ALSTOM MOVES FORWARD ON CHEMICAL LOOPING TESTS AT PILOT FACILITY

Tamar Hallerman
GHG Monitor
07/20/12

Researchers at Alstom Power are testing the technical viability of chemical looping combustion technology on the world’s largest scale yet at company facilities in Connecticut over the next several months. The French power systems equipment manufacturer last week began running tests on the oxidizer loop of its 3 MWt pilot unit, which is receiving National Energy Technology Laboratory support and is utilizing calcium sulfate, or gypsum, as an oxygen carrier in circulating fluidized bed ash. The tests are part of a series expected to be undertaken over the next year examining the technical integration of the process, which has been praised by many as one that could help spearhead cheaper and more efficient second-generation carbon capture technology. “The challenge of this technology is getting all of the reactions and the thermal energy properly integrated together with the transport of the solids,” said John Marion, director of technology and R&D for Alstom Power’s boiler division, in an interview. “At this point we’re trying to be systematic in terms of taking the steps to do that.”

Alstom’s prototype and pilot testing in the U.S. and Europe is ahead of the pack in helping advance a category of CO2 capture technology that has been of keen interest to the Department of Energy over the last decade. Chemical looping is considered a new class of carbon capture most similar to oxy-combustion technology—both aim to combust fuel in a pure oxygen environment, producing a flue gas which largely contains just CO2 and water vapor. But while oxy-combustion typically uses an expensive air separation unit—which carries a large energy penalty of 15-20 percent of the power plant in addition to another 6-7 percent energy penalty for CO2 compression—chemical looping ditches the separation unit and instead uses two circulating fluidized bed reactors, one for air and one for fuel. The first reactor loop reacts the coal with a solid oxygen carrier—either a metal oxide like iron, nickel or copper, or an alkali such as calcium sulfate—at high temperatures to make CO2 directly. Meanwhile, the second reactor regenerates the solid oxygen carrier, which has been depleted of its oxygen, by a reaction with the air and then transports it back to the fuel reactor so that the process can be run again, leaving pure CO2 that is essentially ready for sequestration or processing. Meanwhile, the process gives off heat, which can generate steam that can turn a turbine and generate electric power.

Flexible Option

Researchers have praised the technology for being flexible—developers like Alstom say it can be used for gasification and hydrogen production as well on new plants and retrofits. “This is, I would say, a game-changing technology for power generation, particularly for high-efficiency, coal-based power with carbon capture,” Marion said. He added that early estimates show that, if successfully deployed on a large scale, chemical looping could have capital costs that are roughly 20 percent lower than competing technologies currently being developed elsewhere, as well as an energy penalty as low as 10 percent, a large decrease over current technologies. “We believe that it’s the lowest levelized cost option of any capture technologies that we’ve looked at so far,” he added.

Chemical looping is seen as a particularly attractive option due to its projected cost savings above currently available capture technologies. That is due to a variety of reasons, according to the Global CCS Institute’s Carl Bozzuto, who previously worked at Alstom Power as a vice president for technology. In a webinar on the topic last week, Bozzuto said that cost savings are achieved due to the significantly smaller building volume of reactors and materials used—such as the boiler and gasifier—compared to other capture technologies. The absence of an air separation unit also leads to significant cost savings, he said. “Essentially we’re doing the reactions in what one might consider a conventional fluidized bed equipment, without adding either a full scrubbing system or an air separation plant to the total cost of the plant,” Bozzuto said. He added that the technology’s operating temperatures can also help achieve cost savings. “Chemical looping combustion is a potential breakthrough technology [because] it operates the reactors at a temperature that’s higher than the steam temperature—essentially any of the inefficiencies in the separation and capture of the CO2 show up as heat rejected to the steam cycle, where at least some of that energy can be recovered,” he said.

Marion said that another reason for the lower costs and higher efficiency is because chemical looping systems use solids to carry the oxygen in and out of the process, leaving essentially no thermodynamic penalty associated with either the carbon separation or the oxygen production. “This is all taking place at temperatures which are not impeding the basic thermodynamics of the power plant. So the only real penalty is associated with the compression system, which is less than 10 percent of the overall process, as compared to conventional technologies of 20-25 percent,” Marion said.

Other Chemical Looping Variations Being Developed Elsewhere

In addition to the 3 MWt calcium sulfate pilot system, Alstom is also moving forward with research on another prototype in Europe, this one using ilmenite, a titanium-iron ore metal oxide carrier, via a 1 MWt system in Germany for a European Union project called ÉCLAIR. Both projects are building off of previously concluded research completed on a 65 kWt proof-of-concept prototype system, which looked at 15 and 40-foot cold flow models and helped verify the basic physics and chemistry of the process, according to Marion.

Elsewhere, other groups are also looking at the technology on bench and small pilot scales, with a particularly large interest in the U.S., Europe and China. At the National Energy Technology Laboratory’s capture technology conference last week in Pittsburgh, representatives from the University of Utah and Ohio State University spoke about their chemical looping work that has been funded in part by DOE. Research at the University of Utah is looking at copper as a potential metal oxygen carrier, JoAnn Lighty, a professor of Chemical Engineering, told GHG Monitor on the sidelines of the meeting. The metal is promising because it is non toxic and widely available, she said. “The copper releases oxygen to combust the coal, versus gasify it, which makes it different from [other] systems,” she said. “The idea is that if it releases the oxygen, you have a combustion reaction, which is faster than gasification in terms of the amount of time it would take to burn out or char.”

Meanwhile, researchers at Ohio State University have been moving forward on tests using their ‘Coal Direct Chemical Looping’ technology, which is being developed particularly for coal retrofits. The group used nearly $4 million in funding from DOE, the Ohio Coal Development Office and other industry groups to design, construct and demonstrate an integrated 25 KWt coal direct chemical looping sub-pilot unit to show the process’ technical and economic attractiveness, said OSU’s Andrew Tong in a presentation. The group also has a $5 million DOE Advanced Research Projects Agency-Energy (ARPA-E) grant to test their iron-based oxygen carrier at the National Carbon Capture Center in Wilsonville, Ala.

Technology Still Faces Barriers

However, the technology is still in its fairly early stages of research and development and will take years of more thorough testing and scale up before it can be seen as a real option for CO2 capture, experts say. Lighty said that several technical issues must be resolved before widespread deployment is possible. She listed oxygen carriers and their interactions with coal ash particles and the separation of the oxygen carrier near the end of the looping process as technical unknowns that still must be resolved. “Those operating conditions are really things that need to be worked out as the technology advances to larger scales,” she said.

But even if the technology does not reach its full potential, Marion said, its impact on the field in terms of cost savings and efficiency could still be significant. “The numbers are pretty dramatic in terms of the potential for this technology. In all of the studies that we have done… this [technology] produces the lowest cost of electricity with carbon capture and sequestration of all options, and so this motivates us to carry on with the technology,” he said. “While we would probably still characterize this technology as high risk because we’re trying to make it work and prove that it works, it could also be high reward because it’s really distinguished from all of the options we’re aware of. We think that even if we’re overly optimistic, the potential improvements are so great that it’s motivated us to carry forward.”