Filtration

Filtration (过滤)The separation of solids form a suspension in a liquid by means of a poroous medium or screen which retains the soilds and allows the liquid to pass is termed filtration.形成一个分离的固体悬浮在液体通过的多孔介质或屏幕的固体颗粒和保留允许液体通过被称为过滤。

In general,the pores of the medium will be larger than the particles which are to be removed,and the filter will work efficiently only after an initial deposit has been trapped in the medium.In the chemical laboratory, filtration is often carried out in a form of Buchner funnel ,and the liquid is sucked through the thin layer of particles using a source of vacuum:in even simpler eases the suspension is poured into a conical funnel fitted with a filter paper.一般来说,孔隙介质的颗粒将大于中移走,并将与过滤能工作的很有效率只有经过一初始存款已陷于媒介。

在化学实验室,进行过滤是经常在某种形式的Buchner漏斗,液体吸通过颗粒的薄层使用的一个来源:甚至在真空悬架系统是简单的简化了倒进一个锥形的漏斗配有一个滤纸。

In the industrial equivalent of such an operation, difficuities are involwed in the mechanical handling of much larger quantities of suspension and solids .A thicker layer of solids has to form and, in order to achieve a high rate of passage of liquid through the solidshigher pressures will be needed, and it will be necessary to provide a far greater area. A typical filtration operation shows the filter medium, its support and the layer of solids, or filter cake, which has already formed.The volumes of the suspensions to be handled will from the extremely large quantities involved in water purification and ore handling in the mining industry to relatively small quantities in the fine chemical industry it is the solids that are required and their physical size and properties are of paramount importance. Thus the main factors to be considered when selecting equipment and operating conditions are:在工业中也有类似的这种手术是involwed,贵州省在机械处理更大的数量的悬架和固体a的更浓的层固体要形成和计划,以实现高比率的通道的固体颗粒的液体通过将需要更高的压力,而这将会是必要的,以提供一个更大的区域。

一个典型的过滤操作显示过滤介质,其支持层的固体颗粒、或滤饼,已经形成了。

一卷卷的粒子处理将从极大量涉及饮用水净化和矿石处理采矿业中的相对少量的精细化工是固体,是必需的,并且他们的物理尺寸和性能是极为重要的。

因此时应考虑的主要因素,选择设备和操作条件是:a) The properties of the liquid, particularly its viscosity, density andcorrosive properties.b)The nature of the solids –its particle size and shape, sizedistribution,and packing characteristics.c)The concentration of solids in suspension.d)The quantity of material to be handled,and its value.e)Whether the valuable product is the solids, the fiuid, or both.f)Whether it is necessary to wash the filtered solids.g)Whether very slight contamination caused by contact of thesuspension or filtrate with the various components of the equipment is detrimental to the product.h)Whether the feed liquor may be heated.i)Whether and form of pretreatment would be helpful.一)性能的液体,特别是它的粘度、密度和腐蚀等性能。

b)的本质——它的固体颗粒大小和形状、大小分布、及包装的特点。

c)浓度的滞留固体颗粒的侵扰。

d)数量资料的处理方式,和它的价值。

e)是否有价值的产品是固体,fiuid,或两者兼而有之。

f)是否需要洗后的固体。

是否有很轻微的污染g)引起的暂停或滤液联系与不同的部件的设备是有害的产品。

部落)是否可能被喂白酒。

我)是否和形式的预处理可能是有用的。

Filtration is essentially a mechanical operation and is less demanding in energy than evaporation or drying where the high latent heat of the liquid, which is usually water, has to be provided. In the typical operation the cake geadually builds up on the medium and the resistance to flow progressively increases. During the initial period of flow, particles are deposited in the surface layers the cloth to form the true filtering mendium. This initial deposit may be formed from a special initial flow of precoat material. The most important factors on which the rate of filtration then depends will be: a) The drop in pressure from the feed to the far side of the filtermedium.b)The area of the filtering surface.c)The viscosity of the filtyate.d)The resistance of the filter cake.e)The resistance of the filter medium and initial layers of cake. The type of filtration described above is usually referred to as cakefiltration the proportion of solids in the suspension is large and most of the particles are collected in the filaer cake which can subsequently detached from the medium. Where the proportion of solids is very small, as for example in air or water filtration, the particles will often be considerably smaller than the pores of the filter medium and will penetrate a considerable depth before being captured; such a process is called deep bed filtration. In the next lesson the types of filtration equipment will be considered.。