Electrostatic Precipitators EP

1
Electrostatic Precipitators (EP)
2
Electrostatic Precipitators (EP)

• 1. High-voltage single-stage precipitators
  operate in the 30,000 to 100,000-V range and are
  used at large industrial plants such as
  coal-fired utility boilers
• 2. Low-m voltage precipitators have design
  capacities approaching 10 m3/s (20,000 ft3/s),
  with an air velocity of about 0.5 m3/s (100
  ft3/s)

3
(No Transcript)
4
Electrostatic Precipitators (EP)

• 3. Electrostatic precipitators are extremely
  efficient (99 or higher) for a wide range of
  particle sizes even sub-micron-size particles
• 4. Can handle large volumes of gas - 25 to 1000
  m3/s (50,000 to 2,000,000 ft3/s)
• have low pressure drops and operate continuously
  with little maintenance

5
Electrostatic Precipitators (EP)

• 5. The size-efficiency relationship for an
  electrostatic precipitator is a curvilinear
  function similar to that for a cyclone
• Efficiency 1- exp-(Aw/Q)
• A area of the collection plates, m2
• w drift velocity of the charged particles, m/s
• Q flow rate of the gas stream, m3/s

6
Principle of Operation

• (1) The removal of particles from a gas stream
  by an EP depends on the fact that charged
  particles in an electrostatic field will migrate
  towards regions of opposite polarity.
• (2) Uncharged particles entering the channels
  receive a charge (usually negative) from the
  electrodes or ionized gas and then move towards
  the walls of the channel which are earthed.

7
(No Transcript)
8
Principle of Operation

• (3) For effective dust removal, the voltage
  between the discharge electrode and collector
  plates must be sufficient to achieve a stable
  corona discharge but insufficient to cause
  excessive sparking.

9
Principle of Operation

• (4) The required treatment time in an EP, and
  consequently its size, depends directly on the
  required degree of cleansing of the gas and the
  physical properties of the dust.
• (5) Particles of the dust attracted to the
  earthed collector sheets form an agglomerated
  layer on the surface which must be periodically
  removed.

10
Method of cleaning

• Dry rapping
• Striking the surface of the collectors with a
  hammer device
• Continuous or periodic flushing with a liquid
  (normally water) which usually results in a
  slurry effluent

11
Resistivity

• Resistivity is a term that describes the
  resistance of the collected dust layer to the
  flow of electrical current.
• Between 104 and 107 ohm.cm -- low resistivity
• Between 107 and 1010 ohm.cm -- normal resistivity
• Above 1010 ohm.cm -- high resistivity

12
Specific collection area

• The specific collection area (SCA) is defined as
  the ratio of collection surface area to the gas
  flow rate into the collector
• SCA A / Q
• A Total collecting surface (sq. meter)
• Q Gas flow rate (cubic meter per hr)

13
Aspect ratio

• The aspect ratio (AR) is the ratio of the total
  length to height of the collector surface.
• AR effective length / effective height
• Have a EP many times larger in length than in
  height would be ideal. However, space limitations
  and cost could be prohibitive.