Electrostatic Precipitator, About Electrostatic Precipitator, Working Principle of Electrostatic Precipitator (For CBSE, ICSE, IAS, NET, NRA 2022)

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  • A dry electrostatic precipitator electrically charges the ash particles and imparts a strong electric field in the flue gas to collect and remove them.
  • An ESP is comprised of a series of parallel, vertical metallic plates (collecting electrodes) forming lanes through which the flue gas passes.
  • Centered between the collecting electrodes are discharge electrodes which provide the particle charging and electric field.

Plan View of a Typical ESP

Plan View of a Typical ESP

About Electrostatic Precipitator

  • An ESP is defined as a filtration device that is used to remove fine particles like smoke and fine dust from the flowing gas.
  • It is the commonly used device for air pollution control.
  • It is used in industries like steel plants, thermal energy plants.
  • In the year 1907, chemistry professor Frederick Gardner Cottrell patented the first electrostatic precipitator that was used to collect sulphuric acid mist and lead oxide fumes that were emitted from various acid-making and smelting activities.

Working Principle of Electrostatic Precipitator

Working Principle of Electrostatic Precipitator
  • The working principle of the electrostatic precipitator is very simple.
  • It consists of two sets of electrodes,
    • Positive
    • Negative
  • The negative electrodes are in the form of a wire mesh and the positive electrodes are in the form of plates.
  • This electrode is vertically placed and is alternate to each other.
  • The gas borne particles such as ash are ionized by the high voltage discharge electrode by the corona effect.
  • These particles are ionized to negative charge and are attracted to positively charged collector plates
  • The negative terminal of high voltage DC source is used to connect the negative electrodes and the positive terminal of the DC source is used to connect the positive plates.
  • To ionize the medium between the negative and the positive electrode, a certain distance is maintained between the positive, negative electrode and the DC source resulting in a high voltage gradient.
  • The medium that is used between the two electrodes is air. There might be corona discharge around the electrode rods or the wire mesh due to high negativity of negative charges.
  • The entire system is enclosed in a metallic container consisting of an inlet for flue gases and an outlet for filtered gases.
  • There are plenty of free electrons as the electrodes are ionized which interact with the dust particles of the gas making them negatively charged. These particles move towards positive electrodes and fall off due to gravitational force.
  • Now the flue gas is free from the dust particles as it flows through the electrostatic precipitator and discharged to the atmosphere through the chimney.

Efficiency of Electrostatic Precipitator

Where,

  • η = Fractional collection efficiency
  • W = Terminal drift velocity in
  • A = Total collection area in
  • Q = Volumetric air flow rate in

Types of Electrostatic Precipitator

Following are the four types of ESPs

  • Plate precipitator
  • Dry electrostatic precipitator
  • Wet electrostatic precipitator
  • Tubular precipitator

Plate Precipitator

  • It is basic precipitator type that consists of rows of thin vertical wires and stack of vertically arranged large flat metal plates that are placed at a distance of 1 cm to 18 cm apart.
  • The air stream is passed horizontally through the vertical plates and then through the large stack of plates.
  • To ionize the particles, a negative voltage is applied between the wire and the plate.
  • These ionized particles are then diverted towards the grounded plates using electrostatic force.
  • As the particles get collected on the collection plate, they are removed from the air stream.

Dry Electrostatic Precipitator

  • It is used to collect pollutants like ash or cement in a dry state.
  • It consists of electrodes through which the ionized particles are made to flow through and a hopper through which the collected particles are extracted out.
  • The dust particles are collected from a stream of air by hammering the electrodes.

Wet Electrostatic Precipitator

  • It is used to remove resin, oil, tar, paint that is wet in nature.
  • It consists of collectors that are continuously sprayed with water making the collection of ionized particles from the sludge.
  • They are more efficient than dry ESPs.

Tubular Precipitator

  • It is a single-stage unit consisting of tubes with high voltage electrodes that are arranged parallel to each other such that they are running on their axis.
  • The arrangement of the tubes could either be circular or square or hexagonal honeycomb with gas either flowing upwards or downwards.
  • The gas is made to pass through all the tubes.

Advantages and Disadvantages

Advantages of Electrostatic Precipitator

  • The durability of the ESP is high
  • It can be used for the collection of both dry and wet impurities
  • It has low operating costs
  • The collection efficiency of the device is high even for small particles
  • It can handle large gas volumes and heavy dust loads at low pressures

Disadvantages of Electrostatic Precipitator

  • Can՚t be used for gaseous emissions
  • Space requirement is more
  • Capital investment is high
  • Not adaptable to change in operating conditions

Electrostatic Precipitator Applications

A few electrostatic precipitator applications are listed below:

  • Two-stage plate ESPs are used in the engine rooms of shipboard as the gearbox produces oil mist which is flammable in nature. The collected oil is reused in gear lubricating system.
  • Dry ESPs are used in thermal plants to clean the air in ventilation and air conditioning systems.
  • They find applications in the medical field for the removal of bacteria and fungus.
  • They are used in zirconium sand for detaching the rutile in plants.
  • They are used in metallurgical industries to clean the blast.

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