SO2, NOx Mercury emissions

Pre-combustion pollution controls used in gasification have some inherent clean-up advantages.  The conditions used to gasify coal -- high pressure and partial oxidation- mean that the pollutants are concentrated and therefore easier to remove.  Sulfur removal rates are 99.9% or even 99.99% in most gasification applications. Mercury removal using carbon beds is relatively inexpensive, and removes 99.9% or higher levels of mercury from the syngas created by gasifying coal. In a carbon bed, the impurities (in this instance, mercury) are attracted to the top surface area of the carbon, capturing the mercury.  Also, the mercury is captured in a fairly small carbon bed volume, allowing more options to ensure long-term isolation from the environment.

 

Tanks

Mercury removal tanks using a single packed bed of sulfur impregnanted carbon. Photo credit: Eastman Chemical

 

 

 

Post-combustion NOx controls allow IGCC NOx rates to approach a deeply lowered rate of emission.                                   Below are SO2 and NOx charts that compare exiting coal plant emissions in 2002.  As the charts show, IGCC plants offer deep pollutant reductions. For more detailed emissions comparisons, see the USEPA Report, “Environmental Footprints and Costs of Coal-Based Integrated Gasification Combined Cycle and Pulverized Coal Technologies” here)

 

Emmision Rates

The average of the best 38 coal plants in the U.S. emits 0.934 pounds of SO2 per MWH, while the best IGCC plant emits only 0.099 pounds of SO2 per MWH. All of the tradtional pulverized coal plants emit at least 10.272 pounds of SO2 per MWH.

 

 

 

NOx Emissions Chart

All of the coal plants in the U.S. emitted 2.778 pounds of NOx per Megawatt Hour. While the best coal plant emitted 0.361 pounds of NOx per MWH in 2008, the best IGCC plant emitted just 0.1 pounds of NOx per MWH in 2008.