Oxyfuel technology may offer solutions to the problems and promises of coal—and at new technologies that capture and store CO2 Generating Controversy.
In conventional combustion, coal is burned in air. Air is three quarters nitrogen, and that nitrogen ends up in emissions. But in oxyfuel technology, the nitrogen is removed at the outset, and so emissions are nitrogen-free. Sulfur is scrubbed from the emissions the usual way.
Lars Strömberg was former chief engineer of the oxyfuel pilot project and is now Vattenfall's head of research.
STROMBERG: If we can take away this nitrogen from the combustion process, then the fuel gases consist mainly of water vapor and carbon dioxide only, which means that if we can condense the water vapor, we have more or less pure carbon dioxide. Therefore, we don't need any separation technologies.
SWEET: Removing nitrogen from air is the most costly part of the oxyfuel process. Strömberg believes it can be made more efficient and inexpensive in the future.
STROMBER: Yes, definitely. First of all, the cost will decrease with size. Secondly, we can reuse parts of the energy in the power process.
SWEET: If the cost of obtaining pure oxygen from air can be reduced by using waste heat from the plant, the oxyfuel process may be an attractive way of doing carbon capture.
When people talk about capturing and storing carbon from coal combustion in the United States, the focus usually is on a technology called IGCC. IGCC involves gasifying the coal to generate electricity, but it doesn't work well with coals that are dirty and inefficient, like lignite or soft coal.
Studies comparing the relative costs of capturing carbon, using IGCC versus oxyfuel, usually give a slight edge to IGCC. Cost estimates are in the same ballpark, however, and the IGCC plants in operation have never actually captured carbon.
Because of oxyfuel's simplicity and its suitability for lower-grade coals, the U.S. power equipment manufacturer Babcock & Wilcox also has been taking a strong interest in this approach. Speaking to a congressional committee last March, Babcock CEO John Fees said the company is putting its eggs in the oxyfuel basket.
And let me repeat that: It's the first commercial scale, near zero-emission coal plant with carbon storage in North America.
SWEET: Since last summer, Babcock & Wilcox has been testing oxyfuel combustion at a research plant in Ohio that's the same size as Vattenfall's German facility. But the Ohio test facility does not have the equipment to separate oxygen and nitrogen on-site or to capture carbon dioxide and store it in the ground at the end of the process.