1. Electrostatic Precipitators (ESPs)
Applications for ESPs
Efficiency of ESPs
Estimating costs of ESPs

2. impaction
Brownian
Motion
(diffusion)
interception
Removal mechanisms for particles in a gas stream.
streamlines

3. General ESP thoughts ?? Dirty air flows into device and is ionized
Ionized air charges particles
Particles get collected on oppositely charged plates
Particles removed from plates ??
Mechanism=
ESP is the only pollution control device that works primarily on the particles and not on the gas stream.

4. Pictures of how they work
One stage esp (
Animation from
Two stage esp (

5. What happens to the collected particles??
Particles can be sprayed off
Particles can be rapped off
They can then either be disposed of or reclaimed.
For example, fly ash can be used in cement.

6. Advantages Disadvantages General ESP thoughts
High efficiency for even small particles
Low pressure drops even with high flow
Dry or wet collection
Wide range of temperature
Low operating costs
Disadvantages
Take up lots of space
High capital cost
Not flexible to change
May need a pre-cleaner at high concentrations…cyclone?

7. When would I use an ESP??? Size classification is not desired
High efficiency is required
Valuable material needs to be recovered
High flow rates need to be processed
Power plants
Cement plants
Paper mills
Steel foundries
Indoor air quality

8. ESP general design General Assumptions:
Particles move in x direction with velocity U with no x-dir mixing
Particles uniformly distributed in y and z directions
ESP electric fields are constant
Particles quickly attain terminal velocity (w)
No re-entrainment of collected particles
Collecting plates
Charging wires H U D L
Mass removed = -

9. Mass removed = [flux toward plate (y-dir)]*[area normal to flux]
w = the ‘drift’ velocity
Putting it all together: H w
Integrating:
Deutsch equation:

10. Calculating drift velocity
Force balance (surprise!)
External Force= qEco/mp
particle mass
charge
collecting field strength
permittivity
charging field strength
constant
W is sometimes referred to as the
“precipitation parameter or migration velocity”

11. It's not a perfect world Particles aren’t spherical
Fields aren’t uniform and neither is gas flow
Re-entrainment happens...
Instead of the theoretical drift velocity ‘w’, someone goes out and measures an effective drift velocity ‘we’.
Effective drift velocity is what’s plugged into the Deutsch Eqn.

12. How many plates??? n=number of actual plates
Ns=number of actual plates
n=5
Ns=3
N=n*Ns=15 = total number of plates
Where does ‘-1’ come from?
Collection area: A=Ap(n-1)Ns=Ap(N-Ns)
Ap=2LH
What is collection area in terms of L and H?

13. Just the facts, ma'am Negative or positively charged wires can be used
negative wires are generally more effective
negative wires produce more ozone than positive wires
Particle resistivity affects particle collectability.
Different materials have different resistivity.
SO2 can actually improve resistivity characteristics of particles! (very convenient!)

14. Costs for ESPs Capital Costs depend on total plate area ‘A’
Purchase price = aAb
a=962, b=0.628 for 10,000 ft2 < A < 50,000 ft2
a=962, b=0.628 for 50,000 ft2 < A < 100,000 ft2
Total delivered equipment cost (DEC)=1.18*(purchase price)
Installation
~2.2*DEC (Table 5.3 breaks the 2.2 into parts)
Operating Costs - depend on power consumption
Corona Power Pc = IcVavg=kAwe
Fan pulling the air through the plates (Chapter 8)