2. Electrostatic precipitator
A device that removes suspended dust particles from a gas or exhaust by applying a high-voltage
electrostatic charge and collecting the particles on charged plates.
Figure 1:Electrostatic Precipitator at Chevron Pascagoula
Source: http://www.hamonusa.com/hrc/products/esp
3. Operating Principle
3) The charged particles
agglomerate on the collecting
plates where the charge bleeds off.
Rappers dislodge the agglomerated
particulate, which falls into the
collection hoppers for removal.
1) Particles suspended in a gas enter
the precipitator and pass through
ionized zones around the high voltage
discharge electrodes. The electrodes,
through a corona effect, emit
negatively charged ions into the gas
which travel to the grounded
collecting plates.
2) The ionized field around the
discharge electrodes charges the
particulate causing it to migrate
to the grounded surface of the
collecting plate.
4. Equation Designing used or ESPs
Cunningham correction factor
C= 1 +
2𝜆
𝑑
.(A1 + A2 .𝑒
−𝐴3.𝑑
𝜆 )
C is the correction factor
λ is the mean free path
d is the particle diameter
An are experimentally determined coefficients.
For air (Davies, 1945):
A1 = 1.257
A2 = 0.400
A3 = 0.55
Calculate the drift speed using the Cunningham Correction
Factor
Drift Speed
𝐷𝑟𝑖𝑓𝑡 𝑠𝑝𝑒𝑒𝑑 =𝑤𝑒=
𝐶𝑞𝐸
3𝜋𝜇𝑓𝑑𝑝
q = charge acquired by each particle
E = electrical field = voltage difference divided by
electrode-plate distance d
C = Cunningham slip factor (to be obtained from
formula
𝜇𝑓= fluid viscosity = 1.81 x 10-5 kg/m.s for air at
ambient temperature
𝑑𝑝 = particle diameter
5. Calculate the Efficiency of ESPs
Other Equations for Overall Collection Efficiency of
ESPs
𝜂 = 1 − exp(−
𝑤𝑒𝑊𝐿
𝑄
) = 1 − exp(−
𝑤𝑒𝐴
𝑄
)
where
A=WL is the collecting plate area.
𝜂 =
𝐴𝑚𝑜𝑢𝑛𝑡 𝑟𝑒𝑚𝑜𝑣𝑒𝑑
𝐴𝑚𝑜𝑢𝑛𝑡 𝑒𝑛𝑡𝑒𝑟𝑖𝑛𝑔
=
𝐶𝑖𝑛−𝐶𝑜𝑢𝑡
𝐶𝑖𝑛
=1−
𝐶𝑜𝑢𝑡
𝐶𝑖𝑛
= 1 − exp(−
𝑤𝑒𝐿
𝑈𝑑
)
𝐹𝑙𝑜𝑤 𝑠𝑝𝑒𝑒𝑑 = 𝑈 = 𝑄/𝑊𝑑
Source: http://engineering.dartmouth.edu/~d30345d/courses/engs3
7/esps.pdf
Source: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-
66322001000300010
7. Plate-Wire Precipitators
- gas flows between parallel
plates of sheet metal and high-
voltage metal wires
- suitable for handling large
volumes of gas
- Eg: cement kilns, incinerators,
boilers, cracking units
Flat Plate Precipitators
- For smaller precipitators
- increase average electric field
and provide additional
surface area
- less susceptible to back
corona but has higher
rapping losses
PLATE PRECIPITATORS
TUBULAR PRECIPITATORS
• tubes arranged as a circular, square, or hexagonal
honeycomb with gas flowing upwards or downwards
• designed as one-stage unit (all gas passes through the tube,
eliminating sneakage)
• used in applications involving wet or sticky particulate
Source: http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators
8. Single stage
use very high voltages to charge
particles
operate in parallel
incorporate charging and collection
together in the same stage
Two stage
operate in series
separate particle charging and
collection stages
more time for particle charging, less
susceptibility to back corona, and
economical construction for smaller
sizes
applied to submicron sources emitting
oil mists, smokes, fumes,
or other liquid aerosols
9. Dry ESPs Wet ESPs
capture particles in dry product
streams
strip wet (saturated) gas streams of
particles
use periodic rapping to separate the
accumulated dust
use water sprays to condition/trap
particles for collection
not suitable for submicron particulate
applications due to particle size,
resistivity
can remove very fine (submicron)
particulate that dry ESPs cannot
capture
Disadvantage:
- rapping will project some of these
particles (10-15 %) back into the gas
stream (known as reentrainment)
Disadvantages:
- costly because they incorporate water
and corrosive gases
- Particulate matter is collected as a
slurry instead of a dry solid (expensive
to handle and dispose)
10. USAGEEXAMPLES
Used in the desalination of crude oil by using a desalter.
- Desalination is necessary to avoid corrosion from acids formed by salts in downstream oil
refinement equipment.
The picture shown below is of a refinery boiler that has a wet electrostatic precipitator installed
for treatment of flue gas emissions.
Source: PPC Air Pollution Control,
Longview, TX
11. Used in a variety of industries for emission reduction of particles to control air pollution.
Two examples of precipitators used in particle emission reduction:
- dry electrostatic precipitator used in boiling and drying processes
Source: PPC Air Pollution Control, Longview, TX
12. - wet electrostatic precipitator used to treat fryer vent exhaust in the food processing industry.
Source: PPC Air Pollution Control, Longview, TX
