June 15, 2007

Climate change concerns drive projects to curb CO2

Bill Ellison, PE

The best of the rest

In other sessions, presenters brought attendees up to speed on the use of advanced combustion technologies to mitigate CO₂ emissions. For example, Keith Morris—chief engineer for the Americas region at Doosan Babcock—presented details of his company's supercritical and ultrasupercritical boiler designs using oxy-fuels. He said he considers retrofits of existing plants a "major priority." In its vision of CO₂ capture-ready plants, Doosan includes plants that have been upgraded to increase their thermal efficiency and to enable the cofiring of biomass.

Among Doosan's clients are the 500-MW subcritical Units 1 and 2 of SSE's Ferrybridge Power Station in Yorkshire, UK, which will be converted to run at supercritical pressures and temperatures while maintaining their net power output. Estimates place the total cost of converting each unit at $480 million, or about $1,000/kW. When the project is completed in 2011, cycle efficiency will have risen substantially, from 37.2% to 46.2%. Doosan is actively developing oxy-coal firing technologies as well. For example, the company plans to use an existing 90-MW multifuel burner test facility to demonstrate, assess, and commercially develop its oxy-fuel firing process.

Oxy-fuel combustion (Figure 4) was also the subject of a presentation by Minish Shah of Praxair Inc. In his view, making a plant CO₂-capture-ready will require giving it the ability to fire air or oxygen. Based on Praxair's R&D efforts to date, including operating pilot plants as large as 5 MW_t, developers already have determined the optimum oxygen concentration for flame stability and a way to use flue gas recirculation to maintain heat fluxes. According to Shah, the developmental steps that still need to be made include:

• Validating models for flue gas recycling, flame properties, heat fluxes, and temperatures by demonstrating them at 10 MW to 100 MW.
• Determining suitable materials for boiler components.
• Designing a boiler with minimum air in-leakage.
• Adequately controlling its emissions of SO_x, NO_x, and mercury.
• Managing trace impurities in flue gas.

No technical track on climate change would be complete without an update on the progress of the DOE's $250 million FutureGen project (Figure 5). Jerry Oliver of the FutureGen Industrial Alliance provided it. This 275-MW research plant, still on track to be completed by 2012, will use IGCC to generate electricity and hydrogen with near-zero emissions. It also will capture and sequester, in underground geologic formations, the 1 million metric tons of CO₂ it will produce each year.

5. The industry's Holy Grail. An artist's rendering of the near-zero-emissions FutureGen plant, scheduled to come on-line in 2012. Courtesy: U.S. Department of Energy
 

According to Oliver, FutureGen has moved beyond the development and initial conceptual design phase into Phase 2, the detailed design phase. Phase 3, featuring even more detailed design, is scheduled to begin next year. In the final phase, a program of modeling and monitoring will verify the safety and permanence of CO₂ sequestration.