FILTRATION Part II MOHD SHARIZAN MD SARIP PHD

FILTRATION Part II MOHD SHARIZAN MD SARIP, PHD

COURSE OUTCOME Understanding theory for filtration process. Distinguish different types of filters, such as cake filter, clarifying filter, and crossflow filter. Demonstrate the concept for pressure drop and specific cake resistance through compressible and incompressible filter cake and calculate the filter medium resistance. Discuss different type of equipment for filtration process.

DETERMINATIO N OF SPECIFIC CAKE RESISTANCE & FILTER MEDIUM RESISTANCE

RATE OF FILTRATION -( P) or Pressure drop rate of filtration = driving force/resistance Filter cake ( ) Filter medium (Rm) Viscosity ( )

Factor affected on filtration Pressure drop ) ∆P( Area of filtering surface )A ( Volume of filtrate ) V ( Resistance of filter cake ) α( Resistance of filter medium )Rm( Viscosity of slurry ) μ(

PRINCIPLE IN CAKE FILTRATION Pa Rtotal Rcake ΔPcake =Pa – P’ P’ ΔPmedium =P’ - Pb Pb Rmedium ΔP Rtotal = Rcake+ Rmedium ΔP =ΔPcake + ΔPmedium = Rc + Rm rate of filtration = driving force/resistance =ΔPc + ΔPm

Relation between W and V W = kg acculamated dry cake solids c or cs= kg solid / m 3 filtrate V = volume of filtrate p =density of filtrate cx =mass fraction of solid in the slurry m= mass ratio of wet cake to dry cake

Equation for continuous process tc=total cycle time f= fraction of the cycle used for the cake formation or fraction of submergence of the drum in the slurry.

EXAMPLE 1 Volume flow rate of filrate ? If 3. 1 kg slurry /s , cx is 0. 3 kg solid/kg slurry and c is 300 kg solid / m 3 filtrate ? 0. 0031 m 3 filterate /s Area of filter ? f = 30% , pressure drop = 70 kpa, tc = 250 s, specific cake resistance =1 x 1011 , viscosity = 0. 8937 x 10 -3 39. 16 m 3

FILTER CAKES CLASSES Filter cakes may be divided into two classes : incompressible cakes In the case of an incompressible cake, the resistance to flow of a given volume of cake is not appreciably affected either by the pressure difference across the cake or by the rate of deposition of material. On the other hand, with a compressible cake, increase of the pressure difference or of the rate of flow causes the formation of a denser cake with a higher resistance.

INCOMPRESSIBLE CAKES Incompressible cake: � Solid concentration remains constant � Porosity of the filtered cake remains constant � Cake volume increases by a constant amount for each unit of suspension

INCOMPRESSIBLE CAKES Dry mass solids per unit area, w Specific cake resistance, α c = dry solid concentration (kg/m 3)

EXAMPLE 2

SOLUTION

COMPRESSIBLE CAKE Compressible cake: � Solid concentration doesn’t remain constant! � Cake resistance, Rc is even higher! � Rc increases with pressure drop over the cake, ∆Pc

COMPRESSIBLE CAKE Where 0 : the resistance at unit applied pressure drop n : a compressibility index obtained from experiments (n = 0 for incompressible substance)

COMPRESSIBLE CAKE

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