Coal, the dirtiest of fossil fuels, has been vilified for years. Yet researchers have been making progress in limiting the pollutants it emits. Now coal is seeing a resurgence in attention, mostly due to the technologies attempting to make coal cleaner.

Coal is one of the oldest fuels in humanity. But it’s also one of the dirtiest. It powered our Industrial Revolution, then we learned that burning it releases greenhouse gases that have been linked by scientists to negative climate change. As such, it has suffered a decade-long slide and been vilified for emitting pollutants such as nitrogen oxides, mercury and sulfur into the air.

It has also played an increasingly larger role in meeting the world’s energy needs ever since. Now this dirty little fossil fuel continues to gain a renaissance of attention.

The major advantage of coal is that there is so much of it, enough to last the world for another 200-300 years at current rates of consumption, which makes it incredibly economical. And the U.S. has more coal than any other country in the world — about one quarter of the world’s reserves. Further, its competition has weaknesses that can be exploited: natural gas, albeit with significantly lower emissions and capital cost, has seen upward-moving prices of late; meanwhile, renewable energy sources remain inadequate as a large-scale source of electricity; and nuclear energy continues to possess numerous stigmas.

Perhaps the most important reason for coal’s resurgence are the technologies attempting to make coal burn cleaner to recover waste coal, major efforts of which promise greater environmental benefit. Researchers already have made progress in limiting emissions in recent years. For example, about 98 percent of sulfur can now be removed from emissions, according to Gordon Couch, a technologist with the International Energy Agency’s Clean Coal Centre in London, reports National Geographic this month.

Yet coal combustion continues to produce large amounts of carbon dioxide (CO2), the major greenhouse gas considered a chief cause of climate change. Beyond its effects on human health, burning coal produces twice as much CO2 as natural gas, according to Harvard Magazine’s May-June 2006 cover article. Hence the long-term goal of clean-coal research of zero-CO2 emissions.

For instance, many researchers hope to turn coal into clean natural gas. The concept isn’t new. Cities in the 1800s used massive, dirty ovens to turn coal into town gas to fuel streetlights and gas lamps in homes. During WWII, Nazi Germany turned coal into liquid fuel for tanks. The U.S. government even promoted research projects to produce gas and liquid fuel from coal during the 1970s energy crisis, efforts later abandoned after the crisis passed.

Take Greatpoint Energy, for example. The Cambridge, Mass.-based company is refining a process called catalytic gasification to convert coal into methane or substitute natural gas, says NPR. In the process, “coal is mixed with a catalyst and fed into a gasifier: a tall, narrow, metal cylindrical container.” The coal and catalyst are combined with steam and subjected to pressure inside the gasifier, thus causing a chemical reaction that converts them into carbon monoxide and hydrogen. Further, the catalyst enables the company to separate out about half of the CO2. It works at a lower temperature than other technologies, which makes the process much cheaper.

As well, the Fischer-Tropsch process — a nearly century-old chemical technique for converting coal into liquid fuels — has been improved significantly. Researchers can shuffle the carbon atoms derived from cheap fuel sources — such as coal — to form more desirable combinations such as ethane gas and diesel fuel, according to a study in last month’s journal Science (via National Geographic). Scientists scrambled the makeup of hydrocarbons using two chemical processes (one of which earned last year’s Nobel Prize in chemistry). The reaction produced ethane gas and diesel fuel. Rutgers University chemist Alan Goldman says the synthetic diesel is “much cleaner burning than conventional diesel, even cleaner burning than gasoline.” The technology has the potential to one day wring more diesel fuel and ethane gas from hydrocarbon byproducts produced by oil refineries.

In March, the world’s largest prototype carbon-capture coal plant opened in Denmark. Researchers there aim to develop new types of solvents that can be used to trap CO2 and convert it into a solid form as carbon. The gas is washed with a liquid solvent, then compressed and put down a hole. The idea is to improve the capture rate of CO2. New solvents and carbon-capture techniques developed at the plant will also be cheaper and more energy efficient than those currently available.

The plant’s goal is to develop technology that will allow the European Union (EU) to capture and store 10 percent of its total carbon dioxide emissions and 30 percent of the CO2 produced by conventional power stations.

However, the “front-runner” of next-generation clean-coal technology is coal gasification, in which both steam and oxygen are used to turn coal into a synthetic gas that primarily consists of hydrogen. The gas is then combusted to generate electricity. This gas gives off greater concentrations of CO2 than combusted coal, thus making the emitted gas easier to trap.

The captured CO2 is sequestered by directing it into underground reservoirs where engineers anticipate that it will remain buried forever. The CO2 can also be pumped into oil and gas formations to help push the fuel to the surface. In doing this, Audis says, we can actually recover more oil and gas, as the CO2 can be used to force them out of the ground.

Plants that implement this two-part engineering solution — gasification and underground burial — are more efficient than traditional plants and can be engineered to produce a variety of liquid and gaseous fuels, including methanol, diesel, hydrogen and natural gas (methane).

So, could humanity’s oldest and dirtiest fossil fuel one day be our “cleanest” fuel? What are your thoughts?

References

Clean Coal? New Technology Buries Greenhouse Emissions
by James Owen
National Geographic News, May 2, 2006

Fueling Our Future
by Jonathan Shaw
Harvard Magazine, May-June 2006

Turning Dirty Coal into Clean Energy
by Elizabeth Shogren
NPR Morning Edition, April 25, 2006

The End of Oil? Breakthrough Turns Coal Into Clean Diesel
by Sean Markey
National Geographic News, April 18, 2006

Simpler and Cheaper Clean Coal Technology
by Peter Fairley
MIT Technology Review, April 26, 2006