University shows the world how to burn cleaner coal and reduce emissions
Almost 30 years ago, Virginia Tech engineering researchers Roe-Hoan Yoon, Gerald Luttrell, and Gregory Adel received a grant from the University Coal Research Program, United States Department of Energy, to develop a method of recovering fine coal particles dispersed in water.
The coal fines are produced during the process of mining coal and cleaning, or washing, it in water. The three researchers had proposed to Department of Energy that they could recover the coal fines using small air bubbles, called microbubbles.
Their research effort resulted in a commercially successful technology, which is being marketed under the trade name Microcel flotation column. Although it was developed originally for coal companies to recover fine coal from waste streams, the technology is now used in both the coal and minerals industries. Two companies, Metso Minerals and Eriez Manufacturing, are marketing them worldwide under license agreements from Virginia Tech. It took a while, however, for the technology to achieve the worldwide prominence it has today.
Eriez has hired four Virginia Tech doctoral graduates, all trained on the Microcel technology. The expertise and scientific background they acquired during their studies at the university were instrumental in bringing the technology to the market place. Mike Mankosa, Class of 1983, is now serving as the vice president of operations, and has recently received the Outstanding Alumni Award from the mining and minerals engineering department for his achievement.
During the past 10 years or more, Yoon, a member of the National Academy of Engineering, and his colleagues have been developing advanced dewatering technologies. Because the coal is washed in water during the Microcel process, it is necessary to remove the water before shipping and utilization. One of the advanced dewatering technologies involves specialty chemicals that can be added to various vacuum or pressure filters. It is licensed to Nalco, a $3.5 billion company, for worldwide distribution. Steve Abbatello, Class of 1982, is responsible for this activity as the strategic business unit leader of the Global Mining and Metals Division of Nalco.
To facilitate the marketing and sales of the specialty chemicals, Nalco opened a laboratory at Virginia Tech’s Corporate Research Center and hired two of Yoon’s former Ph.D. students and two undergraduate students as co-op students. “Industry needs the high-tech trainee to understand the value of the technology and to be able to transfer it properly to the industry,” Luttrell said.
Advanced separation technologies developed by Yoon and his colleagues at Virginia Tech will also be used in developing countries like India and China to reduce the emission of carbon dioxide, or CO2, the major green house gas. As part of the Asia-Pacific Partnership on Clean Development and Climate (APP) program, the United States Department of State is funding Virginia Tech to help India burn coal more cleanly and reduce CO2 emissions in coal-burning power plants.
The most exciting offshoot to the technology development may lead to a leap in science. Yoon is expounding upon his effort to prove the existence of the large attractive force between hydrophobic substances, such as coal, placed in water. As the force is observed only between hydrophobic surfaces, it is referred to as “hydrophobic force naturally.” It was first reported in Nature by Professor Jacob Israelachvili of the University of California and Professor Richard Parshley of Australian National University in 1982. However, its scientific origin is still not known, and many scientists argue that it is due to artifacts. Yoon says he believes it is real.
The difficulty in accepting the existence of the hydrophobic force for many scientists lies in the fact that the attractive force is detected at relatively large distances, with up to 60 to 80 nanometers (nm) separating two hydrophobic surfaces. (One nm is one millionth of a millimeter.) Some researchers suggested that the hydrophobic force was created by the nano-sized air bubbles existing on hydrophobic surfaces, which has recently been disproved by Yoon and his colleagues at Virginia Tech in a scientific publication.
Yoon believes that the new attractive force originates from the tendency of water molecules to re-orient themselves around hydrophobic surfaces. “Understanding the basic sciences involved will have far-reaching consequences in engineering and science. Further, all of the fossil energy resources, such as coal, oil, natural gas, bitumen in oil sands, kerogen in oil shale, and methane hydrate, are more or less hydrophobic. Therefore, understanding the nature of the hydrophobic force will help exploring and utilizing these resources efficiently and in a manner that can improve the environment,” Yoon said.
Yoon and his graduate students used the hydrophobic force in mathematically modeling the process of coal particles being collected by air bubbles during flotation, which is one of the most important separation processes used in the minerals and coal industries. FL Smith, the largest flotation machine supplier in the world, is funding the project to further develop the model for optimal design and operation of new flotation machines.
In addition, Yoon can also explain the formation of methane hydrate in ocean floors and permafrost using the improved understanding of basic sciences involved in the hydrophobic interaction. Methane hydrate refers to the methane (CH4) molecules encapsulated in ice crystals, and is dubbed as “the ice that burns.” The amount of methane, the cleanest form of fossil fuel, present as hydrate in the world amounts to 400 million trillion cubic feet (tcf), which is 73.000 times larger than the conventional natural gas resource, and is larger than all fossil energy resources combined.
“On the other hand, methane is a 21-times more potent green house gas than CO2,” Yoon said. “Therefore, we are better off to recover and utilize it.” According to the United States Geological Survey (USGS), the Blake Ridge deposit off the shores of the Carolinas alone has approximately 1,300 trillion cubic feet of methane as hydrate, which is more than six times larger than the total conventional natural gas reserves left in the United States. He pointed out that Virginia Tech has the largest and closest mining school to this enormous resource.
Yoon is pleased that he has recently received significant funding from the Department Energy to expand his hydrate research. As part of this, his group is exploring the possibility of separating different gasses, such as CO2 and nitrogen, from each other by selectively forming gas hydrates. Over the 30 years, his center has received $15.3 million from the Department of Energy.
“Success of the new program will help increase the availability of low-cost energies to sustain economic growth, prosperity, and way of life. Furthermore, the long-term, high-risk research projects based on fundamental research will serve as vehicles for training students to become future leaders in industry and academia,” Yoon said.