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Sampling methods using sorbent traps have been used extensively over the past 20 years for speciating mercury in flue gas. The Flue Gas Adsorbent Mercury Speciation (FAMS) method is an example. This method has gained widespread acceptance as the preferred alternative for mercury speciation due to its simplicity, sensitivity, and repeatability. However, FAMS and other sorbent trap methods were developed primarily for measurements made in the relatively clean, dry, and cool flue gas present downstream of the particulate control devices. Application of sorbent traps to measure mercury in the high temperatures and high particulate loadings that exist upstream of the APC system or the saturated drop-laden gas downstream of FGD requires modifications to the approach. This presentation addresses the use of sorbent traps to speciate mercury throughout the air pollution control system of a coal-fired utility. Specific sampling approaches to accommodate testing at high temperatures, high dust loadings, and saturated gas streams are discussed. Data are presented for measurements made from points ranging from near the exit of the boiler to the outlet of a wet scrubber. We discuss the interpretation of the results and examine metrics used to assess data quality.
Citation preview
Mercury Speciation Measurements from
Boiler to Stack
Presented by Clean Air Engineering
There is a growing need to measure speciatedmercury throughout air pollution control systems at coal-fired power plants.
There are two major drivers for this…
Emissions Standards for Boilers and Process Heaters and Commercial/Industrial Solid Waste Incinerators
Emissions Standards for Boilers and Process Heaters and Commercial/Industrial Solid Waste Incinerators
aka, the Boiler MACT
National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units
And
National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units
And
aka, the EGU MATS
Both of these rules require reductions in mercury emissions
So-called “co-benefit” control from existing air pollution control devices is one approach to reduce mercury emitted to the atmosphere
Another would be add-on controls, such as sorbent injection
APHFGD
ESP/FFSCR
Boiler
Hg0
Hg0
Hg+2
HgP
Hg0
Hg+2
HgP
Hg0
Hg+2
HgP Hg+2
Hg0
Hg+2
Hg0
Hg+2
Sorbent SorbentSorbentSorbent
700˚F + 130˚F +Flue Gas Temperature
Sorbent
Consequently, there is much interest in the fate of mercury across the various air pollution control systems of power plants
Co-benefit and add-on controls generally rely on operational measures to…
• Promote oxidation of Hg0 to Hg+2
• Promote adsorption of Hg onto particles
To understand these relationships requires knowledge of the different species of mercury throughout the APC system…
i.e., from boiler to stack
This is difficult thing to model…
It relies on a variety of factors…
Such as…
– coal
– ash
– flue gas temperature
– flue gas chemistry
– retention time in APCDs
– scrubber chemistry
– boiler operation
And previous efforts to measure it have been handicapped by a lack of standardization in the test methods
Not to mention the characteristics of the flue gas being measured…hot, dirty, interferences such as NH3, HBr, etc.
The traditional test method to measure speciated mercury is the Ontario Hydro Method(ASTM D6784)
It looks like this schematically
This method has a reputation of being cumbersome and difficult to reproduce...
And there is a known issue with mercury partitioning in the particulate fraction…
And it takes several hours to perform. The cost of data is relatively high.
All of which has led to the prevalence of using Sorbent
Trap Methods to measure Hg
EPA Method 30B is the sorbent trap
reference method
Method 30B
Spiked
Section 1 Section 2
Method 30B does not speciate Hg. For that, we turn to the FAMS approach (aka, Modified Method 30B)…
FAMS Method
Potassium Chloride
Potassium Chloride
Activated Carbon
Activated Carbon
PM FilterGas Flow
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Section 2 Section 3 Section 4 Section 5
Oxidized Mercury Section (S1-S3)
AGS
Glass Wool Plug
Section 1
Elemental Mercury Section (S4-S5)Particulate Mercury(semi-quantitative)
Hg0Hg+2
HgP
FAMS has its limitations though…
You can measure particulate-bound mercury with FAMS…
…by adding a filter ahead of the traps.
Filter KCl Trap Carbon Trap
But there is a problem with this when used upstream of particulate control.
Unless the duct is traversed and sampling is performed isokinetically, particle size variation will bias the particulate collected.
Does the particulate captured from this location using only one test port mean anything?
Does the particulate captured from this location using only one test port mean anything?
Probably not!
Does the particulate captured from this location using only one test port mean anything?
Probably not!
But often, that is the approach taken.
There are other limitations to FAMS, such as temperature…
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
The carbon should not exceed about 450°F
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
The KCl should stay below 250°F
There are also known flue gas matrix interferences…
Speciation TrapsLimitations
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
Such as NO/SO2 oxidation effects
NO + SO2 → NO2
Hg0 + NO2 → Hg2+
This is mitigated by the addition of an acid gas scrubber (AGS) ahead of the sorbents…
But do we know how the AGS affects speciation? The assumption is that only oxidized mercury collects on it. Is that true? Does the AGS promote any conversion?
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
And then there are the interactions between mercury, flue gas, and particulate that collects on the pre-filter…
For example…
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
Species Flyash Effects:
HgP Increase from adsorption of Hg2+ and Hg0
Hg2+ Increase from catalytic oxidation of Hg0
Hg0 Loss through adsorption
SO3
HClNOx
LOIIron{
And the location of the filter also has an effectns
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
Species Flyash Effects:
HgP Increase from adsorption of Hg2+ and Hg0
Hg2+ Increase from catalytic oxidation of Hg0
Hg0 Loss through adsorption
In hot gases, being at the front can reduce these impacts.
Section 1 Section 2 Section 3 Section 4Section 5
PM Filter KCl CarbonAGS
Species Flyash Effects:
HgP Increase from adsorption of Hg2+ and Hg0
Hg2+ Increase from catalytic oxidation of Hg0
Hg0 Loss through adsorption
And the location of the filter also has an effect
To combat the temperature limitations, some tests have been done with the traps located outside of the hot flue gas…
Like this...
Temperature controlled
box
300-700°F 250°F
APHFGD
ESPSCR
Sometimes this data does not make sense.
Location HgP
Hg+2
Hg0
HgT
Hgvap
Run 1 SCR Inlet 1% 11% 7% 9% 9%
AH Inlet 25% 21% 88% 19% 19%
ESP Inlet 79% 44% 30% 13% 23%
WFGD Inlet 35% 6% 17% 6% 7%
Stack 15% 12% 20% 17% 18%
Run 2 SCR Inlet 66% 2% 42% 4% 5%
AH Inlet 32% 8% 2% 5% 8%
ESP Inlet 86% 8% 42% 6% 11%
WFGD Inlet 4% 1% 76% 3% 3%
Stack 5% 13% 12% 5% 5%
Run 3 SCR Inlet 44% 1% 54% 3% 4%
AH Inlet 22% 12% 2% 12% 12%
ESP Inlet 90% 43% 9% 24% 35%
WFGD Inlet 59% 4% 1% 3% 4%
Stack 1% 65% 2% 6% 6%
Relative Deviation
Paired Trap Agreement (%RD)
And paired trap agreement is poor
HgP
Hg0
Hg+2
The problem is that mercury will re-partition and convert as it traverses the temperature gradient of the probe.
And what you collect in the cool traps is different than what was in the gas stream.
HgP
Hg0
Hg+2
HgP
Hg0
Hg+2
Problem Statement
So we need to design a sorbent trap probe to allow Hg speciation measurements in flue gas with:
– high dust
– high temperature
– reactive interferences
A solution is to filter hot, shorten the gas path prior to adsorption, and cool the traps in-situ.
Here is one way…
a Forced-Air Cooled Probe
300-700°F
And take some additional measures…
Minimize test duration
TemperatureTest Duration
↑
↑↓
Particulate
Minimize sample flow rate
TemperatureSample Rate
↑
↑↓
Particulate
Move pre-filter up front
Potassium Chloride
Potassium Chloride
Activated Carbon
Activated Carbon
PM FilterGas Flow
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Section 2 Section 3 Section 4 Section 5
Oxidized Mercury Section (S1-S3)
AGS
Glass Wool Plug
Section 1
Elemental Mercury Section (S4-S5)Particulate Mercury(semi-quantitative)
Add a dust shield
Also…
Placement of trap thermocouples is critical
Potassium Chloride
Potassium Chloride
Activated Carbon
Activated Carbon
PM FilterGas Flow
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Section 2 Section 3 Section 4 Section 5
Oxidized Mercury Section (S1-S3)
AGS
Glass Wool Plug
Section 1
Elemental Mercury Section (S4-S5)Particulate Mercury(semi-quantitative)
And…
Strict QA/QC is critical
Potassium Chloride
Potassium Chloride
Activated Carbon
Activated Carbon
PM FilterGas Flow
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Section 2 Section 3 Section 4 Section 5
Oxidized Mercury Section (S1-S3)
AGS
Glass Wool Plug
Section 1
Elemental Mercury Section (S4-S5)Particulate Mercury(semi-quantitative)
You cannot waive your hands at QA/QC for FAMS. Just as in 30B…
If the goal is to measure speciated mercury, PAIRED FAMS traps should be collected…
Common industry practice of pairing a total trap with a FAMS trap does not give adequate QC metrics.
These are important QC metrics for each species measured.
• Relative Deviation
• Breakthrough
• Spike Recovery
Our recommendations…
QA/QC
Specification
Applicable
Sample
Fraction Acceptance Criteria Frequency
Consequences if
Not Met
Paired sorbent
trap agreement
HgP None N/A N/A
Hg+2 ≤15% RD if Hg+2>1 μg/dscm, ≤25% RD or
≤0.25 μg/dscm absolute difference if
Hg+2≤1 μg/dscm
Every run Invalidate run for
Hg+2
Hg0 ≤10% RD if Hg0>1 μg/dscm, ≤20% RD or
≤0.2 μg/dscm absolute difference if Hg0≤1
μg/dscm
Every run Invalidate run for
Hg0
Hgvap
HgT
≤10% RD if Hgi>1 μg/dscm, ≤20% RD or
≤0.2 μg/dscm absolute difference if Hgi≤1
μg/dscm
Every run Invalidate run for
HgT or Hgvap
Paired Trap Agreement (%RD)
Breakthrough & Spike Recovery
QA/QC Specification
Applicable
Sample
Fraction Acceptance Criteria Frequency
Consequences if Not
Met
Oxidized
Breakthrough
(KCl sections)
Hg+2 Section 3 KCl contains ≤10% of
the Section 1 and 2 masses if
Hg+2>1 μg/dscm, Section 3
contains ≤20% of the Section 1
and 2 masses if Hg+2≤1 μg/dscm
Every trap Invalidate trap data for
Hg+2 and Hg0
Elemental
Breakthrough
(carbon sections)
Hg0 Section 2 carbon contains ≤10%
of the Section 1 mass if Hg0>1
μg/dscm, Section 2 contains ≤20%
of the Section 1 mass if Hg0≤1
μg/dscm,
Every trap Invalidate trap for Hg0,
HgT, and Hgvap
Field Recovery Test Hg0 Average recovery between 85%
and 115% for Hg0
Minimum three
spikes per
program
Flag data
Following these measures, good data that makes sense can be obtained…
APHFGD
ESPSCR
Location HgP
Hg+2
Hg0
HgT
Hgvap
Run 1 SCR Inlet 2% 20% 7% 1% 1%
AH Inlet 1% 1% 3% 0% 0%
ESP Inlet 5% 0% 1% 0% 0%
WFGD Inlet 1% 1% 7% 1% 1%
Stack 13% 8% 6% 3% 5%
Run 2 SCR Inlet 1% 6% 3% 4% 4%
AH Inlet 0% 2% 6% 0% 0%
ESP Inlet 27% 1% 6% 1% 2%
WFGD Inlet 1% 2% 2% 3% 3%
Stack 8% 32% 3% 6% 6%
Run 3 SCR Inlet 0% 4% 0% 1% 1%
AH Inlet 1% 5% 11% 1% 1%
ESP Inlet 3% 0% 9% 0% 0%
WFGD Inlet 0% 1% 27% 2% 2%
Stack 3% 1% 8% 6% 8%
Relative Deviation
Paired Trap Agreement (%RD)
Breakthrough
Location Trap A Trap B Trap A Trap B
Run 1 SCR Inlet 0% 0% 0% 2%
AH Inlet 0% 1% 7% 0%
ESP Inlet 0% 0% 0% 0%
WFGD Inlet 0% 0% 0% 0%
Stack 0% 0% 8% 0%
Run 2 SCR Inlet 0% 0% 0% 0%
AH Inlet 0% 0% 0% 0%
ESP Inlet 0% 0% 0% 0%
WFGD Inlet 0% 0% 0% 0%
Stack 0% 0% 0% 0%
Run 3 SCR Inlet 0% 0% 5% 2%
AH Inlet 2% 0% 0% 0%
ESP Inlet 0% 0% 29% 0%
WFGD Inlet 0% 0% 0% 37%
Stack 0% 0% 15% 0%
Breakthrough
Hg+2
Fraction Hg0 Fraction
10% maximum (20% at stack) targeted acceptance limit
Spike Recovery (Hg0)
Location Run 1 Run 2
SCR Inlet 110.8% 87.7%
AH Inlet 93.6% 113.6%
ESP Inlet 101.4% 111.9%
WFGD Inlet 108.0% 101.5%
Stack 103.2% 100.1%
Program Average 103.4% 102.9%
85% - 115% targeted acceptance range
The take-away…FAMS has potential, but standardization of a FAMS protocol is needed to ensure good results across the industry.
There may be better alternatives…
Source: Apogee Scientific, Inc.
An Inertial Probe removes particulate without filtration
Source: Apogee Scientific, Inc.
A sorbent trap placed downstream of the inertial probe should not suffer from filtration effects
This approach needs more work to determine its viability.
What about Bromine?
Potassium Chloride
Potassium Chloride
Activated Carbon
Activated CarbonGas Flow
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Section 2 Section 3 Section 4 Section 5
AGS
Glass Wool Plug
Section 1
1.8ng2.0ng ND
7.6ng ND
Here are data from a trap downstream of a wet scrubber with brominated PAC added upstream
Not much mercury anywhere…
Potassium Chloride
Potassium Chloride
Activated Carbon
Activated CarbonGas Flow
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Glass Wool Plug
Section 2 Section 3 Section 4 Section 5
AGS
Glass Wool Plug
Section 1
1.8ng2.0ng ND
7.6ng ND
Here are data from a trap downstream of a wet scrubber with brominated PAC added upstream
Not much mercury anywhere…except in the prefilter
AGS
13.9ng
Bromine creates a problem for speciation, with or without particulate matter present.
A mercury monitor may be a solution
Source: Ohio Lumex Co.Source:ADA-ES, Inc.
Mercury AnalyzerConvertor
Scrubber
Hg0 + Hg+2
Hg0Hg+2→ Hg0
Hg CEMS measure Total Vapor-Phase Mercury downstream of the convertor
Hg0 + Hg+2
Mercury AnalyzerConvertor
Scrubber
Hg0Hg+2→ Hg0
Hg+2
Hg0Hg0 + Hg+2
Or elemental mercury if the convertor is bypassed and the gas is scrubbed
Hg0 + Hg+2
Mercury AnalyzerConvertor
Scrubber
Hg0Hg+2→ Hg0
Hg+2
Hg0Hg0 + Hg+2
Oxidized Mercury is the difference in the two configurations
Hgtotal
Hg+2
Hg0
0
0.2
0.4
0.6
0.8
1
1.2
1.46
:24
7:2
4
8:2
4
9:2
4
10
:24
11
:26
12
:25
13
:25
14
:26
15
:26
16
:27
17
:27
18
:23
Time
Co
nc
. u
g/m
3
Hg-Elemental Hg-Oxidized Hg-Total
Summary
• Mercury speciation measurements are crucial 1st step in compliance strategy
• FAMS is practical method of choice
Summary
• Mercury speciation measurements are crucial 1st step in compliance strategy
• FAMS is practical method of choice
but…
• Temperature and particulate effects must be minimized to prevent speciation bias
• Rigorous QA/QC needs to be imposed
• Industry standardization needed
And…
• There’s more than one way to skin a cat…different forms of filtration and mercury CEMS need consideration.
For more information on measuring mercury and fate-of-
mercury balances, contact CleanAir today.800-991-3300
contact@cleanair.com
Thanks!
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