A Rice University research team is one of 16
chosen by the U.S. 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-mW coal-fired power plant emits enough carbon dioxide 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,” says
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 carbon dioxide, but if we can find a feasible way, it could really change
George Hirasaki, Warudkar’s adviser and the principal investigator on the
new DOE grant, says the petrochemical industry has tried-and-true technology for
capturing and removing carbon dioxide from high-pressure natural gas.
Unfortunately, that technology is costly for separating carbon dioxide from
flue gas at normal air pressure. Hirasaki says 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 says natural gas producers today use a two-phase chemical process to
remove naturally occurring carbon dioxide. 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 carbon dioxide and drains
away while the purified natural gas bubbles out of the column. In the second
phase of the process, the carbon dioxide-containing amine is recycled with
intense heat, which drives off the carbon dioxide.
“This is a proven process, but it is impractical to scale it up at a
power plant,” says Hirasaki, Rice’s A.J. Hartsook Professor of Chemical
and Biomolecular Engineering. “At a 500-mW 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 carbon dioxide 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 says. “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
Warudkar says, “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 says.