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 Speciation Versus Coal Type

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

60.0

80.0

100.0

120.0

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

0

200

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)Thermal Desorption of Gold Filter

Thermal Desorption of Silver Plated Filter

0

20

40

60

80

100

120

140

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

50.00

60.00

70.00

80.00

90.00

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

Rem

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

50.00

60.00

70.00

80.00

90.00

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

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

THANK YOU FOR YOUR TIME

QUESTIONS ?

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

70.00

75.00

80.00

85.00

90.00

95.00

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

200

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)

Mercury Removal Efficiency of Metallic Filter After Thermal Desorption

Mercury vapor concentrations were 20ug/m3 - 30 ug/m3

65.00

70.00

75.00

80.00

85.00

90.00

95.00

100.00

0:00:00 6:00:00 12:00:00 18:00:00 24:00:00 30:00:00 36:00:00

Time (hours)

Effic

ienc

y (%

)