Download presentation
Presentation is loading. Please wait.
1
Filtration Department of Chemical Engineering,
By Sidra Jabeen Department of Chemical Engineering, University of Engineering & Technology Lahore
2
Lecture includes: What is filtration? Understanding of the basic terms
How filtration is done? Types of filtration Rate of filtration Filter Media Filter Aid 4/23/2017
3
Filtration Removal of solid particles from a fluid by passing it through a septum on which the solids are deposited 4/23/2017
4
1. Solid Particles Concentration Valuability Solubility Size
Traces to High % Dissolved Desired Waste Undissolved Ultra filtration Micro filtration Nano Filtration 4/23/2017
5
2. Fluids A continuous substance which can Flow Liquid Gas 4/23/2017
6
3. Septum or Filtering Media
Membrane Filter Paper 4/23/2017
7
4. Solid Deposition In the form of cake on the septum Or Trapped inside the pores of the septum 4/23/2017
8
Example The solid remaining in the filter paper is called the residue.
The residue can be dried by spreading it out on the filter paper and allowing the liquid to evaporate. The liquid which has passed through the filter paper is called the filtrate. 4/23/2017
9
How filtration is done? Fluid flows through the filter medium by virtue of pressure difference across the medium. Through Feed Side Pump Blower Liquid height of column etc Through Product Side By generating Vacuum 4/23/2017
10
Types of filtration Two basic types of filtration are
Cake filtration Solid particles form a layer of solids on filtering media (called as cake). Deep or Depth bed filtration Solid particles are caught inside the pores of filtering media. 4/23/2017
11
1. Cake Filtration Solid particles are retained on septum as a layer of solids called as “cake” 4/23/2017
12
2. Deep Bed Filtration Further of two types Clarifying filtration
Cross flow filtration 4/23/2017
13
a. Clarifying Filtration
Solid particles are trapped inside the septum 4/23/2017
14
b. Cross flow Filtration
Some of the liquid passes through the septum leaving behind conc. solution 4/23/2017
15
4/23/2017
16
Factors affecting Rate of Filtration
Drop in pressure from the feed to the far side of septum Area of the filtering surface Viscosity of the solution Resistance of the filter cake 4/23/2017
17
Filter Media Common names Desired Properties Filter Paper Membrane
Screen Porous Solids Desired Properties Good Filtration Should not Plug Chemically Resistant Physically Strong Cheap 4/23/2017
18
Material of construction of filter media
Woven Materials (Cotton, Wool, Silk etc) Perforated Metal Sheeting Granular Materials (Sand, Asbestos etc) Porous Solid Felted-Fiber materials (Porous Paper) 4/23/2017
19
Filter Media Structure
Cloth Metal 4/23/2017
20
Filter Aids Filter aids are granular solids which are used in combination with filtration to enhance rate of filtration. For example, Diatomaceous silica, perlite, purified wood cellulose etc. Filter aids are used in two different ways: Added before filtration As a pre-coat 4/23/2017
21
Filter Aids Added before filtration
This increases the porosity of the cake and reduces resistance of the cake during filtration. As a pre-coat They can be used as a precoat before the slurry is filtered. This will prevent solids from plugging the filter medium and also give a clearer filtrate. Use of filter aids is usually limited to cases where the cake is discarded. 4/23/2017
22
Types of Filters 4/23/2017
23
Classification of Filters
Filters are classified on following three different basis: Mechanism The driving force Operation
24
On the basis of mechanism
Cake filters Clarifying filters Cross flow filters On the basis of driving force Pressure Filters Vacuum filters Centrifugal filters On the basis of operation Continuous filters Batch or discontinuous filters
25
Classification of filters
Pressure filters Pressure applied at feed side Vacuum filters Vacuum applied at product side Centrifugal separators Spinning the slurry to force separation Continuous filters Flow of fluid and discharge of solids (cake) is continuous or uninterrupted. Batch filters Flow of fluid is continuous but it has to be interrupted to permit discharging of the accumulated solids. 4/23/2017
26
Cake filters They can be pressure filters (filter press, shell & leaf filter) Or they can operate under vacuum (rotary drum filter) Or cake filtration can be carried in centrifugal filters (suspended batch centrifuges) Either type can be batch or continuous. 4/23/2017
27
1.Filter Press Pressure filter operate in batch mode
Sets of plates (circular or square) Plate faces covered by septum Slurry enters at one end Solids (cake) collect in chamber and liquid pass out ‘Jammed’ filter Wash liquid, air or steam used to remove residual liquid Press opened and cake removed Washing is time consuming and labor intensive 4/23/2017
28
Filter Press Pink : Plates Yellow : filter Cloth Blue : Filtrate
4/23/2017
29
Filter Press 4/23/2017
30
2. Shell and leaf filter Pressure filter operating in batch mode
Stack of leaves inside the closed tank Feed enters in the side of the tank Pass through leaves covered with filter Liquid leaves into discharge manifold Cake is removed by gravity force and vibration Cake is effectively removed and economize labor 4/23/2017
31
3. Shell and leaf filter 4/23/2017
32
Shell and leaf filter cake disposal
4/23/2017
33
3. Rotary Drum Filter Vacuum filter with continuous operation
Drum turns at 0.1 – 2 rpm in slurry trough Filter covers the face of the drum Rotary drum filter has four zones: Filtering zone Washing and drying zone Cake removal zone Dead zone Vacuum is applied in first two zones Permeate and washing liquid discharge into separate compartments Doctor blade is used in third zone 4/23/2017
34
Rotary Drum Filter 4/23/2017
35
Rotary Drum Filter 4/23/2017
36
Rotary Drum Filter 4/23/2017
37
Rotary Drum Filter 4/23/2017
38
4. Suspended Batch Centrifuge
Centrifugal filter operating in batch mode Perforated baskets 750 – 1200 mm in dia. and 18 – 30 inch deep Basket rotates at 750 – 1200 rpm Feed taken from inlet is centrifuged Clear liquid pass out leaving behind solid cake in basket Wash liquid sprayed to remove soluble solids and cake dried For cake removal, basket is turned at 30 – 50 rpm and cake is cut off with unloader knife 4/23/2017
39
Suspended Batch Centrifuge
4/23/2017
40
Clarifying Filtration
4/23/2017
41
Clarifying Filtration
Removal of the Small amounts of solids or liquids droplets from the fluids. Principle of Clarification Particles are trapped inside the filter media or on its surfaces Caught by the surface forces Reduce the active dia. of the channel 4/23/2017
42
Liquid Clarification: Cartridge Filter
Series of thin disks with close clearances in a vertical stack Disks carried on a vertical hollow shaft Liquid admitted under pressure Trapping of the solids between disks Liquid flows out through the casing Comb cleaner pass between the disks and drop solids to the bottom of casing 4/23/2017
43
Cartridge Filter 4/23/2017
44
4/23/2017
45
Gas Clarification For atmospheric dust – Pad filters
For process dusts – Bag Filters 4/23/2017
46
Pad Filter Before After Air passed through pads of filter media
Pad may be dry or coated with viscous oil For light duty – pads are disposable For heavy duty – reused by rinsing and recoating Before After 4/23/2017
47
Bag Filter or Bag House Contains one or more large bags of fabric material inside metal casing Dust laden gas enters the filter at the bottom Solid particles trap inside the bag and clean gas leave at the top Solids are discharged by shaking mechanism 4/23/2017
48
4/23/2017
49
Cross flow Filtration 4/23/2017
50
Definition Filtration in which flow of the suspension is parallel to the filtering media used to get concentrated slurry 4/23/2017
51
Cross flow filtration Operation
The feed is passed across the filter membrane at positive pressure relative to the permeate side. A proportion of the material which is smaller than the membrane pore size passes through the membrane as permeate or filtrate; everything else is retained on the feed side of the membrane as retentate. 4/23/2017
52
4/23/2017
53
Conventional Filtration
Difference b/w cross flow & Conventional filtration Cross Flow Filtration Flow of fluid is parallel to the surface Majority of the feed travels across the surface of the filter Process feed remains in the form of a mobile slurry, suitable for further processing It is possible to fractionate particles by size Conventional Filtration Flow of fluid is perpendicular to the surface Solids in the feed trap inside the filter or retain on the filter Process feed is transformed into solid cake & filtrate It is simply the separation of solids from liquids, no fractionation 4/23/2017
54
4/23/2017
55
Performance of cross flow filtration
Fouling of the membrane Permeate flux Percent rejection Back flushing Factors for optimizing permeate flux Trans-membrane pressure Shear rate 4/23/2017
56
Types of cross flow filtration
Reverse Osmosis Microfiltration Ultrafiltration Nanofiltration 4/23/2017
57
Reverse Osmosis The pressure driven transport of solvent from a solution through a membrane is known as reverse osmosis Applications Separating low-molecular-weight substances in solution Concentrating Cleaning wastewater Demineralization 4/23/2017
58
Points of discussion Osmosis Osmotic pressure Reveres Osmosis
4/23/2017
59
Micro filtration Used for the particles in the size range of μm. Applications Fermentation Biomass clarification and recovery 4/23/2017
60
Ultra filtration Used for the particles in the size range from 1μm down to μm. Applications used in the fractionation of milk as well as protein fractionation 4/23/2017
61
Nano filtration Used for the particles up to 1nm
Nanofiltration is the process with the characteristics b/w those of Ultrafiltration and reverse osmosis. Applications Pharmaceutical processing Water treatment 4/23/2017
Similar presentations
