Working toward cleaner coal: Part 1
This article first appeared in the St. Louis Beacon, July 29, 2009 - If you are reading this story on a computer, you are probably using electricity from coal.
Our modern lifestyle depends upon an uninterrupted and inexpensive supply of electrical energy. Coal-powered electric plants operate around the clock to fill the demand for energy.
How much coal?
1 kilowatt hour (kWh) is the amount of electricity needed to burn a 100 watt light bulb for 10 hours.
Two pounds of coal were burned to produce that kWh, producing 1.34 pounds of carbon dioxide. (A figure from 1999).
The average household in the U.S. uses 936 kWh/month. That amount of electricity takes 1,872 pounds of coal -- nearly a ton -- and produces 1,254 pounds of carbon dioxide.
Currently, half of the electrical power in the U.S comes from burning coal. The percentage is even higher in Missouri -- 76 percent. And in the St. Louis area alone, electrical consumption -- and therefore the use of coal -- is up 50 percent since 1990.
Most scientists and policy makers agree that we must make a transition to renewable and cleaner sources of energy as quickly as possible. In the meantime, however, a great deal of the electricity that we rely upon 24/7 will be generated by burning fossil fuels.
The Obama administration recognizes that we will continue to burn coal to generate electricity; in May it earmarked $2.4 billion for clean coal research. To the environmental lobby, "clean coal" is an oxymoron. Coal as a power source is inherently dirty: first in its mining, then through pollutants in smokestack emissions and in the release of vast quantities of the greenhouse gas carbon dioxide (CO2) into the atmosphere.
"Perhaps we should have named our organization the Consortium for Clean-er Coal Utilization," said Pratim Biswas, a professor at the Washington University School of Engineering.
The Consortium for Clean Coal Utilization is a partnership among Washington University and local energy and coal companies to advance research and education in this area. Arch Coal and Peabody Energy have committed $5 million each to the research effort. Ameren has put in $2 million. A main goal is to establish a research facility bigger than a university lab, but smaller than a commercial one.
Among energy options, coal has many advantages, points out Professor Rich Axelbaum, head of the consortium. It is plentiful, inexpensive and most of the world either has coal reserves or access to them. For areas that have no access to hydroelectric power, the only 24/7 alternative to fossil fuels is nuclear power. That option is politically contentious on national and international fronts.
To understand both the problems and the prospects for coal, it's useful to look at the progress that has been made.
Efforts To Clean Coal
Coal plants used to put out so much particulate matter from their smokestacks that people could sometimes see the pollution in the form of soot or smog.
Thanks to advances in technology, pollution from burning coal has been greatly reduced. Particulates and smokestack emissions that cause acid rain have been all but been eliminated in many areas. And engineers have also devised ways to tackle mercury contamination.
Beginning in the 1950s, two technologies arose to control smog and soot from burning coal. One is a fabric filter or "baghouse" analogous to a vacuum cleaner.
The other is the electrostatic precipitator, much like the air purifying devices many St. Louisans have in their homes. With the electrostatic precipitator, particles from flue gas are given a negative charge and then collected on positively charged metal plates. The plates are cleaned regularly, and the collected "fly ash" is used to make concrete.
Today, the more than 1,000 coal-powered electrical plants in the country are equipped to remove particles greater than 2.5 microns. (A micron is a millionth of a meter, or one thousandth of a millimeter.) Most toxic metals (with the exception of mercury) are removed with these particles. Ameren plants in St. Louis remove 99 percent of particulate matter from flue gas.
Controlling the Causes of Acid Rain
Acid rain is caused by oxides of sulfur and nitrogen. Technology to remove sulfur dioxide from flue gas began development in the 1960s and 1970s. "Scrubbers" remove the sulfur from flue gas by reacting it with a calcium compound -- either limestone or lime. The resulting calcium sulfate (gypsum) goes into the manufacture of wallboard.
Technology to remove nitrogen oxides was developed in the 1980s and 1990s. "Low NOx burners" are installed in all U.S. coal-fired electrical plants, but they are only 25 percent efficient in normal operation. Another technology "selective catalytic reduction" is analogous to catalytic converters in cars. It is more efficient, but also much expensive. By 2006, about 40 percent of the country's coal-fired plants had this technology. No St. Louis area Ameren plants use it.
Mercury is Poised for Regulation
Coal powered electrical plants leak mercury into the atmosphere. The element mercury is a poison, and accumulates in animal tissues. Mercury is a "trace" component of coal, but burning vast quantities of coal releases significant amounts of gaseous mercury into the atmosphere. Research on control of mercury emissions has been a hot topic for about 15 years. As a result of that research, legislators can now respond to the public demand for mercury control. For example, Washington University researchers Biswas and Axelbaum have been using nanotechnology to build mercury traps.
Jo Seltzer is a freelance writer with more than 30 years on the research faculty at the Washington University School of Medicine and seven years teaching tech writing at WU's engineering school.