OSU Research Promising For Future of Coal
COLUMBUS, Ohio – A “dramatically different” energy generating process developed at Ohio State University could keep Ohio Valley residents working in local coal mines for generations to come.
A research team led by Professor Liang-Shih Fan is using Coal-Direct Chemical Looping to generate electricity and capture 99 percent of the carbon dioxide that results from the process. That means American coal could continue to be a viable fuel for decades to come, even under strict federal limits on carbon emissions.
Consol Energy, which operates the McElroy and Shoemaker mines in Marshall County, is a sponsor of the project and has been an active participant in the research, said Daniel Connell, who works in Research and Development for Consol and has studied the possibilities for marketing the new technology.
“We’re interested in this technology because it’s one of the most promising technologies we’ve looked at in terms of reducing costs associated with capturing carbon emissions,” Connell said.
What makes the chemical looping process environmentally friendly is that the coal is burned in a sealed reaction chamber that traps the pollutants.
Fan, who is guiding work by graduate students in the Department of Chemical & Biomolecular Engineering at Ohio State, said the process uses two reaction chambers. In the first chamber, the carbon from coal reacts with oxygen from iron oxide catalysts at high temperatures to form carbon dioxide while iron oxides are converted to iron.
“In this step, steam is also produced. Thus, the carbon dioxide and steam rise; the carbon dioxide can be easily separated and captured by cooling the steam to form water,” Fan said.
Iron and coal ash are left behind, and Fan said the iron is easily separated from the coal ash because of the size difference. The coal ash is removed from the entire system. The iron is then delivered to a second chamber, where iron combustion takes place with air to produce heat that can be used for electricity generation. The combustion converts iron to iron oxides, which are then used again in the first chamber with fresh, unreacted coal.
Since 99 percent of the carbon dioxide produced can be captured, Fan said it can be used for multiple purposes, including enhanced oil recovery and chemical synthesis. It also could be “sequestered,” or stored underground.
Connell said more traditional carbon capture techniques are fairly expensive with “fairly large energy penalties,” meaning they consume a lot of the power that otherwise could be distributed via the electrical grid.
“This is a dramatically different approach to carbon capture,” Connell said. “Most involve some sort of scrubbing of the flue gas. But in this process, we completely change the way coal is burned. Instead of combusting coal in air, it circulates iron-oxygen carrier particles that pick up oxygen in one reactor and transfer it to the coal in the other reactor.
“In other plants, carbon dioxide is diluted in nitrogen. But this process produces a gas stream that is pretty pure carbon dioxide and water. You can condense the water, isolate the carbon dioxide and compress it for geologic storage. It’s a revolutionary type of approach.”
But carbon is not the only concern when it comes to Ohio Valley coal, as much coal from the region contains other pollutants such as sulfur. According to Fan, however, such chemicals are “easily manageable” in the CDCL process.
Fan said any sulfur oxides generated from the chemical looping process can be captured by a traditional flue gas desulfurization unit. The process would produce less nitrogen oxide than traditional, higher-temperature coal combustion, and the compound that is produced would be captured by a traditional selective catalytic reduction unit.
“In terms of pollutant removal, an advantage for chemical looping is that since the flue gas is more concentrated than it would be in a typical power plant flue gas, the equipment needed for removal of SO2 and NOx is smaller,” he noted.
Only a couple of solid waste products – coal ash and iron oxide – result from the CDCL process, according to Fan. The iron oxide is used to form beads that are reused in the process. And gypsum – often used by companies such as Marshall County’s CertainTeed to produce drywall – could come from the flue gas desulfurization unit.
After Fan’s team successfully produced and sustained the CDCL reaction for 203 continuous hours, it was announced a pilot power plant that will use the technology is under construction at the U.S. Department of Energy’s National Carbon Capture Center in Alabama. That plant is expected to use a very similar process called Syngas Chemical Looping to produce electricity.
Syngas, or synthesis gas, is produced from coal by burning it with small amounts of oxygen, preventing the complete combustion of coal. The products of this reaction are primarily carbon monoxide and hydrogen.
“The purpose of the reactor is experimental in nature, to simulate a chemical looping reactor before building a larger power station, so it means little to the average consumer at the present,” Fan said. “However, in the long term, the development of such a system would benefit the consumer greatly in the cost of electricity under a carbon-constrained economy, i.e., carbon cap and trade.”
Connell said the OSU team’s sustained CDCL reaction was achieved in a unit that fits inside a university building, producing 25 kilowatts of energy. The pilot plant in Alabama will produce about 10 times that much power, he said. A larger pilot plant likely will follow, he noted, producing “a couple of megawatts.”
Since commercial power plants can produce anywhere from 50 to 1,000 megawatts of electricity, Connell said it will take “an absolute minimum” of five to 10 years to bring the technology to market.
“Both the SCL and CDCL technology can meet the U.S. (Department of Energy’s) goal of less than 35 percent increase in cost of electricity for the production of a new power plant,” Fan added. “The commercial scale size of these processes could also be used for re-powering existing coal-fired power plants or newly constructed coal-fired power plants.”
So what type of impact could the new technology have on the national and local economies?
“The CDCL technology would be a job creator in a number of ways,” Fan said. “First, the design and construction of CDCL power plants would be needed to replace the aging fleet of coal-fired boilers in the United States. Once the plants are up and running, the plants would require teams of engineers and operators to run the systems. Thus, the jobs would be increased in the coal industry and power generation industry.
“This could indirectly influence the amount of coal mined by increasing coal supply to meet coal demands in a cleaner process,” he continued. “The CDCL process would also be beneficial to the coal miners of America, since it would still allow for the production of coal even under a carbon-constrained economy.”