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

Introduction Released by natural and anthropogenic processes Deposited on land and water and converted to methyl mercury Accumulates in food chain Affects central nervous system, kidneys, and development

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, HgCl 2 ) –Particulate (Hg p ) –Elemental (Hg 0 ) One Hg 0 control method includes injection of activated carbon into a gas stream with removal by the particulate control device

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 Hg 0 over a short residence time Examine –Particle size, residence time, temperature on capture –Effect of flue gas components: NOx, SOx, H 2 O –Increasing reactivity of carbon

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

Hg Flow Reactor Hg 0 /N 2

Carbon Properties

Effect of Particle Size FGD 100 °C 86 ppb Hg 0 N 2 carrier

Effect of Residence Time WPL 150 °C 124 ppb Hg 0

Effect of Temperature FGD SP2 44 ppb Hg 0 Temperature (°C)

Effect of Vapor-Phase Moisture WPL 150 °C 124 ppb Hg 0

Effect of Sulfur Dioxide WPL 100 °C 124 ppb Hg 0

Effect of Nitric Oxide FGD 100 °C 86 ppb Hg 0

Effect of Nitrogen Dioxide FGD 100 °C 86 ppb Hg 0

Effect of Sulfur and Nitrogen Dioxide FGD 100 °C 86 ppb Hg 0 Add 22 ppm NO 2 and 500 ppm SO 2

WPL in Flue Gas WPL 100 °C 86 ppb Hg 0 7% O 2, 6.8% H 2 O, 200 ppm NOx, and 500 ppm SO 2

Effect of Carbon Moisture Content FGD 100 °C 86 ppb Hg 0 N 2 carrier

What is going on??? Hg 0 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

WPL in Flue Gas WPL 150 °C 124 ppb Hg 0 C:Hg=3100:1 Methane flue gas doped with 200 ppm NO x, with and without SO 2

FGD in Flue Gas FGD 100 °C 86 ppb Hg 0 C:Hg=10k:1 Methane flue gas doped with 200 ppm NO x, with and without SO 2

Chlorine Impregnated FGD FGD 100 °C 86 ppb Hg 0 N 2 Carrier Carbon to Mercury Ratio FGD washed with 0.05N HCl

Chlorine Impregnated FGD FGD 100 °C 86 ppb Hg 0 Carbon to Mercury Ratio

A vertical flow reactor was used to examine the removal of Hg 0 using activated carbon Higher Hg 0 removal with decrease in particle size Slightly higher Hg 0 removal with increase in residence time Higher Hg 0 removal with decreasing temperature The addition of vapor-phase moisture resulted in a drop in Hg 0 removal compared to tests in dry N 2 Sulfur dioxide competed for or poisoned the active sites for Hg 0 adsorption thereby reducing Hg 0 removal Summary

Nitric oxide reduced Hg 0 removal by competing for the active sites Nitrogen dioxide oxidized the Hg 0 and increased removal Tests in nitrogen and flue gas revealed that Hg 0 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 Summary

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