1. B.E. 5 TH SEM CHEMICAL ENGINEERING DEPARTMENT MECHANICAL OPERATION( 2150502) Prepared by: Group No:-08 Sr. No.Enrollment No.Topic 1130190105029Centrifugal Filter 2130190105030Introduction, Cake Filter 3130190105031Discontinuous Vacuum Filter 4130190105032Continuous Vacuum Filter 5130190105033Filter Press Guided by: Prof. A. M. Patel

2. I NTRODUCTION :-  The mechanical operation of separating a solid from a liquid by means of a porous medium is called filtration.  The medium retains the solid in the form of porous cake, while the liquid passes through it.  The driving force is required for a separation by filtration may be divided into four category gravity, vacuum, pressure and centrifugal.

3. Examples of filtration:-  Separation of suspended impurities from water in water purification.  Separation of organic and inorganic materials from their slurry such as calcium carbonate, ammonium sulphate, sugar, paranitroaniline. Types of filtration :-  Basically there are two types of filtration. (1) Cake filtration (2) Deep bed filtration

4.  In the cake filtration, the proportion of solid in the suspension is large and most of the solid particles are collected in the cake which can be detached from a filter medium.  While in the deep bed filtration, the proportion is very small and the particles of the solid being smaller than the pores of a filter medium.  Ultimately get trapped inside the filter medium and usually no layer of solids will appear on the surface of the medium.

5.  Accordingly the filters are divided into two main groups (1) clarifying filters:  It is used to remove small amount of solid to produce a sparkling clear liquid.

6. (2) Cake filters: Cake filter is used to separate large amount of solids in the form of cake of crystals.

7.  Cake filtration operation is shown in figure  During the initial period of flow solid particles are trapped within the porous of medium forming a true filter medium.  The liquid is passes through a bed of solid and through a filter medium. Principles of cake filtration :-

8.  In the early stage of filtration, the rate of filtration is high.  As the cake thickness is increases, the arte of filtration is decreases for a given pressure difference across the filter medium.

9.  Construction :- This is the simplest type of pressure filter. It consists of plates and frames arranged alternately and supported on a pair of rails. The plate is a solid piece having a ribbed surface. The frame is hollow and provides the space for the filter cake. By this alternate arrangement of frame and filter the chamber form in which cake will deposited. The plate and frame are square or rectangular in shape which made from cast iron, stainless steel, nickel, aluminium, monel, wood, hard rubber or plastics (polypropylene).

10. Filter Cloth Frame and Plate Coated materials are also be used(rubber or lead or epoxy resin covered).

12. Filter cloths are placed over each plate to cover the plate surfaceon both sides so that hollow frame is separated from the plate by the filter cloth. The plate and frame have circular holes on the corners for feed and discharge. The filter cloth also having holes. The filter cloth themselves act as gaskets. By using the hand screw or hydraulically the press is closed and a continuous channel is formed along the whole length. At the bottom of the plates, holes are cored which connect the faces of the plates to the outlet cocks.

13.  Working :- Slurry to be filtered is pumped through the feed channel. It runs into the chambers formed and filled the chamber completely. The filtrate passes through the cloth, runs down the faces of plates and finally leaves the filter through discharged cocks. The solids are deposited on the filter cloth. After some time chamber is fully charged then the press is said to be jammed. To remove soluble impurities from the cake wash liquid may be introduced in the press, then blown with air to remove the residual liquid from it. The press is then dismantled, and the cake of solids scrapped off from each plate and dropped to a conveyor or storage bin.

14. In simple washing, the wash liquor is introduced through the feed channel and leaves the filter through outlet cocks. It is suited when cake is uniform and permeable. Filtrate is discharged by to way which is : 1. Open Discharged, 2. Close Discharged The close technique is used when toxic or volatile materials are to be filtered. In many presses, arrangement is done for steam heating. Due to this, the viscosity of the filtrate is reduced and a higher rate of filtration is achieved. The plate is ranging from 100 X 100 mm to 1500 X 1750 mm. Operating pressure upto 700 kPa are common. The press may be operated upto 7 MPa by using suitable material of construction.

15.  Advantages :- i.Simple in construction. ii.Low first cost. iii.Very low maintenance and hence, its cost is low. iv.It provides large filtering area per unit for floor space occupied. v.High operating pressure are easily obtained. vi.It is possible to alter the capacity. vii.Most joints are external, so leakage is easily detected. viii.Flexibility.

16.  Disadvantages:- i.Labour requirement is very high. ii.Filter cloth life is relatively short. iii.Not suitable for high throughputs. iv.Presses frequently drip and leak, making housekeeping in the area a problem. v.Cake washing is likely to be imperfect.

17. Shell and Leaf filter  This filter is used under higher pressure and batter washing of the cake is needed.  These filters provide large surface area by using varieties of filter leaves.  In the horizontal tank design shown in fig.,a set of vertical leaves is held on a retractable rack.  The slurry to be filtered fills the space around the leaf and is forced to flow through the leaf by applying pressure on the slurry or vacuum within the leaf.

18.  The filter cake builds upon the outside of leaf.  Filtrate passes from within the leaf to the filtrate discharge system.  This is widely used for filtrations involving filter aids.

19. Discontinuous vacuum filter  Pressure filter are usually discontinuous; vacuum filter are usually continuous.  A discontinuous vacuum filter, however, is sometime a useful tool.  A vacuum nutsche is little more than a large buchner funnel,1 to 3m(3 to 10ft) in diameter and forming a layer of solid 100 to 300 mm(4 to 12 in)thick.

20.  Because of its simplicity, a nutsche can readily be made of corrosion-resistant material and is valuable where experimental batches of a variety of corrosive material are to be filtered.  Nutsches are uncommon in large-scale processes because of the labor involved in digging out the cake; they are useful.  however, as pressure filter in some batch operations in which the cake must be dried in the filter itself before discharge.

21. Rotary Drum Filter

22.  Construction :-  A Rotary drum filter is from 50 to 400 cm in diameter and 50 to 800 cm long.  Outer surface is formed of Plate and which turns at 0.1 to 2 r/min.  Inside the outer drum, there is a smaller drum with a solid surface.  The annular Space between the two drum is divided into number of components by radial partitions and separate connection.  As the drum rotates, vacuum and air are alternately applied to each compartment.

23.  Working :-  The drum is immersed to desired depth in the slurry.  Vacuum is then applied to the portion of drum which is submerged in the slurry through the rotary valve.  The liquid (filtrate) is sucked into the compartment and solid get deposited on the cloth drum.  It is higher speeds and high rate of filtration will be achieved.  The filtrate from the compartment than goes to a filtrate collecting tank through the internal pipe and rotary valve.

24.  Cake is formed comes out of slurry, the cake is washed by spraying wash liquid.  The wash liquid leaves the filter through the rotary valve and is collecting separately in a separate tank.  After washing,cake enter into a drying zone as the drum rotates where the cake is dry by solid.  Vacuum is cut off and the cake is removed by scrapping it off using a adjustable doctor blade.  Once the cake is removed from the drum sector, it re-enter the slurry and the cycle is repeated.

25. Centrifugal filters  A centrifugal or centrifuge is any rotating machine in which centrifugal force is utilised for phase separation. The essential components of machine are: 1. A rotor in which centrifugal force is applied 2. A drive shaft 3. A drive mechanism. e.g. Electric motor 4. A frame for support 5. Casing

26. Top Suspended Basket Centrifugal:-

27.  Construction:-  It consists of a basket with perforated sides.  Diameter of basket ranges from 750-1200 mm and depth from 450-750 mm.  Basket rotates at speeds between 600-1800 rpm.  The shaft is driven from above by electric motor.  The filter medium is placed around inside surface of basket.  The basket and other parts may be constructed of mild steel, monel and stainless.

28.  Working:-  Accelerate the machine upto speed suitable for feeding.  Feed the slurry to be filtered.  Accelerate the machine to full speed for deliquoring.  Apply wash liquor to the filter cake.  Spin to dryness.  Decelerate to unloading speed.  Unload

29. Advantages:-  Compact and occupy very small space.  Very high separating efficiency. Disadvantages:-  Construction is complicated.  Capacity is limited.  Not suitable for cake forming solids.