Role of Coal in Modern Electricity Generation Systems

Role of Coal in Modern ElectricityRole of Coal in Modern ElectricityGeneration SystemsGeneration Systems

Energy and Environment Seminar SeriesEnergy and Environment Seminar Series

John KramlichJohn KramlichUW Mechanical EngineeringUW Mechanical Engineering

December 2, 2010December 2, 2010

US Energy Usage (Quads=E+15 BTU)

Coal

Total

Renewable

Nuclear

Natural Gas

Petroleum

TotalElectricityHeatingTransportation

US Energy Usage

Coal

Total

Renewable

Nuclear

Natural Gas

37.10.410.326.3Petroleum


US Energy Usage

Coal

Total

Renewable

Nuclear

23.86.916.20.7Natural Gas

37.10.410.326.3Petroleum


US Energy Usage

Coal

Total

Renewable

8.58.500Nuclear


37.10.410.326.3Petroleum


US Energy Usage

Coal

Total

7.74.12.70.8Renewable

8.58.500Nuclear


37.10.410.326.3Petroleum


US Energy Usage

22.520.51.80Coal

99.640.521.427.8Total

7.74.12.70.8Renewable

8.58.500Nuclear


37.10.410.326.3Petroleum


Historical Trends

US Energy Usage

20.5Coal

40.5Total

4.1Renewable

8.5Nuclear

6.9Natural Gas

0.4Petroleum


~1 cubickm/yr

ConventionalPower Plant

Air

Coal:100%

CO2

H2OSO2

NOParticles

~36%

~64%

Generator

Scrubber for SO2

Catalyst for NOElectrostatic Filter for Particles

Steam

Pump

CoolingWater

The AchillesHeel

• Huge thermodynamicirreversibility betweenflame and steam

• Option 1: Plug the holewith a new cycle

• Option 2: Move the steamcloser to the combustion

Research: Increasemaximum metalurgicaltemperature

Insert aSecond

Cycle

Insert aSecond

Cycle• Second cycle is

mercury

• More heat accepted athigher temperatures

• Several of these plantsbuilt and operated inthe 1930’s-1940’s

Still undermetallurgical limit

IncreaseSteam

Pressure• Supercritical Rankine

• Many new boilers todayResearch: Corrosionresistance at high T and30 MPa (300 atm)

Coal Composition

• C• H• O• N (~1%)• S (0.5-6%)• Main Minerals

• Trace Minerals

• CO2

• H2O

• N2 or NO• SO2

• Ash (Si, Fe, Na, K, Mg,Ca, Al)

• As, Se, Pb, etc., U, Hg

Environmental Cost Huge

Catalystfor NOcontrol

Ash Control SO2 Scrubber Hg Control

Scrubber cost at Centrailia:$200,000,000 for 1340 MW($149/kW)

Research: Economical andeffective Hg control

Mercury Problem

US Anthropogenic

159 tons/yr

US Coal52 tons/yr

• Original proposal: -38 tons by 2010 -18 tons by 2018• Vacated by court• New rule on the way

Environmental Fate

Emission at Surface

Elemental - Hg:• Lifetime: 0.5-1.5 years• Time to distribute worldwide

Oxidized - HgCl2:• Lifetime: hours• Falls in footprint downstream of source

Health Effects

• Water-soluble Hg to lakes• Bacteria convert oxidized Hg to

methylmercury (highly absorbable, fatsoluble, goes to brain)

• This biochains up to fish, which are themain path for human exposure

• Reference dose: 0.1 µg/kg body weight/day(0.18 g/lifetime)

State of the Art

FuelAir

1. All Hg in fuel is vaporized

2. All vaporized Hg is initially elemental

3. At furnace exit, oxidized vs. elemental varies.

4. Fraction captured is highly variable (5-95%). Correlates with oxidized, but with scatter. •Oxidized: >80% •Elemental: <30%Sc

rubb

er5. Spray dryer elemental: •~40% •With activated carbon /iodine: >90%6. Force oxidation ahead of scrubber (meets interim regulation)

Oxidation Reactor

Competition: Gas TurbinesAir Pump

Fuel

Burner Turbine

Generator

Hot Exhaust

Combined Cycle

Generator

Generator

GasTurbine

Generators recover ~58% of fuel energyLosses are ~42%No need for SO2, NO, particle cleanupStill make CO2

CO2

Hot Exhaust

NaturalGas

Air

~42%

Pump

CoolingWater

• Connects gas turbine andsteam together

• Each solves the othersproblems

• No environmental cleanupoften needed

Not as Simple as it Seems; But still, why not gas?

Coal is Cheaper, Gas is Unstable

2001

20052008

Coal=1.25 $/Million BtuCoal=2.5

Retail gasoline: $22.5/million Btu

Integrated Gasification Combined Cycle

Coal for Combined Cycles

Air AirSeperator Gasifier

N2

Coal

S, N2

O2

Water

Generator

Generator

GasTurbine

Hot Exhaust

COH2

FuelCleaning

Air

• Mass flow of air/products ~15x fuel flow

• Cleanup much easier on fuel stream than productgas

-Smaller equipment

-Larger driving forces for mass transfer

• Currently, fuel cooled to room temperature forcleaning

Integrated Gasification Combined Cycle

Coal for Combined Cycles

Air AirSeperator Gasifier

N2

Coal

S, N2

O2

Water

Generator

Generator

GasTurbine

Hot Exhaust

COH2

FuelCleaning

Air

• Fuel cooling a thermodynamic loss

• Research: Hot gas cleanup approaches

Remaining Losses

• In a well-optimized IGCC system, one of thelargest remaining thermodynamicirreversibilities is the combustor

• Approach is to replace the combustor withan adiabatic solid oxide fuel cell

Solid Oxide Cell System

Air

CO/H2

Compressor Turbine

To SteamCycle

Air

CO/H2

Compressor Turbine

To SteamCycle

Combustor Solid Oxide Fuel Cell

Electricity

Research: Lower T, lower cost SOFC

Mountaineer West Virginia1st Pilot Sequestration Plant

1.5% of Plant Output

Process Flow Chart

Spray Absorber

(NH4)2CO3 + CO2 + H2O -> 2(NH4)HCO3

Regeneration

2 (NH4)HCO3 -> (NH4)2CO3+ CO2+ H2O

Steam reverses the absorption reaction

Releases pure CO2 and H2O

CO2/H2O Compressor Station

Well InjectionPoint

• Water/CO2 mixpressurized to ~100 atm.

Injection to 8000 ft

Oxyfuel Alternative

• Must pay for air separation

• No need to process large gasflow through scrubber

Economics-New Capacity• Simple boiler, no environmental control: 2 ¢/kW-hr

• Coal supercritical: 10.5 ¢/kW-hr, 14 ¢/kW-hr with 90% carbon capture

• IGCC 11.5 ¢/kW-hr, with carbon capture 16 ¢/kW-hr

• Gas combined cycle 9 ¢/kW-hr

• Nuclear 12 ¢/kW-hr

• Solar tower 12, solar trough 20, PV 16-20 ¢/kW-hr

• Wind 6-11 ¢/kW-hr (including tax credits)

http://www.ethree.com/clientlist.html

http://bit.ly/Lazard2009

• Two years ago, people were looking at nuclear, supercritical Rankine coal

• Now they are looking again at gas. If gas prices stay down, this could be alonger term direction.

Role of Coal in Modern Electricity Generation Systems

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