Because of its abundance and low cost, scientists at the National Energy Technology Laboratory are looking for ways to make coal a cleaner energy resource.

Energy use always comes at a price—not just in dollars and cents, but in land use, air and water emissions, impact on wildlife and national security. Whether tapping the energy in the sun or wind, a reservoir, an atom’s nucleus or the chemical bonds in the world’s fossil resources, we must consider the price we pay for energy’s considerable benefits.

The coal conundrum is how to minimize its environmental impacts—including the release of carbon dioxide, the major greenhouse gas—while taking advantage of its abundance and low price.

In the United States, for instance, there are an estimated 275 billion tons of recoverable coal—enough to meet current demand levels for another 250 years. Most is used for electricity generation. While coal currently accounts for some 37 percent of installed generation capacity, it actually supplies just over half of the country’s power.

The situation is similar in Russia, China, India and Australia where, collectively, there are close to another 400 billion tons of recoverable coal reserves. China is building coal-fired power stations at an average of one a week to feed its booming economy.

While the global recession may dent demand and, therefore, the rate of coal-use expansion, its use won’t stop or reverse. Consequently, the race is on to find ways to make coal use cleaner than ever before.

The National Energy Technology Laboratory (NETL) is zeroing in on the problem and developing a suite of technologies to capture carbon dioxide, mercury and sulfur from flue gases. The laboratory studies both pre- and post-combustion solutions since, while new plants may be fitted with precombustion capture, old plants can be fitted for post-combustion capture equipment to lessen their environmental impact. NETL is having notable success.

“NETL has an impressive history developing science and engineering solutions to solve America’s energy problems. Three quarters of the Nation’s coal-fired power plants already employ technologies developed with NETL support,” said NETL Director Carl O. Bauer. “The laboratory is successful because its research addresses energy supply, cost and the environment concurrently, helping to achieve greater energy security at lower cost while reducing our environmental footprint.”

Among NETL’s research interests are the effects of the ionic liquid membrane, sorbents, aqueous ammonia, integrated pollutant removal, chemical looping and oxyfuel demonstration of re-heat combustion—all of which have a role in either making coal combustion more efficient or cleaning the exhaust gases. Ionic liquids, for example, are used as solvents to aid carbon dioxide capture from coalderived flue gases. They are also converted into membranes to enable removal of carbon dioxide from flue gas.

Once carbon dioxide is captured from flue gases, it can be stored or “sequestered” in terrestrial ecosystems and geologic formations such as depleted oil and gas wells, unmineable coal seams and deep saline formations. In the United States alone, the latest DOE Carbon Sequestration Atlas of the United States and Canada suggests that there is storage space for more than 1,100 years of carbon dioxide production.

One of NETL’s goals is to develop technologies to capture, transport and store carbon from flue gases for less than a 10 percent rise in energy’s cost. The carbon sequestration program, which started in 1997 with funding of just $1 million, has now grown to $150 million a year, indicating the degree of importance now placed on the key issue.

Another NETL goal has been to make the capture of mercury—which is released by coal combustion—effective and affordable. NETL has achieved this goal..

For 15 years, starting in the early 1990s, NETL conducted a comprehensive program to develop cost-effective technologies to control mercury emitted from coal-fired power plants. By 2007, NETL technologies were being implemented on a commercial scale and the program was deemed a success.

In 2008, researchers Hank Pennline and Evan Granite won an R&D 100 award—known as the “Oscars of Invention”—for the development of mercury control technology. Future mercury research has transitioned from government to private sector leadership.

Yet another environmental concern is the sulfur that is released by burning coal, which can contribute to the formation of acid rain. NETL has more than two decades of experience developing scrubbers, sorbents and other technologies to strip the sulfur from the flue gases at coal-fired power plants.

In one example, NETL’s Ranjani Siriwardane and Dan Cicero won an R&D 100 award in 2001 for devising, developing and commercializing a method using sorbents to remove sulfur from the gas stream of coal gasification plants down to the parts-per-million level from as high as 4 percent.

With plentiful and inexpensive worldwide coal supplies, coal is almost certain to be used for heat and power for decades—if not centuries—to come. Technologies developed at NETL will help solve the coal conundrum and ensure that it is used cleanly and efficiently..