This document discusses tuning the electrical properties of powdered activated carbon (PAC) to improve electrostatic precipitator (ESP) performance when PAC is injected for mercury control. Volume resistivity testing of different PAC formulations found one formulation (γ-PAC) improved ESP collection efficiency by 1% and reduced mass penetration by 50% compared to fly ash alone. A novel resistivity test fixture was used to rapidly evaluate PAC formulations under temperature and humidity. Lab ESP tests showed preferential collection of particles depended on PAC formulation. Comparing initial and collected resistivities provided insight into how formulations enriched fly ash or PAC in the dust cake. Tuning PAC's electrical properties can optimize mercury capture and particulate matter collection in ESPs.

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Tuning Electronic Properties of
PAC for Enhanced Electrostatic
Precipitator Performance
EUEC – San Diego, CA
February 18, 2015
C8.1 HG Control & ESP
Herek L. Clack1, Eric M. Lee2
,
Chris Vizcaino3, Roger H. Cayton3 and Joe Wong3
1University of Michigan, Ann Arbor, MI
2Illinois Institute of Technology, Chicago, IL
3ADA-Carbon Solutions, Littleton, CO

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Challenges of Sorbent Injection for ESPs (1/2)
 Retrofitting Coal Fired Power Plants using Activated Carbon Injection (ACI)
upstream of ESPs is cost effective.
 Maximizing mercury adsorption capacity and maintaining ESP PM collection
efficiency are both important.
 Full-scale PAC injection testing at the Brayton, Meramec, Monroe, and
Pleasant Prairie sites did not negatively impact stack opacity1.
 However, at Conesville, testing of 18 different sorbents resulted in increased
ESP sparking, decreased ESP power, or increased opacity in most cases1.
____________________
1Clack, H.L. “Estimates of Increased Black Carbon Emissions from Electrostatic Precipitators during Powdered Activated Carbon Injection
for Mercury Emissions Control”. Environmental Science & Technology 46 (2012), pp. 7327–7333.

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Challenges of Sorbent Injection for ESPs (2/2)
 Stanton Unit 1: gas sampling particulate filters at ESP outlet darkened (may
have reflected load changes)1.
 Limestone Unit 1: roughly half of the particulate loading measurements (EPA
Method 17) taken during PAC injection exceeded baseline measurements
taken without PAC injection1.
 Lausche: observed opacity increases were highly dependent on particle size
and injection rate1.
• 20 μm MMD: 5% constant opacity for injection rates up to 8 lb/MMacf.
• 5 μm MMD: 9% opacity (nearly doubled) at 2.5 lb/MMacf.
• 1 μm MMD: 15-16% opacity (more than tripled) at 1.5 lb/MMacf.
____________________
1Clack, H.L. “Estimates of Increased Black Carbon Emissions from Electrostatic Precipitators during Powdered Activated Carbon Injection
for Mercury Emissions Control”. Environmental Science & Technology 46 (2012), pp. 7327–7333.

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Preferential PM Collection on ESP Discharge Electrode
 Our previous studies1,2 using a lab-scale ESP revealed effects of PAC on PM
collection:
• PAC alone collected on both collection and discharge electrodes.
• Fly ash (FA) alone (lignite and IL bit.) collected primarily on collection
electrode.
• FA + PAC admixtures collected 4-10% on discharge electrode, where PAC
concentration was enriched by up to 50% from inlet values.
 Question #1: How do PAC electrical properties affect FA + PAC collection?
 Question #2: How can PAC electrical properties be tuned for improved
collection of FA + PAC admixtures within ESPs.____________________
1Prabhu, V. et al. “Evidence of powdered activated carbon preferential collection and enrichment on electrostatic precipitator discharge
electrodes during sorbent injection for mercury emissions control”. Fuel Processing Technology 93 (2012), pp. 8-12.
2Prabhu, V., S. Lee, H.L. Clack. “Electrostatic Precipitation of Powdered Activated Carbon and Implications for Secondary Mercury
Adsorption within Electrostatic Precipitators”. Energy & Fuels 25 (2011), pp. 1010-1016.

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Volume Resistivity Testing, Inferred Differential Collection
 Volume resistivity of PM is important to ESP performance.
• Optimum PM collection and ESP rapping efficiency: 108 - 1013 ohm-cm.
• Fly ash: 1011 to 1013 ohm-cm, depending on composition, LOI.
• Conventional PAC: 104 ohm-cm.
• Using ACI, collected PM resistivity varies as particle size decreases and
as PAC concentration increases, and has different implications from
front to rear field.
 Volume resistivity conventionally measured after passive exposure &
conditioning of PM samples in controlled T/RH environmental chamber.
 For faster evaluation, developed a novel test fixture combining T & RH
conditioning with volume resistivity measurement.

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Volume Resistivity Test Set-up
• T = 102.5 ± 0.5 [oC]
• RH = 10.8 ± 0.6 [%]
(Downstream Sensor)
Desiccant Air Dryer
Heat Ropes
Distilled Water Impinger
Ceramic Air Heater
Resistivity Test Cell
T, RH
T, RH
Gravitational Water
Leveler
Powder
Sample

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Novel Flow Through Resistivity Test Fixture
 Low sheath flow (3 SCFH) to
prevent particle loss.
 Heated and moisturized air
diffused through powder
samples by a sintered filter
(0.5 μm).
 Powder sample compression
to minimize systematic
measurement error.
 E = 0.05 [kV/cm].

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Volume Resistivity Test Parameters
PRB FA enriched with 1% (by weight) PAC samples
• Baseline PAC - ε
• Treated PACs - α, β, γ, and δ
Resistivity data serves as baseline data for evaluating:
• Content of PAC within dustcake collected from an ESP.
• Potential for PAC and fly ash penetration through an ESP.

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Volume Resistivity: PAC Formulations a through e
 Volume resistivity measurements show differentiation between five PAC
formulations.
• Charge dissipation causes slow measurement creep
• Reported values at t = 60s (ref. IEEE 548 test method).
34500
87125
41000
55250 55250
0.0E+00
1.0E+04
2.0E+04
3.0E+04
4.0E+04
5.0E+04
6.0E+04
7.0E+04
8.0E+04
9.0E+04
1.0E+05
100% α 100% β 100% γ 100% δ 100% Ɛ
VolumeResistivity[ohm-cm]
0.0E+00
1.0E+04
2.0E+04
3.0E+04
4.0E+04
5.0E+04
6.0E+04
7.0E+04
8.0E+04
9.0E+04
1.0E+05
0 20 40 60 80
VolumeResistivity[ohm-cm]
Time [s]
100% α
100% β
100% γ
100% δ
100% Ɛ

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Volume Resistivity: 100% PAC vs. 1% PAC FA Admixture
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1.00E+11
1.00E+12
1.00E+13
1.00E+14
α β γ δ Ɛ 100% PRBVolumeResistivity[ohm-cm]
100% PAC 1% PAC + 99% FAPAC formulation ε added to
PRB yields resistivity similar to
PRB alone.
PAC formulations α, β, γ, δ
added to PRB variously
increase or decrease resistivity.
Suggest PAC formulations
selected to tune fly ash
resistivity for optimized
mercury capture and PM
collection.

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Lab-Scale Cylindrical ESP Test Set-up
Upper
Extension
Venting gap
 Voltage range: 0 to -25 kV.
 Upper extension acts as grounded
perf. plate, preventing particle loss
from EHD-induced reverse flow.
 Increased PM loading
compensated by increased
current.
 Gravity fed.
 Max. collection efficiency ~ 93%.
 Unavoidable fine particle loss
through ½” venting gap.

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Lab-Scale ESP Test Results: PRB FA+1% PAC (1/2)
 Collection bin contents:
coarse particles with high
terminal velocities.
 Discharge electrode: fine
particles (~ 0.06%).
 Collection electrode: majority
of collected PM.
 Calculated loss: remainder
needed to close mass balance,
mostly particle loss due to
EHD flows at inlet. 0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
1% α 1% β 1% γ 1% δ 1% ε PRB
MassRatio{%]
Calculated Loss
Collection Bin
Collection Electrode
Discharge Electrode

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Lab-Scale ESP Test Results: PRB FA+1% PAC (2/2)
 Admixtures with γ-
formulation: improved
collection by 1% and
reduced mass out by 50%,
compared to 100% PRB.
 Admixtures with α-, β-, δ-,
and ε-formulations:
decreased particle
collection and increased
penetration compared to
100% PRB.
85 86
90
86 84
89
9 8
3
9 9 6
6 6
7
5 6
5
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
1% α 1% β 1% γ 1% δ 1% ε PRB
MassRatio{%]
Calculated Loss
Collection Bin
Collection Electrode
Discharge Electrode

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Pre-/Post-Test Volume Resistivity Comparisons (1/2)
 Compares volume
resistivities of initial feed
and collection electrode
dustcake.
 Decreases imply PAC-
enrichment.
 Increases imply FA-
enrichment.
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
1.E+14
1% α 1% β 1% γ 1% δ 1% ε PRB
VolumeResistivity[ohm-cm]
Initial Collected

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Pre-/Post-Test Volume Resistivity Comparisons (2/2)
 100% PRB increase implies
other effects, e.g., exclusion
of coarsest particles.
 γ-, β-, δ-, and ε-admixtures
suggest PAC-enriched
dustcake.
 α-admixture suggests FA-
enriched dustcake.
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
1.E+14
1% α 1% β 1% γ 1% δ 1% ε PRB
VolumeResistivity[ohm-cm]
Initial Collected
+1471%
-7%
-7%
-94%
-50%
+350%

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Conclusions
 Volume resistivity used as experimental parameter in PAC
formulations to evaluate the impact of ACI on ESP performance.
 Used novel flow-through volume resistivity test fixture to measure
PAC formulations and their PRB FA admixtures under elevated
temperature and humidity.
 ESP differential collection test indicates different collection behaviors
as a function of different PAC formulations.
 Comparison of volume resistivities of initial feed and collected
dustcake provides insight into preferential collection behaviors.
 PAC development can incorporate tuning electrical properties to
achieve optimum mercury capture and PM collection in ESPs.
 γ-PAC: 1% improvement of collection efficiency and 50% reduction of
mass out, compared with PRB FA.

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Questions?
Herek L. Clack
University of Michigan
hclack@umich.edu
Eric Monsu Lee
Illinois Institute of Technology
elee11@iit.edu
Chris Vizcaino
ADA-Carbon Solutions
Chris.vizcaino@ada-cs.com
Roger H. Cayton
ADA-Carbon Solutions
Roger.cayton@ada-cs.com
Joe Wong
ADA-Carbon Solutions
joe.wong@ada-cs.com