GOLD FILTERS FOR REMOVING MERCURY FROM COAL FIRED POWER PLANTS
Transcript of GOLD FILTERS FOR REMOVING MERCURY FROM COAL FIRED POWER PLANTS
GOLD FILTERS FOR REMOVING MERCURY
FROM COAL FIRED POWER PLANTS
Kumar Ganesan
Department of Environmental
Engineering
Overview
• Background on mercury regulations• General view of mercury at coal-fired power
plants• Current and proposed mercury control devices• Development of metallic filters
Overview• Laboratory Testing of
Filter
• Field Testing at a Power Plant Stack
• Designing of Pilot Scale System
Overview (cont.)
• Theoretical Evaluation
• Design Optimization
• Potential Commercial Applications
• Future Work
Project Focus
• The filter is designed to remove mercury vapor from coal-fired power plant flue gas
• This presentation highlights the work completed to date
Background• Coal contains low levels of mercury
that range from .010 to 3.5 ppmw.
• Coal is burned in approximately 1700 power plants in the US.
• EPA’s 1998 Air Toxics Report to Congress indicated that mercury posed the greatest concern of all the toxics emitted from power plants.
Background (cont)• The US EPA is planning regulations
for a 70-90% reduction in mercury emissions from power plants beginning 2007.
• Power plants emit 45 tons of mercury per year in the US.
• A major public health concern
Mercury Regulations
• Mercury is a leading concern among the air toxic metals in the 1990 Clean Air Act Amendments– Volatile, persistent, bioaccumulation of
methylmercury– Neurological health impacts
• Coal-fired power plants are #1 anthropogenic source of mercury in the U.S.
• In 2003 EPA proposed a rule requiring utilities to install controls known as “maximum achievable control technologies” (MACT) – 29% reduction of mercury by 2007
Mercury Regulations
• Proposed 2003 rule also established a market-based cap-and-trade program for new and existing coal-fired power plants– Each state allocated specific amounts of emission
“allowances” to be distributed to its utilities to cap mercury emissions
– Utilities may sell or bank excess emission allowances
– A cap of 15 tons will be set in 2018 (69% reduction)
Mercury and Coal-Fired Power Plants
• Largest single-known source of mercury in the US– 45 tons of mercury released annually (EPA 1999)– 1/3 of the total anthropogenic emission
Main Forms of Mercury in Flue Gas
• As elemental mercury vapor
• Oxidized mercury
• Particle bound mercury
Mercury and Coal
• Bituminous coals (Appalachian) have high mercury, chlorine, and sulfur contents resulting in a high percentage of mercury (II)
• Sub-bituminous (Western) and lignite coals have low mercury, chlorine, and sulfur contents resulting in a high percentage of elemental mercury
Mercury Removal by Exisiting Control Devices
• 40% of mercury from coal-fired power plants s– Wet scrubber (SO2 – removes oxidized mercury)– ESP/baghouse (particulate bound mercury)– Combustion residues (ash)
• Oxidized mercury can be controlled by a wet scrubber -- elemental mercury cannot
• No single best technology that can be broadly applied
Proposed Mercury Control Devices• Activated carbon injection
– Mercury adsorbs to the carbon and is collected by r baghouse
Proposed Mercury Control Devices
• Scrubbers– Oxidized mercury is water soluble– Oxidize elemental mercury to mercury (II)
• Mercury still present in the ash or sludge
Mercury and Gold
• Mercury has historically been used in gold/silver mining to extract precious metals from ore
– The chemistry and kinetics of the amalgamation process are not well understood
• Most mercury sensors consist of a gold trap
Development of Metallic Filters
• Copper mesh sponges plated with gold/silver• Laboratory Tests• Thermal desorption system for the filter• Perform field tests
INITIAL TESTS USINGGOLD FILTERS
• Testing Filter Removal Efficiency in the lab
• Field Testing for Real World Performance
Experimental Setup
• Expose filter to 20-30 ug/m3 at a flow rate of 5 L/min
• Tests with single filter and multiple filters
Results: Gold Filter EfficiencyMercury Removal Efficiency
0.0
50.0
100.0
150.0
200.0
250.0
Day 1 Day 2 Day 3 Day 4
6-10-04 to 6-30-04 (12 hour sample/day)
Hg
conc
entr
atio
n ug
/m3 &
Per
cent
Red
uctio
n
Inlet ug/m3 Outlet ug/m3 % reduction
Results: Gold Filter EfficiencyMercury Removal Efficiency
0.0
20.0
40.0
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Day 1 Day 2 Day 3 Day 4 Day 5
7-9-04 to 7-23-04 (12 hour/day)
Hg
conc
entr
atio
n ug
/m3 &
perc
ent r
educ
tion
Inlet ug/m3 Outlet ug/m3 % reduction
Field Measurements with Mercury Tracker-3000
Date Time Inlet ug/m3 Outlet ug/m3 % red9/21/04 4:15 PM 26.4 0.5 98.1
4:30 PM 9.3 0.3 96.8
5:00 PM 3.5 0.1 97.1
5:20 PM 9.6 0.2 97.99/22/04 10:35 AM 42.3 0.7 98.3
11:00 AM 47.3 1.1 97.7
Thermal Desorption of Metallic Filter
220 oF
175 oF
320 oF
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Time (hours)
Mer
cury
Rel
ease
d (u
g/m
3)Thermal Desorption of Gold Filter
Thermal Desorption of Silver Plated Filter
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20
40
60
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160
0:00:00 0:30:00 1:00:00 1:30:00 2:00:00 2:30:00 3:00:00 3:30:00 4:00:00
Time (hours)
Mer
cruy
Rel
ease
d (u
g/m
3 )
220oF
280oF
150 oF
Mercury Removal Efficiency of Gold and Silver Plated Filter After 1st Thermal Desorption
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100.00
0:00:00 6:00:00 12:00:00 18:00:00 24:00:00 30:00:00 36:00:00 42:00:00
Time (hours)
Mer
cury
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oval
Effi
cien
cy (%
)
Gold FilterSilver Filter
Mercury vapor concentrations were20 ug/m3 - 30 ug/m3
Mercury Removal Efficiency of Gold and Silver Plated Filter After 2nd Thermal Desorption
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0:00:00 6:00:00 12:00:00 18:00:00 24:00:00 30:00:00 36:00:00 42:00:00
Time (hours)
Mer
cury
Rem
oval
Effi
cien
cy (%
)
Gold FilterSilver Filter
Mercury vaporconcentrations were20 ug/m3 - 30ug/m3
Thermal Desorption Results
• Both the gold and silver filter show 90%+ mercury removal efficiency initially
• The gold filter’s duration at 90%+ efficiency was longer than silver (2.8 days versus 20 hours)
• Thermal desorption of the gold and silver filters occurs at low temperatures (150oF) with rapid desorption above 300oF
Current/Proposed Work
• Field testing with larger scale setup
• Optimize thermal desorption process
• Optimizing gold and silver plating thickness for cost effective efficiency
Conclusions• GOLD FILTERS WERE EFFECTVE IN
REMOVING MERCURY VAPOR (90%) IN THE LAB
• INITIAL FIELD TESTS WITH GOLD FILTERS SHOW SIMILAR RESULTS
• FIELD TESTING FOR ONE CONTINUOUS WEEK SHOWED OVER 90 % REMOVAL
• THIS MERCURY REMOVALSYSTEM IS PATENDED
Proposed Work
• Custom Made Filters
• Field Testing With Larger System
• Testing at Different Temperatures and
Relative Humidity
• Recovery of Mercury
ACKNOWLEDEMENTS
• DOE/CAST FOR FUNDING THE PROJECT
• Joey Philips, Graduate Student• Pete Knudsen, CAST project coordinator at
Montana Tech• MSE Inc for the mercury generator• PPL Montana for helping in power-plant tests
TECHNOLOGIES CURRENTLY EVALUATED
Pre-combustion and post-combustion technologies to remove mercury
Coal pre processing helps to reduce mercury in coal
Post-combustion technologies may meet the reduction requirements
POST-COMBUSTION TECHNOLOGIES
• Carbon Injection
• Using SCR/SNCR System with ESP/Scrubbers
• Selenium Filters
• Other Processes
MAIN DRAWBACKS
• Mercury is merely transferred to another phase
• Disposal of the waste may cause problems in the future
• Mercury can easily leach in the Hg+2 form than as elemental mercury
• Effectiveness depends on the type of coal
Mercury Removal Efficiency of Metallic Filter
Mercury vapor concentrations were 20 ug/m3 - 30 ug/m3
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100.00
0:00:00 12:00:00 24:00:00 36:00:00 48:00:00 60:00:00 72:00:00Time (hours)
Effic
ienc
y (%
)
Thermal Desorption of Metallic Filter
220 oF
175 oF
320 oF
0
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400
600
800
1000
0:00:00 3:00:00 6:00:00 9:00:00 12:00:00
Time (hours)
Mer
cury
Rel
ease
d (u
g/m
3)