1. Pulverized Coal Combustion
Particulates and NOx

2. Coal as a Fuel
Advantages
Disadvantages

3. Coal as a Fuel Primary Advantages Primary Disadvantages
High Energy Density
Widely Available Globally
Inexpensive
Easily Transported
Easily Stored On-Site
Good Choice for Baseload Generation
Contaminants
Mineral Matter
Sulfur
Nitrogen
Trace Elements
CO2
Focus of Technology Development

4. Early Air Pollution in England
In 1306, to clean up London's air, King Edward I, outlawed coal burning exclaiming "…whosoever shall be found guilty of burning coal shall suffer the loss of his head."
After deforestation, rather than freeze and starve, people began burning c0al again.
In 1590, Queen Elizabeth bans burning coal again, without the death penalty

5. Addressing Pollutants
1930’s: soot and smoke (dirtied cities)
Taller stacks
1960’s: partial combustion products, fly ash
Precipitators, scrubbers
1980’s: SOx
Phase 1: Low sulfur coal,
Phase 2: Scrubbers
1990’s: NOx,
Phase 1: Low NOx burners, over-fire air, gas recirculation
Phase 2: Selective Catalytic Reduction, Non-Catalytic Reduction
2000: Mercury
Scrubbers, Activated Carbon Injection (ACI)
2010’s CO2 ?

6. Pollution Abatement Pollutant Technology Consequence Industry Response
Ash Particulates
Mechanical capture
Increased solid waste
Utilization of ash
SOx
Scrubbers
Utilization of scrubber byproduct
NOx
Low NOx Burners, SCR, SNCR
Increased carbon content in ash
Beneficiation of ash to remove carbon
Mercury
Scrubbers, ACI
CO2
Capture: Scrubbers
Storage: underground injection?
Significant energy penalty (30%)
Water displacement
R&D to improve efficiency ?
Reduced emissions (i.e. cleaner air) Increased solid & liquid waste

7. World’s Tallest Stacks
2nd
GRES-2 Power Plant,
Ekibastuz, Kazakhstan
1377 ft
Inco Superstack at the Inco Copper Cliff smelter,
Sudbury, Ontario
1277 ft

8. Electrostatic Precipitators (ESPs)

9. ESP
Applicable boiler sizes: 25 MW to 1300 MW.
Source: babcock.com

11. ESP Performance Normally applied in several stages (2 to 4)
to maximize collection efficiency
Source: EPA

12. Baghouse
limited by operating temperature
Source: pcsesp.com

13. Fly Ash Collection
Fly Ash Silo

14. Burner Designs Original Recent Past Current
Sources: Babcock and Wilcox
Unizar

15. Principle of Low NOx Burners
Fuel and air mixed at an angle
Suppression of fuel and air in initial combustion stage
Fuel not burned initially mixes with air not used initially
Higher temp region cannot develop
Lower flame temp and local oxygen partial pressure

16. Low NOx Burners

17. Comparison of Flames Decreasing NOx HT-NR HT-NR2 HT-NR3
Stable, brilliant flame
Higher NOx
Lower Combustion Efficiency
Wider, shorter flame
Lower NOx
Higher Combustion Efficiency
Source:

18. Nitrogen Oxides (NOx) Contribute to acid rain
Can also form ozone and reduce visibility
Formed from 2 sources
fuel
combustion air
Initial control (late 70’s) was staged combustion
Fire in stages
Restrict oxygen where temp. is highest
Led to low NOx burners
Installed at 75% of large coal plants
Typical NOx reductions of 40 to 60%
Source:

19. Selective Non-Catalytic Reduction (SNCR)
Post combustion process
Lower temperature required
Typically at top of boiler by-pass
Nitrogen-based reagent injected
Typically urea or ammonia
NOx converted to N2 and H2O
Typical NOx reductions of 35-50%

20. Selective Catalytic Reduction (SCR)
Source: procom.kaist.ac.kr

21. SCR Reactor

22. Reaction Mechanism in SCR Reactor
Selective Reactions
6NO + 4NH3 → 5N2 + 6H2O
4NO + 4NH3 + O2 → 4N2 + 6H2O
6NO2 + 8NH3 → 7N2 + 12H2O
2NO2 + 4NH3 + O2 → 3N2 +6H2O
NO + NO2 + 2NH3 → 2N2 + 3H2O
Non-selective Reactions
2NH3 + 2O2 → N2O + 3H2O
4NH3 + 3O2 → 2N2 + 6H2O
4NH3 + 5O2→ 4NO + 6H2O

24. Global NOx Concentrations

26. NOx is a precursor to acid rain (HNO3) and ozone (O3)

28. SO2 Combines with water vapor to form dilute acid Sulfur sources
acid rain
Sulfur sources
coal
volcanoes
biological decomposition
Clean Air Act (1970) reduced SO2 emissions
Initial reductions by coal cleaning
First US commercial coal-utility scrubber built in 1967
Union Electric, MO
Clean Air Act (1977) essentially mandated scrubbers
52 scrubbers operating in 1982
190 scrubbers operating in 2008
Mandatory after 2018
Typical SO2 reductions >90%
Source:

29. US Coal Production
Million tons
Source: EIA

30. Source: EPA

32. Rainfall pH
1994
2000
2009

33. EPA Train Wreck Chart

34. Annual SO2 and NOX Emissions
2005
2009

37. Source: wattsupwiththat.com

41. Vintage protest images
1994 ?
1985

42. There are about 1,500 active volcanoes in the world
Emission rates of SO2 from an active volcano range from <20 tonnes/day to >10 million tonnes/day
Mount Pinatubo (1991) injected about 20 million metric tons of SO2 into the stratosphere
In 2016, US electric plants will emit 1.1 million metric tons of SO2
There are about 1,500 active volcanoes in the world