液力过滤与液力压密脱水的理论(Ⅱ)

将滤室固定不变的板框或箱式压滤机的操作过程分成滤饼过滤阶段和液力压密脱水阶段两个过程来研究。在滤饼过滤阶段 ,应用表面过滤机理 ,采用传统的鲁思过滤基本方程和平均过滤比阻的理论进行研究。在液力压密脱水阶段 ,应用达西定律建立了液力压密基本微分方程 ,根据研究得出滤饼渗透系数与孔隙率在压密脱水阶段的线性取代关系的结论 ;滤室固定的限制条件和物料平衡条件 ,推导出液力压密的脱水方程式。分析了影响液力压密脱水的时间因素和液力压密速率的各操作参数。建立了完整的液力过滤和压密脱水理论 ,为自动压滤机的设计提供了理论指导     

过滤过程的计算

<正> 多种压滤机的滤室容积都是固定的,这类压滤机的操作一般分为前期的过滤阶段和后期的压密阶段。过滤阶段,滤饼各处的空隙率是不同的,越靠近滤布,滤饼空隙率越小,滤饼表面空隙率最大。过滤阶段终了,如果继续向滤室压送悬浮液,则滤饼平均空隙率降低,湿含量减少,这就是压密阶段。     

内嵌式空间格架滤板

本文简述了过滤基本理论，分析了条状支承滤板的过滤特性，根据过滤基本方程式提出了内在式空间格架滤板的新结构，还从上部进料与中部进料分析了对滤饼的影响，以及增加空气或蒸汽脱水过程，降低滤饼含湿率的应用。     

科技动态

高压膜压滤机　　据Ｆｉｌｔｒａｔｉｏｎ＆Ｓｅｐａｒａｔｉｏｎ (英 ) 2 0 0 1,38(5 ) :14报道 ,德国Ｎｅｔｚｓｃｈ过滤有限公司研制的膜压滤机能在高压下运行 ,以产生更干燥的滤饼。该压滤机的主要特征是膜充气压达 3ＭＰａ。在循环过滤期间 ,通过调节泥浆密度和流量来自动控制泵的吸入量。当压出室被充满并自动关闭泥浆泵后 ,膜开始充气 ,这时处理器开始工作。对于如高岭土之类的物料 ,该高压膜压滤机与箱式压滤机一样以高达 6ＭＰａ压力进行脱水 ,剩余含水率约为 2 6 %。这意味着当需要下一个干燥过程时 ,节省的能量是可观的。膜滤板…     

厢式压滤机滤板受力数值模拟及滤室边长优化设计

采用Ansys软件对厢式压滤机滤板受力和挠度形变进行数值模拟,着重分析凸台支柱数量的影响。基于变分法滤板挠度计算找出滤室边长尺寸与滤板设计厚度的关系,建立厢式压滤机滤板总体积、滤板组总长度与滤室边长的函数关系,以此对滤板结构进行优化设计。经优化后的滤板与1250型滤板相比,污泥脱水的工作效率得到明显提高——在整机滤室容积不变的情况下,虽滤板耗材增加了7.51%,但过滤面积增加了近50%,继而在泥饼达到同等含水率时压滤时间缩短了36.9%。     

Kotobuki旋转式压滤机——一种连续、自动运行的过滤、洗涤设备

<正>旋转式压滤机是一种动态过滤设备,由捷克斯洛伐克国立有机化合成研究所于1964年首先发明。日本KotobuKi工程和机械公司自1972年以来对该设备进行研究、开发,并以其独到之处在日本国内享有较高的声誉。 KotobuKi旋转式压滤机的结构如图1所示。滤板与搅拌叶轮交替设置,形成多级滤室。滤板与搅拌叶轮间有窄小的缝隙,其尺寸决定了薄层滤饼的厚度。滤板上刻有让滤液流通的沟槽,两侧复盖着过滤介     

膜压式自动板框压滤机最佳操作条件的计算

膜压式自动板框压滤机问世以后,由于提高了滤饼脱水率,其成本大大低于加热干燥脱水的方法,因而在化工、冶金、环保等行业得到广泛应用。但是,国内大多数使用单位缺乏对该设备操作过程最佳条件的研究,致使设备未能达到较为理想的生产能力和经济效果。本文根据压榨过滤理论,试图通过数学模拟的方法对膜压式自动板框压滤机的最佳操作条件,特别是对过滤压力和压榨压力的选择作一些探讨,为生产使用单位提供一套生产操作优化计算方法。这种方法已在某化工厂15m~2BAJI自动板框压滤机压滤KCl盐泥中得到初步验证。     

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。     

“四合一系统”对苄达赖氨酸、醛糖还原酶抑制剂干燥工艺的选定

“四合一系统”应用中100/1200压滤机选用KD55滤板,入料压力为0.7～0.8 MPa;压榨压力为0.8 MPa;穿流吹饼压力为0.75 MPa,穿流吹饼时间为5 min。通过2个月的连续批次试验,过滤面积相同时,采用大深度的腔室可以提高设备产能,并且滤饼含水率无明显差异。采用KD55滤板的压滤机,比采用KD50、KD40滤板的压滤机效能要高。     

磷酸铁锂净化压滤机的设计与应用浅析

针对磷酸铁锂悬浮液的高氯离子、强腐蚀性、细粒度等物料特点,为解决磷酸铁锂滤饼洗涤与净化过滤难题,提出一种新型重防腐隔膜压滤机。其是在传统隔膜压滤机基础上,对隔膜滤板、过滤板等零部件进行优化改进,实现进一步降低滤饼水分、改善滤饼洗涤效果和延长滤板使用寿命的目的;并对压滤机进行重防腐处理,使其满足在高氯离子、极强腐蚀性等恶劣工况下正常使用要求;增加滤布快速清洗、振动辅助卸料等装置,有效提高隔膜压滤机工作效率。     

A Mean Phi Model for Pressure Filtration of Fine and Colloidal Suspensions

A working model for engineering analysis of pressure filtration is presented. Based on the filtration characteristics of fine and colloidal suspensions, the process was divided into two stages. A time‐invariant spatially uniform volume fraction of solids approximation is invoked in the growing filter cake stage (stage 1). A time‐dependent spatially uniform volume fraction of solids assumption is made in the cake consolidation stage (stage 2). The two models, named collectively as Mean Phi (M‐P) model, have a common physical basis, seamless continuity between the stages and internal consistency. The M‐P model has only three parameters: terminal or equilibrium volume fraction of solids in the filter cake that is related to its compressive yield stress, critical volume fraction of solids, which joins stage 1 and stage 2, and a permeability factor, which is common to stages 1 and 2. The model is validated with a large number of colloidal suspensions filtered under highly diverse physical‐chemical process conditions. A Pareto profile is identified that relates the timescale of filtration and the extent of dewatering achieved, the two most important performance indices of the process.     

Data Analysis and Modeling of Constant Pressure Batch Dewatering of Fine Particle Suspensions

The problems of data analysis and modeling of experimental constant pressure batch dewatering of materials forming compressible cakes are considered. Dewatering in these materials is typically completed in two stages, viz. cake formation and cake consolidation. A data representation method especially useful for determining the transition point between the filtration and consolidation stages, as well as for comparing accuracy of model predictions, is illustrated. It is shown that dewatering occurs via one of three qualitatively different pathways. A simplified model for engineering analysis of the process is presented. A time-invariant spatially uniform volume fraction of solids approximation is invoked in the cake formation stage. A time-dependent spatially uniform volume fraction of solids assumption is made in the cake consolidation stage. The two models contain four model parameters and have a common physical basis in Darcy's law. Interrelationships between key process parameters are determined and employed to predict the temporal evolution of dewatering in the cake consolidation stage as well as the end point of dewatering.     

Avoiding filter cake cracking: Influence of consolidation on desaturation characteristics

In cake filtration processes with an air-blowing step, cracking is an undesirable phenomenon as it leads to deterioration of the filtration process by highly increasing gas throughput. This leads to higher residual moisture if the pressure difference cannot be maintained and an increase in overall cost. Crack formation can be avoided by compacting the filter cake before desaturation. While this action will make the separation process applicable by highly reducing gas consumption, there are also potential negative effects. Compaction increases filter cake resistance and might therefore slow down desaturation kinetics. Therefore, the authors investigated how the filter cake characteristics governing desaturation change from the nonconsolidated to the consolidated state of the filter cake and compared these findings to the actual dewatering kinetics. The results showed that for the case where cracking could be oppressed, dewatering kinetics of the consolidated cake are actually faster than for the nonconsolidated cake, despite higher resistance of the consolidated cake. Thus, compaction is an appropriate action when dealing with filter cake cracking.     

Models of rotary vacuum drum and disc filters for flocculated suspensions

Models for rotary drum and disc filtration of compressible suspensions are developed using one‐dimensional compressional rheology theory. The models account for cake formation while the drum or disc is submerged in the feed slurry, saturated cake consolidation upon surfacing due to capillary pressure, and cake desaturation. Desaturation does not occur for vacuum pressures below a critical value given by the material properties, or is incomplete if the formation and consolidation angles are too large. The disc filter model is formulated by applying the drum filter solutions to concentric annuli. The effect of different operating parameters such as submerged depth, rotational rate, slurry concentration, and vacuum pressure are investigated. The throughput varies linearly or quadratically with the drum or disc radius respectively, proportionally with the square‐root of the angular rotational speed and linearly with the submerged angle. The angles for cake consolidation and desaturation are independent of the rotational rate. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Prediction of the air consumption when dewatering a filter cake obtained by pressure filtration

In this communication, we report some data for the dewatering of a coal flotation concentrate in which very fine particles occur Dewatering is carried out by pressure filtration (up to 6 bar) followed by blowing to partially dry the cake (the filtration and dewatering phase respectively). For the systems studied, a reasonable prediction of the air consumption in either a lab filter, or a one-element test filter, or a full-scale continuous filter is possible, based on measurement of the liquid permeability for saturated flow in a lab filter cake. Together with scaling-up characteristics of the filtration step (not reported here), this gives the possibility of a reliable prediction of the required size and energy consumption of a large-scale continuous-pressure filter based on bench-scale test data.     

Creep effects in activated sludge filter cakes

Constant-pressure and stepped-pressure filtrations have been used to study the creep behaviour of filter cakes formed of activated sludge, anatase, or poly(styrene-co-acrylic acid) particles, respectively. No creep is observed in the case of the anatase filter cake, whereas the poly(styrene-co-acrylic acid) and activated sludge filter cakes exhibit pronounced creep behaviour. The consolidation stage for the poly(styrene-co-acrylic acid) filter cake can be divided into a primary consolidation stage controlled by hydrodynamic effects and a secondary consolidation stage controlled by creep effects. Up to 70% of the consolidation stage was secondary consolidation. Furthermore, the retardation time due to creep deformation was found to be much longer than the filtration time, which suggests that creep does not influence the filtration stage. The creep behaviour observed in activated sludge is pronounced, however no clear transition between primary and secondary consolidation was found. The retardation time is of the same magnitude as the filtration time. This suggests that activated sludge filtration is strongly influenced by creep, and may explain the difficulties in modelling activated sludge filtration and dewatering.     

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.     

Numerical modelling of fixed-cavity plate-and-frame filtration: Formulation, validation and optimisation

A model of fixed-cavity plate-and-frame filter presses is developed based on the theoretical framework developed by Buscall and White (1987. The consolidation of concentrated suspensions. Part 1. The theory of sedimentation. Journal of the Chemical Society. Faraday Transactions. I, Physical Chemistry in Condensed Phases 83, 873-891) and the piston-driven filtration model of Landman et al. (1991. Dewatering of flocculated suspensions by pressure filtration. Physics of Fluids. A, Fluid Dynamics 3(6), 1495-1509). The model properly accounts for compression of the suspension network structure within a filter cake in one dimension over a fixed cavity and allows for the effect of membrane resistance and ramping pressures. The model is validated by comparing on-site measurements of actual process performance at two water treatment plants with model predictions based on fundamental material properties of the feed slurries, the operating conditions and the press dimensions. The material properties are measured using laboratory based filtration tests. The model is then used to investigate the optimisation of press throughput and cake solids for a ferric water treatment slurry.     

Scale-up of steam pressure filtration

The characteristic of steam pressure filtration is the distinctive and even dewatering front. First, the interest has been focused on the main dewatering mechanism of steam pressure filtration. The question was whether the even and sharply distinctive dewatering front remains stable when the filtration face is scaled up by the factor 50. The experimental studies were carried through on a 3.75 m² disc filter which was modified for steam pressure filtration. A temperature sensor was installed in the rotating disc of the filter. The temperature at the filter cloth, opposite to the steam atmosphere is measured. The steam break through which determines the end of the mechanical displacement of the filtrate can be detected. The duration until the steam breaks through the filter cake in pilot scale is compared to the duration measured in lab scale. A simple calculation is presented which computes approximately the steam break through. The calculated steam breakthrough is also compared to the experimental data. The degree of moisture reached using the pilot scale steam filter is compared to conventional pressure filtration on the same pilot filter and data measured in lab scale.