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Author Topic: How does carbon sequestration work, given that carbon dioxide is a gas?  (Read 16638 times)

Offline Atomic-S

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I understand that it is proposed to eliminate carbon dioxide emissions by storing the stuff underground. Seeing that CO2is a gas, how is it going to be kept there? In tanks?
« Last Edit: 14/06/2008 21:56:32 by chris »


 

paul.fr

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I believe they make the gas, in to liquid carbon dioxide.
 

Offline Atomic-S

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Stored in what?
 

paul.fr

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The link below has some information

http://www.statoil.com/statoilcom/SVG00990.NSF?OpenDatabase&artid=01A5A730136900A3412569B90069E947

Quote

Unwanted carbon dioxide from Statoil's Sleipner West field in the Norwegian North Sea is being stored 1,000 metres beneath the seabed. This solution won the chief executives health, safety and environmental prize for 2000

 

another_someone

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One concern I have about this sequestration (going off at a tangent) is what happens if the site where the CO2 is buried becomes unstable.

This may be analogous to the problems with storing radioactive waste, but one has to remember that more people died at Lake Nyos from CO2 than are known to have died from Chernobyl.  Yes, there are longer term effects of Chernobyl, but our justification for burying CO2 is because we are frightened of the long term effects of CO2 - so no difference there.
 

Heronumber0

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Is there not a way that photosynthetic bacteria or other photosynthetic organisms get involved in using up excess carbon dioxide and turning it into biomass? Then these can be somehow introduced back into the food chain if numbers get excessive?
 

another_someone

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Is there not a way that photosynthetic bacteria or other photosynthetic organisms get involved in using up excess carbon dioxide and turning it into biomass? Then these can be somehow introduced back into the food chain if numbers get excessive?

This is why people are arguing for reforestation (using the trees to soak up the CO2).

The trouble is that if one follows that to where you have suggested of taking it back into the food chain (and this happens with forests as well), is that what the food chain does is convert the carbon in the biomass back into CO2, so you are back to square one.

Yes, you could probably accelerate the cycle by using something like algae or cyanobacteria, rather than trees. Even better if one were to use GM cyanobacteria to produce products that are useful to us.

If, on the other hand, you convert the carbon into inert long chain polymers, you can lock the carbon up for centuries, or maybe millennia (ofcourse, this is when people complain about non-biodegradable plastics becoming a pollutant themselves, but they do at least lock in the carbon, which biodegradable plastics will not).
« Last Edit: 14/07/2007 13:18:19 by another_someone »
 

Heronumber0

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I was just wondering if excess carbon dioxide can be taken in by algae or cyanobacteria then got jumpy thinking about the effect of giving these organisms a free hand in the environment, that's whay I mentioned re-introduction tinto the food chain. However, how do you collect up the excess CO2 to turn it into plastics, would it be by liquefaction of CO2? If so that may also be an energy - consuming process. I just wonder if we cannot have huge algal/bacterial farms that convert the CO2 into plastic monomers then use hydrogen from these same organisms to power plastic manufacturing processes... I think I've got it another-s! This time next year we'll be millionaires.
 

another_someone

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I was just wondering if excess carbon dioxide can be taken in by algae or cyanobacteria then got jumpy thinking about the effect of giving these organisms a free hand in the environment, that's whay I mentioned re-introduction tinto the food chain. However, how do you collect up the excess CO2 to turn it into plastics, would it be by liquefaction of CO2? If so that may also be an energy - consuming process. I just wonder if we cannot have huge algal/bacterial farms that convert the CO2 into plastic monomers then use hydrogen from these same organisms to power plastic manufacturing processes... I think I've got it another-s! This time next year we'll be millionaires.

My thoughts were indeed along the lines of bioplastics, but durable rather than biodegradable bioplastics, and the use of photosynthetic microbes (such as GM algae or GM cyanobacteria) rather than larger plants such as cereals which seem to be the mainstay of present bioplastics.
 

Offline chris

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Another approach is to react the CO2 with something so that it becomes inert. One aproach being tested in America is to dissolve the CO2 in water and pump this into porous lava deposits. The acidic CO2-saturated water then reacts with minerals in the rock to form calcium carbonate (limestone).

Here's the item I covered as a news story on the programme recently:

http://www.thenakedscientists.com/HTML/content/news/news/772/

Chris
 

Offline dentstudent

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This is why people are arguing for reforestation (using the trees to soak up the CO2).

The trouble is that if one follows that to where you have suggested of taking it back into the food chain (and this happens with forests as well), is that what the food chain does is convert the carbon in the biomass back into CO2, so you are back to square one.
 

This is marginally out of context, but I think that it is a point worth raising. What George says is true, in that when you grow trees, they absorb CO2. If you use trees as a fuel for example, CO2 is released back into the atmosphere. There are 2 issues here. Firstly, as a tree grows, there is biomass from the trees that is assimilated into the soil. Most of this is in the form of leaf litter, but there are many others (bark, fallen branches etc). This transfers CO2 into the soil which will not then be released when the wood is burned. The harvesting process of forests (in Europe) have moved away from “whole tree harvesting” – this means that when trees are felled, the branches are left at the site, and it is only the stem that is removed. The reasons for this are several-fold, but primarily are for the purposes of reducing soil erosion during the harvesting process (the branches are laid out as to be a road), for ecological niches, for nutrient retention and to provide a micro-climate for natural regeneration of the forest. The upshot of this is that there is a net accumulation of CO2 in the soil.
Secondly, the release of the CO2 from the timber is only putting back what was taken out (less the above). As long as the fuel-wood comes from a forest that is sustainable (ie (broadly) that the growth of the forest is greater than or equal to the rate of extraction) then there is no net release of CO2 to the atmosphere. In essence, this means that you can burn as much wood as you like, because you are not going to increase overall CO2. This is a key reason why wood is better than fossil fuels – any burning of fossil fuels adds to the overall CO2 content because it was locked up.
 

another_someone

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This is marginally out of context, but I think that it is a point worth raising. What George says is true, in that when you grow trees, they absorb CO2. If you use trees as a fuel for example, CO2 is released back into the atmosphere. There are 2 issues here. Firstly, as a tree grows, there is biomass from the trees that is assimilated into the soil. Most of this is in the form of leaf litter, but there are many others (bark, fallen branches etc). This transfers CO2 into the soil which will not then be released when the wood is burned.

I don't see this as being the case.

Leaf litter is not an inert plastic that stays around for eternity, it is either consumed by animals (e.g. insects) or microbes, and what remains is the wast products from these organisms.  The process of breaking down the forest litter has the effect of releasing  carbon back into the atmosphere.

The best contexts for long term storage of carbon is peat bogs, because they are anaerobic, and so do not provide an environment where the carbon can be oxidised.
 

Offline dentstudent

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This is marginally out of context, but I think that it is a point worth raising. What George says is true, in that when you grow trees, they absorb CO2. If you use trees as a fuel for example, CO2 is released back into the atmosphere. There are 2 issues here. Firstly, as a tree grows, there is biomass from the trees that is assimilated into the soil. Most of this is in the form of leaf litter, but there are many others (bark, fallen branches etc). This transfers CO2 into the soil which will not then be released when the wood is burned.

I don't see this as being the case.

Leaf litter is not an inert plastic that stays around for eternity, it is either consumed by animals (e.g. insects) or microbes, and what remains is the wast products from these organisms.  The process of breaking down the forest litter has the effect of releasing  carbon back into the atmosphere.

The best contexts for long term storage of carbon is peat bogs, because they are anaerobic, and so do not provide an environment where the carbon can be oxidised.

Is anything stored for an eternity? Even plastics break down after a few hundred thousand years, which is nothing compared to an eternity! Yes, of course there are other, longer-term methods. If you look at the temporal scale of locking up C, and see that in some cases this is shorter than others. It is possible to argue therefore that fossil fuels are renewable, it just takes a long time! So, on what scale are you basing carbon sequestration? It's incorrect to state that because one is a short-term part of the cycle, that it isn't a cycle.

Also, the process of litter breakdown by soil fauna is not a 100% efficient process, and so there will be residual storage. Below about 25°C, the process in soils is a net accumulator.

I was going to put into the previous log about growing trees and then burying them, but I have no figures about C relationships on this. Another thought might be large pontoons of logs floated out to sea, and like shipwrecks, let them sink where they'll become assimilated (eventually) into the seabed (although this needs thinking through too....)

« Last Edit: 16/07/2007 10:38:09 by dentstudent »
 

Offline dentstudent

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Also...

http://www.abc.net.au/rural/news/content/2006/s1844101.htm

Australian scientists are adapting a soil fertility technique used in the Amazon to reduce greenhouse gas emissions.

For thousands of years, Amazonian Indians burned their waste organic matter in low-intensity fires and added the charred material to their land.

The method improved fertility on intensively-managed soils, but is now being considered as a way of trapping excess carbon.

Researcher Lucas Van Zweiten says carbon can be stored for thousands of years.

"In composting, the majority of carbon in the composting process is lost naturally to microbial degradation to carbon dioxide," he said.

"In pyrolisys up to 50 per cent of carbon is maintained as char which can last for several thousand years in the soil."
 

another_someone

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Is anything stored for an eternity? Even plastics break down after a few hundred thousand years, which is nothing compared to an eternity!

Plastics have a wide range of stability, and it depends on whether it is exposed to UV or air, which will accelerate breakdown.

If you want greater stability than that, I would think various carbides would be extremely stable over millions of years.

It is possible to argue therefore that fossil fuels are renewable, it just takes a long time!

Indeed so.

Also, the process of litter breakdown by soil fauna is not a 100% efficient process, and so there will be residual storage. Below about 25°C, the process in soils is a net accumulator.

I suppose the test of this is to measure the carbon content (as a percentage of total mass) of the litter on the forest floor, and then measure the carbon content of the soil about 10 feet below the surface (maybe even deeper, if a carbon gradient continues deeper), and thus assume that any reduction in carbon content in the lower soil must represent carbon that has been either incorporated into the biomass, or into the atmosphere.


I was going to put into the previous log about growing trees and then burying them, but I have no figures about C relationships on this.

This is in essence the same as burying waste paper, which is presently considered unfavourably.  Ofcourse, most waste paper is buries in shallow pits, rather than subject to deep burial, which might make a difference; but one major problem with this (and this also remains a problem with organic matter buried beneath the forest floor) is that it tends to create methane, which then seeps to the surface (unless it can be contained behind an impermeable barrier).

 

another_someone

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Also...

http://www.abc.net.au/rural/news/content/2006/s1844101.htm

Australian scientists are adapting a soil fertility technique used in the Amazon to reduce greenhouse gas emissions.

For thousands of years, Amazonian Indians burned their waste organic matter in low-intensity fires and added the charred material to their land.

The method improved fertility on intensively-managed soils, but is now being considered as a way of trapping excess carbon.

Researcher Lucas Van Zweiten says carbon can be stored for thousands of years.

"In composting, the majority of carbon in the composting process is lost naturally to microbial degradation to carbon dioxide," he said.

"In pyrolisys up to 50 per cent of carbon is maintained as char which can last for several thousand years in the soil."


This is interesting, as it turns the whole notion arguing against the burning of the Amazon on its head - but then, increasingly, forest fires are being seen as not an enemy of the forest, but just part of the natural life cycle of the forest.
 

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