The laboratory and field data show relatively good agreement. The AFBC ash must be treated as a special case for fabric filters, and careful selection of cleaning method and fabric must be made to minimize the inherently high pressure drop characteristics of this ash.     

Fine dust filtration using a metal fiber bed

A bed-type filter composed of thin metal alloy fiber was closely examined with dust capturing in cold and hot runs. The investigation of an individual mechanism across the filter bed indicated that the aerated dust could be initially collected by depth filtration, and after a while, surface filtration dominated the overall dust collection. The present metal fiber bed was comparable to the conventional ceramic filters because of its good collection efficiency with low pressure drop. It also showed potential to be used as a prefilter in a diesel exhaust trapping system.     

Fine Dust Filtration Using a Metal Fiber Bed

Abstract

A bed-type filter composed of thin metal alloy fiber was closely examined with dust capturing in cold and hot runs. The investigation of an individual mechanism across the filter bed indicated that the aerated dust could be initially collected by depth filtration, and after a while, surface filtration dominated the overall dust collection. The present metal fiber bed was comparable to the conventional ceramic filters because of its good collection efficiency with low pressure drop. It also showed potential to be used as a prefilter in a diesel exhaust trapping system.     

并流旋转床气体出口压降数值分析

气体出口是旋转床的重要组成部分,对旋转床流场与气相压降有着重要的影响。研究并流旋转床结构、构建气体出口物理模型,利用RNG k-ε湍流模型,探索不同气体出口结构对并流旋转床流场的影响。模拟结果表明:具有4个切向气体出口的DCRPB3615型旋转床有利于旋转床内速度分布均匀、降低湍动能,减小气相压降。模拟与实验对比表明,DCRPB3615压降比单一径向出口的CRPB3615型旋转床降低10%左右。     

错流式生物滴滤床净化甲苯废气

采用焦化厂污泥为菌源驯化甲苯降解菌,接种错流式生物滴滤床,净化含甲苯废气。研究了生物滴滤床的挂膜启动和长期运行情况,填料和营养液对滴滤床去除能力的影响,并对长期运行的压降进行了观察分析。反应器挂膜启动需要6 d时间,稳定运行的平均去除效率为95％,单位体积最大去除负荷为251 g/(m³·h)。结果表明,采用错流式生物滴滤床可以有效去除甲苯废气;以比表面积大的生物陶粒作为填料以及定期适量更换营养液,均有助于提高生物滴滤床的去除能力;错流式生物滴滤床具有压降小、气液分布均匀的特点。     

Filtration of fly ash using a fluidized-bed filter

This study focuses on the control of particulates with a fluidized-bed filter in exhaust gas stream. The fluidized-bed filter classified in the granular bed filtration technology was employed to demonstrate the performance for removal of fly ash at indicated operating velocities, fixed bed heights, and bed temperatures; then the collecting mechanisms of particulates by fluidized-bed filter were studied. The size distribution of fly ash passing through the fluidized-bed filter was also analyzed. The results indicate that at higher operating velocities and fixed bed heights, the removal of fly ash is more efficient and inertial impaction is the main mechanism when the fluidized-bed is operated at room temperature (25 degrees C). While operating at higher temperatures (200 degrees C), efficiency of 93.2% to 99.4% can be achieved for submicron particles. It is supposed to be the diffusion mechanism that is responsible for collecting such small particles, and high temperature is a favorable condition because of diffusion.