Describe the carbon capture technology and how Dr. Rochelle will improve it. The amine-based technology involves two steps for treating carbon dioxide produced by burning coal: absorption and stripping.In the first step, the carbon dioxide gas is dissolved (absorbed) into a solution containing an organic chemical such as monoethanolamine. The amine solution is added into a column containing metal strips. The column provides a surface for interacting with carbon dioxide in smokestack gas pumped into the column. As the solution passes down the column it contacts the stack gas and captures the carbon dioxide. The amine solution containing the carbon dioxide pools at the bottom of the column.
After the monoethanolamine solution fully absorbs the carbon dioxide, Dr. Rochelle’s second step concentrates and isolates the carbon dioxide. The amine solution is added into the top of another, stripper column. As it flows down the metal strips within it, carbon dioxide is transferred to water vapor that rises from the bottom. At the bottom the amine solution is boiled to produce the water vapor used for stripping. The amine solution without carbon dioxide is then recycled to the absorber to pick up more carbon dioxide from the stack gas column to produce water vapor. The carbon dioxide is collected as pure gas at the top of the stripper column.
To store the carbon dioxide underground (carbon sequestration) it would be compressed to high pressure and cooled to form a liquid. With the same decades-old process now used to recover oil from reservoirs, the he liquid carbon dioxide can then be injected underground into sandstone formations for storage.
Who is engaged in the carbon capture-related research? Dr. Rochelle's research group in the Department of Chemical Engineering includes 10 Ph.D. students working on the carbon absorption/stripping program. Two senior researchers and three staff members are performing prototype plant testing with Dr. Frank Seibert, head of the Separations Research Program.
For carbon sequestration, five faculty members and five graduate students are addressing sequestration and enhanced oil recovery in the university’s Department of Petroleum and Geosystems Engineering with Dr. Steven Bryant. Several senior researchers and staff members are studying carbon sequestration in the Gulf Coast Carbon Center of the university’s Jackson School’s Bureau of Economic Geology with Dr. Ian Duncan.
Can this technology be used on existing and new power plants in Texas? This is retrofit technology that can be added without modifying existing technology in current or future conventional coal-fired power plants. Sandstone formations that could be used to inject the captured carbon dioxide are abundant in Texas.
How does the amine-based technology differ from power production with coal gasification? Gasification is more risky because it requires that new technology be incorporated with existing technology throughout a power plant. Solid coal is reacted at high pressure with pure oxygen and steam. In the next step the gaseous product is cooled and converted to carbon dioxide and hydrogen. Then the carbon dioxide and other pollutants are captured from the hydrogen in several sequential steps similar to the absorption/stripping process that would be used with conventional coal-fired power plants. Finally the hydrogen is burned with air in a gas turbine to produce power.
When can carbon capture technology be used on coal-fired power plants? Absorption/stripping with a liquid amine has already been used for 70 years to remove carbon dioxide produced by burning natural gas. And a few coal-fired power plants that are small (less than 40 Megawatts equivalent) have technology to remove carbon dioxide from smokestack gas. However, the energy required for the carbon dioxide capture process has been a factor in preventing its widespread use.
The second-generation, amine-based technology that Rochelle is developing could be ready to be tested on a prototype, 20 megawatt, coal-fired plant by 2009; on a 200 megawatt prototype, by 2011; and on an 800-megawatt commercial plant that matches the size of many coal-fired power plants being planned, by 2013. If the testing of the technology on these three prototypes occurs as expected, the updated technology could be available for widespread application on existing and new coal-fired power plants by 2015.
What will be accomplished in the ongoing work funded by TXU? The six-year program funded by TXU will address shortcomings in the amine-based capture process and in subsequent carbon storage. Dr. Rochelle’s laboratory is optimizing the use of a chemical additive to enhance the absorption step of carbon dioxide capture. To reduce energy needs, Dr. Rochelle’s group will also study whether the carbon dioxide stripper can be turned off during times of peak demand on the power grid, and how to reduce the cost and maintain reliability of the absorber equipment needed for capture carbon when the equipment is expanded to meet the needs for an 800-megawatt power plant. This size plant will require four absorber chambers, each about 50 feet in diameter and 100 feet tall.
In addition, the lab will study how to reduce the degradation of the amine in the presence of oxygen, sulfur dioxide, and other smokestack gas impurities. And Dr. Rochelle's group will study how to minimize chemical byproducts of the carbon capture steps that are environmental pollutants themselves.
The challenge in carbon sequestration is ensuring the liquid carbon dioxide stays within sandstone formations. A strategy for immobilizing the liquid carbon dioxide that was developed at the university’s Center for Petroleum and Geosystems Engineering will be examined in further detail. Dr. Steven Bryant will lead this effort, which will include examining the effect of rock properties and alternative modes of injection on secure storage schemes.
More details are given in the prospectus for the TXU Carbon Management Program at:
http://www.che.utexas.edu/rochelle_group/TXU%20Carbon%20Management%20Program%20Prospectus.pdf.pdf
