OSU's run is the longest to date for a "chemical looping" reactor consuming coal, according to the U.S. Department of Energy, and in Fan's view it means the technology is ready for testing at pilot scale.
OSU's chemical looping reactor (the centerpiece for a US $7.1 million ARPA-E project that began in 2010) is so named because it circulates its components in a continuous loop in a manner that controls the interaction of pulverized coal and oxygen to prevent ignition of the coal. "We carefully control the chemical reaction so that the coal never burns—it is consumed chemically, and the carbon dioxide is entirely contained inside the reactor," says Fan.
Tiny iron oxide beads (see right bottle in photo above) roughly 1.5-2 millimeters across efficiently and precisely manage the oxygen supply to the coal particles (left bottle in photo), which are 15-20 times smaller. The beads enter the first reactor chamber oxidized and react with the coal particles, heating the iron oxide and producing CO2. The CO2 bubbles up and out and is captured, while the beads flow on into a second chamber where air flow reoxygenates the beads and carries away their heat (25 kilowatts for their 8-meter-tall lab-scale reactor). The oxidized beads then loop back to start another round.
In principle OSU's chemical looping reactor should be more efficient to operate than conventional oxyfuel reactors, which rely on power-hungry air separation units for their oxygen supply. Modeling of a full-scale plant by coal-fired utility Consol Energy, a partner on the ARPA-E project, suggests that it should at least meet DOE's goal for carbon capture technology: greater than 90 percent capture while raising the cost of coal-fired power generation by less than 35 percent.
Engineering firm Babcock & Wilson, another OSU partner, picked up $988,000 in DOE funding last year to design a larger, pilot scale test of Fan's reactor.
Meanwhile Fan and his partners are already moving towards pilot-scale testing of a simplified version of their looping reactor at the U.S. Department of Energy’s National Carbon Capture Center in Wilsonville, Ala. Rather than combusting pulverized coal, it will consume a blend of carbon monoxide and hydrogen -- the gas stream produced when coal is gasified. OSU plans to have it running towards the end of 2013.
Photo: Jo McCulty/Ohio State University
Peter Fairley has been tracking energy technologies and their environmental implications globally for over two decades, charting engineering and policy innovations that could slash dependence on fossil fuels and the political forces fighting them. He has been a Contributing Editor with IEEE Spectrum since 2003.