《过滤英汉互译.doc》由会员分享，可在线阅读，更多相关《过滤英汉互译.doc（5页珍藏版）》请在三一办公上搜索。
1、FiltrationDefinetionThe term filtration has different meaning or connotations to various people. Outside the water works profession, even in other technical disciplines, filtration is commonly thought of as a mechanical straining process. It may also have this same basic meaning in water works pract
2、ice as applied to the passage of water through a very thin layer of porous material deposited by flow on a support septum. This type of alter has a few rather specialized applications to water treatment as described later. However, most frequently in water works parlance, filtration refers to the us
3、e of a relatively deep(1.5 to 3 ft) granular bed to remove impurities from water. This general type of filter has a wide range of applications. In contrast to mechanical strainers which remove only part of the coarse suspended solids, the newest types of filters used in water purification remove all
4、 suspend solids, including virtually all colloidal particles. Over the years the meaning of the term filtration as used by the water works industry has changed as improved filters have been developed and as the nature of the physical and chemical processes involved in filtration have become better u
5、nderstood. In an effort to distinguish recent new and improved filters from older conventional types, the term “separation bed” has sometimes been applied to mixed media alters which incorporate: (1)coarse-to-fine in-depth filtration,(2)the application to the filter influent of a polymer, alum, or a
6、ctivated silica as a filter aid,(3)continuous monitoring of filter effluent turbidity, and(4)pilot filter control of coagulant dosage. However, separation beds are still referred to.by many as ”filters” and the important distinctions in functions and efficiency are often overlooked or not understood
7、.Water filtration can be further defined as a physical-chemical process for separating suspended and colloidal impurities from water by passage through a bed of granular material. Water fills the pores of the filter medium, and the impurities are absorbed on the surface of the grains or trapped in t
8、he openings. In nature, filtration is an active and important process in the purification of underground waters, and in water purification plants, it is an indispensable unit process.Filter Types There are several ways to classify filters. They can be described according to the direction of though t
9、he bed, that is, downflow, upflow, radial flow, horizontal flow, fine-to-coarse, or coarse-to-fine. They may be classed according to the type of filter media used such as sand, coal(or anthracite),coal-sand, multilayered, mixed-media, or diatomaceous earth, Filters are also classed by flow rate. Slo
10、w sand filters operate at rates of 0.05 to 0.13gpm/ft2. Another flow characteristic of filters is pressure or gravity flow. Gravity filter units are usually built with open top and constructed of concrete or steel while pressure filters are ordinarily fabricated from steel in form of a cylindrical t
11、ank. Available head for gravity flow usually is limited to about 8 to 12ft, while it may be as high as 150 psi for pressure filters. Because pressure filters have a closed top, it is not possible to routinely maintain a visual condition of the filter media. Further, it is possible to violently distu
12、rb the media in a pressure filter by sudden changes in pressure. These two factors have in the past tended to limit municipal application of pressure filters to treatment of relatively unpolluted waters such as the removal of hardness, iron, or manganese from well waters of good bacterial quality. T
13、he susceptibility to bed upset and the inability to see the surface of the media in pressure filter have been compensated for to some extent at least by the use of quick-opening manholes and particularly by the recent development and application of recording turbidimeters for continuous monitoring o
14、f the filter effluent turbidity. The introduction of a 3 in layer of coarse(1mm)high density(specific gravity 4.2)garnet or ilmenite between the fine media and the gravel supporting bed has virtually eliminated the problem of gravel upsets and another of the concerns about the use of pressure filter
15、s for production of potable water.Rapid or high rate alters operate at about 30 times the rate of slow filters, so they must be cleaned about 30 times as often. A common method for cleaning slow sand filters is to scrape a thin layer of media from the surface of the bed, wash it, and return it to th
16、e bed. Rapid filters are washed in place by reversing the flow through the media to expand and scour the media. This hydraulic leaning process can be supplemented in various ways as necessary such as water jet agitation of the expanded media, mechanical stirring by rakes, or by injecting air into th
17、e bed before or during backwashing. With the scraping method used to clean slow sand filters, it was advantageous to collect as much of the foreign material as possible at the top surface of the bed. This favored the use of a fine-to-coarse filter medium. With modern hydraulic backwashing supplement
18、ed by water or air jet agitation, it is possible to thoroughly clean granular beds at all depths, making it feasible to tailor the graduation of the fine media(coarse-to-fine)for optimizing the filter cycle rather than the cleaning cycle of filter operation. 待添加的隐藏文字内容3过滤定义过滤这个专业术语不同的人有不同的理解。水处理以外的其
19、他技术领域，过滤普遍被认为是一种简单的机械过程。在水处理过程中，如果只是使水流通过架起的过滤层将水中杂质截流在多孔介质薄层上，这样的滤池也具有同样的基本概念。专门应用于水处理方面的改型滤池有不少，后文将详细叙述。然而，在水处理的常用术语中，过滤就是利用相对较厚的粒床（1.5到3英尺）出去水中杂质。这种普通类型的滤池已得到广泛的应用，与能除去水中部分粗大悬浮固体的机械过滤相比，应用于水体净化的新型的滤池的发展革新以及对过滤过程中物理化学作用的进一步认识，应用于水处理工业中的过滤一词的含义也在变化。为了把近期改进的过滤方式与老式的传统方式区别开来，有时用“分离床”表示综合一下四种功能的过滤形式，（
20、1）在深度上从粗到细的过滤，（2）进水中加了聚合物、矾、活化硅酸等助滤剂的过滤，（3）可连续监测滤后水的浊度，（4）由此控制混凝剂用量。然而，分离床仍然被很多人看做是滤池，人们经常忽视或者不知道两者功能和效率方面的显著差异。过滤可以进一步的定义为当水流通过颗粒物质层时，将水中悬浮的或胶状的杂质分离的物理化学过程。当水流充满滤料的细孔时，水中的杂质就被吸附到颗粒的表面或被孔口截留下来。实际上，在地下水处理过程中，过滤是一个有效而又重要的过程，因此，在水处理厂过滤是一个不可或缺的单元。滤池类型滤池的分类有几种不同的方式。根据水流流经滤层的方向，可以将滤池分为降流式、升流式、辐流式、平流式、细粗式、
21、粗细式；根据所用滤料的不同，滤池可分为砂型、煤（或无烟煤）型、煤砂型、多层滤料型、混合型及硅藻土型等。滤池也可以按滤速分类，慢速砂滤池的运行滤速为0.050.13加仑/平方英尺，快速砂滤池的运行滤速为12加仑/平方英尺，高速砂滤池的运行滤速为315加仑/平方英尺.滤池也可按水流特点分为压力流或重力流滤池。重力流滤池一般敞口修建，通常是混凝土或钢结构；压力流滤池往往建成圆柱形的钢罐。重力流滤池的可利用水头通常不会超过8到12英尺，而压力流滤池的可用水头可能高达150磅/平方英寸。因为压力流滤池的顶部是封闭的，所以要想在可视条件下对滤料进行日常维护是不可能的。另外，压力滤池内的滤层可能因为压力的突
22、变而发生剧烈的扰动。在过去的一段时间里，在处理一些相对无污染水的市政工程中，正是这两个因素使其应用受到限制，例如从水质条件好的井水中除去硬度、铁或锰。尽管压力滤池存在滤床易受扰动及不能观查滤料表面的特点，但由于快开检查井的运用，尤其是近年来浊度计在连续监测滤池出水浊度方面的应用和发展，使其缺点得到了一定程度的弥补。在细滤料和卵石承托层之间增设一层3英寸（1mm）的高密度（密度4.2）石榴石和卵石承托层之间增设一层3英寸(1mm)的高密度（密度4.2）石榴石或钛铁矿技术的引入，实质上已经解决了卵石扰动的难题，现在人们所关注的是另一个问题，即压力滤池在饮用水净化方面的问题。 快速及高速滤池的滤速大
23、约是慢滤池的30倍，所以他们的清洗频率也是慢滤池的30倍左右。慢滤池的常规清洗方法是从滤床表面刮掉很浅一层滤料来清洗，清洗干净后再放回原处。快滤池是适当地使水流反向通过滤料层使滤层平膨胀和擦洗来清洗。如果必要的话，当需要时这种水力冲洗过程可以通过很多种途径进行补充，比如在反冲洗之前或之中进行水射搅拌、机械搅拌或者在滤层中注射空气等方法使滤层膨胀。慢滤池采用刮掉上层滤料清洗的方式有利于尽可能多地手机停留在滤层表面的滤后物质。这比较适合于滤料从细到粗的滤池。现代水力反冲洗技术是以气和水喷射搅动作为补充的，它的应用使彻底清洗滤层的每一个深度成为可能，这让我们在滤池运行时可以通过选择细滤料的级配（粗到细）来优化滤池过滤周期而不用担心滤池的清洗周期。
