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January 13th, 2010

Can natural gas-SOFC combo be cheapest route to cleaner electricity?

Published on January 13th, 2010 | By: pwray@ceramics.org
Credit: Thomas Adams

Credit: Thomas Adams

Two researchers at MIT say they have what will be “the lowest price option” for power generation in the future if a carbon tax is every levied in the United States (as long as the tax is $5 – $15 per metric ton of emitted CO2).

The duo – Thomas Adams and Paul Barton – have proposed a novel electricity generation process that weds natural gas and solid oxide fuel cells using off-the-shelf technology, and have applied for a patent for their concept. A paper on their work has been printed in the Journal of Power Sources.

Their process contains a steam reformer that prepares the gas for use within the fuel cells. The reformer and water-gas shift reactor creates a fuel mix absent carbon monoxide, thus avoiding the problems created by carbon deposition issues in SOFCs when CO is present. CO2 is generated, but they say it will be “mostly pure” and can be captured with very little energy penalty using a multistage flash cascade process. High-purity water is another byproduct.

Adams and Barton developed the concept while looking at possible “clean-coal” approaches, and they admit their system could also work with pulverized coal. But, the relatively greater abundance of natural gas and its smaller amount of CO2 emissions (an MIT news story reports that existing natural-gas power plants produce one-third to one-half the CO2 of coal-burning plants) provide two strong reasons for using this fuel.

And price – under the right circumstances – could be a third reason. Adams and Barton developed and used a computer simulation methodology to analyze the relative costs and performance of their system versus other existing or proposed generating systems, including natural-gas or coal-powered systems incorporating carbon capture technologies.

They found that even if the cost of fuel cells remains more than double the DOE’s target for 2010, their SOFC system has the lowest lifecycle costs of electricity produced, even though the up-front capital costs could be three to four times greater than for natural gas or coal combustion systems.

The simulation even indicated that the lifecycle cost of this novel system is lower than that of a combined-cycle natural gas plant, even without carbon pricing. They say that even with a carbon tax around $5 to $10 per ton, their system would be cheaper than coal plants, currently the lowest-cost option for electricity generation.

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5 Responses to Can natural gas-SOFC combo be cheapest route to cleaner electricity?

  1. labman57 says:

    The danger of CO with noble-metal catalysts (e.g., Pt) in fuel cells that operate at low temperatures is “poisoning” of the catalyst.

    This is not an issue with an SOFC which uses less costly metals due to the much higher operating temp. In fact, it is true that (in theory) CO can be directly oxidized at the anode of these fuel cells so long as the operating temp is in excess of ~750 degrees C. (At lower temp, carbon deposition, aka coking, rxns are favored.)

    However, when internally reforming methane, the high molar concentration of steam usually results in water-gas shift, and the CO is converted into CO2 (along with steam converted into H2). So in fact, relatively little CO is present to actually be oxidized in the critical electron-generating steps within the anode.

  2. wizard says:

    What is the MMBTU/hour of natural gas consumed by an SOFC? at 400kW.

  3. Praveen says:

    Natural gas usage in SOFCs is a mature technology and systems in the scales of 1W -1 MW have been successfully demonstrated with and without fuel preprocessing step. I still do not understand what the innovation is in this study. If CO is deemed as a serious contaminant for SOFCs then what is the advantage of SOFCs over PEM fuel cells? CO in fact is a fuel and if properly designed the cell can and has run in the past for >20,000 hours without any isssues.

  4. Peter Wray says:

    Eric – in a story about Barton and Adams’ work that appeared in the Autumn issue of MIT’s EnergyFuture, magazine, this explanation is provided:

    “[T]he MIT SOFC design contains two innovations. First is the inclusion of the water-gas shift reaction. Without that step, carbon monoxide goes directly into the fuel cell. Over time, black carbon deposits will build up and interfere with fuel cell operation. While MIT’s SOFC process can be built with existing technology, other designs will have to wait until carbon-resistant fuel cell materials can be tested and demonstrated.”

  5. While I agree that SOFCs are probably the most efficient method to produce electricity from natural gas while simultaneously producing a “pure” CO2 stream for ease of sequestration, I am not sure what the novelty of this is since these facts have been known for some time. Moreover, I don’t see why they incorporate both a steam reformer and then a water gas shift reactor to convert CO to CO2 as stated above “to prevent carbon deposition” since a major benefit of SOFCs is their fuel flexibility and thus their ability to internally steam reform and use CO as a fuel.

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