What Is It, and How Does It Produce Electricity?
Coal is dirty. Coal is the “problem” fuel. Both mining and burning coal pollute land, water, and air. Coal is a major contributor to global warming and climate change. But we have plenty of coal, and coal has plenty of energy in it. And we need energy. The question is, can we find a way to use our coal but avoid its severe pollution problems?
Enter “clean coal.” Clean coal is the name that has been given to a process whereby coal is chemically washed of minerals and impurities and before being burned, either gasified (turned into a cleaner burnable gas such syngas as hydrogen) or liquefied (turned into a cleaner-burning liquid fuel—the process is called liquifaction). This processing captures the two worst coal-related pollutants (sulfur dioxide and carbon dioxide). The waste gases from burning this improved coal (which would normally blow up the smokestack) are considerably less environmentally damaging than if we simply burned the original coal.
The captured sulfur dioxide can be turned into sulfuric acid, a commercially valuable product. The big question is how to keep the captured C02 out of the atmosphere. Clean coal’s answer is carbon sequestration. What is that? Sequestration is a process in which the captured C02 gas is pumped, under high pressure, deep underground into rock formations where it can’t escape back to the surface.
If utility companies process coal in this way, it really is a clean, green fuel! Why go to all this trouble (and great expense) to make coal cleaner when other energy technologies lurk just over the horizon? There are two simple reasons:
1. Coal is cheap and abundant. The United States has an estimated 268 billion tons of recoverable coal—three times the total energy that Saudi Arabia has in oil— enough to last well over a century. Coal represents much of America’s energy riches.
2. Electrical energy demand in the United States has increased almost 30 percent in the past decade and will increase by about 2 to 3 percent each year through 2020. Renewable energy technologies may hold great promise, but none are available right now in sufficient quantities and proven reliability to meet this increased demand.
Utilities must add new capacity every year, and coal is a proven, available, economical technology. Over 100 new coal plants are currently in the planning stages. Some will likely be shifted to other technologies. But most will be built as planned—as new American coal-fired power plants. China and India are turning to new coal power plants in even greater numbers than is the United States. If we want electricity without shortages and blackouts over the next 30 years, we must consider coal. Cleaning coal is one key to our near-term energy survival.
That’s the plan. To date—while each of the necessary individual technologies works reasonably well—the combination of all of these measures to control the negative impacts of coal has pushed the cost of the electricity produced by these plants unacceptably high. We can clean coal. But no utility can currently afford to do it.
Worse, “clean coal” does not address the impacts of coal mining. Picture a Western coal strip mining operation: A dragline (a giant steam shovel) with an arm longer than a football field gulps 100 cubic yards (2,700 cubic feet) of dirt at a time, ripping away the overburden (dirt, grass, rocks, trees, etc.) of an 80-foot-thick seam of coal that lies a hundred feet beneath. Snaking lines of massive trucks with 12-foot-tall tires and each carrying 400 tons of coal form long, curving lines from pit to train loaders. Mile-long trains creep through, loading continuously, never fully stopping. Eighteen trains a day, every day. 250,000 tons of coal each day. And that’s just from a single mine! Square miles of earth ripped off and carried away each day. Wyoming mining has torn up 110,580 acres of prairie. Only 41,000 of those acres have been backfilled, regraded, and seeded. Nothing in the “clean coal” program addresses the impacts of this earth-altering process.
What’s Happening Now?
Research, backed by billions of federal dollars, races forward on two fronts. The first is new, economical ways to store captured carbon. British researchers have found that they can inject C02 into certain undersea sandstone deposits where the carbon will mix with seawater to form clays and carbonate rocks. They are designing a “zero emissions” coal plant to go online in 2014. With U. S. Department of Energy support, FutureGen is designing the first American near-zero-emissions coal gasification plant in Mattoon, Illinois. Plant operators will capture 60 percent of its C02 production, compress it to a near-liquid state, and pipe it a mile down into porous sandstone capped by impermeable shale. (A plant in Spremberg, Germany, is already successfully using this sequestration process.)
The PurGen company has proposed building a clean coal plant in Linden, New Jersey, using coal gasification technology. The company plans to liquefy the captured C02 and pump it 140 miles out into the ocean, then bury it 8,000 feet below the seafloor in a massive layer of sandstone capped by impermeable shale rock. Plant designs are complete. But the plant is still five years away from production.
Other researchers are experimenting with more exotic schemes. Oceanic plankton absorb carbon from the atmosphere to build their shells. Why not use the sequestered C02 as a fertilizer for vast fields of plankton? Several prototypes for this scheme are now being tested. Others want to turn C02 into rock by injecting it under high pressure into types of limestone formations where the C02 will dissolve to form carbonate rock. This is now being tested in Oman.
Finally, some researchers want to build “artificial forests”—stands of treelike towers that absorb carbon along major roads. If these towers absorb enough carbon, they will offset anything that is emitted by a coal-fired power plant.
The second area of current research is finding new (cheaper) ways to perform coal gasification and liquifaction. Although progress is being made, it is much slower than originally forecast, and that is delaying several planned gasification projects. GE & Chevron have formed a coal gasification partnership and plan a 600 Mw gasification plant in Indiana. It was originally due to go online in 2011 but has been delayed because of the nagging high cost of gasification.
How Does It Measure Up?
(The Good, the Bad, and the Ugly)
On the plus side for clean coal:
• Coal is cheap, abundant, and a U. S. resource. No importing is required.
• New technology can drastically reduce both sulfur and carbon emissions from coal plants.
• Carbon sequestration can almost eliminate the release of CO2. This new technology makes coal as clean to burn as any available source of electricity.
On the negative side for clean coal:
• Coal mining is both dangerous and polluting.
• Taken in concert, the technologies that make coal clean also make the electricity it produces too expensive to be competitive.
• The individual technologies for clean coal have been tested, but no one has put them all online at a plant that had to produce electricity 24/7 to see if they really work.
What’s the Bottom Line? (How Much Can It Help?)
• Potential: The pluses and minuses almost don’t count when it comes to coal. Coal is going to be used. Coal could provide all of the electricity we will need for the next 100+ years.
• Key Factors: Proving the technology. Liquefaction and gasification systems are developing slowly and are still too expensive. Carbon sequestration is still just theory and hasn’t been tested in the United States in a working power plant. Finally, these technologies are collectively still too expensive.
• Timeline: Look for the first clean coal demonstration plants to go online by 2015. Best guess is that their efficiency will increase and their cost will come down so that new coal plants will be mostly shifted to clean coal by 2025. By 2050 other technologies (fusion, hydrogen, solar) will begin to take over electrical production, and coal will fade, as oil has already done.
Classroom Activities
1. When we say coal is “dirty,” what does that mean? “Dirty” how? Does that mean “dirty to hold?” “Dirty to be around?” “Smoky when we burn it?” Or does it refer to what is released when we burn coal?
What pollutants are released when coal is burned that make it dirty? What pollution comes from the mining and processing of coal? Research and make as complete a list as you can of the factors that have given coal the label “dirty.”
Do the environmental hazards on your list come from all coal, or just from some types of coal? Is there a difference between types of coal? Between coal mined in different regions?
2. More generally, where are the major coal deposits in the United States? In the world? Outline and shade major coal deposits on a map of North America. Now research the characteristics and properties of coal from each major coal mining region. Are any of the differences significant to a utility that is going to burn the coal to produce electricity? If so, how?
3. Are different processes and techniques used to mine coal in different regions of the United States? Research each major technique. What does it look like? What kind of equipment is used? How big is that equipment? What are the advantages and disadvantages of each? What are the dangers and hazards of each?
4. Now let’s look at burning coal. It has been many decades since coal has been used for home heating in this country (though a century ago it was common). Most Americans alive today have never seen coal burn. What does a lump of coal look like? Feel like? How much heat does a single lump of coal contain? How long will it burn? Does it glow, or does it burst into brilliant flames? Does it billow smoke into the air as it burns? How close could you put your hands to a burning lump of coal before they became uncomfortably hot? These are questions best answered by an experiment.
What you’ll need:
Several fist-sized lumps of coal An outdoor fire pit A long-handled propane lighter A hammer
A section of newspaper Lots of hand wipes
Procedure: Buy a few of lumps of coal. You’ll have to use the phonebook or Internet to seek out a coal supplier in your area. Pass a lump of coal around and let every student feel it and visually examine it. (This is when the wipes come in handy.) Place one lump in the fire pit and light it with the propane lighter. Was it easy to light? What did it look like as it burned? Could you feel the heat as it burned? What did it smell like? Did it produce lots of smoke? Lots of ash? How long did it bum? Did the burning coal release lots of C02? Did it release other pollutants? Could you actually tell, or are you just reporting what research has established?
Let each student write up his or her impressions and images of burning coal. In their essays, have students also compare burning this lump of coal to burning a similar-sized piece of wood.
Repeat the burning experiment. But first place a lump of coal inside a folded section of newspaper. Use a hammer to crush and pulverize the lump. Now pour the granules into a pile in your fire pit and light those. Was it easier to light and burn the granules? Why? Did they burn faster? Hotter? Research how utility companies process their coal in preparation for feeding it into their power plant boilers.
For Further Reading
ABDO Publishing. Future Energy. 6 vols. Edina, MN: ABDO Publishing, 2010.
Douwe, Klaes. Clean Coal. Hauppauge, NY: Nova Science Publications, 2009.
Fix, Alexandra. Energy. Portsmouth, NH: Heinemann Library, 2007.
Miller, Bruce. Clean Coal Engineering Technology. Portsmouth, NH: Heinemann, 2010.
Miller, Bruce. Coal Energy Systems. New York: Academic Press, 2004.
Parker, Steve. Coal. New York: Gareth Stevens, 2004.
Sechrist, Darren. Powerful Planet: Can Earth’s Renewable Energy Save Our Future? New York: Gareth Stevens Publishing, 2009.
Termuehlen, Heinz. Clean and Efficient Coal-Fired Power Plants: Development Toward Advanced Technologies. New York: American Society of Mechanical Engineers, 2003.
Web Sites
www. AmericasPower. org
An industry site advocating clean coal and describing the clean coal technological process.
www. howstuffworks. com/clean-coal. htm
A good basic description of the process of creating clean coal.
www. fossil. energy. gov/programs/powersystems/cleancoal/
Department of Energy site on its clean coal program.
www. washingtonpost. com
A good article that looks critically at the process of clean coal.
www. greenpeace. org/…/clean-coal…/dean-coal-myths-and-facts
An environmental association’s assessment of the pros and cons of clean coal.
www. americaspower. org/The-Facts/Clean-Coal-Technology
An industry assessment of the pros and cons of clean coal.
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What Is It, and How Does It Produce Electricity?
Most industrial processes require massive amounts of heat as well as electricity. Typically, these two energy sources are planned for and supplied separately. Coke furnaces, giant boilers, glass furnaces, refinery furnaces, etc., billow rolling blasts of shimmering heat. Much of that heat, after it performs some chemical or physical process, becomes an unwanted stream of waste that the plant must dispose of. Power plants provide electricity by using heat to create steam. And then they, too, must deal with a constant searing flood of waste heat.
Why not use this waste heat instead of treating it like contaminated garbage to be thrown out with the trash? That is the idea of cogeneration. Like energy recapture schemes, cogeneration systems focus on using waste streams of industrial heat to create a second product. If the plant’s first job is to create electricity, then it can find some nearby facility that can use the heat to heat buildings or conduct some industrial process. If the plant’s first job is to create industrial heat, then it can use the waste heat to generate electricity.
By definition, cogeneration is the production of two useful forms of energy in a single energy conversion process. Cogeneration plants are often called combined heat and power (CHP) systems.
How does it work? A conventional power plant sucks in 130 units of energy from its fuel source to produce 35 units of electrical energy The other 95 units of energy are vented as waste heat. A CHP plant would use that 95 units of waste heat to produce 66 units of useful heat for some industrial process, actually venting only 29 units of energy as waste heat. (To produce that same 66 units of heat energy, an industrial boiler would consume 78 units of energy from a fuel and vent 12 units of energy as waste heat.)
Now add up the total energy required (and wasted) by the conventional and CHP systems. If what you need is 35 units of electricity and 66 units of heat, a CHP plant requires only 130 units of initial energy from a fuel and vents only 29 energy units as waste heat. The conventional system (separate electrical and heat production facilities) requires 208 units of fuel and vents 107 units as waste heat. CHP systems require much less fuel and produce far less waste heat and other pollutants associated with burning fuel.
CHP plants are excellent choices for industrial plants, some commercial malls, and even large residential complexes—and certainly for urban power plants located near other industrial facilities. However, only 9 percent of all U. S. electricity was produced by cogeneration plants in 2000. (Much of that was in privately owned industrial facilities and not connected to the grid.) The number of cogeneration plants hasn’t risen since then.
The U. S. Department of Energy (DOE) wanted to double U. S. cogeneration capacity between 1998 and 2010. It didn’t come close to meeting that goal. Why? There are two general reasons. The first is finding a steady market for both the heat and the electricity a
CHP plant produces. Utilities say that they have no immediate market for heat in the vicinity of most power plants. The second reason is the red tape of governmental regulations. Most industrial plants say that the red tape is too daunting to make it worthwhile to set up their own electrical production.
What’s Happening Now?
Cogeneration systems are used more heavily in Europe than in the United States. Forty percent of Denmark’s total electrical capacity is cogeneration. So is 30 percent of Finland’s, 15 percent of Germany’s, 30 percent of the Netherlands’, and 20 percent of the Czech Republic’s. The recently completed Conoco 730 MW CHP plant in Immingham, UK, supplies electricity and heat to several refineries and is currently the largest CHP plant in the world.
The United States had no cogeneration plants in 1980. The rise from there has been much slower than the DOE hoped. The DOE is working to smooth regulations to make it easier for companies to set up cogeneration plants and re-energize the growth of cogeneration systems.
The greatest innovation in cogeneration is the in-home residential cogeneration unit (currently available only in Europe). The size of a small dishwasher, the unit fits under the kitchen counter, runs on either natural gas or propane, produces electricity with a Sterling engine, and supplies the house with hot water. Models won’t be available in the United States until regulations for in-home electrical generators are revised.
How Does It Measure Up?
(The Good, the Bad, and the Ugly)
On the plus side for cogeneration:
• Cogeneration systems increase overall efficiency.
• Cogeneration systems release less waste heat into the atmosphere.
• Cogeneration systems reduce pollution. Less fuel burned means less pollution out. On the negative side for cogeneration:
• Cogeneration requires a demand for electricity and a demand for heat to exist at the same place and on the same cycle.
• Cogeneration systems are both small and privately owned. Owners often can’t afford to install the most modern pollution control equipment.
• Cogeneration systems face many regulatory and permitting hurdles.
• The initial cost is high for cogeneration systems. Too high for many potential users.
What’s the Bottom Line? (How Much Can It Help?)
• Potential: Cogeneration is an off-grid technology, which can significantly reduce the industrial and commercial demand for electricity from the grid.
• Key Factors: Cogeneration is being held back in the United States by regulation, not by the technology.
• Timeline: Look for industrial cogenerations systems to steadily increase, but to never become major contributors to the electrical grid.
Classroom Activities
Cogeneration is the process of using the burning of one fuel for multiple purposes. Utilities and large factories burn fuel to produce electricity and then use the stream of waste heat either as space heat, as heat for some industrial process, or to heat water. Cogeneration is all about more completely and efficiently using the heat released by some fuel-burning process.
You probably don’t have the equipment at your home or school to produce electricity, but you can still explore the concept of cogeneration.
1. Start with a simple incandescent lightbulb. (A 60 watt bulb or higher will work best. Do not use a florescent tube.) You turn the light on to create light—light to read by, light to see by. That is product number one.
What else does your lightbulb produce? If you are unsure, hold your hand above the bulb. What do you feel? Heat. This is waste heat. It has nothing to do with your primary product, light. What could you do with this waste stream of heat?
What about baking something with the waste heat? Place a greased, cast iron skillet on a support frame an inch or two above the lightbulb. Prepare a cake or cornbread mix according to the package directions and pour it into the skillet. Monitor the baking closely while you read a book by the bulb’s light. Bake until done. Then slap a marker into your book and enjoy some fresh-baked cake!
That is cogeneration. You used one lightbulb for reading light and for cooking heat. (You could just as easily have used the waste heat to heat water for tea or hot chocolate instead of baking.)
But don’t stop with one useful application of your waste heat. Keep going. Plenty of heat escaped from your baking skillet and rose to the ceiling. Build a large, funnel-shaped hood out of sheet metal, plastic, or even cardboard and support it above the baking skillet. Collect this rising heat and use it to dry slices of your favorite fruit that you place on a drying rack above.
Notice that at every step you turn waste energy into productive energy and thereby reduce your total demand for energy. You would have had to use electricity or natural gas to bake cornbread and to dry fruit if you hadn’t done it with waste heat from your lightbulb. The energy you didn’t use is energy you saved.
2. Start with a candle and see how many uses you can make of the light and heat it produces. What other classroom cogeneration schemes can you find or create? What about at your school? Is there a central boiler? What is it designed to do? What happens to its waste heat? Is there anything useful you could do with that waste heat?
3. Research local cogeneration plants. Local utilities and city/county planners may be able to help you find some companies that have built cogeneration units. What do their cogeneration facilities look like? What do they produce besides electricity (hot water, space heat, etc.)? How much money do these companies save each month through their use of cogeneration?
For Further Reading
ABDO Publishing. Future Energy. 6 vols. Edina, MN: ABDO Publishing, 2010.
Ballard, Carol. From Steam Engines to Nuclear Fusion: Discovering Energy. Portsmouth, NH: Heinemann, 2007.
Bowden, Rob. Energy Sources: The Impact of Science and Technology. New York: Gareth Stevens Publishing, 2009.
Claybourne, Anna. Blackout!: Electricity and Circuits. Milwaukee, WI: Raintree, 2005.
Gibilisco, Stan. Alternative Energy Demystified. New York: McGraw-Hill, 2006.
Royston, Angela. Sustainable Energy. London: Arcturus Publishers, 2010.
Sechrist, Darren. Powerful Planet: Can Earth’s Renewable Energy Save Our Future? New York: Gareth Stevens Publishing, 2009.
Web Sites
www. cogeneration. net/
An overview of cogeneration technologies and applications.
www. cogeneurope. eu/wp…/04/david-marriott-pp-presentation. pdf
Describes the European effort to expand the use of cogeneration.
www. eia. doe. gov/emeu/mecs/…/cogeneration_technology. htm
The Energy Information Administration site on cogeneration technologies.
www. energytech. at/kwk/portrait. html
A good overview of cogeneration systems.
www. powergenworldwide. com/index/cospphome. html
Describes worldwide efforts to advance cogeneration systems.
www. explainthatstuff. com > AZ index
Describes how cogeneration works and the pros and cons of cogeneration.
