关于过滤理论与滤饼可压缩性的探讨：———第一部分 表层过滤的特性和沉降的？

从料浆沉降和过滤成饼两个角度同时研究过滤速率和成饼速率以及滤饼的渗透率和可压缩性,提出了更为全面的滤饼比阻关系式。证明滤饼渗透率首先和料浆的浓度及沉降速度有关,因此笔料交的预处理及料浆的化学环境密切相关。     

粉尘沉积形成滤饼结构的分形研究

粉尘在过滤过程中,随过滤时间的增加,在过滤介质内部不断沉积形成滤饼,目前人们还主要从过滤的整体行为的角度去研究过滤问题,由于测试手段和研究方法的限制,对直接决定过滤行为的滤饼结构则研究很少。然而,要想深化对过滤机理的认识,揭示滤饼中粉尘颗粒之间的相互作用力与形成滤饼孔隙率的关系,了解滤饼中"尘滤尘"的机理,以提出提高粉尘捕集效率,减少过滤阻力,寻求强化清灰的措施,就必须对滤饼的内部结构进行研究。通过对滤饼结构进行分形研究,寻求滤饼结构分形维数与物料的比表面积及各操作条件的关系,探索滤饼孔隙率、滤饼厚度及粉尘颗粒直径、粒径分布与滤饼分形维数的关系。     

滤饼结构的分形研究

概括地介绍了分形理论在滤饼结构研究中的应用 ,并采用电子扫描与计算机图象处理技术 ,并根据分形理论对以平板陶瓷膜为过滤介质的十字流微滤稳态阶段的滤饼结构进行了理论及实验研究。     

关于过滤理论与滤饼可压缩性的探讨——第一部分表层过滤的特性和沉降的密切关系

从料浆沉降和过滤成饼两个角度同时研究过滤速率和成饼速率以及滤饼的渗透率和可压缩性,提出了更为全面的滤饼比阻关系式。证明滤饼渗透率首先和料浆的浓度及沉降速度有关,因此和料浆的预处理及料浆的化学环境密切相关。明确了滤饼都是可压缩的,其可压缩性分为两大类：滤饼中颗粒的位移、迁移和团聚颗粒的变形,由于它们的被压缩的机理不同,所以和有关因素的相关关系也不同,分析和论述了主要的关系。全文分为两大部分,相对独立。但本文不涉及滤饼的压榨     

关于过滤理论与滤饼可压缩性的探讨——第二部分 滤饼的可压缩性及比阻

从料浆沉降和过滤成饼两个角度同时研究过滤速率和成饼速率以及滤饼的渗透率和可压缩性,提出了更为全面的滤饼比阻关系式,证明滤饼渗透率首先和料浆的浓度及沉降速度有关,因此和料浆的预处理及料浆的化学环境密切相关。明确了滤饼都是可压缩的,其可压缩性分为两大类：滤饼中颗粒的位移、迁移和团聚颗粒的变形,由于它们的被压缩的机理不同,所以和有关因素的相关关系也不同,分析和论述了主要的关系。全文分为两大部分,相对独立     

气压压滤器的设计

气压压滤器是以惰性气体为压力源的过滤设备。本文讨论了气压压滤器的应用领域,针对不同的滤饼量,采取不同形式的结构,设计了不同的气压压滤器,并设计了一套气压压滤工艺流程。最后,对设计的气压压滤器进行了计算校核。     

生产无机盐的主要过程及设备——过滤(概述)

<正>过滤是一种分离悬浮在液体或气体中的固体颗粒的操作,现仅讨论悬浮液的过滤。悬浮液称为滤浆,滤浆中的固体颗粒称为滤渣,积聚在过滤介质上的滤渣称为滤饼,透过滤饼和过滤介质的澄清液体称为滤液。评价过滤操作优异的标志之一是过滤速度,影响过滤速度的因素主要有压力差、过滤面积、滤饼的阻力、滤液的黏度、过滤介质和最初滤饼层的     

过滤介质滤饼可剥落性研究

本文通过实验研究，考察了滤饼的颗粒性质、饱和度、厚度、操作压差、滤布性质等因素对这过滤介质卸饼性能的影响，提出了评定过滤介质滤饼可剥落性实验方法的建议。     

化工学报HUAGONG XUEBAO1995年第46卷总目次

题目作者期页二元水溶液渗透蒸发膜扩散过程的修正自由体积模型—·。……………………··祁喜旺陈洪纺1（1）气压过滤的成饼动力学及其滤饼的分形结构—…·徐新阳徐继润邓常烈罗茵康雁1（8）亲和膜吸咐分离人v-免疫球蛋白—…………………·,……··鲍时翔石国君姜伟苏志国1（15）粟酒裂殖酵母絮凝颗粒均匀悬浮体系酒精生成动力学—…………………………………………………··,·奏金来白凤武冯朴苏谢健李宁1（20）有限长圆柱状催化剂内扩散效率因子多态研究（I）研究方法的开发-””“‘“””””’”’““’””‘”’”’“““…     

滤饼孔隙率的模拟研究

采用计算机模拟方法,对滤饼中颗粒的凝聚机理进行简化,将所过滤的物料外形形态简化为球形颗粒,进行计算机程序设计,模拟物料在纤维过滤介质中过滤形成滤饼的过程,模拟得出滤饼结构,并进行孔隙率计算,在简化模型的基础上,分析滤饼孔隙率,滤饼厚度以及固体颗粒粒径的相关关系,探索滤饼结构研究的新方法及新途径。     

覆尘滤袋综合渗透率的分形求解

基于分形理论计算滤袋及滤饼构成的综合渗透率,描述其渗流特性。结合滤饼扫描电镜实验与图像处理技术分析滤饼孔隙结构;利用改进的毛细管模型近似模拟滤饼孔隙通道,根据流体动力学原理得到了滤饼渗透率的分形表达式,并由达西定律计算得覆尘滤袋综合渗透率,并用其对袋式除尘器流场压力分布进行数值模拟。结果表明,滤饼孔隙结构具有自相似特点。覆尘滤袋综合渗透率为(1.615~4.784)×10?12 m2,模拟所得的滤袋内外压差与实验结果的相对误差小于26%。覆尘滤袋综合渗透率计算方法合理,可较好地描述复合多孔介质的渗流特性。     

Experimental study of cake formation on heat treated and membrane coated needle felts in a pilot scale pulse jet bag filter using optical in-situ cake height measurement

Pulse-jet bag filters are frequently employed for particle removal from off gases. Separated solids form a layer on the permeable filter media called filter cake. The cake is responsible for increasing pressure drop. Therefore, the cake has to be detached at a predefined upper pressure drop limit or at predefined time intervals. Thus the process is intrinsically semi-continuous. The cake formation and cake detachment are interdependent and may influence the performance of the filter. Therefore, understanding formation and detachment of filter cake is important. In this regard, the filter media is the key component in the system. Needle felts are the most commonly used media in bag filters. Cake formation studies with heat treated and membrane coated needle felts in pilot scale pulse jet bag filter were carried out. The data is processed according to the procedures that were published already [Powder Technology, Volume 173, Issue 2, 19 April 2007, Pages 93-106]. Pressure drop evolution, cake height distribution evolution, cake patches area distribution and their characterization using fractal analysis on different needle felts are presented here. It is observed that concavity of pressure drop curve for membrane coated needle felt is principally caused by presence of inhomogeneous cake area load whereas it is inherent for heat treated media. Presence of residual cake enhances the concavity of pressure drop at the start of filtration cycle. Patchy cleaning is observed only when jet pulse pressure is too low and unable to provide the necessary force to detach the cake. The border line is very sharp. Based on experiments with limestone dust and three types of needle felts, for the jet pulse pressure above 4 bar and filtration velocity below 50 mm/s, cake is detached completely except a thin residual layer (100-200 μm). Uniformity and smoothness of residual cake depends on the surface characteristics of the filter media. Cake height distribution of residual cake and newly formed cake during filtration prevails. The patch size analysis and fractal analysis reveal that residual cake grow in size (latterly) following regeneration initially on the base with edges smearing out, however, the cake heights are not leveled off. Fractal dimension of cake patches boundary falls in the range of 1-1.4 and depends on vertical position as well as time of filtration. Cake height measurements with Polyimide (PI) needle felts were hampered on account of its photosensitive nature.     

Optical in-situ measurement of filter cake height during bag filter plant operation

A pilot scale jet pulsed bag filter test facility is operated at conditions similar to those of the industrial bag filters. The facility is equipped with a stereo vision based optical system for in-situ cake height distribution measurements on the bag filter surface. Experimental data are presented and data evaluation procedures are discussed to elaborate the features of the measuring system.The results show that the cake height distribution becomes narrower towards the end of filtration cycles. A steep pressure drop rise is observed at the start of a filtration cycle in the absence of re-attachment and a non-uniform bag cleaning, which may be attributed to different cake properties. The specific cake resistance remains constant over the linear part of the pressure drop curve indicating a non-compressible cake formation.The analysis of residual cake patches shows a large number of small sized cake patches and a few large sized cake patches on the filter surface. The cake patch size increases with the cake formation. The fractal analysis of patches boundary indicates preferential cake formation at the boundary of the residual cake patches shortly after regeneration.     

Flow Resistance in Filter Cakes Due to Air

Abstract

The objective of this work is to show that air bubbles can adversely effect the performance of pressure filtrations. The effect of air on liquid flow resistance is measured in a well-characterized filter cake of Lucite particles. Air is introduced into the cake by allowing air bubbles to become entrained with the particles in the slurry at the start of filtration. Filtration with entrained air bubbles is compared to filtration without air bubbles. Experimental measurements show a significant increase in flow resistance due to the presence of air in a pressurized cake filtration. The presence of air bubbles in the filter cake can result in misinterpretation of experimental data. This in turn can increase operating and experimental testing costs and complicate efforts to predict filtration performance.     

Statistical evaluation of hyperbaric filtration for fine coal dewatering

A statistical design of parametric study of pressure filtration for fine coal dewatering is presented. The effects of five major parameters of the dewatering, i.e. applied pressure, filtration time, cake thickness, solids concentration and slurry pH, on cake moisture reduction and air consumption were investigated. The study was conducted starting with two level factorial experiments to identify the most significant parameters, and concluding with response surface methodologies to establish an optimum operating condition for the dewatering of fine coal. It was observed that applied pressure, cake thickness and filtration time were identified to be the key operating variables for reduction of filter cake moisture as well as air consumption. With the key parameters, an optimum condition for the dewatering was determined to be an applied pressure of 93 psi with a cake thickness of 2.5 cm and a filtration time of 4.8 minutes for the laboratory filtration system. At these optimum conditions the filter cake containing about 22 percent moisture by weight and consuming air by 4.1 m³/(m²·min·kg) on dry solid basis was obtained.     

热压过滤诸影响因素的研究

设计了一套实验室型热气体压滤机,在此设备上进行了热压过滤实验,研究了一些操作因素对浮选精煤过滤效果的影响。结果表明：在热压过滤条件下,可以提高过滤速度,并有效地降低滤饼水分,浆体浓度、气体温度、过滤压差和吹气时间都对过滤有较大影响。     

Performance of fibrous filters during nanoparticle cake formation

Fibrous filters are highly efficient in removing micrometer particles, but their performance in the nanometer particle range is still little known. The aim of this study was to evaluate pressure drop and collection efficiency during nanoparticles cake formation using commercial fibrous filters. The filter media used were High Efficiency Particulate Air (HEPA) and polyester filters. The aerosols were generated by a commercial inhaler using a 5 g/L solution of NaCl and the particles produced were in the size range from 6 to 800 nm, with a peak at around 40 nm. A superficial velocity (v_s) of 0.06 m/s was employed. During the filtration, the maximum pressure drop established was ?P ₌ ?P_f +980Pa, where ?P_f is the initial pressure drop of the filter. The collection efficiency was determined for a clean filter and for intermediate pressure drops. The filtration curves obtained showed that the HEPA filter provided greater surface filtration, compared to the polyester filter. Comparison of the collection efficiencies for clean filters revealed that the HEPA filter was highly efficient, even in the absence of cake, while the polyester filter showed initial collection efficiencies of between 20 and 40% for particles in the size range from 100 nm to 1000 nm. However, after formation of the filter cake, the collection efficiencies of both filters were almost 100% during the final stage of filtration. This shows that the fibrous filter can be applied in several industrial processes with highly efficient nanoparticle separation, after the formation of a thin layer cake filtration.     

Comparison of different scraper designs for crossflow filtration with rotating discs and cake limitation by scrapers

Results from filtration experiments comparing the filter cake formation of different scraper designs during multiple-pass operation of the continuous pressure filter at laboratory scale are to be presented. The main interest in this investigation was to clarify the influence of different scraper designs on the filter cake growth depending on the rotation speed of the filter discs. The influence of different scraper designs on flow conditions between the filter discs and the action of the scrapers was also examined. The results of the filtration experiments showed, that the formation of the filter cake essentially depends on the rotation speed of the filter discs. The main mechanism during the formation of the filter cake of finely dispersed solids is the effect of cake thickness limitation by turbulence eddies. The dominating mechanism during the formation of the filter cake of solids with a wide spectrum will be the effect of particle segregation. In experimental studies the comparison of three different scraper designs (straight and curved scraper with different scraper profiles) was done in order to investigate the influence of the scraper shape to the formation of the filter cake at different rotation speeds and to achieve a basis for scraper design optimization. Summing up, a scraper profile with increased overflow velocities (e.g. the ‘plough 120° scraper’-profile) in a curved form (in order to improve the normal flow velocity at the inside part of the filter discs) would improve the filtration behaviour compared to the straight, flat scraper most efficiently.     

The Effect of Particle Sedimentation on Gravity Filtration

ABSTRACT

Simulation of cake formation of mono-sized and dual-sized particles under gravitational sedimentation and filtration is presented. The dynamic analysis proposed by Lu and Hwang in 1993 is applied to examine the local cake properties formed under a falling head by considering the hindered settling effect of particles in the slurry and the variation of the pressure drop across the filter septum. Results of this study show that, at a given position in a cake, the solid compressive pressure reaches a maximum value and then decreases for a gravity filtration due to the decrease in the driving head. A cake constructed with dual-sized particles has a more compact structure than does one with mono-sized particles, and larger particles will form looser packing than will smaller ones for mono-sized particles. A dual-dispersed suspension with a lower fraction of large particles will result in the lowest cake porosity and the highest specific filtration resistance of cake. Comparison of the porosity distribution in filter cake formed by means of gravity filtration and constant head filtration shows that the porosity near the filter septum of gravity filtration has a convex behavior while that of constant head filtration has a tendency toward concavity. This discrepancy is mainly due to the change in the driving head during the filtration process. Both theoretical and experimental results show that the uniformity of particle size distributions in the filter cake will be much better when the relative settling velocity between large and fine particles is reduced.