orgin of esp
TRANSCRIPT
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History of Electrical Precipitation
Date
1600
1745
1824
1878
1885
Significance
William Gilbert, English court physician, publishes De Magnete
Benjamin Franklin describes the effects of points in drawing
and throwing off the electric fire.
M. Hohlfeld, German mathematician, describes theprecipitation of fog in a jar containing an electrified point
R. Nahrwold notes that the discharge from an electrifiedsewing needle surrounded by a tin cylinder greatly increases
the collection of atmospheric dust. Nahrwold repeats theexperiment with a glycerin coating to help particles adhere.
Sir Oliver Lodge attempts, unsuccessfully, to remove leadfume from from a smelting works in North Wales
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History of Electrical Precipitation
Frederick Cottrell
Incorporated more reliable rectifier
transformer circuits in ESP design - able tosustain higher voltages
Successfully collected sulfuric acid mist in
Berkeley, CA laboratory in 1906
First successful commercial precipitator
used to collect H2SO4 in Pinole, CA
200 cfm capacity
1912, large scale ESP used to collect
cement kiln dust at 1,000,000 cfm in
Riverside CA
Frederick Cottrell1877 - 1948Source: U.S. Department of Agriculture
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Advantages to Electrical Precipitation
Electrostatic Precipitators (ESPs):- collect particles from 0.01 m to 100 m with 99% efficiency
- operate at high temperatures, up to 1200 F (650 C)
- operate at high gas pressures, up to 150 psi (10 atm)
- operate at high flow rates, up to 3,000,000 cfm (1500 m3/s)
- operate at high particle loadings, 500 grams/m3
- have low energy costs, 200 1000 Watts/1000cfm- have low pressure drop
ESPs can be used when:
- large volumes of particulate air pollutants are produced- no explosion hazard exists
- high efficiency needed
- continuous processes (expensive to build but inexpensive to operate)
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Industries and their pollutants
where ESPs are commonly used
Process Principal Material CollectedElectrical Utility Fly Ash (SiO2, Al2O, Fe2O3)
Industrial Boiler Houses Fly Ash
Steelmaking Furnaces Iron Oxide (Fe2O3)Cement Kilns Calcium Oxide, Silicon Oxide
Pulp and Paper Sodium Sulfate
Metal Machining Oil Mist
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Multi-stage wire-plate ESP
Gas inlet
Collected dust to hopper
Flow
straighteners
Collectionplates
Corona wire
electrodeswith rappers
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Electrical Precipitators in use
Wire plate type design
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Electrical Precipitators in use
Courtesy of Dr. Wayne T. Davis, Univ. of Tennessee
http://members.aol.com/apcutk/esp.htm
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Examples of discharge electrodes
Courtesy of Dr. Wayne T. Davis, Univ. of Tennessee
http://members.aol.com/apcutk/esp.htm
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Practical considerations:
Removing collected dust
Collected particles must be disposed of properly
Dust coated electrodes can- lower electric field strength
- increase likelihood of spark
- cause back corona
Result: Decreased collection efficiency
Methods used to clean collecting plates- Wire - cylinder design: washing
- Wire - plate design: rapping
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Practical considerations:
Removing collected dust: Rapping
Electrode rapping
Collecting plate rapping
Courtesy of Dr. Wayne T. Davis, Univ. of Tennessee
http://members.aol.com/apcutk/esp.htm
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Practical considerations:
Dust resistively
Highly insulated particles are poor conductors
Resistive to charging Not easily collected
Particle resistivity (-cm) related to: Elemental composition
Moisture content of air
Gas temperature
Above 1010-cm, particle collection becomes difficult
Conditioners Added to gas stream to increase particle conductivity
Examples include: H20, NH3, H2SO4
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Practical Considerations:
Particle re-entrainment
Re-entrainment occurs when collected particles arere-released into the air stream
Sources of re-entrainment:
Highly turbulent flow velocity concentration
Rapping observed as puffs exiting the precipitator
Back corona
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Take 5!
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Personal ESP sampler developed at UNC
+
dc power
corona collection
substrate
inlet
ionizing wire
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ESP sampler current-voltage characteristics
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7
Voltage, kV
Curre
nt,A
10 mil #1
10 mil #2
10 mil #3
Current ~ ion concentration, NiVoltage ~ electric field strength, E
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Ozone output vs. ESP power
0
100
200
300
400
500
600
0 500 1000 1500 2000
Power, mW
Ozone,ppb
20 mil #1
10 mil #1
20 mil #2
10 mil #2
20 mil #3
10 mil #3
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ESP collection efficiency vs. flow
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
0.01 0.1 1 10
Particle Diameter, microns
Collection
Efficiency
2.04.0
6.0
8.0
Flow, Lpm
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Review: Semi-Volatile Compounds
10-8 torr < vapor pressure < 10-2 torr
Semi-volatile aerosols:- exist in both particle and vapor phases
- can readily transfer mass between phases
- important for exposure health effect studies
- lung deposition behavior- atmospheric transport
- emission regulations
evaporation
particle
phase
adsorption/
absorption
vapor phase
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Filters cannot sample semi-volatile mists accurately
Metalworking fluids aresemi-volatile
Particles evaporatefrom filter over time
Underestimation of
worker exposure
Mist Vapor loss
Filter
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ESP Advantages, Disadvantages
Advantages
Collection substrate has low surface area lower vapor adsorption artifact
Collected particles coalesce together
less potential for particle evaporation artifact
Disadvantages
Corona discharge generates O3 some potential for chemical artifact
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Comparison of sampling methods for mineral oil mist
PVC PTFE GF ESP DataRAM DustTRAK
0.0
0.2
0.4
0.6
0.8
1.0
Mis t
Con
cent r
atio
n,mg
/m
filters
optical particle counters
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Sampling semi-volatile aerosols
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Sampling semi-volatile aerosols
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Sampling semi-volatile aerosols