THICKNEES, HYDROCYCLONES,

FILTRATION,AGITATION AND MIXING

PRESENTED BY:

SHIVAYOU PANDEY-2019UGMM008

ANAND SHANKAR-2019UGMM061

SHIVA CHANDRA-2019UGMM092

❖ FILTRATION

Filtration is the process of separating solids from liquid by Means of a

porous Medium which retains the solid but allow the liquid to pass.

❖ DIFFERENT TERMONOGIES

➢ Feed or slurry: The suspension of solid and liquid to be

filtrated is known as slurry or feed.

➢ Filter Medium : The porous medium used to retain the

solids.

➢ Filter Cakes: The accumulation of solids on the filter is

referred as filter cake.

➢ Filtrate: The clear liquid passing through the filter is

filtrate .

➢ Factors affecting Rate of the Filtration

❖ Pressure.

❖ Viscosity.

❖ Surface area of filter media.

❖ Temperature of liquid to be filtered.

❖ Particles Size.

❖ Pore size of filter media.

❖ Thickness of cake.

❖ Nature of Solid Materials ( Porosity of filtrate Cake).

➢ FILTER MEDIA -The surface up on which solids are deposited in a filter is

called the filter medium

➢ PROPERTIES OF IDEAL FILTER

1 Chemically inert.

2 High retention Power.

3 Sufficient Mechanical Strength.

4 Absorbs negligible amount of material.

5 Resistant to the corrosive action of liquid.

FILTER MEDIA

Filter Media selection:-

Selection of filter media depends on followings:

1. Size of particle to be filtered .

2. Amount of liquid to be filtered.

3. Nature of product to be filtered.

TYPES OF FILTER MEDIA

1. Filter Paper

2. Cotton wool

3. Glass wool

4. Fine Muslin

5. Filter cloth

6. Membrane filter

7. Sintered glass filter

TYPES OF FILTER

Cake filter.

Pressure filter.

Leaf filter.

Vacuum filter

➢ CAKE FILTER

➢ A filter cake is formed by the substances that are retained on a filter.

➢ The filter cake grows in the course of filtration becomes thicker as

particulate matter is being retained.

➢ On increasing layer thickness the flow resistance of the filter cake

increases.

➢ After a certain time use of the filter cake has to be removed from the

filter.

➢ PRESSURE FILTER

➢ Most filtration units produces a cake ,which at long cycles may become

dry at the expense of declining flow rates.

➢ Keeping constant rate filtration is difficult as the pressure drop must be

increased during the cycle.

➢ After this short early stage , the cake is going to offer resistance to flow

rather than the filter medium.

➢ These cake filters operate with above atmospheric pressure upstream

from the filter medium.

➢ Both continuous and discontinuous pressure filters are possible

➢ DISCONTINOUS PRESSURE FILTERS

In industrial application point of view , the rate of filtration is very

important factors in the design of filtration equipment.

In general, in pressure filters ,large pressure differential can be

maintained across the filter medium to give a rapid filtration even with

viscous liquids or fine solids.

The most common two types of pressure filter are ;

1. Filter presses.

2. Shell and leaf filters.

➢ PRESSURE FILTER

➢ LEAF FILTERS

➢ Another alternative of pressure filtration are pressure vessel filters that

make use of filter leaves as basic filter element.

➢ A filter leaf consists on wire mesh screen or grooved drainage plate over

which the filter medium is stretched.

➢ Leaf may be suspended from the top or supported from the bottom or

center.

➢ Supporting element is usually hollow and forms an outlet channel for

filtrate.

Each leaf is a hollow wire framework cover by a sack of filter cloth.

Number of these leaves are hung in parallel in a close tank.

Slurry enters the tank and is forced cloth , where the cake deposits on

the outside the leaf.

Filtrate flows inside the hollow framework and out a heater

➢ VACCUM FILTER

1. In vacuum filters sub- atmospheric pressure is maintained downstream

side of filter medium while an atmospheric one is kept upstream

➢ 2. Because pressure drop across the filter is limited to one atmosphere

,they are not suited to batch operations

➢ GRAVITY SEDIMENTATION

Gravity sedimentation or thickening is the most widely applied

dewatering technique in mineral processing, and it is a relatively

cheap, high- capacity process, which involves very low shear forces,

thus providing good conditions for flocculation of fine particles.

➢ USES

The thickener is used to increase the concentration of the suspension

by sedimentation, accompanied by the formation of a clear liquid. In

most cases the concentration of the suspension is high and hindered

settling takes place.

➢ WORKING OF THICKNESS

➢ TYPES OF THICKNESS

1.CONTINOUS THICKNESS

1. As in batch sedimentation some zones will be present in continuous

thickness.

2. however once a steady state has been reached( where slurry fed per

unit time to thickness is equal to rate of sludge and clear liquor

removal)the height of each zone will be constant.

3. continuous thickness are large diameter, shallow- tanks with slowly

revolving rakes for removing the sludge

4. slurry is fed at the center of the tank.

5. around top edge of the tank is clear liquid overflow

6. rakes serve to scraps the sludge toward center of bottom for

discharge

7. motion of rake also stirs only the sludge layer

8. this gentle stirring aids in water removal from the sludge

9. In thickness the entering slurry spreads radially through the cross

section of thickness and liquid flow upward and out of the overflow

2.CAISSION THICKNESS

In which the center column is enlarged sufficiently to house a central

control room; the pumps are located in the bottom of the column, which

also contains the mechanism drive heads, motors, control panel,

underflow suction, and discharge lines. The interior of the caisson can be

a large heated room. The caisson concept has lifted the possible ceiling

on thickener sizes; at present they are manufactured in sizes up to 180m

in diameter.

3.CABLE THICKNESS

Have a hinged rake arm fastened to the bottom of the drive cage or

center shaft. The hinge is designed to give simultaneous vertical and

horizontal movement of the rake arm. The rake arm is pulled by cables

connected to a torque or drive arm structure, which is rigidly connected

to the center shaft at a point just below the liquid level. The rake is

designed to automatically lift when the torque developed due to its

motion through the sludge rises. This design allows the rake arm to find

its own efficient working level in the sludge, where the torque balances

the rake weight efficient

HYDROCYCLONES

An introduction to basic hydrocyclones

A Hydrocyclone is a device to classify, separate or sort particles in a

liquid suspension based on the ratio of their centripetal force to fluid

resistance.

>Based on differences in specific gravity a cyclone will then produce

two products – an underflow and an overflow.

BASIC DIAGRAM OF HYDROCYCLONE

1) the liquid-solid mixture enters

2) heavy solids leave

3) cleaned liquid leaves

WORKING PRINCIPLE

A cyclone uses centrifugal force that is generated by a slurry entering

the feed chamber under pressure to make the separations. This

centrifugal force causes the larger particles to be ‘slung’ to the cone

wall while the finer material is kept closer to the center.

The vortex finder draws the water and fine material to the overflow

while the coarser material makes its way out the apex.

➢ INTERNAL WORKING OF CYCLONE

➢ Slurry enters through the feed inlet.

➢ Cycloning starts to take place in the feed chamber. Heavier particles

move to the outer walls and move toward the apex. Lighter particles

stay near the center of the cone and are carried away by the vortex

finder.

➢ FACTORS AFFECTING HYDROCYCLONE PERFORMANCE

1. Vertex finder

2. Pressure drop

3. Apex diameter

4. Feed flow rate

5. Cyclone diameter

6. Cyclone length

7. Particle size

1.VERTEX FINDER DIAMETER

Change Effect Reasons

increases Decrease efficiency

Coarser particles will mix with finer particles

Decreases Increase efficiency

Only finer particles will flow through the vortex finder

2.PRESSURE DROP

Change Effect reasons

Increase Efficiency increases Flow rate increases

Decreases decreases decreases

3.APEX DIAMETER

Change Effect Reasons

increases Decreases efficiency Large volume of fluids will loose along with finer particles

decreases Increases Large volume of Fluids will be available for overflow

3.FEED FLOW RATE

Change Effects reasons

increases Increases efficiency Increases G.forces

Deceases decreases Decreases G. forces

4.CYCLONE DIAMETER

Change Effects Reasons

increases Decreases efficiency

Decreases G.forces

decreases increases Increases G.forces

5.CYCLONE LENGTH

Change Effects reasons

increases Increases efficiency

Residence time increases

decreases decreases decreases

7.PARTICLE SIZE

Change Effects reasons

increases Increases efficiency

More likely for particles to migrate to exterior wall

decreases decreases To interior wall

USES

A hydrocyclone is most often used to separate "heavies" from a liquid

mixture originating at a centrifugal pump or some other continuous

source of pressurized liquid.

A hydrocyclone is most likely to be the right choice for processes

where "lights" are the greater part of the mixture and where the

"heavies" settle fairly easily.

APPLICATIONS

In pulp and paper mills to remove sand, plastic particles and other

contaminants.

In the drilling industry to separate sand from the expensive clay that is

used for lubrication during the drilling.

In industry to separate oil from water or vice versa.

In metal working to separate metal particles from cooling liquid.

In potato processing plants to recover starch from waste water.

In mineral processing, hydrocyclones are used extensively both to

classify particles for recirculation in grinding circuits and to differentiate

between

the economic mineral and gangue.

To remove sand and silt particles from irrigation water for drip irrigation

purposes.

MIXING AND AGITATION

INTRODUCTION

“Agitation”:- refers to the induced motion of a material in a specified way,

usually in a circulatory pattern inside some sort of container. Purpose is to

make homogeneous phase

“Mixing”:- random distribution, throughout a system, of two or more initially

separate ingredients.

Single homogeneous material can be agitated but can not mixed until some

other material is added to it.

OBJECTIVES:

1. To increase the homogeneity of material on bulk.

2. To bring about intimate contact between different species in order for a

chemical reaction to occur.

3. To change the texture.

4. To enhance heat and mass transfer.

5. To dispenses a liquid which is immiscible with the other liquid by forming an

emulsion or suspension of few drops.

MIXING MECHANISM

Three basic mechanisms:-

convection:- movement of group of particles because of the direct action of

an impeller or moving device .

example- trough mixer with spiral ribbon

diffusion:- diffusion refers to random dispersion or individual particles in the

inter particle void spaces throughout the mixer .

example- simple barrel mixture

Shear mixing:- groups of particles are mixed through the formation of slipping

planes developed by the action of blade. newly formed slipping planes in turn

allow particles to diffuses through new void spaces.

DEGREE OF MIXING

Mixing index (M):- a dimensionless fraction measure of a variance or standard

deviation that can correlate with time .

where M- mixing index in fraction

S^2-variance at any given time ,

’n’ is the number of samples taken

X1, X2, …. Xn ,are fractional compositions or component X in a 1,2 …… n

samples.

for an unmixed system of two separate components:

variance after complete mixing

Where, N number of particle is mixed sample, if sample is large quantity then

N is also large (Infinity) then

RATE OF MIXING

Rate of mixing at any time under constant working condition ought to be

proportional to the extent of mixing remaining to be done at that time

where M is the mixing index and k is the constant and on integrating form t=0

to t=t during which M goes from 0 to M,

POWDER MIXERS

➢ Tumbling mixer

➢ Types: horizontal drum, double Cone, V –cone and cube.

➢ 1. operate in Batch Mode being partially filled with solids

➢ 2. Tumbling mixture are run at a fraction of the critical speed

required for centrifugation with a particle maximum speed of

about 100 RPM.

➢ 3. such mixers may have baffles fitted to the inner walls which

helps to lift solids or alternatively may be fitted with clothes to

assist convections.

a. Horizontal cylinder :

b. Double cone Blender: the double cone Blender consists of two cone-

shaped sections, typically with 45 degree slopes.

c. V cone Blender: V cone Blender consists of two large diameter pipe

sections cut at a 45 degree and welded together to form a V.

d. Y cone Blender: in the same way, the Y-cone Blender has a third

section that extend the volume of the Blender in a bisectional direction

with respect to the other pipe sections.

TUMBLING MIXERS

VERTICAL SCREW MIXER

1.cylindrical or cone shaped vessel.

2. The screw may be mounted centrally or Orbit around the central axis

of The vessel near the wall.

3. materials are lifted from the bottom are then Exchange with materials

on the way up.

4. useful for mixing small quantities of additive into large masses of

materials.

LIQUID MIXING

liquids are mixed usually by impellers, which produce shear forces for

inducing the necessary flow pattern in the mixing container.

mixing occurs due to resultant effect of three components acting on

liquids:

1. Radial component 2.Tangential/circular component

3. Axial/longitudinal component

➢ The type of flow depends on:

➢ 1.Type of impeller

➢ 2. Characteristic of fluid

➢ 3. Size proportion of tank , baffle and impellers.

❖ FLOW PATTERNS

Radial component:-

Direction:- acts in the direction perpendicular to the impeller shaft.

Effect:- excessive radial flow take the material to the container wall,

then the material falls to the bottom and rotates as a mass beneath the

impeller.

tangential component:-

Direction:- acts in the direction tangent to the circle of rotation around

the impeller shaft .

Effect:- if shaft is placed vertically and centrally, tangential flow follow a

circular path around the shaft and creates a vortex in the liquid.

Axial component:-

Direction:- acts in the direction parallel to the impeller shaft.

Effect:- inadequate longitudinal component causes the liquid and solid

to rotate in layers without mixing.

❖ Types of agitator/impeller

Type of agitator /impellor – paddle ,propeller, turbine.

1. Consisting of a pair of flat blades mounted on a shaft.

2. Paddles rotate at a low speed of 100rpm.

3. They push the liquid radially and tangentially with almost No

axial unless blades are pitched.

In deep tank several paddles are attached one above the other on the

same shaft.

Advantages:- vortex formation is not possible with paddle impellers

because of low speed mixing.

Disadvantages:- mixing of the suspension is poor therefore baffled tanks

are required.

Turbines

• They resembles multi bladed paddle agitators with short blades, turning

at high speeds on a shaft mounted centrally in the vessel.

• Blades may be straight or curved, pitched or vertical.

• Diameter of impeller turbine is smaller than with paddles, ranging from

30 to 50% of vessel diameter.

• The principle currents generated by turbines are radial and tangential (

the tangential component induces vertexing and swirling which must be

stopped by baffles.

PROPELLER 1. primarily used to blend low viscosity liquids.

2. impeller diameter is much smaller than that of turbine mixers.

3. The mixer shaft is usually positioned on an angle and off centre

.

4. Two are more propellers are used for deep tank.

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