Coal is the most prevalent source of power in the United States today, providing between 50-54% of America’s electricity and about 95 percent of Indiana's electricity. From an energy security perspective, the fuel has many advantages. The American West and Midwest have plentiful coal supplies – enough to supply all of the country’s power needs for many decades. The fuel is widely available and relatively inexpensive. However, the carbon dioxide (CO2) emissions contribute to global climate change and to consequent impacts on ecological systems and the economies that rely on them. Worldwide, coal plants alone are responsible for almost 30% of the man-made carbon dioxide released into the atmosphere every year.

Clean coal technologies ameliorate some of these environmental concerns. Clean coal technology refers to a collection of procedures to increase the efficiency of or reduce emissions from coal-burning power plants. These technologies are classified into three categories according to the stage of the process in which they occur. At the combustion level, clean coal technologies separate out the impurities or add products that prevent dangerous bi-products from forming. Conversion technologies gasify or liquefy coal so that impurities can be separated out in advance of burning (in order to burn the cleaner parts of coal). Post-combustion “scrubbers” remove sulfur and other impurities from flue gas after burning but before emissions are released into the air, lessening the acid rain and smog-related pollutants.

(Source: Craig Canine, “How to Clean Coal,” OnEarth Magazine, Fall 2005)

One promising conversion technology, called the integrated gasification combined cycle (IGCC) process, generates carbon-neutral electricity by capturing CO2 emissions for permanent disposal, or sequestration. Carbon sequestration refers to the long-term storage of carbon dioxide so that the build-up of carbon dioxide (a damaging greenhouse gas) in the atmosphere will slow. IGCC technology also allows plants to be up to 15% more efficient – meaning that they need to burn less coal to produce the same amount of power. The IGCC technology also allows the chemical elements that make up coal to be converted to gas and refined in advance of burning the fossil fuel, producing a dramatic reduction in emissions of particulate matter, nitrous oxide, and sulfur dioxide, improving air quality and human health. The remaining carbon dioxide emissions can be captured so that they are not released into the atmosphere.

Several potential uses for captured CO2 emissions have been proposed including pumping carbon into oil fields to help maintain pressure and facilitate extraction, pumping carbon into disused coal fields to dislodge methane, and long-term storage in aquifers. A subterranean aquifer is an underground body of water confined within permeable rock by overlying and underlying impermeable layers of rock or sediment. A saline aquifer contains brackish water or seawater trapped in an aquifer. Scientific studies suggest that deep saline aquifers beneath ocean waters may be within sufficiently impermeable rocks to seal away CO2. If this is true, aquifers could act as huge underwater storage containers for captured carbon. Some studies indicate total aquifer capacity to be 50,000 billion tons of CO2, or enough to bury all of the projected CO2 emissions for the next two centuries. However, at present sequestration in aquifers is untested and serious scientific questions remain.

The FutureGen project, sponsored by the Department of Energy, aims to provide IGCC technologies that eliminate pollutant emissions, manage carbon emissions, and remain cost competitive.

The Department of Energy lists four main goals of coal technology: clean(er) power generation; secure reliable energy supplies; reduce global greenhouse gas emissions; and a move towards a hydrogen economy.

Sources:

• Canine, Craig. 2005. “How to Clean Coal,” OnEarth Magazine, Natural Resources Defense Council
• “Can Coal Be Clean?” The Economist, November 30, 2006
• National Mining Association
• Energy Information Association