"Direct carbon" fuel cells

doug · 09-01-2009, 03:10 PM

Is There Some Light at the End of Coal's Long, Dark Tunnel? - NYTimes.com

Quote:

Some think that the only way to clean up coal is to stop burning it altogether. Now a handful of researchers and companies are pursuing a technology to do just that, but one that has the potential of keeping part of the nation's economy coal-fired.

They are skipping the burning step. "Direct carbon" fuel cells efficiently produce electricity straight from the carbon source, which can be anything from coal to coconut shells.

...

... direct carbon fuel cells (DCFCs) -- an umbrella term that encompasses a range of fuel cell technologies -- convert carbon sources to electricity in a single reaction step, just as current fuel cells do with hydrogen. Under various schemes that pulverize coal and feed it into the fuel cell in a slurry of molten salt or other superheated material, the carbon in the coal reacts in the cell to produce a moving stream of electrons, or electricity.

Researchers estimate that real-world efficiencies of DCFCs could approach up to 70 percent, the highest of any fuel cell class.

TEG · 09-01-2009, 05:01 PM

Isn't what we need just the opposite? A machine that uses electricity (from Solar/Wind/Wave/Geotherm) to get CO2 from the air and turn it into some coal like substance so we can bury it again to re-sequester it?

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I guess the coal industry wants more research dollars to investigate alternate ways to process coal one way or another.

It seems like all the pre-processing to purify, clean, and heat the coal based slurry would use up a lot of the energy such a device would produce.

JRP3 · 09-01-2009, 08:43 PM

Not to mention coal mining itself is pretty destructive.

doug · 09-01-2009, 11:28 PM

Quote:

Originally Posted by TEG

Isn't what we need just the opposite? A machine that uses electricity (from Solar/Wind/Wave/Geotherm) to get CO2 from the air and turn it into some coal like substance so we can bury it again to re-sequester it?

While I appreciate your sentiment here, I think I already said elsewhere earlier today that this is a poor way to reduce the amount of CO2 in the atmosphere. By volume, the concentration of atmospheric CO2 is 387 ppm. While that number is alarming to climate scientists, it's still less than 0.04% of the atmosphere.

You're far better off grabbing that CO2 at the point of production, before it is diluted in the air. Better yet, reduce the level of CO2 exhaust by increasing efficiency. And obviously better still, generate electricity in a way that is carbon free or at least carbon neutral.

For example, "clean coal" is an oxymoron, but practically speaking (since we will continue to use coal for the near future) there is such a thing as cleaner coal. (Reducing NOx and particulates is a good thing.) Increasing efficiency should correspondingly reduce emissions and usage. I prefer we move away from fossil fuels all together, but while we're transitioning to renewables, we should use those fossil fuels in the least destructive and most efficient way that's practical. I find most carbon sequestration schemes dubious, but if you're going to do it, it's at the output of the power plant.

Nevertheless, without knowledge of the details, it is possible that preparing coal for use in DCFCs may not provide an energy advantage. There could, however, be other advantages (NOX and particulates again, or ease of carbon capture).

Anyhow, it's the use of biomass as a feedstock that interests me:

Quote:

Perwich noted that biomass, such as wood or farm wastes, will likely be the initial fuel for the cells...
...many early applications will likely rely on smaller, biomass-powered cells, Rastler said.

If practical, it would be cool if DCFC plants could be used in conjunction with agribusinesses. Waste biomass could be used to generate electricity. The exhaust CO2 could be pumped into green houses (or used help grow fuel algae or some other plant material). I prefer CO2 reuse to sequestration.

Carbon Management Program: Direct Carbon Fuel Cells

Direct carbon fuel cell - Wikipedia, the free encyclopedia

Serge · 09-02-2009, 10:36 AM

Quote:

Originally Posted by doug

While I appreciate your sentiment here, I think I already said elsewhere earlier today that this is a poor way to reduce the amount of CO2 in the atmosphere.

While reducing the amount of CO2 in the atmosphere is something we should focus in the long-term, the current [short-term] challenge is to reduce the amount of new CO2 being pumped into atmosphere.

Quote:

For example, "clean coal" is an oxymoron, but practically speaking (since we will continue to use coal for the near future) there is such a thing as cleaner coal. (Reducing NOx and particulates is a good thing.) Increasing efficiency should correspondingly reduce emissions and usage.

This is unfortunately, the uncomfortable truth. While the proportion of clean-energy production is growing [and should be stimulated further], new coal-burning plants are still being built, even if to replace the older ones. Hopefully this technology can provide an alternative to this part of the energy production equation. In addition to higher efficiency an additional benefit is ability to better contain pollutants (mercury, sulfur-oxide, etc.) instead of venting them out the smokestack.

frenska · 02-02-2010, 02:11 PM

I'm trying to calculate the flow rates (MeOH and O2) for a 5cm2 DMFC.

I've already found out that the MeOH flow is 0.52ml/min.
Considering the stoichiometry of the reaction CH3OH +3/2 O2 -> CO2 + H2O
I've calculated the moles of O2 8.64e-6mol/s.

So I've simply to determine the flow in ml/min. It shouldn't be a big deal but I'm not sure if:
a) I should use the gas law PV=nRT
b) I can simply use the molecular weight and the density of O2

Thanks for your help

johnr · 02-02-2010, 07:41 PM

I vote for "clean coal" for the 2009 oxymoron of the year award!