5.3: FILTRATION NOOR MUHAMMAD SYAHRIN BIN YAHYA

Transcription

1 5.3: FILTRATION NOOR MUHAMMAD SYAHRIN BIN YAHYA

2 INTRODUCTION Filtration is the removal of solid particles from a fluid by passing the fluid through a filtering medium, or septum, on which the solids are deposited. Industrial filtration range from simple straining to highly complex separation. The fluid may be a liquid or gas; the valuable stream from the filter may be the fluid or the solids, or both. Sometimes it is neither, as when waste solids must be separated from waste liquid prior to disposal. In industrial filtration the solids content of the feed range from a trace to a very high percentage. Often the feed is modified in some way by pretreatment to increase the filtration rate, as by heating, recrystallizing, or adding a filter aid such as cellulose or diatomaceous earth. Most industrial filter are pressure filters, vacuum filter, or centrifugal separator.

3 INTRODUCTION They are also either continuous or discontinuous, depending on whether the discharge of filtered solids is steady or intermittent. Filter is divided into three main groups: Cake filters Clarifying filters Cross flow filter. Cake filters: separate relatively large amounts of solids as a cake of crystals or sludge. Often they include provision for washing the cake and for removing some of the liquid from solids before discharge. Clarifying filter: remove small amounts of solids to produce a clean gas or a sparkling clear liquid such as beverages. Cross flow filter: the feed suspension flows under pressure at fairly high velocity across the filter medium. A thin layer of the solids may form on the surface of the medium, but the high liquid velocity keeps the layer form building up. The filter medium is a ceramic, metal or polymer membrane with pores small enough to exclude most of the suspended particles.

4 DEFINITION The separation of solids from a suspension in a liquid by means of a porous medium or screen which retains the solids and allows the liquid to pass.

5 STEP INVOLVED IN FILTRATION 1. Draining the liquor. 2. Filtration 3. Filling with wash water 4. Washing 5. Draining the wash water 6. Opening, dumping and reassembling 7. Filling with slurry

6 PRINCIPLE OF FILTRATION

7 PRINCIPLE OF FILTRATION Since the filter medium is permeable only to the fluid, it retains the solid particles and permits only the fluid to pass through which is collected as the filtrate. The volume of filtrate collected per unit time (dv/dt) is termed as the rate of filtration. As the filtration proceeds, solid particle accumulate on the filter medium forming a packed bed of solids, called filter cake. As the thickness of the cake increases. 1. Resistance to flow of filtrate increases 2. Rate of filtration gradually decreases If rate is maintained to be constant then pressure difference driving force (- P) will increase. Therefore, a batch filter is operated either at constant pressure or at constant rate.

8 CONSTANT PRESSURE & RATE FILTRATION

9 CAKE FILTRATION Definitions: Cake filtration consists of passing a solid suspension (slurry) through a porous medium or septum (e.g., a woven wire). The solids in the slurry are retained on the surface of the medium where they build up, forming an increasing thicker cake. As more slurry is filtered the solids retained on the medium provide most of filtering action. In cake filtration the cake is the real filtering element.

10 CAKE FILTRATION As time goes by the thickness of the cake increases, as more solids are filtered. This results in a corresponding increase of the pressure resistance across the cake. If the cake is incompressible (i.e, it does not change its volume as pressure builds up) the pressure resistance increases proportionally to the cake thickness. However, since most cakes are compressible the pressure across the cake typically increases even faster than the cake build-up.

11 EXAMPLES OF CAKE FORMING FILTERS Filter presses Belt filters Vacuum filters: Rotary vacuum belt filters Rotary vacuum precoat filters Vacuum disk filters

12 FILTER PRESSES

13 BELT FILTERS

14 ROTARY VACUUM BELT FILTERS

15 ***NOTE Cake filtration is intrinsically a batch process. Hence, it can be expected that as filtration proceeds the cake will build up and the pressure drop across the cake will increase. Mathematical modelling of batch cake filtration is based on the determination of the rate of formation of the cake and the calculation of pressure drop at any given time. Continuous filtration is often modelled as a succession of batch processes carried out over infinitesimally small time intervals.

16 TYPE OF FILTER CAKE FILTER CLARIFYING FILTER TYPE OF FILTER CROSS FLOW ULTRA FILTER

17 CAKE FILTER A filter cake is formed by the substances that are retained on a filter. The filter cake grows in the course of filtration, becomes thicker as particulate matter is being retained. With increasing layer thickness the flow resistance of the filter cake increases. After certain time of use the filter cake has to be removed from the filter, e.g. by back flushing.

18 CLARIFYING FILTER Any filter, such as a sand filter or a cartridge filter, used to purify liquids with a low solid-liquid ratio; in some instances colour may be removed as well.

19 CROSS FLOW FILTERS Cross flow filters feed suspension flows under pressure at high velocity across filter medium. Thin layer of solids may form on surface, but high velocity keeps layer from building up. Medium is ceramic, metal, or polymer with pores small enough to exclude most of suspended particles. Some liquid passes through as clear filtrate, leaving more concentrated suspension behind.

20 FILTER MEDIA: When choosing a filter material we must consider cost, particle size, operating temperature, and chemical resistance. 1. PO (PONG) Polypropylene Felt This non-woven material is our popular workhorse. Polypropylene offers excellent chemical resistance. It s cost effectiveness makes it ideal for applications up to 200F. This felt material can come plain (untreated felt) or glazed (high heat applied to exterior surface fibers). 2. PMO Polypropylene Mesh Similar to nylon mono filament mesh, polypropylene mono filament mesh has better acid resistance than nylon and is more cost effective for temperatures up to 200F. 3. PEMF Polyester Microfiber Felt This material is grown from raw microscopic fibers. It s long life and ultra-fine micron rating make it possible to use bag filters for applications that once required expensive high maintenance cartridges. It has a higher melting point than polypropylene microfiber making it ideal for hot oil and other applications up to 325F. 4. NMO Nylon Mesh This monofilament mesh is a woven material in which each thread is a single filament. This material s strength enables it to be used in a variety of different applications.

21 FILTER MEDIA:

22 INDUSTRIAL FILTRATION EQUIPMENT 1. DISCONTINUOUS PRESSURE FILTERS: Apply large P across septum to give economically rapid filtration with viscous liquids or fine solids. Plate and Frame Filter Press Shell and Leaf Filters 2. CONTINUOUS VACUUM FILTER: Vacuum filters are simple and reliable machines and therefore have gained wide acceptance in the chemical, food and pharmaceutical industries. Rotary Drum filter Horizontal Belt filter

23 Plate and Frame Filter Press

24 Plate and Frame Filter Press

25 Shell and Leaf filter

26 Shell and Leaf filter

27 Rotary Drum filter

28 THE HORIZONTAL BED FILTER

29 THE HORIZONTAL BED FILTER

30 THE HORIZONTAL BED FILTER

31 THANK YOU NOOR MUHAMMAD SYAHRIN BIN YAHYA nmsby.yolasite.com