Slashdot Mirror
Hydrogen-Powered cars with Zero-Carbon-Emission?
Roland Piquepaille writes "Researchers from the Georgia Institute of Technology have a bright idea — at least at first sight. They want to create a sustainable transportation system by using hydrogen-powered cars. They would like to create an infrastructure where people could use a liquid fuel for driving while the carbon emission in their vehicles is trapped for later processing at a fueling station. 'The carbon would then be shuttled back to a processing plant where it could be transformed into liquid fuel.' Where will all this liquid carbon be stored? The researchers don't know. They suggest that it could be stored in geological formations or under the oceans."
There were already some pretty good ways of storing hydrogen for cars and the issue was just creating the hydrogen in the first place.
Not really. The Department of Energy has estimated that one would need at least a device capable of storing up to 0.6 kg of hydrogen per kg (e.g. a 100kg storage tank has 6kg of raw hydrogen in it) before hydrogen is just barely usable as a transportation fuel source. Ideally, 12% wt/wt storage is necessary to achieve the 300 miles per tank that most cars get today on gasoline. The best storage systems (circa 2004 when the report came out) topped out around 8% for liquified hydrogen tanks, but those are very difficult to use in practice because the hydrogen leaks out quickly. All other systems topped out around 4% and required either high temperature (metal hybrides) or very high pressures (700bar, approximately 10000 psi), again making them not yet ready for widespread use.
Hydrogen production is still an issue too though. Most of what we get now is a byproduct from natural gas processing, so it's still not carbon-neutral.
(Disclaimer: This topic is actually part of my master's thesis.)
First, let's ignore how much energy we're throwing away in step 2 by not utilizing the full energy potential stored in the hydrocarbon molecules. Second, somehow we'll expend more energy to liberate the hydrogen and capture the carbon, both without oxidizing them. Third, we're going to tote around another 75 - 100 pounds of weight with the stored (and somehow liquefied) carbon that will be returned. Less energy potential that ever reaches the engine/fuel cell, and even more expended to refine something fairly energy dense into something that's a fair amount less energy dense.
The problem with this idea is there's too much fixation on sequestering every last bit of carbon, rather than focusing on a bigger, more important concept called energy efficiency. Work on improving that and the carbon emission reductions usually follow.
Combustion Carbon will be in the form of Carbon Monoxide (CO) and/or Carbon Dioxide (CO2). We do not have technology to create solid forms of carbon (quickly enough) to be useful on a passenger vehicle. (but that would be cool)
Both of these waste carbon gases (CO2 and CO) require significant refrigeration with high compression to store them in any significant quantity and that, my friends, *Requires tremendous Energy*. The work of "sequestering" the Carbon and storing it will eat away any profits in the manufacturing of and efficiency of the vehicle and it will add complexity to an already complex piece of machinery. Not to mention there will have to be one or more pressurized vessels (think explosion, frostbite, and suffocation hazards potentials too).
Carbon Sequestering is a pipe dream (thermodynamically) but it is great for getting venture capital from those investors who have not studied and understood the principles of thermodynamics and basic organic chemistry and who also want to claim that they are investing in "green" technology. (And there may just be tax breaks for such obvious non-competitive investments like 'Sequestering' to the 'Fossil Fuels Industries'??)
"Carbon Sequestering" is really only handy (though still very efficient) if you happen to be talking about a sessile terrestrial power installation over a suitable subterranean geological Carbon gas receiving reservoir. Like this one: http://science.slashdot.org/article.pl?sid=08/02/03/1845204&from=rss (A budget increase from 1.0 Billion to 1.8 Billion proves its inefficiency alone, and that's before you consider how much more fuel is required to capture all of the HOT exhaust and cool it down to the point it could be compressed and injected into exhausted/abandoned Oil or gas 'injection' wells.
The "Oceans" basically make CaCO3 (Calcium Carbonate) out of CO2 and CO (with the help of Trillions of organisms) and it falls to the ocean floor and becomes rock eventually. This is the PRIMARY carbon "sink" on the planet. I would put more research into helping that process (oceanic Carbon capturing) and focus on Electric Cars powered by Hydrogen cells and NOT Hydrocarbons and not Hydrogen combustion engines... they are too inefficient. Carbon is simply not needed in the fuel cycle. (Unless you want fuel cells that run off of Natural Gas (Methane/Ethane AKA CH4/C2H5) or some form of Alcohol (Methanol/Ethanol AKA CH3OH/C2H5OH)).
Ultimately, using electricity to power the car's electric motor is the only truly efficient way to go (as of today)... It is only a matter of whether it is powered from a battery that is charged with electricity from the grid (preferably Nuclear and/or Hydroelectric), from an internal generator burning fuel (like modern diesel/electric Trains), and/or capacitors, solar cells, or small nuclear reactors... Burning Carbon-containing fuels (from whatever source...but note: they *WILL be from Fossil Fuels* as long as they are cheaper) is just more of the same since the invention of the combustion heat engine. It is business as usual.. Using Corn to make alcohol is a pretend market that will utterly fail without the heavy government subsidies it is seeing. (Research ADM and its lobbying efforts.)
Carbon Sequestering is really interesting, but it requires TOO MUCH energy to do.. Last time I checked, you use about 2 Watts of power to remove about 1 Watt of heat from your home/office using efficient air conditioning. What will it require in energy to remove the heat and to compress (compression releases MORE heat BYW) the exhaust of a car buring some Carbon-containing fuel? Exactly. Electric is the ONLY way to!
I might be one of "global warming idiots" - for not knowing too much about it, but I failed to see how water is as bad as CO2 in this issue. Earth, as we know, has 3/4 of its surface covered by water, thus the atmosphere is basically saturated for water vapour, i.e., no matter how much water (liquid, vapour, ice, all forms combined) exists on this planet, the amount of water vapour in atmosphere as a whole system is almost constant as long as the climate (temperature, pressure) doesn't change dramtically.