^{Fluidized bed boilers are capa-ble of burning a wide range of fuels cleanly, including biomass fuels suchas wood waste.} 

^{What is Coal-Gasification?}

^{"Clean coal technology" describes a new generation of energy processes that sharply reduce air emissions and other pollutants compared to older coal-burning systems. In the late 1980s and early 1990s, the U.S. Department of Energy conducted a joint program with industry and State agencies to demonstrate the best of these new technologies at scales large enough for companies to make commercial decisions. More than 20 of the technologies tested in the original program achieved commercial success.}

^{The early program, however, was focused on the environmental challenges of the time - primarily concerns over the impact of acid rain on forests and watersheds. In the 21st century, additional environmental concerns have emerged - the potential health impacts of trace emissions of mercury, the effects of microscopic particles on people with respiratory problems, and the potential global climate-altering impact of greenhouse gases.}

^{With coal likely to remain one of the nation's lowest-cost electric power suppliers for the foreseeable future, President Bush has pledged a new commitment to even more advanced clean coal technologies. As the President said in presenting his National Energy Policy to the American public on May 17, 2001 , "More than half of the electricity generated in America today comes from coal. If we weren't blessed with this natural resource, we would face even greater [energy] shortages and higher prices today. Yet, coal presents an environmental challenge. So our plan funds research into new, clean coal technologies."}

^{Building on the successes of the original program, the new clean coal initiative encompasses a broad spectrum of research and large-scale projects that target today's most pressing environmental challenges.}

^{Initially, the demonstration portion of the program, the Clean Coal Power Initiative, is providing government co-financing for new coal technologies that can help utilities meet the President's Clear Skies Initiative to cut sulfur, nitrogen and mercury pollutants from power plants by nearly 70 percent by the year 2018. Also, some of the early projects are showing ways to reduce greenhouse gases from coal plants by boosting the efficiency at which they convert coal to electricity or other energy forms.}

^{Coal gasification offers one of the most versatile and cleanest ways to convert the energy content of coal into electricity, hydrogen, and other energy forms.}

^{The first pioneering coal gasification electric power plants are now operating commercially in the United States and in other nations, and many experts predict that coal gasification will be at the heart of the future generations of clean coal technology plants for several decades into the future. For example, at the core of the U.S. Department of Energy's FutureGen power plant of the future will be an advanced coal gasifier.}

^{Rather than burning coal directly, gasification breaks down coal - or virtually any carbon-based feedstock - into its basic chemical constituents. In a modern gasifier, coal is typically exposed to hot steam and carefully controlled amounts of air or oxygen under high temperatures and pressures. Under these conditions, carbon molecules in coal break apart, setting into motion chemical reactions that typically produce a mixture of carbon monoxide, hydrogen and other gaseous compounds.}

^{Gasification, in fact, may be one of the best ways to produce clean-burning hydrogen for tomorrow's automobiles and power-generating fuel cells. Hydrogen and other coal gases can also be used to fuel power-generating turbines or as the chemical "building blocks" for a wide range of commercial products.} 

^{The Energy Department's Office of Fossil Energy is working on coal gasifier advances that enhance efficiency, environmental performance, and reliability as well as expand the gasifier's flexibility to process a variety of feedstocks (including biomass and municipal/industrial waste).}

^{Environmental Benefits}

^{The environmental benefits stem from the capability to cleanse as much as 99 percent of the pollutant-forming impurities from coal-derived gases. Sulfur in coal, for example, emerges as hydrogen sulfide and can be captured by processes used today in the chemical industry. In some methods, the sulfur can be extracted in a form that can be sold commercially. Likewise, nitrogen typically exits as ammonia and can be scrubbed from the coal gas by processes that produce fertilizers or other ammonia-based chemicals.}

^{The Office of Fossil Energy is also exploring advanced syngas cleaning and conditioning processes that are even more effective in eliminating emissions from coal gasifiers. Multi-contaminant control processes are being developed that reduce pollutants to parts-per-billion levels and are effective in cleaning mercury and other trace metals in addition to other impurities.}

^{Coal gasification may offer a further environmental advantage in addressing concerns over the atmospheric buildup of greenhouse gases, such as carbon dioxide.. If oxygen is used in a coal gasifier instead of air, carbon dioxide is emitted as a concentrated gas stream. In this form, it can be captured more easily and at lower costs for ultimate disposition in various sequestration approaches. (By contrast, when coal burns or is reacted in air, 80 percent of which is nitrogen, the resulting carbon dioxide is much more diluted and more costly to separate from the much larger mass of gases flowing from the combustor or gasifier.)}

^{Efficiency Benefits}

^{Efficiency gains are another benefit of coal gasification. In a typical coal combustion plant, heat from burning coal is used to boil water, making steam that drives a steam turbine-generator. Only a third of the energy value of coal is actually converted into electricity by most combustion plants, the rest is lost as waste heat.}

^{A coal gasification power plant, however, typically gets dual duty from the gases it produces. First, the coal gases, cleaned of their impurities, are fired in a gas turbine - much like natural gas - to generate one source of electricity. The hot exhaust of the gas turbine is then used to generate steam for a more conventional steam turbine-generator. This dual source of electric power, called a "combined cycle," converts much more of coal's inherent energy value into useable electricity. The fuel efficiency of a coal gasification power plant can be boosted to 50 percent or more.}

^{Future concepts that incorporate a fuel cell or fuel cell-gas turbine hybrid could achieve even higher efficiencies, perhaps in the 60 percent range, or nearly twice today's typical coal combustion plants. And if any of the remaining waste heat can be channeled into process steam or heat, perhaps for nearby factories or district heating plants, the overall fuel use efficiency of future gasification plants could reach 70 to 80 percent.}

^{Higher efficiencies translate into more economical electric power and potential savings for ratepayers. A more efficient plant also uses less fuel to generate power, meaning that less carbon dioxide is produced. In fact, coal gasification power processes under development by the Energy Department could cut the formation of carbon dioxide by 40 percent or more compared to today's conventional coal-burning plant.}

^{The capability to produce electricity, hydrogen, chemicals, or various combinations while virtually eliminating air pollutants and potentially greenhouse gas emissions makes coal gasification one of the most promising technologies for the energy plants of tomorrow.}

^{COAL is our most abundant fossil fuel. The United States has more coal than the rest of the world has oil. There is still enough coal underground in this country to provide energy for the next 200 to 300 years.}

^{But coal is not a perfect fuel.}

^{Trapped inside coal are traces of impurities like sulfur and nitrogen. When coal burns, these impurities are released into the air.}

^{While floating in the air, these substances can combine with water vapor (for example, in clouds) and form droplets that fall to earth as weak forms of sulfuric and nitric acid – scientists call it "acid rain."}

^{There are also tiny specks of minerals – including common dirt – mixed in coal. These tiny particles don't burn and make up the ash left behind in a coal combustor. Some of the tiny particles also get caught up in the swirling combustion gases and, along with water vapor, form the smoke that comes out of a coal plant's smokestack. Some of these particles are so small that 30 of them laid side-by-side would barely equal the width of a human hair!}

^{Also, coal like all fossil fuels is formed out of carbon. All living things - even people - are made up of carbon. (Remember - coal started out as living plants.) But when coal burns, its carbon combines with oxygen in the air and forms carbon dioxide. Carbon dioxide is a colorless, odorless gas, but in the atmosphere, it is one of several gases that can trap the earth's heat. Many scientists believe this is causing the earth's temperature to rise, and this warming could be altering the earth's climate (read more about the "greenhouse effect").}

^{Sounds like coal is a dirty fuel to burn. Many years ago, it was. But things have changed. Especially in the last 20 years, scientists have developed ways to capture the pollutants trapped in coal before the impurities can escape into the atmosphere. Today, we have technology that can filter out 99 percent of the tiny particles and remove more than 95 percent of the acid rain pollutants in coal.}

^{We also have new technologies that cut back on the release of carbon dioxide by burning coal more efficiently.}

^{Many of these technologies belong to a family of energy systems called "clean coal technologies." Since the mid-1980s, the U.S. Government has invested more than $2 billion in developing and testing these processes in power plants and factories around the country. Private companies and State governments have been part of this program. In fact, they have contributed more than $4 billion to these projects.}

^{How do you make coal cleaner?}

^{Actually there are several ways.}

^{Take sulfur, for example. Sulfur is a yellowish substance that exists in tiny amounts in coal. In some coals found in Ohio , Pennsylvania , West Virginia and other eastern states, sulfur makes up from 3 to 10 percent of the weight of coal.}

^{For some coals found in Wyoming , Montana and other western states (as well as some places in the East), the sulfur can be only 1/100ths (or less than 1 percent) of the weight of the coal. Still, it is important that most of this sulfur be removed before it goes up a power plant's smokestack.}

^{One way is to clean the coal before it arrives at the power plant. One of the ways this is done is by simply crushing the coal into small chunks and washing it. Some of the sulfur that exists in tiny specks in coal (called "pyritic sulfur " because it is combined with iron to form iron pyrite, otherwise known as "fool's gold) can be washed out of the coal in this manner. Typically, in one washing process, the coal chunks are fed into a large water-filled tank. The coal floats to the surface while the sulfur impurities sink. There are facilities around the country called "coal preparation plants" that clean coal this way.}

^{Not all of coal's sulfur can be removed like this, however. Some of the sulfur in coal is actually chemically connected to coal's carbon molecules instead of existing as separate particles. This type of sulfur is called "organic sulfur," and washing won't remove it. Several process have been tested to mix the coal with chemicals that break the sulfur away from the coal molecules, but most of these processes have proven too expensive. Scientists are still working to reduce the cost of these chemical cleaning processes.}

^{Most modern power plants — and all plants built after 1978 — are required to have special devices installed that clean the sulfur from the coal's combustion gases before the gases go up the smokestack. The technical name for these devices is "flue gas desulfurization units," but most people just call them "scrubbers" — because they "scrub" the sulfur out of the smoke released by coal-burning boilers.}

^{How do scrubbers work?}

^{Most scrubbers rely on a very common substance found in nature called "limestone." We literally have mountains of limestone throughout this country. When crushed and processed, limestone can be made into a white powder. Limestone can be made to absorb sulfur gases under the right conditions — much like a sponge absorbs water.}

^{In most scrubbers, limestone (or another similar material called lime) is mixed with water and sprayed into the coal combustion gases (called "flue gases"). The limestone captures the sulfur and "pulls" it out of the gases. The limestone and sulfur combine with each other to form either a wet paste (it looks like toothpaste!), or in some newer scrubbers, a dry powder. In either case, the sulfur is trapped and prevented from escaping into the air.}

^{The Clean Coal Technology Program tested several new types of scrubbers that proved to be more effective, lower cost, and more reliable than older scrubbers. The program also tested other types of devices that sprayed limestone inside the tubing (or "ductwork') of a power plant to absorb sulfur pollutants.}

^{But what about nitrogen pollutants? That's another part of the Clean Coal story.}

^{Knocking the NOx Out of Coal}

^{Nitrogen is the most common part of the air we breathe. In fact, about 80% of the air is nitrogen. Normally, nitrogen atoms float around joined to each other like chemical couples. But when air is heated — in a coal boiler's flame, for example — these nitrogen atoms break apart and join with oxygen. This forms "nitrogen oxides" — or, as it is sometimes called, "NOx" (rhymes with "socks"). NOx can also be formed from the atoms of nitrogen that are trapped inside coal.}

^{In the air, NOx is a pollutant. It can cause smog, the brown haze you sometimes see around big cities. It is also one of the pollutants that forms "acid rain." And it can help form something called "groundlevel ozone," another type of pollutant that can make the air dingy.}

^{NOx can be produced by any fuel that burns hot enough. Automobiles, for example, produce NOx when they burn gasoline. But a lot of NOx comes from coal-burning power plants, so the Clean Coal Technology Program developed new ways to reduce this pollutant.}

^{One of the best ways to reduce NOx is to prevent it from forming in the first place. Scientists have found ways to burn coal (and other fuels) in burners where there is more fuel than air in the hottest combustion chambers. Under these conditions, most of the oxygen in air combines with the fuel, rather than with the nitrogen. The burning mixture is then sent into a second combustion chamber where a similar process is repeated until all the fuel is burned.}

^{This concept is called "staged combustion" because coal is burned in stages. A new family of coal burners called "low-NOx burners" has been developed using this way of burning coal. These burners can reduce the amount of NOx released into the air by more than half. Today, because of research and the Clean Coal Technology Program, more than half of all the large coal-burning boilers in the United States will be using these types of burners. By the year 2000, more than 3 out of every four boilers will have been outfitted with these new clean coal technologies.}

^{There is also a family of new technologies that work like "scubbers" by cleaning NOx from the flue gases (the smoke) of coal burners. Some of these devices use special chemicals called "catalysts" that break apart the NOx into non-polluting gases. Although these devices are more expensive than "low-NOx burners," they can remove up to 90 percent of NOx pollutants.}

^{But in the future, there may be an even cleaner way to burn coal in a power plant. Or maybe, there may be a way that doesn't burn the coal at all.}