纤维过滤滤饼孔隙率计算机模拟

基于受限扩散模型,建立纤维介质表面粉尘颗粒沉积形成滤饼的模拟模型。粉尘颗粒在远离过滤介质的控制面上释放,假设对流扩散运动为颗粒输送和沉积的主要机理。定义Pe数为颗粒对流作用与扩散运动的比值,讨论不同Pe数对滤饼孔隙率的影响。对Pe数范围为0.25~1600进行模拟计算结果表明,Pe数对滤饼的孔隙率影响显著。当颗粒的扩散运动强于对流运动,颗粒沉积形成的滤饼为较为松散的结构,当Pe数较大时,颗粒沉积形成的滤饼为较为紧密的堆积结构。此外,考虑到实际过滤过程中粉尘颗粒大多为非等径粒子,也对多分散粒子对滤饼形成及孔隙率的影响作了分析。     

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。     

滤饼内过滤比阻分布存在极值问题的探讨

本文以文献压缩透过试验数据为基础,推导出过滤比阻极小值α_(z,min)和临界空隙率ε_(zc)的计算公式,讨论了不同ε_(zc)下α_z分布可能出现的情况。并指出一般情况下,过滤比阻α_z的幂定律近似是有效的;仅当临界空隙率ε_(xc)小于滤饼表面空隙率ε_1时,α_z的幂定律关系才无效,但这类物料至今未见报道。     

滤饼过滤过程的计算机模拟研究

利用自行设计的计算机模拟程序 ,对物料粒度、浆体浓度、过滤压差对过滤脱水的影响以及滤饼分层现象进行了计算机模拟 ,并通过实验进行了验证。结果表明 ,模拟结果虽然在数值上与实验结果有一定差距 ,但定性方面能够很好地与实验结果相吻合。     

空气过滤形成滤饼的模拟研究

提出了一个新的模型,用于预测空气过滤中捕集效率和滤饼层空隙率。模型中粒子的产生符合正态分布,其落点符合随机均匀分布。模型预测的捕集效率随粒径和孔径比的增大而增大,滤饼层空隙率随粒径和孔径比的增大而减小。粒子的分散度对滤饼结构的影响较小。     

滤饼过滤理论与实践:过去、现在和未来

本文综了当前滤饼过滤理论的发展过程,包括Ｒｕｔｈ＆Ｃａｒｍａｎ的早期工作。Ｔｉｌｅｒ－Ｓｈｉｒａｔｏ过滤方程以及日前一些行之有效的理论观点,着重强调了滤饼沉积过程中逐层分析的概念及相关的计算方法,同时对这些理论运用于实践中的可行性进行了评述。     

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。     

滤饼过滤过程的计算机模拟程序设计

详细介绍了滤饼过滤过程中各物理量的计算公式、计算机模拟程序的设计 ,为滤饼过滤过程的研究提供了一种新的研究方法     

气压过滤的成饼动力学及其滤饼的分形结构

用自制的实验室型气压过滤机并结合滤饼内部结构的测试,研究了气压过滤的成饼动力学及其滤饼结构的分形特征。结果表明,气压过滤条件下,虽然过滤压差较大,但成饼阶段仍遵循Darcy定律;气压过滤的滤饼结构为一分段Sierpinski分形,其分维数值介于1.775～1.885之间。     

离心过滤中滤饼含液量影响因素的研究

本文对离心过滤中影响滤饼含液量的主要因素进行分析。选择细粒级的五种物料，在三足式过滤离心机上做脱液实验，获得的脱水和动力学试验数据，经因次分析，计算机处理，得到实验条件下滤饼含液量Ｗｔ的准数方程：研究结果表明：影响滤饼含液量的因素，首先是物料的物理性质：固体密度ρｓ，颗粒表面积体积平均粒径ｄｓｖ和悬浮液粘度μｓｕｓｐ；其次是操作参数：转鼓角速度ω，脱液时间ｔ和滤饼厚度ｈ。实验条件：Ｆｒ＝１０４８～１５１０，ｄｓｖ＝１．２９～２４．８μｍ，μｓｕｓｐ＝１～１０ｍＰａ·ｓ     

Vibration-enhanced compaction of filter cakes and its influence on filter cake cracking

Filter cake cracking is a common problem in cake filtration that can be avoided by compacting the filter cake prior to air-blowing. Here, we present a new method for compaction by applying vibration in the form of oscillatory shear. The shrinking and cracking behavior of the model material is analyzed by combining laser displacement measurements and image analysis. Then, the compaction results are presented and discussed regarding the process time and energy consumption. Finally, we show how compaction by oscillatory shear influences the cracking behavior of the filter cake. Significant reduction in cracking could be achieved.     

Granular-bed filtration assisted by filter cake formation 3. Penetration of filter cakes by a monodisperse aerosol

For several types of granular solids (sands, silicon carbide and copper shot), penetrations have been measured for a monodisperse aerosol (1.1 μm Dow microspheres) passing through fly ash deposited upon horizontal surfaces of the solids. Fractional penetrations can run as low as 10⁻⁵. Pressure drop data for dust cake/granular medium combinations are also given. The data illustrate significance of dust autohesivitiy and dust/granular solid adhesivity for granular-bed filtration assisted by dust cake formation.     

Cake properties of nanocolloid evaluated by variable pressure filtration associated with reduction in cake surface area

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869–3877, 2014     

A new procedure for determining specific filter cake resistance from filtration data

A new procedure has been developed for the determination of specific filter cake resistance from experimental filtration data. Unlike the conventional procedure which treats constant-pressure filtration data through the t/V vs. V plot and yields a single value of the average specific cake resistance (α_av) from a given experiment, this new procedure allows the establishment of the relationship of α_av vs. the cake compressive stress (p_s) over a range of p_s values. Results from the new procedures were compared with those obtained from the procedure based on the t/V vs. V plot as well as those from compression-permeability (C-P) measurements. Discussions on the possible improvement of the new procedure are also presented.     

Filtration in coal liquefaction: preparation of filter aid from filter cake

In this study the preparation of filter aid from filter cake is considered. Two methods of preparation, carbonization at 550–600 °C and combustion at 800–1000 °C, are used and the optimum conditions determined. The performance of the products is assessed as both a precoat and body feed by comparison with a commercial grade of diatomite. It is shown that efficient filter aids, with performances comparable to that of diatomite, may be produced from filter cake.     

袋式除尘器滤饼固定化研究

为研究滤饼微观结构,对滤饼固定化方法进行了研究。首先介绍了传统的树脂包埋法,分析了该方法的优缺点。提出了一种新型的滤饼固定化方法——羧甲基纤维素钠(CMC)黏合法。经检测证明,CMC黏合法固定过程耗时短,方法简单,可真实反映滤饼结构。     

滤饼结构造影测试的研究

滤饼过滤是固液二相分离的基本形式,了解滤饼孔隙率及其变化是影响滤饼过滤的关键。文中在简单比较了扫描电镜(SEM)、核磁共振(MRI)、CT扫描等方法的基础上,采用了CT扫描技术。研究重点是针对文中所研究的物料,选择合适的样品预处理及图像数值计算方法。实验证明,采用经过改进的CT扫描测试,可获得视野较宽的清晰图像,并用于孔隙率计算,作为滤饼结构研究的有效工具。文中最后也提出了应进一步提高的努力方向。     

纤维素助滤剂的预敷过滤性能

对高黏度物料加入纤维素助滤剂的预敷过滤性能进行了研究,说明不同的预敷条件对预敷层的过滤性能会有很大影响。通过改变预敷压力和浓度,对纤维素滤饼层的过滤比阻、可压缩性系数和孔隙率进行了研究。实验表明,纤维素预敷层的比阻随压力增加而增加,随浓度增加而减小;孔隙率随压力增加而减小,随浓度增加而增加;可压缩性系数随浓度增加而增加。纤维素助滤剂为中等可压缩性物料,孔隙率大。研究结果可为高黏度物料用纤维素预敷过滤的工程应用提供参考。     

Modeling of the pressure drop across polydisperse packed beds in cake filtration

Filtration is the separation of solid–liquid mixtures. In this study, we assess the predictive power of Kozeny–Carman model for systems operated at low Reynolds numbers and relatively high pressure drops. We find substantial agreement between the K-C model and experiment only for systems that exhibit tight void size distribution. Dramatic disagreement is observed for particle beds that exhibit wide void size distributions. We propose a modified modeling approach, based on a bimodal void distribution, by introducing two quantities: the fraction of expanded voids and the ratio of void sizes. The simulation results are found to be much more similar to the experimental flow rates than those calculated using the K-C model. The modified model is deemed reliable at predicting the flow behavior, provided that an accurate representation of the void size distribution is available.