Role of Coal in Modern Electricity Generation Systems
Transcript of 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
TotalElectricityHeatingTransportation
US Energy Usage
Coal
Total
Renewable
Nuclear
23.86.916.20.7Natural Gas
37.10.410.326.3Petroleum
TotalElectricityHeatingTransportation
US Energy Usage
Coal
Total
Renewable
8.58.500Nuclear
23.86.916.20.7Natural Gas
37.10.410.326.3Petroleum
TotalElectricityHeatingTransportation
US Energy Usage
Coal
Total
7.74.12.70.8Renewable
8.58.500Nuclear
23.86.916.20.7Natural Gas
37.10.410.326.3Petroleum
TotalElectricityHeatingTransportation
US Energy Usage
22.520.51.80Coal
99.640.521.427.8Total
7.74.12.70.8Renewable
8.58.500Nuclear
23.86.916.20.7Natural Gas
37.10.410.326.3Petroleum
TotalElectricityHeatingTransportation
US Energy Usage
20.5Coal
40.5Total
4.1Renewable
8.5Nuclear
6.9Natural Gas
0.4Petroleum
TotalElectricityHeatingTransportation
~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• 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)
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
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
Regeneration
2 (NH4)HCO3 -> (NH4)2CO3+ CO2+ H2O
Steam reverses the absorption reaction
Releases pure CO2 and H2O
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.