Sulfur Dioxide Control Technologies In Electric Power Plants

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Sulfur Dioxide Control TechnologiesIn Electric Power Plants

CCTR Basic Facts File #5Brian H. Bowen, Marty W. Irwin

The Energy Center at Discovery ParkPurdue University

CCTR, Potter Center, 500 Central DriveWest Lafayette, IN 47907-2022

http://www.purdue.edu/dp/energy/CCTR/Email: [email protected]

April 2007

Indiana Center for Coal Technology ResearchCCTR

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Source: http://www.fossil.energy.gov/programs/sequestration/publications/programplans/2006/2006_sequestration_roadmap.pdf

CCTR Indiana Center for Coal Technology Research

Roadmap Performance TargetBest technology Capability

Source: DOE EPRI CURC http://www netl doe gov/technologies/coalpower/cctc/ccpi/pubs/CCT Roadmap pdf

Total control & elimination of SO2 is on the roadmap for prevention of acid rain

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Sulfur in CoalsAlthough coal is primarily a mixture of carbon (black) & hydrogen (red) atoms, sulfur atoms (yellow) are also trapped in coal, primarily in two forms. In one form, the sulfur is a separate particle often linked with iron (green, pyritic sulfur) with no connection to the carbon atoms, as in the center of the drawing (fools gold). In the second form, sulfur is chemically bound to the carbon atoms (organic sulfur), such as in the upper left

Source: http://www fossil energy gov/education/energylessons/coal/coal cct2 html

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Amount of Sulfur in Coals

Source: “Expanding the Utilization of Indiana Coals”, http://discoverypark.purdue.edu/wps/portal/Energy/CCTR_Research

Indianaaveragesulfurcontent= 2.1%by weight

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Emission Control Strategies for Power Plants

Clean Air Act of 1970 established national standards to limit such pollutants as Sulfur Dioxide, SO2

1977 Amendment resulted in installation of SO2control technologies for coal-fired boilers

1990 Clean Air Act Amendments required further reductions in SO2 and NOx power plant emissions that contribute to acid rain

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Coal is being burned more cleanly today than ever before.Air pollution from coal is decreasing, while coal use is increasing. Coal-fired power plants in the U.S. have reduced their SO2 (Sulfur Dioxide) emission rate (lbs SO2/Ton coal burned) by 71% from 1976 to 1999

Coal Use & Reductionsin SO2 Emissions from Power Plants

Source: http://www.coaleducation.org/Ky_Coal_Facts/environment/air_quality.htm

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Indiana Coal-Fired Generation & Emissions

Indiana Emissions per MWh

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

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Met

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SO2

Nox

Source: http://www.eia.doe.gov/cneaf/electricity/epa/emission_state.xls

SO2 EmissionsTons/MWh

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SO2NOx

13 lbs SO2/MWh

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SO2 Emissions from Utilities by State in 2000 (Tons)

4th598,053WV

577,122TX2nd951,373PA1st1,232,450OH

5th585,141KY3rd878,196IN

437,593IL

SO2 RANK

SO2emissions

(Tons)

http://www.epa.gov/cleanenergy/egrid/index.htm

Sources: http://www.eia.doe.gov/cneaf/electricity/st_profiles/sep2004.pdfEPA eGRID2002 Version 2.01 State File,

2004 Indiana SO2 emissions from utilities = 797,000 Tons

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Methods of Controlling SO2From Coal-Fired Power Plants

Methods include:• Cleaning the coal to remove the sulfur• Switching to lower SO2 fuel• Purchasing SO2 allowances• Installing flue gas desulfurization systems, FGD

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Source: rgy.gov/programs/sequestration/publications/programplans/2006/2006_sequestration_roadmap.pdf

Clean Coal & Remove SO2

Coal washing involves grinding the coal into smaller pieces & passing it through a process called gravity separation. Technique involves feeding the coal into barrels containing a fluid that has a density which causes the coal to float, while unwanted material sinks & is removed from the fuel mix

http://news.bbc.co.uk/1/hi/sci/tech/4468076.stm

Coal washing removes 25%to 40% of the sulfur.Only the pyriticsulfur is washed out.Organic sulfurdoesn’t wash out

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Source: http://www.eia.doe.gov/cneaf/coal/statepro/imagemap/wy.htm

Switch to Lower SO2 Coal

Wyoming low sulfur coal- Massive increase in production over past 30 years as a result ofthe clean air legislation

Midwest utilities are importing western coals withtheir low sulfur content but transportations costsare increasing & extra railroad capacity is needed

What is the transportationcost ($/Ton mile)?

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SO2 Allowance Prices, $/Ton SO2

Source: Coal Age, February 2006, page 37

Emissions Trading (Cap and Trade) • An administrative approach used to control pollution by providing economic incentives for achieving reductions in emissions

Increasing SO2allowance prices

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Flue Gas Desulfurization Systems, FGD

FGD systems are normally known as wet scrubbers or dry scrubbers (defined according to the state of the by-product)

• Wet Scrubbers – Most common technology

Others (used to much lesser extent):• Spray dryers• Dry (sorbent) injection systems• Regenerable systems• Circulating fluid-bed & moving bed scrubbers• Combined SO2/NOx removable systems

Source: Bruce G. Miller, “Coal Energy Systems”, 2005

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Flue Gas Desulfurization, FGD since 1970s

FGD systems are used to remove SO2. "Wet scrubbers" are the most widespread method & can be up to 99% effective

A mixture of limestone and water is sprayed over the flue gas & this mixture reacts with the SO2 to form gypsum (a calcium sulphate), which is removed and used in the construction industry

Source: http://news.bbc.co.uk/1/hi/sci/tech/4468076.stm

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Duct Sorbent Injection

Duct Spray DryingSecond most used method – over 12,000MW of total capacity.Lime is usually the sorbent used. A slake-lime slurry is sprayedDirectly into the ductwork to remove SO2. Reaction products& fly ask are captured down-stream in the particulate removalDevice

Dry Sorbent Injection (in-duct dry injection)Hydrated lime is the sorbent typically used. It is injected eitherupstream or downstream of a flue gas humidification zone

Regenerative ProcessesRegenerate the alkaline reagent. Process is costly.

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Extent of Global SO2 Controlled Capacity on Power Plants (MW)

100,000**230,000*2000

75,000130,0001990

25,00030,0001980

NoneNone1970

USAWorldYear

* 87% are wet scrubbers** 10% of U.S. total 1,105,227MW (78% of MW are thermal)

Source: Bruce G. Miller, “Coal Energy Systems”, 2005

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Scrubber Capital Costs

Medium Removal Technology$50,000/MW, with 70% SO2 removal

High Removal Technology$250,000/MW, with 95% SO2 removal

< $150,000 /MW, SO2 emissions could be cut in half & mercury emissions could be reduced by >60%

Sources: http://www.epri.com/portfolio/product.aspx?id=2055http://www.paconsulting.com/news/by_pa/2004/Is+it+time+to+take+another+look+at+PRB+coal.htm

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Scrubbers on Indiana’s10 Largest Power Stations 2005

Source: http://www.ladco.org/reports/rpo/MWRPOprojects/Emissions/FinalReport_Methods.pdf

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Indiana’s 10 Largest Power Plants& Emission Controls (IDEM January 2007)

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U.S. Department of Energy (DOE)Carbon Sequestration Program

“To capture by 2012 fossil fuel conversion systems that offer 90% CO2 capture with 99% storage permanence at less than a 10% increase in the cost of energy services”


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2003 Actual SO21990 CAA phase IICAIR 2010CAIR 2015

SO2 Phase II Clean Air Act & Estimated CAIRAllowances on Indiana’s 10 Largest Power Stations

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EPRI 2007 Analysis ofScrubber Technologies

• Multipollutant capabilities of new SO2 control systems - will look at how well each system supports the co-capture & retention of Hg,reduction in opacity & PM2.5 emissions, & possible moderate removal of NOx, while providing reliable, high levels of SO2 removal

• Determine how FGD suppliers & architect/engineers are minimizing water consumption

• Provide a system that uses microchip-based sensors that could facilitate & expand FGD chemistry measurements

Source: http://www.epri.com/portfolio/product.aspx?id=2055

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Sulfur Dioxide Control Technologies In Electric Power Plants