Published on October 26th, 2011 | by Andrew5
Fuel Cell-Coal Plant CO2 Capture: Clean Tech Breakthrough or Ill-Conceived Diversion?
October 26th, 2011 by Andrew
Connecticut’s FuelCell Energy recently received an award from the Dept. of Energy (DOE) to employ its patented Direct FuelCell (DFC) technology in building a pilot demonstration CO2 capture system attached to a coal-fired power plant. This third post on the project – see Parts 1 & 2– explains the way the system is designed to work and what the project aims to achieve.
Back in August, the DOE announced $41 million of funding to help further develop and test 16 advanced post-combustion coal plant CO2 capture technologies. FuelCell Energy’s DFC-coal plant CO2 capture system was one of the 16 projects to win an award.
The DOE’s primary target objectives are straightforward and the same for all the projects receiving funding: capture at least 90% of the plant’s carbon dioxide (CO2) emissions with no more than a 35% increase in the plant’s cost of electricity (COE).
If successful, the technology will not only turn out to be more efficient in terms of capturing CO2 from coal-fired power plants, it would do so as significantly lower cost than is otherwise possible at present. Additionally, it would add ‘clean’ electricity to the plant’s output, while also eliminating the plant’s N2O emissions, a greenhouse gas 300-times more powerful than CO2 at trapping heat in the atmosphere.
How It Works
Here’s the basics regarding how FuelCell Energy’s technology is designed to work.
Post-combustion of processed coal to produce steam and electricity, the coal plant’s emissions – its flue gas – will be channeled and concentrated as it makes its way to the membrane-based carbonate DFC fuel cell system’s cathode intake.
The flue gas – typically anywhere between 5%-15% CO2, with the rest a mix of N20 and air – will be concentrated to the point that makes it much easier to siphon it off from the bulk of the air and nitrogen oxide (NOX) that makes up the plant’s flue gas emissions.
The air will continue to the DFC system’s cathode intake, where a catalyzed chemical reaction will take place that results in the production of oxygen that will be used in the fuel cell’s electricity production process. The nitrogen, along with excess, free oxygen, will be vented out of the system’s exhaust.
Ninety-percent (90%) or more of the now separated flow of CO2 gas will then either be captured as a gas or condensed into liquid form depending on whether it would be stored or sold on for industrial or commercial use.
At the other end of the fuel cell system, a stream of natural gas – methane (CH4) – will be channeled to the anode intake of the DFC system’s fuel cell stacks. On its way there, it will be mixed with water, in vapor form, and reformed, a process in which the methane will react with oxygen in the water vapor to transform the methane into CO2 and the virtually pure hydrogen (H) gas the DFC stacks needs to produce electricity.
Like the CO2 captured from the flue gas, 90% or more of the CO2 produced from methane reformation will be condensed and captured in gas or liquid form depending on whether it is to be stored or sold on for industrial or commercial purposes.
FuelCell Energy’s Value Proposition
FuelCell Energy director of investor relations Kurt Goddard supplied the equation for the chemical reaction that takes place at the DFC’s anode, which is also shown in the diagram preceding the previous section:
CH4 + 2H2O –> 4H2 + CO2
Goddard explained that at the 2.8 megawatt (MW) scale envisioned for the DOE project, the DFC process is about twice as efficient in terms of CO2 emissions per unit of electricity produced than a coal-fired power plant.
“For a 2.8MW fuel cell, the methane input is about 1000 pounds per hour, and the CO2 produced is about 2500 pounds per hour. A 2.8 MW coal plant would produce about twice as much CO2, because it is much less efficient and needs more carbon based fuel.
“In the carbon capture system, the coal plant’s CO2 is mixed with the DFC plant CO2 and about 90% of the mix is separated out from the fuel cell waste stream as gas or liquid depending on how the CO2 is going to be used or disposed of.”
FuelCell Energy views the resulting gains in the efficiency of both capturing and avoiding direct CO2 emissions into the atmosphere and producing “ultra-clean” electricity as making the DFC system a potentially breakthrough technology.
“Here is the value proposition that we are trying to prove with the award,” Goddard continued. “We can capture 90% of the CO2 emitted by a coal fired power plant within the cost parameters specified by the DOE and we do this while also generating ultra-clean power rather than using power, which current CO2 capture technologies do.”
Net CO2 Emissions
Readers of past posts in this series questioned the benefits that would be gained by employing this technology on an industry-wide basis, as well as the conception of the DOE’s coal plant-CO2 capture program in the first place.
Notably, one of their main points was that they would not result in a net reduction of CO2 emissions. Put to Goddard, he responded, “A net reduction’ isn’t what the DOE is trying to accomplish nor are we. The goal is to efficiently and cost effectively capturing CO2 to prevent the release into the atmosphere.
“Fuel cells generate power very efficiently with substantially less CO2 output than a coal-fired power plant if the fuel cell is fueled with clean natural gas, and is typically classified as carbon-neutral if fueled by renewable biogas. We have a number of installations fueled by renewable biogas, including municipal water treatment facilities and a food processor, for example.”
With the assistance of comments from readers, as well as industry participants, I hope to continue exploring the merits and demerits of developing of an efficient, cost-effective method of capturing CO2 from coal-fired power plants’ emissions.
To be included is delving into the impact fuel cell-CO2 capture technology not only from coal plants but from other hydrocarbon sources might have in terms of energy economics, as well as on our evolving energy resource mix and on renewable energy development and growth.
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