Clean Coal Drives Big Results: Key U.S. Emissions Rates Drop 60 Percent in Eight Years
By Jacob Williams, Vice President, Global Energy Analytics, Peabody Energy
As the U.S. uses more coal – an abundant and affordable resource used to produce more than 40 percent of U.S. electricity – air quality is improving every day. Since 1970, key emissions rates from U.S. coal plants have decreased 90 percent while related coal use has increased 170 percent.
Significant progress has been made since 1970. From 1970 to 2005, U.S. coal plants achieved a dramatic reduction in key emissions rates (Figure 1).
Such reductions were achieved through installation of flue-gas desulfurization devices (“scrubbers”), particulate controls such as baghouses or electrostatic precipitators and through switching to lower sulfur coals (e.g. Powder River Basin coal). The annual emissions rate reduction over this period was 4.1 percent CAGR or a 77 percent reduction since 1970.
What is not widely known is the significant progress toward near zero emissions from coal that has been achieved over the last eight years. To this end, from 2005 to 2013, the decrease in emissions rates for the U.S. coal plants was a greater percentage on a per annum rate than recorded in the previous 35 years.
During this period, the average emissions rate reduction for SO2 and NOx emissions from coal plants was 68 percent and 55 percent, respectively (Figure 2).
This equates to an annual emissions rate reduction of 9.4 percent. This significant reduction in coal plant emissions is a direct result of investments made over the last few decades in clean coal technology research and development. By the end of 2013, the full suite of particulate, NOx and SO2 controls had been installed on more than 90 percent of the U.S. coal fleet.
These advanced technologies include SO2 scrubbers, low NOx burners and Selective Catalytic Reduction (SCR) devices and higher efficiency wet and dry precipitators and baghouses.
Plants in the Central and Eastern U.S. represent 85 percent of the U.S. plants and have made the greatest progress toward improving air quality.
In fact, in its 2014 State of the Air Report, the American Lung Association reports that the ten counties in the U.S. with the worst air quality are in California, whose electricity is less than 1 percent coal-fueled.
Progress toward ensuring near zero emissions from coal continues and the cleanest plants in the U.S. stand as a testament to this progress.
The emissions profile for the top five “cleanest” coal plants, based on SO2 and NOx emissions data, demonstrate that the existing fleet can achieve key emissions rates more than 70 percent below the current average for the fleet. The plants with the lowest emissions rates represent both new and older plants and consume various types of coal. As these plants demonstrate, adding emissions controls to a coal plant dictates, in large part, how low a coal plant’s emissions will be, regardless of the plant’s age or cycle efficiency.
The five coal plants with the lowest SO2 emission rates (Table 1), have SO2 rates that are more than 90% below the U.S. average.
Four of the five use low-sulfur PRB coal in their scrubbed plants. Three of the five plants with the lowest SO2 emission rate are more than 30 years old.
Dynegy’s Coffeen plant is 40 years old and has the lowest SO2 emission among plants in the U.S. In addition to using PRB base coal, the Central Illinois plant added a Hitachi wet scrubber in 2009. It’s SO2 emission rate in 2013 was 98 percent below the U.S. average.
Similarly, the five coal plants with the lowest NOx emission rates in the U.S. (Table 2) are more than 70 percent below the U.S. average for this key emission. Three of the five plants with the lowest NOx emissions rates are over 40 years old. Gen On’s 1200 MW Morgantown plant, built in 1970, has the lowest NOx emission rate in the U.S. The Maryland plant added Low-NOx burners in 1995 and a Babcock Power SCR in 2008. At an average NOx emissions rate of 0.34lbs/MWh in 2013, it was more than 80 percent below the U.S. average NOx emissions rate of 1.97 lbs/MWh.
As it relates to the measure of heat rate, or CO2 efficiency, the age of the plant does matter.
|AEP’s ultra-super critical plant, John W. Turk, is the most efficient coal-fired plant in the U.S. (Table 3).|
The newer super and ultra-super critical plants are the most efficient plants in the U.S. Four of the top five most efficient plants went commercial began operations in the last five years. AEP’s ultra-super critical plant, John W. Turk, ranks highest on the list of most efficient plants (Table 3).
This 600 MW plant with a Babcock & Wilcox boiler in Arkansas had an average heat rate of 8,858 btu/kWh in 2013 which was 16 percent lower than the U.S. coal fleet average of 10,424 btu/kWh.
The top 5 most efficient coal plants had an average heat rate of 9,120 btu/kWh, which is 13 percent better than the U.S. average.
The advanced technologies being deployed and in use today drive tremendous progress toward reducing emissions and serve as the standard for the future.
The goal of near-zero emissions is attainable in light of the significant SO2 emissions reductions achieved at Dynegy’s Coffeen plant, NOx at Gen On’s Morgantown plant and for lowest heat rate at AEP’s John W. Turk plant.
These top performing plants underscores the importance of continued investment in advanced coal technologies.
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