Orgin of Esp

8/12/2019 Orgin of Esp

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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




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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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Removing collected dust: Rapping

Electrode rapping

Collecting plate rapping




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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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