HOUSTON -- (Sept. 20, 2011) -- A Rice University research team is one of 16 chosen by the Department of Energy (DOE) to develop innovative new technologies that can significantly reduce greenhouse gas emissions by capturing carbon dioxide from power plants.
Coal- and natural-gas-fired power plants account for about half of the carbon dioxide that humans add to the atmosphere each year. For example, a 500-megawatt coal-fired power plant emits enough carbon dioxide (CO2) each day to fill the Houston Astrodome more than 400 times.
"The sheer quantity of carbon dioxide emitted by power plants represents both a daunting challenge and a terrific opportunity," said Rice graduate student Sumedh Warudkar, a co-investigator on the Rice University team. "It's a difficult technical challenge to capture such a large volume of CO2, but if we can find a feasible way, it could really change things."
George Hirasaki, Warudkar's adviser and the principal investigator on the new DOE grant, said the petrochemical industry has tried-and-true technology for capturing and removing CO2 from high-pressure natural gas. Unfortunately, that technology is costly for separating CO2 from flue gas at normal air pressure. Hirasaki said Rice's team will create new technology that uses similar principles but takes advantage of high-tech materials. The team includes Michael Wong, professor of chemical and biomolecular engineering and of chemistry and Warudkar's co-adviser; Ed Billups, professor emeritus of chemistry; and Ken Cox, professor in the practice of chemical and biomolecular engineering.
Hirasaki said natural gas producers today use a two-phase chemical process to remove naturally occurring CO2. The natural gas is piped upward through a vertical column while an ammonia-like liquid called amine flows down through the column. The liquid amine captures the CO2 and drains away while the purified natural gas bubbles out of the column. In the second phase of the process, the CO2-containing amine is recycled with intense heat, which drives off the CO2.
"This is a proven process, but it is impractical to scale it up at a power plant," said Hirasaki, Rice's A.J. Hartsook Professor of Chemical and Biomolecular Engineering. "At a 500-megawatt plant, the heat required for the second phase would consume about one-quarter of the steam that would otherwise be used to generate electricity."
As part of his dissertation research, Warudkar spent the past three years developing a novel system for separating CO2 from the smoke stacks of coal-fired power plants. In Warudkar's system, both phases of the process are carried out a single column. Using process simulations, Warudkar showed he could significantly reduce the heat requirement by keeping part of the column in a vacuum and using specialized materials to filter the liquids and gases.
"The idea is to use waste heat -- recycled steam that has already been used for electrical generation," Hirasaki said. "Ed Billups' and Michael Wong's groups are going to work with us to chemically modify the ceramic foam surface inside the column so that we can optimize its performance. Ultimately, we hope to wind up with a column that is many times smaller and more efficient than what would be required with existing materials and technologies."
Warudkar said, "Because we're experimenting with a new process, a lot of optimization will be required. Ken Cox will help us meet the energy integration objectives by leading our efforts in thermodynamic modeling."
The team's goal is to work toward a full-scale test of the technology within three years, Hirasaki said.
Warudkar, who is also president of Rice's Graduate Student Association, took the lead role in developing, writing and submitting the DOE proposal. "Sumedh deserves the credit for this," Hirasaki said. "He worked hard to make it happen, and the support speaks to the quality of the research he's conducted here over the past three years."