Filtration By Sidra Jabeen Department of Chemical Engineering

Filtration By Sidra Jabeen Department of Chemical Engineering, University of Engineering & Technology Lahore

Lecture includes: What is filtration? Understanding of the basic terms How filtration is done? Types of filtration Rate of filtration Filter Media Filter Aid 2 11/9/2020

Filtration Removal of solid particles from a fluid by passing it through a septum on which the solids are deposited 3 11/9/2020

1. Solid Particles Solubility Dissolved Concentration Size Traces to High % Valuability Desired Waste Undissolved Micro filtration 4 Nano Filtration Ultra filtration 11/9/2020

2. Fluids A continuous substance which can Flow Gas 5 Liquid 11/9/2020

3. Septum or Filtering Media Filter Paper 6 Membrane 11/9/2020

4. Solid Deposition In the form of cake on the septum Or Trapped inside the pores of the septum 7 11/9/2020

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. 8 11/9/2020

How filtration is done? Fluid flows through the filter medium by virtue of pressure difference across the medium. Through Feed Side v Pump v Blower v Liquid height of column etc Through Product Side v. By generating Vacuum 9 11/9/2020

Types of filtration Two basic types of filtration are 1. Cake filtration Solid particles form a layer of solids on filtering media (called as cake). 2. Deep or Depth bed filtration Solid particles are caught inside the pores of filtering media. 10 11/9/2020

1. Cake Filtration Solid particles are retained on septum as a layer of solids called as “cake” 11 11/9/2020

2. Deep Bed Filtration Further of two types a) Clarifying filtration b) Cross flow filtration 12 11/9/2020

a. Clarifying Filtration Solid particles are trapped inside the septum 13 11/9/2020

b. Cross flow Filtration Some of the liquid passes through the septum leaving behind conc. solution 14 11/9/2020

15 11/9/2020

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 16 11/9/2020

Filter Media Common names ØFilter Paper ØMembrane ØScreen ØPorous Solids Desired Properties ØGood Filtration ØShould not Plug ØChemically Resistant ØPhysically Strong ØCheap 17 11/9/2020

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) 18 11/9/2020

Filter Media Structure • Cloth 19 • Metal 11/9/2020

Filter Aids o 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. o Filter aids are used in two different ways: Ø Added before filtration Ø As a pre-coat 20 11/9/2020

Filter Aids Ø Added before filtration This increases the porosity of the cake and reduces resistance of the cake during filtration. Ø 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. 21 11/9/2020

Types of Filters 22 11/9/2020

Classification of Filters are classified on following three different basis: I. Mechanism II. The driving force III. Operation 23

On the basis of Cakemechanism filters 1. 2. Clarifying filters 3. Cross flow filters On the basis of driving force 1. Pressure Filters 2. Vacuum filters 3. Centrifugal filters On the basis of operation 1. Continuous filters 2. Batch or discontinuous filters 24

Classification of 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. 25 11/9/2020

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. 26 11/9/2020

1. Filter Press Ø Pressure filter operate in batch mode Ø Sets of plates (circular or square) Ø Plate faces covered by septum Ø Slurry enters at one end Ø Solids (cake) collect in chamber and liquid pass out Ø ‘Jammed’ filter Ø Wash liquid, air or steam used to remove residual liquid Ø Press opened and cake removed Ø Washing is time consuming and labor intensive 27 11/9/2020

Filter Press Pink : Plates Yellow : filter Cloth Blue : Filtrate 28 11/9/2020

Filter Press 29 11/9/2020

2. Shell and leaf filter Ø Pressure filter operating in batch mode Ø Stack of leaves inside the closed tank Ø Feed enters in the side of the tank Ø Pass through leaves covered with filter Ø Liquid leaves into discharge manifold Ø Cake is removed by gravity force and vibration Ø Cake is effectively removed and economize labor 30 11/9/2020

3. Shell and leaf filter 31 11/9/2020

Shell and leaf filter cake disposal 32 11/9/2020

3. Rotary Drum Filter Ø Vacuum filter with continuous operation Ø Drum turns at 0. 1 – 2 rpm in slurry trough Ø Filter covers the face of the drum Ø Rotary drum filter has four zones: 1. 2. 3. 4. Filtering zone Washing and drying zone Cake removal zone Dead zone Ø Vacuum is applied in first two zones Ø Permeate and washing liquid discharge into separate 33 compartments Ø Doctor blade is used in third zone 11/9/2020

Rotary Drum Filter 34 11/9/2020

Rotary Drum Filter 35 11/9/2020

Rotary Drum Filter 36 11/9/2020

Rotary Drum Filter 37 11/9/2020

4. Suspended Batch Centrifuge Ø Centrifugal filter operating in batch mode Ø Perforated baskets 750 – 1200 mm in dia. and 18 – 30 inch deep Ø Basket rotates at 750 – 1200 rpm Ø Feed taken from inlet is centrifuged Ø Clear liquid pass out leaving behind solid cake in basket Ø Wash liquid sprayed to remove soluble solids and cake dried Ø For cake removal, basket is turned at 30 – 50 rpm and cake is cut off with unloader knife 38 11/9/2020

Suspended Batch Centrifuge 39 11/9/2020

Clarifying Filtration 40 11/9/2020

Clarifying Filtration Removal of the Small amounts of solids or liquids droplets from the fluids. 41 • 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 11/9/2020

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 42 11/9/2020

Cartridge Filter 43 11/9/2020

44 11/9/2020

Gas Clarification For atmospheric dust – Pad filters For process dusts – Bag Filters 45 11/9/2020

Pad Filter 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 46 After 11/9/2020

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 47 11/9/2020

48 11/9/2020

Cross flow Filtration 49 11/9/2020

Definition Filtration in which flow of the suspension is parallel to the filtering media used to get concentrated slurry 50 11/9/2020

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. 51 11/9/2020

52 11/9/2020

Difference b/w cross flow & Conventional filtration 1. 2. 3. 4. 53 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 1. Flow of fluid is perpendicular to the surface 2. Solids in the feed trap inside the filter or retain on the filter 3. Process feed is transformed into solid cake & filtrate 4. It is simply the separation of solids from liquids, no fractionation 11/9/2020

54 11/9/2020

Performance of cross flow filtration Fouling of the membrane Permeate flux Percent rejection Back flushing Factors for optimizing permeate flux 1. 2. 55 Trans-membrane pressure Shear rate 11/9/2020

Types of cross flow filtration Reverse Osmosis Microfiltration Ultrafiltration Nanofiltration 56 11/9/2020

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 57 11/9/2020

Points of discussion Osmosis Osmotic pressure Reveres Osmosis 58 11/9/2020

Micro filtration Used for the particles in the size range of 0. 1 - 5 μm. Applications • Fermentation • Biomass clarification and recovery 59 11/9/2020

Ultra filtration Used for the particles in the size range from 1μm down to 10 -3 μm. Applications Ø used in the fractionation of milk as well as protein fractionation 60 11/9/2020

Nano filtration Used for the particles up to 1 nm Nanofiltration is the process with the characteristics b/w those of Ultrafiltration and reverse osmosis. Applications Pharmaceutical processing Water treatment 61 11/9/2020

62