1. Session 8 – Fossil Energy Systems
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Exploration, Discovery and Extraction
Transportation and Storage
Fossil Fuel Conversion
Fossil Fuel Combustion
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2. Exploration, Discovery and
Extraction
• Coal: extraction and transportation
• Petroleum: quest for deposits; improved
extraction
– Offshore: few feet in 70s to a mile or more
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3. Storage and Transport
Natural Gas
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Low density – less efficient to transport
Stored in caverns, depleted reservoirs (UG)
Mercaptan added as odorant; yellow pipe
Stored as LNG (above ground)
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Liquefaction at -163 °C; maintained at < 83°C
Cryogenic vessels and fixed tanks
1/614th the volume of gaseous form
Not explosive in liquid state
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7. Fossil Fuel Conversion Systems
Energy Flows
Stack Heat
Electrical Energy
Output
Fuel Input
Cooling
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8. Fossil Fuel Conversion Systems
Energy Flows for a 400 MWe Unit
•At 40% thermal efficiency, the
input energy is 1GWth
•For 90% efficient boiler,
100 MW goes up stack
•The remaining waste heat
requiring removal is 500 MW
Stack Heat
100 MW
400 MWe
1 GW
Fuel Input
Boiler
Turbine/
Env Generator
500 MW
Cooling
Note: Configuration of subsystems varies for gas-fired unit8
9. Fossil Fuel Conversion Systems
Energy Flows for a 400 MWe Unit
Daily Operation at 1 GW
requires 8.19 E10 Btu:
Stack Heat
100 MW
Natural Gas
81,900 MCF/day
or
Coal
3000 MT/day
or
Oil
400 MWe
14,600 barrels
per day
Boiler
Turbine/
Env Generator
500 MW
Cooling
Note: Configuration of subsystems varies for gas-fired unit9
Adapted from Krenz, Energy Conversion and Utilization, Allyn and Bacon, 1976
10. Fossil Fuel Conversion Systems
Energy Flows for a 400 MW Unit
Stack Heat
Electrical Energy
Output
Fuel Input
Turbine/
Generator
Cooling – 500 MW
Cooling Rate Required:
500 MW = 1.7 E9 Btu/h = 4.1 E10 Btu/day = 1.0 E13 cal/day waste heat
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11. Fossil Fuel Conversion Systems
Cooling Choices
Direct Condensing (Conduction)
Evaporative (Cooling Tower)
Natural Convection
Diagram of a typical water-cooled surface condenser
Requires nearby river or lake
If limit on ΔT= 10°C,
water req’d = (1E13 cal/day)/10°C
=1E9 kg water/day = 1E6 m3/day
= 264 million gallons/day
= 410 cubic feet per second
(The St. Louis River at Scanlon has
a 100-yr mean flow of 1060 cfs).
Forced Convection
For latent heat of evaporation of water
of 540 cal/g, and
Assuming 1E13 cal/day of cooling,
need 1.85 E10 grams of water/day
or ~ 5 million gallons/day
Direct – 264 E6 gal/day – water conserved
Evaporative – 5 E6 gal/day – water lost
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13. Synthetic Fuels
(Syn Fuels or Alternative Fuels)
• Alternative to Petroleum-derived fuels
– Interest proportional to fear of import disruption
– Attractive due to lower sulfur, carbon mgmt.
• Input: Coal, biomass, oil shale
• Output: Methane and other compounds
“Coal to gas”
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14. Syn Fuel Process
Coal Pyrolysis
Gas (H2, CH4, CO2, CO)
COAL
Heat w/o
O2
Liquids (Tar, Light Oils, Liquor)
Char (a solid, also called coke)
SynGas is the mixture of H2 and CO in different proportions, and serves
as a building block for other fuels, such as substitute diesel, gasoline and
hydrogen.
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15. Great Plains SynFuels Plant
Beulah, North Dakota
• Lignite coal input (6 million tons annually)
• 54 billion cubic feet of Natural Gas annually
(U.S. production= 19 trillion cf/yr)
• Subsidiary of Basic Electric Power Coop.
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16. Great Plains SynFuel Plant
Methanation: CO and CO2
reacts with H2 to form CH4
Byproducts Annually
•Anhydrous Ammonia 4E5 tons
•Acids for Manuf.
33E6 lbs
•Krypton, Xenon
3E6 liters
•Liquid Nitrogen
24E6 gal
•Naptha
7E6 gal
•Phenol
33E6 lbs
•CO2 for oil recovery 200E6
SCF/day
Graphic and data from Dakota
Gas Co. website,
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www.dakotagas.com
17. More Notes on Combustion
• Heat released used to combust more fuel
• Combustion dominates fossil fuel conversion
• Combustion dominates anthropogenic CO2 emissions to
atmosphere
• Combustion creates diverse pollutants
• Stationary technology well developed, controlled
• Revolutionary advances unlikely
• Combustion requires:
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Contact between fuel and oxidant molecules
Reactants must be heated to be able to react “fast enough”
Reaction must last “long enough” to allow complete reaction
Three T’s: turbulence, temperature, time
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18. Fuel Cells
• Hydrogen + Oxygen = electricity + water + heat
• Oxidation occurs, but not as fast as in combustion
• Why not directly convert chemical energy to electrical
energy (with up to 75% efficiency), than be limited by
thermodynamic conversion efficiencies of 35 to 40%?)
• Today’s technology most promising for vehicles
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19. Fuel Cells
• Zero Emission Vehicles (ZEVs) relied primarily on
batteries prior to 2003; then, litigation in California shifted
work to fuel cells; 5 of 6 automakers abandoned
batteries temporarily
• Today: fuel cells 20 times more costly than IC engine;
last three years, hydrogen storage problems, no stations
• Carmakers propose making 2500-5000 fc vehicles by
2014
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20. Fuel Cells
Basic fuel cell:
2H2(gas) + O2(gas)→ 2H2O
Separate into half reactions at each electrode:
H2 + 2OH- → 2H2O + 2e-Anode
O2 + 2H2O + 4e- → 4OH-
Cathode
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21. Sidebar: Anodes and Cathodes
• Anode: “ACID”: anode current into device
where “current” is always positive charge
flow
Cathode
(pos
Term)
Anode
(neg
Term)
Fuel Cell
(+) Cathode
(
+
)
D-cell
battery
(-) Cathode
Δ Diode
(+) Anode
(-) Anode
“Electrons always flow from anode to cathode outside the device, regardless
of device type”
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22. Fuel Cells
H2
O2
Supply H and O to cell
But need to separate gases, while
allowing movement of electrons
and ions between electrodes
Porous partition or membrane used
Hydrogen gives up electrons on the left (electrons flow out of cell),
making the left electrode the Anode
Hydrogen is oxidized at the Anode
On the right, the negatively charge ions (anions) that result from
the reduction of oxygen flow to the left (cathode to anode) through
the electrolyte and the membrane
The electrolyte conducts charged particles much larger than electrons,
and can be a liquid or solid. A “solute” that produces a conducting
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solution is an “electrolyte” (e.g., acids, sodium chloride)
23. Fuel Cells
Advantages
• Low maintenance, high reliability if stationary
• Low noise level, only emission is water
• Can stack and parallel cells for V and I
Disadvantages
• Poor voltage regulation (drops under load)
• Best for applications with steady loads
• High cost, durability in changing environments, weight
• Cost effectively supplying the hydrogen
• Matching rate of hydrogen supply to cell load
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