Elemental Mercury Capture by Activated Carbon in a Flow Reactor

1. Elemental Mercury Capture by Activated Carbon in a Flow Reactor Shannon D. Serre Brian K. Gullett U.S. Environmental Protection Agency National Risk Management Research Laboratory Air Pollution Prevention and Control Division Research Triangle Park, North Carolina 2003 ACERC Conference February 20, 2003

2. Mercury from Coal-Fired Power Plants • EPA has decided to regulate the emission of mercury from coal-fired boilers • Announce regulations by Dec. 15, 2003 • 48 tons emitted from U.S. CFPP in 1999 • Present as • Ionic or Oxidized (HgO, HgCl2) • Particulate (Hgp) • Elemental (Hg0) • One Hg0 control method includes injection of activated carbon into a gas stream with removal by the particulate control device

3. Approach • Bench-scale Hg research has been done in fixed-bed reactors • Most coal-fired utilities have ESPs • Dispersed-phase capture • Reactivity is more important than capacity • Mercury flow reactor is used to simulate in-flight capture of Hg0 over a short residence time • Examine • Particle size, residence time, temperature on capture • Effect of flue gas components: NOx, SOx, H2O • Increasing reactivity of carbon

4. In-flight capture Duct/ESP Seconds Reactivity Packed-bed capture Baghouse/FF Minutes/hours/days Breakthrough/capacity Flow Reactor Fixed-Bed Reactor

5. Hg Flow Reactor Hg0/N2

6. Carbon Properties

7. Effect of Particle Size • FGD • 100 °C • 86 ppb Hg0 • N2 carrier

8. Effect of Residence Time • WPL • 150 °C • 124 ppb Hg0

9. Effect of Temperature • FGD • SP2 • 44 ppb Hg0 Temperature (°C)

10. Effect of Vapor-Phase Moisture • WPL • 150 °C • 124 ppb Hg0

11. Effect of Sulfur Dioxide • WPL • 100 °C • 124 ppb Hg0

12. Effect of Nitric Oxide • FGD • 100 °C • 86 ppb Hg0

13. Effect of Nitrogen Dioxide • FGD • 100 °C • 86 ppb Hg0

14. Effect of Sulfur and Nitrogen Dioxide • FGD • 100 °C • 86 ppb Hg0 Add 22 ppm NO2 and 500 ppm SO2

15. WPL in Flue Gas • WPL • 100 °C • 86 ppb Hg0 7% O2, 6.8% H2O, 200 ppm NOx, and 500 ppm SO2

16. Effect of Carbon Moisture Content • FGD • 100 °C • 86 ppb Hg0 • N2 carrier

17. What is going on??? • Hg0 is not soluble in water • Evaporation of water from the carbon surface • Cooling the carbon, higher capture at a lower temperature • Maximum evaporative cooling effect ~40 C • Tests with dry carbon (WPL and FGD) at 50 C show minimal removal at a C:Hg of 10K:1 • Formation of new C-O functional groups through weathering of the carbon during hydration? • Boehm titrations did not reveal an increase in C-O functional groups

18. WPL in Flue Gas Methane flue gas doped with 200 ppm NOx, with and without SO2 • WPL • 150 °C • 124 ppb Hg0 • C:Hg=3100:1

19. FGD in Flue Gas Methane flue gas doped with 200 ppm NOx, with and without SO2 • FGD • 100 °C • 86 ppb Hg0 • C:Hg=10k:1

20. Chlorine Impregnated FGD FGD washed with 0.05N HCl • FGD • 100 °C • 86 ppb Hg0 • N2 Carrier Carbon to Mercury Ratio

21. Chlorine Impregnated FGD • FGD • 100 °C • 86 ppb Hg0 Carbon to Mercury Ratio

22. Summary • A vertical flow reactor was used to examine the removal of Hg0 using activated carbon • Higher Hg0 removal with decrease in particle size • Slightly higher Hg0 removal with increase in residence time • Higher Hg0 removal with decreasing temperature • The addition of vapor-phase moisture resulted in a drop in Hg0 removal compared to tests in dry N2 • Sulfur dioxide competed for or poisoned the active sites for Hg0 adsorption thereby reducing Hg0 removal

23. Summary • Nitric oxide reduced Hg0 removal by competing for the active sites • Nitrogen dioxide oxidized the Hg0 and increased removal • Tests in nitrogen and flue gas revealed that Hg0 removal correlates with carbon moisture content • Increasing the moisture content increased the reactivity • Removing free moisture resulted in a less reactive carbon • Chlorine impregnated FGD • >80% removal in flue gas tests at C:Hg ratio of 6000:1

24. Information • www.epa.gov/mercury • serre.shannon@epa.gov