Saturday, January 24, 2009
You Do The Math - Mercury, Coal, and CFL's
You Do The Math – Mercury, Coal And Compact Fluorescent Lights
by Curt Tricarico
Have you heard a lot of warnings lately about the mercury in compact fluorescent lights? The spiral or hoop shaped CFL’s save you money and energy, reduce carbon dioxide emissions, and slow global warming. But, do they put more or less mercury into the environment? Don’t let others deceive you, grab your calculator, because today you do the math.
A year ago the National Electrical Manufacturer’s Association voluntarily limited typical CFL’s that you would buy (those under 25 watts) to 5 milligrams (mg) of mercury. However, Phillips has a bulb with only 3.8 mg called the Alto.
If you are a Dayton, Power and Light customer in Dayton, Ohio, all your electricity comes from coal, and this is true for many US residents. Department of Energy (DOE) statistics show that only half of the nation’s electricity comes from coal. According to the EPA, coal powered electric utilities in the US are responsible for over half of the nation’s mercury emissions from fossil fuels. Total emissions are 48 tons of mercury a year.
Let’s see, 48 tons at 2000 pounds per ton, and 2.20462 pounds per kilogram, and 1 million milligrams per kilogram, come to 8.7 billion CFL’s worth of mercury. That’s like each of the US’s 300 million residents breaking open 29 CFL’s each year and wafting the mercury high into the air. That’s a powerful perspective, but not a proper analysis by a long shot. Most of a home’s energy needs are heating and cooling, not lighting.
According to the EPA most coals contain between 0.1 and 0.3 ppm (parts per million) of mercury. The US Geological Survey reports that the US average is 0.17 ppm, while the Indiana Geological Survey reports that the Illinois and Indiana coal bed averages a modest 0.11 ppm.
However, different coals also have different energy content. So, we must use a coal’s mercury content per BTU (British Thermal Unit). US coal ranges from 5 to “20 plus” pounds of mercury per trillion BTU’s. The Illinois coal bed averages 9.2 pounds while a south central coal bed averages “20 plus” pounds. DP&L uses Kentucky coal that ranges from 10 to 15 pounds per trillion BTU.
In this map created by the USGS, the coal fields in
green have 5 to 10 pounds of mercury per trillion BTU's,
blue have 10 to 15,
orange have 15 to 20
red have 20 or more
Another important conversion factor is the efficiency of coal fired electric utilities. For instance, if your utility is 33% efficient from lump of coal to your outlet, they must burn 3 times as much coal as a light bulb actually needs. Actual efficiency of US utilities seems to be hard to determine, with several articles in print or online mentioning they are anywhere from 25% to 35% efficient. There are new designs that are 50% efficient, but which number do you use? Let’s go straight to the source, the Energy Information Administration, a part of the DOE.
In 2006 the total amount of coal used in the US to generate electricity was 1,035,346 thousand tons, and the electricity generated was 1,990,926 thousand megawatt-hours. Dividing the two gives us 1.9 megawatt-hours per ton of coal. Converting tons to kilograms, and megawatts to kilowatts, we get 2.12 kilowatt-hours (kWh) per kilogram of coal.
Various sources say coal has 21 million BTU per ton, and anywhere from 24 to 35 megajoules per kilogram. Since there are 3414.42 BTU per kWh, and 3600 kilojoules per kWh, then coal has between 6.67 and 9.7 kWh per kilogram. Since the US production was 2.12 kWh per kg, the efficiency ranges from 21.85% to 31.78%.
We’re finally ready to compare a fluorescent bulb to an incandescent. But which fluorescent should we use? A 25-watt fluorescent puts out about the same light as a 100-watt incandescent, and is a recommended replacement. One CFL used properly lasts about as long as 10 incandescents. Used improperly, turning it on and off frequently, the CFL burns out much faster.
For a best case scenario for CFL’s, lets put a Phillips Alto CFL that lasts 10,000 hours in the boxing ring against 10 incandescents using the worst coal in the country with the least efficient utility. And, we’ll assume nobody recycles their fluorescent lights, but rather breaks them open on July 4th to hear the pop and watch the pretty white cloud waft to the neighbor's house.
The Alto has 3.8 mg of mercury, and uses 25 watts for 10,000 hours, coming to 250 kWh of energy. Since a kWh is equal to 3414.42 BTU’s, the Alto uses 853,605 BTU’s. But the utility uses nearly 5 times that, 3.9 million BTU’s, resulting in 0.000078 pounds of mercury released into the air. This equals 35.44 milligrams.
The ten incandescents also run 10,000 hours, but use 4 times more energy, so they put 141.8 mg of mercury into the air. In this heavyweight match, the Phillips wins with a total of 39.24 mg of mercury, keeping 102.5 mg of mercury out of our fish. The total reduction is over 72%.
A worst case scenario for CFL’s pits a NEMA standard CFL, that lasts, say, 3000 hours due to improper usage, against 3 incandescents using that "clean" Illinois coal burned by the most efficient utility, 31.78 percent. In one corner the CFL has 5 mg of mercury and uses enough coal to put another 3.36 mg in the air. The incandescent bulbs put 4 times that in the air, or about 13.45 mg. In this bout, the CFL saves over 5 mg of mercury, almost 38%.
So, either in a best case or worst case scenario, the CFL eliminates a substantial amount of mercury from our environment. Even if half the nation’s electricity came from a mercury-free-from-start-to-finish energy source, which doesn’t exist, a CFL still reduces mercury emissions between 19 and 36 percent.
How about the near future and those proposed 50% efficient utilities? Will that eliminate the need for a CFL? Turns out there’s a new CFL on the market called a cold cathode fluorescent (CCFL) that contains 1/2 the mercury of a typical CFL, runs cooler, costs only $15, and lasts a whopping 25,000 hours whether or not you use it properly. Right now there’s only a 13-watt version, but a 25-watt version should be just around the corner. And, if produced, would reduce mercury emissions by 71.5% in it’s lifetime, even if the cleanest coal was used.
The EPA has proposed a rule to reduce total mercury emissions of the nation by 70% by 2017. The coal will literally be washed, which has reduced mercury content by 39% in tests on the Illinois coal by the Indiana Geological Survey. However, 2017 is ten years away.
Even if they washed all Illinois coal tomorrow, and then washed it a few more times, and were able to reduce the mercury by 90%, from 9.2 pounds to 1 pound per trillion BTU, and we only used utilities with a 50% efficiency, one CCFL would still reduce mercury emissions by almost 43 percent. If half your energy came from a magically clean energy source, a CCFL would still reduce mercury by over 21 percent. Seems that no matter how you slice it, a compact fluorescent is the way to go.
DP&L coal usage: Kelly 937-331-3900
mercury in CFL: Wickipedia
mercury in coal: EPA, USGS
mercury in coal, Hg reduction by washing, Hg reduction law: Indiana Geological Survey
mercury in CFL, watch battery, amalgam filling
coal energy density, coal plant efficiency: DOE, EIA
1995 through 2006, all energy sources used for electricity and heat http://www.eia.doe.gov/cneaf/electricity/epa/epates.html
energy in coal: Wickipedia
regional coal fired power plants in Ohio:
Dayton, Cincinnati, Columbus, Ohio River Valley coal fired power plants:
Dayton, Springfield coal fired power plants:
Yellow Springs energy sources: