Electrostatic Precipitator

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Electrostatic Precipitator

• By
• Anup Dutt Sharma (CH05B006)
• Mayank Shende (CH05B055)
• Srikanth (CH05B059)

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What is an ESP???

• An electrostatic precipitator (ESP), or
  electrostatic air cleaner is a particulate
  collection device that removes particles from a
  flowing gas (such as air) using the force of an
  induced electrostatic charge.
• Electrostatic precipitators are highly efficient
  filtration devices that minimally impede the flow
  of gases through the device, and can easily
  remove fine particulate matter such as dust and
  smoke from the air stream.

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Principle behind ESP

• Precipitators function by electrostatically
  charging the dust particles in the gas stream.
  The charged particles are then attracted to and
  deposited on plates or other collection devices.
  When enough dust has accumulated, the collectors
  are shaken to dislodge the dust, causing it to
  fall with the force of gravity to hoppers below.
  The dust is then removed by a conveyor system for
  disposal or recycling.

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Particles it can separate
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• Six activities typically take place
• Ionization - Charging of particles
• Migration - Transporting the charged particles to
  the collecting surfaces
• Collection - Precipitation of the charged
  particles onto the collecting surfaces
• Charge Dissipation - Neutralizing the charged
  particles on the collecting surfaces
• Particle Dislodging - Removing the particles from
  the collecting surface to the hopper
• Particle Removal - Conveying the particles from
  the hopper to a disposal point

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Most Basic-The Plate Precipitator

• The most basic precipitator contains a row of
  thin wires, and followed by a stack of large flat
  metal plates, with the plates typically spaced
  about 1 cm apart.
• If the applied voltage is high enough an
  electric discharge ionizes the air around the
  electrodes. Negative ions flow to the plates and
  charge the gas-flow particles.
• The ionized particles, following the negative
  electric field created by the power supply, move
  to the grounded plates.

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Components

• The major precipitator components that
  accomplish these activities are as follows
• Discharge Electrodes
• Collecting plates
• Power Supply and controls
• Rapping Systems
• Hoppers and Dust Handling
• Flue Gas Conditioning

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• Discharge Electrodes - Discharge electrodes emit
  charging current and provide voltage that
  generates an electrical field between the
  discharge electrodes and the collecting plates
• Power supply and controls - The power supply
  system is designed to provide voltage to the
  electrical field (or bus section) at the highest
  possible level.
• Rapping Systems - Rappers are time-controlled
  systems provided for removing dust from the
  collecting plates and the discharge electrodes
• Hoppers and Dust Handling - Precipitator hoppers
  are designed to completely discharge dust load on
  demand.

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Types of ESP

• Dry ESP
• They are employed on hot process
  exhausts(250-850F) that operate above the dew
  point of the gas stream.
• Wet ESP
• Wet ESP's are employed on exhausts that
  contain wet, sticky, tarry, tacky or oily
  particulates.
• Wet ESP uses a water flushing system to
  remove the particles from the collecting surface
  

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Parameters of operation

• Gas flow rate
• A precipitator operates best with a gas
  velocity of 3.5 - 5.5 ft/sec. At higher velocity,
  particle re-entrainment increases rapidly. If
  velocity is too low, performance may suffer from
  poor gas flow distribution or from particle
  dropout in the ductwork.
• Particle size
• .

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• Particle resistivity
• The higher the resistivity, the harder it is
  for a particle to transfer its electrical charge
  
• Gas temperature
• Change in temperature changes the electrical
  resistivity and also the choice of material for
  construction of the ESP.
• Interactions Particle size distribution and
  particle resistivity affect the cohesiveness of
  the layer of precipitated material on the
  collecting plates

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Design considerations

• Precipitator SizeWhen sizing the precipitator,
  it is important to provide a cross-section that
  will maintain an acceptable gas velocit
• Gas Velocity DistributionImproving gas velocity
  distribution in the precipitator reduces particle
  re-entrainment and boosts precipitator
  efficiency. Gas velocity distribution can be
  modified by using flow control devices and
  baffles
• Particle Re-entrainmentMinimizing re-entrainment
  of dust particles is important to improvement of
  precipitator efficiency.
• Corona Power
• An optimum amount of power should be supplied
  taking into consideration the cost factor and the
  required efficiency.

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Advantages

• Versatility-effective performance on a wide range
  of industrial processes
• Low pressure loss- typically less than 1 bar
• Designs can be produced to cover a temperature
  range from ambient up to 850C
• Low maintenance requirements
• Electrostatic Precipitator can be installed on
  any existing wet scrubber installation

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Disadvantages

• It cant be used with materials explosive in
  nature.
• Gases passing through ESP should not contain
  entrained droplets any other sticky material.
• It works best for particles having resistivity
  ranging between moderate levels(108 to 1010
  ohms-cm)
• During startup of the unit, warm exhaust gases
  enter the precipitator. This can cause the
  formation of water or water and acid droplets
  which could cause severe corrosion in the unit.
  (overcome by using a bypass)
• Toxic gases such as ozone and oxides of nitrogen
  may be produced by negatively charged discharge
  electrodes.

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Related Techniques

• Gravity Settling Chambers
• Baffle Chamber
• Mechanical Collectors
• Particulate Wet Scrubbers
• Cyclone Separators
• Fabric Filters
• Comparison Between ESP and Other Technique
• In a ESP the energy input works only on the
  paticles being collected but not on the entire
  gas stream as in other separators
• An ESP can handle input streams at a higher
  temperature.
• ESPs have higher efficiency as compared to any
  other collection devices.

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• ESPs can operate more range of particles than
  other separators.

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Cost comparison
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Bibliography

• Applied Electrostatic Precipitation By K. R.
  Parker
• www.neundorfer.com/support/knowledge-base.aspx
• www.ppcbio.com
• http//www.epa.gov/eogapti1/module6/matter/control
  /control.htmesptypes
• http//en.wikipedia.org/wiki/Electrostatic_precipi
  tator