Introduction to Unit operations and filtration.pptx

Unit operation and Filtration method in Chemical Engineering

1. Objectives Importance of Unit Operations in Chemical Industry. Identify relevant Unit Operations in Process Flow Diagrams. Get to know the basic concepts behind Unit Operations. Recognize typical Equipment Design & Operation.

2. Unit operations – Quick revision What is a Unit Operation? It is a basic step in a process. Unit Operation is a physical change to which material is subjected. Does not involve any chemical reaction Manufacture of Common Salt All steps are Unit operations

3. Unit operations – Quick revision Broad Classification

4. Unit operations Where are they required ? Preparation of reactants Separation / purification of products. Recycling unconverted reactants Energy transfer into / out of chemical reactor.

5. 1. Filtration Filtration: Removal of solid particles from fluid by passing the fluid through a filtering medium or septum on which solids are deposited. It ranges from simple straining to highly complex separations. Valuable stream from filter may be fluid or solids or both. Sometimes its neither, as when waste solids must be separated from waste liquid prior disposal.

6. Classification based on application Solid content of feed ranges from trace to a very high percentage. Three main groups:

7. Classification based on operation

8. Cake Filters Discontinuous Pressure Filters Pressure filters can apply a large pressure differential across the septum to give economically rapid filtration with viscous liquids or fine solids Common Types are: Filter Press Shell and Leaf Filter Automatic Belt Filter

9. Filter press Contains a set of plates designed to provide a series a chamber in which solids may collect. The plates are covered with filter medium. Slurry is admitted to each compartment under pressure, filtrate passes thorough medium and out a discharge pipe, leaving a wet cake of solid behind. Operated at pressure: 3 to 10 atm.

10. Shell & Leaf Filter For higher pressures than possible with plate and frame press. For better washing of cake is needed. Tank Filter leaves on retractable rack.

11. Cake Filters - Vacuum Operated Discontinuous Vacuum filter: Vacuum Nutsche Filter Continuous Vacuum filter: The filtrate is sucked through a moving septum to deposita cake of solids. Some part of ilter is in the filtering zone at all times, part in washing zone and part is being relierved of its laod of solids so that the filtration is uninterrupted. Generally Differential pressure is 250 – 500 mm Hg Common Types are: Rotary Drum Filter Horizontal belt Filter

12. Rotary Drum Filter Consists of horizontal drum with slotted face turns at 0.1 to 2 rpm in an agitated slurry trough. Generally 30 % of filter area is submerged in slurry.

13. Rotary Drum Filter

14. Horizontal Belt Filter When feed contains coarse fast –settling particles , rotary –drum filter works poorly. For such application, a top fed horizontal belt conveyor is used.

15. Cake Filters – Centrifugal Solids that form a porous cake can be separated from liquid. Slurry is fed to a rotating basket having slotted or perforated wall covered with a filter medium, leaving the solids behind. More dry solid cake. Common types: Discontinuous - Suspended Centrifuge Continuous - Conveyor Centrifuge.

16. Top Suspended basket Centrifuge Perforated baskets range from 750 to 1200 mm in dia. Operating speed: 600 to 1800 rpm.

17. Automatic Batch Centrifuge Basket rotates at constant speed on horizontal axis. Feed slurry, wash liquid and screen rinse are successively sprayed into basket at app. Intervals for controlled lengths of time.

18. Continuous filtering Centrifuge For coarse crystals. Consists of slotted wall rotating basket with woven metal. Feed through rotating funnel. Reciprocating piston for collection of filtered solids.

19. Filer Media Must retain solids to be filtered. Must not plug or blind. Must be chemically and strong enough physically to withstand process conditions. Permit cake formed to discharged cleanly and completely. Must not be expensive. Common Filter media: Canvas cloth. Woolen cloth Metal cloth of SS or monel Glass cloth. Paper Synthetic fibres like nylon, polypropylene, polyesters are chemical resistant.

20. Filer Media Must retain solids to be filtered. Must not plug or blind. Must be chemically and strong enough physically to withstand process conditions. Permit cake formed to discharged cleanly and completely. Must not be expensive. Common Filter media: Canvas cloth. Woolen cloth Metal cloth of SS or monel Glass cloth. Paper Synthetic fibres like nylon, polypropylene, polyesters are chemical resistant.

21. Filter Aids Slimy or very fine solids that form a dense and impermeable cake quickly plug any filter medium that is fine enough tot retain them. Filtration of such material requires that porosity of cake be increased to permit passage of filtrate at a reasonable rate. Filter aid such as diatomaceous silica, perlite, purified wood cellulose will help in filtration of such liquids. Filter aid can be mixed in feed slurry or as precoat to the filter medium.

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