what type of vegetation uses the most co2?


by keepitmoving
Tags: type, vegetation
keepitmoving
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#1
Oct29-09, 07:55 AM
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what type of vegetation uses the most co2?
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Xnn
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#2
Oct29-09, 11:29 AM
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Those that grow the fastest.

Plants such as sugercane, which use C4 photosynthesis are especially good.
Bob S
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Oct29-09, 10:24 PM
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Another C4 is miscanthus (used for energy production). It grows about 2 x as fast as switchgrass.
http://en.wikipedia.org/wiki/Miscanthus_giganteus
Maize (corn) is also a C4.
Bob S

keepitmoving
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#4
Oct29-09, 11:20 PM
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what type of vegetation uses the most co2?


is it practical to plant large amounts of these types of vegetation to make up for increased co2 production?
vanesch
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Oct30-09, 02:07 AM
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Quote Quote by keepitmoving View Post
is it practical to plant large amounts of these types of vegetation to make up for increased co2 production?
And once you have them grown up, what do you do with them ? Burn them ? Let them decompose ?

The only way would be to put them in a deep repository, where their desintegration will not release CO2 to the atmosphere.
mheslep
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Oct30-09, 08:17 PM
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Quote Quote by keepitmoving View Post
what type of vegetation uses the most co2?
Quote Quote by Xnn View Post
Those that grow the fastest.

Plants such as sugercane, which use C4 photosynthesis are especially good.
As algae grows faster than anything I can think of, in all kinds of conditions, I expect it captures the most CO2.
Biophreak
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#7
Nov4-09, 08:45 AM
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As Vanesch stated, the problem with the plant method of removing CO2 from the atmosphere is that once the plant dies, it will decompose, which ITSELF releases CO2 into the air. Forests and oceans are the planet's two major CO2 sinks, but forests have trouble sequestering CO2 for much longer than the life of the plants that make them up.

Also, if you buried the plants deep underground, you'd only be doing farmers a disservice, because every time you remove decomposition products from your soil, you are eliminating nutrients that are necessary for future plant growth, thus requiring the farmer to fertilize his/her land.
Wallace
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Nov4-09, 08:54 AM
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One proposal is to grow these kind of crops then turn them into charcoal which is in turn used to enrich agricultural land, and to do this on a huge scale. See http://www.biochar.org.

The problem though is that this kind of option is often pushed as a magic cure to the CO2 problem that will let us carry on using as much energy as we like made in whatever is the cheapest way (in short term sums).

For instance in Australia, Biochar is being pushed strongly by the Conservative side of politics as an alternative to any other approach to dealing with climate change. While this kind of things has some merit, it is no cure all since the amount of land you'd need to dedicate to this is enormous and given humanities innate stupidity, we'd probably do something like clear the Amazon, defeating the purpose. Basically all the dumb things we are currently doing in the biofuels industry.
Biophreak
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Nov4-09, 09:10 AM
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I don't know all of the specifics of how biochar works, but a major issue that I can see is that to even MAKE charcoal, lots of energy is required- charcoal forms when organic materials are submitted to very high temperatures and pressures. Finding a carbon neutral way of doing this seems to be the real challenge.
Wallace
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Nov4-09, 09:24 AM
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I believe that suitable processes have been developed. I'm not sure of the details, but I think suitable processess have been developed. My rough understanding is that you subject the organic matter to a high heat in an oxygen free environment and it decomposses into char (carbon) and useable forms of fuel. You can use some of that fuel to supply the heat and thus can perform this processing without external energy input, resulting in charcoal and surplus fuel which can be used for energy production. Of course the burning of this fuel will release some amount of carbon but I think the whole process is carbon negative, for instance you could imagine running any farm equipment used on the fuel derived in the processing (you'd probably still have plenty left over).

If anyone knows any more about this please chime in. There is some info on the wikipedia site (see the entry on Pyrolysis) but I don't have much of a background in the details.
Biophreak
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#11
Nov4-09, 11:30 AM
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[QUOTE=Wallace;2425078]You can use some of that fuel to supply the heat and thus can perform this processing without external energy input, resulting in charcoal and surplus fuel which can be used for energy production.

You're talking about a process where you end up with more energy than you started with...that's not quite possible. Furthermore, you'd be burning the charcoal (thereby producing CO2 and CO), to get rid of organic matter. The thing is, the high temperature environment required has to be sustained over a long period of time, which requires a LOT of energy. If this method really worked, then oil companies would be busy converting organic material into oil again- but they know that you will never get more energy out of a system than you put into it. In fact, because of dissipative losses, you will NEVER get more energy out of a process than you put into it. This is why using water as a hydrogen source for fuel cells is impractical- in order to liberate the H from H2O, you need to electrolyze the water, and the energy to do this comes from a power plant somewhere else, and the energy put into water to liberate the H is less then the energy that is produced when the H is consumed.
Wallace
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Nov4-09, 02:46 PM
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Hang on, back up a moment, we seem to be talking about very different things! Remember that what you start with is organic matter with stored chemical energy (which originates from the Sun). I'm not suggesting you end up with more than this energy when you finish the process (in fact you have much less). You're not getting energy from nowhere, you have this stored energy to utilise.

So, Pyrolysis is the process of converting organic material to char and some lighter fuel in a high heat, no oxygen environment (there is no combustion, no production of CO2). In order for the process to require no input energy overall, is for the fuel you make in these process (generally methane a similar gases) to be sufficient to provide enough heat to keep the process going. There is no in principal reason that this can't be done, and it is possible you'd have some methane left over. The unknown is how much energy is required to complete the conversion. I don't know the details, but there is no reason that this has to take more energy than is stored in the material to start with. You aren't making any fuel in a sense (in the way you compare to electrolizing water), you are converting stored energy in one form of hydrocarbon to another, one that contains less carbon, with the lost carbon converted to char. This takes some energy, but as long as you can get that energy from the converted fuel source you're okay. You do make some CO2 burning that fuel for heat, so the process can't be 100% efficient in terms of converting the total carbon in the material to char, but better than nothing an in principle carbon negative.

As I say, I'm no expert on this process, but in principle it can work. In any case it is being looked at seriously which would not be the case if it was not possible to do this in a carbon negative way. You also get the benefit of making an excellent fertalizer.
Dadface
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#13
Nov4-09, 03:00 PM
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If wer'e considering fast growing plants I think bamboo outstrips everything else.
mheslep
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Nov4-09, 05:35 PM
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Quote Quote by Dadface View Post
If wer'e considering fast growing plants I think bamboo outstrips everything else.
I can't see how. Some Algae strains can double their mass every two days in good light, temperature, and CO2 concentration.
http://www.aquatext.com/tables/algaegrwth.htm
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Nov5-09, 05:11 AM
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Quote Quote by mheslep View Post
I can't see how. Some Algae strains can double their mass every two days in good light, temperature, and CO2 concentration.
http://www.aquatext.com/tables/algaegrwth.htm
Point taken,bamboo seems to grow really slowly when compared to algae.Perhaps bamboo wins the prize for the fastest growing complex plant ie ones with shoots and stems etc.

This has caused a thought to pop into my head.I wonder if there is a relationship between complexity of plant and growth rate.Could it be that the simpler the plant the faster it grows?Does the same apply to the animal world?


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