Mechanical separationMechanical separation

TopicTopicElectrostatic separationsElectrostatic separations

synopsissynopsis What is electrostatics?What is electrostatics? Why a charged comb attracts paper and dry Why a charged comb attracts paper and dry

dandruff (yuk!)?dandruff (yuk!)? What is electrostatic separation?What is electrostatic separation? PrinciplePrinciple Types of electrostatic separationsTypes of electrostatic separations

wet electrostatic separations wet electrostatic separations dry electrostatic separations dry electrostatic separations

Technique of charging (Charging mechanism)Technique of charging (Charging mechanism)ion bombardmention bombardment Contact electrificationContact electrificationConductive inductionConductive induction

Synopsis (con’d)Synopsis (con’d) ApplicationsApplications Electrostatic separation machinesElectrostatic separation machines Electrostatic precipitator.Electrostatic precipitator.

DefinitionDefinitionConstructionConstructionFunctional descriptionFunctional description

TypesTypesWet electrostatic precipitatorWet electrostatic precipitatorDry electrostatic precipitatorDry electrostatic precipitatorApplicationsApplications

What is What is electrostatics?electrostatics?

Definition Definition

Electrostatics is the Electrostatics is the branch of science branch of science that deals with the that deals with the phenomenon arising phenomenon arising from stationary or from stationary or slow-moving electric slow-moving electric charge.charge.

Why a charged comb attracts Why a charged comb attracts paper and dry dandruff (yuk!)?paper and dry dandruff (yuk!)?

Why?Why? Suppose the comb ends up positive.Suppose the comb ends up positive.

Then near side of paper ends up slightly negative Then near side of paper ends up slightly negative from attraction of opposite charges.from attraction of opposite charges.

The other side ends up slightly positive due to The other side ends up slightly positive due to repulsion of similar charges.repulsion of similar charges.

What is electrostatic What is electrostatic separation?separation?

Definition Definition

Separation of finely Separation of finely pulverized materials by pulverized materials by placing them in placing them in electrostatic separators. electrostatic separators. Also known as high-Also known as high-tension separation. tension separation.

Pulverized materialPulverized material:-:- A A substance that is reduce substance that is reduce to fine particles, by to fine particles, by crushing or grinding.crushing or grinding.

Principle Principle Electrostatic Electrostatic

separation is a separation is a method of separation method of separation based on differential based on differential attraction or repulsion attraction or repulsion of charged particles of charged particles under the influence of under the influence of an electric field.an electric field.

Applying an Applying an electrostatic charge to electrostatic charge to the particles is the particles is necessary step before necessary step before particle separation particle separation can be accomplished.can be accomplished.

Charging Mechanism Charging Mechanism

Charging mechanism Charging mechanism

Various techniques can be used for charging Various techniques can be used for charging these include these include

Contact electrificationContact electrification Conductive inductionConductive induction Ion bombardmentIon bombardment

Generally, separators of the conductive-induction Generally, separators of the conductive-induction type have a lower capacity per unit length of type have a lower capacity per unit length of electrode than the ion-bombardment.electrode than the ion-bombardment.

Contact Electrification Contact Electrification

Contact electrificationContact electrification When dissimilar material touch each other, there When dissimilar material touch each other, there

is an opportunity for the transfer of electric is an opportunity for the transfer of electric charges.charges.

High temperatures and low humidity favor the High temperatures and low humidity favor the development of high surface charges through the development of high surface charges through the mechanism of contact electrification. mechanism of contact electrification.

Rubbing the materials together to increase the Rubbing the materials together to increase the area of effective contact can also lead to high area of effective contact can also lead to high surface charges.surface charges.

Contact electrification Contact electrification (con’d)(con’d)

Particles carrying charges of opposite polarity Particles carrying charges of opposite polarity due to contact electrification.due to contact electrification.

Particles carrying charges of opposite polarity Particles carrying charges of opposite polarity due to contact electrification will be attracted to due to contact electrification will be attracted to opposite electrodes when passing through an opposite electrodes when passing through an electric field and thus can be separated from electric field and thus can be separated from each other.each other.

Conductive Induction Conductive Induction

Conductive inductionConductive induction

The term The term conductive induction conductive induction describes the describes the process by which an initially uncharged particle process by which an initially uncharged particle that comes into contact with a charged surface that comes into contact with a charged surface assumes the polarity and, eventually, the potential assumes the polarity and, eventually, the potential of the surface.of the surface.

If a conductor particle and a nonconductor particle If a conductor particle and a nonconductor particle are just separated from contact with a charged are just separated from contact with a charged plate, the conductor particle will be repelled by plate, the conductor particle will be repelled by the charged plate and the non-conducting particle the charged plate and the non-conducting particle will be neither repelled nor attracted by it.will be neither repelled nor attracted by it.

A question arisesA question arises

??

How can electrostatic How can electrostatic separation be done separation be done

through this technique?through this technique?

Conductive inductionConductive induction In electrostatic separation, this is usually In electrostatic separation, this is usually

accomplished by means of a single electrode of accomplished by means of a single electrode of charge opposite in sign to that of the charged charge opposite in sign to that of the charged plate. plate.

The conductor particle is then in the electrical The conductor particle is then in the electrical field between the two electrodes and experiences field between the two electrodes and experiences a net electrostatic force in the direction of the a net electrostatic force in the direction of the second electrode.second electrode.

Conductive induction Conductive induction (con’d) (con’d)

The non-conducting particle, having no net The non-conducting particle, having no net charge, experiences no electrostatic force in a charge, experiences no electrostatic force in a uniform electric field. uniform electric field.

Electrostatic separation of the conductor and Electrostatic separation of the conductor and nonconductor particles can be accomplished by nonconductor particles can be accomplished by movement of the conductors in the electric field.movement of the conductors in the electric field.

Ion bombardment Ion bombardment

Ion bombardment Ion bombardment

The most The most positivepositive and and strongeststrongest method of method of charging particles for electrostatic separation is charging particles for electrostatic separation is ion bombardmention bombardment..

A question arisesA question arises

??

How can separation be How can separation be done through this method ?done through this method ?

Ion bombardment Ion bombardment Both particles are bombarded by ions of Both particles are bombarded by ions of

atmospheric gases generated by an electrical atmospheric gases generated by an electrical corona discharge from a high-voltage electrode corona discharge from a high-voltage electrode (usually a fine tungsten-alloy wire at 20 to 30 kV (usually a fine tungsten-alloy wire at 20 to 30 kV with respect to ground and several centimeters with respect to ground and several centimeters away from the particles).away from the particles).

When ion bombardment ceases, the conductor When ion bombardment ceases, the conductor particle loses its acquired charge to ground very particle loses its acquired charge to ground very rapidly and experiences an opposite electrostatic rapidly and experiences an opposite electrostatic force tending to repel it from the conducting force tending to repel it from the conducting surface.surface.

Ion bombardmentIon bombardment The non-conducting particle, however, being The non-conducting particle, however, being

coated on its side away from the conducting coated on its side away from the conducting surface with ions of charge opposite in electrical surface with ions of charge opposite in electrical polarity to that of the surface, experiences an polarity to that of the surface, experiences an electrostatic force tending to hold it to the electrostatic force tending to hold it to the surface.surface.

Types of electrostatic Types of electrostatic separationseparation

Types of electrostatic Types of electrostatic separationseparation

There are two types of electrostatic separations:There are two types of electrostatic separations:

Wet electrostatic separationsWet electrostatic separations Dry electrostatic separationsDry electrostatic separations

Types of electrostatic Types of electrostatic separations (con’d)separations (con’d)

Wet electrostatic separationsWet electrostatic separations:-:- In wet In wet electrostatics separations dust particles are electrostatics separations dust particles are removed from wet saturated air stream removed from wet saturated air stream (100% relative humidity).(100% relative humidity).

Dry electrostatic separationDry electrostatic separation:-:- In dry In dry electrostatic separation particles are electrostatic separation particles are separated from dry air streamseparated from dry air stream..

Applications Applications

Application of electrostatic Application of electrostatic separation separation

Mineral BeneficiationMineral Beneficiation:-:- Electrostatic methods Electrostatic methods are widely used in the processing of ores with are widely used in the processing of ores with mineral concentrates.mineral concentrates.

Charging by ion bombardment is the technique Charging by ion bombardment is the technique used in most mineral separations.used in most mineral separations.

Plastic and metal recycling:Plastic and metal recycling: Electrostatic Electrostatic separation has been increasingly applied to separation has been increasingly applied to recover nonferrous metals from industrial recover nonferrous metals from industrial plastics (telephone and communication scrap). plastics (telephone and communication scrap).

It also is an important step in the recycling of It also is an important step in the recycling of beverage bottles to reject any remaining beverage bottles to reject any remaining nonferrous metals. (Fig. 19-61nonferrous metals. (Fig. 19-61bb).).

Electrostatic separation Electrostatic separation machinesmachines

Electrostatic separation Electrostatic separation machinesmachines

There are different types of electrostatic There are different types of electrostatic machines which are used in our industry:machines which are used in our industry:

Triboelectric SeparatorsTriboelectric Separators Conductive-Induction MachinesConductive-Induction Machines Ion-Bombardment MachinesIon-Bombardment Machines

But electrostatic precipitator has more But electrostatic precipitator has more importance than all of above so we only importance than all of above so we only discuss it here.discuss it here.

Electrostatic Precipitator Electrostatic Precipitator

Introduction Introduction

Electrostatic Precipitators or ESPs have been Electrostatic Precipitators or ESPs have been used in industry for over 60 years. used in industry for over 60 years.

They can collect particles sized 0.1 to 10 microns They can collect particles sized 0.1 to 10 microns very efficiently.very efficiently.

They are generally more efficient at collecting They are generally more efficient at collecting fine particles than scrubbers or cyclones. fine particles than scrubbers or cyclones.

Electrostatic precipitatorElectrostatic precipitator Definition:Definition:

A device for removing small A device for removing small particles, as of smoke, dust, or oil, from a gas, particles, as of smoke, dust, or oil, from a gas, as air, by passing the gas first through an as air, by passing the gas first through an electrically charged screen that gives a charge electrically charged screen that gives a charge to the particles, then between two charged to the particles, then between two charged plates where the particles are attracted to one plates where the particles are attracted to one service.service.

Electrostatic precipitators are highly efficient Electrostatic precipitators are highly efficient filtration devices.filtration devices.

Construction Construction

constructionconstruction A shell or house contains the electrodes, exhaust A shell or house contains the electrodes, exhaust

gases and rapper.gases and rapper.

The shell must be well built with a rigid frame to The shell must be well built with a rigid frame to hold the components in their proper place.hold the components in their proper place.

Hot temperatures inside the shell can vary Hot temperatures inside the shell can vary greatly from the temperatures outside the greatly from the temperatures outside the shell. shell.

Construction (con’d)Construction (con’d)

Such tremendous temperature differences can Such tremendous temperature differences can cause expansion and contraction to stress joints cause expansion and contraction to stress joints and welds. and welds.

Often shells are insulated to minimize Often shells are insulated to minimize temperature differences and prevent gases from temperature differences and prevent gases from condensing into corrosive liquids. condensing into corrosive liquids.

Functional Description Functional Description

Functional descriptionFunctional description Electrostatic precipitator (ESP's) are used to Electrostatic precipitator (ESP's) are used to

extract airborne dust particles from the air. extract airborne dust particles from the air.

Dust particles are charged by electrodes and Dust particles are charged by electrodes and adhere to the collector plates in the electrostatic adhere to the collector plates in the electrostatic precipitator. precipitator.

Inlet and outlet distribution plates ensure even Inlet and outlet distribution plates ensure even distribution of flue gas over the collector plates. distribution of flue gas over the collector plates.

Functional description Functional description (con’d)(con’d)

Electro-mechanical rappers dislodge the dust Electro-mechanical rappers dislodge the dust particulate from the electrodes and collector particulate from the electrodes and collector plates (rappers are located external to the plates (rappers are located external to the electrostatic precipitator).electrostatic precipitator).

The dust particles fall into a common hopper The dust particles fall into a common hopper where they are exited through an air lock to the where they are exited through an air lock to the residual collecting conveyor system.residual collecting conveyor system.

The clean air is evacuated from the electrostatic The clean air is evacuated from the electrostatic precipitator into the atmosphere.precipitator into the atmosphere.

Dry electrostatic Dry electrostatic precipitator precipitator

Dry electrostatic Dry electrostatic precipitator precipitator

A dry electrostatic precipitator ( ESP ) is a large A dry electrostatic precipitator ( ESP ) is a large box. box.

Particulate control begins when the dust laden Particulate control begins when the dust laden gases are drawn into one side of the box. gases are drawn into one side of the box.

Inside, high voltage electrodes impart a negative Inside, high voltage electrodes impart a negative charge to the particles entrained in the gas. charge to the particles entrained in the gas.

DEP (con’d)DEP (con’d) These negatively charged particles are then These negatively charged particles are then

attracted to a grounded collecting surface which attracted to a grounded collecting surface which is positively charged. is positively charged.

The gas then leaves the box up to 99.9% cleaner The gas then leaves the box up to 99.9% cleaner than when it entered. than when it entered.

Wet electrostatic Wet electrostatic precipitatorprecipitator

Wet electrostatic Wet electrostatic separators separators

For wet electrostatic separations used wet For wet electrostatic separations used wet electrostatic separators.electrostatic separators.

WESP uses a vertical cylindrical tube with WESP uses a vertical cylindrical tube with centrally-located wire electrode (gas flowing centrally-located wire electrode (gas flowing upward) with water sprays to clean the collected upward) with water sprays to clean the collected particulate from the collection surface (plates, particulate from the collection surface (plates, tubes).tubes).

Applications of ESPApplications of ESP

Applications Applications The use of electrostatic precipitators has become The use of electrostatic precipitators has become

common in numerous industrial applications.common in numerous industrial applications. Electrostatic precipitator has ability to handle Electrostatic precipitator has ability to handle

large volumes of gas, at elevated temperatures large volumes of gas, at elevated temperatures and the removal of particles in the micrometer and the removal of particles in the micrometer range.range.

Some usual applications are:Some usual applications are: Removal of dirt from flue gases in steam plants.Removal of dirt from flue gases in steam plants.

Cleaning of blast furnace gasesCleaning of blast furnace gases . .

Presented by:Presented by: section-B section-B